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Cliff321 09-10-2008 12:48 PM

blower fan issues
 
Appliance AprilAire dehumidifier
Problem: it stopped working. Blower motor was stuttering - trying to start but not turning over.

I traced the power: the power supply was OK the Compressor ran OK. It was blower fan and the Run capacitor.
I got a new one. The original equipment company won't sell one at a time but, advised me that it had to be 25 Micro Farad and 450 Vac.

Got such a capacitor from DIGIKEY.
It is a 4 terminal capacitor and the whole thing is a blue poly box. Original was two terminal and an alum canister. Still, it's 25uf and 450 Vac.

Hooked it up. It makes the motor do more than the dead original one.
But the motor still won't come up to speed.

I am wondering if I need a bigger capacitor. Maybe 500 or 550 Vac.

Any ideas?

SD515 09-11-2008 08:32 AM

The capacitor is matched to the motor, not what used to be in there. If the motor calls for a 25mf/450Vac, then that's what you use. Does the motor have more than 1 non-neutral lead?? Maybe it's a multi-speed motor that needs something changed?

J. V. 09-11-2008 10:51 AM

If the voltage and mfd are the same it should work, but. When ordering capacitors you always make sure the cap has the same physical dimensions. I would not use a square cap if the one I needed was round. Thats the problem sometimes when we order on the internet.
Take your motor and capacitor to a local motor shop and ask them to match a cap to the one you took off. You might just have the wrong type.

Ps.....4 terminals leads me to believe you have two caps in one. Both in the same enclosure. Find the right cap and you should be good to go. Or find the right 2 terminals to connect too.

Cliff321 09-11-2008 01:05 PM

SD said:
Quote:

The capacitor is matched to the motor, not what used to be in there. If the motor calls for a 25mf/450Vac, then that's what you use. Does the motor have more than 1 non-neutral lead?? Maybe it's a multi-speed motor that needs something changed?
It's not a multi speed. Just a rather big blower. It is not uncommon to step up voltage a little maybe even make the motor work better. However, I'm unsure what messing with the Micro Farads will do.

The motor has only two inputs.

JV said:
Quote:

If the voltage and mfd are the same it should work, but. When ordering capacitors you always make sure the cap has the same physical dimensions.
That's what I'd have thought. However the engineer at DIGIKEY was unimpressed by the geometry delta. The solder lugs are for a board mount.

JV Said:
Quote:

Take your motor and capacitor to a local motor shop and ask them to match a cap to the one you took off. You might just have the wrong type.
lol if only I had one.


JV said:
Quote:

Ps.....4 terminals leads me to believe you have two caps in one. Both in the same enclosure. Find the right cap and you should be good to go. Or find the right 2 terminals to connect too.

I wondered i that were the case. The DIGIKEY engineer says I just use any two along a long side. Even two on a diagonal. and the others are just riders.


Then I checked to see if the Cap was holding a charge. Nothing. No spark, nothing. I'd have thought it'd be holding some juice. So I'm getting a new one.

I gathered from the folks at ISKRA ( the original manufacturer of my original cap) that this was a custom order cap that Aprilaire had made just for their application. So far in searching out a replacement I've found that a 25 MicroFarad in a 450 Vac capacitor is a bloody rare thing.

micromind 09-11-2008 08:32 PM

Since the new capacitor is from an electronics supplier, I suspect it is for DC only. A motor capacitor must be AC.

There are basically 4 types of electrolytic capacitors.

1) DC, also known as filter capacitors. These are for use on DC circuits only, they will store a charge in only one polarity, not both as in AC. They are typically used to 'smooth out' a pulsating DC circuit, though they may also be used as energy storage. They range from less that 1 ufd to many thousand ufd, and voltages from less that 10 to more than 1000.

2) Motor start capacitors. These are for AC power, though they'll work on DC as well. These are what's under the 'hump' on a capacitor-start single phase motor. They range from about 100 ufd to about 500 ufd. They are designed to be operated for a limited time, usually only a few seconds. they voltage range is usually 110 to 550.

3) Motor run. These are also for AC power, and will work on DC. These are designed to be operated continuously. This is the type you have. They are usually about 10 ufd to 200 ufd. Voltage is usually 110 to 550.

4) Power factor correction capacitors. These are for AC power, and will work on DC. They're usually found in huge industrial buildings, and power plants. They are usually rated in kVars (kilo voltamps reactive), not ufd. They are installed directly across an AC power line, for the purpose of improving power factor. Voltage ranges from 240 to thousands of volts. (I know, this isn't DIY, but they certainly exist, and I've installed plenty of them).

All capacitors are rated in capacitance and voltage. Capacitance is usually expressed as ufd (micro farad). This relates to their ability to stare an electrical charge. A 100 ufd capacitor is smaller than a 500 ufd one, alot like a 1 gallon bucket is smaller than a 5 gallon one. If you're replacing one, the ufd rating must match.

Voltage is simply the maximum amount of electrical 'pressure' it can safely withstand. A replacement capacitor can have a higher voltage rating, but not lower. The voltage rating has no effect whatsoever on capacitance. Be careful when using a higher voltage capacitor, the higher the voltage, the larger the case size.

A word of caution here; when working with capacitors, remember that they can store a charge for a long time (years). This charge can knock you right across the room! Once power has been de-energized, short the terminals out with a screwdriver. If you see a nice arc, and hear a nice SNAP, you'll be glad you did!

Motor run capacitors can be found at motor repair shops, HVAC shops, and industrial supply houses (Grainger and the like).

With the proper capacitor, I'll bet your motor will run fine.

Rob

P.S. Grainger has a 25 ufd motor run capacitor #2GU15. It is rated at 440 volts, there's really no difference between 440 and 450.

Cliff321 09-13-2008 09:26 AM

Muchos gracias
I ordered one.

Apparently GOOGLE does not search their site.


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