choosing the right wire guage

[warbluc]

I am connecting a bunch of batteries and wondering what gauge wire should i use.

I have 21700 batteries with 5000mah and 10a capacity in each cylinder. I have 24 cylinders in a pack with 24 packs to connect.

Here is what i think about the wires.. please correct me if i am wrong.

1) I can connect each batteries in parallel to build a 3.6v 120ah battery pack that can provide 240a current but then i will need to connect each pack with 2/0 gauge wire which for my setup is not possible as each pack is sealed in an aluminium case and is pretty tight so no way to pass a 2/0 gauge or wire through. If i have to, will have to change the design of the casing.

2) I can connect each cylinder in series creating a 86.4v nominal and 5ah pack. Can i use a 14 AWG wire for this since the amp is not going to surpass 15a?

FYI:
My motor is a 12 kw motor.
Total connection length from the batteries to controller / motor would be about 3 -4 ft

 

[amberwolf]

You have to connect the batteries up in series as a voltage that will run your controller and motor at the speed levels necessary to operate the vehicle/bike/etc in the manner you need it to.

You also have to connect them up in parallel sufficiently to provide the current the controller and motor will need to provide the torque levels necessary to operate the vehicle/bike/etc in the manner you need it to.

Once you've figured out what that series/parallel combination is, then you can determine how to build the pack itself. There are dozens of pack build threads for 18650 style packs (which are built teh same way you'd build with your larger cells) that will show you what to do and how to do it, including threads about what *not* to do, if you look thru a search for "18650" in thread / topic title and display by thread/topic.

 

[warbluc]

You have to connect the batteries up in series as a voltage that will run your controller and motor at the speed levels necessary to operate the vehicle/bike/etc in the manner you need it to.

You also have to connect them up in parallel sufficiently to provide the current the controller and motor will need to provide the torque levels necessary to operate the vehicle/bike/etc in the manner you need it to.

Once you've figured out what that series/parallel combination is, then you can determine how to build the pack itself. There are dozens of pack build threads for 18650 style packs (which are built teh same way you'd build with your larger cells) that will show you what to do and how to do it, including threads about what *not* to do, if you look thru a search for "18650" in thread / topic title and display by thread/topic.

My be my question was wrong. I understand that batteries are to be connected in parallel and in series. I have 24 in parallel and 24 in series.

My question was if i should connect 24 in Parallel for a pack or 24 in series for a pack. There will be 24 packs to connect in parallel or in series there after.

If i connect 24 in parallel then it would give me 3.6v pack with 24*5ah = 120 ah pack. If a pack is 120ah and can provide 240A current then I would need a heavy gauge wire to connect each of the 24 packs probably 2/0 gauge.

But if i connect each battery in series for a pack then one pack will be 24*3.6v = 86.4v and 5ah. In that case will i just need 14 gauge wires to connect all 24 pack?

 

[Punx0r]

The done thing is to first connect your cells into parallel groups to achieve the capacity you need, then connect those in series to achieve the required voltage.

 

[kdog]

You can't get away from having the correct amount of copper to carry the current that the controller is demanding no matter whether you series first or parallel first. What changes is only how many wires are involved at any point.
Say you parallel first: then each cell can have a smaller wire ( appropriate for max current /no cells) but then the series connect must be able to carry the max current.
Now say you series first, creating long strings. Then you can have smaller gauge wire through the string BUT, now you have 24 wires of that gauge to tie together to feed the controller = fat wire, same gauge.
Now your problem is (for a 24s24p battery) you have 576 cells to monitor instead of 24 by paralleling first
That's why everyone parallels first.

 

[amberwolf]

But if i connect each battery in series for a pack then one pack will be 24*3.6v = 86.4v and 5ah. In that case will i just need 14 gauge wires to connect all 24 pack?

No, the post I made applies completely to your question--you have to know the stuff listed in taht post to figure out your pack configuration. That's what it's based on, not the wire size you want to use.

After youv'e figured out the system requirements, and determined the pack configuration, *then* you will know what currents will flow, and can *then* determine the wire size needed to support that.

It's highly unlikely your controller would even power on in a 1s confugration. It might blow up in a 24s configuration. Even if it doesn't, it may pull so much current from the battery that it destroys the cells by overheating, or sags so much it shuts off due to low voltage.

That's why you have to determine the system needs *first*, and *then* configure the battery around those, including using wire sizes necessary to provide the current the system needs.


If you prefer, you can simply build it in various configurations and wire sizes and test it to see which ones fail or catch fire, and which ones actually operate it the way you want, but I don't recommend that. (some people *have* done it that way, usually with undesirable results).

 

[kdog]

What controller are you using? You need to work on the controller parameters when designing your battery.
12kw motor? That's huge, going to need lots of amps.
Range, terrain, type of vehicle, req speeds... All important factors to know to when designing a power system.
Its a big project to be cutting your teeth on...im not sure you sound experienced enough.
Don't mess up cause at 12kw you'll know all about it.

 

[e-beach]

As stated, all of the above, however, the size of wiring in your battery pack won't be any more helpful if it is bigger then the battery input wiring on your controller. If the wiring on your battery is of a larger gauge then the wiring on your controller, you will have a choke point at the controller connector.

So, as stated above, what are the specs of your controller and what gauge wire is the battery input wires from the controller? That is where you start.

 

[999zip999]

What is this for ?

 

[SlowCo]

These two threads are very recommended to read before you start building your battery pack:

https://endless-sphere.com/forums/viewtopic.php?f=14&t=84412

https://endless-sphere.com/forums/viewtopic.php?f=14&t=68005 (is for 18650 cells but most info relates to 21700 as well)

And a 12kW motor could be fed double or triple that power for short periods. So you need to know what you controller will take in from your battery in peak amps.