DIY Inverter A/C Compressor - Page 2

Xringer · 08-09-11, 08:35 AM

My guess is lower RPMs likely means more current, which could lead to a hot motor..

I wonder if a current sensor could be used to control AC power input to a motor??

http://ecorenovator.org/forum/applia...r-limiter.html

Something like this circuit breaker, working at high speeds?
Once the motor got running it's max RPMs/load could limited by
the amount of current you allow it to draw..
RPMs would coast down between power cut-offs..?.

If a loaded motor normally uses 8A, but you limit it to 5A, it's bound to run a bit slower..?.

AC_Hacker · 08-09-11, 11:44 AM

Quote:

Originally Posted by Xringer

If a loaded motor normally uses 8A, but you limit it to 5A, it's bound to run a bit slower..?.

Induction motors are a different breed of cat than DC motors.

Here is an excellent explanation of how they work.

Understanding how induction motors actually work will help in giving useful advice.

-AC_Hacker

Xringer · 08-09-11, 01:21 PM

Luckily, I wasn't giving advice, but asking questions.

Wondering if some missing 60hz cycles would cause the motor coast down a bit..
It seems like the motor would be trying to speed up and then slow down,
as the power disappeared, and then reappeared at the next Zero crossing..

To test the idea, I would need to build another control circuit, like this one.
But without the second SSR, since I would only be switching the hot side.
I would also change C1 to a much smaller value, for faster switching.

I'm wondering if the flywheel effect would come into play.?.
Maybe there is a low current setting that would allow my mill-drill to run
without the RPMs zooming up and down too much..?.

What do you think? Is it a waste of time to try it?

AC_Hacker · 08-11-11, 09:12 AM

Quote:

Originally Posted by Xringer

Maybe there is a low current setting that would allow my mill-drill to run without the RPMs zooming up and down too much..?

Is this a problem now?

-AC

Xringer · 08-11-11, 12:26 PM

I have been really busy on other things (getting ready for winter),
so building another power limiting rig is on a back-burner right now.

Once I get it built and tested, I'll know if it makes the RPMs surge,
and post my findings.

08-09-11, 08:35 AM	#11
Xringer Lex Parsimoniae Join Date: Feb 2009 Location: Woburn, MA Posts: 4,918 Thanks: 114 Thanked 250 Times in 230 Posts	My guess is lower RPMs likely means more current, which could lead to a hot motor.. I wonder if a current sensor could be used to control AC power input to a motor?? http://ecorenovator.org/forum/applia...r-limiter.html Something like this circuit breaker, working at high speeds? Once the motor got running it's max RPMs/load could limited by the amount of current you allow it to draw.. RPMs would coast down between power cut-offs..?. If a loaded motor normally uses 8A, but you limit it to 5A, it's bound to run a bit slower..?.

08-09-11, 01:21 PM	#13
Xringer Lex Parsimoniae Join Date: Feb 2009 Location: Woburn, MA Posts: 4,918 Thanks: 114 Thanked 250 Times in 230 Posts	Luckily, I wasn't giving advice, but asking questions. Wondering if some missing 60hz cycles would cause the motor coast down a bit.. It seems like the motor would be trying to speed up and then slow down, as the power disappeared, and then reappeared at the next Zero crossing.. To test the idea, I would need to build another control circuit, like this one. But without the second SSR, since I would only be switching the hot side. I would also change C1 to a much smaller value, for faster switching. I'm wondering if the flywheel effect would come into play.?. Maybe there is a low current setting that would allow my mill-drill to run without the RPMs zooming up and down too much..?. What do you think? Is it a waste of time to try it?

08-11-11, 12:26 PM	#15
Xringer Lex Parsimoniae Join Date: Feb 2009 Location: Woburn, MA Posts: 4,918 Thanks: 114 Thanked 250 Times in 230 Posts	I have been really busy on other things (getting ready for winter), so building another power limiting rig is on a back-burner right now. Once I get it built and tested, I'll know if it makes the RPMs surge, and post my findings.