In-line diode to reduce power

[AC_Hacker]

Originally Posted by Piwoslaw

Now for something totally different: Would the diode trick work on an electric motor? The 100W circulation pump in our central heating furnace is a little oversized (as is the 27kW furnace, 18-20kW would be much more efficient). I'm wondering whether an inline diode would slow it down, reduce it's power draw and by how much? A slower pump would also be much quieter. Unfortunately this one is welded into the furnace's plumbing so no easy way to just replace it with something more efficient My Grandma's furnace has a pump which is not only replaceable, but has 3 different speed/power settings.

If your motor is a "universal motor", that is capable of running on AC or DC, it would work. If it's an induction motor, no love.

Regards,

-AC_Hacker

[NiHaoMike]

Originally Posted by Piwoslaw

Now for something totally different: Would the diode trick work on an electric motor? The 100W circulation pump in our central heating furnace is a little oversized (as is the 27kW furnace, 18-20kW would be much more efficient). I'm wondering whether an inline diode would slow it down, reduce it's power draw and by how much? A slower pump would also be much quieter. Unfortunately this one is welded into the furnace's plumbing so no easy way to just replace it with something more efficient My Grandma's furnace has a pump which is not only replaceable, but has 3 different speed/power settings.

From my (limited) experience, the combustion air pump in a (80% efficiency) furnace uses a shaded pole motor. The diode trick won't work, and you don't want to slow it down as that would richen the mixture. I have heard that some new furnaces with efficiencies above 92% use an inverter drive motor along with a combustion gas sensor (like in a car) to automatically adjust for maximum efficiency.

[Xringer]

I think a diode might not work at all and it might burn the motor up..

For a small AC pump, maybe a motor speed controller that was designed for AC motors?



Big Horn 18852 Router Speed Control (19122)

Years ago, I used one on the large blower on my wood stove.
I could vary the RPMs from full speed to very slow.

[Piwoslaw]

The pump I have in mind is AC powered and pumps water through the furnace to the radiators (it's not for blowing air). I'll look for an AC motor speed controller.
Thanks

[AC_Hacker]

Originally Posted by Piwoslaw

I'll look for an AC motor speed controller.

Before you shell out your money, better check what kind of AC motor the controller you might purchase, is compatible with.

Router motors are not induction motors, they are universal motors.

Electric drills, routers, hand held grinders, etc are all universal motors. They all have brushes... look for the brushes.

I have three AC water circulation pumps in my basement, and they are all AC Induction motors... no brushes, no easy way to control speed.

Check this stuff out before you spend your money.

Regards,

-AC_Hacker

[Xringer]

When searched on AC motor speed controls, I got that router unit as a hit.
I figured it would work with Induction motors because of the description:

"The variable speed dial allows for full horsepower and torque at all speeds
from 0 to full RPM. Use with routers, sanders, grinders, drills & 120v AC
or universal motor 20 amps or less."

I'm pretty sure my old wood stove motor is an induction motor and the speed control
the stove shop sold me looked suspiciously like a regular old incandescent light dimmer..

My circulator pumps are all Taco pumps and they all look a lot like this one..


Except for the Bronze pump that came off the old solar HW unit. It looks like brass..

[NiHaoMike]

You can use an inverter (VFD) to control the speed of an induction motor. Small induction motors can be controlled by phase angle controls (basically dimmers with additional circuits to ensure balanced control - Dimmer curve hacking ). Just try it and if the motor isn't getting excessively hot, it's working properly. Or use a speed control for a ceiling fan, which are induction motors. (One ceiling fan control I have taken apart is a very simple cycloconverter that reduces frequency and voltage by cleverly skipping AC cycles.)