From: Patrick Jankowiak (recycler@swbell.net)
Date: Mon Jul 04 2005 - 22:45:31 PDT
I have seen this, but not often. To avoid the risk of it, use one
fan and a resistor in series with it:
the fan will say 12VDC or whatever voltage. It will also state
the current, such as 0.08A or 0.12A or whatever.
do this math:
volts(VDC) divided by current(A) equals ohms
12VDC divided by 0.08A (or whatever the fan says)
equals 150 (ohms)
volts times current equals watts.
12 times 0.08 equals 0.96 (watts)
You need a 150 ohm, 0.96 watt resistor in series with the fan (in
the red lead) to run it on 24V. I know mil vehicles are 27.5V but
it's not critical.
You can't buy a 0.96 watt resistor, so use a 1 watt one. but for
safety factor, double it to a 2-watt size so it won't burn out.
So go to the electronics store and buy a 150 onm 2 watt resistor.
If your fan is 12V at 0.12A, then the math the same way gives a
100 ohm value required at 1.44 watts, so 100 ohms at 2 watts is OK.
Resistors come in 3 watt sizes also, and 5 watt, 7 watt, etc.
PJ
There you have done it!
PJ
m35products wrote:
> I have generally found that two DC fans in series results in the following:
> One fan stalls, and passes all the current to the other, which spins at
> twice its rated speed.
>
> I found out the hard way when trying to fit a 12-volt eemergency light bar
> to a 24-volt M35/fire engine. The pairs of equivalent lamps were wired in
> series, so they worked OK. However, the motors which rotate the sealed beams
> performed as described above.
>
> apb
>
> www.M35products.com
>
> ----- Original Message -----
> From: "Chris Brunner" <cjbrunner@optonline.net>
> To: "Military Vehicles Mailing List" <mil-veh@mil-veh.org>
> Sent: Monday, July 04, 2005 12:51 PM
> Subject: Re: [MV] m38a1
>
>
>
>>Computer fans are powered by 12v DC. If one were to wire the two fans
>>in series they could successfully use them on a 24v system. If you
>>salvage fans from an old computer, clean them with compressed air being
>>sure to hold the blades stationary. Although they make a cool siren
>>noise when spinning from the air pressure it destroys them almost
>>immediately.
>>
>>Chris
>>
>>Bill Kealey wrote:
>>
>>
>>>TJ, I have no idea how electricity works ... something to do with Voo Doo
>>>is my guess. But, adding to Patricks comments ...
>>>
>>>I am probably wrong but, don't some of the personal computer cooling fans
>>>run off of low voltage DC?
>>>
>>>Maybe you could find one in the right voltage. I have had success in the
>>>past with guys at the electronics repair shops rigging up different
>
> doohickeys
>
>>>or thingamajigs to make electronic (magic stuff to me) gadgets operate
>
> with
>
>>>different voltages than I had available as a source. Inverters?
>
> Converters?
>
>>>Perverters?
>>>
>>>Perhaps you could put together a box with one end holding a filter,
>>>B&S lawn mower engine filter mounted on one end and a hose on
>>>the other should work with the fan in the middle. These fans are
>>>only a couple of inches in diameter and very thin. If enclosed under
>>>the dash or someplace else out of the way but sheltered from moisture
>>>should run a long time and don't use a lot of power. They do provide
>>>a good movement of air for cooling and are relatively silent.
>>>
>>>Perhaps "Radio Shack" or other electronics store has a better fan to
>>>suit your needs.
>>>
>>>Hope this isn't just rambling, as I do that a lot, but helpful in some
>
> way.
>
>>>Bill K.
>>>
>>>********************
>>>
>>>From: "Patrick Jankowiak" <recycler@swbell.net>
>>>
>>>
>>>I don't know much about the M38, but how about a small surplus
>>>24V DC blower or a small fan plumbed to a 1" hose going into the
>>>distributor housing? the fan could draw cooler air from somewhere
>>> convenient. All you should need is about 2 or 3 CFM across the
>>>coil, if you can draw cool air in.
>>>
>>>
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>>>
>>>
>>>
>>===Mil-Veh is a member-supported mailing list===
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>
>
>
> ===Mil-Veh is a member-supported mailing list===
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>
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