Both dc-dc Charger and combiner

[HC43C]

My question is can I use both; more specially I have a start battery which my alternator is currently attached to which powers my dc-dc charger( 30 amp Orion tr) which in the case of motoring, charging my Lithium house bank at the 30 amp rate. I have solar hooked up directly through MPPTs to the house bank. So now if I am not motoring I have no way to charge the start batteries ( also my shore charger charges my house bank). Can I use a combiner ( I currently own a magnum 25amp combiner) to also go back from house to start battery.

[witzgall]

It seems this is setup to me more complicated than it needs to be. Just send all charge sources, properly regulated, to the house bank, and then use the DC-DC charger to keep the start battery happy.

Chris (from Balmar)

[HC43C]

If I did send all charger sources through the house I fear my alternator could be severely damaged with my lithium bank. I went through the trouble of using a dc-dc charger in the first place to eliminate the alternator issue. I could eliminate my ability to charge my lithium bank and simply rewire the dc-dc from house to start but I lose the alternator to house in that perhaps you can elaborate and a more simple method of charging the house using an alternator?

[witzgall]

The best way is to use an externally regulator, paired with an alternator either designed to work with external regulation, or converted to same. For the regulator, our MC-614 works very well, has a lithium battery profile, and should be used with a alternator temp sensor to protect the alternator.

I have seen a trend of many people putting in lithium and going the dc-dc route without changing much else. This approach really robs you of one of the greatest benefits of lithium - fast charging. If you mostly sail from the dock, it is a valid approach IMHO. If you are cruising for multiple days, the limitations become apparent quickly.

Chris

[HC43C]

I have had this setup for a bit now and my limitation is my start battery charging when sailing for a long period of time. If I could go back perhaps I would have spent money differently and went a different route than dc-dc but I have 1000 watts solar with a d400 wind gen, I don’t have a huge issue with power on my house bank. The setup I currently have has the dc-dc charger in the case that my solar and wind were to fail, and I need a back up for charging via the engine which I don’t intend to use outside of propulsion ( which I understand is more limited via the dc-dc charger (30amp) ). I would like to solve my current problem and provide a charge to my start battery with my current set up complicated or not. If the answer is to scrap what I have and do as you say than so be it but I was hoping to see if there is another method first. Thank you though!

[witzgall]

If it just emergency combining that you are attempting address, then a simple cable with an on-off switch would work, appropriately sized and rated. A combiner that is switchable and usually off would work too, I imagine.

In my two-year cruising with LFP, opportunistic alternator charging was a very useful tool. Cruisers motor alot. We had a wind geen too, but 120w of solar and then later an additional 165w.

Chris

[smac999]

why do you need to charge the start battery?

how long is the boat sitting between starts? months?

[HC43C]

Honestly, I think I may be overthinking this all, the longest would be 2-3 weeks. And to be honest my start battery is a cheap little lead acid I can replace and abuse, I get the feeling all this extra is a moot point, but it feels good bouncing ideas off of people. I’m full time cruising so I will be using my motor more often than not. I think you may have struck a chord here smac, and I really appreciate the input from witzgall. Thanks guys !

[SkipMark]

Another option is to attach one of your solar MPPTs to your start battery, and leave the DC-Dc as is so any overflow goes to the house bank.
No need to buy anything else.

[HC43C]

Skipmarc, I thought about that, I have my panels balanced in a series-parallel lineup so to make that work I would need to add another controller and have my solar unbalanced. I may add a small 15 watt or something to do the job somehow, personally I rather not break apart my current solar setup though, good idea though!