Please explain how the Cyrix CT works

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canamsteve asked Feb 24, '24

Please explain how the Cyrix CT works

I have installed a Cyrix-ct in my 4X4 to isolate the main starting battery from the secondary "leisure" battery. The AGM leisure battery is also connected to a solar panel through a Victron regulator but to the charging system through a CTEK (sorry!) Smartpass. I have installed the Cyrix because the Smartpass does not prevent the leisure battery from discharging the starter battery

When I start the vehicle, the starter battery is charged by the vehicle alternator and steadies at ~13.5V. When the Cyrix relay is disconnected, there is starter battery voltage on the Battery 1 (starter) terminal and a very low voltage (~1-2V) on the leisure battery terminal to vehicle earth. The Cyrix-ct does not connect to the second leisure battery. This is no doubt because it is already charged at about 12.7V or because the Smartpass is not backfeeding the leisure battery voltage to the Cyrix at all (the 1-2V present on the Batt 2

If I use the momentary switch on terminal 85 to trigger the Cyrix, it latches and connects the leisure battery - and then stays latched (no connection on T85) for some time (hours) until eventually disconnecting

It was my understanding from the datasheet that this "interconnection" of the two batteries was for emergency starting and should only occur for ~30 seconds - not hours?

I may need to bypass (or remove) the Smartpass system, but before I do so, I'd like to have a better idea on how the Cyrix-ct determines its connections

While the Cyrix-ct seems simple, there is more going on in its "intelligent" operation that is covered in the brief datasheet. If anyone can direct me to a more thorough explanation, I would appreciate it. Many thanks

Cyrix Battery Combiner

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Answer 1 · 2024-02-25T17:51:31Z

canamsteve answered · Feb 25 at 05:51 PM

I have just re-read the data sheet that comes with the Cyrix ct and it refers to its "intelligent" sensing of battery voltages, but does not explain it at all. It literally appears to be a "black box" which does different things at different times, but you have no way of knowing or controlling its operation. I may just end up using it as a manual battery isolator, triggering the relay with a remote switch.

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Answer 2 · 2024-02-25T18:12:26Z

Matthias Lange - DE answered · Feb 25 at 06:12 PM

I think as long as you have that "Smartpass" device installed the Cyrix can't work as it should.

It measures the voltage on both sides and if the voltage on one side rises above the thresholds shown in the datasheet/manual the Cyrix closes.

But if you have only 1-2V on one side it will not close automatically.

If you use the start assist the relay remains closed as long as the voltage is above 12.8V -> see datasheet/manual.

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Answer 3 · 2024-03-05T05:24:49Z

stefan-scholz answered · Mar 05 at 05:24 AM

I‘m using the the Cytrix -Li-ct 12/24-120 in a 12V-system for a RV-application. The setup is designed in order to control the charging line of the Li-Battery and consists of following connections: terminal „30“=Li-battery+, „87“=Output+ from power charger or charger inverter(Alternator),“86“=BMS charge disconnect,“85“=ground. I‘m also not satisfied with the behavior of this ‚intelligent‘ relay, since the cytrix does not return to the „open“-status after system start up without any charging source or - during operation - after switching of any applied charging device, which all together is not in line with one can expect from the product documention. In my application this adds a permanent, unnecessary load of more than 200 mA onto the residual current in the system. As a - workaround - solution i have installed a NC switch (Taster) in the ground-connection to Pin „85“. This allows for manual reset („Stop Assist“) into the „open“ status, which will be kept permanently during the usual normal system operation (without the above mentioned charging).

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