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BMS Choices
#21
Nah Batrium is cool great stuff! But there is so much other cool things out there Smile Even if I got 3 of the batrium im still testing and looking at other things
floydR and Korishan like this post
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#22
So let's say active balancing is not as useless when done right, let's figure out what's a good strategy. This is also for a small setup, let's say under 5kw, so it's assumed that the batteries will be drained as much as possible. Costs is a factor so when in a budget tolerances are greater because let's face it, if you have over 50kw you're going to have less effect of batteries being out of balance just because you most likely will not bottom out. On a smaller pack, I can see us draining the packs every night. Also if charging them is an issue, like if we don't have as many panels as we like, so topping the batteries may be something that may not be achieved.

Much of this is all assumptions for me, but I will get my 3kw up shortly. Then I can start playing! until then, I'll just refrain from commenting what I don't know.
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#23
I guess you have 3kWh up in short and not 3kW?...

Do you want to pay 3x extra on a decent BMS to get active balancing? Isnt it better that you spend 5 min extra to make sure your packs are even? And if you see they are uneven after 5 months you can just move 1-2 cells from one of the high packs to one of the lows.

The size of the pack is not what defines how much you stress your system its about the DOD you need to do per day. The 50kWh pack on a system where you need 50kWh per day is more stressfull than a 3kWh pack that only need 1.5kWh per day Wink

Lets say you have your packs 2Ah wrong from each other. ie lets say its 10% wrong. I would try to get it down to less than 1%. Those last 1% how costly are they? Smile Run the pack 2 cycles and you get the answer on how well balanced they are and with proper bms you see the diff. Then you can add remove Big Grin


Yes Active is cool. But is it needed? Personally I dont think it is on normal system. On other hand on remote systems where you need to have it working for years without touching i think its needed.
The Ultimate DIY Solar and build place
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Current: 10kW Mpp Hybrid | 4kW PIP4048 | 2x PCM60x | 83kWh LiFePo4 | 10kWh 14s 18650 |  66*260W Poly
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#24
(11-24-2017, 01:52 AM)not2bme Wrote: So let's say active balancing is not as useless when done right, let's figure out what's a good strategy. This is also for a small setup, let's say under 5kw, so it's assumed that the batteries will be drained as much as possible. Costs is a factor so when in a budget tolerances are greater because let's face it, if you have over 50kw you're going to have less effect of batteries being out of balance just because you most likely will not bottom out. On a smaller pack, I can see us draining the packs every night. Also if charging them is an issue, like if we don't have as many panels as we like, so topping the batteries may be something that may not be achieved.

Much of this is all assumptions for me, but I will get my 3kw up shortly. Then I can start playing! until then, I'll just refrain from commenting what I don't know.

Perhaps connect a switch to the +or - side of the active balancer then once you have the battery balanced switch the active balancer off. The 4s-8s one says it has a switch but i didn't see one.  only switch on when you have a problem and need time to find it.  a bit more complex to wire it in parallel to the bms. This might be a solution.

later floyd
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#25
(11-23-2017, 12:47 AM)not2bme Wrote:
(11-19-2017, 12:13 PM)daromer Wrote: not2bme they use biderectional dc/dc on an isolated bus. Where all cells send their energy. The one with lower will take and the one with higher will give.

Has anyone ever tested such chinese 16s bms... sounds interesting, at least from a price point of view ?
cheers
karl


Wow good review on the 1s balancer. That got me to look more into active balancers instead of a whole bms. It's more of a dumbed down version that just does the basics, and that active balancing (taking cells from high to low) is a better alternative than passive balancing (like a resistive load). This may also be better for smaller packs so there's less power loss since passive balancing is just dumping the load. Also active means very little heat generated since it's transferring the load (basically charging another cell, well i hope that's the case since it's claiming over 90% efficiency at 1A).

I found two that looks ideal. High active current transfer > 2amps.

8s balancer (scalable to 24s) - Capable of 4 amps active transfer, with serial connection for maybe future arduino BMS?

16s balancer - Has display, and limited bms to control over voltage (through small limited passive load) and a regular active balancer at around 2-3 amps

I only have a 7s so I may try out the 8s balancer, but both may be ideal starter balancers for under $100.
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#26
Charly please edit your message. Its impossible to understand what you wrote.
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#27
@Charly: What daromer means is that you replied "inside" the quote. Please make your replies "outside" the quote section. It is hard to determine what you are responding to as to be able to really understand it, one would have to keep jumping back to the original post to see what the original text was.
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#28
I am thinking about getting 3 or4 36v UPS and using the batteries from arlarmhookup (which I have already) connected in parallel. Might be able to use them without modification. They already have a BMS.   Perhaps using a 36 v lithium hoverboard charger to charge them. if the onboard charging circuit can't be modified  for lithium charging.
got the idea from http://secondlifestorage.com/t-36V-UPS-1...6#pid21676

later floyd
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#29
Ooo, that'd work. Helps to cut down on work needed to rebuild. Just keep a close eye on those bms units on the packs. Better safe than sorry later.
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#30
(12-16-2017, 04:54 PM)Korishan Wrote: Ooo, that'd work. Helps to cut down on work needed to rebuild.  Just keep a close eye on those bms units on the packs. Better safe than sorry later.

Cool fewer sparks, cuts.
will keep a close eye on everything
 I should have watched jehu's video before asking https://www.youtube.com/watch?v=LI132cvpp2U as he does exactly what I was thinking about doing. other than mine will be for my computer rooms.


Combat engineer tested many hoverboard bmses I believe his conclusion was that the bmses were good. but will check again.

I am all for not having to break apart batteries.

I need the Upses
have a mpt7210A solar charge controller
have the hoverboard batteries
 Question how many batteries can I parallel to each ups? each battery is 4 Ahr

later floyd
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