Battery connected backwards to robot

[dardeshna]

So in the rush to get ready for SVR this week, I wired the leads on one of our batteries backwards. I didn't notice and no one else noticed, so when we plugged it in apparently our breaker made a clicking noise and may have tripped at some point. Regardless, it was left plugged in backwards and on for roughly 10 seconds.

The bad part - the damage. Apparently our VRM is shot, our PCM may be nonfunctional, and our PDP only supplies power to certain rails. Is this a problem that someone else has ran into and had to fix? Or are we just out of luck?

Cheers,
Devin Ardeshna (FRC Team 8)

[Jon Stratis]

Sounds like you need to start replacing components. Unfortunately, those components aren't really designed to handle reverse voltage.

[RufflesRidge]

Originally Posted by dardeshna

The bad part - the damage. Apparently our VRM is shot, our PCM may be nonfunctional, and our PDP only supplies power to certain rails. Is this a problem that someone else has ran into and had to fix? Or are we just out of luck?

Interestingly, none of these are the failures I would expect.

The VRM is reverse polarity protected. The PCM is not as explicit in the documentation, but I thought it was as well.

The PDP outputs are just copper, to damage it like that you have described, you would have had to fry the traces off the board. Are you sure it isn't the devices attached to those rails that are damaged?

Your motor controllers are the most likely to be damaged by a reverse polarity event.

[Al Skierkiewicz]

Devin,
To check the output of the PDP disconnect all your loads and try a known good device connected to each output. As pointed out above, there is nothing in the distro that can go bad. However, there is a lot of electronics in the PDP that will be affected by reverse polarity. My suggestion (I know you don't want to hear this) is recycle everything. If it isn't bad now it will fail when you need it the most. The clicking you heard is the resettable breakers.

[anushad]

Are you sure your PDP is shot? Talons/motor controllers burn out super easily; I would check those before replacing the PDP, as it's a pretty nice piece of equipment that is well protected. I wouldn't be surprised if your VRM and PCM needed to be scrapped though; sorry about that.

[Ether]

Originally Posted by dardeshna

I wired the leads on one of our batteries backwards. I didn't notice and no one else noticed

I'm wondering how common this mistake is, and if other teams have implemented a process change as a result.

[brunoUC]

Hello! have you checked the 20A and 10A fuse on the PDP? we had a similar issue and it was a bad fuse.

[ctt956]

Originally Posted by Al Skierkiewicz

Devin,
To check the output of the PDP disconnect all your loads and try a known good device connected to each output. As pointed out above, there is nothing in the distro that can go bad. However, there is a lot of electronics in the PDP that will be affected by reverse polarity. My suggestion (I know you don't want to hear this) is recycle everything. If it isn't bad now it will fail when you need it the most. The clicking you heard is the resettable breakers.

You could also test the outputs with a multimeter.

Hello! have you checked the 20A and 10A fuse on the PDP? we had a similar issue and it was a bad fuse.

In addition to those, I would recommend checking all of the fuses on the robot.

[Alan Anderson]

I know it's prohibitively difficult to put reverse voltage protection on the PDP input. But what about adding an inexpensive (~$2) 70dB buzzer with a diode so that it screams when you apply power backwards? That might give the user a chance to open the breaker quickly enough to avoid frying everything.

[rich2202]

Ever since we fried a D-link in my first year as a Mentor, all the dlink/camera connections are tested for polarity and voltage before first use.

Similarly, a few years ago, our team acquired a Battery Beak to test batteries before use. It has the added feature of testing for polarity. When a battery is first wired, we use the Battery Beak to test for correct polarity.

http://www.andymark.com/product-p/am-0995.htm

[rich2202]

Originally Posted by Alan Anderson

I know it's prohibitively difficult to put reverse voltage protection on the PDP input. But what about adding an inexpensive (~$2) 70dB buzzer with a diode so that it screams when you apply power backwards? That might give the user a chance to open the breaker quickly enough to avoid frying everything.

Ideally, you put it on the Main Breaker, so it screams before you close the breaker and complete the power connection.

[Alan Anderson]

Originally Posted by rich2202

Ideally, you put it on the Main Breaker, so it screams before you close the breaker and complete the power connection.

That only protects against a backwards-wired battery. I'm suggesting something built in to the PDP, which would detect any polarity swaps from the battery through the SB-50 connectors all the way to the PDP input itself. I imagine it could be added to the "smart module" with the CAN connectors.

[IKE]

Originally Posted by Ether

I'm wondering how common this mistake is, and if other teams have implemented a process change as a result.

I deal with a lot of robots each year (about 240 this year after this weekend (though probably only 160 unique teams), and I have not seen this on the battery before that I can recall. That obviously doesn't mean it never happens, but I would say it is not that frequent.
I do/did see frequently where leads get mixed up on motor controllers for the inputs. This was much more prevalent with the old victors/talons than the new ones. This would burn out certain controllers. Most often this occurred during a rushed add or wiring job. One team had burned up the current and spare before having me take a look at their robot.

[Al Skierkiewicz]

It is pretty easy to make an SB50 connector with an LED and resistor in it. Attached to the battery correctly wired and it will light.

[DonRotolo]

Originally Posted by Alan Anderson

That might give the user a chance to open the breaker quickly enough to avoid frying everything.

I think most of he vulnerable items would fry at nearly the speed of light; realistically too quickly for a reaction to help.

A big honkin' diode across the inputs - reverse biased normally - would act like a short in a RP situation and perhaps trip the main breaker while dropping the voltage to a less harmful level. Needs to handle several hundred Amps for many milliseconds.