Re: Power From The Wall
 

I would swap the motors for lower draw ones to make this easier.

From there, you can probably get away with surplus server power supplies.

Similar suggestions to PC ones above, but higher power, cheaper and easier to modify.

http://www.tjinguytech.com/my-projects/HP47A

is a good resource.

Re: Power From The Wall
 

The manufacturer's recommended rated is ~5.5 amps. Charging the battery at 6 amps is pushing it, but allowed because virtually all chargers that are rated for 6 amps only put out 6 amps for a very limited time. Charging a battery at a constant 20 amps is asking for trouble. ([1])

As for the PDB, the short answer is that all chargers are not created equal. Some chargers will cause more damage to the PDB power supplies than others, since the supplies are more sensitive to voltage variances than batteries. ([1],[2])

Re: Power From The Wall
 

Here's what you're not taking into account. With a 20A charger in the system, you're not charging the battery at 20A. You're using the 20A charger to supply the base load of the robot. When the power demand is for greater than 20A, the battery picks up the load. This will discharge it slightly, and once the load has been reduced, it will recharge at a low rate. The only way you exceed the 5.5A rate is if you have started to drain the battery. This could also be solved by using a motorcycle battery in place of the standard FRC battery.

As to the voltage spikes, that's an engineering problem which can be solved a few different ways. One way would be making sure you don't use that kind of charger, another would be to increase the capacitance in the system to dampen the spikes. I'd like to know the load on those chargers when the spikes were recorded.

Re: Power From The Wall
 

I'm interested. Have you got something written up that you could post or link to?

(Not sure what to do with all the wires; see attached pic)

Re: Power From The Wall
 

Here's a couple:

• http://www.instructables.com/id/Conv...Bench-Top-Lab/
• http://makezine.com/projects/compute...upply-adapter/

I've found one that is variable and uses a PWM circuit vs. the typical LM317 adjustable regulator. Here's another one.

Now that I've been reminded, I have an old 480W PSU to repair (solder in some new 2200 uF caps) and convert to a bench power supply. It's a little more wallet-friendly than this

Re: Power From The Wall
 

There are a number of instructional videos on how to convert ATX supplies to benchtop supplies, but this is the one I used: https://www.youtube.com/watch?v=z2oSFpKh_Uw

I added LEDS to the "power good" and "5v standby lines" as status indicators. Not necessary, but it's helpful at times.

SIDE NOTE: I suggest you avoid Dell OEM supplies. They sometimes have different color codes.

Re: Power From The Wall
 

I would say that unless you need the 5V rail, the use of server power supplies I linked are much more cost effective.

Re: Power From The Wall
 

I doubt the LM317 would be capable of putting out the amount of current required for OP's test bed. The cRio alone is rated for 800mA, which is half the LM317's nominal current output. Add a sidedar and some motors, and you're well over the 317's 1.5A rating.

Here's some pics of my conversion. I've done a couple others, and they all work very well.
https://drive.google.com/file/d/0B4P...it?usp=sharing
https://drive.google.com/file/d/0B4P...it?usp=sharing
https://drive.google.com/file/d/0B4P...it?usp=sharing

Ether didn't ask for one capable of powering a robot ;)

That's a good point in case someone wanted to use it though.

Re: Power From The Wall
 

True :D If you're doing something smaller, a LM317 should work fine, just throw a heatsink on it (and, in a cinch, mayonnaise makes an effective thermal paste). The supply pictured is a 270W OEM supply from an early 2000s IBM desktop. I have also converted an off-the-shelf Antec 350W supply, and another OEM supply I had sitting around. All of them work, and I prepared all three in the exact same way, except for the dummy load resistors, which vary due to supply size/what I had sitting around.

Re: Power From The Wall
 

The CNC Lathe at my work has a 20hp vector drive amplifier that powers a DC brushless spindle servo. The problem is that it takes 3 phase 240 volt ac power and cost $5,000.

In realistic terms, maybe try getting as big of a battery as possible? maybe a car battery or a really big lipo (very expensive)?

The thing is, batteries running out of juice isn't necessarily a bad thing. The motors get really hot (especially because they are hauling a 150lbs robot around), the compressor needs to catch up (it only has like a 20% ish duty cylce) and it can give you a way to take turns.

Re: Power From The Wall
 

It's just that I already have a half dozen PC desktop power supplies that I harvested and have been wanting to experiment with them, and possibly find a use for them (other than as a door stop).

Re: Power From The Wall
 

Converted ATX supplies are very realistic. They're designed to provide very consistent power for very sensitive components. The motor will only get severely hot if there is a significant difference between the forward voltage and back EMF. At free speed, the back EMF should match the forward voltage, meaning the motor won't heat up significantly. In other words, OP, don't put any force on the motor, let it spin freely.

Re: Power From The Wall
 

Bummer. I was going to use the Dell (pictured in earlier post).

Do you know of a resource anywhere for decoding the Dell color scheme?

The motherboard is long gone so I can't trace where the wires were going.

Re: Power From The Wall
 

I would imagine the pinouts are still the same since it will conform to the ATX standard. if you have the molex connector on there, check out http://en.wikipedia.org/wiki/ATX#Power_supply

Just beware that ATX supplies can be rather noisy (electrically speaking)