I need help wiring up a microwave fan

[mountainken]

I have a new Microwave that has a three speed exhaust fan with a three stage motor. I have installed a 6 inch
diameter CFM exhaust fan in my attic to keep the noise down at the stove and to exhaust the cooking fumes to the outside of my house. I have removed
the fan motor from the microwave and sealed up the chambers to only exhaust up the top of the unit. Now
I have the wiring diagram and color codes for the motor and have the factory male/female plug ready to hook up to
the new attic exhaust motor. The old motor has four control wires from
the on-board control panel in the Microwave to the motor,plus two wires to the starting capacitor. There are
three wires to control the voltage to three different winding locations on the motor (high,medium,low) plus a
white nutrual. My question is can I take these three wires that have different voltages (starting at 120v.ac) and
install three in-line diodes to protect the control panel from any reversed voltage, and then connect them to a single input at the
motor's connection box? If so what size, make and type of diode should I be looking for and where can I order them? The motor
in the attic is of the type to have a variable voltage controller. I am hoping to be able to use the Microwave's
control panel so I don't have to try and hide a switch under the upper cabinet and end up with a single speed fan! Thank you for any help you
can give me on this. Ken

Frigidaire
mod.# FPMV189KFC


CFM In-line duct fan
0.78 Amps
89 Watts

 

[harold777]

This is reading like a nightmare - can you explain why there is a microwave in the attic? What's wrong with the kitchen and what's this about ducting smells - smells of what?
Are you microwaving someting not to do with domestic cooking - you need to explaiin. Why take the microwave apart?...this is not a good idea IMHO.

 

[KeepItSimpleStupid]

Harold, he's installing an over the range microwave, These have an over the range hood, filter and exhaust fan in them.

I think you want to have the low/med and high speeds of the microwave to turn on the single variable speed of the duct fan, right?

 

[mountainken]

KeepItSimpleStupid, yes you are correct. The noise of the fan drives my wife nuts so she won't use it causing a greasy mess to get off of the walls! I am not even sure if I need the Diodes to protect the control board at the microwave. I thought that I should check with those more knowledgeable about this than myself. Thank you for the reply. What do you think?
Ken

 

[KeepItSimpleStupid]

You should verify that between L M and H and N, there is 120 v for each position. I believe this will be the case. Then you can just connect L to M and H and have a single wire that provides power.

You should check the contact ratings on the FAN switch and/or the current for the internal fan, but what I would do is the following: Put a relay with a 120 V coil in there so all you have is a low voltage contact closure out.

Arrange this circuit to energize the relay when any fan position is selected and provide a potential free low voltage contact to the booster fan. This allows you to not be concerned with restrictions of running 120 V through weird spaces. Provide a connector on the back of the microwave.

Now you can run the 24 VAC control signal to the attic booster similarly as what is done in a home furnace.

In the attic mount a energy limiting control transformer typically used for furnaces in a large J-box with a relay with a 24 VAC coil. If you can't get an energy limiting model, put a 2 A automotive fuse in the secondary. Have that relay turn on the booster. Energy limiting transformers will survive a direct short across it's secondary forever.

If the fan center does not use an energy limiting transformer, get an automotive blade type fuse pigtail and add it in series with the secondary.

You can get all of this functionality (although a little overkill) in what's called a fan center. e,g, https://www.google.com/products/cat...=X&ei=0oDNT-2SINGd6AHnmPDnAg&ved=0CK0BEPMCMAM

It would be nice, but not essential to power this J-box from the same circuit as the microwave.

 

[mountainken]

Thank you for the information. With everything going on with the kitchen remodel I had not thought about all three feed legs being of the same voltage, and it makes perfect since considering the three stage windings on the motor. I will verify the voltage before I proceed with the rest of your instructions. Thank you again for the help Ken.

 

[KeepItSimpleStupid]

There is another possible issue. I don't know if you have to turn on the fan when you use the microwave portion of the oven.

 

[4pyros]

Sounds like a fire code violations.
What if this thing catches on fire!

 

[mountainken]

Gentlemen thank you for your help on this project, all systems worked as planned. All components are properly grounded and as I found out the microwave only had two speed's to begin with so for now it will only have one. There is a possibility of a fan speed controller down the road but for now it works nice and quiet with one. I was able to find a male/female 9 pin 250v. plug at Radio Shack to exit the microwave and connect to a J-box near the AC plug for the power. The Harness exits the J-box in 1/2 inch flex conduit into the attic and up to the CFM Fan control J-box. The power control harness to the attic fan from the microwave is only 12 feet long. I installed a system similar to this in my sister-in law's re-model about 11 years ago and it is still working great today. Thank you again Ken

 

[4pyros]

I was able to find a male/female 9 pin 250v. plug at Radio Shack

Should be rated at 600 volts for AC power.
This all sounds vary scary.
The fan was in the hood for a reason.
What if you have a stove fire will the new blower catch on fire?
What if the new motor over heats from all that grease will it start the attic on fire.
What if your low voltage connector brakes down and starts a fire behind the microwave.
Kids dont try this at home!!!

 

[KeepItSimpleStupid]

4pyros: Check any switch or outlet. No where is there a 600 VAC rating. No where.

It is actually a good idea putting the fan in the attic. Any COMMERCIAL outfit will do this . Look at the number of fans on the top of any restauraunt.

Grease will never get up the stack. There is always a filter first.

He decided to use a high voltage system in flex conduit. Nothing wrong there either.

 

[4pyros]

4pyros: Check any switch or outlet. No where is there a 600 VAC rating. No where.

Its printed on all AC wires as the break down voltage.

It is actually a good idea putting the fan in the attic.

Never it is probably agenst code.

Any COMMERCIAL outfit will do this .

Thay would never do anything that goes agenst code.

Look at the number of fans on the top of any restauraunt.

Thay are fire proof and mounted outside.

Grease will never get up the stack. There is always a filter first.

Can you guarantee it?
Someone some year down the line may take the filter out.
What if the filter gets a hole in it?

He decided to use a high voltage system in flex conduit. Nothing wrong there either.

As long as that multi connductor cable is rated to be run in conduit.

None of this is to code and would have to be fixed if you were to sell the house.

If something goes wrong and the house burns down and kills someone the OP is in for a big lawsute.

Once again kids don't try this at home.

 

[KeepItSimpleStupid]

4 pyros: I have a 120 VAC switch handy. It says 15 A, 120 V AC Only. No where on the switch does it say 600 V. I'll bet outlets are the same way. Wires are another story, be we weren't talking about wires.

Fans are not necessarily outside. Where I worked we had lots of hoods. Nearly all fans were inside, mounted near the roof.

Booster fans are safe. That's why they make them.

So, your saying you cannot install one of these https://www.hvacquick.com/products/residential/Kitchen-Exhaust/Kitchen-Exhaust-Fans/Fantech-RE-fans in your house?

A reminder, the fan we are talking about really has nothing to do with the microwave except it's a mechanical hood and a switch.

You can read but cannot print any pages the NEC code online. I urge you to go to this page https://www.nfpa.org/AboutTheCodes/AboutTheCodes.asp?docnum=70&tab=docinfo, register and Search for "read only" and find the section that prohibits wiring the fan in the manner specified.

 

[harold777]

I suspect that connector is a Sub-Min-D-type - don't know about US Regulations but it wouldn't even begin to be approved in the UK - minimum insulation distance is 3mm on a nominal 240v ac supply. OP can check by comparing the images in Radio Shack catalogue on-line . . . . Mind-you there are some pretty awful connectors, used original in disco-lighting . . . but OP needs to consider the grease (fire hazard) and steam (damp!), IF a connector is permitted (and I don't like the idea), then it needs to be waterproof... heatproof...greaseproof....Yikes!

My Post #2 "... This is reading like a nightmare - ...."

Phone for an eletrician.

 

[KeepItSimpleStupid]

I don't even think you guys have seen an over the range microwave: https://www.diychatroom.com/f47/over-range-microwave-41022/#post249740

 

[4pyros]

I don't even think you guys have seen an over the range microwave: https://www.diychatroom.com/f47/over-range-microwave-41022/#post249740

I have one. I just would not turn it into a fire hazard.

 

[4pyros]

So, your saying you cannot install one of these https://www.hvacquick.com/products/re...antech-RE-fans in your house?

That is not a booster fan.