-
Welcome back Guest! Did you know you can mentor other members here at H-M? If not, please check out our Relaunch of Hobby Machinist Mentoring Program!
How long for capacitors to discharge in a window a/c unit ?
- Thread starter Cr2348455
- Start date
- Joined
- Feb 1, 2015
- Messages
- 10,121
Electric motors of 1/4 hp. and larger will use an electrolytic on the start winding. They usually run on 120 volts even if the motor is a 240 volt motor. The run capacitors can be either electrolytic or oil filled. The length of time that a charge remains on a capacitor will vary so the safest approach is to short the capacitor out prior to doing any work. Any piece of metal will work. A screwdriver blade, a short length of wire, long nose pliers.
For working with 120 volts, any insulating material will work as long as it is dry. I usually just use a pair of deerskin gloves. If working in a damp environment, I wear a pair of heavy rubber gloves.
For working with 120 volts, any insulating material will work as long as it is dry. I usually just use a pair of deerskin gloves. If working in a damp environment, I wear a pair of heavy rubber gloves.
- Joined
- Apr 30, 2015
- Messages
- 12,611
Some of you folks seem awfully eager to get a shock! Large electrolytic capacitors can hold charge for long periods depending on the amount of internal leakage and any external bleed resistance (if present). Old motor start caps may be quite leaky and bleed down fast but I would not bet on it.
Some caps can deliver arm-stiffening shocks after sitting for weeks. Always discharge large capacitors before handling them.
-Mark
Some caps can deliver arm-stiffening shocks after sitting for weeks. Always discharge large capacitors before handling them.
-Mark
- Joined
- Feb 13, 2017
- Messages
- 2,128
When I was in technical school,(1967) it was a common "joke" to charge a capacitor and leave it sitting on a bench. The unaware would pick it up, and quickly drop it in shock. A shocking display, to say the least. . .
It is a common practice to wear leather gloves over the rubber gloves to protect the rubber from "pin hole" leaks. At higher voltages, such a leak can be deadly. For consumer goods, rubber gloves aren't really necessary. I only use them for high (>600V) voltage work. There are exceptions, but it's a matter of personal choice.
As a rule, most capacitors in consumer goods have a "discharge" resistor attached to the cap. When powered down, such equipment will "self discharge" in a few minutes if everything is in place. . . That's the gotcha. It is a general practice, or was in my day, to discharge a cap with whatever tool was most appropriate. Usually a screwdriver. Then hang a shorting strap across the cap. A simple jumper, though small or light, will keep any residual contained. And any static charge to bleed off through the jumper. Static can build up from the water striking a metal surface. It doesn't take much.
Working in the profession has caused several shocks over my working life. None were pleasant, but I'm still alive which should count for something. Putting a shorting strap across anything when the switch is out is as automatic as putting one foot in front of the other when walking. Don't chance it. You may get by a hundred times, but that hundred and first can hurt.
.