Re: Battery connected backwards to robot
 

An interesting cost/benefit analysis... assuming that this worked, adding $2 to the cost of every PDP would cost more than replacing the occasional one that is hooked up backwards.

Sorry to hear about the damage... we hooked up our speed controllers the wrong way in 2004 and let the smoke out of one of them. It has NEVER happened again... I suspect this lesson will remain with your team for just as long!

The moderately expensive screw-ups we make in school and FRC are good learning for preventing the truly expensive screw-ups we can make later in life.
Jason

Re: Battery connected backwards to robot
 

A reverse diode across the input to the PDP would be huge and the short reverse voltage is likely to still produce damage in downstream electronics. Such a diode would need to withstand 600+amps and might allow a volt or more in reverse. The main breaker may still take a second or two to trip at that current. Considering the normal human reaction to the trip, this must survive at least two events before team members will go looking for the actual problem. Inspecting I have been lucky to find two batteries in team's pits that had been wired backwards but never used and one that was being wired backwards while I was in the pit.

Re: Battery connected backwards to robot
 

Honestly I think this might be the best solution. Train team members to check newly wired/acquired batteries with one of these before plugging in for the first time. Cost: a couple of dollars in parts.

Or buy a Battery Beak. More expensive, but handy.

Re: Battery connected backwards to robot
 

That's why I think a warning circuit at the Main Switch would be cheaper and more effective. If voltage is potentially going the wrong way through the switch, it could warn you (buzzer) before you close it and cause damage.

Re: Battery connected backwards to robot
 

Rich,
Two problems there...
1. There is only one polarity of wiring at the Main Breaker.
2. If you close the breaker, death will occur.
I would rather know before I put the battery in the robot. But you know, training will help this situation. Everything is already color coded, red battery terminal, red wire and a big "+" sign on the connector (both sides).

Re: Battery connected backwards to robot
 

Our PDP was re-wired in reverse, and we experienced the same clicking sound. Probably 3 seconds before getting to the breaker.

It was an oversight while trying to re-route wires inside a very crowded robot under the time crunch of getting the drive working (after a few mechanical failures).

Luckily, none of the components beyond the PDP were damaged. Actually the PDP itself still worked for us; however, the CAN was fried and we had to replace the PDP as the firmware version wouldn't be communicated otherwise.

At the moment it happened, we thought the damage would be much worse and I think we were lucky.

Re: Battery connected backwards to robot
 

Hi all,

gaving this some thought: one solution will minimize such disaster:

1. simplest is to use a 120A CB that has an internal electromagnetically activated separate coil.. so a diode in series activates on reverse power opens the CB in 50-100 ms.. I've seen these, never used them and currently disallowed part, but perhaps should be?? may be feature in future.. Emergency STOP signal opens 120A CB safely isolating electrical power, solving runaway flaming motor controllers &/or battery

2. Using supplied 120A CB a team could design a motor driven screw to pull/push the red off button down, activated by series diode (on sw'd side CB=auto turn EM sw deactivate, after some inertia for screw to clear top button after disabling CB) screw designed to be well clear for manual pressing, and screw able to me manually returned to "load")

thinking outside the box :-) for infrequent need in 26 years of competition.

in lieu >600A parallel huge diode for tripping >150A

parallel many high current FETs used as series switch , ~.0001 ohm = .1 milliohm turned on if polarity is proper, again not permitted in current rules)

Re: Battery connected backwards to robot
 

That's my point. Put a diode in the reverse of the expected polarity, and that circuit powers a buzzer. That circuit is always on (regardless of the state of the breaker). If reverse polarity occurs, it buzzes.

Yes, but the buzzer sounds as soon as you connect a battery with the reverse polarity. If you close the breaker while the buzzer is sounding ... Well, that's your fault.

The situation it does not solve is if you reverse wire the breaker to the PDP.

Re: Battery connected backwards to robot
 

Thanks for the advice. I wasn't around, but I think the robot was turned on again after the breaker tripped... Whoops! And as far as fixing the problem of wiring things backwards, well I agree that the best solution is to double check to avoid stupidity :(

The PDP does output power but the status lights don't seem to function... We can play around with the components a bit but we've replaced them with the spare set we kept on last year's robot for the time being.

If the VRM is reverse polarity protected, any thoughts on why it doesn't work now? And also ideas on why the PDP functions partly?

Re: Battery connected backwards to robot
 

The status lights on the PDP and VRM did not turn on after the incident. The PCM's status light was flashing green and orange. We checked both the 20 and 10 amp fuses on the PDP but neither had popped. We managed to replace the PDP and VRM with ones from an old robot and the speed controllers, radio, Roborio, etc... all ran as if nothing had happened. We did not have a spare PCM to switch in the robot was operational minus pneumatics.

Re: Battery connected backwards to robot
 

I have not opened a PDP, but I presume the main part of the PDP is a bus - all hard wired (hard wire does not care about polarity). The part of the PDP that seems fried is all the electronic monitoring parts.

If you are done with competitions, then if the robot works, the robot works. If you are going to Worlds, then swap out the PDP for a good one. They will check that the PDP CAN bus is working (version number check).

Re: Battery connected backwards to robot
 

While reverse polarity protection is usually overlooked since it's assumed that the user should never reverse the input polarity, it's good design practice to put some safeguards in place given that the components teams are required to use are expensive. Many teams are working with the single module given to them at kickoff and would rather spend their budget on travel costs rather than blowing up electronics.

A cost effective, very easy to implement solution would be to use a reversed P-Channel MOSFET in series between the battery input terminal and the PDP distribution node. Afrotechmods has a great video on the subject here. A transistor such as the SUM110P06-07L-E3 would work for the FRC PDP.

If you needed more current capacity (240A pulsed for the P-Type vs 440A pulsed for the N-Type) you could apply the same circuit, substituting a P-Type for an N-Type such as the STB120NF10T4, on the negative (ground) side of the circuit and achieve the same result. Both of these transistors have an RdsON = ~10mOhm meaning that the maximum power dissipated in the transistor under full load will be 4W @ 20A continuous.

Either one of these configurations would adequately protect not only the PDP, but everything else connected to it.

Re: Battery connected backwards to robot
 

You already have this, sort of. Each FET in each motor controller has a diode that will conduct in reverse when biased backward. However, the diodes will still allow approx. 1.2 volts in reverse bias plus wiring losses. That is sufficient to make electronics cross over to the light on the other side. (Stay away from the light, Fluffy)

If you can find the breaker you mention, send me the link, please. The 40 amp breaker we used prior to this one, did/does have a solenoid over current sense, to trip the breaker. It is also sensitive to vibration. So hit a bump with the breaker firmly affixed to robot frame and the main breaker would trip. Search for one of my breaker posts from 2000 on and I think I included an xray of the interior of that device.

Re: Battery connected backwards to robot
 

We connected a battery backwards due to the wires being reversed on the Anderson connector. The operators noticed it wasn't behaving right after being connected and turned on for a couple of minutes. The battery was hot but I don't believe there was any damage to any of the electrical components. They put in a new battery and worked fine through competition season without replacing any parts.

Re: Battery connected backwards to robot
 

Turned what?