Not quite. DC motors can act as both motors and generators. When the motor is
at rest it will draw it's maximum current and will also be at its max torque,
that is the amount of torque that it takes to overcome the stalled rotor and
start spinning. This is when what is known as surge current is drawn. It is
pretty much dependant upon the resistance you mentioned. After the motor spins
up to speed the current draw will go down because of what is known as "counter
emf" in the motor windings. The will be the current you are concerned with. The
best way to measure it, at least as far as I know, is to
use a clamp on ammeter over one of the supply wires to the motor. A in circuit
ammeter will work almost as well but will add some resistance to the circuit
and is also not as convenient.
Bill
Bruce Damen wrote:
> so if you conected a ohm meter on the two wires on the fan would that give
>you your resistance. or one wire to ground of the motor casing...is that the
>resistance of your fan motor?
> not an electrician , how do you figure out what amp of motor you have as
>well???
>
> Bill Bailey wrote:
>
> > 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
--
Bill Bailey
57 Chevrolet 3100
http://members.tripod.com/~oltruck/
oletrucks is devoted to Chevy and GM trucks built between 1941 and 1959
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