Cyrix battery to battery - comments?

[berni109]

I found this the other day while browsing.
Thought this might defeat the clever alternator reducing charge when vehicle battery is charged?
Does anyone have the technical knowledge to comment on using in the van rather than an expensive all singing all dancing battery to battery charger.
Vehicle battery normal lead acid - hab battery agm but will change to gel or lithium.
Attached file is all the tech data I could find.
Thanks if u can help

 

[funflair]

I am not convinced it will get around the "Smart alternator"

Martin

 

[autorouter]

This is a microprocessor-controlled split charge relay. It solves a narrow range of problems, but won't necessarily solve yours. If you already have a split charge relay, switched by the alternator D+ wire, then this will not make any difference. People sometimes report an improvement, but that's mostly because they rewire with thicker wire when installing it, so there's less voltage drop to the leisure battery.

If it's a 'smart alternator with regenerative braking', the alternator stops charging the starter battery when it is about half full. During braking the alternator switches on and fills up the battery using some of the energy that would be wasted in the brakes. I suspect you do not want your leisure battery to be charged on that basis. So this Cyrix combiner is not what you want.

You want something that will take a low alternator voltage and boost it so that the leisure battery is fully charged, and to stop charging when it is full. For that you need a proper battery-to-battery charger.

Another problem the Cyrix combiner has is when the starter battery is charged from anything else, like solar or mains charger. Because the starter battery is being charged, it switches on, connecting the starter and leisure batteries together. That might not be what you want.

 

[berni109]

Ok thanks for the replys. Done some more reading and maybe my van wont have a smart alternator - euro6 2019 when it arrives.
So that's 14.4v(max?) into the vehicle battery while running with fiat electronics taking care of not overcharging(?)
This device will see 14.4v as a charged veh battery and open the connection to the hab battery therefore on a long drive potentially overcharging the hab battery or will the fiat electronics just see this as a bigger veh battery and interven to ensure it's not overcharged?
Just ignoring different charge requirements for diff types of battery for the moment

 

[autorouter]

If the wiring is not too thin, the alternator will treat the starter and leisure batteries as one big starter battery, so it will back off the 14.4V when the current demand from the batteries goes down as they charge up. Just like a standard split charge relay does.

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[berni109]

Need to wait a few days to get my hands on the manuals that I am hoping will arrive with the van. More questions then.