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02-19-2021, 03:24 PM
(This post was last modified: 02-20-2021, 08:50 AM by fredhargis.)
The start cap on my DC popped today, and it has a bleed down (?) resistor on it. I can find a lot of them online without the resistor but none (with fast delivery) with a resistor. I'm guessing the resistor bleeds the charge out of the cap after it does it's job...but how important is that. Note, I'm not going to buy one without the resistor..just want to educate myself.
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(02-19-2021, 03:24 PM)fredhargis Wrote: The start cap on my DC popped today, and it has a bleed down (?) resistor on it. I can find a lot of them online without the resistor but none (with fast delivery) with a resistor. I'm guessing the resistor bleeds the charge out of the cap after it does it's job...but how important is that. Note, I'm not going to buy one without the resistor..just want to educate myself.
Do you know what the value of the resistor is on your current cap? From what I've seen, it just appears that a resistor is added across the terminals and you could add it to start capacitor without one. Once the motor gets up to speed, the cap is no longer in the circuit and the resistor bleeds the remaining voltage.
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02-19-2021, 06:12 PM
(This post was last modified: 02-20-2021, 06:48 AM by TDKPE.)
I’ve never seen one on a common induction motor, but some hermetic A/C compressors have them. Probably to reduce pitting in the switch should the AC waveform be in the positive portion with the capacitor holding an opposite charge when the switch or contactor is closed.
Can you read the resistance, or the color bands? Can you transfer the old resistor to the new capacitor?
Tom
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It's a safety feature so that someone doesn't get zapped servicing the motor or switch. Odds are pretty good that you can find a similar generic resistor. Just make sure the value and wattage are the same. BBROYGBVGW
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(02-19-2021, 11:14 PM)lincmercguy Wrote: It's a safety feature so that someone doesn't get zapped servicing the motor or switch. Odds are pretty good that you can find a similar generic resistor. Just make sure the value and wattage are the same. BBROYGBVGW
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Better to follow the leader than the pack. Less to step in.
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02-20-2021, 06:34 AM
(This post was last modified: 02-20-2021, 07:14 AM by fredhargis.)
(02-19-2021, 06:12 PM)TDKPE Wrote: I’ve never seen one on a common induction motor, but some heretic A/C compressors have them. Probably to reduce pitting in the switch should the AC waveform be in the positive portion with the capacitor holding an opposite charge.
Can you read the resistance, or the color bands? Can you transfer the old resistor to the new capacitor?
I'll have to look, I'm sure I can see the color bands....don't know if there's any print. I'll post back. This is the 5 HP Leeson that CV uses on it's DCs...and I believe it is a compressor duty motor (don't remember why I think that). I had this same motor on my last DC, and found a replacement nearby where the resistor just clipped onto the terminals (motor shop set this up for me). There's not much chance I could reuse the one I have, it's soldered in. Like a whole lot of other skills, I was shortchanged on being able to solder (except copper pipe).
Here we go: The color bands are left to right as oriented in the pic: copper, orange, green, brown. No markings I can see.
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(02-20-2021, 06:34 AM)fredhargis Wrote: Here we go: The color bands are left to right as oriented in the pic: copper, orange, green, brown. No markings I can see.
Looks like 15 kΩ with +/-5% tolerance. If I'm reading those color bands correctly. It'll take a while to bleed off the charge in that cap, I would think.
Tom
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Thanks, Tom...appreciate it! (and the 3 phase explanation on the other post).
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"Looks like 15 kΩ with +/-5% tolerance. If I'm reading those color bands correctly. It'll take a while to bleed off the charge in that cap, I would think."
There was a time where I could actually do that math.
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Found a decent explanation:
"Some starting capacitors such as those designed by and used in Copeland HVACR compressor motors, include a bleed-through resistor wired between the capacitor's two terminals. Typically a 15K-18Kohm two-watt resistor is used for this purpose
Copeland describes the bleed-through resistor as follows:
The use of capacitors without these resistors will result in sticking relay contacts and/or erratic relay operation especially where short cycling is likely to occur. This is due to the start capacitor discharging through the relay contacts as they close, following a very short running cycle.
The resistor permits the capacitor charge to bleed down at a much faster rate, preventing arcing and over-heating of the relay contacts.
... If sticking contacts are encountered on any start relay, the first item to check is the start capacitor resistor. If damaged, or not provided, install a new resistor, and clean the relay contacts or replace the relay.
Suitable resistors can be obtained from any electronic parts wholesaler or retailer. -"
https://inspectapedia.com/electric/Start...ration.php
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