Re: Fan Power Source

From: jon@dakota-truck.net
Date: Thu Sep 10 2009 - 11:24:46 EDT


"bob" <bocd@optonline.net> wrote:

> Hey Guys

> I know this has been discussed before.....so at the risk of being yelled at
> :o( Is there a high amp power source I can tap into to direct wire my Black
> Magic Fan. I'd prefer not to use a relay or the thermostat if possible.
> I've been using a small 1" square relay and the bugger keeps burning out. I
> guess it's just not heavy duty enough and the amp draw is too high for it.
> If I have to use a relay....anyone have a part number and source?

   There is probably not a high amp power source you can tie into,
especially if your fan is already burning out standard automotive
relays. Reason being is although there is certainly some reserve
designed into the system, I doubt the wiring for the hypothetical high
amp source would have been designed to have two large loads on it.
You could probably get away with tapping into it for a few low draw
loads, but I think trying to wire your fan into an existing circuit is
asking for trouble. Your best bet is a direct connection to the
battery, controlled via a relay.

   Do you know the specs on your fan? Either the amperage or the
wattage should be listed on the fan itself or in the instructions, or
perhaps Black Magic's web site, etc. Either watts or amps would let
us know what size relay and wiring you need.

   Standard automotive relays are usually 30-40 amps. Assuming that
the load is running on 12 volts, that means a 30 amp relay can run a
360 watt fan, and a 40 amp a 480 watt fan. I did a quick google
search and fans seem to be all over the place. Some, like the popular
Taurus fan will apparently draw 100 amps at startup and 50 amps
continuous, which is huge. From what I saw of the Black Magic fans
though, they seem to be much lower, less than 20 amps continuous, but
I'm not sure about the initial load. Those numbers are from a quick
'net search though, nothing definitive, so may or may not be accurate.
The real numbers should be dug up just so we know exactly what we're
dealing with. Several DMLers have installed Black Magic fans, and I
don't recall them having problems with blowing relays though, or
needing anything special as far as a relay goes, so you may be dealing
with something else.

   Assuming for a second though that the numbers above are basically
accurate, if your Black Magic fan is blowing standard automotive
relays, there may be a problem somewhere - perhaps the fan is
defective. If your fan is defective, that's another reason for not
tying it into an existing system - it'll probably take that down too
and could damage whatever you've attached it to.

   If its not defective, and if it really does require a higher
current than a standard 40 amp automotive relay is capable of, there
are higher amperage relays available (local parts store or google
search), or perhaps this next suggestion is in the overkill
department, but the thought struck me that a starter solenoid might do
the trick, without costing a lot of money. Something that can handle
enough current to turn over an engine should have no trouble with a
fan. The only catch there is you'd probably want to find a
"continuous duty" solenoid. These should be available at an auto
parts store or all over the Internet. People use them as switches in
homebrew battery isolation systems, winches, etc. Camping or RV
stores may carry them also.

   

-- 
                                          -Jon-

.- Jon Steiger -- jon@dakota-truck.net or jon@jonsteiger.com -. | '96 Kolb Firefly, '96 Suzuki Intruder, Miscellaneous Mopars | `-------------------------------- http://www.jonsteiger.com --'



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