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 Posted: Fri Feb 9th, 2018 12:07 am
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Vic Valencheck
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I need a 3 speed nichrome speed coil. This one is toasted. I also need a set of brushes with springs. They measure 5/32 x 5/32" and about 3/8" long. Can anyone help me out.






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 Posted: Sat Feb 10th, 2018 04:53 am
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Charlie Forster
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Vic 
try something like this and leave the old nichrome  out if  you have room. https://www.ebay.com/itm/121008618127?ssPageName=STRK:MESINDXX:IT&_trksid=p3984.m1436.l2649

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 Posted: Sat Feb 10th, 2018 06:56 pm
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Vic Valencheck
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Charlie Forster wrote: Vic 
try something like this and leave the old nichrome  out if  you have room. https://www.ebay.com/itm/121008618127?ssPageName=STRK:MESINDXX:IT&_trksid=p3984.m1436.l2649

So I would use 2 resistors in place of the nichrome? One for LOW and the other for Med. speed? What values would I need? 

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 Posted: Sat Feb 10th, 2018 07:38 pm
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Charlie Forster
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75 Ohm 75R 50Wis what Im going to be using in a old Eskimo the old United Electrical .
You might try to get a ohms reading on your old one if possible .
 We used I think some 50 ohms to cut 12 dc down to 6 volt dc for my old pickup .

Last edited on Sun Feb 11th, 2018 06:55 am by Charlie Forster

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 Posted: Sun Feb 11th, 2018 12:36 pm
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Tom Nordin
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Bookmarked this site some time ago - they have a very good selection of brushes, caps, springs, etc:

http://store.eurtonelectric.com/brushes.aspx

If I'm doing my math right:

5/32 = 0.15625
3/8 = .375

This brush & spring set looks like a possibility:

http://store.eurtonelectric.com/15x15x40brush566.aspx

Darryl Hudson can custom make brushes of any size and style too.


P.S. - is your motor a DC only motor, and an AC/DC motor?  What's voltage and current draw - does it say on the nameplate?

Last edited on Sun Feb 11th, 2018 09:20 pm by Tom Nordin

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 Posted: Sun Feb 11th, 2018 01:55 pm
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Tom Nordin
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Okay, based on an eBay pic I found it indicates 110 volts, AC or DC, with a current draw of .35 amps (when on high speed).

Determine resistance:
Ohms law: R = E / I
314 ohms = 110 volts / .35 amps


Determine watts consumed:
Another Ohms law: P = I * E
38.5 watts = .35 amps * 110 volts

I believe two 314 ohm (or there abouts) wire wound/aluminum housed resistors in series could replace your nicrome setup.  Resistor connected between high and medium speeds (I'm thinking half the voltage to the motor, half the speed) should be at least 20 watts, and resistor connected between medium and slow speeds (again I'm thinking one-third the voltage to the motor, one-third the speed) should be at least 10 watts.  Maybe play with resistances to get the speeds you desire, and adjust resistor wattage as appropriate.  Higher wattage is just fine, and I believe you could easily mount a 40 and 20 watt resistor right on top of that metal plate and easily make the connections to the screws.  Somebody check my math, please.

Resistor selection here: https://www.mouser.com/Passive-Components/Resistors/Wirewound-Resistors/Wirewound-Resistors-Chassis-Mount/_/N-7fx9g/

Last edited on Sun Feb 11th, 2018 02:03 pm by Tom Nordin

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 Posted: Sun Feb 11th, 2018 02:27 pm
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Tom Nordin
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P.S. - if you have an ohm meter available, please measure the resistance between one of your brush wires to the corresponding head wire and let us know what you find.  Based on the above detail I believe you will find each coil to be about 150 to 160 ohms.

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 Posted: Sun Feb 11th, 2018 03:44 pm
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Charlie Forster
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Tom
 5/8. s is .625
3/8's is .375
If you get around the swap meet and flee markets  look for  Machinery or (machinest) Hand Book. They have a lot of info in them
 it dosent need to be the latest issue either.

  https://www.ebay.com/itm/1940s-American-Machinists-Handbook-By-Colvin-and-Stanley/312062351319?hash=item48a85d97d7:g:d0gAAOSwQwZaewp7

Last edited on Sun Feb 11th, 2018 04:01 pm by Charlie Forster

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 Posted: Sun Feb 11th, 2018 04:08 pm
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Patrick Ray
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I usually get my brushes from McMaster-Carr
https://www.mcmaster.com/#motor-brushes/=1bix3er

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 Posted: Sun Feb 11th, 2018 05:06 pm
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Vic Valencheck
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Thanks so much guys for your technical input and for the links. They will be a big help.
  Tom, the current is marked .35amp. I think that resistance value of 314 ohms is too high. Don't think you were taking in account for the stator coil resistance. When I go to the shop tomorrow I will measure it. Am I right when I say that when the switch is on high, the speed coil isn't being used? If you put 314ohms on the low or med speed wouldn't the speed go to a crawl? I'm just saying. I guess the best thing would be if someone actually had a good speed coil to take measurements.

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 Posted: Sun Feb 11th, 2018 05:53 pm
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Russ Huber
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FWIW....you could make it into a 2 speed fan(high/low) for pennies on the dollar using a simple non-heat generating diode(3 amp 400 watt+) if you have a UNIVERSAL fan motor. For high speed you simply run full AC current to the motor through the switch.  You then bridge the 2nd and 3rd switch contact terminals and place your diode(half wave rectifier)between the bridged terminals and the wire feeding the motor. That will be your low speed.  Fan speed reduction is done without heat generating resistance.




RECTIFIER DIODE 3 AMP/1000 PIV


Attached Image (viewed 227 times):

fans 1 5740.jpg

Last edited on Sun Feb 11th, 2018 06:10 pm by Russ Huber

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 Posted: Sun Feb 11th, 2018 09:07 pm
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Vic Valencheck
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I see that I have a few options that I can use. Looks like I'll be doing some experimenting.
Thanks for your info Russ.

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 Posted: Sun Feb 11th, 2018 09:25 pm
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Tom Nordin
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Charlie Forster wrote: Tom
 5/8. s is .625
3/8's is .375
If you get around the swap meet and flee markets  look for  Machinery or (machinest) Hand Book. They have a lot of info in them
 it dosent need to be the latest issue either.

  https://www.ebay.com/itm/1940s-American-Machinists-Handbook-By-Colvin-and-Stanley/312062351319?hash=item48a85d97d7:g:d0gAAOSwQwZaewp7


Good fat-finger catch Charlie.  I accidentally used a 5 in the place of 3 in the 3/8 value, yet the answer is correct.  Edited the post.  Thanks!

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 Posted: Sun Feb 11th, 2018 09:42 pm
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Tom Nordin
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I agree, actual resistances of a working coil would be the best.  Here's a quick diagram of what I was thinking:



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 Posted: Mon Feb 12th, 2018 12:22 am
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Vic Valencheck
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Tom Nordin wrote: I agree, actual resistances of a working coil would be the best.  Here's a quick diagram of what I was thinking:




What would you think if I put two 25ohm- 10w resistors in series. Medium speed would be 25ohm and on Low it would be at 50ohm ?

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 Posted: Mon Feb 12th, 2018 12:28 am
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Tom Nordin
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Vic Valencheck wrote: I think that resistance value of 314 ohms is too high. Don't think you were taking in account for the stator coil resistance.

Good point Vic, except I believe you meant rotor/armature rather than stator?  Now that I'm thinking about it I believe each resistor should probably be closer to what others have indicated.  I'll lower my earlier idea to 1/3 of my original value, from 314 ohms down closer to 105 ohms.  On your stator alone (no brushes or rotor/armature involved) I believe you'll read about 105 ohms between a brush wire and the corresponding head wire for each coil.

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 Posted: Mon Feb 12th, 2018 12:40 am
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Vic Valencheck
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So used to saying stator. This is only my second AC/DC fan that I've worked on. I'll get those motor coil values tomorrow.

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 Posted: Mon Feb 12th, 2018 12:55 am
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Tom Nordin
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I'm probably throwing too much into this discussion at this stage - don't want to throw anyone awry.  My last post might be rather inaccurate as well.
Regardless of the resistance, we need to keep the resistor wattage high enough to dissipate the heat.  I think 10 watts is going to be too low, especially for the resistor connected between high and medium.

I can tell you with certainty that I worked on a very similar fan recently and the resistance between each section of the speed switch was exactly two times the resistance of one stator coil as measured between one of the brush wires and its corresponding head wire.  With that in mind get us a resistance measurement tomorrow and let us know.  Once I have that I can rework these figures and hopefully come up with values for resistance and wattage that makes sense for your fan.

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 Posted: Mon Feb 12th, 2018 09:31 am
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Tom Nordin
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Okay, good news.  Just cracked open a Sears Cold Wave fan that is essentially identical to yours - 110 volts AC or DC at .35 amps with three speeds.  Even the speed coil looks the same for the most part.

The two resistances are 45.5 ohms each.  So that takes care of the resistances.  Now the current/watts.

There is no denying the motor itself pulls .35 amps, or 38.5 watts when on high speed (directly across the line voltage).  If you switch to medium the first resistor is added in series.  Still pulling .35 amps, except now about half the voltage is across the resistor, half across the motor, so that resistor should be rated for half the power (at minimum), or about 20 watts.  Flip the switch to low and now both resistors are in series with the motor.  Still pulling .35 amps, except now the voltage is across two resistors and the motor.  That would be approximately 13 watts for each component.  The second resistor should be rated to around 15 watts (at minimum).  Again, higher wattage is just fine.  At the levels listed above, those resistors would be dissipating the max amount off heat they were designed to handle - I bet they'd be very warm to the touch.  So why not cool them down and simply use a 40 watt resistor for medium speed and a 20 watt resistor for slow?  The answer - physical size constraints.  Resistors get physically larger the higher the wattage, and at these values you will find they're bordering on the maximum space you have available to mount them within.

Now, to purchasing what's needed.  You'll find that not all resistance to watt combinations are available.  To cut to the chase 50 ohms is a close figure with a lot of watt value choices:

50 ohms at 20 watts - chassis mount

Length: 49.23 mm - about 2"
Width: 27.43 mm - about 1.1"
Height: 13.87 mm - about .5"

50 ohms at 15 watts - chassis mount

Length: 19.9 mm - about .8"
Width: 21 mm - about .8"
Height: 11 mm - about .4"

At these sizes it looks like you may have just enough room to mount both on that metal plate in your picture.  Be prepared though, you might need to get creative in order to mount these resistor sizes in the space available.

P.S. - on my fan the three speeds are distinctive.  Measuring with an optical tachometer the high speed is about 2100 RPM, medium is about 1650 RPM, and slow is about 1350 RPM.

Last edited on Mon Feb 12th, 2018 02:01 pm by Tom Nordin

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 Posted: Mon Feb 12th, 2018 07:06 pm
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Vic Valencheck
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I took the speed switch apart this morning and discovered that there are two nichrone coils sandwiched together. I was wondering why the top looked good and the bottom was fried. The good coil measures 44 ohms. So two 50 ohm 20 watt resistors should do the trick. The motor coils measure 51 ohms each.




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 Posted: Mon Feb 12th, 2018 08:52 pm
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Tom Nordin
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Good deal, Vic - I think you're well on the way to retrofitting that fan now.  Once you procure those resistors you might consider just connecting things together with clip-leads at first and trying it out before taking the time to mount everything to your existing ceramic base.
You'll find numerous product choices for 50 ohms at 20 watts - Amazon, eBay, and all the independent electronics sites like Mouser, Digi-Key and similar.  Just measure things up to be sure you can mount 'em decently.  Maybe cut a square piece of thin aluminum that you can mount using standoffs and the same holes that sits just above the screw terminals.  Be sure when the bell base fits over it that you don't have a headroom clearance issue.

Don't chuck those old pieces.  You may just want to try your hand at rewinding the bad one, or selling the good one to someone in a similar situation.  Heck, I bet some members would like the bad one just for the form and potential of rewinding it.

Best wishes...

P.S. - the white cardboard stuff that those wires wrap around is asbestos, but hardly enough to be of concern.  Keep it intact as it's integral to the component.  Yeah, yeah - don't scratch & sniff and you'll be just fine...   :D

Last edited on Mon Feb 12th, 2018 09:10 pm by Tom Nordin

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 Posted: Mon Feb 12th, 2018 11:41 pm
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Vic Valencheck
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I was thinking of mounting the resistors on the bad coil plate. It should give it a good heat sink. I can't believe what they but into this fan being just a dime store fan. Brass hardware,porcelain switch, chrome plating. I'll probably have it chrome powder coated. I know it might cost me more then the fan is worth but it will be back to almost original. I'll post when I get it all together again.
  Thanks so much Tom for your input.  :cool:

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