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drumond avatar image
drumond asked

Why is the Cyrix Li CT draining my battery?

Hello,


I thought the Cyrix Li Ct would charge only my 200Ah auxiliary lithium battery in my van.


When I switch on the van engine, it reads 14.2V on my starter engine (the starter battery is an old one, I will replace it next month) and 13.58V on the Lifepo4 (around 50% charge at this very moment).

Or when I turn off the van engine, it's also the other way around, the lifepo4 is depleting and charging my engine battery (they tend to have the same voltage as soon as I switch off the engine, around 13.1V each). I don't want that to happen at all.

It is like my Cyrix Li Ct was useless. For information, I also have a Ve.bus BMS. Everything is plugged like it is shown on the connection diagram given by Victron.

How can I prevent the Lifepo4 to NOT charge the starter battery when the engine is turned off?

Do I have a defective Ve.bus BMS or is it the Cyrix Li Ct that doesn't work properly?


Thank you.

Cyrix Battery Combiner
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2 Answers
Matthias Lange - DE avatar image
Matthias Lange - DE answered ·

A cyrix works in both directions, but you maybe have to wait a moment:
https://www.victronenergy.com/upload/documents/Datasheet-Cyrix-Li-ion-120-A-EN.pdf

If you want it goes only from the alternator into the lithium battery you should use a DCDC-charger.


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drumond avatar image
drumond answered ·

30 minutes later, there was still current going from the Lifepo4 to the starter battery... and the voltage of the Lifepo4 read around 13.15V.

I had to disconnect manually the two batteries between them.

Can the VeBus BMS have something to do with it? There is a cable between the VeBus and Cyrix Li Ct for Charge Disconnection. could the VeBus BMS be faulty too, or is it necessary the Cyrix Li Ct only. Can I test it by manually injecting 12V-13V in the Cyrix Li Ct Charge Disconnect port? I don't know if that would be risky?


Thank you.


EDIT: I unplugged the ground in the Li Ct and there was the sound as it was opening the circuit. Plugged again, tests, now it seems to work as it should do. I am going on with the tests. Everything is ok for now........

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Matthias Lange - DE avatar image Matthias Lange - DE ♦ commented ·

Under normal conditions the charge disconnect port of the BMS is high.
It becomes low/free floating if a cell voltage gets to high or the temperature to high/low.

If you disconnect this wire (or the gnd wire) the cyrix must open.

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drumond avatar image drumond Matthias Lange - DE ♦ commented ·

I can recall it opened when I disconnected it. But by disconnected the ground a short instant and rewire it now everything seems to work. I have just made a batch of trials and everything works like a charm for now. It looks like it had been stuck internally before I discovered the ground wire, I really don't know why it wouldn't work initially.

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Matthias Lange - DE avatar image Matthias Lange - DE ♦ drumond commented ·

Ok, good that it's working now but you should keep an eye on it.
If it's happen again you should get in touch with you dealer for a warranty exchange.

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drumond avatar image drumond Matthias Lange - DE ♦ commented ·

Thank you for your good advice.


I have just tried to unplug the Charge disconnect port of the BMS and the Cyrix opened as it should have to.

I have no idea what made it remain closed this afternoon.

Strangely, everything works as it always should have.


In addition, I put a Blue Sea switch ON/OFF between the Cyrix and the Lifepo4. Thus, the alternator will charge the Lifepo4 only when I decide it to. I have more than 900W solar panels on the roof, and I only need to charge from the vehicle alternator from time to time during winter.

Thank you.

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