lead acid battery monitor / BMS?

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SilverNodashi

Member
Joined
Apr 9, 2018
Messages
57
Hi,

Would it be possible to build a BMS for a 48V lead acid battery bank consisting of 16x 12V/200A batteries, based on circuits for LifePo4 batteries - but using the correct voltage and amperage values?
 

ozz93666

Member
Joined
Feb 22, 2017
Messages
341
My understanding is lead acid don't need a BMS .... look at your car battery , 12V ... 6 two volt cells working in series perfectly happily ...

Your bigger pack of lead acid will be fine ... to get optimum performance ideally they should have started work in this arrangement when new or all be the same capacity ... if not , no damage will ensue ...
 

ChrisD5710

Member
Joined
Sep 13, 2017
Messages
161
That is going to be expensive, 96 cells to monitor, but not impossible. I presume these batteries have flooded cells and accessible inter-cell connections.

To monitor only.

You can use 2 ea. "Cell Log 8S", 2 x 6 cells per battery. They are for Li-Ion, but works fine with 6 lead acid cells. They work down to 1.8 Volts/cell.

---

BMS, no need, here is what You can do.

You need a small Power supply that can deliver 2.5V, 2 - 5 A. (You must feed it from the Mains through an Isolating transformer, or You may get into trouble).

Disconnect each battery/string and leave idle for a couple of hours. Now check cell voltages with the Cell Log.

Boost each cell that shows below 2 volts with f.eks. 5 Ah, leave for 2 Hours and check again.

This way, You should be able to balance the battery before returning it into service.

Best of Luck. :)

ChrisD
 

Wolf

Active member
Joined
Sep 25, 2018
Messages
1,623
Silver,

I have a 12 X 12V battery bank setup and I bought 3 of these https://www.ebay.com/itm/Battery-Eq...?epid=623755338&hash=item33ca277482:rk:1:pf:0 and put them into an enclosure box with Volt meters for each battery and it keeps my bank well balanced.

image_mltftk.jpg


image_qcuxxf.jpg


Monitoring is more manual I found3 batteries in my pack that where bad by looking at the voltmeters.
As you can see the voltages are not the same or at least relatively close.

image_bggwee.jpg


After disconnecting the pack from each other I did a load test on all the batteries and 3 of them showed bad. I also did a specific gravity test. I replaced those three and then the batteries came back into balance. Also it is important that all batteries be of the same lot and build date.

PS I also added ahttps://www.ebay.com/p/PulseTech-Powerpulse-Battery-Maintenance-System-48v/13015951247?iid=192628376955&chn=ps

Wolf
 

SilverNodashi

Member
Joined
Apr 9, 2018
Messages
57
SilverNodashi said:
Hi,

Would it be possible to build a BMS for a 48V lead acid battery bank consisting of 16x 12V/200A batteries, based on circuits for LifePo4 batteries - but using the correct voltage and amperage values?

I am looking to monitor and balance a battery bank, which would be the same concept is a "powerwall". In this case it's a 4s4P bank. The only difference is that it can handle different voltages and amperes.


ChrisD5710 said:
That is going to be expensive, 96 cells to monitor, but not impossible. I presume these batteries have flooded cells and accessible inter-cell connections.

To monitor only.

You can use 2 ea. "Cell Log 8S", 2 x 6 cells per battery. They are for Li-Ion, but works fine with 6 lead acid cells. They work down to 1.8 Volts/cell.

---

BMS, no need, here is what You can do.

You need a small Power supply that can deliver 2.5V, 2 - 5 A. (You must feed it from the Mains through an Isolating transformer, or You may get into trouble).

Disconnect each battery/string and leave idle for a couple of hours. Now check cell voltages with the Cell Log.

Boost each cell that shows below 2 volts with f.eks. 5 Ah, leave for 2 Hours and check again.

This way, You should be able to balance the battery before returning it into service.

Best of Luck. :)

ChrisD

Thanx. I don't want to monitor at cell level. These are sealed lead acid batteries. Different brands and models exist in South Africa, like the Trojan R105-E of Omnipower 200A, etc. Since the batteries are sealed, there's not much I can do from a cell level. But if I could monitor all 16 batteries, reporting to Grafana, I would be able to pickup a problem before it gets out of hand. Victron has a monitor for this but it doesn't work well in a 48V environment since it only monitors three points, which in this case means 0V - 24V - 48V. This means that if the 24V section shows problems, I won't know which one of the two 12V batteries has a problem.
And it's expensive.

Balancing them would be my next quest. Aliexpress has some balancers for 12V batteries.

Getting back to your original statement about being able to monitor the cells. When I go over to 2V cells, I would hopefully be able to reuse the same monitoring system if it can read as low as 1.8V. The victron system can't read below 9V.

Your suggestion of disconnecting each battery is a lot of work, and a lot of downtime each time I have to switch everything off, disconnect, etc, etc. I would rarher prefer to monitor the batteries live.
 

Solexx X

Member
Joined
Nov 16, 2017
Messages
53
SilverNodashi said:
Hi,

Would it be possible to build a BMS for a 48V lead acid battery bank consisting of 16x 12V/200A batteries, based on circuits for LifePo4 batteries - but using the correct voltage and amperage values?
Possible? sure. Worthwhile? I doubt it. Spend your money on a custom configurable charge controller that can be tuned exactly to your solar/generator/turbine and exactly to the battery manufacturers specs. I have had really good luck with strings of 8 (8s)Trojan T105s and a Morningstar Tristar 60 MPPT fed by 6X265 watt Canadian solar panels. I installed a watering manifold on the batteries and I give them a drink about once a month. I also use a part of the potential of a monster Aims 12kW inverter to run my whole house for 6 to 8 hrs when the sun shines and keep the batteries above 70% state of charge unless I have to go deeper overnight in a power outage.SLA obviously don't require watering or equalizing but FLAdo stay well balanced if you equalize them every month or two.

Back to your question. I believe that a high end MPPT charge controller will make your batteries last longer and produce more kWh per useful life than investing in a BMS for any series or series parallel strings of any type of lead acid battery.

Cheers!
 

SilverNodashi

Member
Joined
Apr 9, 2018
Messages
57
SolexxX said:
SilverNodashi said:
Hi,

Would it be possible to build a BMS for a 48V lead acid battery bank consisting of 16x 12V/200A batteries, based on circuits for LifePo4 batteries - but using the correct voltage and amperage values?
Possible? sure. Worthwhile? I doubt it. Spend your money on a custom configurable charge controller that can be tuned exactly to your solar/generator/turbine and exactly to the battery manufacturers specs. I have had really good luck with strings of 8 (8s)Trojan T105s and a Morningstar Tristar 60 MPPT fed by 6X265 watt Canadian solar panels. I installed a watering manifold on the batteries and I give them a drink about once a month. I also use a part of the potential of a monster Aims 12kW inverter to run my whole house for 6 to 8 hrs when the sun shines and keep the batteries above 70% state of charge unless I have to go deeper overnight in a power outage.SLA obviously don't require watering or equalizing but FLAdo stay well balanced if you equalize them every month or two.

Back to your question. I believe that a high end MPPT charge controller will make your batteries last longer and produce more kWh per useful life than investing in a BMS for any series or series parallel strings of any type of lead acid battery.

Cheers!

The best chargers in the world still doesn't properly, or evenly charge batteries in series, and parallel strings which is why you need balancers. With any charger, the electrons flow into the negative pole of the first battery, then into each consecutive battery and then out the positive terminal of the last battery, so the charger only knows the state of the first and last battery and use that for it's calculations. The two (or more, depending on string configuration) suffer from volt drop due to resistance build-up between the batteries.
As I said, Victron has a balancer but it has limitations so I want to build my own.
 

Cherry67

Member
Joined
May 13, 2018
Messages
496
SilverNodashi

The best chargers in the world still doesn't properly, or evenly charge batteries in series, and parallel strings which is why you need balancers. With any charger, the electrons flow into the negative pole of the first battery, then into each consecutive battery and then out the positive terminal of the last battery, so the charger only knows the state of the first and last battery and use that for it's calculations. The two (or more, depending on string configuration) suffer from volt drop due to resistance build-up between the batteries.
As I said, Victron has a balancer but it has limitations so I want to build my own.

------------------------
Sorry, i do not at all agree.
 
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