Re: Which Battery to Buy?
 

We've had pretty good luck with our Enersys batteries, as have others, so I'm curious why you exclude them from the running? We bought a bunch in 2011, and have been acquiring more with the KOP since, and they all worked well this season, even with our admittedly lousy maintenance.

Re: Which Battery to Buy?
 

I know the Enersys work great; I've driver coached with them for many years. They too sometimes get bad cells, but I was curious about experiences with other batteries.

In all of our deconstruction of last year's "stuff", I totally forgot to check on the batteries last night. I'll have to report on this some time next week.

Re: Which Battery to Buy?
 

Interesting....I kind of like sticking with what works.

On the topic of LFP batteries, I was poking around the internets....

http://www.powerstream.com/LLLF-12v.htm

Re: Which Battery to Buy?
 

It is not that difficult for these batteries to be used "Properly". Typically, they have much higher ratings than lead acid batteries, yielding a much harder to reach "danger zone". Some Lithium Polymer (LiCoO2 gelled) batteries can handle currents as high as 250 amps/hour. Most of these batteries are only dangerous when subjected to mechanical parts that can poke or puncture the packets.
Lithium Polymer/Ion batteries can be used quite safely if just a couple guidelines are met. Some of the ones I can think of at the top of my head include:
-Use a hard case (so the cells are isolated from sharp parts)
-Use good safety measures. A properly-rated fuse, built into the battery (for ICOE), an external fuse for excessively high currents that don't reach the battery's limit and then, all the current FRC safety measures should suffice!
-USE THE RIGHT CHARGER

I really think that the cons of Lithium-based batteries are quite sparse as compared to the pros.
I really believe that FRC is not making the move to renovate the battery technology because GelCel Lead Sulfuric Acid batteries have proven their existence to be reliable. After all, they are the oldest technology for rechargeable batteries. This is the reason why we cannot blame the experts for their decision. However, as long as the safety specifications are met, the newer technologies are extremely safe.
It is EXTREMELY uncommon to have our telephones explode when we drop it or keep it plugged in overnight. Arguably, one could say that the batteries are smaller. Yet, they contain similar (or even the same) chemistry and reactions and are equally as succeptible to these failures. I guess that a cell phone battery explosion is not as spectacular :D as a Lithium car battery substiture, but they are equally as dangerous.

In short, Lithium-based battery technologies are not as dangerous as feared to be. An integrated charge controller can be used to maintain charging safety. A thermal resistor can be used to shut down the battery in case of an approaching thermal runaway. A fuse/breaker can be used to ensure that the battery maximum ratings are never reached.

Not to mention, How light are Lithium batteries. I would not have to be as scared to drop a lithium battery (as long as the casing is strong) on my foot as a lead sulfuric acid battery.

Mr. Skierkiewicz,
you were speaking about lead acid maintenance. Gel-cel batteries are not meant to be maintained. They are not supposed to require hydration. The main caveat to this sealed design is sulfation. You cannot do much to prevent this process from happening, especially at the juice we pull out of these cells. Thankfully, newer Lithium-based designs do not experience as many lost chemicals due to a similar process!

Re: Which Battery to Buy?
 

LiFePO4 chemistry doesn't have the safety issues of other Lithium chemistries.

I'd argue they're actually safer than the SLA for FRC use.

Re: Which Battery to Buy?
 

Precisely said. With the loss of some energy density it provides much safer operation. There are some emerging technologies such as lithium sulfur and lithium air, which are inert, even in air. These types of batteries are surely much safer than lead acid batteries. Lead

Also, prices are coming down significantly as more manufacturers of these batteries are quickly emerging, so soon, lithium batteries might be more practical (if not already) than SLA and it's close alternatives.

Re: Which Battery to Buy?
 

I was thinking the same after reading more about LiFePO4 a few days ago.

Re: Which Battery to Buy?
 

I think SLA will be around for quite some time at FRC due to its track record. I've been to one event in my entire FIRST existence where a venue was evacuated due to a battery spill (2014 Greater Pittsburgh Regional). I don't know much about the variations in LiFePO4 manufacturing, but I imagine this would weigh highly on it being allowed in the future.

Nuclear fission is safe. Can I use that? :]

LiFePO4 see some extensive use at the University Rover Challenge. Check it out if you want to be part of a growing, challenging competition at a university level!

Re: Which Battery to Buy?
 

It's easy to say that you shouldn't abuse batteries but I've seen people accidentily drill into their battery and the type we use now is surprisingly forgiving.

Re: Which Battery to Buy?
 

There is no way to prevent mistakes like this from causing a dangerous environment. However, Why is the battery in place while someone is working on the robot?

However, there are new chemistries on their way out, like Lithium Sulfur, which have solid electrolytes and are much less likely to explode in case of a puncture!

Most of the sources where I gathered this info isn't what I would call reliable. I got most of my information off Chinese battery manufacturer websites :o .

However, I did come across this article, which seems to be a good source.

Re: Which Battery to Buy?
 

Take a LiFePO4 battery and drill a hole in it, and then attack it with a propane torch. It'll turn out pretty safe given the action. You can also discharge to 0V and bring the battery back to life.

The only disadvantage of a LiFePO4 battery is it's current capacity per cost. If you need 600 AMPs, you can get that cheaper with SLA. However, it's pretty much at the breakeven point when you consider that we can use less batteries, and that the batteries don't need to be replaced as often.

LiFePO4 also doesn't need balancing, and technically could be charged with an SLA charger (it is suboptimal). Reasonable priced non-balancing LiFePO4 chargers exist too.

Re: Which Battery to Buy?
 

Correct me if I'm wrong here, but if I recall correctly, LiFePO4 batteries tend to have their own internal balancing circuits (or maybe it's just the brand I'm familiar with that has 'em).

I'd actually go so far as to say that some types of LiFePO4 batteries would be just about a drop-in replacement for SLAs in FRC robots, if their cost came down a bit. I've worked on a non-FRC robot that, for redundancy purposes, ran two LiFePO4 12V batteries, just about the same size as the current SLAs, on two separate circuits, driving RS-775s and linear actuators. Never had an issue with the batteries. Not sure if they got charged much during competition at all.

Re: Which Battery to Buy?
 

They can, but that will inherently reduce ability to source current (or add a lot of price).

They can be run w/o any balancing circuitry in the cell or the charger w/o issue. It just reduces the total # of cycles it can do. This is still more than enough cycles for an FRC team.

Re: Which Battery to Buy?
 

Here's a way to make it safe to drill into a battery: choose a battery type that doesn't have a violent reaction when a cell is breached. For example, the type we use currently or, according the AdamHeard, LiFePO4.

Also, your team might remove the battery before working on the robot but it seems to me that most teams don't. Maybe I haven't been looking closely enough, but it's seemed to me that at competition the only time a team removes a battery is to put a fresh one in.

Re: Which Battery to Buy?
 

That might very well be true, especially at competitions. Next thing we know is we are putting tungsten (or stronger) casing around the battery :D.

I really don't think there is any protection against stupidity other than brain!