lifepo4 BMS

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lifepo4 BMS

Postby jbates58 » Mon Jun 05, 2017 9:18 pm

hi all

i am looking to install 4 100AH winsoton cells in my 4x4, and am wanting a BMS for them.

they will primarily be fed from a single 250W panel (more than ample for the draw against them), and hopefully the alternator aswell.

i currently am using a Victron 100/75 mppt reg, and am hoping to retain it. as its programmable, i can set the upper charge limits, and the LVD aswell.

but i am struggling to find an BMS for the 4 cells, as it is a large investment, and i want it to last the distance.

can anyone make a good suggestion? as it will be used to power fridges, small inverter, lights etc... so not to sure what i need in terms of balancing current etc...

thanks

Jason
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Re: lifepo4 BMS

Postby Gordon-Loomberah » Tue Jun 06, 2017 3:13 pm

Welcome to the Energy Matters Forums Jason :)

The Victron should do the job as long as you can set absorb and float voltages suitable for the Winstons, and absorb time.

Often 12V LiFePO4 batteries are sold without a BMS, as the claim is that the cells are closely matched before combining into a battery, and should stay close together in voltage. Whether or not this is the case with yours, I don't know.
EV Power sells cell balancing modules, but these only operate at quite high cell voltages, so may not be of much use if you dont charge to 3.6V/cell or more.
There are other more expensive cell balancing arrangements, as discussed in some of the Lithium battery threads on the forum.
As far as a BMS goes, perhaps you could use something fairly simple like a Morningstar RD1 relay driver to disconnect the load or charger when battery voltage goes, respectively, too low or high.

If you are careful and keep a close eye on your battery voltage and behaviour under load, then you may not need a BMS. A good quality volt meter in an easily read location would be a good idea. If you wanted to go further, you could even go for 4 digital volt meters, one on each cell.
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Re: lifepo4 BMS

Postby tom rickard » Tue Jun 06, 2017 9:31 pm

REC-BMS do a module for exactly what you describe

https://www.solar4rvs.com.au/bms.html
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Re: lifepo4 BMS

Postby jbates58 » Tue Jun 06, 2017 9:59 pm

tom rickard wrote:REC-BMS do a module for exactly what you describe

https://www.solar4rvs.com.au/bms.html


was hoping to get something a bit cheaper.

but thats basically what i am after.

Jason
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Re: lifepo4 BMS

Postby tom rickard » Wed Jun 07, 2017 3:28 pm

If you decide to go for a cheaper option, make sure you keep an eye on charge rates when the temp is above 35'

Good luck.
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Re: lifepo4 BMS

Postby Monkeytom » Mon Jun 19, 2017 11:05 pm

I used the evpower cell top units daisy chained with a contactor, and a second cheap lipo voltage monitor with programmable Hi and Lo voltage alarms that connect to each cell
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Re: lifepo4 BMS

Postby Warpspeed » Tue Jun 20, 2017 12:53 pm

I am building a BMS right now myself.

Part of this is based around a two pole DC circuit breaker fitted with a shunt trip.
The circuit breaker obviously provides a manual battery disconnect and over current protection.

Associated with this is a programmable voltmeter that provides a four digit display of battery voltage, but more importantly it has two internal alarm relays that can be independently programmed for a very precise pull in and drop out voltages for each relay (10mV steps).
These alarm relays operate the shunt trip and flip the circuit breaker to off off, if there is an under voltage or over voltage situation detected by the voltmeter.
This works on total measured battery voltage which should be fine for very few cells.

Its pretty simple, and fairly low cost, and requires just a bit of wiring up, and then programming the voltmeter.
This is the voltmeter I am using:
http://www.lightobject.com/Programmable-4-Digit-Red-LED-ACDC-Volt-Meter-with-Dual-Control-Good-for-HHO-System-P408.aspx

I know you already have set up over voltage and under voltage with your controller, but it really needs a second level of protection.... just in case.
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