I have been playing with the charger now (connected to a laboratory power supply able to provider 600W).
Actually it is a bit a stupid device and if I read the manual it is not really doing as promised. Or at least, the behaviour is not as what I would expect based on the manuals description.
The manual gives a specific behavior for 'traditional' versus 'smart alternator'.
But actually it should say it has a difference between IGN cable active or not.
IGN cable "active" ( = running engine and IGN sensing cable connected): Start loading service/home battery at 12V starter battery and stop when the starter battery is at 11.5V; 11.5 volts is almost a death battery (is it?, some charts say it only has 10% left)?; anybody knows if a 11.5V AGM battery can still start the engine? In practice, it just means if you start the engine, the IGN signal triggers the charger to start charging.
So with the IGN cable active, it will always be charging the service battery from the starter battery. No matter what the alternator is doing -unless the alternator goes above 16V). So the strategy with the IGN cable active, is to keep charging the home battery from the starter battery. No matter what the alternator is doing. Up to the alternator to keep the starter battery alive.
If you disconnect the IGN cable (= engine stops), it will stop charging if the voltage is below 13.2V. But if the voltage is above 13.2V it will jump into 'traditional' mode). See next ;-). I have no idea in how far a smart alternator would ever charge the battery up to 13.2V. Would it?
If the IGN is not connected (=no running engine and IGN cable connected or not); the DC-DC charger will start charging when the alternator brings the voltage to 13.2V. But 13.2 volt could also be a highly charged battery. And it will charge until the starter battery drops below 12.7V; that is about 15%DOD. So it might continue charging for quite some time after the engine stops. Specific if the alternator brought the battery to 100% of its capacity. I don't know how far this is an issue. At least it would means that a starter battery with such a charger would run more cycles. So in this mode the alternator starting will start the charging. That goes on until the alternator stops and the battery goes below 12.5V (would a smart alternator do that?). If the alternator starts charging the battery again, the charger will work again until the battery reaches 12.5V? In how far do alternators allow a battery while driving to go below 12.5V?
And also: This 'traditional' behaviour is maybe also not so bad to be used with a smart alternator. But maybe a smart alternator never produces 13.2V (which would surprise me, or am I wrong).
Related here: I somehow was expecting the 'smart alternator' mode, to be a mode where he would charge first of all from the alternator. But that is maybe my wrong expectation. I thought some charger check the D+ signal to know if the alternator is running and start charging at that moment. Here the logic on 'smart' seems revered. Just consume what is in the started battery and leave it up to the alternator to keep the starter battery alive. Maybe that is not so bad after all.
Side note: the charger takes more current if the starter battery voltage (or what come from the alternator) is higher.
But there is a big difference in this relation current/voltage in the traditional versus smart mode (read: IGN not active versus active). In traditional mode at 13V, it would only charge about 10-15A, in 'smart' mode is would charge about 30A. Maybe this could be a driver to choose using the IGN cable or not.
But anyway: If I want to control if the charger can work from the engine or not: the only option seems to be to put a relay between starter battery and charger. The IGN sensing cable is of no use. And maybe this should be a relay feeded by the home battery. And if the home battery is low: the relay should allow the charging...
Walter
