when i use a shore line to charge AGM battery at the same time it goes thru the cyrix and also charges the main or vehicle battery (which is generally a wet/lead acid battery, the wet/lead battery over heats and gets destroyed.) has any one found a solution to this problem. It seems to have started about a year ago.
Welcom Alain. Using shore power to charge with what kind of charger? Converter, inverter/charger? How is the system wired? We will need more information.
It seems that it is a problem that Victron did not take into account, when they created the Cyrix, but to be honest it seems that most battery separators that work the same way have the same problem.
To answer your question, it seems that any charger that you use be it an inverter, DSL or any make that charges AGM or Lithium battery the same problem will happen. Let me explain what i feel is going on. When the main vehicle battery is fully charged the cyrix closes and sends 12/13 volts to the axillary batteries to charge them, which work relatively well except as you know wet or lead acid batteries do not have the same algorism as AGM, so when you use a AGM 120vac charger which uses a shore line or a generator it charges the AGM batteries at a bulk charge of 14.6 at the same time it is charging the vehicle batteries because the cyrix is open and since the intelligent charger does not recognize that the vehicle batteries are fully charge, it keeps on sending high voltage till the AGM batteries are fully charged, once the AGM are fully charge the charger goes into float mode which is not a problem. I feel the reason that we never notice it before was that either the vehicle batteries where not fully charged, and the cyrix stayed open, or that the aux batteries where around 90% and that the short time that was needed to bring them up to 100% did not affect the vehicle batteries, they might have gotten a bit warm but was never notice.
The solution I found was to add a 200 amp NC relay with a diode on the charger positive side so as not to have a return of 12v. Then when the charger is on the relay is open and stops the charger from going and charging the vehicle batteries.
It is a solution but not ideal.
I built a similar installation in an RV for my brother in law. I made a switch that can disable the Cyrix, or activate the start-assist.
As a solution you could add a small relay on the shore AC input that breaks the ground connection of the Cyrix when activated. Without the ground, the Cyrix will not close and overcharge the starter battery.
I decided to just add a diode after the Cyrix which works, the relay I would only use if the client wants to use the aux battery to start his/her truck.