police lightbar power supply

You can build a regulated power supply from an old ATX psu. a 600+ watt psu with a single 12v rail should give you the 40 amps you need. Here are some sites with instructions to give you an idea what it would take to build: http://askville.amazon.com/correct-procedure-convert-computer-ATX-power-supply-lab/AnswerViewer.do?requestid=32107235 http://www.wikihow.com/Convert-a-Computer-ATX-Power-Supply-to-a-Lab-Power-Supply http://web2.murraystate.edu/andy.batts/ps/powersupply.htm http://www.instructables.com/id/Convert-an-ATX-Power-Supply-Into-a-Regular-DC-Powe/ If you don't have an old psu that provided enough current, you can always find them online to fit your budget. The components can be purchased from online sources like digikey.com. I have built 1 out of a 200W supply that works well for testing various electronics. Since you only need a 12V, I would just build it to supply 12V only and insulate all of the other wires and not bother terminating them.This information is provided only as a reference.

All circuits should be verified with a digital multi-meter prior to making any connections.

Be aware that a "40 amp power supply" usually is only rated for 2/3 of the rated 40 amps for continuous use. So, if you need 40 amps for 30 minutes you better be looking for a 60 amp supply. More money... I think your cheapest way out is to get a car battery and a charger. Go to a sure nuff battery supplier (not and auto parts store or a big box store) and ask for a reconditioned battery. Chargers can be bought pretty cheap. Get a low output one and use it only for charging, not at the same time as the lightbar is being used.Joe in Texas