Dc to dc charger

[larman]

I am thinking of adding a dc to dc charger was curious if it would charge two batteries run in parallel?

 

[DavidM]

Yes, it will charge two 12V batteries in parallel. Make sure that they are the same type.

But, why a DC to DC charger? What is the source of the charge?

David

 

[larman]

The source would be the battery/alternator from the engine. This would help charge the house bank so I can charge them while underway without having to run my generator and ac battery charger.

 

[Osprey69]

The Balmar recommendation (as I have read from other manufacturers as well) is to charge house first then down to start battery. Balmar version is Digital Duo. Used if for decades on my sailboat.

 

[Bmarler]

Might an automatic charge relay work for that?

 

[tiltrider1]

If you have mixed battery chemistry then a dc to dc charger makes sense. If the chemistry is the same then directing the alternator to the house and using a smart ACR to charge the start batteries makes more sense.

 

[Mac2]

The source would be the battery/alternator from the engine. This would help charge the house bank so I can charge them while underway without having to run my generator and ac battery charger.

Make sure you have an external alternator regulator, so you don't burn up your alternator, which was designed to only recharge a start battery. Don't ask how I know this....

 

[SeaGator]

As others have said, if you are charging same type flooded, AGM or gel batteries, use a Blue Sea ACR (automatic charging relay). If you are charging different battery chemistries like a lithium house bank, then you must use a DC to DC charger.

 

[SailorGreg]

The advantage of a dc dc converter, whether same or different battery chemistry, is that it will charge the start battery at the appropriate voltage ( bulk, abs, float) regardless of the charge stage of the house batteries.

 

[larman]

My only concern is the load on the alternator. I have a 100 amp alternator. I am sure it would be working a long while underway to recharge the housebank.

 

[Bmarler]

My only concern is the load on the alternator. I have a 100 amp alternator. I am sure it would be working a long while underway to recharge the housebank.

That’s a valid concern, depending on the batteries you install. But, most internally regulated alternators will not put out rated amps for long.
Really though, an externally regulated alternator is the best move for good charging performance from the main engine.

 

[SteveK]

FWIW. I have two internal reg alternators, each charging a AGM battery from which a DC2DC charger (one each) is charging the LFP bank.
To protect the ALT I am using DC2DC that is rated about 75% of max ALT output. Charging input 100A per hour underway.

 

[larman]

My alternator is rated at 100 amp I was thinking of getting the 60 amp dc2dc charger.

 

[CharlieO.]

I have the stock alternator on my Lehman - 55 amp. I thought I’d buy the victron 30 amp dc to dc charger, but after consulting with Peter Kennedy at PKYS decided to do the 18 amp charger. Turns out the lithium battery I purchased recommends a 20 amp charge rate. I haven’t actually received the battery yet to double check the specs.

 

[SteveK]

I have the stock alternator on my Lehman - 55 amp. I thought I’d buy the victron 30 amp dc to dc charger, but after consulting with Peter Kennedy at PKYS decided to do the 18 amp charger. Turns out the lithium battery I purchased recommends a 20 amp charge rate. I haven’t actually received the battery yet to double check the specs.

Yes if you only have one battery, if you have 2 then 40A, 3 then 60A

 

[CharlieO.]

I am starting out with just one battery.