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Air compressor reset
- Thread starter David
- Start date
So if the pressure switch isn't unloading then that could cause too much current draw.
Elektrishun
Ultra Member
If that last scenario plays out, motor stalls attempting a second cycle, then @slow-poke will likely be correct about a failing start capacitor.
@David
Edit - have the capacitors been checked, yet?
Elektrishun
Ultra Member
I think you've stated that the thermal overload has tripped even at a lower pressure reading - correct?
No not yet. I don't have gear to test them.
Elektrishun
Ultra Member
Ok
Have you ever been at the air compressor location to see what happens after it successfully starts the first time and before the thermal overload trips?
Yes, it starts and runs exactly as I expect it to run. Cuts off at 135 psi.
Elektrishun
Ultra Member
Ok, but what about when it attempts a second cycle? Any signs of motor hum/buzz, hot to touch, before the thermal overload trips?
No, nothing like that. After it cuts off at 135 psi, I can drain the tank down to refill pressure and it just won't start unless I reset it. Which make me think that the overload is tripping when the pressure switch cuts in. Weird coincidence?
Elektrishun
Ultra Member
Trying to make sure I understand:
- first cycle air compressor runs as it should, reaches pressure setting, shuts off
- second cycle, no symptoms of a struggling motor/pump, no heat at motor, but fails to start
- at this point thermal overload is found in tripped position
Curious, if you were there after the first cycle and monitored the thermal overload trip button could you verify how soon after the first cycle it tripped?
And as soon as you notice it is tripped can you reset it right away? Normally, you have to wait for the bimetallic strip to cool (10-15 minutes according to the manual) otherwise you will be forcing the button.
You have it exactly right.
I have the on/off switch for the compressor plug inside. I switched it on the other night and nothing happened. So I went to the compressor and pressed the reset. it would not stay 'pressed', I had to hold it down to get it to keep running.
I can definitely be at the compressor to see when the overload trips.
Elektrishun
Ultra Member
Unless I am missing something...
If you have to press hard on the button then you are forcing the bimatellic strip to make contact. That means it got hot enough to bend and needs to cool to relax into position for a normal manual reset.
But, if you can't observe ANYTHING at the compressor or with the clamp-on ammeter that would suggest abnormal operating conditions then in my opinion the thermal overload switch is not working correctly.
Edit - heating and bending without excess current.
Let me measure the current from start to finish tomorrow and also observe the overload switch to see when it trips.
My gut feel with almost zero knowledge is that the overload switch is tripping at too low a temperature.
slow-poke
Ultra Member
Getting closer...
I'm curious if the pressure is lower, as in low enough for the first start in the morning possibly after some overnight leak down that a somewhat normal cycle occurs then either:
1) The unloader did not unload enough to allow a low enough current 2nd start, or
2) The unloader is okay, but the capacitors are degraded enough that excessive current on the second start with now higher pressure than the overnight leaked down pressure causes the overload to trip, or
3) The overload is maginal.
Assuming the overload is not tripped after the first in the morning pressure up, if you then turn off the power and drain the tank to very low or no pressure and then power up I'm guessing it will pressure up in a seemingly normal way as if first try in the morning.
Both the capacitors and overload are available next day from Amazon for $10-20ish or same day from whatever electrical place is near you. DMM with capacitance range up to at least 100uF would allow you to rule out the capacitors which is still my most suspected of the three just because electrolytic capacitors have a expected lifetime that varries from 1000 hours for cheap capacitors to 10,000 hours for really good capacitors. With the bean counter mentality and a Sanborn is no Quincy you can be sure those factory fitted capacitors are the 1000 hour variety.
Side note 1
When designing electronic circuits intended to have long term reliability electrolytic capacitors are the achilles heel. For small capacitances, alternatives to electrolytic's exist that will last > 50 years however for large values electrolytic capacitors are the only option so we select high quality ones: Rubycon, Nichicon, KEMET, Panasonic, or United Chemi-Con, but good is not cheap. Also over-designing selecting say a 100uF when a 47uF is enough buys you a whole bunch more time. I have 50 year old lab equipment with the original electrolytic caps that still works perfectly but that little instrument cost $20k back in the day.
Side note 2
When I was living in Mississauga there was a surplus electronic shop (A1) 15 minute drive from home, he would sell new start/run capacitors for $5-10 each, I asked him how many do you sell, he stated more than you can imagine sometimes 10-20 a day especially when it's hot and everyone's A/C won't start.
Same capacitor at the local rake em over the coals electrical distributor that first question is "business name or account number?" Over $100 and I will need a specific model number and it will most likely be a special order.
Amazon is likely your best option unless you have the equivalent of A1 near you. The only thing I miss from the GTA is A1 and the fantastic ethnic food.
Side note 3
I have a vested interest in you troubleshooting this to completion so when my Sanborn fails to start you will have done the troubleshooting for me; These weak links in a design are more often the rule than the exception. Back in my high school days I did warranty repairs for GM and Ford radio/cassette players. Often I would read the ticket and know which specific component I needed to change before I powered it up or took the cover off.
I'm curious if the pressure is lower, as in low enough for the first start in the morning possibly after some overnight leak down that a somewhat normal cycle occurs then either:
1) The unloader did not unload enough to allow a low enough current 2nd start, or
2) The unloader is okay, but the capacitors are degraded enough that excessive current on the second start with now higher pressure than the overnight leaked down pressure causes the overload to trip, or
3) The overload is maginal.
Assuming the overload is not tripped after the first in the morning pressure up, if you then turn off the power and drain the tank to very low or no pressure and then power up I'm guessing it will pressure up in a seemingly normal way as if first try in the morning.
Both the capacitors and overload are available next day from Amazon for $10-20ish or same day from whatever electrical place is near you. DMM with capacitance range up to at least 100uF would allow you to rule out the capacitors which is still my most suspected of the three just because electrolytic capacitors have a expected lifetime that varries from 1000 hours for cheap capacitors to 10,000 hours for really good capacitors. With the bean counter mentality and a Sanborn is no Quincy you can be sure those factory fitted capacitors are the 1000 hour variety.
Side note 1
When designing electronic circuits intended to have long term reliability electrolytic capacitors are the achilles heel. For small capacitances, alternatives to electrolytic's exist that will last > 50 years however for large values electrolytic capacitors are the only option so we select high quality ones: Rubycon, Nichicon, KEMET, Panasonic, or United Chemi-Con, but good is not cheap. Also over-designing selecting say a 100uF when a 47uF is enough buys you a whole bunch more time. I have 50 year old lab equipment with the original electrolytic caps that still works perfectly but that little instrument cost $20k back in the day.
Side note 2
When I was living in Mississauga there was a surplus electronic shop (A1) 15 minute drive from home, he would sell new start/run capacitors for $5-10 each, I asked him how many do you sell, he stated more than you can imagine sometimes 10-20 a day especially when it's hot and everyone's A/C won't start.
Same capacitor at the local rake em over the coals electrical distributor that first question is "business name or account number?" Over $100 and I will need a specific model number and it will most likely be a special order.
Amazon is likely your best option unless you have the equivalent of A1 near you. The only thing I miss from the GTA is A1 and the fantastic ethnic food.
Side note 3
I have a vested interest in you troubleshooting this to completion so when my Sanborn fails to start you will have done the troubleshooting for me; These weak links in a design are more often the rule than the exception. Back in my high school days I did warranty repairs for GM and Ford radio/cassette players. Often I would read the ticket and know which specific component I needed to change before I powered it up or took the cover off.
Attachments
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Ironman
Ultra Member
My suggestion is to tie the terminals together on that button, and set up a outboard overload protection switch, if you start caps are healthy.
My personal preference is for unloading valves. My Quincy has them and I use a delay relay set to 12 seconds so the motor starts unloaded and turns the compressor for 12 seconds before it starts to pump. This is ideal in an unheated building in winter.
My personal preference is for unloading valves. My Quincy has them and I use a delay relay set to 12 seconds so the motor starts unloaded and turns the compressor for 12 seconds before it starts to pump. This is ideal in an unheated building in winter.