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Discussion Starter #1
If you build a 64S pack out of bare cells yourself, how do you get about balancing that?

Any commercially available chargers/balancers don't support anywhere near that amount, what solutions are commonly used for this by DIY battery builders here?
 

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Discussion Starter #3
Did you mean 64 cells? What is the voltage of one cell?
Yes, 64 cells in series, like in "sixty four".

Nominal voltage of one cell is 3.3V.

64 * 3.3V = 211.2V

At full discharge to 0, the voltage of one cell is 2.0V, so that would make 128.0V at full discharge.

What's nice with such setup is that you can use pretty much any worldwide (with wide 100V-250V AC range) switch-mode power supply directly with the battery and it will work both for a fully charged battery and all the way down up to fully discharged.

That's why I want to use such setup - to be able to plug in most standard power supply's of electronic devices directly to the battery.

And for a 22kW charge from a standard European three-phase 400V 32A socket, only 100A of current goes between the charger and the battery - which is easier to manage then 400A for a 48V battery for example.
 

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Any commercially available chargers/balancers don't support anywhere near that amount, what solutions are commonly used for this by DIY battery builders here?
There are actually a couple I know of off the top of my head:

Manzanita Micro
and
Elithion Lithiumate

If you have questions, let me know, I'm familiar with both systems.
 

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Whaty about the mini BMS? I don't think number of cells matters....check their site. Great product, price and they have a guy always on this site wanting to help.
 

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Yeah, MiniBMS like a nice product. Don't see what the max number of cells is anywhere, so check into it. It may be just what you need.
 

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I had made separate balancers for 40..100Ah cell with 1.7A shunting current (actually any amp value is available). They have been designed to fit WB (Thunder sky) cells. But I think they should fit other cells, too. I need to know the size of your cells to make useful advice.
I'm sorry for advertisement, if not allowed.
 

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Discussion Starter #8
I need to know the size of your cells to make useful advice.
That will be only 3Ah (3 times 18650 1Ah parallel). Or maybe 4.

But I might be adding more cells in parallel as I gather more money, so the battery will grow, and the balancing circuit should be expandable too.

In parallel I don't need any balancing, they will self-balance, yes?
 

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In parallel I don't need any balancing, they will self-balance, yes?
They will self balance within that cell group of parallel cells. You still need to balance the pack. You might have one group at 3.1V and another at 3.3V. They all need to start at the same voltage.
 

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So you got a 64S 3P out of 18650 cells, correct?
I think (no experience) it could be a little tricky to wire them up to a balancing system and let every connection be in place for a long time ... I will follow your thread to see it :)
Good luck.

What kind of cells did you chosen? The NCR-18650A for example should be chargeed at 885mA, so three parallel would be 2,66A, not 4Amps ...
 

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Discussion Starter #12
So you got a 64S 3P out of 18650 cells, correct?
I think (no experience) it could be a little tricky to wire them up to a balancing system and let every connection be in place for a long time ... I will follow your thread to see it :)
Good luck.

What kind of cells did you chosen? The NCR-18650A for example should be chargeed at 885mA, so three parallel would be 2,66A, not 4Amps ...
Yes, 64S3P. Cells are A123 (cheap B-grade) of course (why does anyone buy anything else?), and each can be charged at 5A, so three in parallel makes 15A.

I am seriously thinking that instead of buying an expensive charger and complicated balancer, to hook up 64 different DC-DC converters - one for each group of 3 parallel cells. Like the guy here does: http://electricporsche.rwaudio.com/2010/11/electric-porsche-charger-design/

Do you think that's a good idea in my situation?
 

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The theoretical idea is great. I thought about something similar a while ago, but the practical issue is a little bit "ugly" to me :)

So many connections and electric components that could be fail ... and if you count every dollar (euro) you ivested, it could be easyer to get a charger of the shelf.
 

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That would create a very balanced pack, its a great idea, BUT, you still need LVC. If any cell goes too low, you need to know about it.

If one "charger" fails, you wouldn't know if it was only the DC-DC converter route. So maybe some cell-logs and that would be a great solution.

(note: I have a similar setup waiting to be put together, 32 3.7V DC-DC converters with 48V input and a couple 48V AC-DC power supplies)

Still a lot of work for that many cells in series.
 

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Discussion Starter #15
I have a similar setup waiting to be put together, 32 3.7V DC-DC converters with 48V input and a couple 48V AC-DC power supplies
Can you provide a link or part number to the DC-DC converters you use? And how much they did cost you per piece?
 

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Can you provide a link or part number to the DC-DC converters you use? And how much they did cost you per piece?
I'm doing the same thing with ~96 Syncor modules, they were under $5 each NOS from ebay. Unfortunatially the seller has now sold out of them but the model # is PQ48033QGA25NKS they turn up once in awhile as surplus.

Image below is using 4 of them to charge a 4S3P pack of headway cells.
 

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Discussion Starter #17
rwaudio: out of curiosity - is there a reason you don't use A123 here? Cause these blue cells don't look like A123, and I am curious are there any reasons to use anything else then A123 cells nowadays?
 

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Yes, 64S3P. Cells are A123 (cheap B-grade) of course (why does anyone buy anything else?), and each can be charged at 5A, so three in parallel makes 15A.

I am seriously thinking that instead of buying an expensive charger and complicated balancer, to hook up 64 different DC-DC converters - one for each group of 3 parallel cells. Like the guy here does: http://electricporsche.rwaudio.com/2010/11/electric-porsche-charger-design/

Do you think that's a good idea in my situation?

lol, perhaps I should read back far enough in the thread. That's my blog, the PCB should make it a simple clean install without any messy wiring. I don't think I would try this setup without a pcb as there would be too much room for failure. This route is really only good if you can find the parts for the right price. In my setup I paid 500 shipped for 100 dc/dc converters and under 300 shipped for a pair of 1500w 48v supplies. So in the end I will have a 3kw charger that will self balance, the pcb's have voltage monitoring built in so that takes care of the LVC. The pcb's will cost a bit because of the low quantity, but easily worth it in terms of reliability and simplicity of assembly.

miernik, those are headway 10ah cells, however with the last few builders having quality issues with their headways I've ordered the same A123 20AH cell that you bought. I might change the battery, however the charger will work just as well.
 

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Miernik,

Mine are Vicor, custom model number and sold out. They were $10 each shipped. Found on ebay, seller has none left.

The MAIN reason people don't use A123, is they're expensive for a large pack with any sort of real range, and a REAL PAIN IN THE ASS to put a pack together. You cannot compress the ends, because it interferes with the pressure seal. You should NOT solder them, because it can lead to damage, so the only way you should put them together, is with a tab welder, which is an added expense.

Another HUGE reason, is that most of the "A123" B cells are unknown as to their authenticity. There are many conterfiet cells on the market, so its a crapshoot. Every chinese company is trying to make a buck.

They're also not very energy dense and can be heavy for a large pack, and have lots of connections. Its also very hard to replace a single cell if one goes bad.

Headway's are good for energy, decent for power and a hell of a lot easier to put together. I think rwaudio used them only for his 12V aux battery.
 

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Discussion Starter #20
The MAIN reason people don't use A123, is they're expensive for a large pack with any sort of real range, and a REAL PAIN IN THE ASS to put a pack together. You cannot compress the ends, because it interferes with the pressure seal.
Wait, do you mean that this: http://www.tppacks.com/proddetail.asp?prod=Battery-Pack-Kit is not a good method to making an A123 pack?

I planned on doing something like that, will it damage the cell by pressure?

As for expense: if you divide the cell price not only by the capacity, but also by the number of cycles it will live, aren't A123s the cheapest cells there are? Especially B-grade 18650 1Ah for 2.05 USD a piece from A123RC.

I do plan to test a few thousand cycles on a few cells before buying a large amount of them, and I hope they'll still have about 50% capacity after 3000 cycles. If one 4C charge/discharge cycle takes half and hour, then after 1500 hours = 62.5 days, so after 2 months continuous test I will know what remains of them after 3000 cycles. Or did anyone do such a test already?
 
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