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Looking for some general advice on Lifepo4

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Greenan_Energy

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Dec 2, 2019
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Hello, I've just bought 8 *200ah(24V) cells with a bms off RJ Energy that arrived in perfect condition yesterday and looking for some advice.

1. Should I bottom balance them even if the bms will balance them.
2. I'm wanting a charging range between 15% to 85% using a Victron battery protect. With these types of cells what would the upper(85%) voltage range be and lower(15%) range of its a 24V system
3.If I want to charge the battery bank using a Victron 24V 20A charger what setting do I use. I see there is a Li-ion setting, would that work with Lifepo4 or is there a setting that needs to be pre programmed.

Thank you in advance and apprciate any form of advice
 
They should have told you .
Parallel them all together when you have them at an equal voltage . Usually they ship at about 2.80V .
Charge wth a voltage of 3.65V at a constant current not exceeding the charge rate of your cells .
When they reach 3.65V current will have dropped away to nothing.
Never go to 3.65v again ,stay under 3.5v
That said what some do is connect a 5V 20 amp source with a resistor to them and watch where they are going.
Do not use a Li-ion setting ,it is 4.2V much too high for LFP if it happens to go overvoltage.

Pack them together in series and connect your devices and use them for a while .
One day when they are reasonably well down on charge pull the pack apart again and bottom balance them .
I find bottom balancing avoids overcharge happening to any cell so I get that done fairly quickly.

I set my victron as LFP at 27.5v and the pack seems to hold at about 27.2v on a daily basis.
I set low cut off at 25v
The BMS will not balance the cells . What it does only is move a little current (under an amp) out of a cell thats getting too high .Its wasted as heating the resistor. If you have more than an amp coming in then that cells voltage continues to rise anyway .

I suggest you buy an 8s active cell balancer (inductor or capacitor type) and keep it attached at all times.
 
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Hey April, thanks for the reply. I'm almost positive the bms I got has a self balancing feature. I think it's the same one Will uses in some of his videos called the Dali Bms. I've attached a picture of it below to be sure. If it is, will I still need to bottom balance them. With the Victron charger how did you set those limits. Also once the system is in place and being charged by a solar array what items would you use to set the high and low limits. Thanks again
 

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Ill check the Daly but Im pretty sure it is passive . ie works as I described above.Yes moves 200mA +_5mA when the cell reaches 3.5v See bottom chart below (some show it as 30mA only depends on current size of unit .See its specs.

You need to bottom balance from time to time if you want the cells to keep pace with each other. Their capacities change as you use them in practice.

My Victron has bluetooth and a phone app . I think I set it through there.It had a little plastic jumper supplied too that you inserted somehow to set the battery type ..read the manual.

what items would you use to set the high and low limits.
Click to expand...
Don't follow you?

 
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Yeah none of my victron equipment has Bluetooth. I should probably get the dongle so. I mean to keep the charging range between 15%-85%
 
Greenan_Energy said:
Is bottom balancing still needed if an active balancer is installed. If so, why.
Click to expand...
There is a specific bottom balancing video here (plus a few more):
www.mobile-solarpower.com

DIY LiFePO4 Video Series

Copyright Prowse Publications LLC © 2023 Prowse Publications LLC (www.mobile-solarpower.com) is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program...
www.mobile-solarpower.com

EDIT: Sorry, now I see what you are getting at. Thats a GREAT question!
My guess is that it becomes a good baseline start with all the cells equal and eventually reduces the amount of work that an active balancer would do.
 
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Yeah there's always a reason for these things. But with that being said, the active balancer is automated and has nothing but work and time on its hands. Maybe if its too great of an imbalance the active balance is too slow to catch up to the imbalance itself maybe??? Its just I live off grid and have no car so will be an effort to bring it to a location to recharge it after bottom balancing it. So if the active balancer is enough, it would save me a great effort
 
It's the heart of winter here in Ireland. I could but would probably take too long, so wouldn't be realistic
 
Greenan_Energy said:
It's the heart of winter here in Ireland. I could but would probably take too long, so wouldn't be realistic
Click to expand...
If you cannot even charge your batteries with your solar setup this might say something about the viability of solar power as your energy source.

Its pretty windy there year around right? Day and night too... just a thought.
 
It is viable, just don't really want to be at the mercy of the weather over the following week. I'd much prefer to have my batteries full and just go about my business if you know what I mean
 
Yes, at the end of January I'm completing a wind turbine emulator for my final year project. Great minds think a like!!
 
Imagine 4 water tanks lined up and set up so whatever water went in was distributed as 1/4 of the volume to each tank . If they all start the same ,at the end they will all be filled to close to the same level.

If they start out unequal one tank will be full first leaving the others partially filled.
Imagine if the imbalance is half a tank difference. Thats the sort of scenario you will run into along the way.
 
MisterSandals said:
Is there a reason you cannot recharge it with solar after bottom balancing?
(i'm doing this now but the clouds are blocking my power supply)
Click to expand...
You can . Thats what you balance them for.

MisterSandals said:
Can you recommend an 4s active cell balancer or two?
(4x 206ah LiFePO4, modest 30A charging)
Click to expand...
Go onto ali-express and search for "active cell balancer"
reason being the price is coming down .

Greenan_Energy said:
Is bottom balancing still needed if an active balancer is installed. If so, why.
Click to expand...
To get your cells right to start a bottom balance is the only way I can see to equalise the cell voltages exactly . This can be done at any voltage but is usually done at under 2.8v to be effective.
Then recharging with an active cell balancer attached seems to keep the cells sane and within 100mV of each other. Just practical experience .
Remember the BMS is doing the hard yards supervising the high and low cell voltages and disconnecting the pack if one cell goes out . Thats its job .
The active balancer keeps cells within 100mV while you are using them.
I definitely use both and have lost cells without them attached because the voltages have either gone over or gone under the limits and destroyed my cell. They are not like lead . You can't get them back.
 
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April said:
Go onto ali-express and search for "active cell balancer"
reason being the price is coming down .
Click to expand...
Any thoughts on this balancer? I like the made in America aspect as well as "not taking 4 weeks to get here" aspect.

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Carl is a Good person to work with.(electric car parts company is based about 10 miles from where I live.) But..... That balancer is made in China. Works well and is costly.
 
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