PHOTOVOLTAIC BATTERIES

[Alex_Blackwood]

Re: Smoke and mirrors...

Hasn't everyone rather got away from what Bob wanted to know. Interesting as all the discussions are he basically wants to know how to measure the state of charge and can he charge from his DYNASTART?
I still think that for simplicity a good multimeter measuring voltage will tell him the basic state of charge, even if the solar cells are connected you can see the battery voltage rise as the charge progresses.
I am not sure about the Dynastart and if it would damage the cells or if it would work with a battery management system. I think most of these are designed for use with alternators. I would however have thought that a simple change over switch Solar/Engine would solve the problem.
The correct rate of charge for his batteries is 2.25-2.35 volt/cell at a max of 15amps. He needs to check that: a) his present fit of Solar cells produce that voltage (current will vary with state of charge). b) that his Dynastart will not exceed the maximum voltage and current requirements.
I have already suggested he contacts ADVERC. (adverc.co.uk) as I am sure they can come up with something devinative.

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[pvb]

Sidetracked...

Isn't getting sidetracked one of the more interesting aspects of these forums? If it was all just Q&A it'd be a dull old place!

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[bob_tyler]

Re: Smoke and mirrors...

"Hasn't everyone rather got away from what Bob wanted to know."

In a way yes but I have found it a fascinating discussion although a good 80% has been technically over my old head.

There is an ammeter on the engine switch panel which shows up to about 25amps immediately after starting, dropping steadily to about 1 or 2 amps (just on the + side) after a few minutes. Could that initial output damage these rather unusual batteries?

A second, rather simpler question. If my consumption at any time is about 1 amp, does that mean I can go on (perhaps in the dark ie solar panels getting no light) for 100hrs - ie until the 200 total amp hour batteries are half discharged.

Many thanks to all who have put in a lot of effort, time and thought to enlighten me even though some of it is without success. That's my fault.

Bob

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[Alex_Blackwood]

Re: Smoke and mirrors...

I was not being critical chaps, just thought a little re-focusing might help. I agree the forum would be dull without all the discussion. My experience is in heavy electrics (440volt - 6.6Kv that sort of thing) with a little bit of electronic experience. The small boat stuff is to a certain extent still "makee learnee" to me. Everyday is a school day! even after 40 odd years. Long may it continue to be so! Every thing that is written in the forum is a source of that knowledge so keep it up.
Bob.
I would not think that the initial 25amps would do any damage if it falls off fairly quickly. The 15amp max for your batteries is, I think, quoted for a continuous charging rate. You may not get 25amps on your service batteries, if they are a larger ah capacity than the engine start battery or if the charge state is higher. The current drawn will depend on the resistance of the battery circuit. The internal resistance of the battery will increase as the charge state and battery voltage increase, drawing less current from the charging source.
You could try disconnecting the solar cells and taking the charging leads off the engine battery and connecting them to the service batteries and give the engine a run. Keeping a very close eye on the charging rate on the ammeter and also if possible measure the voltage at the battery terminals on starting and runnining the engine. If the charge current falls back below 15 amps within a minute or so and the voltage does not rise above above 14.2 -ish then you are OK. As you don't have a battery management system you would have to be careful not to overcharge the batteries, both engine and service, if you have to run the engine for long periods.
As for discharge rates your batteries may be rated at the 20hr rate ie 200ah will be fully discharged (or charged) after 20hrs at 10 amps. What you say about the half discharge after 100hrs @ 1amp is for the sake of simplicity just about right. There would be a slight discrepancy due to fall in voltage = more current. However as a rule of thumb I would go with your figures. As a matter of interest batteries were somtimes rated at the 10hr rate but I think the 20hr rate is modern practice.
I would also be interested to know what the voltage output of your solar cells are when disconnected from the batteries, you really want it to be around 13-14 volts.
I hope the above is of some use. No doubt all my mistakes (if any) will be sorted by the rest of the readers.

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[MainlySteam]

Re: Hmmm...

<<<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.>>>

Agree... but with the addition of key switched interconnection to allow engine starting with domestic battery for case of failed engine cranking battery.

John

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[mica]

Re: LINK 10

We have a Link 10 fitted and it is very good. We bought it from Merlin Equipment. around £200 a couple of years ago. I think Barden's sell them too, but I am not sure. If you want more information send me a pm.

Regards,
Mica

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