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Old 08-29-2011, 11:45 AM   #1
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Dimmer switch on fan

I have a 1.2 amp 12 volt fan that is too effective which results in it producing enough noise and wash to push a cargo jet down the runway...I'd like to slow it down with a 12 volt 2 pole dimmer switch. I've found them for $20 but think this is a little excessive. Anyone have a source for one that is somewhat more reasonable?

Thanks...Big Wind Boyd
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Old 09-03-2011, 01:32 AM   #2
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A single pole double throw switch and an automotive resistor would do the same thing.
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Old 09-04-2011, 04:20 PM   #3
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i was thinking of a voltage regulator or some diodes in series. problem with both is going to be the heat. the regulator may need a sink.
the diodes, get 2 amp or above and connect them in series until u get the output voltage u need.

resistors will need to be abt 10 watt and will also generate heat.

read the fdw voltage drop of the diodes from the spec sheet. i usually think of silicone as having a 0.6 volt drop. found some at radio shack that had a little over 1 volt drop. u can keep putting them in series until u get the speed u want. i would think if u drop the voltage 3 volts, it will make a significant difference (just a guess).

i used this idea several years ago to supply 9 volts to a microphone from a 13.8 volt source. didn't like buying the batteries.

if u go the 3 leg voltage regulator, u may try putting a variable resistor (POT) on the ground leg to vary the voltage continuously from 5v to 12v. haven't used this idea. believe it will work...just haven't tested it.

i would use that with the switch mentioned by Boyd above. both ideas will work. there are some large wattage automotive resistors (i'm thinking u would start with 5 ohms and work from there). i'm thinking that when u cut the voltage abt 3 or 4 volts, u will see quiet a difference.
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Old 09-05-2011, 09:34 AM   #4
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the regulator would be a 5v regulator. unfortunately, the regulator idea will probably wind up costing more than the $20 by the time u buy the heat sink and package them.
diodes have a (near) constant voltage drop regardless of applied voltage.
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Old 09-10-2011, 08:41 AM   #5
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Sparky Jim

Jim, I am amazed with your extensive knowalge of electronics, if only I were so enlightened.

Relieved and cheered when I learned of a buddy that would be returning to my area via Elkhart, IN., I asked that he snoop around the RV outlets for a dimmer/rheostat that would handle 1.5 amps. Eureka! Yesterday he said he had located one and is bringing it home. Thanks again, "Sparky."
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Old 09-11-2011, 08:40 PM   #6
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i believe i missed on the wattage of the resistors. looks like i gave it far too much safety factor. if u found one that will handle 1.5 amps, sounds good to me.
glad u found what u needed.
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