UPS design

LowQCab

Joined Nov 6, 2012
4,023
Commercial Products are extensively tested before being Mass-Produced,
and the sophisticated Battery-Management-Systems they use are
tweaked extensively to insure reliable, and safe, operation.

This is a totally different scenario when compared to a DIY project.

It ain't that simple.
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bassbindevil

Joined Jan 23, 2014
824
4S "BMS" boards will work with 4S, 4S2p, 4S3P, etc. With more cells in parallel, it's possible that the balancing circuit will take a lot more time to bring the cells into balance. Some of the BMS modules don't include balancing, but you can buy separate balance modules.

I'd expect that if you search forums dedicated to single-board computers like the Raspberry Pi you'll find discussions of "UPS" options.
 

Thread Starter

PsySc0rpi0n

Joined Mar 4, 2014
1,755
4S "BMS" boards will work with 4S, 4S2p, 4S3P, etc. With more cells in parallel, it's possible that the balancing circuit will take a lot more time to bring the cells into balance. Some of the BMS modules don't include balancing, but you can buy separate balance modules.

I'd expect that if you search forums dedicated to single-board computers like the Raspberry Pi you'll find discussions of "UPS" options.
Can you link me an example of a BMS without balancing and one with balancing?
For instance, this one says "with balance"
https://www.aliexpress.com/item/32952189551.html

Is this one coming with that balancing you mention?
 
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bassbindevil

Joined Jan 23, 2014
824
The visible difference between balancing and non-balancing "BMS" ( in quotes because a true BMS has more smarts; these are just protection modules) is that balancing needs a set of low-value, higher-power resistors (620 or 62 ohms in the linked example), and an additional row of 6-legged chips. That would be one chip and one resistor per series bank. There may also be one or two big low value resistors that are used to detect current (R005 in the linked example), though some boards seem to get away with using the resistance of PCB traces instead.
Here's a 3S 20A board without balancing. I needed a more compact board to fit in a small case, and this was the only option I found. https://www.aliexpress.com/item/1005001636556505.html
I got a HX-JH-001 balancing board to go with it:
https://www.aliexpress.com/item/32829691294.html

There's also some boards that use just one big chip; there again I'd expect to see a set of balancing resistors, so I'm pretty sure this one doesn't balance:
https://www.aliexpress.com/item/32712310939.html

I picked up an active balancer, anticipating possible situations like balancing a set of big LFP cells or vehicle-sized 18650 battery, since it claims 1.2 amps balancing current; plus it has LEDs to indicate status. It doesn't care about the actual voltages, just that they're equal, so should work with various chemistries. Original ebay listing is gone, but it looks exactly like the 5S version here:
https://www.ebay.com/itm/165814835782
 

Thread Starter

PsySc0rpi0n

Joined Mar 4, 2014
1,755
The visible difference between balancing and non-balancing "BMS" ( in quotes because a true BMS has more smarts; these are just protection modules) is that balancing needs a set of low-value, higher-power resistors (620 or 62 ohms in the linked example), and an additional row of 6-legged chips. That would be one chip and one resistor per series bank. There may also be one or two big low value resistors that are used to detect current (R005 in the linked example), though some boards seem to get away with using the resistance of PCB traces instead.
Here's a 3S 20A board without balancing. I needed a more compact board to fit in a small case, and this was the only option I found. https://www.aliexpress.com/item/1005001636556505.html
I got a HX-JH-001 balancing board to go with it:
https://www.aliexpress.com/item/32829691294.html

There's also some boards that use just one big chip; there again I'd expect to see a set of balancing resistors, so I'm pretty sure this one doesn't balance:
https://www.aliexpress.com/item/32712310939.html

I picked up an active balancer, anticipating possible situations like balancing a set of big LFP cells or vehicle-sized 18650 battery, since it claims 1.2 amps balancing current; plus it has LEDs to indicate status. It doesn't care about the actual voltages, just that they're equal, so should work with various chemistries. Original ebay listing is gone, but it looks exactly like the 5S version here:
https://www.ebay.com/itm/165814835782

Ok, I see.
Just one note. I already gave up on building an UPS for my RockPro64 out of Li-Ion cells, following @LowQCab's advices, but I still want to build a rechargeable battery with these batteries.

So, if I buy one of those battery management systems like the one I linked in my previous post and a balancer like this, I'll be ok?
https://www.aliexpress.com/item/32952189551.html
and
https://pt.aliexpress.com/item/1005004893493685.html
 
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bassbindevil

Joined Jan 23, 2014
824
No, the "BMS" you linked to DOES have balancing, so you don't need a separate balance module.

I forget if it's been discussed, but you'll also need a suitable charger; it bears repeating that the "BMS" does not regulate charging, it just protects against catastrophic overcharging. Wall-wart and power brick chargers are available which are designed with the necessary current and voltage limiting and regulation for lithium battery charging; they'll be specified for the final voltage (8.4, 12.6, 16.8), mention something like LI-ION BATTERY, and have an LED that changes colour to indicate charging status. You can also charge using a hobby charger like the Imax B6, but a wall-wart is cheaper, easier, and more fool-proof. Chargers like that occasionally show up at thrift stores, but your best bet is to buy one online. Other options are DC-input charging modules that can be powered from a laptop brick or even a solar panel. I've used one based on SY6912, until smoke came out one day when I plugged it into the battery pack, so I hesitate to recommend those. To replace it I got one using the MAX745; costs more, but it looks versatile (can be set for various pack voltages) and adjustable:
https://www.analog.com/en/products/max745.html
https://www.aliexpress.com/item/32852271325.html

And there are step-up charging chips that run from USB-C, which may not deliver as much charging current as a step-down, but ought to be a good back-up if you don't want to lug around a power brick or wall wart.
https://www.aliexpress.com/item/1005003082097543.html
 

Thread Starter

PsySc0rpi0n

Joined Mar 4, 2014
1,755
Wall-wart and power brick chargers are available which are designed with the necessary current and voltage limiting and regulation for lithium battery charging; they'll be specified for the final voltage (8.4, 12.6, 16.8), mention something like LI-ION BATTERY, and have an LED that changes colour to indicate charging status.
The wall-wart that is actually feeding the RockPro64 is capable of multiple output voltages and up to 4.5A of current. But as it is serving the board, I can't use it to charge the battery. However, I have 2 adjustable power supplies that can provide up to 30V @ 5A. Can't these be used to charge the battery pack after it has been assembled with the BMS?
 

bassbindevil

Joined Jan 23, 2014
824
Those power supplies won't know how to do the correct charging profile for lithium batteries, but they could be used to power one of the charging chips I suggested (MAX745 for example).
 

Thread Starter

PsySc0rpi0n

Joined Mar 4, 2014
1,755
Those power supplies won't know how to do the correct charging profile for lithium batteries, but they could be used to power one of the charging chips I suggested (MAX745 for example).
And if I want to avoid the MAX745-like chips, which type of wall-art I need to buy?
 

Thread Starter

PsySc0rpi0n

Joined Mar 4, 2014
1,755
@bassbindevil I'm a bit lost about wall-wart, power bricks, laptop chargers.

You mention that wall-wart and power bricks are suitable to charge batteries because they have proper current and voltage limiting and regulation for lithium battery charging.

My question is if use one of those MAX745 modules along with the BMS (with balancing) and power these two with my external power supplies is ok or not, to charge battery pack that I want to build with the batteries I have here lying around doing nothing..
 

bassbindevil

Joined Jan 23, 2014
824
Normal power adapters (wall warts, bricks) produce a regulated constant voltage. Lithium-ion chargers adjust the voltage and current as appropriate for filling up a battery safely.

Anyway, yes, a module like the MAX745 (configured appropriately for number of cells and current limit and voltage) can be powered from an external DC supply. Your "BMS" should keep the cells balanced.
If a wall-wart charger is going to be more convenient, search ebay for the words lithium charger and the pack voltage (4.2V, 8.4V, 12.6V, 16.8V) and you should find some.
 

Thread Starter

PsySc0rpi0n

Joined Mar 4, 2014
1,755
Normal power adapters (wall warts, bricks) produce a regulated constant voltage. Lithium-ion chargers adjust the voltage and current as appropriate for filling up a battery safely.

Anyway, yes, a module like the MAX745 (configured appropriately for number of cells and current limit and voltage) can be powered from an external DC supply. Your "BMS" should keep the cells balanced.
If a wall-wart charger is going to be more convenient, search ebay for the words lithium charger and the pack voltage (4.2V, 8.4V, 12.6V, 16.8V) and you should find some.
I think I'll go with the MAX745 and the BMS. That's a way of me learning something else and keep active at home!
However, the MAX745 modules needs to be specific for the number of batteries I have and also for the type of setup or just about any of those modules will be ok? For instance, the one you linked in post #26 is ok to use with 8 cells of 18650 3.6Vin a 4s2p setup?

Edited;
Why some modules has 2 R100 resistors, like this one from Aliexpress
1675538092054.png

and others only have one, like this from ebay:
1675538148092.png

I was trying to find modules with free shipping or at least cheaper than the ones in Aliexpress which are aroun 50% of the price of the module, but couldn't find modules with those 2 resistors with cheaper shipping costs!
 
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bassbindevil

Joined Jan 23, 2014
824
The number of cells in series is what is important. More cells in parallel just means longer charging time.
I don't know about those resistors. You might find useful feedback from buyers at Amazon.com, if searching doesn't turn up information from blogs or forums, or a Youtube video. As for where to buy, check ebay; occasionally vendors there are cheaper than Aliexpress.
 

Thread Starter

PsySc0rpi0n

Joined Mar 4, 2014
1,755
The number of cells in series is what is important. More cells in parallel just means longer charging time.
I don't know about those resistors. You might find useful feedback from buyers at Amazon.com, if searching doesn't turn up information from blogs or forums, or a Youtube video. As for where to buy, check ebay; occasionally vendors there are cheaper than Aliexpress.
I cuoldn't find any available MAX745 based module in Amazon. The only one I found was unavailable!
And on ebay, I can only find with that single resistor while in Aliexpress I find both with 1 resistor and with 2 resistors, however, the shipping prices are prohibitve!

But now another question:
1675725593495.png

Is this the correct wiring scheme? What about the question in red? I'm not sure where should I connect in my case.
(Notice: I know that there are missing the mid points)

If I ignore the vales in the silk screen, I would connect it like:

0V
1S - 3.6V (4.2V in the above image)
2S - 7.2V (8.4V in the above image)
3S - 10.8V(12.6V in the above image)
4S - 14.4V(16.8V in the above image)

Like this (hope it's not confusing)
1675727405481.png
 
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bassbindevil

Joined Jan 23, 2014
824
If your cells are lithium-ion, then 3.6 V is "half full"; they're 4.2V at full charge, so connecting the "14.4" terminal to 16.8 is correct. (I have encountered lithium iron phosphate (LFP) cells in 18650 form factor, which are 3.6V when full, but those are unusual.)

The (-) and (+) terminals on the BMS are used for both charging and load. If you connect the charger directly to the pack it'll bypass the protection stuff. (Some BMSes have separate charging and load terminals, but those are less common.) Wall-wart or solar panel goes to the input terminals on the MAX745 module only. See the corrected connections below.

I dug out my two modules: they're from different vendors, but board layout looks identical. Both have the two R100 resistors, but some obvious differences are that one coil is 120, other is 150; one ISET pot is 104, the other 204. No JZ-745 silkscreen like an ebay listing. MAX745 date codes are 9909 and 0034, so I'd guess old stock. They don't look scratched up like some obviously salvaged semis I've seen on new boards. I still haven't tried them out, so can't offer definite advice on adjustments. Datasheet says the voltage adjust only changes it by about 5% from 4.2V/cell; doesn't refer to current adjust pot, just the shunt resistors on the output. Two R100 in parallel give about 3.7A, but maybe ISET modifies that? I'm not going to attempt to trace how the pot is connected at this point in time. If you'd prefer lower charging current, remove one shunt resistor. I generally don't charge an 18650 with more than 1A, but that's conservative; getting 4A from your wall-wart or brick might be the real limitation. Lower current should make it run cooler and last longer as well.

Here's a good discussion of your BMS:
https://circuitdigest.com/electronic-circuits/how-to-use-a-4s-40a-bms-module-to-build-battery-packs
I didn't find an equivalent quality review of the MAX745 module, though.

max745 bms 4S proper.png
 

Thread Starter

PsySc0rpi0n

Joined Mar 4, 2014
1,755
Hi.
One more question before I decide if I purchase these 2 items or not.
Where you wrote LOAD, what load would this be?Would it be my RockPro64 boar?
 

LowQCab

Joined Nov 6, 2012
4,023
Storing a Lithium-Based Cell,
for long periods,
with a Full-Charge, ( ~4.2-Volts ),
will shorten its Life-Expectancy.

So You can expect brand new Cells to be Charged to about `~3.6-Volts.
This is the ideal "Storage-Voltage" for Lithium-Based-Cells, while they are not being used.

When Lithium-Based-Cells are not expected to be used for several Days,
the Cells should be "DISCHARGED" down to approximately ~3.6-Volts.
This is why virtually all "Hobby" Chargers,
( for Radio-Controlled Planes, Boats, Quad-Copters, etc ),
will have a "Discharge" function to bring the Cell-Voltage down for storage.

This is why using Lithium-Based-Cells for a UPS application is not a good plan.

Sealed-Lead-Acid-Batteries "Like" to be kept in a Fully-Charged-State,
so they are a good match for the requirements of a UPS application.
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Thread Starter

PsySc0rpi0n

Joined Mar 4, 2014
1,755
Storing a Lithium-Based Cell,
for long periods,
with a Full-Charge, ( ~4.2-Volts ),
will shorten its Life-Expectancy.

So You can expect brand new Cells to be Charged to about `~3.6-Volts.
This is the ideal "Storage-Voltage" for Lithium-Based-Cells, while they are not being used.

When Lithium-Based-Cells are not expected to be used for several Days,
the Cells should be "DISCHARGED" down to approximately ~3.6-Volts.
This is why virtually all "Hobby" Chargers,
( for Radio-Controlled Planes, Boats, Quad-Copters, etc ),
will have a "Discharge" function to bring the Cell-Voltage down for storage.

This is why using Lithium-Based-Cells for a UPS application is not a good plan.

Sealed-Lead-Acid-Batteries "Like" to be kept in a Fully-Charged-State,
so they are a good match for the requirements of a UPS application.
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I already got your point. I'm no longer trying to build an UPS. Just a normal Li-Ion battery that can be charged!

I didn't understand this:
So You can expect brand new Cells to be Charged to about `~3.6-Volts.
And then this:
the Cells should be "DISCHARGED" down to approximately ~3.6-Volts.
Brand new cells at 3.6V and discharged cells at the same 3.6V? So, they are expected to have the same voltage when charged and discharged? I got confused here!
 

LowQCab

Joined Nov 6, 2012
4,023
Lithium-Based-Cells have 3 very important "states" of Charge that
You must learn about before You start using them,
that is, if You expect to get good long Service-Life out of them, and not start a FIRE.

2.6-Volts ...........
This is the LOWEST Voltage that the Cells should ever experience.
Less Voltage than this can permanently Damage the Cell.
( 2.8-Volts is a safer minimum-Voltage ).
If a Lithium-Based-Cell is left in this condition for a long period of time
the Cell will sustain permanent damage.

3.6-Volts ............
If the Cell is not going to be used for more than ~24-hours,
then the Cell must be DISCHARGED to this Voltage for "Storage",
and then re-Charged later,
shortly before the Cell will actually be put into service.

If the Cell is not used for more than ~24-hours,
and is "put-away", and forgotten, in a "Fully-Charged-State"
the life expectancy of the Cell will be shortened, to some degree,
and/or,
the Cell may swell-up and possibly catch on FIRE.

4.2-Volts .........
This is the maximum Voltage that a Lithium-Cell can be
charged to without sustaining permanent damage to the Cell.
The Battery should never be left in this condition for long periods of time.
Charging above this Voltage will shorten the Service-Life of the Cell.
Charging above this Voltage for long periods of time will almost certainly result in a FIRE.

You can follow these well established Rules,
or learn the hard way, exactly why these rules were established,
it's your decision.
I would suggest that You do some serious research on Lithium-Based-Cells
before You wind-up learning the hard way,
and then start blaming it on a poorly manufactured Cell.

But of course You may actually get a poorly manufactured Cell when You buy stuff from China.
You never know exactly what you're going to get from China,
but if You don't follow the Rules, then it's still all on You.
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