13-10-2014 19:53

nlj007

Re: paper: Team 900 Battery Cart

Team 900 is proud to present our battery cart. Shoutout to 1311 Kell robotics for the inspiration!

If you have any questions feel free to ask!

13-10-2014 19:57

kevin.li.rit

Re: paper: Team 900 Battery Cart

Isn't the SB50 rated for 50Amps? not 120?

Do you charge batteries with this closed? If so are there any heat issues?

13-10-2014 20:58

ehoyla

Re: paper: Team 900 Battery Cart

Thanks for the shout out Zebracorns
Our battery box is slightly different but fundamentally the same. We have never had an over heating issue though we typically leave it open unless students are sitting on it. Though we have left it closed for several hours without a problem.

13-10-2014 21:07

marshall

Re: paper: Team 900 Battery Cart

Nope. It is not possible to close the lid and charge the batteries. There are a lot of people that seem to have that question though. The cart is intentionally designed so that it cannot charge with the lid closed. In fact, it won't close with the batteries left plugged in. The center rail is too high.

The SB50s are indeed rated for 50 amps. I think the student corrected the link but not the wording. We'll correct it. Thanks for pointing it out.

13-10-2014 21:24

ebarker

Re: paper: Team 900 Battery Cart

That is a question I'd like to throw some math at.

In typical operation at competition the amount of heat generated is negligible. With 14 batteries, most fully charged and floating there is very little current draw. The couple of batteries that are fast charging are responsible for the most heat.

The math I'd like to do is this..... 14 depleted batteries each being charged by a 5A smart charger. The chargers will be throwing off some heat and the rest of the energy being pushed into the battery.

Question: Does charging lead acid batteries experience a temperature rise while charging ?

The only time the system is working very hard is when we are doing an all day show with 3 or 4 robots running continuously for 8 hours. Batteries are moving so fast it isn't worth closing the lid.

But at competition the heat is not even noticeable, and closing the lid gives us a nice place to sit.

We are making one significant upgrade to the system. We are installing a rail down the center and bolting the SB50 connectors in place, and dressing the wires down. That will be a big improvement.

Ed

13-10-2014 21:28

nlj007

Re: paper: Team 900 Battery Cart

Thank you for the feedback! We have corrected the Amp rating and added a blurb on the lid not closing while batteries are plugged in.

13-10-2014 21:32

nlj007

Re: paper: Team 900 Battery Cart

Thanks for the input Ed! As shown in this guide, we have the SB50s bolted to a rail down the center with the wires dressed down and out. It makes plugging and unplugging the batteries much easier!

13-10-2014 21:36

ebarker

Re: paper: Team 900 Battery Cart

A little light reading here

The heat coming the battery is I R losses due to internal resistance, and the chemical reaction is exothermic.

And there are some switching losses in the chargers. And yes I still don't have a hard number, and I probably will not go that far. But it is an interesting question.

13-10-2014 21:57

marshall

Re: paper: Team 900 Battery Cart

Indeed. Thank you Ed. You have an amazing group of students and mentors working with you and we definitely would not have come up with our cart without seeing yours first.

14-10-2014 09:41

FrankJ

Re: paper: Team 900 Battery Cart

You could always put a thermometer in the box to test that. Adding vent holes maybe with a small ventilation fan solve any heat issues. Ventilation holes would be a good idea in there is any gassing from the batteries. SLA batteries are sealed after all so gassing really shouldn't be much of an issue for normal circumstances.

14-10-2014 20:32

ebarker

Re: paper: Team 900 Battery Cart

The box naturally has 2 holes, and we add a 3rd large hole for cabling. We are going to put a small fan in on of the holes when we get around to it. Just have not needed it for heat.