24-01-2014 21:54

SenorZ

Re: pic: Battery connector.....

Yowza. I haven't been in FRC too long, but I've never seen a battery cable melt like that.

24-01-2014 22:12

m1506m

I actually see this on the larger versions of these connectors on the fork trucks we drive at work. Not too often, but try getting a battery off a charger when the two connectors melt together.

24-01-2014 22:17

kevin.li.rit

Re: pic: Battery connector.....

Someone once told me that the 6AWG connectors were only rated for 80Amps...

24-01-2014 22:34

Michael Hill

Re: pic: Battery connector.....

Quote:

Originally Posted by kevin.li.rit Someone once told me that the 6AWG connectors were only rated for 80Amps...

24-01-2014 22:34

apalrd

Re: pic: Battery connector.....

Quote:

Originally Posted by kevin.li.rit Someone once told me that the 6AWG connectors were only rated for 80Amps...

25-01-2014 12:28

Joe Ross

Re: pic: Battery connector.....

Quote:

Originally Posted by Michael Hill I once met a rep from Anderson who was amazed and seemed concerned at how many amps we pull through them. So take that for what you will.

25-01-2014 13:02

EricVanWyk

Re: pic: Battery connector.....

Would you mind if I used the image at the top of this thread in a blog post for Mooshim? We're posting a video on how to measure contact resistance to identify this type of situation before it manifests as shown.

25-01-2014 15:57

Dad1279

Re: pic: Battery connector.....

Was that pre-assembled or did your team fasten the wires?

I've seen students (and mentors) get the connector in the shell upside down/backwards.

25-01-2014 17:50

apalrd

Re: pic: Battery connector.....

Eric: Sure, go ahead, I have 2 pics of this one if you want them.

This particular connector came from the KOP, where it was pre-terminated on the Anderson end and we crimped/dip soldered the other end with a large ring terminal.

We now buy fully terminated cables from AM or CTRE for the batteries, and make our own from #4 wire for the robot. We crimp both ends on a large press crimp, and dip solder the ring ends (not the connector ends) before assembly.

This cable came from the 2012 practice robot which melted 3 connectors. we also melted two on our 2011 comp bot during the off-season. This is the least bad failure of all of those, in two cases the black wire came through the red connector so the copper was showing all the way down the connector.


FIRST should really switch to the next size up connector.

25-01-2014 18:37

cgmv123

Re: pic: Battery connector.....

Quote:

Originally Posted by apalrd FIRST should really switch to the next size up connector.

26-01-2014 00:39

Al Skierkiewicz

Re: pic: Battery connector.....

Andrew,
I would like to examine this connector up close. I may need to disassemble the connector. Any way you can ship this to me? Jim or Ike has my contact info.
What hit me first off in the picture is why the red wire is not melted as the black wire is. They both pass the same amount of current.

28-01-2014 15:13

apalrd

Re: pic: Battery connector.....

Quote:

Originally Posted by Al Skierkiewicz Andrew, I would like to examine this connector up close. I may need to disassemble the connector. Any way you can ship this to me? Jim or Ike has my contact info. What hit me first off in the picture is why the red wire is not melted as the black wire is. They both pass the same amount of current.

28-01-2014 18:21

MrBasse

Re: pic: Battery connector.....

I'm suprised that nobody has said anything about the fact that a robot that can do that repeatedly is designed wrong. If you stay within the limits of your supplied hardware you wouldn't have this issue. Nowhere in the rules does it say you have to draw the amperage that you are. Would it make for a slightly les competitive machine? Maybe. Would it reduce the risk of melting connectors and destroying components? Definitely.

It just seems to me the a lower amperage rated connector is something that would result in an engineering challenge. I'm pretty sure that is what most of us are here for.

This seems comparable to someone complaining that their drill press doesn't work very well as a mill...

28-01-2014 18:31

Nuttyman54

Re: pic: Battery connector.....

Quote:

Originally Posted by MrBasse I'm suprised that nobody has said anything about the fact that a robot that can do that repeatedly is designed wrong. If you stay within the limits of your supplied hardware you wouldn't have this issue. Nowhere in the rules does it say you have to draw the amperage that you are. Would it make for a slightly les competitive machine? Maybe. Would it reduce the risk of melting connectors and destroying components? Definitely. It just seems to me the a lower amperage rated connector is something that would result in an engineering challenge. I'm pretty sure that is what most of us are here for. This seems comparable to someone complaining that their drill press doesn't work very well as a mill...

28-01-2014 18:36

Thad House

Re: pic: Battery connector.....

Quote:

Originally Posted by MrBasse I'm suprised that nobody has said anything about the fact that a robot that can do that repeatedly is designed wrong. If you stay within the limits of your supplied hardware you wouldn't have this issue. Nowhere in the rules does it say you have to draw the amperage that you are. Would it make for a slightly les competitive machine? Maybe. Would it reduce the risk of melting connectors and destroying components? Definitely. It just seems to me the a lower amperage rated connector is something that would result in an engineering challenge. I'm pretty sure that is what most of us are here for. This seems comparable to someone complaining that their drill press doesn't work very well as a mill...

28-01-2014 18:40

MrBasse

Re: pic: Battery connector.....

I had a feeling I would be disagreed with on that. I don't have a problem with that a all. I feel that the connector is definitely under rated for its purpose. But what I am saying is that we all know that rating going in. It wouldn't hurt to design for your components.

28-01-2014 18:50

Mykey

Re: pic: Battery connector.....

Forklift at work...



I tend to agree that the source of the problem is not the connectors. It sounds like you have an issue in your robot.

The only way I can think of their being an uneven current flow is if you have a short through the frame to ground. Also, if one connection starts to fail before the other, then the resistance on one side will increase at a higher rate than the other. This could cause uneven heat production. Seems unlikely though.

28-01-2014 19:03

Nirvash

Just from my experience with electronics and people using undersized connectors, it isn't odd to see one connector fail first or more dramatically.

28-01-2014 19:25

apalrd

Re: pic: Battery connector.....

Way way way back when the Anderson SB-50 connector was selected and apparently Anderson approved the higher current rating, the kit (this is back when you could only use parts from the kit or Small Parts) contained 2 Bosch drill motors and 2 Fisher-Price motors, and an assortment of small motors. The batteries were the same as they are now, but they used a 60a main fuse instead of the 120a main breaker we now use. Shortly after, the Victor was used, then the IFI control system. Now the rules allow 18 motors of similar power to those 4 drill and FP motors, robots have nearly tripled in speed, and the games are significantly more complex.

Now, we design to the 120 amp breaker, and put a lot of effort into keeping that breaker from tripping. Sometimes we design a bit too close, and it safely trips, and we take steps to prevent it from tripping again. We know what it will take, thanks to data sheets and trip curves. We already do a lot of design based on the main breaker and 40a branch breaker trip curves. We know when they will trip, we can run simulations of accel events, travel times, and distances to optimize our gear ratio to our strategy. We know how far we want to push the main breaker and we certainly know that when we exceed it, we have to scale back a bit but the failure is safe (even if it could cost us a match). In addition, in our pursuit of perfection, we design to push the robot as hard as possible during a competition. Maybe we push too hard. Then we go and drive the competition-designed robot for hours to practice, or at fast pace off-season events, and the issues show up.

We don't have a number or 'melt curve' for the 50 amp plastic connector (and I can not design my robot to 50a instead of 120a and stay competitive) so we can't design around it. Sure, we could empirically melt a whole bunch of connectors with a several hundred amp current limited lab power supply and huge load (the only reasonably safe way to do it) to get data on connector melting vs time vs load, or we could spend $5 more and buy a properly sized connector so the engineered electrical limiting device (the breaker) trips first and safely instead of the undersized connector.

The whole point of the main breaker is to safely cut power when we exceed the electrical limits imposed by the FIRST electrical system. We shouldn't rely on a plastic connector to fail (possibly shorting and causing several hundred amps from the battery to start a fire) as an energy limit. The connector is far too small for our application (even if it was approved for the current draw way back when) and the company even makes a connector the right size for us.



It's not the robot, it's several robots over several years of practice and off-season events, designed at relatively common FRC speeds with quite efficient drivetrains. We run them (on the practice bot) for hours at a time, running roughly 50% duty cycle, but we can't upgrade the connector on the practice bot without upgrading all of the batteries (which we also need to take to competition, and plug into the comp bot).

28-01-2014 19:35

MrBasse

Re: pic: Battery connector.....

And again, I'm not saying that you aren't doing anything that a lot of FRC teams are doing everyday. I think it is safe to say that everyone pushes the limits of the Anderson connector. However, I think what we can learn is that you have pushed it too far a few times. Either by design or by use. I'm not saying you should design for 50A, as that would take the amazing machines you make down quite a few levels. I agree that FIRST should upgrade the connector to a higher rated connector. However, I also know that they haven't. I also haven't seen hundreds of other teams reporting melted connectors. So perhaps it is something in the way you have designed/built/run your machines.

I appreciate the response and I see where you are coming from, but perhaps that should be where you go back and modify your approach a little rather than complain about the supplies you have been specified. Last year we ran our robot for hours and never melted a connector, the year before the same, the year before the same. Thousands of other teams have done the same (though maybe they are all being oddly quiet about this). It's not an attack at you, just a sign that something you are doing isn't quite jiving with the required components. The downside is that this problem creates a very unsafe condition.

28-01-2014 19:49

apalrd

Re: pic: Battery connector.....

I'm not complaining about the part as specified, I'm complaining that we are stuck using a part that was specified 15 years ago with 1/5th the power in the kit and 1/2 the main fusing capacity.

I don't think it's an issue of FIRST actually wanting us to use the connector for engineering reasons, I think it's a case where FIRST is using the same connector they have been using because they have been using it forever and have no motivation to change. I am trying to give FIRST a good motivation to change to an appropriate connector.

Since we went up to #4 main battery cables, we haven't melted any connectors. Using #4 was our engineering change to both melted battery connectors and main breaker trips, and it generally worked.

28-01-2014 19:56

EricH

Re: pic: Battery connector.....

Quote:

Originally Posted by MrBasse Last year we ran our robot for hours and never melted a connector, the year before the same, the year before the same. Thousands of other teams have done the same (though maybe they are all being oddly quiet about this). It's not an attack at you, just a sign that something you are doing isn't quite jiving with the required components. The downside is that this problem creates a very unsafe condition.

28-01-2014 20:08

sanddrag

Re: pic: Battery connector.....

I'm curious about the condition of the contact itself, prior to melting. Was it significantly worn or scratched from touching wires directly to it to test motors, or clipping alligator clips to it?

28-01-2014 20:09

MrBasse

Re: pic: Battery connector.....

Quote:

Originally Posted by EricH If I may ask: How many motors are you guys running at a time? 4 CIMs? 6? A couple of window motors? A compressor? And how long at a time? 2.5 minutes? An hour? 6 hours? See, here's the thing. Sure, hundreds of teams may have run their robot for hours over the season last year. But there are teams who will literally stop driving around only to change or charge the battery in any given multi-hour session. These teams may have 6 CIMS, a pair of MiniCIMs and a pack of other motors of the 550 and 775 varieties, plus the compressor, active at the same time, for much if not all of that time. That's one large amount of current potentially being pulled. Now, I haven't heard of any failures locally, but that doesn't mean that it's not happening--or not at the edge of happening. (The other possible explanation is that the connectors are wearing out due to fatigue/heating of the area around them, then not seating properly and adding a spark to the mix--then they melt, then they burn.) And I'm pretty sure the Bees tend to run on the high end of both total run time, and time in a session, as well as lots of motors, and they tend to run enclosed bots, which will get some heat build up inside. If you're running on the low end of all of those with an open bot, you probably won't see anything similar.

28-01-2014 20:33

Dale(294engr]

Re: pic: Battery connector.....

This is a contact resistance problem, (one black, one red)

caused by improper connector seating (i.e. not fully inserted / mated)

exacerbated by crud, dirt, scratches on the contact surfaces +alignment

worsened with use (insertion cycles), years of use / misuse

(so these units more likely to be relagated for use only with practice robots)

analysis:

Two considerations:

P=I^R 1st order heating /melting localized at conductors contact point

2nd order Vdrop=IR = degraded robot performance: less I due to less V

A good estimate for average competition Robot current draw is ~50A

50^2= 2500 * RohmsPerContact =.001 ohm (1 milliohm arbirtary example)

P=2.5W =no problem with heating, no time limit

now include intermittent multi motor high current start / reverse periods .1-.3 sec of currents up to ~400A ^2 = 160,000 *.001 = 160W which is only a problem if it exists too long i.e. allowing build up heat at connector contact(s) junction.

at ~1sec expect some melting!!

Realistically.. Anderson contact resistance greater than .001 ohm happens
then at .002 ohm double the above.. .003 triple, .004 quad etc.

2nd order performance problem is connector contact IR drop,
i.e. Voltage drop (V-IR)
or sag as it may be referred to

400A *.001 = .4v loss * 2 for both sides) = .8v droop or 11.8v available to all robot systems

(brief battery Vsag is ~= .1v/50A so 400A is 4v additional loss
.. 12.6 -4.8 = 7.8v available to motors (and all electronics)
(simplified, disregards that motors will draw less current as Vbatt sags)


(12.6-.8v = 11.8v for new battery, fully charged, discharging at 50A so must subtract an additional .1v for internal battery Resistance sag at 50A delivery, Batt Voltage now is 11.7v Best Case!)

.. critically, motors provide less torque as less peak current is available as more voltage is dropped across contact resistance(s)
(plus all other connections & wire, to & from all motors)

.. before the melt and fall apart.. melt progresses quickly past a certain point, the contact resistance quickly rises, hastening the melting process due to I^2R heating leading to a forced disconnect due to melting apart.

The single surface contact area used by Anderson has always concerned me.
Seems a bifruc pin into a barrel would guarantee more surface area at the cost of a slightly larger physical connector (or perhaps two, one single for each side - just need to assure logistics of improper polarity mating.. opposite sex for + & -and a way to prevent plugging Battery into itself unfused..

Perhaps ALL batteries should be fused at the battery side.

I have witnessed upset robots battery terminals short against aluminum frame, overheat and smoke. Batteries have lead internal "fuse" safety link connections between the 6 ea 2v cells.. so depends on the condition in competition of battery charge state /condition plus resistance of terminal to frame "short" to determine when & if link melts (fuses), opening the circuit, or just smokes until the stored charge is consumed... in heat!

Good luck in competition

.. and may all your connector contact reisistances << .001 ohm until after the championships...

28-01-2014 22:34

nuttle

Re: pic: Battery connector.....

I'd also very carefully check the condition of the contacts. Could you have a charger cable that is scratched up and damaging the battery connectors? This could be the type of thing you'd only see upon close inspection. Also, anyone happen to know how many mate/unmate cycles are specified before contact resistance becomes too high? For example, plating wears away, metal oxidizes, and you now have much more resistance? Or, maybe the spring loses enough force that the contact is no longer very good?

Also, can't count the number of times I've seen someone use the leads as a carry handle, but that's another topic.

28-01-2014 23:00

Al Skierkiewicz

Re: pic: Battery connector.....

Guys,
Hold on so we get some real facts listed. The SB 50 was not introduced when we went to the IFI controllers. It became mandated much later. WildStang used a similar connector for many years prior to the start of the SB50. The battery is capable of 600+ amps when fully charged and that drops off with discharge. The main breaker is also capable of 600+ amps for several seconds without trip. The SB50 is rated for 50 amps continuous, that is every hour for every day, for ever. The rating is verified by UL testing based on temperature rise over long term use, that is more than a day at continuous current. The test includes a safety margin meaning a fixed amount of excess current will not raise the temperature beyond the safe limits set by the UL test. The UL test data is on the Anderson website if you search for it. As I remember the safety margin is like 100%. That is 100 amps continuous for more than a day without exceeding the set temperature.
Andrew, there are many reasons for connector failure, that is why I would like to look at the connector if possible. I have seen some failures, I would like to add to my data with your connector.
Please remember that the 120 amps forktruck connector may be terminating a 24, 36 or even higher voltage. Please do not be lulled into believing your are talking apples and apples when just looking at the connector.

29-01-2014 01:24

EricH

Re: pic: Battery connector.....

Quote:

Originally Posted by MrBasse Would you run your KOP compressor for an hour straight and expect it to maintain peak function?

29-01-2014 02:16

Nirvash

Re: pic: Battery connector.....

Quote:

Originally Posted by MrBasse Would you run your KOP compressor for an hour straight and expect it to maintain peak function?

29-01-2014 03:52

Tristan Lall

Re: pic: Battery connector.....

I'm just waiting for someone to show up with active cooling on their battery connector. (This isn't as ridiculous as it seems, if your intention is to follow the rules, and yet still extract maximum performance from your robot.)

I actually thought it was FIRST's intention to allow the SB120 (and other) connectors this year, when I noted on kickoff day that the rules referred to Anderson connectors without referencing the KOP checklist or the SB50 model. But it appears that in order to avoid undersized Anderson connectors being used, FIRST amended the rule to specify the SB50 only, rather than any SB-series connector rated by APP for at least 50 A. (Some teams were already using the SB120, which was at least plausibly legal in some years, but probably illegal in others.)

Quote:

Originally Posted by Al Skierkiewicz Hold on so we get some real facts listed. The SB 50 was not introduced when we went to the IFI controllers. It became mandated much later. WildStang used a similar connector for many years prior to the start of the SB50.

29-01-2014 08:06

Al Skierkiewicz

Re: pic: Battery connector.....

The SB50 was "recommended" in 2003 and 2004 but was not required until 2005 when the battery was no longer weighed with the robot. We used an Anderson 50 amp connector that Motorola used for attaching batteries to cell phone amps in the field. They use the same contacts in a different housing as I remember.

29-01-2014 08:30

Chadfrom308

Re: pic: Battery connector.....

The monsters have never had this happend, but we did fry a couple of wires that were going to motors that got caught up and stalled.

Also, last year it probably didn't help that we had an OCCRA 80A breaker on our robot

Needless to say that is never going to happen again.

29-01-2014 10:39

Joe Ross

Re: pic: Battery connector.....

Quote:

Originally Posted by Al Skierkiewicz The SB50 was "recommended" in 2003 and 2004 but was not required until 2005 when the battery was no longer weighed with the robot. We used an Anderson 50 amp connector that Motorola used for attaching batteries to cell phone amps in the field. They use the same contacts in a different housing as I remember.

29-01-2014 11:30

Al Skierkiewicz

Re: pic: Battery connector.....

Yes,
But it is not identified as an SB50 nor is it shown on the electrical drawing. In the KOP it is not even listed as to manufacture.

29-01-2014 11:38

Joe Ross

Re: pic: Battery connector.....

Quote:

Originally Posted by Al Skierkiewicz Yes, But it is not identified as an SB50 nor is it shown on the electrical drawing. In the KOP it is not even listed as to manufacture.

29-01-2014 12:42

Al Skierkiewicz

Re: pic: Battery connector.....

OK, Joe, I knew this was a WildStang rule. It is all flooding back to me now. Thanks for finding the thread. As Aidan explained in that thread, Anderson was fully included in the testing at the time. We did some independent testing and thought our connectors were better but after further investigation at the time, we did adopt the SB50. We have now 10 years of use with our current style of battery and these connectors over thousands of matches. They seem to be doing very well. Even Raul eventually relented.

30-01-2014 10:03

Al Skierkiewicz

Re: pic: Battery connector.....

Look what my students found last night while unpacking some stuff.
I will have to post the picture somewhere else, I can't post pics here.

31-01-2014 14:14

apalrd

Re: pic: Battery connector.....

Would it be possible for FIRST to allow both the SB-50 or SB-120? I can't imagine any issues (other than 'the rules don't allow it') to use the next size up connector.

31-01-2014 14:35

Joe Ross

Re: pic: Battery connector.....

Quote:

Originally Posted by apalrd Would it be possible for FIRST to allow both the SB-50 or SB-120? I can't imagine any issues (other than 'the rules don't allow it') to use the next size up connector.

31-01-2014 14:44

apalrd

Re: pic: Battery connector.....

Quote:

Originally Posted by Joe Ross I assume you've already seen Q81?

31-01-2014 14:47

Karthik

Re: pic: Battery connector.....

Quote:

Originally Posted by apalrd Would it be possible for FIRST to allow both the SB-50 or SB-120? I can't imagine any issues (other than 'the rules don't allow it') to use the next size up connector.

31-01-2014 15:41

sanddrag

Re: pic: Battery connector.....

I'd like to see a bigger connector, to allow for the use of 4ga wire without having to cut it down to fit in a 6ga terminal.

In 2003, we used some big single-pole Anderson connectors on our battery, and it was legal at that time. But, it was denied in later years.

31-01-2014 16:21

Bill_B

Re: pic: Battery connector.....

Bigger connector is heavier, so to the extent that battery and attachment is excluded from the weight of the robot, a team using larger connectors can add more weight this way. Heavier wire and heavier connector = advantage? This is without current carrying advantage of some degree.

31-01-2014 16:29

cgmv123

Re: pic: Battery connector.....

Quote:

Originally Posted by Bill_B Bigger connector is heavier, so to the extent that battery and attachment is excluded from the weight of the robot, a team using larger connectors can add more weight this way. Heavier wire and heavier connector = advantage? This is without current carrying advantage of some degree.

31-01-2014 16:31

apalrd

Re: pic: Battery connector.....

The weight of a plastic connector is a drop in the bucket compared to the brick of lead, which varies by pounds between batteries of different manufacturers.

The big advantage is in current carrying capacity, which FIRST already limits using the 120a breaker. Most of the benefits are thermal, and prevent the wires from becoming sticky or melting (we frequently run the robot hard enough for the #6 wire on the battery to become sticky in 1 match time, at the very least it's always warm to the touch).

IMHO, the goal is usually to reduce weight for performance. If we ever are trying to add weight, it's always for CG management (esp. the 2012 bridge balance, or 2013 hanging).


I really want to put an end to the near-failures of the main power system we see every year. Even if the connectors don't fail catastrophically like the one in this picture very often, the wires are always sticky, and showing signs that they are undersized. And even if the connector is adequate, we can't easily put a larger wire in the connector, even if there are no rules prohibiting us from using a larger wire (currently we can use #4 wire for the battery side cable, so any argument of weight or capacity of the wire is null).

31-01-2014 16:45

Al Skierkiewicz

Re: pic: Battery connector.....

Quote:

Originally Posted by apalrd The weight of a plastic connector is a drop in the bucket compared to the brick of lead, which varies by pounds between batteries of different manufacturers.

31-01-2014 17:05

apalrd

Re: pic: Battery connector.....

Quote:

Originally Posted by Al Skierkiewicz I assume you are talking about the battery. If your battery weighs less than 12 to 13 pounds, you have vented a considerable amount of moisture to the atmosphere. There is a difference in the FR rated case but then again slight. Otherwise there is little difference in batteries.

31-01-2014 18:19

Al Skierkiewicz

Re: pic: Battery connector.....

http://www.chiefdelphi.com/media/photos/39426
Check out this from 2004, found my electrical students as we check through and unpack our boxes from our other build space.

Joe as promised...

01-02-2014 00:37

cglrcng

Re: pic: Battery connector.....

I did see that exact type of thing happen on our robot last year except not quite that far as they shut it off at the breaker. When the drive team came back from an early AM qualifying round, the student w/ the battery in his hands complained that I gave them a dead battery..."No way, no how" I said...as I checked it w/ a multi-meter myself I said just before handing it to him before the round.

I immed. began to inspect the battery Anderson clip Battery half (since it actually burned my hand during the semi-disgusted hand off) - and I saw melting of the clip & cables, and it was still very hot to the touch, so I took it apart and looked at the ends inside the clip...They were a bright orange copper color instead of alum. color.

I abruptly said...You do not have a battery problem folks..."You have a frame grounding problem," and pulled out the multi-meter from atop the battery cart and we began looking for the problem immediately. Sure enough, a frame grounding problem was immediately noted by a simple OHM check. That frame was grounded.

The hunt began....Sure enough, it took a while, but we found that (2 of the students had removed and reinstalled the CRIO the night before just before pit closing), and there was a nice short bright & shiny chromed Phillips Head screw near the bottom on the outside of the CRIO that was touching the lower chassis frame rail, that wasn't doing so the day before, (the CRIO's all come w/ that very unnecessary grounding screw), but, the CRIO is not supposed to be grounded to the frame in that manner at all. Same issue also cropped up w/ a grounded camera a few years back at champs that took a while to find.

Once that grounding issue to frame was cleared up...I have never seen that Anderson connector problem again. A simple ohm (00.00 meter read), check from battery to frame should tell you that you may just have the same exact problem I personally think.

I do know if they had not shut that robot power main breaker off very quickly, it could have been as bad as your pic or much, much worse. It did melt the outside insulation of the cables together right above the Anderson connector for about 2 inches (that was correctable as they pulled right apart and were still insulated properly, but those cable ends were junk), and melted slightly the connector itself...It was quite hot! That was very apparent.

Post back if you find it was a frame grounding issue please.

01-02-2014 00:54

Nirvash

Re: pic: Battery connector.....

Quote:

Originally Posted by cglrcng I did see that exact type of thing happen on our robot last year except not quite that far as they shut it off at the breaker. When the drive team came back from an early AM qualifying round, the student w/ the battery in his hands complained that I gave them a dead battery..."No way, no how" I said...as I checked it w/ a multi-meter myself I said just before handing it to him before the round. I immed. began to inspect the battery Anderson clip Battery half (since it actually burned my hand during the semi-disgusted hand off) - and I saw melting of the clip & cables, and it was still very hot to the touch, so I took it apart and looked at the ends inside the clip...They were a bright orange copper color instead of alum. color. I abruptly said...You do not have a battery problem folks..."You have a frame grounding problem," and pulled out the multi-meter from atop the battery cart and we began looking for the problem immediately. Sure enough, a frame grounding problem was immediately noted by a simple OHM check. That frame was grounded. The hunt began....Sure enough, it took a while, but we found that (2 of the students had removed and reinstalled the CRIO the night before just before pit closing), and there was a nice short bright & shiny chromed Phillips Head screw near the bottom on the outside of the CRIO that was touching the lower chassis frame rail, that wasn't doing so the day before, (the CRIO's all come w/ that very unnecessary grounding screw), but, the CRIO is not supposed to be grounded to the frame in that manner at all. Same issue also cropped up w/ a grounded camera a few years back at champs that took a while to find. Once that grounding issue to frame was cleared up...I have never seen that Anderson connector problem again. A simple ohm (00.00 meter read), check from battery to frame should tell you that you may just have the same exact problem I personally think. I do know if they had not shut that robot power main breaker off very quickly, it could have been as bad as your pic or much, much worse. It did melt the outside insulation of the cables together right above the Anderson connector for about 2 inches (that was correctable as they pulled right apart and were still insulated properly, but those cable ends were junk), and melted slightly the connector itself...It was quite hot! That was very apparent. Post back if you find it was a frame grounding issue please.

01-02-2014 01:26

BBray_T1296

Re: pic: Battery connector.....

Quote:

Originally Posted by Nirvash Also if a grounded frame was passing current, you have the even bigger issue of a positive line shorting to the frame as well.

01-02-2014 01:43

Nirvash

Re: pic: Battery connector.....

Quote:

Originally Posted by BBray_T1296 The same amount of current leaves (red) the battery as enters (black). Either could have melted, the red just gave first

01-02-2014 01:52

cglrcng

Re: pic: Battery connector.....

A simple check w/ a multi-meter will tell the tale. (But I know it happened, and our Ohmmeter did not lie...There was resistance present). Removed that screw, no resistance present. No more frame grounding issue

All I can tell you is; Removing the very unnecessary grounding screw on the blunt flat end of the CRIO cured up the frame ground issue immediately. The CRIO is powered by a regulated 24V power supply from the PD Board and am told by many since the incident (we have not before or since melted any of our Anderson connectors 2.5 minutes or hours), should never touch the frame (or ground to the chassis). That screw is chromed and unpainted. (And now completely gone from all of our Team CRIO's).

Go to this link; Scroll down to the Pic below "Attach To Robot" (where they instruct teams to attach your completed Control system boards to the robot).

http://wpilib.screenstepslive.com/s/...m#!prettyPhoto

Now, make that pic larger using the symbol lower right, look at the flat end of the CRIO in the left part of the pic. You will see the grounding screw I am talking about on the right hand side. (And that one is actually very close to that frame itself though not actually touching it in the pic, but could very easily later). Ours was caused by a hasty reinstall by 2 very tired students is all.

http://wpilib.screenstepslive.com/s/...dware-overview

"The PD provides a regulated 24V power supply to power the cRIO, a special, regulated 12V power supply for powering the robot radio and a 5V power supply for powering an Axis camera."

Are you absolutely sure it could not possibly have caused that? We know why that screw grounded to frame, and we know it cured up our issue, that bot still sits in our shop and still runs today. And did the rest of that day.

01-02-2014 02:10

cglrcng

Re: pic: Battery connector.....

Nirvash,

Ever taken a No Good CRIO apart that has been used on a competition bot before? One that has been drilled on for a season or 2, etc.....Alum. flakes are everywhere on the surface of the board. I didn't actually check that screw to see if there was any positive current present w/ the battery connected...The battery was already out and in hand when we received the bot back at the pit.

I was only saying check it first. Thousands of hours of runtime, and only a few failures, points away from the Anderson Connectors in my mind is all.

The most costly failures I have seen so far have been caused by a wayward staple (from the back of a bumper), down in a sidecar crossing about 10 pins, and some magic smoking motors turned to actual flame. But 2 major items that will frame ground are that CRIO and the rear grounding lug if used for mounting on the older cameras. Though Jags & CAN I am not at all happy with since it cost us big 2 years ago repeatedly.

I'd bet Texas Instruments could tell us why that screw is even there.

01-02-2014 03:10

Bill_B

Re: pic: Battery connector.....

Quote:

Originally Posted by apalrd The weight of a plastic connector is a drop in the bucket compared to the brick of lead, which varies by pounds between batteries of different manufacturers. ....

01-02-2014 07:56

Al Skierkiewicz

Re: pic: Battery connector.....

In the event of a frame fault, the cRio and/or DSC can produce some really crazy issues. In this case I suspect that the fault may have caused multiple motors to turn on in opposite directions or were commanding movement when none was possible. Why? High current in the #6 wire has to go someplace. If it shorted in a #18, then the breaker trips and the wire goes poof. If multiple loads are drawing extreme currents, then no breakers trip and no other wire gets hot enough to melt. When robots get crazy, suspect a frame fault first and look for it. It is sometimes difficult to find. You can try by pulling breakers and adding them back one at a time while looking for the issue. This is how the Banebot shorts were found a few years ago.

01-02-2014 08:05

dradel

I'm going with one or more of the following possibilities. Loose connection causing resistance, a failing crimp causing resistance, corrosion on the terminal causing resistance, or possibly a loose fit between the terminals when plugged together causing resistance.

01-02-2014 08:10

Michael Hill

Re: pic: Battery connector.....

Quote:

Originally Posted by Nirvash What I mean is, if your frame is 'grounded', it has the same potential of the negative terminal on the battery. No current should flow across it unless something with a positive potential is also shorted to the frame.

01-02-2014 09:11

apalrd

Re: pic: Battery connector.....

I do not know if there were grounding issues with either robot, but neither robot acted erratically at any time (one of them was competing in an off-season).

We know that one of them was drawing significant drivetrain current because the frame re-bent. Our 2011 robot crate was dropped while loading on it's way to the championship and the frame bent, but we hammered it straight at CMP. It re-bent at the Kettering Kickoff off-season, and melted 2 battery connectors in the same day. The replacement connector was taken from a battery as we did not have spares (they had never failed before).

The other robot was a practice robot. We geared it a bit too high, and practiced with it very hard. Eventually we added large KOP fans (the metal kind that were in the kit for a few years) to the drive motors to help them cool down (the CIM motor wires were getting very hot). The front roller was also very lossy so we threw more motors at it to get it to a reasonable speed (we had a 'joe johnson style' cross feed roller using bevel gears). The robot in general was a power hog without any additional issues. The main breaker should have tripped if we were using too much current, it did not.

During the 2012 comp season, we tripped the main breaker 3 times, then started cooling the main breaker using a cold bag of washers (set in a cooler of dry ice between matches), and replaced the battery cable to prevent failures at MSC.


The point is there are robot use cases that can melt the battery connector BEFORE the main breaker trips. This is a SAFETY ISSUE. Even if we are drawing too much current, the whole point of the main breaker is to open before any major safety issues happen.