Battery required by rule
 

A local battery supplier does not offer the right batteries for us.
It leads me to wonder several things:
1. what if any are the differences between these two batteries?
2. Is one or the other preferable for competition use?
3. Do you have a preferred source of supply for either one?
4. What speculation will you offer about why only these specific batteries are allowed for FRC competition use?

Re: Battery required by rule
 

To answer question 3, AndyMark is an obvious source.
http://www.andymark.com/product-p/am-0844.htm
I haven't shopped around to see if there's a better deal, but $89 for two doesn't seem too bad.

My opinion on question 4: The GDC wants to allow enough energy that we can do interesting and educational things with our robot, but not so much that it becomes unsafe. Allowing only one battery (or one of two nearly identical batteries) makes it much easier to accomplish that goal.

Re: Battery required by rule
 

But watch the shipping cost -- sometimes more than the batteries.

Re: Battery required by rule
 

Good point. Regular shipping is $19.10 (for me, in New York, I just checked). But overnight is $167 - ouch!

They are heavy (13.8 pounds each), so be sure to check shipping before you buy from anyone online.

Re: Battery required by rule
 

Both types of batteries are exactly the same in terms of specs and output. And I have seen teams use both interchangeably during competition.
Just remember to take care of your batteries!

Re: Battery required by rule
 

I like the look of the Enersys batteries better than the MK ones, but that's purely a personal aesthetically-based decision.

Re: Battery required by rule
 

Multiple teams have found the Enersys battery to be inferior to the MK battery in terms of performance.

Re: Battery required by rule
 

The specs are similar in many ways, but they are not identical.

The spec'd max discharge current of the MK ES17-12 is far higher than that spec'd for the Yuasa NP18-12. Whether or not that corresponds to reality is a separate question.

Re: Battery required by rule
 

I wonder when FRC will decide to switch to 3-cell LiPo batteries instead?
They are much lighter, smaller, and have a more favorable voltage curve compared to lead-acid.

Re: Battery required by rule
 

Well I take that back then...
In running though our batteries about half and half of each we have not been able to notice a difference so far.
But thanks for the info, sorry for the mis informed response.

LiPo would be nice....

Re: Battery required by rule
 

I prefer the MK battery since they are manufactured in nearby Anaheim and I can pick them up at will call for $40 each, no shipping.

Call MK and see if they have a distributor that is local to you and save the shipping.

Re: Battery required by rule
 

MK ships everywhere in CA via UPS ground for free as well. I don't know if that extends to neighboring states also.

Re: Battery required by rule
 

The MK may perform better when they're good, but I've had many MK batteries fail. Probably due to abuse, but still, I have many dead MKs.

The old old dark gray Exides are still going strong.

Re: Battery required by rule
 

Good to know about the differences, thanks. The exides may be going strong, but doesn't the rule preclude their use this year?

Re: Battery required by rule
 

As soon as someone suggests a specific part number for a LiPo or LiFePO4 pack that meets the energy/power requirements AND is cost-comparable and readily available.

Re: Battery required by rule
 

Not until all teams learn what robust bumper mounting means.

Re: Battery required by rule
 

I use liPo and LiFe batteries all the time in my personal projects and toys and love them.

I hope FRC doesn't switch anytime soon; they simple aren't safe and robost enough for the average FRC team.

The "average" "big" battery is a 2s 5 AH and that's enough energy to cause serious fire and injury, a 3s 18 AH would be a bomb.

Re: Battery required by rule
 

There is a type of lithium battery something with iron phosphate maybe. Anyways you can drive a nail through it and it will not produce any fire or smoke. The lithium batteries have a more favorable voltage cure, they are lighter, plus they last considerably longer cycle wise, enough to make up for the cost. I am in favor of them except that special chargers and battery management systems are required to use them. I think it would be nice to have them as an option but leave the current lead ones for anyone who wants to use them. Rookie team might have a problem with lithium.

Re: Battery required by rule
 

The LiFePO4 type batteries are pretty expensive.

Here's a cost comparison from my senior design project, LiFePO4 compared to sealed lead-acid (SLA). Note that in this particular application, weight is a HUGE disadvantage, to the tune of -10 points per kilogram (and any GDC members reading this: don't get any ideas, please!). I want to say that it's a total of 24V available, but for competition we're running 12V.

Cost (for 2 12V cells)
SLA: $72
LiFePO4: $358 (plus $50 for charger)

Weight (for 2 12V cells)
SLA: 12.7kg
LiFePO4: 6.5kg

Re: Battery required by rule
 

The main problem with Li batteries is like you say, cost. The other is that only some are safe considering the beating our bots take. I think the good one is a LiFeP. Probably more expensive too.

Mostly I'd just as soon stick with what we have because of the investment we have in both batteries and chargers. I could see stocking up on batteries and chargers the first year being a kilobuck expense.

Also, even though we are only 4 years old, we've yet to build a bot that even comes close to running out of juice in one match.......

Here's to a great year!

Mike

Re: Battery required by rule
 

And doesn't catch fire!

Re: Battery required by rule
 

Last year we bought 4 batteries from AndyMark for free shipping to CMP in St. Louis. A couple of mentors from our team were going to volunteer, so we picked them up and drove them back. Don't know if AM is offering the same deal this year. I think they were bringing an otherwise empty truck to CMP so that they could bring a field back with them.