Historic Size of Battery
 

To familiarize our students with a revised design process, we decided to design a new battery cart and went through all the steps of the process. The students really like the new design that came out of it comparing to our current battery cart and they want to build it.

I am aware that FIRST has changed the battery teams are allowed to use before. Does anybody know if the size of the batteries in past years are all about the same size? If we know that the size changes, then we will use the maximum dimensions from previous years so it will accomodate most batteries. Does anybody know if we will be using the same battery next year?

Re: Historic Size of Battery
 

The batteries have all been identical in physical dimensions for almost a decade, if not longer.

Re: Historic Size of Battery
 

First has changed batteries in the past. Initially, (1996) the batteries used were drill batteries and plugged into the drill housing for each drive motor. As things progressed and First adopted the IFI controllers, we started using the motor cycle battery in the size which we are now using. However, over the years, the battery has changed vendor, terminal arrangement, and chemistry (gel vs. AGM), each of which produces a slightly different size. Current batteries expand with heat, so if you make the tolerances small, it is possible you won't be able to remove the battery as temps flucuate.
As First and their vendors change, so to will batteries. There has been some talk for a year or so, that MK is working on a newer battery. It is more powerful and I expect it to be a little larger then the current battery.
I have seen many battery carts, but designers should remember that hot batteries do not charge properly and although the battery can be used in any configuration, charging is best done with battery terminals up.

Re: Historic Size of Battery
 

Al said it well.
I would just add that having an extra inch or so for fingers to get at the batteries is valuable. If they rattle around, some closed-cell foam can be cut to take up the space yet leave flexibility for the future. (Foam that's soft but quite stiff, made of a slippery plastic I think is polyethelyene. Usually found in white, it is not styrofoam)

Re: Historic Size of Battery
 

Another thing you could do is to get all the design work done, then hold off on building the car until after kickoff, when you know for sure what the batteries will be.

Or if you're into assumptions, you could read the list of rookie/veteran parts variables

http://usfirst.org/uploadedFiles/Com...write%20up.pdf

and assume that since veteran teams are not getting as many batteries as rookie teams, that the same batteries will be used next year. But note that it also says that battery rules are under review.

Re: Historic Size of Battery
 

Thanks Cory, Al, Don and Jim,

We will modify our design slightly to charge the batteries in upright position.

We will leave half an inch in each direction to accomodate slightly bigger batteries in the future and swelling during charging.

We will put inserts to take up the slack and change them to different sizes to accomodate batteries of different sizes in the future. I like the idea of using light weight slippery plastics. What will be a good way to secure these inserts that is removable?

We are going to CAD it tonight and build it during Christmas holidays.

Re: Historic Size of Battery
 

The loopy side of velcro should do the trick, and it's soft enough that if a battery needs to be inserted without any plastic spacers, it would just slide past.

Alternately, depending on how its built, the spacers between batteries themselves can be adjusted. I'm looking for a picture of my team's station to tell you what I mean...

Re: Historic Size of Battery
 

Don't forget that the batteries need space on all sides for cooling during charging, If you leave .1/2 inch, ensure that there enough airflow.

Re: Historic Size of Battery
 

What do you mean when you say charging is best done with battery terminals up? If you charge it on it's side, are there any negative affects?

If anyone else knows about charging orientation?

Your reply is greatly appreciated.

Thanks,

Jason Law

Re: Historic Size of Battery
 

Al is much more experienced here, so anything I say takes a very distant second to anything he says.

A typical battery that size has a liquid or gel in it--something that can flow within limits--and a series of plates. Essentially, there is a chemical reaction happening. When the battery is recharged, the reaction is reversed. The reason to recharge upright would be to ensure that the plates are fully coated for maximum reverse reaction occurrence, or more speed/better depth of charge. Discharging can be done in any orientation because the reaction will concentrate in the contacted area. Charging, you don't necessarily want that.

Oh, and charging on the side has another drawback: should a seal break, the acid or other liquid can leak. Charge upright, and it's easier to clean up than if it spills out.

Oh, and for those inserts: there is a type of pink foam that is fairly dense, closed-cell, I think (not sure of exact type/brand). It cuts easily with a hotwire, great for spacing/organizing.

Re: Historic Size of Battery
 

Thanks for the quick reply. Would you say that charging on the side shortens the life of the battery or would it simply not charge fully?

Thanks,

Jason Law

Re: Historic Size of Battery
 

I participated in a similar project a few years ago. In the process we took photos to benchmark what other teams were doing. Those photos are available at http://picasaweb.google.com/Mark.Kra...tBenchmarking# for anyone doing a similar project.

Re: Historic Size of Battery
 

I defer to Al on that one, because I don't know. Here's what I know about batteries:

1) You charge them, they work, unless there's something wrong.
2) Typical lead-acid or gel-type construction internals.
3) Typical FRC batteries have a joint near the top and none visible near the bottom.

My response was based on 2) and 3) in that list.

Re: Historic Size of Battery
 

Al seems to be more concerned about the battery being able to vent properly

http://www.chiefdelphi.com/forums/sh...87&postcount=7

Re: Historic Size of Battery
 

Here's MK Battery's reference document for sealed lead-acid batteries: Valve-Regulated Lead-Acid (VRLA) Technical Manual. There's a lot of excellent advice in there regarding best practices.