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RE: [oletrucks] Voltage reducer

To: "'Bill Bailey'" <billb@gamewood.net>, Samsred72@aol.com
Subject: RE: [oletrucks] Voltage reducer
From: "Hanlon, Bill" <Bill.Hanlon@COMPAQ.com>
Date: Wed, 22 Dec 1999 08:32:24 -0600
Your math is off a bit Bill.  Ohm's law says 
Current(in Amps) = Voltage / Resistance (in Ohms).

Given that this is a 12 volt system (else why have the 
dropping resistor) the maximum current would be 12 
amps, even if the resistance provided by the motor 
was zero.  Continuing on, 
Power(in Watts) = Current X Voltage giving a 
maximum power dissipation across the one Ohm 
resistor of 12 Watts.  In the real world it is 
more likely about half that.  

If Sam has access to a voltmeter he could measure 
the voltage drop across the resistor and across 
the fan motor with the fan running in "high" speed.
The drop should be 6 volts across each is the 
resistor is the proper size.  

-----Original Message-----
From: Bill Bailey [mailto:billb@gamewood.net]
Sent: Tuesday, December 21, 1999 11:58 AM
To: Samsred72@aol.com
Cc: oletrucks@autox.team.net
Subject: Re: [oletrucks] Voltage reducer


It's probably working right, hot is a very subjective term but they do get
exteremely warm.  Amp draw on my fresh air (a 12 V motor) was about 4 amps
as I recall. That's 16 watts when drawn through a 1 ohm resistor. That'll
get your attention.  Your motor is a 6 V which means it would draw more than
mine. If we use mine as a reference and assume that they all present about
the same load (somewhat of a leap of faith) then yours would draw 8 amps
(mine =12V x 4 amps for 48 watts so yours would be 6V x 8 amps for 48 watts.
That would mean the 1 ohm would dissipate about 64 watts ( 8amps x 8amps x
1ohm). If your reducer has a greater rating than that you are ok. But even
so it would be like putting your hand to a 60 watt light bulb..HOT!!
For more on this type of thing you can see my webpage which has an
electricity section that explains this in more detail.
http://members.tripod.com/~oltruck

Bill

Samsred72@aol.com wrote:

> I have a question pertaining to reducing the voltage to the heater motor.
I have a reducer in the line now that looks like a long cylindrical and
hollow ceramic tube. It states on it... Clarostat VP-50-K 1ohm. If this is
the proper reducer it seems to be working improperly. As the fan is drawing
current this reducer gets hot enough to burn you quickly. I don't think it
is heavy enough to carry the amps required by the motor. If so, can anyone
tell me the amp draw of the "fresh air heater" motor so that I can get the
proper reducer without taking off the cover... it's cold out side ya know?
>
> Sam
> '49 3100 Chevy
> oletrucks is devoted to Chevy and GM trucks built between 1941 and 1959

--
Bill Bailey
57 Chevrolet 3100
http://members.tripod.com/~oltruck/


oletrucks is devoted to Chevy and GM trucks built between 1941 and 1959
oletrucks is devoted to Chevy and GM trucks built between 1941 and 1959

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