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Author Topic: Dust Collector blowing fuses...  (Read 1598 times)

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Dust Collector blowing fuses...
« on: April 28, 2016, 12:01:41 PM »
I purchased a dust collector from Harbor freight that works great when attached to the wall outlet, but when I attached it to an Opto22 relay to be controlled programmatically it blew the 30A fuse on the 120v side of the Opto22 that I had placed in-line. The specs for the dust collector show it as 20A and when plugged into my wall outlet which has a 20A breaker it never trips it....

Soo my guess is it had to do with startup surge or something like that that the fuse cannot handle but the breaker can. My question is if it would be okay to just remove my inline fuse and rely solely on the breaker for protection? Could my opto22 handle the startup surge without damage? (it is a 25A relay which is higher than the breaker) should I just try to get a slow burning fuse instead?

Just curious what my options are. Thanks.

Matt
Re: Dust Collector blowing fuses...
« Reply #1 on: April 28, 2016, 04:02:21 PM »
Just buy some slow blow fuses.

Jeff
Re: Dust Collector blowing fuses...
« Reply #2 on: April 28, 2016, 04:21:22 PM »
Fuses open allot faster than circuit breakers. Circuit breakers have a time over current curve. A 20A breaker can take up to 3 minutes to open when it reaches 18-20 amps. The typical start up current of a motor is 6 times the full load current until the motor reaches full rpm. It's safe to bypass the fuse and just use the circuit breaker for motor protection. 
Re: Dust Collector blowing fuses...
« Reply #3 on: April 28, 2016, 04:41:58 PM »
Do you think that start up current would fry my Opto22 relay which is rated at 25A?
Re: Dust Collector blowing fuses...
« Reply #4 on: April 28, 2016, 10:16:18 PM »
Depends on the Opto22 relay type. Is it a solid state type or contacts? Is the motor 120 or 220V and what is the HP? The blower motor probably takes 2 or 3 seconds to reach full speed which is fast enough not to cause relay overloading damage. The problem occurs when the motor is turned on and the relay contacts arc for a few millisecond. This causes contact pitting over time and eventual failure. 
Re: Dust Collector blowing fuses...
« Reply #5 on: April 28, 2016, 10:36:59 PM »
Relay damage doesn't happen on start. No current flows until the contacts actually touch. No gap no arc. When the relay opens and the magnetic field collapses it generates a huge inductive surge voltage that arcs across the contacts. Hence motor rated mechanical relays have double break contacts to break the arc faster. In the early days of digital meters I blew a couple up before I realized what was happening!
Re: Dust Collector blowing fuses...
« Reply #6 on: April 29, 2016, 01:37:37 AM »
The opto22 is a solid state relay. The motor is 120v and 2 H.P.


Depends on the Opto22 relay type. Is it a solid state type or contacts? Is the motor 120 or 220V and what is the HP? The blower motor probably takes 2 or 3 seconds to reach full speed which is fast enough not to cause relay overloading damage. The problem occurs when the motor is turned on and the relay contacts arc for a few millisecond. This causes contact pitting over time and eventual failure.