Legality of Different Battery Connector

[sanddrag]

Last year we were able to use different battery connectors as long as they were rated for more than the ones in the kit and were still quick disconnect. Can we do that this year? Rule <R20> says The 12v battery must be wired directly to a quick connect / disconnect connector (provided in the kit) that
in turn feeds power to the Main Power Disconnect Switch and Circuit Breaker Assembly. Does "(provided in the kit)" mean we have to use the one in the kit? If we are allowed to use these, do they have to be available from the electronics suppliers? Following the flow chart, I get hung up on this box Is the part an Additional Electronics component? I see it as an electrical, not electronic, component. Can someone verify the usage of these? Our intent of usage is not unsafe or maliciously amateur in any way whatsoever.

[jonathan lall]

They clearly mean the Anderson connectors provided are preferable at the very least (surely a good safety precaution to standardize to help the inspectors out), but your interpretation of it being electrical and not an electronic component (which of course have rules tacked on) is reasonable. I'd stay on the safe side and not try to interpret the rules here; this is probably a question for the Question/Answer System since the change in wording from last year means different semantics are intended, although the main clause of <R20> is clearly in turn feeds power to the Main Power Disconnect Switch and Circuit Breaker Assembly. If you mentioned what was acceptable last year in a QA post, and state your general intentions, FIRST would probably welcome it.

[KenWittlief]

If you put a different style of connector on your two new batteries, then where are you going to get fresh batteries from when you make it into the elimination rounds, and might have to play 3 or 4 matches with only a 5 minute break between them?

FIRST supplies charged batteries during the elimination rounds and the finals. If you dont have the same connector you would have to buy several new batteries and bring them all, keep them all charged...

you defintely dont want to use last years batteries during a match - they do lose capacity - any gain you had from a superiour connector would be lost by the weaker (old) batteries.

[Al Skierkiewicz]

If First had intended all teams to use the supplied connector, the phrase would have been worded "The 12v battery must be wired directly to the quick connect
connector provided in the kit."
Later in the robot section this rule appears...
5.8.7.2 Battery Recommendations / Cautions
To connect the 12V battery to the rest of the control system, FIRST recommends using the ring terminal contacts and red Anderson Power Products connectors provided in the Kit. This allows for a quick exchange of batteries on the robot.
We use a modular connector similar to the Anderson products but rated for 100 amps. We have seen many teams burn up the supplied connector on high current. In the event we would need to borrow a battery, we have made adapters.

[sanddrag]

FIRST supplies charged batteries during the elimination rounds and the finals. I do vaugely remember something about this but I think we never used them because we didn't want to trust batteries that weren't our own. I do like the idea of an adapter in the event that we absolutely have to use other batteries.

[Aidan F. Browne]

The intention of this rule and the others regarding power connections is to have every robot be wired the same way from the battery all the way to the speed controlers / relays.

The primary reasons for this are safety and ease of robot inspection. There are secondary benefits - like being able to share/borrow batteries.

So lets not get technical with the words here. FIRST gives you the batteries, quick-connects, main breaker and fuse panels -- its pretty easy to just wire them together.

The intent of <R20> is that you wire your power this way.

:)

Aidan

[Rickertsen2]

It seems to me that the intent of this rule is obvious. Use whatever connector you wnat as long as it is rated properly.

[DanL]

I was searching about this a few days ago... I found a big discussion thread about how in the past, teams have melted the Anderson quick-disconnects, and so, they switched to different ones (Anderson's product line (http://www.andersonpower.com/products/mp/mp.html)).

My opinion on this: given the 'spirit-of-the-rule' philosophy introduced this year, I believe any quick-disconnect will be okay. However, as it was pointed out, if your team does choose to go for a different type, borrowing batteries will be a bit of a hassle.

[Justin Stiltner]

On the subject of the charged batteries for the elemination matches... we have asked for charged batteries the 2 times we have been in the finals at VCU and both times we were given the "deer in the headlights look" and were told that if our batteries were bad they would replace them at the parts desk, however they werent charged.

[Joe Ross]

If you put a different style of connector on your two new batteries, then where are you going to get fresh batteries from when you make it into the elimination rounds, and might have to play 3 or 4 matches with only a 5 minute break between them?

FIRST supplies charged batteries during the elimination rounds and the finals. If you dont have the same connector you would have to buy several new batteries and bring them all, keep them all charged...

you defintely dont want to use last years batteries during a match - they do lose capacity - any gain you had from a superiour connector would be lost by the weaker (old) batteries.

First, as Justin stated, FIRST does not officially provide batteries for the finalists since 1998. It is possible that the event staff had some batteries you could use, but that is event specific. You do have a valid point about borrowing batteries, though, but it is not hard to work around at all. You just create a short piece that has both one of your new connectors and one of the FIRST connectors. Then, just put that inline with your borrowed battery and your robot.

Now, as an engineer, lets look at the ratings of the provided connector, the battery, and the circuit breaker. The battery can provide 230 amps for 5 seconds (per the data sheet posted by FIRST). That's not a problem, though, because we have a circuit breaker that will cut off at 120 amps, right? No, per the data sheet posted by FIRST, the breaker will provide 200% of its rated current for 10 seconds, which means that the battery can short, and the breaker will never trip. Now lets look at the ratings of the connector. Its an Anderson Power SB 50. You can get the data sheet from http://www.andersonpower.com. You will see that the connector is rated for 50 amps, and will withstand 230 amps for less then 1 second. So, the battery can provide that current for 5 seconds, and the connector can withstand it for less then 1. There is some saftey margin involved, but is it 5x or greater? For the answer to that, I point you to this picture: http://www.chiefdelphi.com/forums/pictures.php?s=&action=single&picid=3832

Do most teams get away with it? Yes. Is it good engineering practice? I don't think so. Your connectors should be rated to be safe during a short. However, even if you don't short your batteries, but run at 80 amps for 30 seconds, you still exceed the current capability.

On a somewhat unrelated note, team 696 lost the Fall Classic because thier battery disconnected in the middle of a match. So, definetly make sure that whatever connectors you do chose don't come undone easily.

[sanddrag]

On a somewhat unrelated note, team 696 lost the cal games because thier battery disconnected in the middle of a match. So, definetly make sure that whatever connectors you do chose don't come undone easily.You must have meant the Fall Classic. We weren't at the Cal Games. Our connectors were actualy somewhat diffcult to pull apart but whoever put in the battery that time forgot to put the retaining harware to keep it inside the robot.

[Al Skierkiewicz]

Now, as an engineer, lets look at the ratings of the provided connector, the battery, and the circuit breaker. The battery can provide 230 amps for 5 seconds (per the data sheet posted by FIRST). ... For the answer to that, I point you to this picture: http://www.chiefdelphi.com/forums/pictures.php?s=&action=single&picid=3832

One needs to consider a few other factors in this discussion. On peaks (not sustained loads) this battery is capable of much higher currents at full charge (400 amps or above). The circuit breaker as well can handle short peaks at 600% it's rated trip point or 720 Amps. These peaks in and of themselves, are not sufficient to damage the provided connectors. Some teams are just designing their robots to run at excessive currents, where the average is well over 50 Amps. Add to this the practice of charging with alligator clips which damage the connectors, partially engaged connectors, dirt and other contaniments, and the resistance at the terminals of the connector skyrocket. This increased resistance translates the high current to heat and the connector fails. Moral of the story is then to change the design for lower currents, install a mating connector on your charger that matches your battery, keep the contacts clean and make sure the connector is fully mated when going in to competition.

[Tom Schindler]

Add to this the practice of charging with alligator clips which damage the connectors, partially engaged connectors, dirt and other contaniments, and the resistance at the terminals of the connector skyrocket. This increased resistance translates the high current to heat and the connector fails.


On this same subject....

after the battery connector in that picture was melted, i brought it over to a FIRST employee who happened to be at the UTC scrimmage, he took them back to FIRST to have them looked at.

The conclusion they reached was that there was an intermittent connection. Since the connector was not connected at the time the high current flowed, it arced and started melting through the plastic. This could have been caused by either someone not connecting them fully together, or by the extensive use of alligator clips, which resulted in a rough surface on the metal connectors.

Moral of the story here is make sure whatever you use, they are firmly connected together, and firm enough to hold through the match. The FIRST provided connectors are safe, so long as you check them before the matches. Having a mating connector on your chargers instead of alligator clips helps also.

Tom