# Police Lightbar Project

Discussion in 'Electronic Basics' started by [email protected], Jun 29, 2005.

1. ### Guest

My friend acquired a police lightbar from an old police cruiser, and we
thought it might be fun to use it with our band on stage. I haven't had
a chance to look at it closely yet to inspect the ratings and such, but
I'd like to be able to convert it so instead of running of a car's 12V
battery that it be plugged in to run on 120V AC. I believe this thing
probably draws 30 to 40 amps from the car battery.

Can anybody tell me how I would go about with this conversion? The
light bar has three stages (spots, intersection lights, main spinning
lights). I'm creating a stompbox that we can use to turn off/on each
stage. I know how to do this. I just don't know how to do the 12V DC
conversion to 120V AC.

I hope I'm correct in assuming that I can decrease the amperage
significantly by increasing the voltage (P=I*V) or else it becomes
unusable in an outlet served by a 15A breaker.

Any suggestions on how to do this conversion? It seems that it should
be pretty easy. I just don't know the steps involved.

Jason

2. ### Tom BiasiGuest

Hi Jason,

Your easiest solution would be to power it from a 12 Volt supply. Get the
max. current specs at 12 V. and get a power supply that can handle it.
Converting all the circuits to 120 V internally is probably not worth the
trouble.- IMHO.
Regards,
Tom

3. ### CheapscateDaveGuest

I would bet a cheap 10 to 20 amp battery charger will work. The light
bar has no internal electronics so the ripple from the charger should
not be a problem.
Dave

4. ### ehsjrGuest

First, find out how much current you really need. My bet is
that it needs *WAY* less than that.

Next, the easiest conversion is a DC power supply that provides
12 volts at the current you really need. A 30 to 40 amp supply
is not cheap, so it is mandatory that you find out how much
current you really need.

It also it is possible to use 12 volts AC with a transformer
to run bulbs in the unit. The bulbs will work fine on AC or
DC - but there may be motors and blinkers in the unit that
will work on DC only. A transformer should cost less than a
DC supply.

Converting by changing the parts in the unit to 120 vac parts
brings up safety issues, but it is probably a non-starter
anyway. It would mean gutting the unit down to an empty shell,
then installing 120 vac stuff in it to replace the 12 vdc stuff
you removed. The installation of the new bulb sockets would
likely be a mechanical nightmare.

Ed