PHOTOVOLTAIC BATTERIES

[bob_tyler]

The boat I have recently bought is fitted with two of these to run everything except the engine starting.

The engine starts by and charges its own lead-acid battery.

The other batteries, which are connected together, are solely charged by solar cells on the cabin top.

The batteries are GNB Sunlyte 12-5000X.

How do I check the charge they are holding (or not). The little Gunson tester checks the lead acid battery OK but reads very low on the solar charged batteries despite the fact that all lights, instruments, autohelm etc are working fine - lights are bright.

Info gratefully received preferably in basic terms - not highly technical.

Bob

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[Alex_Blackwood]

I would suggest that the only way of measuring the battery state is by VOLTAGE READING, 14.2 - 14.4 volts.
I have had a look around the web as I am not familiar with photovotic applications and have come up with the following: e-marine.com/products/batteries/agm.html
Also: advanced power products.com Both deal with Photovoltic batteries. Another site to look at for genereral interest in marine electrics, with a chapter on marine batteries in general is: myweb.tiscali.co.uk/montecarlo/marine-electrical/
Good Luck, stick a post up if the above is any good.
Alex.

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[bob_tyler]

The odd thing is that I don't think that they are lead/acid but a "patented MFX alloy".

Wouldn't that affect a voltage reading?

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[pvb]

They are lead acid...

Sunlyte batteries are lead acid, Bob. They are sealed, maintenance-free batteries which incorporate little pressure valves to minimise loss of electrolyte (these are also called VRLA batteries - "valve regulated lead acid"). The electrolyte is held in glass mat separators, so the batteries can be used horizontally or vertically (this is called AGM - "absorbed glass mat"), and this also helps to minimise electrolyte lossthrough gassing. The plates are lead alloy; positive plates are "proprietary MFX alloy" - whatever that is - and negative plates are lead-calcium alloy. Sealed batteries usually use lead-calcium plates as this reduces charge current when fully charged and thus minimises electrolyte loss.

If everything is working fine, I'd be tempted not to worry about the batteries. If you really want to measure their voltage accurately, you need to remove the input from the solar panels and leave the batteries to stand for a couple of hours before measuring the voltage with a digital voltmeter. If you want to see exactly what's happening, invest in a Link 10 battery meter, which will show you how much energy you've used (in amp-hours) and how much the solar panels have recharged the batteries.

I guess the big question will be how well the solar panels will cope with your energy demands when using the boat in the duller months of our spring & autumn.

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[William_H]

Photovoltaic (solar cells) are really good where there is plenty of sun. I have a small 2 watt panel that keeps a small batery charged for radio night sailing and gps. No motor on the boat usually.
If I had an engine with charger then that would be my main charging source. You can get lots of current with the engine running to charge all batteries in a fairly short time. I would suggest you connect both batteries together to provide a charge from the solar panel while you are away. This should overcome natural discharge and give you happy starting. I would also suggest a switch to connect your services batery to the engine battery when running the engine to ensure you have lotts of charge. Having said that of course if with your present arrangement the engine starts and the lights radio etc work when you want them to, thats all that matters.
Battery condition is best checked by accurate voltmeter. 12 with no charging is good. 11v is sad. 13 to 14 means it is being charged. You may however do better with an amp meter after disconnecting the panels make the connection through the ampmeter. I would guess at a figure less than 1 amp depending on the size. ( mine gives about 60 mliamps or .06 amp but it is tiny.
Incidently I have had dissapointing experience with solar panels they seem to die after 2 or 3 years from corrosion. My current one sits on the boom cover and is taken in before sailing. I am now on about number 5 panel so keep an eye on yours for moisure ingress aroand the edges. good luck will PS if you have small SLA battery it may not appreciate a lot of amps from the engine generator. You could fit a .5 ohm rsistor about 5 watt to limit the current . Get this from a tv serviceman or electrician.

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[bob_tyler]

Re: They are lead acid...

Many thanks to both the above for their mainly non-technical answers which have slightly improved my understanding.

I don't know the power (if that's the right word) of the solar cells that do the charging. They are on the cabin top. If I posted the area of cells on this forum would that help.

Secondly, if I switched the generator (Dynastart) from my engine, after it has charged the engine battery, to charge the photovoltaics (2 x 100ah in parallel) is their a risk of overcharging them and causing damage? Could this damage the solar cells to which the batteries are permanently attached?

Again, many thanks to both respondents above.

Bob

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[Mike2822425]

Re: They are lead acid...

Dynastart!!! Now thats a whole new kettle of fish! What engine do you have? I love Dyna. but she has been untrue to many. Come clean and tell us the name of your beloved charger!

Mike.

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[bob_tyler]

Re: They are lead acid...

Vire 7. Crossed fingers and legs, it starts immediately whether hot or cold.

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[Alex_Blackwood]

Bob, Sorry for a complete load of "Round Objects" in my initial reply. You will of course be completely unable to accesss any of these sites I gave you. I can get the montecarlo/electrics one as I have it in my web favourites. However using the search engine and I cannot even find any of them again! My humble apologies.
Try putting Sunlyte into your search engine, you should be able to come up with some info.
I have found out that that the charging rate for what I think are your batteries is 2.25 - 2.35 volts/cell. (13.5 - 14.1 volts from the charger). The maximum charging current is 15amps. (The current will fall as the battery charges so you would only expect the max. with a flat battery).
If your Dynastart has an output within these limits you can happily charge from the engine.
I am not sure what effect it would have on your solar cells. In theory the cells will be seeing a back EMF of around these voltages from the battery in any case. The problem could arise if you have higher voltage spikes or if you had the cells connected to the Dynastart when starting the engine. Difficult without seeing the set up. Why don't you contact ADVERC and ask advice. They are quite good and although any advice will of course involve their kit, you should at least have the definative answer.
Once again sorry about first reply.

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[bob_tyler]

Re: They are lead acid...

Where can one get a Link 10 meter and roughly how much?

Have searched the net without success.

Bob

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[pvb]

Link 10...

Link 10 is also marketed as the "E-Meter", identical product. It's by far the smartest battery monitor around, but it's not cheap. Any good chandler ought to be able to get one for you, try for a target price around £250. Or try a specialist online supplier such as <A target="_blank" HREF=http://www.power-store.com>Power-Store</A>. Probably the cheapest way would be to order from West Marine, who list it at $230.

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[tome]

Re: Link 10...

You may want to consider the Link 20 which monitors two battery banks, it's not a lot more expensive.

Merlin launched the Link 20 and 1000 intelligent battery monitors to complement the existing 10 and 2000 models. The Link 20 has the same features as the Link 10, including volt, amp and amp-hour display, battery condition LEDs, charge remaining and low-level alarm, but monitors two battery banks simultaneously. The Link 1000 has the same functions, but with inverter controls.

Prices: Link 20, £299; Link 1000, £249; Powerline isolators from £35

Enquiries: Merlin Equipment, Unit 1, Hithercroft Court, Lupton Road, Wallingford, Oxon OX10 9BT, UK. Tel: +44 (0)1491 824333; Fax: +44 (0)1491 824466


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[pvb]

Re: Link 10...

Bit of confusion there. The Link 1000 is the same as the Link 10 (ie single battery bank) but with inverter/charger control functions (providing you have a Freedom inverter/charger). The Link 2000 is like the Link 20 (ie monitors 2 battery banks) but with inverter/charger control functions (again, only for Freedom products).

Personally, for most boats, I don't think it's necessary to monitor twin battery banks, because the engine start battery is almost always fully charged. The important thing is to make sure the domestic battery bank is correctly charged.

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[tome]

Re: Link 10...

Sorry about confusion, it was lifted straight from the ybw review.

I'm thinking of adding a second domestic battery bank so fitted the Link 20, meanwhile I use it to monitor engine and domestic. I agree with with what you say, but it is useful to check charge rates and also see that there's no drain from the engine battery.

One other advantage of the Link (whether 10 or 20) is that you can see that your nav bulbs are working when you switch them on by looking at the change in current draw.

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[pvb]

Re: Link 10...

Good thought about checking nav lights!

A second domestic bank isn't a good idea - much more efficient just to add batteries to your existing bank. The bigger the overall amp-hour rating of the bank, the easier it is to recharge and the longer the batteries will last.

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[tome]

Re: Link 10...

There are some reasons for splitting your domestic batteries into 2 banks;

1 Redundancy and fault isolation (eg short cell in a battery can drag down non-isolated batteries)
2 Critical circuit isolation and switchover (VHF, bilge pump, split lighting circuit)
3 Power management (ability to run a bank down below 50% in an emergency, plus charge cycle management)
4 Disaster recovery (ability to shut down one bank whilst working on the other without loss of services)
5 etc

It's really down to having all your eggs in one basket, and a split domestic supply will last as long as a consolidated single bank. If you have voltage sensed charging (Adverc, Sterling, decent 4 stage mains) you can easily split the charge via diodes.

Regards
Tom


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[pvb]

Hmmm...

Lots of reasons there, Tom. But your first, and probably the most valid reason, also applies to split banks unless you only have one battery in each bank. I'm a firm believer in keeping boat systems as simple as possible, because I've seen the chaos which can occur when unfamiliar crew members throw the wrong switch. For that reason, I just have a starter battery circuit, with a simple on/off switch, and a domestic battery circuit, with another simple on/off switch.

You'll know, of course, that a split domestic supply will only last as long as a consolidated single bank provided both banks are parallelled. Otherwise, Peukert's Exponent comes into play, and the battery capacity effectively reduces.

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[tome]

Re: Hmmm...

No black and white here, so in the end it's a matter of preference. I could say that my view is based on professional experience, but this would belittle your perfectly valid alternative reasoning. As is so often the case, there are two ways of looking at this.

Peukerts exponent is merely a way of estimating battery capacity based on current draw. Standard specifications define capacity in terms of a 20 hour depletion, and Peukert merely seeks to analyse the effects of variation. It's irrelevant in this discussion IMHO.

Fair winds
Tom

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[pvb]

Smoke and mirrors...

The old "professional experience" argument does take some beating, I'd agree.

As far as M Peukert is concerned, I reckon his findings are relevant. If you split a given battery bank into two parts, and then discharge each part separately, you'll reduce the overall effective capacity by about 16%. I don't think that's irrelevant for most cruising yachts.

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[tome]

Re: Smoke and mirrors...

Agree, should have said irrelevant provided the bank capacity is matched to current demand (which it should be by design).

Also, your point about simplicity is valid so in the end it's down to preference.

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