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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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Justin Cook avatar image Justin Cook ♦♦ drumond commented ·

@drumond Just for reference, you can also put a much cheaper and smaller on/off toggle switch on the ground wire to the Cyrix. Off = no ground = Cyrix stays disconnected. On = grounded = Cyrix connects/disconnects per its trigger voltage thresholds.

...not to dissuade you from the Blue Sea switch - they're fantastic and I love them... just, you don't technically need one there.

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drumond avatar image drumond Justin Cook ♦♦ commented ·

You are absolutely right, but with the Blue Sea I am really sure there is no electronic or whatsoever in place, I don't really know what's inside the Cyrix nor trust electronics during emergencies, and the first reason is when I bought the Blue Sea I wasn't aware of all the capabilities of the Cyrix, and how it really worked (my bad).

With the more expensive Blue Sea, when switched off, it is really switched off. I didn't have to think about that when I made the purchase.


I still don't know how the Cyrus li ct works and why everyone is buying one for their van when in reality all they need is a more appropriate dcdc charger.

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Justin Cook avatar image Justin Cook ♦♦ drumond commented ·

Haha fair enough. I personally generally try to dissuade customers from buying the Cyrix in these applications unless there's no room for anything else. It does the job, and keeps both batteries from ever being dead, and has the added benefit of being bidirectional so that if you're charging your LFP bank from an external source, your start battery will also be charging... but a good B2B charger is always a much more polished and customizable way to get a good charge into an LFP bank.

People mostly just like the small form factor and relative cheapness of the Cyrix... and it really does work, it's just not the best solution available for charging an LFP bank from the alternator/start battery.

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drumond avatar image drumond Justin Cook ♦♦ commented ·

What happens when the Lifepo4 voltage is 14.2V, does the Cyrix Li Ct remain closed, and the vehicle alternator still delivers all its current to the already filled Lifepo4? Could seriously reduce the life expectancy of the Lifepo4.

I am looking for a way to use the relay from the BMV702 or CCGX, that would open the Cyrix when the Lifepo4 exceeds 13.8V but I know nothing about Victron relays, and how to wire them to the BMV702 and the Cyrix Li Ct. If a relay was installed, I wouldn't have to pull over while I am driving and turn off manually the Cyrix Li Ct with the Blue Sea switch, and always checking the Lifepo4 voltage on road.


Regards.

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Justin Cook avatar image Justin Cook ♦♦ drumond commented ·

@drumond, well if the LFP bank is at 14.2, it's not going to be presenting as much of a load to the alternator anyway, so the current will be tapering off regardless unless your start battery is shot... and your BMS should be triggering the Cyrix off before any overcharge condition is encountered anyway. That being said, yes, it'd be super easy to program the BMV relay to turn off the Cyrix.

Think of the BMV relay as a simple bridge. When it's closed, it's passing through. When it's open, it's not passing through. So if it were me, I'd simply use the BMV to interrupt your Cyrix ground wire, then program the BMV to open the relay at whatever voltage you want your max to be (let's say 14.2). You set the BMV relay to be NC (normally closed) and tell it to open at 14.2. Then when your LFP bank reaches 14.2, the BMV relay opens, interrupting the Cyrix ground wire, and without a ground connection the Cyrix opens, disconnecting the two banks.

The steps to program it are a bit of a pain (this is why I love the BMV-712, because the bluetooth interface makes programming all this a breeze) but it's detailed starting on page 23 of the manual.

Relay Mode (f11) will be "default"

Invert Relay (f12) will be "on"

High Voltage Relay (f20) will be set to (for the purposes of this example) "14.20v"

Clear High Voltage Relay (f21) will be set to whatever v you'd like the Cyrix to reconnect at... say, "12.2" or something.

You'll have to play with the voltage settings to get it just the way you want it, but that's fundamentally how you do it. Just remember that you're using the BMV relay to interrupt the Cyrix ground connection. You want the relay normally closed so that the Cyrix is operational, and in function 20 you're setting the voltage that you want the relay to open, disconnecting the Cyrix ground connection and thus disconnecting the two banks, and then in function 21 you're setting the (lower) voltage at which you want the BMV relay to close again, thus rendering the Cyrix operational once more.



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drumond avatar image drumond Justin Cook ♦♦ commented ·

Really cool your answer, thank you.

So, wiring speaking, I simply connect the Cyrix ground to one port of the relay at the back of the bmv702 and the other relay port of the bmv702 to the ground and that's all?

I will study your previous reply meticulously the following days.

I have several Victron bluetooth dongles so I figure the 702 can operate as a 712 while the dongle is inserted.


Thank you.

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Justin Cook avatar image Justin Cook ♦♦ drumond commented ·

@drumond, yep, chassis or battery NEG in one port and the wire to the Cyrix ground on the other port... doesn't matter which port goes to which thing.

And just to make sure, since no one has specifically talked about using the BMV relay as a ground interrupt before, I hooked one up here on my test bench just to make sure it'd work that way, and indeed it does.

Since you have the dongle, that's perfect, that makes setting the BMV relay states and playing around with the trigger voltages so much easier for you... good luck!

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