The battery charger circuit has errors:
1) A sealed lead-acid battery should be charged at 1/10th its current rating.
2) The 7815 voltage regulator is rated at a current of 1A but its typical max output current is 2.1A.
3) The 1N4004 diodes are rated for no more than 1A continuous current.

It is not wize to operate parts at currents higher than their max allowed current.

You don't need the voltage doubler parts of the voltage regulator circuit.

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Uncle $crooge

 

Ok, so if the charging circuit is got it wrong, would you please be able to explain what I can do to rectify the circuit so it gives an appropriate output to charge a 5aH SLA battery?

 

Hold Up!: I just re-read through the details of the charger circuit on its website (12V powered, 12 V battery charger) and happened to see this:

and this...

Also I went and emailed the creator of the circuit (who apparently has been using the circuit no problem with many types of sla over the years) and he said it definitely doesn't put out a charging current of 2.1A but something more like 0.4A

@ audioguru: I think you might be wrong... are you sure you haven't missed anything in the circuit that would mean it actually does provide the correct current?

 

The circuit has two 10 ohms in parallel that I didn't see. Their total is 5 ohms.They limit the charging current. Good.

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Uncle $crooge

 

Yay! Finally that's cleared up Anyway though, back on topic, would how I've linked everything together in M$ Paint masterpiece work as I have envisaged?

 

I have never seen a DC jack that disconnects something and replaces it with something else. They usually just disconnect a non-rechargeable battery when the adapter is plugged in.

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Uncle $crooge

 

I'm not entirely sure about this as I only learnt about it yesterday here: Automatic switch from battery to ac-dc? but as I understand you get "switching" dc sockets like this one here: Surplustronics - DC jack socket. Panel-mount. High quality which have three terminals you can connect to a 12v component and a battery. The positive terminal for the battery "breaks" when an adapter is plugged in, switching the 12v component over to ac-dc power. This is the sort of socket I have put the diagram. I went over the idea in the thread linked above and was told it was alright.

 

Your circuit will work when the switch is drawn like a switch instead of like a box.

Attached Thumbnails

 

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Uncle $crooge

 

Thanks audioguru I guess it's a bit clearer now. Big ups for your continued help.

 

I'm pretty much satisfied now ... but just in case anyone would like to continue the discussion - it would be even better if I could wire everything up without a switch involved. (I won't hold it against anybody if no one can be othered )