need something to limit current travel to one direction ...... - Team Camaro Tech
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post #1 of 7 (permalink) Old Oct 21st, 02, 02:48 PM Thread Starter
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Location: Pocono Mts. Pennsylvania
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hooking up the electrical connections on my LT1 swap .. i have a fuse panel that powers my electric water pump, elec fuel pump, computer, etc ... this is wired to power these items when the ignition is on.

now i want to also be able to power the elec water pump from a switch inside the car. i hooked this up with a relay and power to the pump.

it works ok, but when i power the pump with the switch inside the car, the power backfeeds the fuse panel turning on the fuel pump, etc..

i need a way to keep power from feeding back to the fuse panel..

how can i accomplish this?
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post #2 of 7 (permalink) Old Oct 21st, 02, 04:00 PM
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What you are looking for is a diode. Stop by your local electronics store and describe to them what you are trying to do. They can help you select components that are properly sized for your application. Good luck.


[This message has been edited by rcatalano (edited 10-21-2002).]
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post #3 of 7 (permalink) Old Oct 21st, 02, 04:08 PM
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rcatalano is correct in that you need to install a diode to limit the reverse voltage.

I have used Radio Shack Cat. No. 276-1144 Epoxy rectifiers(diodes) for general small amperage circuits.

You'll probably need a diode with a 10 or 20 amp rating for your water pump.
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post #4 of 7 (permalink) Old Oct 21st, 02, 07:48 PM
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You could also accomplish what you want by using a relay that closes a circuit and also opens a second circuit when activated. When the relay is activated by a switch inside the car to turn on the pump the relay would also disconnect the power from the fuse box. I believe this is called a double pole, double throw relay.
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[This message has been edited by BTC (edited 10-21-2002).]
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post #5 of 7 (permalink) Old Oct 21st, 02, 07:49 PM
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A water pump is a big load for a diode. It can be done though. The diodes aren't rated for current except for surge currents. Power is what kills diodes and that power is dissapated as heat. That probably means your diode will need a heat sink if your feeding the water pump directly.

If your pump is powered from a relay then you'll be fine with a diode. If not then consider installing a relay. You won't want to mess with a diode and heat sinks and such. A relay coil draws a few milliamps of current which will be no problem for most diodes. A 1 Watt diode should be plenty large for the relay coil configuration.


PS Just caught BTC's reply. That's a good suggestion as well.

[This message has been edited by dnult (edited 10-21-2002).]
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post #6 of 7 (permalink) Old Oct 22nd, 02, 02:17 AM Thread Starter
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how can i tell if i have a double pole double throw relay?

the relays i have do not have any instructions with them.

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post #7 of 7 (permalink) Old Oct 22nd, 02, 04:28 AM
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Count the number of terminals on the bottom of the relay. Single Pole, double throw will have 5 Teminals, Relay coil power, and ground, the the Common, Normally Open (NO) and Normally closed (NC) contacts. Douple Pole Double throws will have 8 terminals as they have two sets of common, NO and NC contacts.

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