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Old 13-07-2018, 11:24   #1
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Charging dinghy from mothership

Hi all,

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.

What is the best way to hook up the dinghy batt to the mothership if I want to charge?
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Old 13-07-2018, 11:36   #2
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Re: Charging dinghy from mothership

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.
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Old 13-07-2018, 12:18   #3
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Re: Charging dinghy from mothership

A few thoughts:

1. If you charge from the house bank overnight, with no other charge source, you will deplete the house bank. Can you afford the AmpHours "lost"?

2. You can certainly charge the dink from your boat system. Might be best to use an echo charger or charge relay that diverts charge from the house bank when the house bank is already charged, much like used to charge a start battery. An advantage is this works whatever charge source your house bank is using: solar, wind, shore AC or engine.

3. Some solar controllers have a "load" output that diverts unused solar power to another load. This can be used to charge your dink without depleting the house bank.
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Old 13-07-2018, 12:26   #4
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Charging a single battery from a large battery bank

Jamhass,

Thanks so much for your reply.

1. If you charge from the house bank overnight, with no other charge source, you will deplete the house bank. Can you afford the AmpHours "lost"?

Yes. House bank is almost 500ah and dinghy batt is only 105ah... also dinghy batt is not totally discharged and house bank should be full at end of day.

2. You can certainly charge the dink from your boat system. Might be best to use an echo charger or charge relay that diverts charge from the house bank when the house bank is already charged, much like used to charge a start battery. An advantage is this works whatever charge source your house bank is using: solar, wind, shore AC or engine.

Thanks. Is it as simple as hooking something like this up between my house bank and dinghy batt when I want to charge? - https://www.amazon.com/Xantrex-82-01.../dp/B0016G8RT8

3. Some solar controllers have a "load" output that diverts unused solar power to another load. This can be used to charge your dink without depleting the house bank.

Good to know.
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Old 14-07-2018, 05:15   #5
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Re: Charging dinghy from mothership

Sterling DCDC charger if the dinghy batt is worth the expense.

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

much better all round if you can charge the dinghy from an actual source, like solar during the day, or dino juice.
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Old 14-07-2018, 08:46   #6
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Re: Charging dinghy from mothership

Quote:
Originally Posted by john61ct View Post
you could easily be reducing House lifespan by a lot if this is a regular thing

much better all round if you can charge the dinghy from an actual source, like solar during the day, or dino juice.
I believe you, but just curious why this would be. My house bank is nearly 500ah of new fla golf cart batts. Dink battery is a new 105ah AGM. If the AGM was partially discharged, say down to showing 12.0V and the house bank is fully charged, would charging it really pull the house bank down that far?
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Old 14-07-2018, 10:24   #7
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Re: Charging dinghy from mothership

My solution was to install a female cigarette lighter recepticle in the transom is Seaweed. There was a Beckson plate nearby so I also have a place to stash the charger. Well, it's really the cut off wires from a real battery charger wired to a male lighter plug.

Prior to the cigarette recepticle install I used these


I do not charge so much as equalize with the boat. In other words, Algae's battery level is the same as Seaweed's by morning. I have been using this technique for several years. Installing the outlet at the transom was a big improvement. I should have done that long before.

Then I upgraded:


Good luck.

Side note: Even if your dinghy battery was flat and required 50 amps to fully recharge, that's a very low percentage of your house bank. I would not be concerned.

P.S. - You may find these articles of use:
http://janice142.com/Articles/TrollingMotor Woes.html
And
Janice142 article More Trolling Motors
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Old 14-07-2018, 10:30   #8
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Re: Charging dinghy from mothership

Standard ciggie sockets are IMO a dangerous abortion, avoid like the plague for anything important, or that you use regularly, or for more than a few minutes. inherently poor design, IMO a dangerous abortion,* avoid like the plague

Never more than 5-6A and for short periods, even then they are risky.

Blue Sea has a nice socket design that twist-locks with the matching plug, but will also accept standard ciggie plugs for smaller (<10A) loads.

Also the BMW/ Hella/ Merit/ Powerlet "Euro-style DIN" (ISO 4165) style is very robust.

Anderson plugs for high amps. *

If you standardize on one of the last two types, there are adapters for guests, temporary use of devices with standard ciggie plugs.

___
* any battery charging should be considered high amps
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Old 14-07-2018, 10:32   #9
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Re: Charging dinghy from mothership

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Originally Posted by Peregrine1983 View Post
I believe you, but just curious why this would be.
Not a matter of degree, the concept is flawed from the get go.

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

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.
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Old 14-07-2018, 18:02   #10
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Re: Charging dinghy from mothership

Quote:
Originally Posted by jamhass View Post
...use an echo charger...
Some solar controllers have a "load" output that diverts unused solar power to another load. This can be used to charge your dink without depleting the house bank.
This.

Don't connect directly to house bank.
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Old 14-07-2018, 19:32   #11
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Re: Charging a single battery from a large battery bank

Quote:
Originally Posted by Peregrine1983 View Post
Jamhass,


Thanks. Is it as simple as hooking something like this up between my house bank and dinghy batt when I want to charge? - https://www.amazon.com/Xantrex-82-01.../dp/B0016G8RT8
Yes...But ...

As already noted, use a "proper" connector, one at least rated for the current the echo charger (or ANY charge source) is capable of delivering. Moreover, make sure to properly fuse the connector on the BOAT side.

One additional advantage of an echo charger is that it (should) limit the current to a level your wiring can safely handle.

For example: "simply" connecting your dink battery to the house can be dangerous. A depleted dink bat connected directly to a fully charged house bank can induce very high currents, potentially leading to damage to the wiring, connectors, etc, even leading to the possibility of fire. Consider that you would never (or should never) try to jump-start your car with a home-style extension cord.

Additionally, connecting directly to either battery (just like jumping your car) can cause sparking and possible fire due to the hydrogen released by the batteries.

Were it me, I would also add a heavy-duty switch or circuit breaker in the system so that the act of connecting the dink wiring to the boat does not instantaneously cause the current to flow and arcing to occur.
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Old 14-07-2018, 19:41   #12
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Re: Charging dinghy from mothership

The Echo charger will only work when an active charge source raises voltage.

It is limited to 15A, and will not go over 14.4V.
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