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Model Engineering in UK - Model engineering, metal crafts in UK
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Posted by Brad. on February 27, 2008, 11:39 am
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Hoping someone can help on a little problem of mine !!
I have a 2.2KW 3phase extractor fan motor which is bifurcated (inside
seperate ducting within the flue). The fan motor is controlled by a
transformer type device rather than an inverter. The motor seems to be
getting very hot at slower speeds. I am considering extra cooling by
inserting a 4" axial fan (bathroom extractor fan) into the ducting access
plate to add extra cooling. Question is, is there an easy way on monitoring
the motor's temperature? to avoid burning the thing out? I thought about
one of those digital thermometers with a long probe that you can use when
cooking turkeys etc. Would this work? What sort of temperature would be
normal for a fan motor running at low speeds?
Any help would be greatly appreciated.
Cheers.
Brad.
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Posted by Richard on February 27, 2008, 3:18 pm
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wrote:
>Hoping someone can help on a little problem of mine !!
>I have a 2.2KW 3phase extractor fan motor which is bifurcated (inside
>seperate ducting within the flue). The fan motor is controlled by a
>transformer type device rather than an inverter. The motor seems to be
>getting very hot at slower speeds. I am considering extra cooling by
>inserting a 4" axial fan (bathroom extractor fan) into the ducting access
>plate to add extra cooling. Question is, is there an easy way on monitoring
>the motor's temperature? to avoid burning the thing out? I thought about
>one of those digital thermometers with a long probe that you can use when
>cooking turkeys etc. Would this work? What sort of temperature would be
>normal for a fan motor running at low speeds?
>Any help would be greatly appreciated.
>Cheers.
>Brad.
>
Monitoring with a digital thermometer is perfectly reasonable. Make
sure you get good themal contact between the probe and motor, ideally
glue it on with a blob of epoxy. Check the motor spec for the
acceptable running temp. - some motors can run at what seems to be
frightening temperatures. I once queried Bosch on the subject
regarding a system I was testing and they said "...if the paint's not
peeling it's fine" ! That's NOT to say the same necessarily applies to
your motor, but check the OEM's spec as you may be worrying
needlessly.
Richard
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Posted by Brad. on February 28, 2008, 6:35 pm
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"Richard" <sharkface-pilot at toucansurf dot com> wrote in message
> wrote:
>
>>Hoping someone can help on a little problem of mine !!
>>I have a 2.2KW 3phase extractor fan motor which is bifurcated (inside
>>seperate ducting within the flue). The fan motor is controlled by a
>>transformer type device rather than an inverter. The motor seems to be
>>getting very hot at slower speeds. I am considering extra cooling by
>>inserting a 4" axial fan (bathroom extractor fan) into the ducting access
>>plate to add extra cooling. Question is, is there an easy way on
>>monitoring
>>the motor's temperature? to avoid burning the thing out? I thought about
>>one of those digital thermometers with a long probe that you can use when
>>cooking turkeys etc. Would this work? What sort of temperature would be
>>normal for a fan motor running at low speeds?
>>Any help would be greatly appreciated.
>>Cheers.
>>Brad.
>>
>
> Monitoring with a digital thermometer is perfectly reasonable. Make
> sure you get good themal contact between the probe and motor, ideally
> glue it on with a blob of epoxy. Check the motor spec for the
> acceptable running temp. - some motors can run at what seems to be
> frightening temperatures. I once queried Bosch on the subject
> regarding a system I was testing and they said "...if the paint's not
> peeling it's fine" ! That's NOT to say the same necessarily applies to
> your motor, but check the OEM's spec as you may be worrying
> needlessly.
>
> Richard
Many thanks for the advice about my motor, I feel quite a lot better now.
Cheers.
Brad.
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Posted by John on February 29, 2008, 4:59 am
Please log in for more thread options There are various ways of measuring motor temperature. The most
suitable depends upon where the motor is and how often you want to
check the thing.
At the simplest end are self adhesive strips with a temperature scale
that changes colour. These can be reversible or not so you can either
see the actual temperature or the highest achieved.
The digital probe you mentioned are good. Get the probe as close to
the windings as possible and with good thermal contact. Watch the
battery life if it's on for a long time.
You can also use an infra red non contact thermometer. These can be
used at a distance but be aware that the read area increase with
distance.
Remember that the heat is developed in the windings and they're
normally the critical point of failure. The closer you can get to them
when measuring the temperature the better. The motor name plate should
give you the insulation class, probably a letter but I'm a bit out of
touch now. This relates to the max temperature the insulation will
take. As Richard says, modern motors are designed to run very hot.
You mention the motor gets hot at slow speed. This is a common failing
on motors driven via a variable speed drive. Their own fan runs at
motor speed and it's output reduces dramatically as the speed drops.
ISTR it's a cube law. If a motor is to be run at high power output at
a lower speed, an auxiliary fan is normally needed to keep it cool.
Other points worth checking are that the motor is clean and not
covered in a nice thick layer of insulating dust. Also make sure it's
not been painted umpteen times. Paint can build up to a surprising
thickness.
John
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Posted by David Powell on March 1, 2008, 2:49 pm
Please log in for more thread options In article
wrote:
>There are various ways of measuring motor temperature. The most
>suitable depends upon where the motor is and how often you want to
>check the thing.
>At the simplest end are self adhesive strips with a temperature scale
>that changes colour. These can be reversible or not so you can either
>see the actual temperature or the highest achieved.
>The digital probe you mentioned are good. Get the probe as close to
>the windings as possible and with good thermal contact. Watch the
>battery life if it's on for a long time.
>You can also use an infra red non contact thermometer. These can be
>used at a distance but be aware that the read area increase with
>distance.
>Remember that the heat is developed in the windings and they're
>normally the critical point of failure. The closer you can get to them
>when measuring the temperature the better. The motor name plate should
>give you the insulation class, probably a letter but I'm a bit out of
>touch now. This relates to the max temperature the insulation will
>take. As Richard says, modern motors are designed to run very hot.
>You mention the motor gets hot at slow speed. This is a common failing
>on motors driven via a variable speed drive. Their own fan runs at
>motor speed and it's output reduces dramatically as the speed drops.
>ISTR it's a cube law. If a motor is to be run at high power output at
>a lower speed, an auxiliary fan is normally needed to keep it cool.
>Other points worth checking are that the motor is clean and not
>covered in a nice thick layer of insulating dust. Also make sure it's
>not been painted umpteen times. Paint can build up to a surprising
>thickness.
>
To some extent the slow speed effect is self compensating on a fan.
The OP said it was a bifurcated fan, the sort of thing you find used
as a boiler's ID fan. Maybe the heat is coming from the flue.
Another thought, is it a pukka job or something that some sheet (there
may be a bad pun here) metal-basher bodged up using a normal fan? If
the latter then the motor isn't getting the expected cooling air.
Regards,
David P.
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>I have a 2.2KW 3phase extractor fan motor which is bifurcated (inside
>seperate ducting within the flue). The fan motor is controlled by a
>transformer type device rather than an inverter. The motor seems to be
>getting very hot at slower speeds. I am considering extra cooling by
>inserting a 4" axial fan (bathroom extractor fan) into the ducting access
>plate to add extra cooling. Question is, is there an easy way on monitoring
>the motor's temperature? to avoid burning the thing out? I thought about
>one of those digital thermometers with a long probe that you can use when
>cooking turkeys etc. Would this work? What sort of temperature would be
>normal for a fan motor running at low speeds?
>Any help would be greatly appreciated.
>Cheers.
>Brad.
>