Out of the batteries for sale on Andy Mark, is there truly any difference between them? If so, which is the best? We are looking at the MK ES17-12 or am-0844. We are also looking at the Power Patrol SLA1116 or am-3062.
all first legal batteries have pretty much the same spec. I haven’t noticed any real differences between our mixed collection, but we don’t have a statistically significant sample size (I’d be surprised if any team has enough data to be significant.)
Our MK perform better than our Enersys/Genesis ones.
please define “performs better”. More Amp hours? more recharge cycles? Lasts 10 minutes instead of 9?
I don’t have any documented evidence on discharge rates, instantaneous current draw, internal resistance, etc. This is all purely empirical, but I have noticed that the MK batteries perform better than the Genesis and PowerPatrol batteries.
The MK batteries seem to handle high current draw better. By this I mean that the internal resistance of the MK batteries does not increase as fast as the other two brands under heavy current draw, or equivalently as the internal temperature of the battery increases.
Our robot drive train this year uses a 2-cim gearbox and 3 x driven 8" pneumatic wheels per side. We noticed that the Genesis/PowerPatrol batteries’ ability to provide instantaneous current to the robot decreases to the point of being unable to drive over defenses at about 2 minutes into a match. The MK batteries seem to provide about 5 minutes of power before failing. In both cases, once the battery is allowed to cool, they are both able to provide another 2 minutes of drive time before requiring a recharge.
I hope to build an active load after this season to properly characterize the batteries over time, but for now that is what we have observed this season.
Hope this helps!
I have not seen any significant differences. Most batteries are made by a small number of manufactures. The size we use allows only so much lead, fiberglass and plastic in the volume. That is why all 18 amp hr. batteries are the same size. You will find different ratings among different manufacturers, but if you examine them closely, the data is more massaged by marketing people to make their battery sound better for a given market. That being said, off brand batteries may have taken significant short cuts in manufacturing and may not meet specifications of the name brands. We had two batteries of the same local manufacture in Australia, fail while charging at that regional using a known good charger.
In regards to brand differences, I’ve heard similar things in the past. Sounds like a materials/construction difference. These batteries, as I remember being taught when I was a student years ago, aren’t meant for the [strike]abuse[/strike] use demanded by FRC. Thus, the specs may all be the same on paper, but that’s only good for typical batteries in typical use. Our use isn’t typical, so brand differences are, theoretically, plausible.
Batteries really should be a bigger subject in FRC. If you’re using a motor shooter, your battery will make or break your shot range and how reliable it will be. We experienced this in 2014, where we had a mini toughbox with two CIM motors attached to a thrower. We also experienced a huge increase in range by applying an electronic anti-oxidization agent to the terminals of our motor controllers.
Every battery you buy will have a different maximum AH, and how much draw it can handle. You can get a little battery beak from Andymark, and it will calculate it in %. Our good batteries are 130%. We had to throw about 6 batteries to the side before this years competition and used mostly new batteries because our older ones would only get about 50% charge.
There’s a lot more to testing batteries, and if you’re building something that is very reliant on fluctuations in electricity, you should make a test setup to get the exact discharge of each battery.
You shouldn’t really design your shooter to be affected by your battery levels. You should figure out at what speed you want to shoot, and ensure your setup can go faster than that. That way, at the end of your match, when your voltages are lower, your controls will still let you get to your desired RPM.