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Discussion Starter #1
I am fitting solar panels and want to disconnect solar whilst the engine is running.... I will terminate the solar charger at the starter battery in the engine bay.

Does anyone know of a easy way to pick up the ignition switch position or alternator excitation to drive my disconnect relay near the battery box...?

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Discussion Starter #3
In order to not reverse bias the voltage regulator in the alternator when the the solar panels are active which will reduce the charging capability of the alternator and also to avoid confusing the mppt charger when the alternator is presenting voltage to the battery...

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Never ever has a mppt charger become confused by an alternator charging the battery, a disconnector while the engine is running is nevre fitted by solar panel installers. Why is it a problem if the alternator charging is reduced? It saves fuel :)
 

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Ah interesting so its generally fine to stick em in paralell? Hmm I'm sure that will confuse the mppt as to the state of the batteries ... I suppose that will terminate the charging cycle early anyway leaving the alternator in charge ...

So the recived wisdom is to just stick em parallel eh... ?

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Discussion Starter #6

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I've got mains charger, solar charger and alternator and I've had them all running at once without a single problem.

As you say, whichever ones have the lower charging threshold voltage simply back off and leave the "winner" to get on with it. If the solar controller gets confused, it will sort itself out when you turn the engine off (in my experience).
 

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Same here.
Roger
I've got mains charger, solar charger and alternator and I've had them all running at once without a single problem.

As you say, whichever ones have the lower charging threshold voltage simply back off and leave the "winner" to get on with it. If the solar controller gets confused, it will sort itself out when you turn the engine off (in my experience).
 

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Discussion Starter #9
Problem is though when you have the choice do you want a 20A charge or 90A charge? Sounds to me its hit or miss. If you start the engine on a sunny day... with a semi discharge battery your alternator may not get a look in if it has a lower OP voltage ... it depends on what you're calling a problem...

Another potential problem might be to open circuit the output of the mppt when its charging at full tilt...

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Another potential problem might be to open circuit the output of the mppt when its charging at full tilt...
If you fit a "disconnect relay" then yes, that would be a potential problem if you were to start the engine with the panel in full sunshine, though I would hope that any decent solar charge controller could cope with its load side going open circuit without warning? If not, it's probably not fit for purpose.

If, on the other hand, you don't fit a "disconnect relay" then the MPPT controller will detect the rise in battery voltage due to the alternator output and switch itself off - no open circuit output involved.

Don't worry about a 100 or 200W solar panel overwhelming the output from your alternator - it's not lilkely to happen in any normal set of circumstances, because of the nature of the wiring involved.
 

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TBH, overthinking a non-issue :)

Having said that, what IS a good idea if you are able to do so is set the Absorption Voltage on the SOLAR Controller to be higher than the Mains Charger. This means that when you are plugged into EHU and the batteries are just about done, the mains charger will go into float thinking the batteries are fully charged, and the solar will take over the maintenance charge. That way you will be using the 'free' energy of the sun rather then pulling power (albeit a very tiny amount) from the mains, which is not free.
 
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