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Old 01-09-2013, 11:45   #46
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Re: Battery Charging Puzzle

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Originally Posted by Dockhead View Post
I keep my boat on a mid-river mooring in the Hamble River, and when I'm out cruising, I spend most nights at anchor. As a result, I am not very often connected to shore power.

My power system works very well and I really don't worry too much about electrical power, either AC or DC. I have 420 amp/hours * 24 volts of Trojan batteries, a Victron 3kW, 70 amp charger/inverter, and a Kohler 6.5kW heavy-duty generator. On the hook, one (or at most, two) charging run a day for a couple of hours is generally enough to keep us in electrical power and hot water, even with five people on board as we had for this year's summer cruise.

I am especially pleased with the batteries, which have been abused by being run out dead flat two different times and left for weeks like that (once a stupid mistake of mine, another time a shore power failure when the boat was on the hard being refit). At the moment, they are testing better than they did when new with my Argo capacity tester, and they just go and go, despite living a very hard life. I do avoid discharging them below 50%, and I do equalize them from time to time, but without shore power, they are not brought up to 100% charge very often. They are Trojans, not the true heavy duty ones, but the 12v ones which look suspiciously like car batteries/leisure batteries (these were the only ones which would fit my battery boxes).

Now I'm back on the boat for a few days getting her cleaned up and ready to be left alone for a month while I go back to work. And here's my puzzle:

Say you are charging from a generator, and not from shore power, like I am. You do not want to run your generator 24 hours at a time, or even 10 hours at a time, as this is a waste of diesel fuel and engine hours. You are trying to gradually get your batteries up near 100% charge before leaving the boat for a month. How do you do it? Run the genset for 10 hours (or whatever to really get them to 100%, them top them up just before leaving? Or is it better to charge them a little bit at a time every several hours?

It seems to me that the batteries are accepting more charge per hour of genset run if I charge them a little bit at a time. It seems to me that the surface charge dissipates between runs, extending the bulk phase of charging. The less charge being accepted, of course, the less efficient is your genset run.

I do have a small Honda petrol generator which I bought specifically to put a finishing charge on the batts the last day before leaving the boat. However, the carburetor is clogged again (I bought from a guy who had let it sit unused for five years) and I really don't have time to faff around with it.

I'll be interested in your views on this.
We have a similar situation to you, but have a 7-year old Victron Phoenix Multi 12/120/2500. If we are leaving the boat for any length of time, we "trick" the charger into giving longer absorption charges simply by turning it off and then on again, as soon as it reaches Float.
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Old 01-09-2013, 11:47   #47
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Re: Battery Charging Puzzle

I suppose if you cannot find any other way to do it, the flexible panels will work, but that's pretty expensive per watt!
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Old 01-09-2013, 12:09   #48
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Re: Battery Charging Puzzle

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I suppose if you cannot find any other way to do it, the flexible panels will work, but that's pretty expensive per watt!
Yes, I know, but nearly as pricey as Aurinco & Solbian! I've been holding off on the assumption that time is on my side -- price & efficiency-wise -- with this newer technology. Then again, it would likely take only a modest-sized, much less expensive conventional mono panel to meet my limited goal. I do have an out-of-the-way space just forward of the companionway & dodger -- about 18" x 42" as I recall. PITA to run wires, but what else is new?!
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Old 01-09-2013, 12:52   #49
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Re: Battery Charging Puzzle

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. . . PITA to run wires . . .
Doesn't that just describe every boat project involving in any way electricity?
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Old 01-09-2013, 12:54   #50
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Re: Battery Charging Puzzle

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Originally Posted by Forever Freedom View Post
We have a similar situation to you, but have a 7-year old Victron Phoenix Multi 12/120/2500. If we are leaving the boat for any length of time, we "trick" the charger into giving longer absorption charges simply by turning it off and then on again, as soon as it reaches Float.
I don't know if yours does this, but mine has a "forced absorption" mode, which is evoked in a way similar to the way you evoke equalization mode (flip remote control switch back and forth until lights all flash, then wait for "absorption" light to flash, and flip back).
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Old 01-09-2013, 13:05   #51
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Re: Battery Charging Puzzle

I'm probably not helping much, since I'm not familiar with your vessel and what options you have. I currently don't own a boat, but I've been doing a lot of research into ~45' cruising catamarans. So everything I've looked at has had panels mounted on an arch over the dinghy, or maybe a few on the bimini, cockpit roof or cabin roof. Obviously anything shaded by the sails or boom isn't going to produce much power.

Since you are only going to use this while moored, have you considered a locking but removable mount on the stern handrails or one of the side rails? Dismount it and stow it below on your return...
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