[EVDL List]

Lee Hart wrote
>
> ...
> To avoid having it suddenly cut all power, it could be configured like
> an RPM limiter or current limiter, which back off the power gradually
> rather than suddenly cut out completely.
>

Great idea... but how much current should I allow through the motor when it
is stalled? And how much time should I let pass between tach pulses before
activating the stall detection function in the first place? What about if
the commutator is already hot? What about different size motors - surely a
big GE 11" can take more stall current than a little 6.7 incher?!

Etc. and so on.






--
View this message in context: http://electric-vehicle-discussion-list.413529.n4.nabble.com/How-To-Burn-Up-Your-DC-Motor-tp4577309p4581224.html
Sent from the Electric Vehicle Discussion List mailing list archive at Nabble.com.

_______________________________________________
| Moratorium on drag racing discussion is in effect.
| Please take those discussions elsewhere. Thanks.
|
| REPLYING: address your message to xxx@xxx.xxx.edu only.
| Multiple-address or CCed messages may be rejected.
| UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
| OTHER HELP: http://evdl.org/help/
| CONFIGURE: http://lists.sjsu.edu/mailman/listinfo/ev

[EVDL List]

It seems like some reasonable percentage (15-25%?) of your motor
current limit would be a good stall current, or else add that as a
configurable value: "Stall current limit" next to the stall detect
enable checkbox.

The time between tach pulses probably won't be too critical - if a
brush covers 3 comm bars, one comm bar overheats in two seconds and
the motor had 37 comm bars, then even three RPMs (one rotation in 24.6
seconds) would be sufficient to prevent stall failure. But since you
can't reasonably measure three RPMs fast enough to protect the
commutator, one pulse per second would give you fast enough response
and limit "nuisance trips" to only be possible below 30 RPMs (if you
have two pulses per rotation).

I don't think you need special code to handle an already hot
commutator: you don't reduce the drive current limit for a hot
commutator either. That would fall under your examples of
over-limiting it and causing problems.

I'm not one of your customers; I'm just brainstorming what controller
behavior would be a decent compromise between reasonable effort to
implement, protecting the motor, and avoiding nuisance trips.

-Morgan LaMoore

On Mon, Apr 23, 2012 at 12:56 PM, Jeffrey Jenkins
[quote]<xxx@xxx.xxx.com> wrote:
>
> Lee Hart wrote
>>
>> ...
>> To avoid having it suddenly cut all power, it could be configured like
>> an RPM limiter or current limiter, which back off the power gradually
>> rather than suddenly cut out completely.
>>
>
> Great idea... but how much current should I allow through the motor when =
it
> is stalled? And how much time should I let pass between tach pulses before
> activating the stall detection function in the first place? What about if
> the commutator is already hot? What about different size motors - surely a
> big GE 11" can take more stall current than a little 6.7 incher?!
>
> Etc. and so on.
>
>
>
>
>
>
> --
> View this message in context: http://electric-vehicle-discussion-list.413=
529.n4.nabble.com/How-To-Burn-Up-Your-DC-Motor-tp4577309p4581224.html
> Sent from the Electric Vehicle Discussion List mailing list archive at Na=
bble.com.
>
> _______________________________________________
> | Moratorium on drag racing discussion is in effect.
> | Please take those discussions elsewhere. Thanks.
> |
> | REPLYING: address your message to xxx@xxx.xxx.edu only.
> | Multiple-address or CCed messages may be rejected.
> | UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
> | OTHER HELP: http://evdl.org/help/
> | CONFIGURE: http://lists.sjsu.edu/mailman/listinfo/ev

_______________________________________________
| Moratorium on drag racing discussion is in effect.
| Please take those discussions elsewhere. Thanks.
|
| REPLYING: address your message to xxx@xxx.xxx.edu only.
| Multiple-address or CCed messages may be rejected.
| UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
| OTHER HELP: http://evdl.org/help/
| CONFIGURE: http://lists.sjsu.edu/mailman/listinfo/ev

[EVDL List]

Peri Hartman said:
> The Leaf seems to have a bit of this problem.
> If parallel parking on a hill, and you're using the brake,
> I think it's ignoring the accelerator pedal till you take
> you [sic] foot off the brake. This results in a small
> surge causing a small bump into the vehicle in front
> (or back). Not sure of the best way to solve this,
> but something to think about.

Hi Peri,
I doubt that this is a stall detect feature, it sounds to
me like they made sure to never get the problem that Toyota
struggled to dismiss - the unintended acceleration.
This problem cannot occur if the brake overrides the
accelerator, which is what I see in your description.
This was actually already present on the Prius (you could
hit both accelerator and brake, though there was some effect,
the engine would still rev up higher at standstill, which can
be (mis-)used to fast-charge the battery pack.

When I made a short trip in a Leaf thanks to a local owner
who let me, I forgot to check if it has a hand (parking) brake
because that is the usual way to manage movements on an incline
so you do not need to move your foot between throttle and brake
(or worse - drive with 2 feet).
There was a reason that my driving instructor referred to those
two pedals as "water and fire".

Another observation - parallel parking, if performed with
enough space between two other vehicles, can be done in
one single movement, so you do not need to alternate
between acceleration and brake, unless there is limited space
and you need to make it a 2-point manouvre, then I was taught
to use the hand (or parking) brake on an incline, which should
avoid the accelerator override - though I did not test it.

Cor van de Water
Chief Scientist
Proxim Wireless Corporation http://www.proxim.com
Email: xxx@xxx.xxx Private: http://www.cvandewater.com
Skype: cor_van_de_water XoIP: +31877841130
Tel: +1 408 383 7626 Tel: +91 (040)23117400 x203

_______________________________________________
| Moratorium on drag racing discussion is in effect.
| Please take those discussions elsewhere. Thanks.
|
| REPLYING: address your message to xxx@xxx.xxx.edu only.
| Multiple-address or CCed messages may be rejected.
| UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
| OTHER HELP: http://evdl.org/help/
| CONFIGURE: http://lists.sjsu.edu/mailman/listinfo/ev

[EVDL List]

Yes, one could use the parking brake - it is strictly physical brakes. I
haven't tried it for parking and my foot is plenty fast enough on hills not
to need it.

The reason I haven't tried the parking brake for parallel parking is that it
is controlled by a servo, not by a lever. So you cannot feel when it is
engaging or disengaging. Thus, and I may be wrong, it seems it would be
hard to know how much and when to push the accelerator. I'll try it and
see.

Parking is tight in the city, so one movement parking is usually not
possible. Sometimes it takes 4 or 5 times back and forth. Don't always
have to park on a 20% grade, though.

Peri

-----Original Message-----
From: xxx@xxx.xxx.edu [mailto:xxx@xxx.xxx.edu] On Behalf
Of Cor van de Water
Sent: 23 April, 2012 12:13 PM
To: Electric Vehicle Discussion List
Subject: Re: [EVDL] How To Burn Up Your DC Motor

Peri Hartman said:
> The Leaf seems to have a bit of this problem.
> If parallel parking on a hill, and you're using the brake, I think
> it's ignoring the accelerator pedal till you take you [sic] foot off
> the brake. This results in a small surge causing a small bump into
> the vehicle in front (or back). Not sure of the best way to solve
> this, but something to think about.

Hi Peri,
I doubt that this is a stall detect feature, it sounds to me like they made
sure to never get the problem that Toyota struggled to dismiss - the
unintended acceleration.
This problem cannot occur if the brake overrides the accelerator, which is
what I see in your description.
This was actually already present on the Prius (you could hit both
accelerator and brake, though there was some effect, the engine would still
rev up higher at standstill, which can be (mis-)used to fast-charge the
battery pack.

When I made a short trip in a Leaf thanks to a local owner who let me, I
forgot to check if it has a hand (parking) brake because that is the usual
way to manage movements on an incline so you do not need to move your foot
between throttle and brake (or worse - drive with 2 feet).
There was a reason that my driving instructor referred to those two pedals
as "water and fire".

Another observation - parallel parking, if performed with enough space
between two other vehicles, can be done in one single movement, so you do
not need to alternate between acceleration and brake, unless there is
limited space and you need to make it a 2-point manouvre, then I was taught
to use the hand (or parking) brake on an incline, which should avoid the
accelerator override - though I did not test it.

Cor van de Water
Chief Scientist
Proxim Wireless Corporation http://www.proxim.com
Email: xxx@xxx.xxx Private: http://www.cvandewater.com
Skype: cor_van_de_water XoIP: +31877841130
Tel: +1 408 383 7626 Tel: +91 (040)23117400 x203

_______________________________________________
| Moratorium on drag racing discussion is in effect.
| Please take those discussions elsewhere. Thanks.
|
| REPLYING: address your message to xxx@xxx.xxx.edu only.
| Multiple-address or CCed messages may be rejected.
| UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
| OTHER HELP: http://evdl.org/help/
| CONFIGURE: http://lists.sjsu.edu/mailman/listinfo/ev



_______________________________________________
| Moratorium on drag racing discussion is in effect.
| Please take those discussions elsewhere. Thanks.
|
| REPLYING: address your message to xxx@xxx.xxx.edu only.
| Multiple-address or CCed messages may be rejected.
| UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
| OTHER HELP: http://evdl.org/help/
| CONFIGURE: http://lists.sjsu.edu/mailman/listinfo/ev

[EVDL List]

Lee Hart wrote
>
> The perfect is the enemy of the good. You'll do nothing if you try for
> perfection. Aim for good instead. :-)

I admit I'm often guilty of that. In this case, though, I'm mainly trying to
avoid instilling a *false* sense of security. I distinctly remember George
Hamstra telling me that "hill holding" was really hard on the motor, but I
only vaguely remember any numbers (this conversation took place over 4 years
ago).


Lee Hart wrote
>
> As a first try: Assume the RPM sensor produces something like 4-8 pulses
> per revolution, and your current limit is set to 1000a. When you apply
> current to the motor, if there are no RPM pulses for 1 second, start
> ramping down the current limit. Ramp it down 100a every 0.1 second, so
> at 1.9 seconds it will be down to 100a current limit.

Sounds reasonable for a WarP-9. I think it might be dangerous to extrapolate
too far afield, though. For example, a Kostov 9" motor certainly can't take
1000A for 1 second when stalled. A GE 13", however, might just be able to
take the full 3000A output of a Soliton Shiva before the comm explodes. All
I know for sure is that obtaining good data on this is *expensive*.

I appreciate the suggestion all the same. I'll give it some (unpaid) thought
and see if I can come up with a way around the various issues. That said,
adding Yet Another Warning to the Fine Manual might be in order.





--
View this message in context: http://electric-vehicle-discussion-list.413529.n4.nabble.com/How-To-Burn-Up-Your-DC-Motor-tp4577309p4581831.html
Sent from the Electric Vehicle Discussion List mailing list archive at Nabble.com.

_______________________________________________
| Moratorium on drag racing discussion is in effect.
| Please take those discussions elsewhere. Thanks.
|
| REPLYING: address your message to xxx@xxx.xxx.edu only.
| Multiple-address or CCed messages may be rejected.
| UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
| OTHER HELP: http://evdl.org/help/
| CONFIGURE: http://lists.sjsu.edu/mailman/listinfo/ev

[EVDL List]

T24gTW9uLCBBcHIgMjMsIDIwMTIgYXQgODoxMiBQTSwgQ29yIH ZhbiBkZSBXYXRlciA8Q1dhdGVy
QHByb3hpbS5jb20+IHdyb3RlOgo+IFBlcmkgSGFydG1hbiBzYW lkOgo+PiBUaGUgTGVhZiBzZWVt
cyB0byBoYXZlIGEgYml0IG9mIHRoaXMgcHJvYmxlbS4KPj4gSW YgcGFyYWxsZWwgcGFya2luZyBv
biBhIGhpbGwsIGFuZCB5b3UncmUgdXNpbmcgdGhlIGJyYWtlLA o+PiBJIHRoaW5rIGl0J3MgaWdu
b3JpbmcgdGhlIGFjY2VsZXJhdG9yIHBlZGFsIHRpbGwgeW91IH Rha2UKPj4geW91IFtzaWNdIGZv
b3Qgb2ZmIHRoZSBicmFrZS4gwqBUaGlzIHJlc3VsdHMgaW4gYS BzbWFsbAo+PiBzdXJnZSBjYXVz
aW5nIGEgc21hbGwgYnVtcCBpbnRvIHRoZSB2ZWhpY2xlIGluIG Zyb250Cj4+IChvciBiYWNrKS4g
wqBOb3Qgc3VyZSBvZiB0aGUgYmVzdCB3YXkgdG8gc29sdmUgdG hpcywKPj4gYnV0IHNvbWV0aGlu
ZyB0byB0aGluayBhYm91dC4KPgo+IEhpIFBlcmksCj4gSSBkb3 VidCB0aGF0IHRoaXMgaXMgYSBz
dGFsbCBkZXRlY3QgZmVhdHVyZSwgaXQgc291bmRzIHRvCj4gbW UgbGlrZSB0aGV5IG1hZGUgc3Vy
ZSB0byBuZXZlciBnZXQgdGhlIHByb2JsZW0gdGhhdCBUb3lvdG EKPiBzdHJ1Z2dsZWQgdG8gZGlz
bWlzcyAtIHRoZSB1bmludGVuZGVkIGFjY2VsZXJhdGlvbi4KPi BUaGlzIHByb2JsZW0gY2Fubm90
IG9jY3VyIGlmIHRoZSBicmFrZSBvdmVycmlkZXMgdGhlCj4gYW NjZWxlcmF0b3IsIHdoaWNoIGlz
IHdoYXQgSSBzZWUgaW4geW91ciBkZXNjcmlwdGlvbi4KCgpJIG Rvbid0IHJlYWQgaXQgbGlrZSB0
aGF0LgpPbiBteSBmYWN0b3J5IGJ1aWx0IEVWLCBpdCBoYXMgdG hpcyBzYW1lIGZlYXR1cmUgLSBp
dCB3b24ndCBkcml2ZSBpZgp5b3UndmUgZ290IHlvdXIgZm9vdC BvbiB0aGUgYnJha2UuICBBbmQg
dGhlcmUgaXMgYSBzbGlnaHQgZGVsYXkKYmV0d2VlbiB0YWtpbm cgeW91ciBmb290IG9mZiB0aGUg
YnJha2UgYW5kIGl0IGFsbG93aW5nIGRyaXZlLCBzbyB3aGF0Cm hhcHBlbnMgb24gYSBoaWxsIGlz
IHRoYXQgaXQgZmlyc3Qgcm9sbHMgYmFjayBhbmQgdGhlbiBzdW RkZW5seQpsdXJjaGVzIGZvcndh
cmRzLCBiZWNhdXNlIGJ5IHRoYXQgdGltZSB5b3UndmUgZ290IH lvdXIgZm9vdCB3ZWxsIGRvd24K
b24gdGhlIGFjY2VsbGVyYXRvciBiZWNhdXNlIG5vdGhpbmcgaX MgaGFwcGVuaW5nLgoKT2YgY291
cnNlLCB5b3UncmUgc3VwcG9zZWQgdG8gdXNlIHRoZSBoYW5kYn Jha2UgZm9yIHN1Y2ggbWFuZXV2
ZXJpbmcsCm9uIGFueSB2ZWhpY2xlLiAgQW5kIGNlcnRhaW5seS Bub3QgdXNlIHlvdXIgbGVmdCBm
b290IG9uIHRoZSBicmFrZQpwZWRhbCwgYXMgSSBkbyBvbiBteS BvdGhlciBFViB3aGVyZSB0aGUg
YmxvY2tpbmcgZmVhdHVyZSBpcyBkaXNhYmxlZAo6KQoKX19fX1 9fX19fX19fX19fX19fX19fX19f
X19fX19fX19fX19fX19fX19fX19fX18KfCBNb3JhdG9yaXVtIG 9uIGRyYWcgcmFjaW5nIGRpc2N1
c3Npb24gaXMgaW4gZWZmZWN0Lgp8IFBsZWFzZSB0YWtlIHRob3 NlIGRpc2N1c3Npb25zIGVsc2V3
aGVyZS4gIFRoYW5rcy4KfAp8IFJFUExZSU5HOiBhZGRyZXNzIH lvdXIgbWVzc2FnZSB0byBldkBs
aXN0cy5zanN1LmVkdSBvbmx5Lgp8IE11bHRpcGxlLWFkZHJlc3 Mgb3IgQ0NlZCBtZXNzYWdlcyBt
YXkgYmUgcmVqZWN0ZWQuCnwgVU5TVUJTQ1JJQkU6IGh0dHA6Ly 93d3cuZXZkbC5vcmcvaGVscC9p
bmRleC5odG1sI3VzdWIKfCBPVEhFUiBIRUxQOiBodHRwOi8vZX ZkbC5vcmcvaGVscC8KfCBDT05G
SUdVUkU6IGh0dHA6Ly9saXN0cy5zanN1LmVkdS9tYWlsbWFuL2 xpc3RpbmZvL2V2Cg==

[EVDL List]

The parallel parking discussion raises another difference between the Leaf and an i-MiEV. The i allows some preload of the motor while still on the brake, such as when starting motion while pointed uphill. Also,when 'idling' in drive at 1-2 mph, a definite 'cogging' can be felt.

Lee raised in this thread that it's bad for a synchronous motor to be powered forward while rotating in reverse, IIRC. A real common occurrance could be when shifting from Reverse to Drive in a fixed gear, synchronous AC-motored EV like the i, such as when backing out of the driveway or starting on a hill. On the scale of Makes a bit of Heat to Really Bad for the Motor, how bad would the practice of shifting to Drive while rolling in Reverse be? There is no lockout to prevent this action on the i.

-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.sjsu.edu/mailman/private/ev/attachments/20120425/9b9aff48/attachment.html
_______________________________________________
| Moratorium on drag racing discussion is in effect.
| Please take those discussions elsewhere. Thanks.
|
| REPLYING: address your message to xxx@xxx.xxx.edu only.
| Multiple-address or CCed messages may be rejected.
| UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
| OTHER HELP: http://evdl.org/help/
| CONFIGURE: http://lists.sjsu.edu/mailman/listinfo/ev

[EVDL List]

It's closer to "makes a bit of heat", and the controller software
should make sure that the amount of heat is acceptable.

Lee's comment on not motoring forward while going in reverse was about
AC induction motors, not synchronous (PM) motors.

With an AC drive, the peak current through a phase (transistor and
winding) is 1.4 times higher than the RMS current. So if you have a
synchronous motor stalled so that one phase is at peak current, that
phase will see twice as much power dissipation as usual, which could
overheat it.

The same thing can happen with an AC induction motor if it is moving
backwards at exactly the slip speed; in that case, one phase sees DC
and could see a DC current of 1.4 times the RMS design value.

If the inverter software limits the current in such situations to less
than 70% of the normal continuous current limit, then that should
limit the current to the normal ratings and avoid overheating
everything. I would hope that the car companies thought about these
situations and protected against them in software.

With a 3-phase drive, stalling puts 1.4 times normal current though a
phase, leading to twice normal resistive power dissipation. With a
commutator, assuming the brushes cover 1/4-1/3 of the commutator bars
at any given time, stalling leads to 1.73-2 times the normal current
through the comm bars as well as vastly reduced cooling, leading to
3-4 times the power dissipation with nowhere to get rid of the heat
and less mass to absorb the heat.

So stalling is much harder on a commutator than it is on a 3-phase AC motor.

-Morgan LaMoore

[quote] Jay Donnaway <xxx@xxx.xxx> wrote:
> The parallel parking discussion raises another difference between the Lea=
f and an i-MiEV. The i allows some preload of the motor while still on t=
he brake, such as when starting motion while pointed uphill. Also,when '=
idling' in drive at 1-2 mph, a definite 'cogging' can be felt.
>
> Lee raised in this thread that it's bad for a synchronous motor to be pow=
ered forward while rotating in reverse, IIRC. A real common occurranc=
e could be when shifting from Reverse to Drive in a fixed gear, synchronous=
AC-motored EV like the i, such as when backing out of the driveway or star=
ting on a hill. On the scale of Makes a bit of Heat to Really Bad for th=
e Motor, how bad would the practice of shifting to Drive while rolling in R=
everse be? There is no lockout to prevent this action on the i.

_______________________________________________
| Moratorium on drag racing discussion is in effect.
| Please take those discussions elsewhere. Thanks.
|
| REPLYING: address your message to xxx@xxx.xxx.edu only.
| Multiple-address or CCed messages may be rejected.
| UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
| OTHER HELP: http://evdl.org/help/
| CONFIGURE: http://lists.sjsu.edu/mailman/listinfo/ev

[EVDL List]

I have frequently thrown the gears in the opposite
directoin of movement and taken off without trouble,
both with my Prius (PM AC motors) and the EV Electricar
(Hughes AC induction motor).
I never managed to keep the field stalled...

[top]

Regards,

Cor van de Water
Chief Scientist
Proxim Wireless Corporation http://www.proxim.com
Email: xxx@xxx.xxx Private: http://www.cvandewater.com
Skype: cor_van_de_water XoIP: +31877841130
Tel: +1 408 383 7626 Tel: +91 (040)23117400 x203

-----Original Message-----
From: xxx@xxx.xxx.edu [mailto:xxx@xxx.xxx.edu] On Behal=
f Of Morgan LaMoore
Sent: Wednesday, April 25, 2012 10:00 PM
To: Electric Vehicle Discussion List
Subject: Re: [EVDL] How To Burn Up Your DC Motor

It's closer to "makes a bit of heat", and the controller software should ma=
ke sure that the amount of heat is acceptable.

Lee's comment on not motoring forward while going in reverse was about AC i=
nduction motors, not synchronous (PM) motors.

With an AC drive, the peak current through a phase (transistor and
winding) is 1.4 times higher than the RMS current. So if you have a synchro=
nous motor stalled so that one phase is at peak current, that phase will se=
e twice as much power dissipation as usual, which could overheat it.

The same thing can happen with an AC induction motor if it is moving backwa=
rds at exactly the slip speed; in that case, one phase sees DC and could se=
e a DC current of 1.4 times the RMS design value.

If the inverter software limits the current in such situations to less than=
70% of the normal continuous current limit, then that should limit the cur=
rent to the normal ratings and avoid overheating everything. I would hope t=
hat the car companies thought about these situations and protected against =
them in software.

With a 3-phase drive, stalling puts 1.4 times normal current though a phase=
, leading to twice normal resistive power dissipation. With a commutator, a=
ssuming the brushes cover 1/4-1/3 of the commutator bars at any given time,=
stalling leads to 1.73-2 times the normal current through the comm bars as=
well as vastly reduced cooling, leading to
3-4 times the power dissipation with nowhere to get rid of the heat and les=
s mass to absorb the heat.

So stalling is much harder on a commutator than it is on a 3-phase AC motor.

-Morgan LaMoore

[quote] Jay Donnaway <xxx@xxx.xxx> wrote:
> The parallel parking discussion raises another difference between the Lea=
f and an i-MiEV. The i allows some preload of the motor while still on t=
he brake, such as when starting motion while pointed uphill. Also,when '=
idling' in drive at 1-2 mph, a definite 'cogging' can be felt.
>
> Lee raised in this thread that it's bad for a synchronous motor to be pow=
ered forward while rotating in reverse, IIRC. A real common occurranc=
e could be when shifting from Reverse to Drive in a fixed gear, synchronous=
AC-motored EV like the i, such as when backing out of the driveway or star=
ting on a hill. On the scale of Makes a bit of Heat to Really Bad for th=
e Motor, how bad would the practice of shifting to Drive while rolling in R=
everse be? There is no lockout to prevent this action on the i.

_______________________________________________
| Moratorium on drag racing discussion is in effect.
| Please take those discussions elsewhere. Thanks.
|
| REPLYING: address your message to xxx@xxx.xxx.edu only.
| Multiple-address or CCed messages may be rejected.
| UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
| OTHER HELP: http://evdl.org/help/
| CONFIGURE: http://lists.sjsu.edu/mailman/listinfo/ev

_______________________________________________
| Moratorium on drag racing discussion is in effect.
| Please take those discussions elsewhere. Thanks.
|
| REPLYING: address your message to xxx@xxx.xxx.edu only.
| Multiple-address or CCed messages may be rejected.
| UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
| OTHER HELP: http://evdl.org/help/
| CONFIGURE: http://lists.sjsu.edu/mailman/listinfo/ev

[EVDL List]

[quote]On 25 Apr 2012 at 11:29, Morgan LaMoore wrote:

> With an AC drive, the peak current through a phase (transistor and
> winding) is 1.4 times higher than the RMS current. ...
>
> The same thing can happen with an AC induction motor if it is moving
> backwards at exactly the slip speed; in that case, one phase sees DC
> and could see a DC current of 1.4 times the RMS design value.

Wait, I'm confused here. Is it 1.4 times HIGHER, or 1.4 times AS HIGH AS?

They're not the same thing. 1.4 times higher is equivalent to 2.4 times as
high as.

I'm thinking it must be 1.4 times AS HIGH AS, since that number rings an RMS
bell for me, but I'm not 100% sure.

Sometimes I think the English language was deliberately designed to confuse
people.

David Roden - Akron, Ohio, USA
EVDL Administrator

[top]

= = = = = = = = = = = = = = = = = = = = = = = = = = =
EVDL Information: http://www.evdl.org/help/

[top]

= = = = = = = = = = = = = = = = = = = = = = = = = = =
Note: mail sent to "evpost" and "etpost" addresses will not
reach me. To send a private message, please obtain my
email address from the webpage http://www.evdl.org/help/ .

[top]

= = = = = = = = = = = = = = = = = = = = = = = = = = =


_______________________________________________
| Moratorium on drag racing discussion is in effect.
| Please take those discussions elsewhere. Thanks.
|
| REPLYING: address your message to xxx@xxx.xxx.edu only.
| Multiple-address or CCed messages may be rejected.
| UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
| OTHER HELP: http://evdl.org/help/
| CONFIGURE: http://lists.sjsu.edu/mailman/listinfo/ev