good way to keep spare batteries topped off??

Technical Electrical
1

Hi all,

What’s a good way for a team to keep its every growing collection of batteries fully charged?

Diligence in manually rotating the charger?

A circuit which electronically rotates the charger?

Something else?

Thanks,
ER

2

just keep charging batteries on their chargers and hopefully as you use up one another is fully charged.

3

Our solution was to create a bay so that multiple batteries could charge simultaneously.

4

I hope you are not using the “alligator” clips to connect the charger. Scratches caused by that connection have a serious and deleterious effect on current flow from the battery in service.

5

We have a 3 row cart, the 2 bottom rows are for getting good full charges, and the top row is equiped with chargers to “top them off”. So batteries off the top of battery cart into the robot, then battery from robot to bottom, and batteries done on bottom to the top of the battery cart.

6

Are you talking about during a competition, or in general? You don’t really need to keep the batteries totally charged for storage. They won’t discharge significantly over a month or two of neglect; you just need to make sure they don’t start out empty, keep them from getting too hot or cold, and charge them fully before you use them again.

At competition, just have someone responsible for wrangling batteries. As soon as one shows fully charged (hopefully using a smart charger with a simple green light), disconnect it and flag it as ready to be put to use*. Whenever a charger is available, connect it to the used battery that’s been waiting the longest for a charge.

Keep a consistent rotation for matches, so you don’t end up using one battery more often than others. If you find you have more chargers than you need at any time, you can go ahead and “top off” the ones that are ready for use if you want to.

  • That’s what the AndyMark battery flags are for. You can’t use a battery without taking out the flag, so they are a great way to keep track of the charged ones. If you put only flagged batteries on a robot, and if you put in a flag only when you take the battery off the charger, you won’t accidentally use an uncharged battery.
7

For this season we built a battery rack which can charge up to 6 batteries at once. We have two heavy duty 3 battery marine charger when a battery is full the a light above the battery turns green. We then cap it to show it is charged.

8

Is that the reason why some of our older batteries barely last 10 minutes? I better tell my team. What is an alternate of charging? Instead of the alligator clips, use the big red plug thing? Do we have to modify the charger ourselves or are there ones already in production that we can just buy?

9

Thanks guys! I appreciate your very informative posts.

10

We just basically clipped the alligator clips on the anderson disconnect plugs and taped it up.

11

This is one of those things for which you have a hard time remembering the source. I’m pretty sure it is mentioned in a presentation given by Al Sk. for the 2009 conference session. 2009CON_Robot_Electrical_Design_Skierkiewicz

I highly recommend the hour spent watching this recording of him talking about the heart and life blood of FRC robots. I suppose you’re going to ask where to get it. Still scratching my head on that one. Google Al’s name, exclude chief delphi, should get you close to it online.

12

I’d recommend just having a power strip and a couple of extra chargers.

We have three batteries and one charger, so we have a completely different problem.

Thaine

13

A wheeled battery cart that you can just wheel in and out of the competition is a great way to keep track of all your batteries and keep them charged. We built one onto a 2 wheeled dolly using wood. Other teams I’ve seen get more elaborate. Just get creative and come up with a simple design.

14

We cut the alligator plugs off of the charger and splice terminated them to the Anderson plug.

15

Especially for rookies:

It is important to note that extra batteries and chargers shouldn’t be considered optional – they are necessary to compete. Depending on the year, we would sometimes go through a battery every match (and in other years it would take three times that, or more, to drain a battery to the point where we wanted to replace it).

Stalled drive motors due to pushing matches, extreme amounts of pneumatic usage (and thus a continuously-running compressor), etc, can really create quite a drain, and it would be quite disappointing to get into the tournament at your regional and not have sufficient batteries for the job!

Every game should start with a fully topped-off battery, and some of those chargers are S-L-O-W. Make sure you have enough!

16

Wow…thank you!

http://media.wpi.edu/News/Events/Robotics/First/2009/Conference/2009CON_Robot_Electrical_Design_Skierkiewicz.wmv

That is a wonderful presentation! I would definitely recommend it.

17

Since someone has posted about using the clips to attach to the Anderson plugs, I feel I need to address that for two reasons. The first is that it is impossible not to scratch the surface of the contact using this method. The scratches reduce the effective contact area to a fraction of what is needed. The result is a high resistance contact that is prone to heating. The heat can reach a point where the connector will actually melt and burns are also possible.
The second, is not as obvious. The clips are now connected to a battery that is capable of producing currents high enough to weld. If they were to short together not only would this current flow but a high risk of battery damage or fire could result. Do not use the clips connected to the Anderson plug contacts to charge batteries.
If I see this at an event, I will remind you. The Anderson plug with contacts is listed for $3.50 on the AndyMark site. Pretty cheap insurance considering.

18

Thanks for all of the discussion on this topic.

Questions:

  • Is it OK to charge the batteries in parallel? (I realize it will take longer.)

  • Are there any safety issues with placing a depleted battery in parallel with fully charged ones?

19

Don’t do it.

If you have taken great care to ensure that two batteries are in exactly the same condition, always being charged and discharged together for their entire lifetime, you can get away with it. If not…don’t do it.

Are there any safety issues with placing a depleted battery in parallel with fully charged ones?

Yes, there’s a big safety issue. The depleted battery will pull current out of the charged ones. Depending on how depleted it is, it can suck a lot of current. Things will get hot. Insulation will melt. Smoke will appear. Fire will burn. Demons will roam the…well, you get the picture.

20

To piggy back on Alan’s post above think Ghostbuster’s real wrath of God stuff. OK not that bad, but don’t do it. There is no good reason and a lot of bad ones.