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Discussion Starter #1
Re: What is the typical amperage draw of the field for a sepex motor?

Jeff Major wrote:
> IIRC, 37 percent increase in resistance was 120 degree
> C rise. This is what could be used on a class H
> motor.

What I use is Thot = Tcold + (K x ((Rhot - Rcold) / Rcold))

where K = 256.4 for copper
Thot = hot temperature in deg.C
Tcold = cold temperature in deg.C
Rhot = resistance at hot temperature in ohms
Rcold = resistance at cold temperature in ohms

> Also, he should have the appropriate ventilation during the test.

Yes; run whatever blower or airflow the motor would normally have had.
The easiest way to do such a test is to actually run the motor on the
bench at its normal RPM, so its internal fan (if so equipped) is working
normally. Measure the field resistance when cold (at room temperature)
before you start, and again after running the motor for a while.

> A few years ago, I came across a smaller sepex GE
> motor with a private brand nameplate, so I figured I
> was on my own to figure out how to control it. Also
> had a freebie Curtis sepex with a custom software. I
> was able to adjust field map parameters, but needed
> motor info. So I ran a no load magnetization curve
> and was able to tell when it saturated and how far
> down to field weaken it. Very helpful.

That's a good idea, too. Run the motor and keep increasing the field
strength, noting the RPM decrease it causes. The field is saturating
when 10% more field current only reduces RPM by (say) 5%.

I've often thought one could build a pretty handy motor "characterizer"
with nothing but a battery pack, on/off contactor, and free-spinning
motor. Use a computer with some simple instrumentation to measure
voltage, current and RPM. The software would switch on the motor, and
measure its power as it speeds up. The motor's own inertia forms the load.

--
Ring the bells that still can ring
Forget the perfect offering
There is a crack in everything
That's how the light gets in -- Leonard Cohen
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Lee A. Hart, 814 8th Ave N, Sartell MN 56377, leeahart_at_earthlink.net
 

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Discussion Starter #2
Re: What is the typical amperage draw of the field for a sepex motor?

Zeke Yewdall wrote:
> 155 degree C, as in 312 degrees F? That seems awfully hot for a motor
> to me. I guess it's good, but I thought you were normally supposed to
> keep them below 100C or so...

That's the internal winding temperature. The external temperature will
never get this hot (hopefully!)

--
Ring the bells that still can ring
Forget the perfect offering
There is a crack in everything
That's how the light gets in -- Leonard Cohen
--
Lee A. Hart, 814 8th Ave N, Sartell MN 56377, leeahart_at_earthlink.net
 

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Discussion Starter #3
Re: What is the typical amperage draw of the field for a sepex motor?

Zeke,

We're talking maximum temperature on the insulation.
155 deg C for class F and 180 deg C for class H, which
a lot of motors use. Yea, that's hot. When the coil
insulation is at these limit temps, the outside of the
frame may be in the neighborhood of 100 deg C.

Jeff

--- Zeke Yewdall <[email protected]> wrote:

> 155 degree C, as in 312 degrees F? That seems
> awfully hot for a motor
> to me. I guess it's good, but I thought you were
> normally supposed to
> keep them below 100C or so...
>
> Z
>
> On 7/26/07, Jeff Major <[email protected]> wrote:
> >
> > Hi Zeke,
> >
> > Class F is for 155 degree C max. Most often used
> is
> > an allowable 115 deg C rise (over a 40 deg C
> ambient).
> >
> > Jeff
> >
> >
> >
> >
--- Zeke Yewdall <[email protected]> wrote:
> >
> > > sorry.
> > >
> > > It says
> > >
> > > CL.F DUTY-1 HR 115c
> > >
> > > Z
> > >
> >
> >
> >
> >
>
____________________________________________________________________________________
> > Pinpoint customers who are looking for what you
> sell.
> > http://searchmarketing.yahoo.com/
> >
> >
>
>



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Discussion Starter #4
Re: What is the typical amperage draw of the field for a sepex motor?

Looks like maybe I didn't IIRC correctly. 47 percent
for 120 deg C rise fits the equation better. Or 0.39
percent per degree C. Thanks Lee.

Jeff


--- Lee Hart <[email protected]> wrote:

> Jeff Major wrote:
> > IIRC, 37 percent increase in resistance was 120
> degree
> > C rise. This is what could be used on a class H
> > motor.
>
> What I use is Thot = Tcold + (K x ((Rhot - Rcold) /
> Rcold))
>
> where K = 256.4 for copper
> Thot = hot temperature in deg.C
> Tcold = cold temperature in deg.C
> Rhot = resistance at hot temperature in ohms
> Rcold = resistance at cold temperature in
> ohms
>



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Discussion Starter #5
Re: What is the typical amperage draw of the field for a sepex motor?

--- Lee Hart <[email protected]> wrote:
<snip>
> I've often thought one could build a pretty handy
> motor "characterizer"
> with nothing but a battery pack, on/off contactor,
> and free-spinning
> motor. Use a computer with some simple
> instrumentation to measure
> voltage, current and RPM. The software would switch
> on the motor, and
> measure its power as it speeds up. The motor's own
> inertia forms the load.
>

Hi Lee,

This can be done, but you'd have no torque
measurement. I guess you could figure out the moment
of inertia of the rotor and back calculate it.
Anyhow, I have seen such flywheel dynos years ago.
They had a torque sensor between the motor and
flywheel. Just close the contactor and you'd get the
whole speed torque curve in a second or two. Of
course with series motors, you'd have a sensitive
speed sensor to cut it off before destruction.

Jeff



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Discussion Starter #6
Re: What is the typical amperage draw of the field for a sepex motor?

Jeff Major wrote:
> --- Lee Hart <[email protected]> wrote:
> <snip>
>> I've often thought one could build a pretty handy
>> motor "characterizer"
>> with nothing but a battery pack, on/off contactor,
>> and free-spinning
>> motor. Use a computer with some simple
>> instrumentation to measure
>> voltage, current and RPM. The software would switch
>> on the motor, and
>> measure its power as it speeds up. The motor's own
>> inertia forms the load.
>>
>
> Hi Lee,
>
> This can be done, but you'd have no torque
> measurement. I guess you could figure out the moment
> of inertia of the rotor and back calculate it.
> Anyhow, I have seen such flywheel dynos years ago.
> They had a torque sensor between the motor and
> flywheel. Just close the contactor and you'd get the
> whole speed torque curve in a second or two. Of
> course with series motors, you'd have a sensitive
> speed sensor to cut it off before destruction.

Yes, that's the idea!

I was thinking of a "portable" tester (a box with a battery, big
contactor, and the data acquisition equipment) that one could haul to a
surplus dealer and use it to check out a likely motor without having to
buy it and haul it home to test.

--
Ring the bells that still can ring
Forget the perfect offering
There is a crack in everything
That's how the light gets in -- Leonard Cohen
--
Lee A. Hart, 814 8th Ave N, Sartell MN 56377, leeahart_at_earthlink.net
 
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