hackableFM
New Member
I'm looking for idea's if you can help. I have recently bought a caravan and need to make a 12V Charger/P.S.U to run the low voltage appliances.
My problem is that I can build a charger to charge my leisure batteries easy enough but I also want the same transformer & rectifier to run all 12v appliances at the same time. I have thought about this for days and looked at all sorts of circuits on the net for ideas but I've filled my head with so many idea's now that I can't figure out what is my best move.
I have 2x 12volt 85Ah lead acid batteries wired in parallel giving 170Ah. I expect to pull approx 10 - 15 Amps from the P.S.U. running the radio, fridge & lights etc. I had considered simply making a constant current 13.8volt P.S.U. and connecting that directly accross the batteries and running the appliances direct from the batteries.
Will doing the above risk over charging the batteries? As I have read, most lead acid chargers charge in stages and reduce the charge voltage as the battery becomes full, Bearing in mind that the P.S.U. will be connected for long periods of time and obviously will not be disconnected when the battery reaches the 'Full charge' state.
I am currently building a control unit based around a 16F877 microcontroller which will (Using an LCD display) control water heater, Radio power, light power etc etc etc. It would be nice if I could incorporate this into an already designed PIC controlled charger circuit of some sort.
Ideally I would like this thing to be 'intelligent' so as not to overcook my batteries but at the same time it must be able to supply the relevant voltage & current to run the other electrical appliances. If I end up making the constant current P.S.U. I plan to regulate it using a simple LM317 regulator or similar with 4 or more bypass transistors to boost the current to somewhere near 20A. I have already made up the start of a P.S.U. using a 12v 20A transformer, full wave rectifier and 39,000uF capacitor. This P.S.U. gives me 16.5 volts with no load, and approx 15.5volts with a load of approx 30W. If I were to use 6 X TIP31A transistors as 'bypass' transistors (because I have a dozen of them sitting spare here) what size/value current limit resistors would I need for each one.
Sorry far all the questions in one post but I though I might aswell get them all (hopefully) out of the way.
Thanks for any replies...
Paul.
My problem is that I can build a charger to charge my leisure batteries easy enough but I also want the same transformer & rectifier to run all 12v appliances at the same time. I have thought about this for days and looked at all sorts of circuits on the net for ideas but I've filled my head with so many idea's now that I can't figure out what is my best move.
I have 2x 12volt 85Ah lead acid batteries wired in parallel giving 170Ah. I expect to pull approx 10 - 15 Amps from the P.S.U. running the radio, fridge & lights etc. I had considered simply making a constant current 13.8volt P.S.U. and connecting that directly accross the batteries and running the appliances direct from the batteries.
Will doing the above risk over charging the batteries? As I have read, most lead acid chargers charge in stages and reduce the charge voltage as the battery becomes full, Bearing in mind that the P.S.U. will be connected for long periods of time and obviously will not be disconnected when the battery reaches the 'Full charge' state.
I am currently building a control unit based around a 16F877 microcontroller which will (Using an LCD display) control water heater, Radio power, light power etc etc etc. It would be nice if I could incorporate this into an already designed PIC controlled charger circuit of some sort.
Ideally I would like this thing to be 'intelligent' so as not to overcook my batteries but at the same time it must be able to supply the relevant voltage & current to run the other electrical appliances. If I end up making the constant current P.S.U. I plan to regulate it using a simple LM317 regulator or similar with 4 or more bypass transistors to boost the current to somewhere near 20A. I have already made up the start of a P.S.U. using a 12v 20A transformer, full wave rectifier and 39,000uF capacitor. This P.S.U. gives me 16.5 volts with no load, and approx 15.5volts with a load of approx 30W. If I were to use 6 X TIP31A transistors as 'bypass' transistors (because I have a dozen of them sitting spare here) what size/value current limit resistors would I need for each one.
Sorry far all the questions in one post but I though I might aswell get them all (hopefully) out of the way.
Thanks for any replies...
Paul.
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