Alternator to battery charging via Mastervolt

[Denizen of the Deep]

Hey boaters. My boat has a Mastervolt 12-2000-100 mass combi unit and a 70A alternator charging the service batteries. The Mastervolt's 'smart' 3-phase charger requires mains level voltage to operate.

 

I am wondering whether it's possible or worthwhile inserting some gizmo between alternator and Mastervolt so that the Mastervolt can be offered high voltage from the alternator (some kind of transformer?) that will trigger its smart charging function and save me some engine running time when recharging batteries.

 

Any ideas?

[nicknorman]

Short answer is "no"! You would have to convert the 12v output from the alternator (variable current available, according to rpm) to mains voltage and frequency by an inverter, then put it into the Combi for it to be converted back to 12v-ish again! Very expensive, complicated and inefficient.

 

As an alternative contemplate something like a Sterling A2B which sucks current out of the alternator and raises the voltage to an optimal charging one, or more cheaply an external smart regulator like an Adverc (needs minor surgery to the alternator).

[Barge Maria]

Nicknorman took the words out of my mouth.... or fit solar?

[Phil.]

I sometimes use my travel power to run the mastervolt combi but this would be pricey if you do not have one already. I am also looking at possibly fitting a sterling A2B but have yet to figure out whether it is worth it.

[Paul C]

I thought the general wisdom on aftermarket alternator controllers were, they aren't that good and in fact the standard alternator (controller) does a pretty good job on its own.

[nicknorman]

I thought the general wisdom on aftermarket alternator controllers were, they aren't that good and in fact the standard alternator (controller) does a pretty good job on its own.

I think it depends on the alternator! Alternators have a fairly soft regulation curve such that, for example, if the final low current voltage is 14.4v, during charge the output current will reduce below maximum at say 13.8v or less. In our case, since we have a 175A alternator this doesn't matter too much as we are still getting lots of current, but with a 70A one you will be down to say 30A well before reaching 14.4v. In such a case an external controller can help to keep the current near max until the voltage reaches 14.4v (or whatever).

 

So I think with a large alternator and modest battery bank, it's not worth it. With a smaller alternator and larger battery bank, it perhaps is. Even then, as we know it will only make a difference during bulk phase, it will not help the lengthy absorption phase.

[by'eck]

Another though expensive option is to fit a TravelPower or Dynawatt unit belt driven from engine in similar manner to the conventional nominal 12 volt one. These produce 240 volts AC relatively efficiently and the output could feed your Combi's charger as well as a host of other AC devices whilst engine is running.

Edited September 1, 2015 by by'eck

[ditchcrawler]

I sometimes use my travel power to run the mastervolt combi but this would be pricey if you do not have one already. I am also looking at possibly fitting a sterling A2B but have yet to figure out whether it is worth it.

I wouldn't have thought you would see much gain over the travelpower combi if any.

[Phil.]

I wouldn't have thought you would see much gain over the travelpower combi if any.

I don't think it does do much other than raise the charging voltage slightly and allow me to equalise them. But I now use my solar to do this as it is more effective than the combi.

[ditchcrawler]

I don't think it does do much other than raise the charging voltage slightly and allow me to equalise them. But I now use my solar to do this as it is more effective than the combi.

And if it raises the voltage it would probably back the charger off.

[Denizen of the Deep]

Thanks very much for all your thoughts and replies. Re-thinking