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Originally Posted by patrick_g
I think I may have mentioned that TRANSFORMERS do not put out DC!
Transformers put out AC. Reversing the connections will not possibly make a difference with AC since the connections are being reversed for you by the power company many times a second!
LBROWN59, A battery charger can run a motor like for a pump even though it does not put out smooth DC. The motor integrates the irregular waveform.
If you have even a small 12 volt rechargeable battery like for a riding lawnmower or garden tractor you can hook the battery charger to that and to the pump and get by with a charger rated for around 10-12 amps. IF yoiu are using just the charger to run the pump you will want one with a higher rating, maybe 15-20 amps (which costs more.)
If you use your tractor or truck battery to run the pump (with the engine switched off) and hook up a battery charger rated for 10 amps or more to that battery while pumping fuel it will work fine and you can leave the charger on the battery for just a little longer than fuel pumping to be sure pumping fuel has not run down the battery.
This will let you buy a smaller charger (10-12 amp). I had previously assumed you had a battery charger but if not then buying one is a good idea as they can come in very handy every so often.
Buying a 12VDC power supply will typically cost more than a battery charger of similar rated output and although it would run the pump fine, or power a radio or whatever, a power supply does not make the best battery charger. The best bet is the battery charger for which you will have other uses.
Pat
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I am going to try and add an idea to Pats as usual excellent advice. I did notice when you were talking about the train transformer. I wondered then if you were going to have a problem but thought maybe the train transformer had a dc rectifier circuit in it and it actually put out dc. Now I see that my first concerns were correct. You can use that transformer and get someone that knows some electronics to build you a full wave rectifier and then have dc out. That would not be too hard to do and not super expensive you just need 4 diodes that are rated at 15 or 20 amps. Now that I have said all my techie stuff here is what I would do. I would go to walmart, or samsclub, or auto parts store etc and get one of the smaller battery jumper packs. Sams has one that not only has the battery pack but has a air compressor and emergency light. The one at sams is about 40.00 walmart has them in that price range also. You can hook the jumper cables of the battery pack to the pump and it should run it with no problem. The battery packs come with an ac charger so when you are not using it you can just leave it plugged in and it will keep it charged and ready for use. The other advantage to using a jumper pack is that if you have a dead battery on your tractor or car you can use it to jump start the vehicle since that is what they were originally designed for. Basically they are a 12 volt battery and a trickle charger so the current coming out from them should be pure dc. That is what I would do.