Alt-BEAM Archive

Message #08136



To: beam@sgiblab.sgi.com
From: Guillem Barnolas guillembar@retemail.es
Date: Mon, 06 Dec 1999 21:21:58 +0100
Subject: [alt-beam] Re: What's wrong ?


Bob Shannon wrote:
>
> Mabucci makes over 90% of the worlds small motors, including some of
> the most efficient (for BEAM) small motors you will ever find.
>
> Dont trust everything you read. The most common Mabucci motors are
> very poor indeed, but their higher quality motors are excellent.
>
> The motor will draw more current at higher voltages, not less. Try them out!


Are you sure about this ??? I mean, In all specifications I've seen,
they draw more at less voltages (it also seems weird to me, but specs
are specs (or used to be ;-D)). Thanx for the info.


Greetings, Guillem.



8137 Mon, 6 Dec 1999 12:59:05 -0800 [alt-beam] Re: What's wrong ? "'beam@sgiblab.sgi.com'" Wilf Rigter When you look at spec sheets, different models of DC motors are often
available with the same ratings but with different operating voltages. In
that case the windings must be different and a motor of a given power rated
at 6V will require twice the current current of an equivalent 12V model. But
if the same 6V motor is used at 3V, it will only draw half the current
compared to operation at 6V.

wilf

> -----Original Message-----
> From: Guillem Barnolas [SMTP:guillembar@retemail.es]
> Sent: Monday, December 06, 1999 12:22 PM
> To: beam@sgiblab.sgi.com
> Subject: Re: What's wrong ?
>
> Bob Shannon wrote:
> >
> > Mabucci makes over 90% of the worlds small motors, including some of
> > the most efficient (for BEAM) small motors you will ever find.
> >
> > Dont trust everything you read. The most common Mabucci motors are
> > very poor indeed, but their higher quality motors are excellent.
> >
> > The motor will draw more current at higher voltages, not less. Try them
> out!
>
>
> Are you sure about this ??? I mean, In all specifications I've seen,
> they draw more at less voltages (it also seems weird to me, but specs
> are specs (or used to be ;-D)). Thanx for the info.
>
>
> Greetings, Guillem.



8138 Mon, 06 Dec 1999 13:55:31 PST [alt-beam] What a drag.... beam@sgiblab.sgi.com "Timothy Flytcher" > > The motor will draw more current at higher voltages, not less. Try them
>out!
>
>
> Are you sure about this ??? I mean, In all specifications I've seen,
>they draw more at less voltages (it also seems weird to me, but specs
>are specs (or used to be ;-D)).

There are a lot of variables with amperage draw ... And most of the "spec
sheets" are rated at "zero load" but there is no such thing as zero
load!!!... I spent a summer working for A&M Enterprises
rebuilding/matencance electric motors... We tested bearings by "no load"
amperage... As you apply more voltage the speed of a motor increases... This
increases internal drag and you get higher amperage draw because of the
higher speed... The drag comes from both barring and aerodynamic drag... The
only way to get a true amperage reading, for a given application, is to test
amperage under load... That is, put it in service and test run it with an
amp meter... I have seen the engineers best guess as far off as 50%... It
was always a big joke around the shop...

Timothy...

______________________________________________________



8139 Mon, 6 Dec 1999 14:55:14 -0800 (PST) [alt-beam] negative voltage beam@sgiblab.sgi.com "Travis D." What happens when one applies negative voltage to the
base of a transistor or to an inverter (or even a
buffer like on the 245's)?

Thanks in advance,
Travis
__________________________________________________
Do You Yahoo!?
Thousands of Stores. Millions of Products. All in one place.
Yahoo! Shopping: http://shopping.yahoo.com



8140 Mon, 06 Dec 1999 15:08:25 -0800 [alt-beam] Re: What's wrong ? beam@sgiblab.sgi.com Bruce Robinson Guillem Barnolas wrote:
>
> Bob Shannon wrote:
>>
>> ... The motor will draw more current at higher voltages,
>> not less. Try them out!
>
> Are you sure about this ??? I mean, In all specifications
> I've seen, they draw more at less voltages (it also seems
> weird to me, but specs are specs (or used to be ;-D)).
> Thanx for the info.

It's a complex subject, and you have to be sure you're comparing apples
& apples.

With a synchronous AC motor running under load, if you lower the
voltage, the current will rise a corresponding amount. This is because
the motor "wants" to run at a fixed speed (which is determined by the AC
frequency), and requires a certain amount of power to do so. Power =
current x voltage. So to maintain the speed (and power), lowering the
voltage forces the current to rise.

For my unloaded gearmotor, rated at 12 volts, as I increase the voltage
from 4.5 volts to 9 volts (in 1.5 volt steps), the current also
increases. This is because as the voltage increases, the speed also
increases. More power is required to drive the motor faster. The voltage
increase isn't sufficient by itself, so the current has to rise as well.

The type of motor, the nature of the load, the way you control the motor
-- all these can affect the voltage-current relationship.

Bruce



8141 Mon, 6 Dec 1999 18:07:36 -0500 [alt-beam] Motor stuff and nonsense... "BEAM" "Richard Caudle"
content-transfer-encoding: quoted-printable


---------------------------------------------------------------------------=
-----


Good day, all!

Is there a way to determine the rated voltage other than the label? I have=
several gleaned from CDROMs and not too sure of their voltage rating. I'm=
using 6VDC and they seem to be working fine. I assume that they're 12VDC =
motors. Does it even matter?

Richard Caudle
www.geocities.com/frankendaddy
Home ICQ - Frankendaddy

---------------------------------------------------------------------------=
-----

Guardians of the sacred words: Nee, Ptang, and NeeWhon! =



content-transfer-encoding: quoted-printable



>
Good day, all!
 

Is there a way to determine the =
rated =

voltage other than the label?  I have several gleaned from CDROMs and =
not =

too sure of their voltage rating.  I'm using 6VDC and they seem to be =

working fine.  I assume that they're 12VDC motors.  Does it even =

matter?

 





Guardians of the sacred words: N=
ee, =

Ptang, and NeeWhon!         =





Home