Electric motor weak, why?

Thread Starter

skeer

Joined Oct 28, 2022
45
So I’m pretty decent with electric and electronics in a broad sense.. but I’m having trouble with this. I’ve got an old table drill press powered by a 1/3hp, 110vac, 1600rpm, 6.3A motor.
The bearings are free, not binding in any way. The windings are super clean… no obvious over heating damage or corrosion. Powering it up it appears to hit max rpm’s.., it’s pretty quick, but I’m able to stop the rotation with my hand.
It just has no umph.
Motor has a single capacitor.. unknown whether it’s starting or running but it’s only 14uf. Also of note.. inside the casing I found a quad of diodes, so it’s a DC motor behind a rectifier. I find that odd, but maybe it’s more common than I know.
I have not measured voltage before and after that yet. But is it possible it’s just not getting enough dc voltage?
 

MaxHeadRoom

Joined Jul 18, 2013
28,617
Sounds like a run capacitor,
If it was a DC motor, it would have brushes.
Are you sure the diodes are not for dynamic braking of the AC motor?
 

Thread Starter

skeer

Joined Oct 28, 2022
45
I, uh.. well I guess I don’t know. I’ve never encountered dynamic braking. How would that look as compared to the typical exposed diode rectifier?
 

MaxHeadRoom

Joined Jul 18, 2013
28,617
Actually DC braking is DC injection of the motor windings after the AC has been removed.
It's an old method, I guess you do not have the users manual for it any more?
 

Thread Starter

skeer

Joined Oct 28, 2022
45
Ahh interesting, definitely no manual anymore but I’d be surprised if any sub-$100 drill press from Harbor Freight would go into that sort of detail.
No honestly this resembled the same rectifying diode pattern I’d seen in a hair dryer.
 

Thread Starter

skeer

Joined Oct 28, 2022
45
I’ll pull it back off and check the voltages, it might not be DC but it sure looks like it.
Regardless of if or not, what would be some probable causes of low torque in the absence of physical damage?
 

Thread Starter

skeer

Joined Oct 28, 2022
45
Blah crap.. no it’s not DC. Induction AC. I don’t know what I thought I remembered.
 
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Thread Starter

skeer

Joined Oct 28, 2022
45
So without documentation on the motor I’d have to ohm out the cap leads to figure if it’s a start or a run, or a combo. And since it’s induction, the cap would have to be starting…yeah?
 

panic mode

Joined Oct 10, 2011
2,715
did you do the torque test on actual motor shaft or drill press chuck?

i remember trying to use drill press at work couple of years go. and everything was just like you described, and it was just lose belt.
 

MrSalts

Joined Apr 2, 2020
2,767
One mechanic on site bought a Harbor Freight drill press and they were using it as a cheap arbor press to press lids on sample cans. The quill eventually cracked and the spindle became slightly offset and, when someone tried to use it as a drill, they had a noisy mess with no power to the drill shaft.
Make sure you can spin the spindle when you disconnect the belt. Lower the spindle snd try again.
 

MaxHeadRoom

Joined Jul 18, 2013
28,617
So without documentation on the motor I’d have to ohm out the cap leads to figure if it’s a start or a run, or a combo. And since it’s induction, the cap would have to be starting…yeah?
For that value I would assume it is start/run combined, IOW in circuit all the time, ensure you get a Motor Start rated capacitor, Mouser sell N.A. made, oil filled paper versions.
(Do not buy Chinese origin version). !
 

Thread Starter

skeer

Joined Oct 28, 2022
45
I'd recommend getting one from a reputable manufacturer from a reputable distributor like Digikey,com

But all the other parts in a Harbor Freight drill are likely sourced from random vendors claiming to supply parts of appropriate quality and specifications so this one might be as good as the original.
https://www.amazon.com/Generator-Motor-Capacitor-Condenser-13-5uF/dp/B018G8AA02/ref=sr_1_6?crid=LJL45EJ2B1S&keywords=14uF+capacitor&qid=1672544254&sprefix=14uf+capacitor,aps,101&sr=8-6
You are right.. HB power tools are all manufactured from various foreign suppliers. Which is fine.. you know I’m not running a fab shop or anything.
did you do the torque test on actual motor shaft or drill press chuck?

i remember trying to use drill press at work couple of years go. and everything was just like you described, and it was just lose belt.
“The” torque test, are you referring to a known process or just camping my torque assumptions with it all assembled? If the latter, then yes.
 

Thread Starter

skeer

Joined Oct 28, 2022
45
One mechanic on site bought a Harbor Freight drill press and they were using it as a cheap arbor press to press lids on sample cans. The quill eventually cracked and the spindle became slightly offset and, when someone tried to use it as a drill, they had a noisy mess with no power to the drill shaft.
Make sure you can spin the spindle when you disconnect the belt. Lower the spindle snd try again.
Yup I can attest, the quills are nothing but nicely polished pot metal. And finding a replacement with the correct teeth is impossible. I was bored back in November so I ground out a channel and embedded a couple steel square rods where this one had broken teeth. Re-ground new teeth. It ended up pretty dad gum good to if I don’t say.
Pinion operates smoothly and there’s no binding when extending it and the chuck.
 

Thread Starter

skeer

Joined Oct 28, 2022
45
For that value I would assume it is start/run combined, IOW in circuit all the time, ensure you get a Motor Start rated capacitor, Mouser sell N.A. made, oil filled paper versions.
(Do not buy Chinese origin version). !
Gotcha!
I’m assuming the cap is the original as it’s also Chinese, model CBB60. I took the armature back out this morning because I was measuring continuity from the power cord leads thru to the case. It appears that one of the case bolts has likely rubbed through the winding insulation.
I added heat shrink to the bolts and all but two slide in easily… I’ve looked at best I can since the winding assembly can’t be removed (by me anyway) and I don’t see any broken wires or scorch marks.
 

Tonyr1084

Joined Sep 24, 2015
7,852
My cheap drill press stalls out all the time. Usually the belt slips. But sometimes when it's set to a high RPM output the drill can bind and stop the motor. I have to be quick on the switch when that happens. But like I said, it's cheap. Planning on getting a good quality floor model this year.
 

MaxHeadRoom

Joined Jul 18, 2013
28,617
I’m assuming the cap is the original as it’s also Chinese, model CBB60. I took the armature back out this morning because I was measuring continuity from the power cord leads thru to the case. It appears that one of the case bolts has likely rubbed through the winding insulation.
I added heat shrink to the bolts and all but two slide in easily… I’ve looked at best I can since the winding assembly can’t be removed (by me anyway) and I don’t see any broken wires or scorch marks.
Does it measure open circuit now?
Incidentally, one of the major failures with Chinese imported motorized equipment is the motor capacitors. :(
CDE is a very good replacement manuf.
Mouser or even Amazon sell them.
 

Thread Starter

skeer

Joined Oct 28, 2022
45
Does it measure open circuit now?
Incidentally, one of the major failures with Chinese imported motorized equipment is the motor capacitors. :(
CDE is a very good replacement manuf.
Mouser or even Amazon sell them.
No the cap is testing like I believe they should. Charging a bit off the dmm on led/cont, then measuring a slow dissipate on AC voltage.
But, I think this last bout of opening the case I must’ve damaged something… likely winding wires. It refuses to spin up on its own and if nudged it’ll spin in both directions.
I tried a known good 40uf cap from a Dewalt portable air compressor and still no go.

d@mn now I need to source another motor. Which I wanted to do anyway really.. A 1/3hp is pretty weak. I have an optional motor that I have a question about. I’ll start a new thread for that.

thanks folks!
 
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