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Unread 03-06-2018, 09:25 AM
gpmidi gpmidi is offline
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Battery Cart

This is a battery cart I built a while back for the team I mentor. It's got room for eight FRC standard batteries, two dual fast chargers, one quad slow charger, and a cordless drill battery charger.

While the battery chargers on it aren't' the best out there, they seem to be working pretty well. Plus having the power strip on the side is VERY handy in the pits. All of it is mounted on an old dolly to help keep it portable.

We've considered adding a second set of wheels to make it easier to roll in and out of corners and against walls. However that seems like it'd make it too unstable. So it's not been tried yet.



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Unread 03-06-2018, 09:26 AM
gpmidi gpmidi is offline
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Re: Battery Cart

The two battery testers are very useful too - one small for in the pits - one big for high current testing
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Unread 03-06-2018, 11:19 AM
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Re: Battery Cart

One suggestion, if you're looking for a future upgrade, would be to tie these in inline with the charging cable, so you can see battery voltage as they charge. Granted, it's not as accurate as a battery beak, but it gives a good way to quickly compare batteries without having to wait for the battery beak to boot for each individual battery.



When I was on 703 we integrated these meters into our battery cart and it worked quite nicely (we fix mounted each of the charging cables next to one of these displays which fit under each battery slot). I plan to use them again on my current team when we finally get around to building a proper battery cart.
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Unread 03-06-2018, 07:49 PM
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Re: Battery Cart

I love this idea through the power strip may be overkill but I would agree with the addition of the voltmeters.
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Unread 03-07-2018, 08:38 AM
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Doesn’t the voltmeter just give you the voltage of what the charger is putting out. And not the actual battery voltage or does the charger actually vary the voltage to match the battery as it charges


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Unread 03-07-2018, 09:18 AM
philso philso is offline
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Re: Battery Cart

What method do you use to prevent the batteries from falling out if you hit a bump when moving the cart? Can two people lift the fully loaded cart, say for when you go to tournaments?
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Unread 03-07-2018, 09:29 AM
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Re: Battery Cart

We made a cart of a very similar design, but smaller, it holds 6 batteries and has one three bank charger. Ours can be lifted by two students (it has handles) to load into a vehicle, where it lays on it's back. We've never had any issues with batteries even thinking about falling out.

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Unread 03-07-2018, 09:35 AM
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Re: Battery Cart

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Originally Posted by IceStorm View Post
Doesn’t the voltmeter just give you the voltage of what the charger is putting out. And not the actual battery voltage or does the charger actually vary the voltage to match the battery as it charges


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In my experience, when the battery is actually in a charging state the voltage will be inflated, however it's generally so obviously inflated that you can tell it's charging (It will display something like >14.5v, which is obviously higher than basically any FRC battery charge). Even when charging though it does show relative charge levels between charging batteries (a battery that shows 14.8v while charging will have a higher charge level than a battery showing 14.6v while charging, once both are disconnected).

Once the batteries are "charged" though, the trickle charge has minimum effect on the actual voltage readout, and the readouts display very close to the actual voltage. Again, the intent of these is more for quick comparison (which they are quite effective for) than actual voltage values. If nothing else, you can take the top 2 batteries based on the voltage meters, then use a Battery Beak to confirm the actual charge level, rather than having to test every battery individually.

If you wanted to go beyond just wiring in the voltmeters, you could also wire in a toggle switch between the volt meter and the charger so that you can basically "switch off"/disconnect the charger leaving only the battery connected to the voltmeter, thus displaying the correct voltage.
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Unread 03-07-2018, 11:23 AM
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Re: Battery Cart

This is still one of my favorite battery cart designs that, unfortunately, the OP couldn't get the BOM or drawings posted. I would still like to figure this one out and build it...

https://www.chiefdelphi.com/forums/s...t=battery+cart
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Unread 03-09-2018, 02:21 PM
gpmidi gpmidi is offline
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Re: Battery Cart

Quote:
Originally Posted by cbale2000 View Post
One suggestion, if you're looking for a future upgrade, would be to tie these in inline with the charging cable, so you can see battery voltage as they charge.
Great idea. I'm going to have to try to add them. The only issue will be figuring out a good way to mount them in each bay. But that shouldn't be too hard.

Quote:
Originally Posted by Dwight_2 View Post
I love this idea through the power strip may be overkill but I would agree with the addition of the voltmeters.
Thanks. I agree with adding voltmeters too. It'd make checking which are in better shape much quicker. Although the chargers do a good job of indicating if a battery is fully charged. So there's that.

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Originally Posted by philso View Post
What method do you use to prevent the batteries from falling out if you hit a bump when moving the cart?
The batteries are at enough of an angle that they stay in quite well even when being pulled over moderate bumps.

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Originally Posted by philso View Post
Can two people lift the fully loaded cart, say for when you go to tournaments?
The weight without any batteries is pretty low. It's mostly wood and the dolly. We usually unload the batteries before lifting it as eight batteries gets heavy quick. Plus one person can do it that way.

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This is still one of my favorite battery cart designs...
Oh wow, that's awesome.
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Unread 03-10-2018, 06:32 PM
gpmidi gpmidi is offline
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Re: Battery Cart

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Originally Posted by Dwight_2 View Post
I love this idea through the power strip may be overkill.
I thought we'd have more than enough outlets too. But today we're using up all but two of them on the power strip. Turns out a place to charge cellphones, laptops, and such is pretty popular.
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Unread 03-12-2018, 09:02 PM
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Re: Battery Cart

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Originally Posted by cbale2000 View Post
...a battery that shows 14.8v while charging will have a higher charge level than a battery showing 14.6v.
With modern multistage chargers this is not always true.
At 50% charge, the charger will apply a high voltage for higher current during a bulk charge state.
Then during a finishing stage it applies a voltage that decreases as the state of charge increases, as it approaches full charge.

The best idea is a momentary switch to disconnect the charger, remembering that you still have to account for surface charge. Also a slide switch to disconnect the gauge from the battery during storage might be a good idea.
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Unread 03-12-2018, 09:32 PM
frank-g-e frank-g-e is offline
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Re: Battery Cart

"2 dual fast chargers"
They look like these: NOCO 12 Volt, 20 Amp Genius 2 Bank Battery Charger

Be aware that FRC rules flatly prohibit charging our batteries at a rate greater than 6 AMPs.

R41. Any battery charger used to charge a ROBOT battery may not be used such that it exceeds 6-Amp peak charge current.

You need to be able to show that your charger automatically never exceeds this limit. Modern chargers will determine the size of the battery and self limit the maximum current. This one is an Advanced 8-Step Charger so it is likely OK unless it has a mode where the user can force full 10 AMP current on a channel. Then you can't say that it won't go above 6 AMPs.
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Unread 03-12-2018, 09:58 PM
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Re: Battery Cart

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Originally Posted by frank-g-e View Post
The best idea is a momentary switch to disconnect the charger..

On some multistage chargers, this may confuse the microcontroller and screw up the charging cycle.


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Unread 03-12-2018, 10:38 PM
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Re: Battery Cart

Quote:
Originally Posted by gpmidi View Post
Great idea. I'm going to have to try to add them. The only issue will be figuring out a good way to mount them in each bay. But that shouldn't be too hard.
The easiest way I've found is to bend a few pieces of 1/8" or 1/16" Polycarbonate and use a side-cutting bit on a Dremel to cut out the profiles.

Alternatively if you have access to a 3D Printer you can also print some brackets pretty easily (this is how we mounted one of these displays to our robot this year).
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