So .... charging is now sorted - onto back-up systems

[William_H]

Re: Duh ???? It was a long time ago !! and i may have remembered wrong

Thanks Nigel. just cos I like waffling. someone might be interested.........
The output of your bridge recifier is a series of humps of voltage 100 times per sec. rising from zero to peak voltage. About 40% more than your measured RMS voltage. When you connect a capacitor across the output the voltage of the capacitor rises to the peak and the output is smoothDC. As you start to take current from the supply the transformer recifier has trouble providing the higher voltage because the voltage/current is only being supplied at that voltage on the peaks of the wave so very short time. The output falls and is called poor regulation.

This poor regulation is great for battery charging. During the bulk of the charge the voltage is pulled lower and the current is quite manageable however it has the ability to provide a smaller current at higher voltage. Enough if the size is right to fully charge a lead acid without damaging the battery. Actually it probably will damage the battery unless you disconnect in a reasonable time but there is this tendency to be beneficial.
However to run lights etc is difficult because the voltage can be a bit too high with a small load and possibly a bit low with a large load.
To resolve this problem you connect your battery up to the transformer/recifier. The capcitor in the power supply becomes redundant as the battery is a big capacitor. Providing the battery is not overcharged you have a good regulated supply and a charged battery when you have finished.

I would suggest however that you fit an ampmeter to the charger so you can judge how much current is going in to enable you to decide when the battery is getting too much. A very simple way to reduce current is to fit a large wattage lamp in series with the charger. This will tend to make the regulation of the charger even worse ie limiting the charge current but still providing the higher voltage to top up the battery.
I am actually a fan of simple battery chargers over the step charging type as you have it is just that they can not be left on too long. good luck olewill

 

[Guest]

I see your points ...

When the Radio Spares guy put the kit in my hands .... I asked about the peak and lows of the power output and he reckoned it was not severe enough to worry about. Events proved him right .... it powered the stereo excellently.

I don't want to put the transformer into any charging circuit ... I want to keep that seperate .... so it's purely a 12v power supply to domestics.

The charger I use most now is the simple car charger .. with ammeter I have to say ... built in. Normally sits about 0.5 - 1A .... but up to 4 - 5A after battery drain. I'm not worrid about its being connected all time - as it is plugged into a mains timer ... mechanical click one - don't trust electronic ones - had too many go wrong in houses !!

My auto-float charger is just that ... main charge then clicks to float. Unfortunately the Maplins Charge splitter confuses the charger and it will not work with the splitter. That is why I tried the std charger and found it successful.
This sytem now ensures that my batterys are near full charged when I arrive at boat .... no matter how long away ...

I have always thought that if 240V is available - why use batterys ? Why not keep those for when no 240v ... and that is the crux.

I'm happy enough to tinker around anyway ... even if it's against logic !! It's half the fun of boats !! Boats are completely against logic - bit like women really ..... they cost dear, you moan and groan about them - but you can't live without them !!