Parallel connections of different sizes.
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Why would you do that, vs split the 12s4p to two 12s2p, and what is it for?
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In cases that I have limited space and can only fit so many batterys in certain spots. Just seeing if there are ways of doing it. I have nothing to put it in yet I'm just trying to understand some things.
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I'm confused. Why was 12s4p being considered at all? Two 12s2p fit...
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Like I said in my first post it is just an example.
It shouldn't make much difference as long as the voltages are the same.
Lead acid batteries didn't always like old and new batteries being mixed, but a good BMS should help prevent cells from becoming unbalanced, so it might not make a difference with lithium.
There are some discussions about equalizing packs before merging.
www.diyelectriccar.com
Lead acid batteries didn't always like old and new batteries being mixed, but a good BMS should help prevent cells from becoming unbalanced, so it might not make a difference with lithium.
There are some discussions about equalizing packs before merging.
Allowable voltage delta for initial paralleling of...
What is the allowable voltage delta between 2 125vdc packs to parallel them directly? Less than 0.1v? Less than 0.01v? At what point is it necessary to just add a huge bleed resistor between packs and let the pack voltages self-balance slowly?
www.diyelectriccar.com
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No, nobody does this.
Adding a 4P in parallel to a 2P module does not make a 6P pack--it makes a 2P capacity pack. Like a chain, a pack is only as strong as the weakest link.
You can add modules in series to adjust the overall voltage, like a 4S plus an 8S to make a 12S pack, but all the modules must be of equal Ah capacity (same "nP " size)
Adding a 4P in parallel to a 2P module does not make a 6P pack--it makes a 2P capacity pack. Like a chain, a pack is only as strong as the weakest link.
You can add modules in series to adjust the overall voltage, like a 4S plus an 8S to make a 12S pack, but all the modules must be of equal Ah capacity (same "nP " size)
That doesn't sound right.
You are correct that for series you go by the weakest link.
In parallel, the volts must match, but not the amps. You increase the amps in parallel.
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Not necessarily true. Since parallel is basically a circuit between two batteries, the paralleled batteries will self-balance their voltages to match, and the current draw from each paralleled battery will be proportional to its total capacity. The 'weakest link' analogy is very true for series configurations, not for parallel.
Example, if you have a 12v 10ah battery and a 12v 5ah battery paralleled, and hook up a 30a load, the 10ah battery will supply 20a and the 5ah battery supply 10a, in order to keep the voltages the same.
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It doesn't matter. Nobody would do this, as @kennybobby said.
It was a question asked by someone as "an example" who had no idea what they're doing in this area. They hopefully do now.
For the same weight of pack, and for flexibility of placement, you would never put a 2p in series with a 4p, you would put three 2p in series.
It was a question asked by someone as "an example" who had no idea what they're doing in this area. They hopefully do now.
For the same weight of pack, and for flexibility of placement, you would never put a 2p in series with a 4p, you would put three 2p in series.
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What exactly are you trying to do? Now you're up to 6p, which is 3x the weight of a 2p pack for a given voltage. There's no free lunch anywhere in this stuff...it's going to cost you money. A lot more than just buying a used EV.
You need to determine the kWh, Ah, weight, volume, and voltage of the pack that you need as a minimum and set maximums. Work from there.
You need to determine the kWh, Ah, weight, volume, and voltage of the pack that you need as a minimum and set maximums. Work from there.
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Each module would need its own 12 Cell BMS in the schema that you propose--each little module is really like a pack on its own and needs its own BMS. The strings in the 4P don't have any relation to the strings in a paralleled 2P.
Essentially you are trying to create a range extender arrangement trying to add a little pack to a bigger pack. That is not a good idea unless you are an expert at controlling battery packs.
When the little 2P pack gets depleted before the 4P, then current will flow from the 4P to both the load and the 2P pack. The current doesn't know it is supposed to play nice and share, it goes where the path is lowest resistance unless there are countermeasures with some sort of active controller. Look up the posts by Wolfie (Wolftronix) to see all the work he did just to add equal capacity modules in parallel.
There are many fiery examples of range extenders gone wrong. Good Luck to ya.
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Essentially you are trying to create a range extender arrangement trying to add a little pack to a bigger pack. That is not a good idea unless you are an expert at controlling battery packs.
When the little 2P pack gets depleted before the 4P, then current will flow from the 4P to both the load and the 2P pack. The current doesn't know it is supposed to play nice and share, it goes where the path is lowest resistance unless there are countermeasures with some sort of active controller. Look up the posts by Wolfie (Wolftronix) to see all the work he did just to add equal capacity modules in parallel.
There are many fiery examples of range extenders gone wrong. Good Luck to ya.
The OP is asking about putting two packs in parallel.
So, my car, for example has a 28 kWh pack, consisting of 12 cells per module, and two strings of 8 modules on parallel.
So: 96s2p, for 390v
I can't easily find identical batteries. And it is all tied into the CAN bus, so no just dumping and replacing.
My current thinking is that I have two options.
1) Find another 390v pack with its own BMS, and parallel the two, independent of the kWh.
2) Build a second completely parallel system that can be switched in and out with relays/contactors.
Either method should work for extended range.
There may be some advantages of two independent systems, but also disadvantages of complexity and redundancy.
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It was always at 6p. 12s4p plus 12s 2p equals 12s6p. It fine if that's not how it works but 6p was the end goal in that EXAMPLE. And again there is nothing specific it's going on. Besides rather it's 12s or 20s 2p or 60p the idea would be applied they same way rather it was for a electric car or something small like a bike.
Ok, this appears to be the video associated with those stills.
Interesting comments associated with video. So apparently a charging mishap.
Large bundle of wires, so apparently connected to individual cells in Leaf pack. No second BMS. Likely no thermal protection nor active cooling. Rate of charge not specified. Weather and ambient temp not specified (inside car).
Second pack probably not in a sealed steel case.
Yes, but none of those modules are connected in parallel with any other module. A Mach-E battery consists of entirely 3P modules (for the standard range) or entirely 4P modules (for the extended range), and in each case all modules are connected to each other in series.
By the way, the other module configuration in the Mach-E is 7S4P (or 4P7S, as LG writes it).
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Made of same cells. Sure.
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