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roh roh compressor motor thermal overload is tripping
- Thread starter shannonw
- Start date
Yeah fan may help keep the motor cool, i don't think there's a chance in heck of that working in florida summer =) I open the garage, doors right next to it, give plenty of wall space. Maybe if the space was air conditioned!
but at the end of the day the ss5l5 pump draws 21.5 at 100% duty (125psi). So I think the SPL's they put on these (mine isn't the original motor but it's the same 3450rpm quincy uses on their cheaper ones) just aren't up to it. It may be a 21.5 motor but the 21 amps is considered brief peak usage...long run times = more peak usage so the motor gets hot.
No idea but i guess the run capacitor starts to degrade then the motor overheats.
Or who knows maybe this one is a lemon, or the pump (don't think it's the pump) but lots of these blew the original emerson spl 3450 motors from googling.
I dunno ill ponder this, there's plenty of decent craigslist compressors around. I'd slap a 1725rpm, starter,pulley on it in a heart beat if it was a 2 stage. But may make more sense to just see what is out there and get a 2 stage..we'll see.
but at the end of the day the ss5l5 pump draws 21.5 at 100% duty (125psi). So I think the SPL's they put on these (mine isn't the original motor but it's the same 3450rpm quincy uses on their cheaper ones) just aren't up to it. It may be a 21.5 motor but the 21 amps is considered brief peak usage...long run times = more peak usage so the motor gets hot.
No idea but i guess the run capacitor starts to degrade then the motor overheats.
Or who knows maybe this one is a lemon, or the pump (don't think it's the pump) but lots of these blew the original emerson spl 3450 motors from googling.
I dunno ill ponder this, there's plenty of decent craigslist compressors around. I'd slap a 1725rpm, starter,pulley on it in a heart beat if it was a 2 stage. But may make more sense to just see what is out there and get a 2 stage..we'll see.
choekstr
New member
Forgive my ignorance but if the RPM at the pump remains constant, the RPM of the motor can vary and adjusted at the pulley, why does HP of the motor matter? Why wouldn't one go with a 2HP vs a 5HP motor? It seems to me it would be less power draw, run cooler due to less current passing through it, and the tank would fill up at the exact same rate (since same pump RPM). Does it place more strain on the motor?
Is it the wear and tear on the motor as the reason to go with higher HP? So a 5HP 1725rpm motor might last 6-10 years (shannonw's experience notwithstanding) and a 2HP 1725rpm motor might last only 2-3 years?
I am sure there are a lot of subtleties and variables here but hopefully someone can explain the questions above.
Thanks!
Is it the wear and tear on the motor as the reason to go with higher HP? So a 5HP 1725rpm motor might last 6-10 years (shannonw's experience notwithstanding) and a 2HP 1725rpm motor might last only 2-3 years?
I am sure there are a lot of subtleties and variables here but hopefully someone can explain the questions above.
Thanks!
I'm not at all knowledgable in this but I'll take a stab..and an expert will come in and really explain =)
If you look at the ss5 pump it's draw rate is 21.5 amps at peak fill to make that CFM. So assume you put a 2hp motor on there, that motor load rating is 10 amps or so, so first thing you'd overheat it as the load is so much greater than the motor can handle. So if you put a small pulley where the amp draw of the compressor is within the load of the motor you reduce the compressor rpm and output as well. Though I imagine there's some point where the motor would stall if grossly underrated or overpulleyd.
The deal with the SPL from what i think is it's only expected you'll draw past the 100% load rating of the motor when the load is greatest (highest pressure of the tank it's filling) so it does exceed it although only briefly. So mine keeps burning out SPL rpm motors, a 1725 would be a true 5hp rated for 23 amps, so the compressor at max peak amp load would = 100% of motor load or less. Whereas now it exceeds the motor capacity briefly.
At least that's my very rough understanding. I'm not at all knowledgeable on this...
If you look at the ss5 pump it's draw rate is 21.5 amps at peak fill to make that CFM. So assume you put a 2hp motor on there, that motor load rating is 10 amps or so, so first thing you'd overheat it as the load is so much greater than the motor can handle. So if you put a small pulley where the amp draw of the compressor is within the load of the motor you reduce the compressor rpm and output as well. Though I imagine there's some point where the motor would stall if grossly underrated or overpulleyd.
The deal with the SPL from what i think is it's only expected you'll draw past the 100% load rating of the motor when the load is greatest (highest pressure of the tank it's filling) so it does exceed it although only briefly. So mine keeps burning out SPL rpm motors, a 1725 would be a true 5hp rated for 23 amps, so the compressor at max peak amp load would = 100% of motor load or less. Whereas now it exceeds the motor capacity briefly.
At least that's my very rough understanding. I'm not at all knowledgeable on this...
Though there is the service factor as well which is 1.15 on this one, technically at full load it's within specs. I could reduce the pressure of the cut off switch which would lower the load as well.
Who knows...maybe the motor was a dud, pump could be pulling more too. though when i originally got the pulley size corrected the amp load at peak was in specs ...but can't say i tested that under different air temps,etc they certainly need these run capacitors. It's drawing more now so either the pump is pulling it, or the run capacitor is weakened ( i don't know if they just go bad or reduce output or something over time) or if there's a winding or something.
I ran the motor itself for 15-20 minutes other day and amp load was a constant...but it pulled more than i remember it pulling with no load last time.
Who knows...maybe the motor was a dud, pump could be pulling more too. though when i originally got the pulley size corrected the amp load at peak was in specs ...but can't say i tested that under different air temps,etc they certainly need these run capacitors. It's drawing more now so either the pump is pulling it, or the run capacitor is weakened ( i don't know if they just go bad or reduce output or something over time) or if there's a winding or something.
I ran the motor itself for 15-20 minutes other day and amp load was a constant...but it pulled more than i remember it pulling with no load last time.
smokem2020
Well-known member
Last compressor motor I bought was crazy expensive but still cheaper than getting rewound/repaired.
I was helping a buddy get an old Kellogg compressor up and running. We had no info on it other than a nameplate on the pump that listed a certain RPM and recommended 5HP rating. I ordered a 5HP 1725 RPM Baldor motor without thermal overload protection because I ordered a dedicated mag starter with thermal overload heaters. Then I calculated I'd need an 8.75" diameter motor pulley to get to achieve desired pump RPM. The motor has a 1.15 SF and motor amperage was right around nameplate rating of 21 amps up until about 150 psi tank pressure. Then as pressure increased in the tank, the motor amperage rating climbed to 26-27 amps when pressure switch cut out at 175 psi tank pressure. I immediately knew I'd have to reduce the motor pulley a bit. So I ordered a 8.00" diameter pulley and that solved the problem. The pump ran slightly slower, but at no time was the motor overloaded beyond nameplate amperage rating which is what you want to achieve maximum motor life. I think the pulley brand was Maska and I paid about $40 for it with a type QD bushing.