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jojoguy10 19-09-2014 17:11

Electrical basics
 
Hi there!

Our team is trying to learn some electrical basics. Up to this point, we've just been trying stuff and hoping they work, but we want to know some basic ways of electrical work.

-best methods for wiring; to reduce circuit resistance, loose connections, portability, shorting, damage to wires and connectors, etc

-methods for testing electrical components - motors, controllers, switches, etc.$@# to be used during build and troubleshooting

-battery management - how do we test batteries for how fast they draw down under load (there are some complex methods and equipment that apply a 100 A load for 30 seconds that tell you a lot about a battery that simply looking at as charged voltage does not).$@# A new battery is not necessarily the best battery.

-ability to measure circuit variables (voltage, amperage, resistance).$@# Measuring the resistance of our drivetrain is very difficult and requires special methods that I don't understand (resistance < 0.05 ohms)

-explanation of why we get certain results or don't get them.$@# I still don't understand why we see lower amperage on the competition drivetrain than what is predicted.$@# And I don't even know how to figure out why other than just start replacing things.

-methods to combat tripping our current limits through the various breakers and controllers

Thanks!

VeqIR 19-09-2014 19:40

Re: Electrical basics
 
Hi there,
Definitely a broad set of good questions, so here we go:

- Reducing resistance usually amounts to increasing wire gauge. >= 6AWG for battery/breaker, >= 12AWG for high current motors (CIMs). We're going to 4AWG for our breaker connection and 10AWG for our CIMs this year since we found wires getting warm last year. Also, reduce wire length as much as possible by placing connected components near each other.

- Creating solid connections: it's overkill, but soldering on crimped terminals is the best way to ensure that they stay on place. We strip off the plastic housing on these terminals, slide on some heat shrink, crimp the terminal, solder over the crimp and then heat shrink. We didn't have a single terminal come loose all season.

- Make sure there's electrical tape or (preferably) heat shrink tubing over any bare connections. This reduces chance for shorting and makes things look cleaner.

- It's often overlooked, but put thought in to where you position the components. Minimize wire length from battery->breaker->PD board (within reason, allowing for ease of battery removal). Keep your motor controllers close to your motors, PD board and cRIO. Keep cRIO near to the digital breakout and motor controllers. Before drilling any holes, set out all the components as a test on a similar sized board to make sure you have an optimal arrangement.

- For testing, provided you guys have enough components to recycle, create a test board with all the electrical fixtures on it. This is a great off-season activity and will save you lots of time during build season when you're not having to kludge together something to test components.

- Get a battery beak for battery testing. It's a one-time cost and has saved us more times than you'd think.
http://www.andymark.com/product-p/am-0995.htm. If you want to get fancy, try putting them through a real world loading test with a test bot and five minutes of drive time after a full charge. Measure the battery's discharge level and keep record of your "best" batteries.

- The new PD board will have current measuring capabilities over the CAN bus, so you can use that for your measurement needs.

- You've learned a very important lesson about engineering: theory doesn't always match experimentation -- and that's okay! There are so many variables in one of these systems: battery internal resistance/charge level, motor parameters, electrical parasitics (R/C/L). If you're not getting the current you're expecting, it's most likely that either your computations didn't take all the variables into account or your experimentation is violating some assumption. Oftentimes, replacing components with "known good" ones is the best way to debug a fault.

- As we found out in elims at IRI, once you've tripped a breaker, it is more likely to trip again. For a competition bot, you'll want to replace it just to be paranoid. Keep that breaker for a practice bot.

- Make sure you have your gear ratios such that you will not pull too much current under the inevitable pushing matches. If you have yourself geared for 20fps with 6 CIMs and you get into a pushing match with a robot (or a wall), you're likely going to pop a breaker. If you've already built the system and there's no time left to fix it mechanically, you can also implement a software limit on how much duty cycle you'll put on the motors. This way, the motor controllers will never actually deliver 100% of the rated power to your motors and it should save your breaker.

Let me know if you have further questions!

Richard Wallace 19-09-2014 20:20

Re: Electrical basics
 
Step 1: locate any post by Al Skierkiewicz

Step 2: click on his name in the post heading and select "Find all posts by ..."

(Warning: he has over 9000 posts, and the majority of them are about wiring safety.)

Happy reading! 😊

Al Skierkiewicz 20-09-2014 07:23

Re: Electrical basics
 
To help you in your search,
Center the PD in the robot, this will keep the wiring short. There is no significant advantage to moving to #4 from #6. If you keep it short, the difference is millivolts. #6 is .0005 ohms per foot and #4 is .0003 ohms per foot. #10 is much better than #12.
Uninsulated terminals are available from the same sources and cost less. Use the right crimper. Those meant for insulated terminals will not give you the same crimp force.
Breakers that have tripped will not degrade. If they are repeatedly abused over a long period (5-10 matches) the internal contacts will pit and raise the internal resistance. Under those conditions, replace them. However, if they are warm to begin with, they will trip at a lower current than at ambient temperature.
For a little more than the cost of the Battery Beak, you can get a West Mountain CBA IV USB analyzer. This will draw current for a much longer time and give you a display that you can save to disk, and overlay in the future. This allows you to track the health of the same battery over years. It also will match the curves used by the manufacturer and calculate amp hour ratings. It will show battery cells that do not match. The Beak is great to put in your pocket and know if the battery you put in the robot is charged.
Use the "wire foot" analogy. At 100 amps, 1 foot of wire has a voltage drop that is predictable. #6 will drop 0.05 volts/ft, #10 will drop 0.1 volts/ft and #12 will drop 0.2 volts/ft. The stall current of a single CIM motor is 131 amps under test at 12 volts. On a typical FRC robot this more like 116 amps. That is the current it will draw when starting and anytime you are applying full throttle and the robot is not moving. Yes, 6 CIM drives have the ability to draw over 600 amps from the battery. The internal resistance of the battery is 0.011 ohms/11 wire feet. So at 600 amps, that is 6.6 volts dropped in just the battery. Yes the main breaker can withstand that for short periods but not forever. Loose connections (bad crimps, bad solder jobs, loose battery terminals, loose PD connections, etc.) can amount to several wire feet of loss per connection and can also raise the temperature of the device they are attached to. A loose terminal on the main breaker can raise the internal temperature above 100 degrees.

jojoguy10 20-09-2014 11:13

Re: Electrical basics
 
Thanks for all of the great advice! Right now, we are without an electrical engineering mentor to help us out with this, so we are struggling a bit in this area.

If I have any questions, I will post them here.

Thanks again!

-Joe

M.Kong-Sivert 20-09-2014 11:41

Re: Electrical basics
 
I've been trying for years to convince my team to solder the wires or use heatshrink or both, since our connections kept coming loose, but, while we were talking to some people at a conference, someone gave us a few of these: https://www.wagobox.com/shop/wago-22...412-20pcs.html

We were a little skeptical, but we tried replacing some of our connections with them, and they worked perfectly. If you're not careful, they can pinch your fingers, but they're easy to use, they don't come loose, and they're reusable. We bought a box of them and used them on our robot, and I haven't brought up soldering or heatshrink to my team since then.

If you must crimp, though, make sure the people know how to do it properly. Too many of our connections have come loose because someone didn't crimp the right way.

Richard Wallace 20-09-2014 13:45

Re: Electrical basics
 
Quote:

Originally Posted by M.Kong-Sivert (Post 1400798)
...someone gave us a few of these: ...

AndyMark has them. (link)
They work well.

Al Skierkiewicz 21-09-2014 11:21

Re: Electrical basics
 
They are only rated for 32 amps.

Michael Hill 21-09-2014 11:31

Re: Electrical basics
 
Quote:

Originally Posted by Al Skierkiewicz (Post 1400922)
They are only rated for 32 amps.

Hey, could you shed some light on current/power ratings for me? Something that's always confused me are ratings at high voltages. These say they're rated for 32 Amps @ 400 Volts. Are these the maximum for both current and voltage? That is, you should neither operate above 32 Amps OR 400 Volts? Or is it it a power rating? That is, it's rated for 32 Amps * 400 Volts = 12.8 kW. Or is it a P=I^2*R power? In that case, the current would be the max current no matter the voltage

Al Skierkiewicz 21-09-2014 11:38

Re: Electrical basics
 
Micahel,
The insulation is rated to withstand 400 volts without arcing through the material. If you were to use this for line voltage it would not cause a safety hazard if handled or attached to metal. (line voltage of 120 volts is the RMS rating not the peak.) The current rating is based on temperature rise using continuous current (usually for 24 hours) If you exceed the current, the device will warm and the max voltage rating will likely fall. Once you exceed the melting point of the plastic, it will deform bringing the conducting parts closer to the surface. While CIM motors in an efficient design won't run at 32 amps continuous, under certain conditions, you may exceed that for several seconds to a minute. In that case, high temperature will result. In addition, the temperature will likely also effect the holding tension device and may just release the wire. Your mileage might vary.

Aren Siekmeier 22-09-2014 04:14

Re: Electrical basics
 
Quote:

Originally Posted by Michael Hill (Post 1400924)
Hey, could you shed some light on current/power ratings for me? Something that's always confused me are ratings at high voltages. These say they're rated for 32 Amps @ 400 Volts. Are these the maximum for both current and voltage? That is, you should neither operate above 32 Amps OR 400 Volts? Or is it it a power rating? That is, it's rated for 32 Amps * 400 Volts = 12.8 kW. Or is it a P=I^2*R power? In that case, the current would be the max current no matter the voltage

The current rating of a conductor is itself a power rating, basically how much power can it dissipate as heat. The power dissipated as heat is indeed P=I*V, but this V is the voltage drop across the conductor, not across the load the conductor leads to. The voltage drop across the conductor is given by V=I*R for a conductor resistance R, the power rating is P=I*V=I^2*R, and depends only on the current and the physical characteristics of the conductor (size, resistivity, length...).

The voltage rating of the device is the max voltage before the insulation between conductors or between a conductor and the outside breaks down and allows a current. This is entirely a function of the various dielectric and insulating materials being used between conductors and the electric fields they can withstand before ionizing and carrying a current. The current carried by the insulating conductors has no effect.

So these two ratings are unrelated. You should not exceed either of them, even if you are way under the other one.

vladtheimpaled 22-09-2014 06:45

Re: Electrical basics
 
Quote:

Originally Posted by Richard Wallace (Post 1400759)
Step 1: locate any post by Al Skierkiewicz

Step 2: click on his name in the post heading and select "Find all posts by ..."

(Warning: he has over 9000 posts, and the majority of them are about wiring safety.)

Happy reading! 😊

That awkward moment when Al posts right under you.:) :]

Al Skierkiewicz 22-09-2014 08:03

Re: Electrical basics
 
While we are on the subject...
There are various current ratings for wiring so you need to know when looking at charts and breaker sizes. The current robot rules are written using the NEC guide for conductors in an open space (as opposed to conduit and bundles). This table takes into account the resistance of the wire and the expected temperature rise caused by continuous current in the conductor for general insulation. It also adds a little fudge factor by calculating the voltage drop in a typical house wiring run and making sure that at maximum current, there is still sufficient voltage at the load. The insulation used on the CIM motor wire is (or at least was in the past) a higher temperature rating and is therefore rated for higher current then you would expect for it's size.
Another set of current tables is established by the aircraft industry. That current table is based on the minimum allowed voltage drop to instruments in the cockpit. Adjustments to those tables account for length (both conductors please), load current, bundled conductors and altitude. You can find more from the FAA here...
http://www.airweb.faa.gov/Regulatory_and_Guidance_Library/rgAdvisoryCircular.nsf/0/99c827db9baac81b86256b4500596c4e/$FILE/Chapter%2011.pdf

Richard Wallace 22-09-2014 17:20

Re: Electrical basics
 
Quote:

Originally Posted by Al Skierkiewicz (Post 1400922)
They are only rated for 32 amps.

Or 20A, as stated on the bag -- I think the figure depends on which agency basis is used.

Also the WAGO lever nuts are only sized for 12 AWG and smaller wire -- not really big enough for the 10 AWG many teams (like mine) prefer for drivetrain circuits. We will probably stick with 45A APP connectors for the drivetrain.

Al Skierkiewicz 23-09-2014 08:28

Re: Electrical basics
 
When possible we connect the motors directly to the speed controller by placing the controllers near the motors they drive. This eliminates another connector and therefore another possible failure point. We use screw mount push on connectors on Victors and Jaguars.

Ken Streeter 23-09-2014 22:27

Re: Electrical basics
 
Quote:

Originally Posted by Al Skierkiewicz (Post 1401147)
We use screw mount push on connectors on Victors and Jaguars.

These sound neat. I don't think I've seen these before. Can you provide a pic and/or a supplier/part number?

Thanks!

Al Skierkiewicz 24-09-2014 07:40

Re: Electrical basics
 
http://www.digikey.com/product-detai...7866-ND/293277
We buy one hundred at a time. When needed we use the APP 35 and 45 amp contacts. Crimper is available from West Mountain Radio (outside Milwaukee) as well as other places.

RonnieS 25-09-2014 10:10

Re: Electrical basics
 
Will you still be doing this with the limited length of leads on the new speed controllers? Or splicing in on the PD board side?
-Ronnie

Al Skierkiewicz 25-09-2014 10:33

Re: Electrical basics
 
We will likely add APP connectors to the new speed controller output wiring. I don't like that but we will adapt. I hate adding another point of failure.

JamesCH95 25-09-2014 11:49

Re: Electrical basics
 
Here is a good thread to read if you're having issues with your wiring connections: http://www.chiefdelphi.com/forums/sh...d.php?t=119549

There is absolutely no need to both crimp and solder every electrical connection. Crimping is just fine when it's done properly. I would strongly encourage you to do rudimentary tension testing on a couple crimped fittings. They should be able to sustain far more force than one can every apply by tugging on the connection by hand. Ratcheting crimpers are key to ensuring consistent and strong crimped connections.

Al Skierkiewicz 25-09-2014 13:27

Re: Electrical basics
 
James,
We crimp then solder for one very good reason. We lost a World Championship to Beatty when one of our crimp connections let loose. We have vowed that will never ever happen again.

JamesCH95 25-09-2014 13:36

Re: Electrical basics
 
Quote:

Originally Posted by Al Skierkiewicz (Post 1401539)
James,
We crimp then solder for one very good reason. We lost a World Championship to Beatty when one of our crimp connections let loose. We have vowed that will never ever happen again.

What would you have done if it was a cold or improperly soldered joint to blame?

SteveGarward 25-09-2014 15:18

Re: Electrical basics
 
Final soldered connections for the competition robot are often checked by a mentor, and usually at the request of the student. It's not a lack of trust (on our part) or confidence (on theirs), but a matter of quality assurance by all to ensure we are building the best that we can.

In any case, I would want to be able to say we did everything we could to ensure a good mechanical connection.

Al Skierkiewicz 25-09-2014 15:41

Re: Electrical basics
 
James, we crimp first and then solder. We have had a stunning run of zero electrical failures.

JamesCH95 25-09-2014 16:02

Re: Electrical basics
 
Quote:

Originally Posted by SteveGarward (Post 1401563)
Final soldered connections for the competition robot are often checked by a mentor, and usually at the request of the student. It's not a lack of trust (on our part) or confidence (on theirs), but a matter of quality assurance by all to ensure we are building the best that we can.

In any case, I would want to be able to say we did everything we could to ensure a good mechanical connection.

What we (on 95) have done to ensure a good mechanical connection is to adjust our ratcheting crimping tools and then test the crimp connections that they make. We get awfully close to mil-spec pullout strengths with these connections (around to 130lbs on 10awg connectors, almost 300lbs on 6awg connectors) and dissecting these connections shows nearly continuous metal through the crimped cross-section due to deformation and micro-welding. This qualifies as a "good mechanical connection" in my book at least! :) Two robots and counting on this process (plus pre-season drives and other projects) with zero failures. The two robots before that used soldered connections, also with no failures.

Soldering relieves all of the cold-working from crimping making the crimping process pointless. Most solders only begin to melt at around 200C (depends on formulation), and copper will start to stress relieve around 150-200C (depends on alloy).

I'm not saying that soldering can't work, or doesn't work; my team and I have used numerous soldered connections with great success. Both soldering and crimping are perfectly valid methods of joining connectors to wires. What I am saying is that it is pointless to do BOTH to the same terminal. It is simply a waste of time because soldering essentially undoes crimping.

Al Skierkiewicz 25-09-2014 21:49

Re: Electrical basics
 
James,
Loosing a World Champs to four time winner Beatty Machine is not pointless. We would be the only four time winner instead of the other way around. Since that loss we have won three times by crimping and soldering. You are never going to convince us otherwise. Sorry...

JamesCH95 26-09-2014 08:20

Re: Electrical basics
 
Quote:

Originally Posted by Al Skierkiewicz (Post 1401622)
James,
Loosing a World Champs to four time winner Beatty Machine is not pointless. We would be the only four time winner instead of the other way around. Since that loss we have won three times by crimping and soldering. You are never going to convince us otherwise. Sorry...

Well, I am disappointed to see a sound and technically-valid argument fall on completely deaf ears, especially in FRC.

Al Skierkiewicz 26-09-2014 08:22

Re: Electrical basics
 
I didn't say it was unsound, I am just saying don't fix what ain't broken.

JamesCH95 26-09-2014 09:04

Re: Electrical basics
 
Quote:

Originally Posted by Al Skierkiewicz (Post 1401662)
I didn't say it was unsound, I am just saying don't fix what ain't broken.

Al,

I guess I am not being clear here. Saying "you are never going to convince us otherwise" shows a remarkable amount of close-mindedness, something that I would not have expected. I would think that when presented with a compelling argument and data that anyone in FRC would be open to changing their mind. Perhaps your are not convinced now, and that's fine, but saying that you will never be convinced... that is what disappoints me.

Al Skierkiewicz 26-09-2014 09:11

Re: Electrical basics
 
James,
I don't want to mislead anyone. NASA does not allow soldered connections for the reasons that you have mentioned. The auto industry swears by them. In my heart I know you are right and I use crimped contacts everyday as often as I use soldered contacts. However, in our case, the team will not accept loosing another Championship to Beatty or any team because a of a failed crimp. It's a choice, and that is all it is. We take a lot of pride in our solder jobs and insure that a minimum of solder is used so as to not wick solder into the wire under the insulation. We also make an effort to correctly strain relieve all wiring and to tie it down so that it can't fall off or be pulled out. It is not always pretty but it always works.

Ether 26-09-2014 10:11

Re: Electrical basics
 

Al,

I (and perhaps others) would be interested to know if you did an in-depth root-cause analysis to determine why the crimp failed... and why soldering was the accepted solution instead of, for example, a change in the crimping process or better quality control of the crimping process.



Al Skierkiewicz 26-09-2014 13:31

Re: Electrical basics
 
The wire pulled out during the match. It could have been anything, but we know that soldering following a crimp does produce a more in depth visual check of the terminal. We made soldering standard practice some time ago and when we started using APP terminals, we continued soldering. We use a West Mountain Radio crimper for the APP contacts. All crimps are checked with a tug test prior to soldering. We like backing up the backup.

AdamHeard 26-09-2014 13:33

Re: Electrical basics
 
Quote:

Originally Posted by Al Skierkiewicz (Post 1401622)
James,
Loosing a World Champs to four time winner Beatty Machine is not pointless. We would be the only four time winner instead of the other way around. Since that loss we have won three times by crimping and soldering. You are never going to convince us otherwise. Sorry...

What year was this? 2001?

Al Skierkiewicz 26-09-2014 13:51

Re: Electrical basics
 
I can't remember years, but I can remember standing outside the back of the Einstein Stage at Epcot looking at the bare wire. I don't even know if we were calling it Einstein at that time.

Taylor 26-09-2014 14:08

Re: Electrical basics
 
Some guys wear special backpacks, some guys wear particular jerseys, some guys solder their crimps.
We've all got our superstitions and foibles.

(you don't believe me? Pay attention to yourself next time you eat M&Ms)

Ether 26-09-2014 14:58

Re: Electrical basics
 
Quote:

Originally Posted by Al Skierkiewicz (Post 1401733)
We like backing up the backup.

If what JamesCH95 said in post25 is strictly true, then you're not backing up the backup: you're replacing crimp with solder.

So there's an open question here.



Al Skierkiewicz 26-09-2014 15:01

Re: Electrical basics
 
We are not replacing the crimp, we are adding solder to a crimped connection.

JamesCH95 26-09-2014 15:20

Re: Electrical basics
 
Quote:

Originally Posted by Ether (Post 1401751)
If what JamesCH95 said in post25 is strictly true, then you're not backing up the backup: you're replacing crimp with solder.

So there's an open question here.



Quote:

Originally Posted by Al Skierkiewicz (Post 1401752)
We are not replacing the crimp, we are adding solder to a crimped connection.

I think it is understood that you're soldering a connector that has been crimped.

What I point out (and what Ether is noting) is that by soldering the crimped connection you are stress-relieving the crimped material, removing the effectiveness of the crimping. Because of this, one would get ostensibly the same result by soldering the terminal without crimping first.

Assuming, of course, that what I opine is correct and factual. Edit: this has been my point all along.

Al Skierkiewicz 26-09-2014 16:18

Re: Electrical basics
 
I disagree that the terminal would no longer be crimped after heating it for solder. I will experiment with that concept at a future time and let you know.

Ether 26-09-2014 16:35

Re: Electrical basics
 
Quote:

Originally Posted by Al Skierkiewicz (Post 1401769)
I disagree that the terminal would no longer be crimped after heating it for solder. I will experiment with that concept at a future time and let you know.

Thanks Al. Such data would be a useful addition to the FRC body of knowledge.



FrankJ 26-09-2014 16:50

Re: Electrical basics
 
You never want your solder to be your mechanical connection. So you want to crimp even if you soldier. You might lose some pressure from work hardening lost from solder. I am not going to speculate on that You are not going to lose the deformation though. If look at the automotive industry you will find mostly crimp connections with no solder. Cost could be a factor there. So done right, clearly you don't need solder. But that is with qualified tooling, qualified connectors & testing. Mil-HDBK-217F, a electrical reliability standard has a multiplier of 20 for failure rate calculation for non-qualified crimps to mil-spec crimps. The handbook does not have a base failure rate for crimp+solder. Not really an apples to apples thing, but shows the risks of doing the crimp poorly. The biggest down side to using solder is having the solder wick into the wire causing a stress riser & decreasing flexibility.

As for as I can see: Correctly crimped connectors do not need to be soldered. Solder done right gives you an extra bit of security for when the crimp is not done correctly. In any case you want to properly route your wires so the connection is not under tension & is not carrying the weight of the wires.

MrRoboSteve 27-09-2014 12:12

Re: Electrical basics
 
A bit more on the OPs question. In diagnosing robot failures, it's almost always some sort of mechanical issue. The symptoms you'll have on the field will be jerky, unreliable operation or rebooting of the cRIO/radios.

1. Ensure that terminal screws are tight. When you arrive at the competition -- check to see that they're tight, as the process of shipping/hauling the robot might have loosened the screws.

2. Wires should have strain relief / tie downs near the point of connection to the relay/speed controller. This reduces the chance that movement on the robot causes the screw to come loose.

3. See other discussion in the thread regarding how to fasten terminals to wires. Suffice it to say that there are engineering differences about the best way to do it. For your team, it's most important to select a method that works for you, have a procedure that everyone follows, and inspect the results of every crimp/solder operation.

Most robots I see have the correct wire sizes on them -- I'm not sure if it's because the inspectors are catching it before I seen it, or teams are doing a good job.

wireties 29-09-2014 00:14

Re: Electrical basics
 
Quote:

Originally Posted by Al Skierkiewicz (Post 1401769)
I disagree that the terminal would no longer be crimped after heating it for solder. I will experiment with that concept at a future time and let you know.

FYI - soldering a crimped connection is generally not allowed in high vibration environments like a military ship or plane. Perhaps you compensate for errors in the original crimping but you create another type of vulnerability where the solder stops. When using the correct crimp, tool and procedure crimps are very reliable.

I can see where one might solder a crimped connection on a FIRST robot. It does not have to last all that long. But in a professional environment this is not an acceptable practice. One must use the correct crimp for the wire and insulation type and install with the correct tool and procedure. Curiously the military allows us to solder to braided shields but only with a sleeve that includes heat shrink and glue that stress relieves the solder joint.

Richard Wallace 29-09-2014 06:33

Re: Electrical basics
 
Quote:

Originally Posted by wireties (Post 1402011)
FYI - soldering a crimped connection is generally not allowed in high vibration environments like a military ship or plane.

This is true for consumer appliances also.

Al Skierkiewicz 29-09-2014 08:06

Re: Electrical basics
 
Keith,
We are aware of those dangers and teach our students to carefully solder being sure to watch for solder to wick under the wire insulation. We also take other precautions that would not be practical in mass installations like ships and consumer products. However, our 2006 robot is still in service as a demo and we haven't had a failure in the electrical connections on that robot yet. It needs some mechanical repairs but we have beat it up pretty bad over the years.

kstl99 29-09-2014 08:18

Re: Electrical basics
 
I work in custom automation. The only time soldering to a crimp terminal is allowed is when crimping onto a solid wire such as a resistor. I do like the idea of teaching students how to solder and properly done I can see that soldering would not be a problem, I too believe that with the proper tooling it is not needed and not acceptable in manufacturing. I prefer to teach the students the techniques that are acceptable in manufacturing, and those will last just as long.

FrankJ 29-09-2014 09:47

Re: Electrical basics
 
For those who say soldering a crimp connector is not allowed. Is that a standard, company policy, or long standing practice? One reason I ask is you can buy Mil-Spec solder connectors. The ones I know of have a mechanical strain relief after the solder joint & no crimp so this really is not an apples to apples comparison.

wireties 29-09-2014 22:24

Re: Electrical basics
 
Quote:

Originally Posted by FrankJ (Post 1402027)
For those who say soldering a crimp connector is not allowed. Is that a standard, company policy, or long standing practice? One reason I ask is you can buy Mil-Spec solder connectors. The ones I know of have a mechanical strain relief after the solder joint & no crimp so this really is not an apples to apples comparison.

In my case it is a military standard plus many of my industrial customers have similar restrictions in their quality guidelines. Agree about the mechanical relief, that is an ideal scenario.

AdamHeard 29-09-2014 22:31

Re: Electrical basics
 
We use soldered mil spec connectors on military product at work. The connector backshell has mechanical strain relief to the cable though.

wireties 29-09-2014 22:38

Re: Electrical basics
 
Quote:

Originally Posted by AdamHeard (Post 1402171)
We use soldered mil spec connectors on military product at work. The connector backshell has mechanical strain relief to the cable though.

Lots of ways it can be done - I think it comes down to using the connector, pins and strain relief "as designed". And for better or worse an engineer who designed a crimp connector most likely did not intend it also be soldered (or spend the money to have it tested and qualified with the addition of solder).

Michael Hill 30-09-2014 07:51

Re: Electrical basics
 
Quote:

Originally Posted by AdamHeard (Post 1402171)
We use soldered mil spec connectors on military product at work. The connector backshell has mechanical strain relief to the cable though.

Are you referring to Amphenol-like connectors?

http://www.alliedelec.com/search/pro...x?SKU=70011029

FrankJ 30-09-2014 09:33

Re: Electrical basics
 
Quote:

Originally Posted by Michael Hill (Post 1402212)
Are you referring to Amphenol-like connectors?

http://www.alliedelec.com/search/pro...x?SKU=70011029

That style was the one I was thinking of although that is the industrial version. You can often buy non mil-spec versions of mil-spec connectors for a lot less. Mil-spec can require a lot more testing & QA procedures which add to the cost. The material specs can be relaxed for the non mil-specs version as well. The Mil-Spec MIL-DTL-5015 for circular connector has apparently been superseded by SAE-AS50151.

RonnieS 02-10-2014 10:06

Re: Electrical basics
 
Do you guys buy the 45 amp or 30 amp APP connectors? Also, what experience do you have with the 15 amp versions for smaller wire? We use 12 gauge wire for all motors so the 30 amp will be fine but was wondering if we should maybe buy the 45 amp ones in case we decided to go up to 10 gauge wire? how do the 45 amp connectors crimp to 12 gauge wire?
-Ronnie

EDIT: Do you guys get the ones you can break apart or the ones fused together as one unit?

timytamy 02-10-2014 10:51

Re: Electrical basics
 
Quote:

Originally Posted by Ronnie314 (Post 1402547)
*snip*

We pretty much follow this chart:

We've used the 15A, 30A and 45A contacts on their respective gauges without a problem.

The amperage ratings on the contacts are slightly misleading. All the contacts are rated to 45A, however it's recommended you only pass the listed currents through as that is what APP considers safe for those gauges. eg you can put 45A through the 15A contact, however it's unlikely that the cable it's attached to will survive. That being said, always use an appropriate gauge for each circuit, and sized such that it is legal for the rules. However, if you have 18AWG wire on a 20A circuit (legal per 2014 rules) don't worry too much about using the 15A contact, it's more important you match the contact to the wire gauge than the contact to the current.

We also tend to buy the fused connectors. The vast majority of our cables only need the conventional red/black combination, it's easier than roll pins or glue, and the slight extra cost is negligible. However we do keep a few loose ones about for when they're needed.

Finally I highly recommend getting the TRIcrimp tool for the PowerPoles, it's very easy to use and will crimp all three sizes (to the appropriate sized cable). They're available from Powerwerx and Andymark.

Al Skierkiewicz 02-10-2014 11:20

Re: Electrical basics
 
We have found that the 30 amp contacts can be slightly spread open to make inserting #10 easy. They are slightly large for #12 but a little tight for the #10. WE also now stock the 45 amp which is fine for #10. We use the West Mountain Raido crimper which does all three sizes. I am not entirely happy about the job on the 45 amp though.

Thad House 02-10-2014 11:27

Re: Electrical basics
 
Quote:

Originally Posted by Al Skierkiewicz (Post 1402558)
We have found that the 30 amp contacts can be slightly spread open to make inserting #10 easy. They are slightly large for #12 but a little tight for the #10. WE also now stock the 45 amp which is fine for #10. We use the West Mountain Raido crimper which does all three sizes. I am not entirely happy about the job on the 45 amp though.

Can you use the 30 amp on a 40 amp circuit? We've always used the 30 amps for 20 and 30 amp circuits, and the 45 amps for 40 amp circuits, because we thought you always had to use a connector rated higher.

FrankJ 02-10-2014 12:51

Re: Electrical basics
 
Quote:

Originally Posted by Thad House (Post 1402562)
Can you use the 30 amp on a 40 amp circuit? We've always used the 30 amps for 20 and 30 amp circuits, and the 45 amps for 40 amp circuits, because we thought you always had to use a connector rated higher.

The contacts will mate as long as the connector body is the same size. In FRC terms, the wire size govern the size breaker you use. The bigger concern is having the crimp side fit the wire. Having a poor crimp from the wire not fitting the contact, will cause more heat issues than using the "incorrect" contact. Of course you could always use solder. :]

Thad House 02-10-2014 12:57

Re: Electrical basics
 
Quote:

Originally Posted by FrankJ (Post 1402578)
The contacts will mate as long as the connector body is the same size. In FRC terms, the wire size govern the size breaker you use. The bigger concern is having the crimp side fit the wire. Having a poor crimp from the wire not fitting the contact, will cause more heat issues than using the "incorrect" contact. Of course you could always use solder. :]

I get that, but it looked like Al was saying that they use 30 amp crimps for 10 awg wire, which I would guess is being used in a 40 amp circuit. Which I always thought everything in the circuit had to be rated for 40 amps or more if using a 40 amp breaker.

RonnieS 02-10-2014 13:25

Re: Electrical basics
 
Quote:

Originally Posted by Thad House (Post 1402581)
I get that, but it looked like Al was saying that they use 30 amp crimps for 10 awg wire, which I would guess is being used in a 40 amp circuit. Which I always thought everything in the circuit had to be rated for 40 amps or more if using a 40 amp breaker.

I am wondering the same thing too. But as of now, ill be using the 30 amp ones for 12 gauge and the 15 amp for 18 gauge. We don't use 10 gauge wire right now so I am seeing no need to get them.

FrankJ 02-10-2014 13:33

Re: Electrical basics
 
Realize the battery plugs are "rated" for 50 amps & is on a 120 amp breaker. 6 gauge wire is rated for 101 amps for chassis wiring. But all these ratings are for continuous service. In FRC you are limited by battery size & match length.

Anyway back to the PP-45s. If you look on the data sheet, the rating comes from the UL rating based on 65 C or largest cable size. We are an edge case where peak current is much greater than average current. After heavy use, you can grab the connector without burning yourself, I wouldn't worry about it much. Build a panel that is going to be inspected by an UL inspector is a different subject.

Aren Siekmeier 02-10-2014 13:38

Re: Electrical basics
 
Notice that between the different sizes, the actual contact area between two crimps is roughly the same. What's different is the size of wire they crimp onto, so the current rating is for the wire size, and isn't related to how much current the crimp itself can conduct.

So if a 30A crimp gets a good crimp on 10 or 12 gauge wire, it will certainly carry the current, since it has the same connection contact with another crimp as the 45A crimps do.

timytamy 02-10-2014 20:39

Re: Electrical basics
 
I kinda answered this question already:
Quote:

Originally Posted by timytamy (Post 1402553)
The amperage ratings on the contacts are slightly misleading. All the contacts are rated to 45A, however it's recommended you only pass the listed currents through as that is what APP considers safe for those gauges. eg you can put 45A through the 15A contact, however it's unlikely that the cable it's attached to will survive. That being said, always use an appropriate gauge for each circuit, and sized such that it is legal for the rules. However, if you have 18AWG wire on a 20A circuit (legal per 2014 rules) don't worry too much about using the 15A contact, it's more important you match the contact to the wire gauge than the contact to the current.

Perhaps I wasn't clear enough, the current ratings associated with each contact is only UL's conservative recommendation based on the WIRE they attach to. ie UL's thinks it's not the best idea to pass 40A through the 15A contact, because the 18AWG wire that it's crimped onto won't safely carry that current.

And here's the information straight from PowerWerx:
Quote:

The size of the wire a Powerpole contact will accept is the primary limitation of their ability to carry a load. The size of the flat contact area is actually the same for all 15, 30 & 45 amp contacts. Powerpoles will safely handle higher loads or surges, please read the PP30 data sheet (PDF) for additional information.
The current rating for a cable is actually a far more complex relationship than matching a certain current to a certain gauge, it varies depending on length of run, ambient temperature, melting temp of insulation, airflow around cable, conductor material, type of current, etc. It's actually perfectly safe to pass ~100A through something as small as say 20 AWG, if it's a very short run, this is actually how fuses work (but don't try this on your robot).

That being said generally, these properties are simplified into rating tables, for FRC, it's ok to pass 40A through a 12AWG cable since the longest run that you might have is one or two meters, however the usual application for APP may involve runs up through ten meters in more hostile environments, hence the more conservative ratings.

TLDR: Current ratings on the PPs don't mater, chose a wire that is appropriate for whatever current you are using, and then select the PP for that gauge.

Al Skierkiewicz 03-10-2014 07:32

Re: Electrical basics
 
Tim,
The UL ratings are actually based on heat rise for specific currents under continuous duty. So if the contact rises above a certain temperature after having that current flowing for 24 hours or more, then it will receive a lower rating. We use the 30's because we have lot's of them. We purchased 45 last year to give them a try but don't really feel they are needed in our applications for two minute matches.

jlindquist74 13-11-2014 14:53

Re: Electrical basics
 
Quote:

Originally Posted by Richard Wallace (Post 1400759)
(Warning: he has over 9000 posts, and the majority of them are about wiring safety.)

ObNappa: WHAT! Nine thousand! There's no way that can be right!

cgmv123 13-11-2014 17:18

Re: Electrical basics
 
Quote:

Originally Posted by jlindquist74 (Post 1408438)
ObNappa: WHAT! Nine thousand! There's no way that can be right!

It's over 10,000 now.

Munchskull 13-11-2014 20:39

Re: Electrical basics
 
I am very intrigued to see the variety of ways teams work with their connectors. My question to the teams that solider and crimp is, what type of crimping tool do you use?

cgmv123 13-11-2014 20:57

Re: Electrical basics
 
Quote:

Originally Posted by Munchskull (Post 1408478)
I am very intrigued to see the variety of ways teams work with their connectors. My question to the teams that solider and crimp is, what type of crimping tool do you use?

The proper crimping tool depends on the type of connector. For Anderson Powerpoles, there's only one crimping tool designed to crimp them properly. Other more common connectors can be crimped with several kinds of crimping tools.

Munchskull 13-11-2014 21:00

Re: Electrical basics
 
Sorry I worded that question badly. I meant to ask whether or not their teams used ratcheting crimpers.

JamesCH95 14-11-2014 08:54

Re: Electrical basics
 
Quote:

Originally Posted by Munchskull (Post 1408482)
Sorry I worded that question badly. I meant to ask whether or not their teams used ratcheting crimpers.

If you're soldering the terminal there is no need to use a ratcheting crimper since the crimp is stress-relieved from the soldering process. There are only two reasons to crimp before soldering: to hold the terminal in place and to reduce the amount of solder needed to fill the joint.

Al Skierkiewicz 14-11-2014 09:04

Re: Electrical basics
 
Munch,
We use a ratcheting crimper and then solder. Our crimper is a West Mountain Radio tool but I am sure it was manufactured by someone else and just has their name on it. It may be a better tool than the one linked above as it has terminal retention to assist in holding the terminal prior to crimp. We use a very small amount of solder. We do not want to add to the rigidity of the connection but the solder does give us a little insurance and a slightly lower series resistance.

FrankJ 14-11-2014 09:37

Re: Electrical basics
 
To anneal to soft you need to heat copper alloys to 370C plus range. Most solder for electronics melt in 183-200C range. Unless you are way over heating your joint, I don't think you are annealing of the crimp.

JamesCH95 14-11-2014 10:17

Re: Electrical basics
 
Quote:

Originally Posted by FrankJ (Post 1408548)
To anneal to soft you need to heat copper alloys to 370C plus range. Most solder for electronics melt in 183-200C range. Unless you are way over heating your joint, I don't think you are annealing of the crimp.

Well, I said stress relieving, not annealing. For annealing that number sounds correct, though I haven't looked it up any time recently.

As far as I know, which I'll admit isn't that far, most electrical-grade copper parts such as wire terminals are made from C11000 (aka 110 grade, ETP) copper. C11000 stress relieves at 180C, which as you point out is a 'minimum' soldering temperature. My understanding is that the residual stresses in a crimped connection are a significant part of what gives a crimp terminal it's good electrical and mechanical properties, and soldering heats up the joint enough to relieve those stresses.

See the google book Copper and Copper Alloys, page 252, Table 4, for stress relieving temperatures for various copper alloys.


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