question

kit avatar image
kit asked

Battery Protection for Lithium with REVERSE CURRENT for multi Charger/Inverter

I have an older Phoenix Multi 12V2500VA120A Charger + Inverter in a system that I would like to upgrade to LiFePO4.
Trouble is my batteries have an older BMS without over/under voltage protection and the BP series cannot handle bi-directional current from the charger and to the inverter.

Any recommendations for simple and inexpensive voltage protection system that can integrate with the current hybrid inverter/charger setup?

Bonus points if you can suggest integration of low temperature charge protection as well.

Regards

Phoenix InverterBattery Protect
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1 Answer
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nebulight answered ·

Are they drop in replacement lifepo4 batteries? If so, get a different battery! Over/under voltage protection is a basic feature set for a BMS, and if it doesn't have that, I'd argue it's not a BMS.

If they are raw cells that make up a 12v battery with an external BMS, look at a different BMS. REC-BMS has a solid solution and offers everything you'd need. It's not inexpensive, but it's not terribly expensive either. Electrodacus has a good BMS (SBMS0), but not sure if the older phoenix has inputs required for external control.

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kit avatar image kit commented ·

They are used Valence batteries which have an internal slave BMS for balancing and cell monitoring. This issue comes from them being designed to communicate with a master external BMS that controls a relay to cut power in aforementioned situations. Regrettably this BMS is very expensive, difficult to find and typically locked from the factory.

Having built my own batteries for electric vehicles before I know how difficult it can be to package all the components in a durable way. So I do not want to tear these apart just to slap on a BMS.

Any suggestions closer to what I asked? I just need a simple, cheap, low power way to isolate the batteries from the inverter connected on the same line as the inward charge current.

While I am aware that drop in systems exist with the features I requested in a durable package, I am not trying to go spend three grand when I have perfectly serviceable batteries.

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nebulight avatar image nebulight kit commented ·

To answer your question I don't think you're going to get much help from this forum as I don't believe there is an Victron product that can do what you want. And I'm sure you already know this, but over all pack voltage does not give you any readings of individual cell voltages. Your over all package voltage could be in the normal range, but a single cell could be too low or too high and causing more and more damage.

Back to your question, you aren't going to get a simple, cheap or low power solution without a BMS. You could use a Battery protect in conjunction with a heavy duty contactor (EV200 supports 500 amps). Power the contactor with the output of the BP. However since this is hooked up to an inverter, you should have a pre-charge circuit to protect your inverter and your contactor from high inrush current. This is still not a good idea because the BP has a built in delay of 30 seconds and at high current, 30 seconds could still discharge your lifepo4 battery too low. The BP can do immediate disconnect, but it's only in Li Ion mode, which would require a BMS to disconnect.

I know this isn't the answer you're looking for, but without a BMS, there aren't many options.

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