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Old 08-08-2018, 18:12   #16
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Re: Charging dinghy from mothership

Yes, but (see above). Far from optimal for either side.
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Old 08-08-2018, 18:19   #17
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Re: Charging dinghy from mothership

Optimal can be measured in different ways. It uses the least amount from my house Bank and if you don't leave too early in the morning it will Top the battery up. We're only talking about replacing 20 at the most 30 amp hours and usually less with my setup.
And once the dinghy battery is charged the dinghy dedicated panels may even contribute to charging the house
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Old 08-08-2018, 19:17   #18
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Re: Charging dinghy from mothership

I would minimize that voltage drop. Probably via a DCDC charger so I can control the direction of flow.

And unless the source bank is LFP, only when a charge source is active.
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Old 09-08-2018, 16:25   #19
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Re: Charging dinghy from mothership

So I went to shore half hour ride I parked my dinghy in a place that's shaded. Got back voltage is at 12.3 measured After an hour from when I got back. Plugged into house .7 amps going in. House of 12.4 measured couple minutes after I hooked up. Refrigerator running full blast several fans running.
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Old 09-08-2018, 16:45   #20
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Re: Charging dinghy from mothership

And? Are you saying that is good?

Charge voltage should be well north of 14V.

Not getting to 100% Full will murder the batt get a fraction of its life.

By going into one batt then another you are needlessly wearing out two, twice as fast.

And losing 60-80% of the energy from the original charge source.

Sure can be done but far from best practices.
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Old 09-08-2018, 16:55   #21
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Re: Charging dinghy from mothership

That's not giving any opinions just stating facts. Like I said before I have two solar panels that will Top it up in the morning. Which I believe both house and trolling batteries will be at 12.4. Which doesn't hurt my house and helps my trolling battery.
At 9 a.m. this morning my house voltage was at 13.6 I don't know how long it will take for a higher voltage or to charge my dinghy battery with just the house but it would do it. Just a matter of having the dinghy at the house during the day. Edit my dinghy voltage is at 12.3 it's not going to bring my house down below that and the point that the voltage is that low it's an extra battery in the house.
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Old 10-08-2018, 04:40   #22
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Re: Charging dinghy from mothership

The Gage with my solar panels(12.4 is what it reads this morning which is what it was when I hooked up the trolling batt. last night) does not quite match my Sperry multimeter. anyway 7 a.m. this morning house is 12.54 and dinghy 12.48 according to Sperry. And the 12.3 voltage of my dinghy last night last night was from Sperry. According to the solar panel gauge a little over an amp is going in.
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Old 10-08-2018, 06:23   #23
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Re: Charging dinghy from mothership

Quote:
Originally Posted by Peregrine1983 View Post
I have a solar/electric dink setup that I love, but I want to find a way to also charge it from the mothership’s bigger solar system and battery bank when needed. I have an auto battery charger/maintainer, but this seems it would be inefficient as it would have to run on AC 110v off the mothership’s inverter.

Modern inverters are pretty good. Of the solar power you start with, you'll get maybe 75-80% of those watt-hours into the dinghy battery going through an inverter and charger.


If you use a DC-DC charger, and no inverter, you'll get maybe 85-90% of the watt-hours you started with.


Quote:

What is the best way to hook up the dinghy batt to the mothership if I want to charge?

The best way is to use a DC powered battery charger designed for the purpose, permanently installed below decks, with well-thought out cabling and connectors.


Quote:
Originally Posted by Peregrine1983 View Post
I assume it's not as simple as just creating a connection to my house battery bank. I'm thinking of something that will top it up overnight at anchor.

Correct. Creating a connection to your house battery bank will not provide reliable charging at night. (It could provide good charging during the daytime, as the solar panels on the big boat would end up charging both the house bank and the dinghy)


Quote:
Originally Posted by john61ct View Post
It is **very** inefficient going from batt to batt,

you could easily be reducing House lifespan by a lot if this is a regular thing

I don't believe there's anything to suggest that to be the case. A dinghy charging load is a load like any other, and will not reduce the lifespan of the house bank any more than, e.g. running the chartplotter or a vent fan or autopilot. Most house banks never get enough cycles to cause failure. They fail for other reasons.


Quote:
Originally Posted by john61ct View Post
Not a matter of degree, the concept is flawed from the get go.

Only a tiny fraction of input power makes it into storage.

Well, around 90% of the input power.


Quote:

Moving it from one storage to another is triply wasteful.

And every cycle is a little slice of bank death, you only have so many.

Good quality house banks, properly sized, in a cruising boat, don't ever reach their cycle life. They fail for other reasons. Age, sulfation due to being left, inadvertently, in a discharged state, shorted cells due to low electrolyte levels and overheating, etc.


Whether it is worth the added complexity is something the OP will have to decide.
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Old 08-09-2018, 11:33   #24
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Re: Charging dinghy from mothership

Well I was just rereading and I thought wow that's really high voltage I had early in the morning for my house Bank and then it dawned on me that I have wind generators. Bang head.
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