BATTERY CHARGING WHEN NOT ON BOARD

[David Pakes]

Hi All,
In addition to a starter battery, I have a house bank of four golf cart batteries which are charged by either the engine (Balmar 105amp) alternator, three 135 watt solar panels, shore power or on-board generator. I also have two AGM batteries for the bow thruster which are only charged via the engine’s alternator.
I am away for six months or more when I put the boat up on the hard and I return home to Oz each year. I rely on the solar panels to keep batteries charged but only found out last Oct that the bow thruster batteries are connected only to the alternator.
The boat is presently in Portugal and the yard don’t have a solution to charge the bow thruster batteries using the solar panels, they tell me.
Can anyone assist please with a workable solution while I’m away from the boat ie using the solar panels to charge bow thruster batteries as well as starter and house bank.
Many thanks.
Dave

[sailormed]

Install an Echo Charger. Will charge the bow thruster batteries only when the house batteries are above a certain set voltage.

[uncledom]

The problem your going to run into is the different batteries which take different charging voltages. Perhaps a small separate panel and controler for the AGMs just to keep them trickle charged not to make up for thruster use.

[sailormed]

If you are on the hard with access to 220V, install a trickle battery charger only for the AGM thruster batteries.

[GordMay]

Greetings and welcome aboard the CF, Dave.

[ranger58sb]

Our AGMs have never self-discharged very much over longish winter periods...

-Chris

[ramblinrod]

For only six months, disconnect the negative terminals of all batteries.

[Ahmet Erkan]

Originally Posted by ramblinrod

For only six months, disconnect the negative terminals of all batteries.

Why go through the trouble of disconnecting all batteries? David says all batteries are fine with the solar panels keeping them charged except the two that provides local peak power to the bow thruster.
Actually David also said that one alternator charges all the batteries which implies that all the batteries can be connected in parallel through switches.
Can't be certain without looking at a wiring diagram but it sounds like the problem can be made to go away by leaving the right set of switches closed.
Ahmet

[ccannan]

I disconnect my batteries while away from my boat over an extended period of time (boat in the boatyard). I have AGMs and leave my boat for periods of up to 9 months and haven't noticed any appreciable battery discharge, or any other negative effects. I also disconnect my solar panels from my solar charger. I had a solar charger die on me one winter when I had left it and the batteries connected.

Another reason to disconnect the batteries is to eliminate any possible discharge and or ignition source for a fire.

[hellosailor]

Put a small portable charger, even a car battery charger, on an extension cord and top off the AGMs for a day every second or third month, and they'll be happy enough. It isn't perfect but it is very simple and inexpensive. AGMs don't self-discharge at the same rate that wet cells do. Or, leave one portable solar panel on deck, on the bow, to keep a small charger going on the AGMs.

[David B]

Originally Posted by David Pakes

Hi All,
In addition to a starter battery, I have a house bank of four golf cart batteries which are charged by either the engine (Balmar 105amp) alternator, three 135 watt solar panels, shore power or on-board generator. I also have two AGM batteries for the bow thruster which are only charged via the engine’s alternator.
I am away for six months or more when I put the boat up on the hard and I return home to Oz each year. I rely on the solar panels to keep batteries charged but only found out last Oct that the bow thruster batteries are connected only to the alternator.
The boat is presently in Portugal and the yard don’t have a solution to charge the bow thruster batteries using the solar panels, they tell me.
Can anyone assist please with a workable solution while I’m away from the boat ie using the solar panels to charge bow thruster batteries as well as starter and house bank.
Many thanks.
Dave

We are in a similar situation Dave. We leave ours in the Med and return to Australia for 9 months or so each year. I have not looked at the Hunter wiring, but there is more than a good chance it is similar to ours.

We have generator start, engine start, 4 x service batteries, and 4 x bow thruster batteries. Normally they are all (except the generator) charged from engine or shore power, through a series of splitters. When we leave, I turn all of the isolators off. The charging points go to the battery side of the isolators, so charging is maintained, but the batteries are otherwise totally isolated from the boat.

Charging therefore continues when the yard plugs the power in each month. However with the gen-start battery, (in your case, the bow-thruster batteries) I have a dedicated outlet of the solar controller (a dual battery version) feeding that battery, and the other outlet feeding all other batteries through a splitter. The alternative is as others have suggested - a small charger going to the BT batteries.

Having said all of that, are you sure the BT batteries are only charged by the engine? Perhaps the splitter input from the shore charger(s) is faulty?

I hope that helps. We will be back in Australia in a week if you want to chat about it.

David

[DumnMad]

Originally Posted by ranger42c

Our AGMs have never self-discharged very much over longish winter periods...

-Chris

I understood one of the benefits of AGM was that you could leave it 6 months without any issues. Probably why the solar is not connected.

I'm planning to put them in my little motorhome for that reason.

[David Pakes]

Hi All,

Thank you so much for your very helpful advice and thank you also for the welcome. Lots of good solutions as I anticipated. I think it might be time I did a bit more homework myself and see what might be best and/or simplest for our boat. Any further suggestions always welcome.

Cheers
David

[DumnMad]

Hi David.
Seems like the electrician knew what they was doing by putting the AGM's at the bow-thruster and no connection to the solar. I suggest leave everything as is but get the yard to top up the water in the solar powered golf cart batteries from time to time while you are away.

[Ahmet Erkan]

Originally Posted by DumnMad

Hi David.
Seems like the electrician knew what they was doing by putting the AGM's at the bow-thruster and no connection to the solar. I suggest leave everything as is but get the yard to top up the water in the solar powered golf cart batteries from time to time while you are away.

The electrician might have known AGM batteries are more vulnerable to overcharging but I do not agree with not charging at all as a solution.
Batteries should be fully charged and then left on a "trickle charge" if they are to be stored for an extended time.
A trickle charger helps keep the batteries healthy when the boat is stored on the hard for a lengthy period, but much more importantly the bilge pump shall be operational if the boat is unattended at the slip.
Unfortunately the battery manufacturers do not specify the parameters for a trickle charge. I use a maximum Watts/sqft of dissipative surface area of the battery bank but I don't want the responsibility of suggesting a figure because it should be specified by the battery manufacturers for an allowable temperature rise that does not cause loss of water. The charger should also be smart enough to recharge faster if a load is applied such as a bilge pump activation.
Nothing is easy in engineering.
Cheers.