Fan Load
General question: When you have a simple circuit of a DC brushless
fan powered by say, a 15V power supply, and you want to know what the
current is in your circuit, do you just put an ohmmeter across the
two fan pins to find its resistance then plug into I=V/R?
Thanks
fan powered by say, a 15V power supply, and you want to know what the
current is in your circuit, do you just put an ohmmeter across the
two fan pins to find its resistance then plug into I=V/R?
Thanks
Comments
real accurate value I don't think. It may be close to what the
starting current of the motor is, but once the motor builds up speed
it turns into a generator and generates counter EMF which will cause
the current to go down. Also the current will vary with the amount of
load placed on the motor or how "hard" it is to turn the shaft. If
for instance 6 months down the road the bearings in the fan start to
go bad and start to bind up, the motor will draw a higher current to
maintain its rated speed.
Best and easiest thing you could do to see what the current draw is
would be to hook up a digital multimeter in series with the motor to
read the current. You could then somehow mechanically lock the fan
blades so they could not turn and start the motor and watch what the
current is on the DMM. DO NOT let your motor sit there stalled like
that for any length of time however. A few seconds should be enough
to get the reading and not harm the motor. The value you record
should be about the max current that your motor will ever draw.
Also your DMM is probably only able to handle current up to around 10
or so amps, so if you have a big fan motor this will probably result
in a blown fuse in your meter.
Or, if you have the spec sheet for the fan you could just read that!
--- In basicstamps@y..., pstrittmatter@y... wrote:
> General question: When you have a simple circuit of a DC brushless
> fan powered by say, a 15V power supply, and you want to know what
the
> current is in your circuit, do you just put an ohmmeter across the
> two fan pins to find its resistance then plug into I=V/R?
>
>
> Thanks
My rule of thumb for locked rotor current draw is 2 times running current .
. . . . .so about 300 ma for start-up and 140 ma for running
Richard
Original Message
From: <pstrittmatter@y...>
To: <basicstamps@yahoogroups.com>
Sent: Thursday, August 09, 2001 9:02 AM
Subject: [noparse][[/noparse]basicstamps] Re: Fan Load
> So if, on the back of my motor it says 12VDC and 140mA, is 140mA what
> it will draw at 12 volts?
>
>
> --- In basicstamps@y..., tbanez@h... wrote:
> > I'm not a motor expert but doing what you suggest won't give you a
> > real accurate value I don't think. It may be close to what the
> > starting current of the motor is, but once the motor builds up
> speed
> > it turns into a generator and generates counter EMF which will
> cause
> > the current to go down. Also the current will vary with the amount
> of
> > load placed on the motor or how "hard" it is to turn the shaft. If
> > for instance 6 months down the road the bearings in the fan start
> to
> > go bad and start to bind up, the motor will draw a higher current
> to
> > maintain its rated speed.
> >
> > Best and easiest thing you could do to see what the current draw is
> > would be to hook up a digital multimeter in series with the motor
> to
> > read the current. You could then somehow mechanically lock the fan
> > blades so they could not turn and start the motor and watch what
> the
> > current is on the DMM. DO NOT let your motor sit there stalled
> like
> > that for any length of time however. A few seconds should be
> enough
> > to get the reading and not harm the motor. The value you record
> > should be about the max current that your motor will ever draw.
> >
> > Also your DMM is probably only able to handle current up to around
> 10
> > or so amps, so if you have a big fan motor this will probably
> result
> > in a blown fuse in your meter.
> >
> > Or, if you have the spec sheet for the fan you could just read that!
> >
> >
> > --- In basicstamps@y..., pstrittmatter@y... wrote:
> > > General question: When you have a simple circuit of a DC
> brushless
> > > fan powered by say, a 15V power supply, and you want to know what
> > the
> > > current is in your circuit, do you just put an ohmmeter across
> the
> > > two fan pins to find its resistance then plug into I=V/R?
> > >
> > >
> > > Thanks
>
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
> from the same email address that you subscribed. Text in the Subject and
Body of the message will be ignored.
>
>
> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
>
>
it will draw at 12 volts?
--- In basicstamps@y..., tbanez@h... wrote:
> I'm not a motor expert but doing what you suggest won't give you a
> real accurate value I don't think. It may be close to what the
> starting current of the motor is, but once the motor builds up
speed
> it turns into a generator and generates counter EMF which will
cause
> the current to go down. Also the current will vary with the amount
of
> load placed on the motor or how "hard" it is to turn the shaft. If
> for instance 6 months down the road the bearings in the fan start
to
> go bad and start to bind up, the motor will draw a higher current
to
> maintain its rated speed.
>
> Best and easiest thing you could do to see what the current draw is
> would be to hook up a digital multimeter in series with the motor
to
> read the current. You could then somehow mechanically lock the fan
> blades so they could not turn and start the motor and watch what
the
> current is on the DMM. DO NOT let your motor sit there stalled
like
> that for any length of time however. A few seconds should be
enough
> to get the reading and not harm the motor. The value you record
> should be about the max current that your motor will ever draw.
>
> Also your DMM is probably only able to handle current up to around
10
> or so amps, so if you have a big fan motor this will probably
result
> in a blown fuse in your meter.
>
> Or, if you have the spec sheet for the fan you could just read that!
>
>
> --- In basicstamps@y..., pstrittmatter@y... wrote:
> > General question: When you have a simple circuit of a DC
brushless
> > fan powered by say, a 15V power supply, and you want to know what
> the
> > current is in your circuit, do you just put an ohmmeter across
the
> > two fan pins to find its resistance then plug into I=V/R?
> >
> >
> > Thanks
the fan motor and watch what the current is on the meter.
--- In basicstamps@y..., pstrittmatter@y... wrote:
> So if, on the back of my motor it says 12VDC and 140mA, is 140mA
what
> it will draw at 12 volts?
>
>
> --- In basicstamps@y..., tbanez@h... wrote:
> > I'm not a motor expert but doing what you suggest won't give you a
> > real accurate value I don't think. It may be close to what the
> > starting current of the motor is, but once the motor builds up
> speed
> > it turns into a generator and generates counter EMF which will
> cause
> > the current to go down. Also the current will vary with the
amount
> of
> > load placed on the motor or how "hard" it is to turn the shaft.
If
> > for instance 6 months down the road the bearings in the fan start
> to
> > go bad and start to bind up, the motor will draw a higher current
> to
> > maintain its rated speed.
> >
> > Best and easiest thing you could do to see what the current draw
is
> > would be to hook up a digital multimeter in series with the motor
> to
> > read the current. You could then somehow mechanically lock the
fan
> > blades so they could not turn and start the motor and watch what
> the
> > current is on the DMM. DO NOT let your motor sit there stalled
> like
> > that for any length of time however. A few seconds should be
> enough
> > to get the reading and not harm the motor. The value you record
> > should be about the max current that your motor will ever draw.
> >
> > Also your DMM is probably only able to handle current up to around
> 10
> > or so amps, so if you have a big fan motor this will probably
> result
> > in a blown fuse in your meter.
> >
> > Or, if you have the spec sheet for the fan you could just read
that!
> >
> >
> > --- In basicstamps@y..., pstrittmatter@y... wrote:
> > > General question: When you have a simple circuit of a DC
> brushless
> > > fan powered by say, a 15V power supply, and you want to know
what
> > the
> > > current is in your circuit, do you just put an ohmmeter across
> the
> > > two fan pins to find its resistance then plug into I=V/R?
> > >
> > >
> > > Thanks