DIY Electric Car Forums banner

1 - 9 of 9 Posts

·
Registered
Joined
·
17 Posts
Discussion Starter #1
Appologies if this has already been answered somewhere else, if it has please link and close the thread.

Say I need a pack Voltage between 400-480V If using 3.2cells (125-150 x 10aH)

Would I be able to wire it up using some kind of breaker switch or something where I have multiple smaller Packs say 25cells = 80V and again series these packs. In DIY Lingo "25S 5S"

<-- Positive Side
{[+ -][+ -][+ -][+ -][+ -]} (25Cells in Series)
|
{[- +][- +][- +][- +][- +]} (25Cells in Series)
|
{[+ -][+ -][+ -][+ -][+ -]} (25Cells in Series)
|
{[- +][- +][- +][- +][- +]} (25Cells in Series)
|
{[+ -][+ -][+ -][+ -][+ -]} (25Cells in Series)
|
{[+ -][+ -][+ -][+ -][+ -]} --> Negative Side


My Real Question:
Can Each 25S pack be Charged at 80V and connected in Parallel for Charging so it becomes 25S5P at 80V for charging.
then
Can the Packs be discharged end to end in series to get the high voltage 25S 5S

Will each pack need to be circuit broken in order to connect Parallel OR can this be wired up so that we charge in parallel and discharge in series.

Sorry if I couldn't explain it properly... :(
 

·
Registered
Joined
·
17 Posts
Discussion Starter #3
Sure, you just need 15 disconnects. And be sure you don't ever switch one in the wrong order.
So The 5 or 6 individual 80V packs need to be separated with disconnects.

Why 15?

Its not possible to just put wires in parallel onto one of the packs? that will cause it to go ka-boom? :p

I am considering buying premade packs from a China supplier that come with BMS and everything in a package, they range from 36, 72, 144v etc.
The other option is to buy Pouch or Prismatic Cells and build a battery box custom out of clear plastic and Metal, then i'd need to buy a whole lot of cells and BMS somehow, could get costly.

Thanks for the reply!
 

·
Registered
Joined
·
4,007 Posts
You need to connect all the similar ends for parallel, and then connect one end to the opposite for series. If you try to leave all connected they will short out.

It's the same as connecting one end of a battery to it's own other end, so yes, kaboom!

If you think that's too complex, A123 pouches will be far worse. Most people use larger format prismatic cells in a single series string. With most you don't need a bms.

<-- Positive Side
{[+ -][+ -][+ -][+ -][+ -]} (25Cells in Series)
|---------- /----------- |
{[+ -][+ -][+ -][+ -][+ -]} (25Cells in Series)
|---------- /----------- |
{[+ -][+ -][+ -][+ -][+ -]} (25Cells in Series)
|---------- /----------- |
{[+ -][+ -][+ -][+ -][+ -]} (25Cells in Series)
|---------- /----------- |
{[+ -][+ -][+ -][+ -][+ -]} (25Cells in Series)
|---------- /----------- |
{[+ -][+ -][+ -][+ -][+ -]} --> Negative Side
 

·
Registered
Joined
·
17 Posts
Discussion Starter #5 (Edited)
It's the same as connecting one end of a battery to it's own other end, so yes, kaboom!

If you think that's too complex, A123 pouches will be far worse.
mmm... I Wouldn't be connecting anything in parallel then it would just be simply a 125S or 150S the only thing that I was trying to get my head around was to break them into smaller 25S and connect each of the 5x25S modules in Series.

The issue is then I would need to Break the Connection between each module to reduce the voltage and charge each 80V pack rather than trying to get a 500VDC charger.

[25x3.2Vx20Ah (25S)] - Breaker - [25x3.2Vx20Ah (25S)] - Breaker - etc...

Then Where the Breakers are connect to each side of the Module and use 5 or 6 80V Chargers? Hit the Breakers to disconnect/reconnect which lowers the voltage and allows the management of 80V modules rather than a monolithic 480VDC pack.

Most people use larger format prismatic cells in a single series string. With most you don't need a bms.
No BMS? is that wise? does that mean that the 150 cells are all connected as one giant module and you don't need any individual cell BMS?
Means one heck of a charger, 500VDC charger?!
 

·
Registered
Joined
·
1,317 Posts
What's the difference between 5-6 80v chargers and a single 500v charger?
just get the right product for the job and save the headache/safety risk.

If you do go with 5-6 80v chargers, simply get isolated chargers and you don't have to break up the pack.
 

·
Registered
Joined
·
17 Posts
Discussion Starter #7
If you do go with 5-6 80v chargers, simply get isolated chargers and you don't have to break up the pack.
It would just be easier for placement and moving them around etc if they were 25S rather than trying to build a huge monolithic pack.

Probably Makes sense to use the 1 Big 500VDC as 6 increases complexity etc.
It might have to be a homemade something tho to get the huge Voltages. I am planning an AC conversion however so I may be able to just feed 3PH power into the Inverter and let the "Regen Charging" charge the battery pack. Just need to make sure the Motor doesn't spin, LOL.

Saves me getting a charger completely if the controller just thinks its getting regen, it will feed the power back to the batteries I assume this is how it works?
 

·
Registered
Joined
·
4,007 Posts
What's with the desire for such high voltage? For your first system it will be much cheaper/safer to start with a lower voltage system.

You can make a monitoring system that will keep an eye on your cells without actively trying to manage them, which is at least as risky as not having anything.
 

·
Registered
Joined
·
17 Posts
Discussion Starter #9
What's with the desire for such high voltage? For your first system it will be much cheaper/safer to start with a lower voltage system.
Purely because I would like to use a VFD which normally runs from 415VAC 3PH. To tap the DC bus I estimate I would need around 480VDC (I haven't confirmed this yet).
I am trying to keep the cost down by using Industrial Spares. I know I will attract some flaming for this, I understand sometimes its cheaper to use part actually designed for the task.

Specs from one of the Controllers
DC Bus voltage range: 425 to 815 Vdc (e.g. 150 to 226 lithium cells)
Max continuous AC output voltage 480 Vac (requires Vdc > sqrt(2)*Vac)
Max continuous AC output current 168 A

That is for a giant 220kVA VFD which will be overkill but it gives you an idea.

Thanks!

As for 'regen' charging. Has anyone attempted to feed 3PH AC into the controller and charge the pack as if it was regen? I supose the only challenge is regulating the charge the goes back into the batteries and I supose a bit of loss involved.
 
1 - 9 of 9 Posts
Top