today I wired up my (real) traffic signals that sit on my layout and will buy a controller to make them work like they did on the street. Now looking to hook up a police light bar that sits between them. Any one know what to buy to make a 12 volt car battery operated light bar plug into 120 volt house wiring.
When I hooked up the bar to my transformer, the lights came on but did not turn.
Gary
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You can put a full wave bridge diode on the output of the transformer to get DC to run your light bar. You will need to put an appropriate fuse or circuit breaker in to protect the transformer from overload.
Most older light bars with motors will draw at least 20 amps when all the lights and motors are running. (You can verify this by taking a current reading with your ammeter, while the bar is hooked to a 12-volt car battery). Just take a look at the size of the wires in the harness to understand the amount of amperage needed. In fact, the total draw might even be more like 40 Amps. What is the size of the fuse that came with the control box for the light bar? I suspect that it's in the 30 to 40 range.
So, using the formula Watts = Volts X Amps, a 12 volt light bar using 20 amps will require a 240 Watt supply. Since an entire ZW is barely capable of providing that much power, now you know what's going to happen (or not happen) when you try to use a train transformer.
I would suggest looking for a D-C battery eliminator supply, or making one yourself (much more satisfying) using a substantial 12 Volt A-C transformer (landscape lighting transformers are ideal for this) and rectifying the output with a 50-Amp full wave bridge, which can be bought at Radio Shack or on-line.
I would buy one of those emergency battery start suitcase things,available from harbor freight or any auto parts. Mine plugs into the 120V wall outlet and I run my mobile sirrius receiver off it. It should power your light bar OK in 15 or 20 minute intervals. Then you can take it with you when you travel. Hope this helps Charlie
Why wouldn't you leave it plugged in for continuous service?
Here's a 300W transformer, with FREE shipping. I checked lots of auctions and this is the best deal for your application. Just add a diode bridge, and you're in business.
In fact, you can use two busses from this one, one A-C for the lamps, and a second tap, rectified for the motors. That way, you don't need such a large bridge. Just measure the current draw of the motors, and use the appropriate size. The light bar already has a harness that breaks out these loads, if it's anything like the many that I have worked on.
Seems the nameplate on your lightbar might give current requirements at 12V. But say you need 20 Amps (250 Watts) as suggested. Search eBay for "12V 20A power supply" and they run about 10 cents per Watt shipped which is a fair price for a power converter. You provide your own AC power cord so must know how to mate 3 wires to L, N and ground...or hire a "qualified electrician" as the listings suggest!
Thanks for all your help, looks like I'll be working on the light bar this weekend
Gary
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