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chal 08-15-2013 07:50 AM

yet another battery charging question
Sorry this is one of those things that comes up again and again. I have read many threads on this forum about this topic, and think I now have a fairly clear idea about how to proceed, so this is really a request that someone more expert about these matters than I am can confirm that I'm right - or not!

Also, apologies that this is rather a long post, but I want to be as accurate as possible.

I'm on a swinging mooring, so no mains power. The boat is located in Cornwall, England, so weather not bad by UK standards, but sunshine levels not up to those in places like Florida either. There is also the problem that energy needs tend to be greater in winter when the days are shortest. The boat is an old (1930s) gaffer and this restricts my options because the boom overhangs the stern, making almost all wind generator options impossible. The only thing I can think of that would work would be a vertical axis generator mounted on the mast, but there is no way I could afford that at present. My energy needs are quite modest as I do not have any big power consumers like a fridge, powered anchor winch, etc. Main uses are lighting, some entertainment, and instruments when sailing, and as far as possible all are low energy.

My current setup is:

- I have a single cranking battery - a straightforward car battery of about 70AH, which is about 2 years old and works fine. I have 2 brand new 110AH lead acid leisure batteries (these replace the defunct single 110AH battery that died, so I have doubled capacity there). I have a single 25W solar panel with a built-in PWM controller, and a new 70A alternator with internal regulator. That doesn't sound a lot, but the solar panel has not done a bad job of keeping things going over the last couple of years with relatively little use of the engine.

- the alternator (fitted last year as part of new engine installation) is connected to the cranking battery; the solar panel is connected to the house batteries. The house batteries are wired together in parallel and the bank has an isolation switch. The cranking battery also has an isolator. There is a manual combiner switch, and a paralleling relay. Overall, probably a pretty common basic setup.

Reading the forums, and Calder, I have concluded that not only do I not have enough charging capacity (well, I already knew that much), but what I do have is probably not being used very efficiently. What I propose to do is this:

- wire the alternator to the house bank instead of the cranking battery and replace the the current paralleling relay with a Xantrex echo charger to keep the crank battery topped up

- add a new solar panel; the largest I can fit would be a 90W on the coach roof which would obviously suffer from shading but is about the best I can manage given the constraints of the boat

- use a MPPT charger with this new panel to maximise its charging capability.

This would be about the most that I could afford right now. Longer term, I would be considering replacing the standard alternator controller with a smart controller, and maybe doing the same for the existing 25W solar panel.

My main question is, then: does this seem about right?

The other thing is that, although I really cannot afford to spend more than this, it does occur to me that overall this means having 3 charge regulators plus the echo device, and that seems rather a lot of components all doing the same basic job. Is it possible to have a single controller that could take the inputs of all the different charging sources and provide both the smart output for the house bank and the top-up output for the crank battery, or is it simpler (essential?) to have a controller per charging device.

Many thanks!

Stu Jackson 08-15-2013 01:23 PM

Re: yet another battery charging question
What you described is spot on! I wouldn't change anything. Yes, solar and alternator need their own regulators. 3 regulators? I only see two. Also assume you're getting rid of the isolators. You have a very good design.

chal 08-15-2013 06:00 PM

Re: yet another battery charging question
Great, and thanks for the reply, much appreciated.

btw not very clear but 3 regulators incl the one in the existing 25W solar panel which I have thought I could one day replace with a mppt model: it's quite a small panel but probably occupies best location on boat. However if regulators best separate anyway this is something I can do some time in the future.

I'll go ahead with improved confidence.


xort 08-16-2013 06:36 PM

What about a voltage regulator for the alternator? If it's going to charge the house bank, it should be properly regulated by an external 3 stage regulator

chal 08-17-2013 02:47 AM

Re: yet another battery charging question
I think that is something I will have to add later, though that was why I asked about the possibility of combining regulators.

I don't use the alternator to charge the batteries much apart from when I have the engine running anyway, it would only be if they had been depleted for some reason, in which case I presume a normal regulator wouldn't work too badly and then there would be the mppt input from the solar panel to top it off.

hellosailor 08-17-2013 01:25 PM

Re: yet another battery charging question
Chal, if you have a problem with shade on the coachroof, I would suggest looking at 2-3 smaller panels instead of one larger panel. If you have one panel and any part of it is shaded, typically the output from the entire panel is degraded. If you have two smaller panels, you can lay them out on opposite sides of the coachroof, giving you greater odds that at least one will not be in shade, and will be at full power.

Sometimes one panel is made up with two or more distinct strings of cells in it, so that a shadow just reduces output and takes out one of those strings. You'd need to look into that with the maker, but I'd suggest 2-3 separate panels give you the best odds of keeping at least one out of the shade at any given time.

And beware of cheap "no name" MPPT controllers. In the US we've heard of some being sold that actually are not MPPT controllers at all, just hucksters capitalizing on the extra bucks they can get by calling them that. After all, who is going to open them up to find out?

chal 08-18-2013 09:03 AM

Re: yet another battery charging question

Originally Posted by hellosailor (Post 1075279)
if you have a problem with shade on the coachroof, I would suggest looking at 2-3 smaller panels instead of one larger panel.

Thanks, that's a good idea. The whole issue of where to site the panels is a tricky one. The boat has no pushpit to hang them off as lots of people do. The mooring is on a tidal river that runs pretty much north-south and, owing to its latitude, the sun is always to the south. As the boat swings with the current, the existing solar panel on the forward hatch is either in good sun or shaded by the mast. A panel on the coach roof is almost always going to be in some shade from the boom, and I think even splitting it and having 2 panels, neither would be in full sun for much of the time (there are hills both sides of the river).

I'm therefore wondering if it would not be better to spend the money on the smart regulator for the alternator (instead of the additional solar panel(s) and regulator(s)). I would prefer something a bit more environmentally friendly than running the engine, but if an almost constantly shaded panel would not contribute much power anyway, perhaps it would be better to try to maximise the contribution of the alternator.

That would make the setup:

- batteries as per original post
- existing small solar panel but perhaps with mppt controller
- alternator with smart regulator
- both the above connected to house batteries
- echo charger to keep crank battery topped up

Any thoughts?

Stu Jackson 08-18-2013 12:09 PM

Re: yet another battery charging question
Stay with the solar. Don't waste $$ on an external regulator (yet!!!:)). Here's why:

Musings Regarding External Regulation -

hellosailor 08-18-2013 01:42 PM

Re: yet another battery charging question
Depending on your details, maybe using the solar panel(s) forward of the mast, or even clipped onto the bow, and removed before sailing. Or strapped on top of the boom, and again, removed before sailing. Even if you were moored in a fjord, "something" beats "nothing".

manatee 08-18-2013 03:19 PM

Re: yet another battery charging question
How much current in the river? I've wondered why no ever mentions turbines to make electricity, like this:
Ampair Wind, Hydro and Packaged Power specialists +44 (0) 1258 837 266 | Aquair 100

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