Can anyone tell me if it is possible to charge a small 12v battery (from a lambretta), using the original 6v charging sytem in my Sevens?

I use the 12v battery to run the electrics in my minature caravan and also power the GPS in the car. I can usually charge the battery up at campsites with a mains charger, it would however, be great if there was a way to charge it up using the dynamo, as we drive arund. Am I asking the impossible?

Grateful for any, polite, thoughts.

Cheers

Ruairidh

Ruairidh,
To charge a 12V battery you need a voltage greater than 12V and the standard 6V A7 charging system will never deliver this.

What you need to generate a voltage higher than 12V is a DC-DC converter. Standard DC-DC converters are available to convert 5V to 15V at power levels of 1W upwards. You would need to add some circuitry around the DC-DC converter to limit the input voltage to 5V =/-20% and to provide either a constant voltage or constant current supply to charge the 12V battery.

The GPS system will probably charge ok on a 6V A7 system without any additional circuitry - I know this to be the case for the Tom Tom series GPS's.

If you need any detailled help e-mail me with a contact number.
Dave Griffith

Hi Dave,

I'd ike to talk further on this if possible,

0141 942 8037

Many thanks

Ruairidh

Hi Ruairidh,
Yes it is possible to charge a 12volt battery from a 6 volt battery, what you need is a DC to DC convertor which is basically an electronic device which, in simple terms, creates an alternating current ( AC )from the Drirect Current ( DC ), then transforms the voltage from 6 volt to over 12 volts to allow for losses ( using a transformer a bit like we transform mains voltage to lower voltages ) and then it converts the AC current back to DC.

There is a downside to all this, there are various losses in the system in that you will be putting as much as 3 to 4 times the amps from the battery than you will get out in the higher voltage. It all comes down to the efficiency of the electronics in the convertor.

There may be other simpler ways to achieve what yiou want. You can now get high efficiency photoelectric cells which will help put 12 v charge into a battery and also there are wind generators designed for this as well. Both these items are readily available in the boating market place.

If you want to go down the route of an electronic converter I have a book 'Practical Solid State DC Supplies' which covers DC-DC converters but either you, or a friend, will need some expertise in putting together an electronic circuit. I must say some of the circuits are fairly simple including one which is a 12v, 2.5 amp DC output from a 6v 10 amp DC input; just what you are looking for !!! BUT note 2.5 Amps out - 10 Amps in !

Let me know if I can be of further help

regards

Malcolm

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Steve.