Multiple batteries?

[Dave_4539]

Our team is doing some promotional stuff for parades this summer and are planning on having a pretty heavy robot. Would creating a series of batteries work? As long as voltage stays at 12, but would amps matter in consideration of the PDP and motors?

[GeeTwo]

Don't put the batteries in series; put them in parallel. Putting them in series will increase the voltage.

That is, all of the + leads should connect to one point, and all of the - leads to another.

If doing this, it is best not to mix "good" and "poor" batteries; try to use batteries that have about the same amount of history and health at any given time.

As long as your main breaker is no larger than 120A, you can continue to use the same wires as you use for FRC competition. This means that your combined battery will last longer, not produce greatly increased power.

We use 2 batteries in parallel on our air cannon so that we do not have to do battery changes during a game, and have not had any issues.

[ctt956]

Originally Posted by Dave_4539

Our team is doing some promotional stuff for parades this summer and are planning on having a pretty heavy robot. Would creating a series of batteries work? As long as voltage stays at 12, but would amps matter in consideration of the PDP and motors?

Yes, but they couldn't be wired in series; they would need to be in parallel. I would say just check the max current for the PDP, all of the fuses, the main breaker, and all other electronics, and don't exceed any of them. Note that this will probably make fuses blow more easily, as they have more current passing through from the battery. This means that if you push a motor, the fuse may blow when it wouldn't with one battery. Also be sure that all wires can handle it, and don't do it at competition!

[engunneer]

if your batteries were in parallel, then they would be providing a nominal 12V, but since the charge level of each battery will be different, it is not recommended. They fuller battery would be trying to charge the weaker one.

A better solution might be to have two parallel battery cables, but only use them for a moment while hot swapping. plug in a fresh battery and unplug the used battery, and you can keep going without a full reboot.

[Mr V]

Originally Posted by engunneer

if your batteries were in parallel, then they would be providing a nominal 12V, but since the charge level of each battery will be different, it is not recommended. They fuller battery would be trying to charge the weaker one.

A better solution might be to have two parallel battery cables, but only use them for a moment while hot swapping. plug in a fresh battery and unplug the used battery, and you can keep going without a full reboot.

As long as the batteries are reasonably close in AH rating, SOC and general age there is no problem running a parallel battery bank though preferably you charge them as group too. Virtually every diesel powered truck on the road today runs a bank of at least 2 batteries connected parallel and sometimes 3 or 4 batteries on the larger trucks. They are of course permanently connected and charged as a bank, not individually and are replaced as a group with identical batteries.

[Alan Anderson]

It sounds like this is going to be a "parade bot" rather than something meant to play an FRC game. My advice is to design it to use something with a higher capacity, like a large deep cycle marine battery.

[GeeTwo]

Originally Posted by Alan Anderson

It sounds like this is going to be a "parade bot" rather than something meant to play an FRC game. My advice is to design it to use something with a higher capacity, like a large deep cycle marine battery.

If the budget allows, I agree.

If you use a regular marine deep cycle battery, you will have to take greater care to orient the battery with the proper end up. If that is a problem, upgrade to gel cell.

Do not use a car battery - they are engineered for "cold cranking amps", which means that they can put out a massive current for a short period, but cells tend to short out after a number "deep cycles" (more than 50% discharge), which is how it appears you will use them. Marine batteries are designed to be charged on land and discharged while on the water.

[trumpthero786]

Originally Posted by GeeTwo

If the budget allows, I agree.

If you use a regular marine deep cycle battery, you will have to take greater care to orient the battery with the proper end up. If that is a problem, upgrade to gel cell.

Do not use a car battery - they are engineered for "cold cranking amps", which means that they can put out a massive current for a short period, but cells tend to short out after a number "deep cycles" (more than 50% discharge), which is how it appears you will use them. Marine batteries are designed to be charged on land and discharged while on the water.

Hi. I'm not OP, but I'm curious as to how you would implement these different batteries with FRC electronics. They are 12v just like the FRC batteries but would you just have to find one that has a similar amperage and then connect it as you would a normal battery? Sorry if this my question is silly. I've just never thought about modifications to a normal FRC system am very interested in projects like this.

[GreyingJay]

Originally Posted by trumpthero786

Hi. I'm not OP, but I'm curious as to how you would implement these different batteries with FRC electronics. They are 12v just like the FRC batteries but would you just have to find one that has a similar amperage and then connect it as you would a normal battery? Sorry if this my question is silly. I've just never thought about modifications to a normal FRC system am very interested in projects like this.

The amperage rating of a power supply tells you how much current it is capable of supplying. You can can safely replace any DC power supply with another one that has the same voltage rating and equal or higher current rating.

FRC batteries are 12 volts and rated for about 18 amp-hours. A battery capable of 12 volts at 36 amp-hours, for example, will power your robot for twice as long.

[GeeTwo]

Originally Posted by GreyingJay

The amperage rating of a power supply tells you how much current it is capable of supplying. You can can safely replace any DC power supply with another one that has the same voltage rating and equal or higher current rating.

Provided that you use the same size (or smaller) main breaker (and robustly insulate against any shorts before the main breaker). If you use a larger main breaker, you will need larger main supply wires, and probably a different fuse/breaker panel.

Originally Posted by GreyingJay

FRC batteries are 12 volts and rated for about 18 amp-hours. A battery capable of 12 volts at 36 amp-hours, for example, will power your robot for twice as long.

At least twice as long, probably a bit longer, as the ratings are based on fairly slow steady discharge, and our use in FRC is much faster, resulting in fewer net amp-hours. For example, one of the AM batteries is rated:

Originally Posted by ES17-2 Spec Sheet

Nominal Capacity

• 20 hour rate ( 0.9A to 10.50V ) 18Ah
• 10 hour rate ( 1.71A to 10.50V ) 17.1Ah
• 5 hour rate ( 3.06A to 10.20V ) 15.3Ah
• 1C ( 18A to 9.60V ) 9.6Ah
• 3C ( 54A to 9.60V ) 6.3Ah

In typical FRC usage of 54A, the battery can only provide 1/3 as many amp hours as it can at around 1A. In a pushing contest, that number probably drops by about another factor of three.