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Diode help on a cop bike

MCmechanic

Jun 24, 2010
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Hi, this should be easy but I'm skeptical and I'd like an opinion. I'm wiring up all the strobes on a new cop bike. They want one switch to turn on 4 lights in the rear and one switch to turn on only 2 of the 4 lights. Two seperate circuits with relays, easy enough, but... what type of diode can I put between the circuits to allow current to the 4 light circuit and block current from lighting all 4 when the 2 light circuit is switched on. Up to 15 volts, 10 amps max. Any thoughts????
Thanks...
 

jackorocko

Apr 4, 2010
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You can just modify this design slightly adding in your relays after the switch. Hope it helps
 

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Resqueline

Jul 31, 2009
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jacko's circuit is correct but you may want to use some beefier diodes than the 1N4148 (0.1A). The 1N400x series can stand 1A and the 1N540x is good for 3A.
The x is a number from 1 to 7 and indicates how much voltage they can stand. You can use any number there, a 1 meaning 50V.
If you really need 10A I'd suggest using one (or two) Schottky diode(s) or else a relay to increase the current capacity.
 

MCmechanic

Jun 24, 2010
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Found one at Frys

I found a rectifier diode that handles up to 5 amps and it works. Should I use 2 in parallel to make the current across the diodes lighter? It's about 3 amps across it now.
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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Jan 21, 2010
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3A may sound like it's within the rating of the diode, however if these lamps are traditional bulbs (as opposed to LEDs) then they will draw far higher current when they are switched on. Whilst diodes are typically rated for some larger surge current, this is intended for the fairly infrequent surges you get when devices are first turned on. If these lamps are flashing, then the surge current may be drawn more frequently than the diode is rated for.

Prudence would suggest that a higher rated diode would provide additional safety margin. It is probably less bother finding a suitable diode than actually measuring the duration, frequency, and maximum current of any switch-on surges that may occur.

A schottky diode has lower forward voltage drop, and may be a good idea. However if you use one, I would advise a unit with at least a 100V rating as their reverse current is far higher than for normal diodes, especially at elevated temperatures (which you *may* encounter, depending on where it''s mounted).
 
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