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RICKG
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 Posted: Tue Feb 03, 2015 4:34 pm Post subject: resistor 8710856 or equal |
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need the resistor 8710856 or equal as shown on the wire schematic.. any ideas??
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4x4M38
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4x4M38
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RICKG
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| Posted: Wed Feb 04, 2015 8:45 am Post subject: |
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Thx Brian! Looks like you're on the mark w/50W, 5 OHM.
Eric's site references pt# 870856 and application.
Ebay site references only 50w, 5 ohm.
Both appear to be identical with Ebay price being 1/2 of Eric's.
In either case it appears a mounting bracket will need to be fab'd
to secure it..
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4x4M38
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capescw
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| Posted: Thu Feb 05, 2015 7:20 am Post subject: Ohms Law |
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If you were to assume a dead short in place of the motor, Ohms law for power is e(sq)/r, or (24*24)/50, indicating a worst case of 11.5 watts dissipation in the resistor.
With the motor instead of a dead short, it would be much less, so I believe a 20 watt resistor would be enough. Since it generates a lot of heat, you might consider placing it in the airstream somehow to protect it (and you).
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RICKG
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| Posted: Thu Feb 05, 2015 12:28 pm Post subject: |
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Thanks for your interest here, Bill. The part# spec'd for this app is for the
50W 5 ohm variety. How much heat are we talkin here??
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wesk
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capescw
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| Posted: Thu Feb 05, 2015 4:04 pm Post subject: Comparison |
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Wes (as usual) is correct! The older Christmas tree lights (parallel string) were around 7-1/2 watts, as well as those little night lights (c-7 bulb). About what I'd expect with a good motor. As an aside, the motor with no-load uses very little power, add the fan blade and the associated air flow resistance in the pipes, and the current increases. I only mentioned the 20w resistor because it's going to be a LOT cheaper. mouser.com shows:
5 ohm-50w, p/n 71-HL50-06Z-5, $13.10
5 ohm-20w, p/n 71-HLW20-A1Z-5 $ 3.12 plus shipping.
Radio Shack lists a p/n 25W5D1 (25w/5.1 ohm) for $1.21.
Seems to beat the $18 one!
Now you see where I get my motto! 
_________________
"Frugality keeps me in the Game"
1952 M38 Project "Lazarus"
1951(?) M100 Trailer
1956-60 USAF Special Weapons Program
http://www.bill-capes.com/insanity - Updated 04/26/14 |
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RICKG
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| Posted: Thu Feb 05, 2015 4:28 pm Post subject: |
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The 8710856 50w 5ohm I ordered was $17 bucks for (2) shipped from the e-bay offer. I purchased an extra-I like to have a spare in case I goof up..
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4x4M38
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