Holding on a hill was Those confounded ICE's...

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Holding on a hill was Those confounded ICE's...

Jeff Shanab
On the subject of holding on a hill and restricting the discussion to an AC motor and controller.

On a DC motor the lack of rotation is a huge problem but I am wondering if it can be managable on an AC system.
The magnetic field still rotates so it should still be seen oscillating transformer action to the windings.
The slip is now 100% so if we didn't stop the commutation and instead kept the amount per pulse small couldn't we have a 100% slip
at a certain freq with very small energy pulses? This then becomes small magnetic torques around the rotor diameter that add up to
the torque needed to hold the car. It should be equal to the energy of the slip under the same load if going a speed up a hill or
constant acceleration.

ie 5% slip at 500A at speed the slip energy is 5% of the total power and the rest goes into generating the work
with the rpm = 0 the work is zero and the slip energy remains.

If this is accurate, it is just a control thing, the motor shouldn'd really care, right?



> Yes Lee, but to be fair it is also the normal state my EV's sitting in my garage ;-)
>
>> > -----Original Message-----
>> > From: [hidden email] [mailto:[hidden email]] On Behalf Of Lee Hart
>> > Sent: Wednesday, June 23, 2010 12:32 PM
>> > To: Electric Vehicle Discussion List
>> > Subject: Re: [EVDL] Those confounded ICE's...
>> >
>> > On 6/23/2010 12:12 PM, mark at evie-systems wrote:
>>>> > >> "The complexity of one's life is directly proportional to the number of
>>>> > >> gas engines one owns. Two-strokes count double."
>> >
>>> > > What if they're not running?
>> >
>> > Isn't that their normal state? :-)
>> >
>> > --
>> > Lee A. Hart | Ring the bells that still can ring
>> > 814 8th Ave N | Forget the perfect offering
>> > Sartell MN 56377 | There is a crack in everything
>> > leeahart earthlink.net | That's how the light gets in -- Leonard Cohen
>> >
>> > _______________________________________________
>> > | REPLYING: address your message to [hidden email] only.
>> > | Multiple-address or CCed messages may be rejected.
>> > | UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
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>> > | OPTIONS: http://lists.sjsu.edu/mailman/listinfo/ev
>

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Re: Holding on a hill was Those confounded ICE's...

Stephen Chapman
I think you are forgetting that the current in the rotor is a function of
the slip.  Zero slip produces zero current in the rotor bars.  Most AC
induction motors operate fully loaded at around 3% slip and this produces a
rotor current that is manageable by design.  You are talking about a 100%
slip condition that would produce huge currents in the rotor.
Stephen Chapman

On Thu, Jun 24, 2010 at 1:05 PM, Jeff Shanab <[hidden email]> wrote:

> On the subject of holding on a hill and restricting the discussion to an AC
> motor and controller.
>
> On a DC motor the lack of rotation is a huge problem but I am wondering if
> it can be managable on an AC system.
> The magnetic field still rotates so it should still be seen oscillating
> transformer action to the windings.
> The slip is now 100% so if we didn't stop the commutation and instead kept
> the amount per pulse small couldn't we have a 100% slip
> at a certain freq with very small energy pulses? This then becomes small
> magnetic torques around the rotor diameter that add up to
> the torque needed to hold the car. It should be equal to the energy of the
> slip under the same load if going a speed up a hill or
> constant acceleration.
>
> ie 5% slip at 500A at speed the slip energy is 5% of the total power and
> the rest goes into generating the work
> with the rpm = 0 the work is zero and the slip energy remains.
>
> If this is accurate, it is just a control thing, the motor shouldn'd really
> care, right?
>
>
>
> > Yes Lee, but to be fair it is also the normal state my EV's sitting in my
> garage ;-)
> >
> >> > -----Original Message-----
> >> > From: [hidden email] [mailto:[hidden email]] On
> Behalf Of Lee Hart
> >> > Sent: Wednesday, June 23, 2010 12:32 PM
> >> > To: Electric Vehicle Discussion List
> >> > Subject: Re: [EVDL] Those confounded ICE's...
> >> >
> >> > On 6/23/2010 12:12 PM, mark at evie-systems wrote:
> >>>> > >> "The complexity of one's life is directly proportional to the
> number of
> >>>> > >> gas engines one owns. Two-strokes count double."
> >> >
> >>> > > What if they're not running?
> >> >
> >> > Isn't that their normal state? :-)
> >> >
> >> > --
> >> > Lee A. Hart                | Ring the bells that still can ring
> >> > 814 8th Ave N              | Forget the perfect offering
> >> > Sartell MN 56377   | There is a crack in everything
> >> > leeahart earthlink.net     | That's how the light gets in -- Leonard
> Cohen
> >> >
> >> > _______________________________________________
> >> > | REPLYING: address your message to [hidden email] only.
> >> > | Multiple-address or CCed messages may be rejected.
> >> > | UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
> >> > | OTHER HELP: http://evdl.org/help/
> >> > | OPTIONS: http://lists.sjsu.edu/mailman/listinfo/ev
> >
>
>
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Re: Holding on a hill was Those confounded ICE's...

Chris Zach
Stephen Chapman wrote:
> I think you are forgetting that the current in the rotor is a function of
> the slip.  Zero slip produces zero current in the rotor bars.  Most AC
> induction motors operate fully loaded at around 3% slip and this produces a
> rotor current that is manageable by design.  You are talking about a 100%
> slip condition that would produce huge currents in the rotor.
> Stephen Chapman

As someone who actually holds his 1994 Geo Prizm at the top of his 20
degree slope driveway every morning for about 20-30 seconds I can say
that it does not pull a lot of current, does not melt the motor, and
does not seem to cause problems.

50kw vector controlled AC motor+Dolphin controller, both water cooled,
temps here around 80-90 degrees in the morning. If people are interested
I'll put it at the top of a hill with DOLCOM running so I can report the
exact voltage/current.

Chris

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Re: Holding on a hill was Those confounded ICE's...

Stephen Chapman
Well there you go, reality trumps theory every time.  I was forgetting the
modulation of the rotating field frequency.  Your actual slip at hold is
probably pretty low.  I have to get away from fixed frequency thinking....

On Thu, Jun 24, 2010 at 1:39 PM, Christopher Zach <[hidden email]>wrote:

> Stephen Chapman wrote:
> > I think you are forgetting that the current in the rotor is a function of
> > the slip.  Zero slip produces zero current in the rotor bars.  Most AC
> > induction motors operate fully loaded at around 3% slip and this produces
> a
> > rotor current that is manageable by design.  You are talking about a 100%
> > slip condition that would produce huge currents in the rotor.
> > Stephen Chapman
>
> As someone who actually holds his 1994 Geo Prizm at the top of his 20
> degree slope driveway every morning for about 20-30 seconds I can say
> that it does not pull a lot of current, does not melt the motor, and
> does not seem to cause problems.
>
> 50kw vector controlled AC motor+Dolphin controller, both water cooled,
> temps here around 80-90 degrees in the morning. If people are interested
> I'll put it at the top of a hill with DOLCOM running so I can report the
> exact voltage/current.
>
> Chris
>
> _______________________________________________
> | REPLYING: address your message to [hidden email] only.
> | Multiple-address or CCed messages may be rejected.
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Re: Holding on a hill was Those confounded ICE's...

Jeff Shanab
In reply to this post by Jeff Shanab
No, that is exactly what I was talking about. I think we are in agreement and I was jsut poor at expressing it.
100% of the energy is going into slip rpm.

normally at 3% slip (lets say 60 cycles just to make things easy.) The magnetic filed rotates at 3600rpm.
A 4 pole motor has 2 pole-pairs and sees 1800rpm magnetic. 1800 /1.03 is 1748 rpm. 1750 is a normal rpm for class B
1738 is normal for class D air compressors and such)

so motor rpm is 1750, magnetic rpm is 1800 and slip rpm is 50.

Slip is managed and variable in a AC drive situation.

So isn't an AC motor operating at pull-out torque at zero rpm the same heat load as at stall if no excess energy is being put in, ie
the controller limits to just the slip power for a zero rpm situation.


Of course the hill hold situation is a bit silly. There are many ways to handle this. "hill holder clutch" brakes. etc.

Our hoists use to have a brake built in. When rpm hit zero it engaged and when power was applied, it disengaged.
I wonder if something like that would work here. If rpm goes negative while in fwd, brake is applied. else if powered, brake is
released.


> I think you are forgetting that the current in the rotor is a function of
> the slip.  Zero slip produces zero current in the rotor bars.  Most AC
> induction motors operate fully loaded at around 3% slip and this produces a
> rotor current that is manageable by design.  You are talking about a 100%
> slip condition that would produce huge currents in the rotor.
> Stephen Chapman
>
> On Thu, Jun 24, 2010 at 1:05 PM, Jeff Shanab <[hidden email]> wrote:
>
>> > On the subject of holding on a hill and restricting the discussion to an AC
>> > motor and controller.
>> >
>> > On a DC motor the lack of rotation is a huge problem but I am wondering if
>> > it can be managable on an AC system.
>> > The magnetic field still rotates so it should still be seen oscillating
>> > transformer action to the windings.
>> > The slip is now 100% so if we didn't stop the commutation and instead kept
>> > the amount per pulse small couldn't we have a 100% slip
>> > at a certain freq with very small energy pulses? This then becomes small
>> > magnetic torques around the rotor diameter that add up to
>> > the torque needed to hold the car. It should be equal to the energy of the
>> > slip under the same load if going a speed up a hill or
>> > constant acceleration.
>> >
>> > ie 5% slip at 500A at speed the slip energy is 5% of the total power and
>> > the rest goes into generating the work
>> > with the rpm = 0 the work is zero and the slip energy remains.
>> >
>> > If this is accurate, it is just a control thing, the motor shouldn'd really
>> > care, right?
>> >
>> >
>> >
>>> > > Yes Lee, but to be fair it is also the normal state my EV's sitting in my
>> > garage ;-)
>>> > >
>>>>> > >> > -----Original Message-----
>>>>> > >> > From: [hidden email] [mailto:[hidden email]] On
>> > Behalf Of Lee Hart
>>>>> > >> > Sent: Wednesday, June 23, 2010 12:32 PM
>>>>> > >> > To: Electric Vehicle Discussion List
>>>>> > >> > Subject: Re: [EVDL] Those confounded ICE's...
>>>>> > >> >
>>>>> > >> > On 6/23/2010 12:12 PM, mark at evie-systems wrote:
>>>>>>>>> > >>>> > >> "The complexity of one's life is directly proportional to the
>> > number of
>>>>>>>>> > >>>> > >> gas engines one owns. Two-strokes count double."
>>>>> > >> >
>>>>>>> > >>> > > What if they're not running?
>>>>> > >> >
>>>>> > >> > Isn't that their normal state? :-)
>>>>> > >> >
>>>>> > >> > --
>>>>> > >> > Lee A. Hart                | Ring the bells that still can ring
>>>>> > >> > 814 8th Ave N              | Forget the perfect offering
>>>>> > >> > Sartell MN 56377   | There is a crack in everything
>>>>> > >> > leeahart earthlink.net     | That's how the light gets in -- Leonard
>> > Cohen
>>>>> > >> >
>>>>> > >> > _______________________________________________
>>>>> > >> > | REPLYING: address your message to [hidden email] only.
>>>>> > >> > | Multiple-address or CCed messages may be rejected.
>>>>> > >> > | UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
>>>>> > >> > | OTHER HELP: http://evdl.org/help/
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>>> > >
>> >
>> >
>> > _______________________________________________
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>> >
>> >
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Re: Holding on a hill was Those confounded ICE's...

Lee Hart
In reply to this post by Chris Zach
Christopher Zach wrote:
> As someone who actually holds his 1994 Geo Prizm at the top of his 20
> degree slope driveway every morning for about 20-30 seconds I can say
> that it does not pull a lot of current, does not melt the motor, and
> does not seem to cause problems.

The battery current is low, because the controller is stepping down the
pack voltage perhaps 100:1 (300vdc at the pack, 3vac at the motor). But
it is also stepping the motor current *up* by 100:1 (3a from the pack,
300a to the motor).

The motor stator windings are copper, and liquid cooled. They can
withstand this current for a modest amount of time.

The rotor windings are aluminum, and have no cooling (just the small fan
fins on the end, and they aren't moving at stall). Thus, it's the
squirrel-cage rotor windings that are likely to fail first.

And, you probably don't have a temperature sensor on the rotor.

Thus, I would strongly suggest not doing this on a routine basis.

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

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Re: Holding on a hill was Those confounded ICE's...

Chris Zach
Lee Hart wrote:
> The battery current is low, because the controller is stepping down the
> pack voltage perhaps 100:1 (300vdc at the pack, 3vac at the motor). But
> it is also stepping the motor current *up* by 100:1 (3a from the pack,
> 300a to the motor).

Hm. That brings up another question then; if the controller is gating
300a to the motor then what's going on with the IGBTs? Since they have a
pretty high voltage drop across them (5 volts per side, with two needed
to make a phase signal) we're looking at a 300*5=1,500 watt drop per
IGBT half. So over 66% of the battery current is being cooked off in the
IGBTs (which can take the heat with the thermal sink and water right
under them but wow!). Might explain why they use 400+a IGBTs when the
pack limiting fuse is 250a.

So if we were to posit that the controller+motor is using 10a @300v from
the pack to hold the car then 66% of that would be heat lost in the
controller, 40% in the motor (since there is no motion I would assume
that everything has to be going into heat, correct?). So out of 3,000
watts of potential power, we have 2,000 going into the controller, 1,000
going into the motor.

> The motor stator windings are copper, and liquid cooled. They can
> withstand this current for a modest amount of time.

True. Question: On an AC motor is the heat generated from loss
distributed equally between the stator and the rotor? Or is most of the
heat generated in the stator?

> The rotor windings are aluminum, and have no cooling (just the small fan
> fins on the end, and they aren't moving at stall). Thus, it's the
> squirrel-cage rotor windings that are likely to fail first.
>
> And, you probably don't have a temperature sensor on the rotor.

True, the temp sensors on the motor are in the water loop, and the end
bell of the motor by the shaft. Probably not quick enough to catch a
rotor melt down. But how much heat for how long would be needed to melt
an Al armature on a typical 50kw motor?

> Thus, I would strongly suggest not doing this on a routine basis.

Ok. I don't think though that it would be as bad as stalling the
Elec-trak motor (where all current would be going through 1 set of
armature brushes and nothing really in the field) Not sure if anyone has
reported a blown Dolphin motor; the only motor that I ever heard failing
was due to someone ripping out the front cables due to an error.

Chris

Chris

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Re: Holding on a hill was Those confounded ICE's...

Stephen Chapman
In reply to this post by Lee Hart
Interesting discussion...  In a load holding application, the applied
frequency and current would both be low.  This is not like stalling an AC
motor across a 60Hz line because of the variable frequency drive in use.  AC
servomotors even have a continuous stall rating.
Stephen Chapman

On Thu, Jun 24, 2010 at 2:43 PM, Lee Hart <[hidden email]> wrote:

> Christopher Zach wrote:
> > As someone who actually holds his 1994 Geo Prizm at the top of his 20
> > degree slope driveway every morning for about 20-30 seconds I can say
> > that it does not pull a lot of current, does not melt the motor, and
> > does not seem to cause problems.
>
> The battery current is low, because the controller is stepping down the
> pack voltage perhaps 100:1 (300vdc at the pack, 3vac at the motor). But
> it is also stepping the motor current *up* by 100:1 (3a from the pack,
> 300a to the motor).
>
> The motor stator windings are copper, and liquid cooled. They can
> withstand this current for a modest amount of time.
>
> The rotor windings are aluminum, and have no cooling (just the small fan
> fins on the end, and they aren't moving at stall). Thus, it's the
> squirrel-cage rotor windings that are likely to fail first.
>
> And, you probably don't have a temperature sensor on the rotor.
>
> Thus, I would strongly suggest not doing this on a routine basis.
>
> --
> Lee A. Hart             | Ring the bells that still can ring
> 814 8th Ave N           | Forget the perfect offering
> Sartell MN 56377        | There is a crack in everything
> leeahart earthlink.net  | That's how the light gets in -- Leonard Cohen
>
> _______________________________________________
> | REPLYING: address your message to [hidden email] only.
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Re: Holding on a hill was Those confounded ICE's...

Cor van de Water
In reply to this post by Jeff Shanab
I have actually done this a little different,
after driving home and seeing that some batteries
were starting to sag, I wanted a little load on
the pack to drop it a bit further to spot the
weak batteries.
So, I applied full parking brake, set the gear
selector in Drive and applied full throttle.
The AC motor will load up the rear axle and then
stall, you could hear the field slipping and
rotating in the motor, but even after several
minutes there was no sign of anything overheating,
no weird smells or change in operation.
Just the pack voltage slowly dropping and some
batteries showing weak cells....
This was also a US Electricar with the same motor
but mounted in an S10. Also water-cooled motor and
controller and max motor current 250A.
This controller was capable of 750V though the pack
was only 312V.

Cor van de Water
Director HW & Systems Architecture Group
Proxim Wireless Corporation http://www.proxim.com
Email: [hidden email]    Private: http://www.cvandewater.com
Skype: cor_van_de_water     IM: [hidden email]
Tel: +1 408 383 7626        VoIP: +31 20 3987567 FWD# 25925
Tel: +91 (040)23117400 x203 XoIP: +31877841130

-----Original Message-----
From: [hidden email] [mailto:[hidden email]] On
Behalf Of Christopher Zach
Sent: Friday, June 25, 2010 12:46 AM
To: Electric Vehicle Discussion List
Subject: Re: [EVDL] Holding on a hill was Those confounded ICE's...

Lee Hart wrote:
> The battery current is low, because the controller is stepping down
> the pack voltage perhaps 100:1 (300vdc at the pack, 3vac at the
> motor). But it is also stepping the motor current *up* by 100:1 (3a
> from the pack, 300a to the motor).

Hm. That brings up another question then; if the controller is gating
300a to the motor then what's going on with the IGBTs? Since they have a
pretty high voltage drop across them (5 volts per side, with two needed
to make a phase signal) we're looking at a 300*5=1,500 watt drop per
IGBT half. So over 66% of the battery current is being cooked off in the
IGBTs (which can take the heat with the thermal sink and water right
under them but wow!). Might explain why they use 400+a IGBTs when the
pack limiting fuse is 250a.

So if we were to posit that the controller+motor is using 10a @300v from
the pack to hold the car then 66% of that would be heat lost in the
controller, 40% in the motor (since there is no motion I would assume
that everything has to be going into heat, correct?). So out of 3,000
watts of potential power, we have 2,000 going into the controller, 1,000
going into the motor.

> The motor stator windings are copper, and liquid cooled. They can
> withstand this current for a modest amount of time.

True. Question: On an AC motor is the heat generated from loss
distributed equally between the stator and the rotor? Or is most of the
heat generated in the stator?

> The rotor windings are aluminum, and have no cooling (just the small
> fan fins on the end, and they aren't moving at stall). Thus, it's the
> squirrel-cage rotor windings that are likely to fail first.
>
> And, you probably don't have a temperature sensor on the rotor.

True, the temp sensors on the motor are in the water loop, and the end
bell of the motor by the shaft. Probably not quick enough to catch a
rotor melt down. But how much heat for how long would be needed to melt
an Al armature on a typical 50kw motor?

> Thus, I would strongly suggest not doing this on a routine basis.

Ok. I don't think though that it would be as bad as stalling the
Elec-trak motor (where all current would be going through 1 set of
armature brushes and nothing really in the field) Not sure if anyone has
reported a blown Dolphin motor; the only motor that I ever heard failing
was due to someone ripping out the front cables due to an error.

Chris

Chris

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Re: Holding on a hill was Those confounded ICE's...

Lee Hart
In reply to this post by Chris Zach
Christopher Zach wrote:
> if the controller is gating
> 300a to the motor then what's going on with the IGBTs? Since they have a
> pretty high voltage drop across them (5 volts per side, with two needed
> to make a phase signal) we're looking at a 300*5=1,500 watt drop per
> IGBT half. So over 66% of the battery current is being cooked off in the
> IGBTs (which can take the heat with the thermal sink and water right
> under them but wow!). Might explain why they use 400+a IGBTs when the
> pack limiting fuse is 250a.

When a controller is stepping the voltage way down (and current way up)
like this, the switch on-time is short and the diode on-time is long. If
this is a DC motor control, the diode generates most of the heat.
Example: IGBT = 3v x 300a x 10% on-time = 90 watts; diode = 1v x 300a x
90% on-time = 270 watts.

An AC controller normally uses transistors for both switch and diode. If
it's driving a PM motor ("brushless DC" or synchronous), it is producing
DC at stall, just like a DC motor controller. The same sort of
calculation applies. Note that at stall, one particular transistor or
diode will have a much higher power dissipation that it would have when
the motor is turning! When turning, the peak power keeps moving from
device to device, just as a rotating DC motor keeps putting different
commutator bars under the brushes, so no one bar sees the peak for long.

If the AC controller is driving an induction motor, it is still
producing AC even at stall (just a very low frequency). So the peak
power keeps moving between transistors. Over a cycle, every transistor
and diode gets the same average power, as the peak keeps moving from one
device to another during the cycle.

> So if we were to posit that the controller+motor is using 10a @300v from
> the pack to hold the car then 66% of that would be heat lost in the
> controller, 40% in the motor (since there is no motion I would assume
> that everything has to be going into heat, correct?). So out of 3,000
> watts of potential power, we have 2,000 going into the controller, 1,000
> going into the motor.

Yes, you have the right idea.

> True. Question: On an AC motor is the heat generated from loss
> distributed equally between the stator and the rotor? Or is most of the
> heat generated in the stator?

It depends on load, and the design of the motor. The designer might
choose oversized windings on either rotor or stator, to reduce losses
there under certain operating conditions.

In a servomotor that is expected to be frequently used at low RPM and
high torque, the rotor windings can be oversized, use copper instead of
aluminum, and have extra cooling deal with the extra heat.

In a motor that always runs lightly loaded at high speeds, they can
instead concentrate on improving the stator windings, because rotor
heating won't be a problem.

They can also choose the iron for the stator and rotor independently.
The stator iron has to deal with high frequencies, while the rotor iron
won't see high frequencies unless you force it to run at high slip.

> True, the temp sensors on the motor are in the water loop, and the end
> bell of the motor by the shaft. Probably not quick enough to catch a
> rotor melt down. But how much heat for how long would be needed to melt
> an Al armature on a typical 50kw motor?

I can't say for any arbitrary motor. But I do know you can melt the
aluminum out of a normal AC motor in a very short time -- well under a
minute.

>> Thus, I would strongly suggest not doing this on a routine basis.

> Ok. I don't think though that it would be as bad as stalling the
> Elec-trak motor (where all current would be going through 1 set of
> armature brushes and nothing really in the field)

In a DC motor, the brushes always carry all the current anyway; it's not
the brush that will fail at stall. But the commutator bars are (supposed
to be) moving. Each one carries full current for only the split second
that it passes under the brush. It then moves on, and has time to cool
before passing under the next brush.

At stall, one bar sits under one brush continuously. The bar can't
handle the full current continuously. It will overheat, expand, warp,
break the glue that is holding it in, etc. Later, at high RPM, the now
loosened and warped bar is thrown outwards. Now you have an out-of-round
commutator. It causes the brushes to bounce as they pass over it,
increasing arcing and wear. If the bar sticks up high enough, it can
break the brush. Or if the bar is loose enough, it gets thrown
completely free! Destroyed motor.
  Not sure if anyone has
> reported a blown Dolphin motor; the only motor that I ever heard failing
> was due to someone ripping out the front cables due to an error.

If the controller designers thought about this issue, they would program
it to prevent this problem. It won't allow enough current at stall to
melt the rotor. But this also limits the torque you can get at stall.
--
Lee A. Hart | Ring the bells that still can ring
814 8th Ave N | Forget the perfect offering
Sartell MN 56377 | There is a crack in everything
leeahart earthlink.net | That's how the light gets in -- Leonard Cohen

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Re: Holding on a hill was Those confounded ICE's...

Chris Zach
Lee Hart wrote:
> If the controller designers thought about this issue, they would program
> it to prevent this problem. It won't allow enough current at stall to
> melt the rotor. But this also limits the torque you can get at stall.

This might explain it: The Dolphin controller is a vector controller
with a motor speed sensor on the shaft. Therefore it knows when the
motor is turning, and when it's not. You can limit the torque at stall,
then as the motor starts turning switch to max torque then max speed as
your motor speeds up.

Might explain why it's kind of pokey off the line but once it gets
moving it moves..

I guess you could program this into a zilla type DC controller with a
simple speed sensor on the motor: If motor speed=0, throttle pressed,
and time unit goes by then stop applying power to the motor as the user
is "holding it"

Chris

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