Dimmer Switch For March Pump Speed Control...

[roger mellie]

Hi domonsura

I use the exact same dimmer for my stir plate. It's been working well for the last 12 or so months.

cheers
nifty

Spot On Nifty

Shaded Pole type Motors - like what they use on small fans and washing machine pumps - (dont know about March Pumps - not likely too own one so will never know) - are absolutely fine on Triac based dimmers.

As long as you dont let the rotor sit there locked up - in other words start on 100% speed - I cant see a problem.

Domonsura - when you tried it on the el cheapo ikea dimmer - did it a) get really hot or B) make strange buzzing noises? If not I would think you will be just fine.

Sorry Wortgames to disagree with you - I think you might be right if you are talking about a split phase - cap start type of Squirrel cage 1 phase motor - but I have run numerous things off Triac devices - havent cooked anything yet.

RM

 

[Tony]

I dont have a cheapy dimmer, i have a 6A rated SCR motor speed controller.

http://www.aussiehomebrewer.com/forum/inde...42&hl=speed

I would be interested to know how the little dimmer works.

In mine a variable resistor controlls the gate voltage of a SCR. The SCR is a high current electronic device and as you change the resistance with the little knob, the SCR will switch on and off at a different rate to slow the motor down.

The cheapie may not have this sort of control, especially if it doesnt slow the motor right down.

It may only use a resistor to limit the voltage to the motor. Basicly you get a bigger voltage drop accross the dimmer the more you wind it down so less voltage goes to the pump, thus slowing it down.

This method of speed control is perfect for incandecent light bulbs but doesnt work so well for electric motors.

I do agree with the above comment of the stirplate application. Perfect for that!.

I think mine states its for an Inductive load, which is an AC electric motor.

I didnt get to hook it up this arvo, was busy, but will let you know my findings when i get them.

To be honnest, i wouldnt trust my march pump to the cheapie "unknown"

cheers

 

[roger mellie]

Tony

Google is your friend

http://home.howstuffworks.com/dimmer-switch3.htm

There are a few variants - leading edge or trailing edge circuits.

I think that they work just as well.

RM

 

[Tony]

OK

I just went and had a play!

Running as normal on 240V, a march pump, while pumping water verticly up 1 meter in 1/2" pipe draws about 0.7 Amps or 700mA.

that means its consuming about 170W of power. I didnt test it running dry, i dont like running pumps dry.

So on that note, the cheapie dimmer option would handle it no worries.

I hooked it up to my motor speed controller, wound it up to 10 and switched it on.

It just sat there stalled, humming, and drawing 1.9 Amps

I wound the knob up and down and only the humming sound got lowder and softer.

:angry:

Not sure why, sometimes these devices need a certain current draw or % load to get going and pass power.

looks like im back to the tap throttle

All in the name of research i say!!!

cheers

Edit: Roger, good site but i dont think this baby is Triac based. Triac's are the best as they switch on the positive and negative side of the sinewave.

I think this is SCR based, and thats why it wont fire with the tiny little load on it.

May have to look into building a little triac circuit myself to run it or build a bigger brewery and get a bigger pump.

Oh god what have i done

cheers

 

[scott]

Guys,

Excuse sounding like a smart A$# as an electrical eng I may be able to shed a little 'light'

Tony I do not know what your pump details are but it sounds like an single phase AC motor. Your speed controller from the photo is a single SCR controller. The reason the motor doesn't run is that while this controller does chop the voltage it only does it to one polarity. That is your AC waveform has been chopped but only one half of the cycle. The motor will no longer see an AC waveform. You will need a speed controller or 'soft starter' that is suitable for an AC motor.

Simple light dimmers or other similar speed or temperature controllers work well enough when the load is resitive, ie incandescent or flouescent lighting.

Motors are slightly differrent. Excuse the following jargon. The best speed controllers for any motor is a variable speed drive (VSD) and produces a variable sine wave using a pulse width modulated (PWM) switching of the power transitors. This allows for rated torque up to rated speed and then a reduced torque beyond rated speed. There are limits. At low speeds, as Tony noted cooling is the biggest problem requiring seperately run fans or bigger motors with more thermal mass depending on the speed / torque cycle. This is simply due to the fan not pushing enough air over the motor as most fans are integral to the motor shaft. Beyond rated speed again cooling is a problem as the motor is running at its rated power. Any increase in speed must be match by a reduction in torque otherwise the motor will be overloaded. There are other reasons but not neccessary here.

Soft starters use a back to back arrangement of SCR's (two of Tony's controllers in opposition to each other)and simply chop up the sinusoid positive & negative cycles equally. To the load it presents an AC waveform with a fixed frequency just reducing the effective voltage or RMS voltage. Importantly for a motor it must still be an AC waveform otherwise it will not start. The effect of reducing the voltage also results in less torque which is an important consideration.

The choice of controller depend on the load. In the case of a pump it is refered to as a torque squared load. That is zero torque at zero speed increasing as a squared of the speed. Thus the reduced torque characteristic of the SCR typ eof controller is useful. If you want to run a conveyor full of iron ore or coal you need a VSD capable of full load troque at zero speed to start it.

Speed control of motors is very useful. I have used VSD's for tipping rail cars full of iron ore upside down,....good fun In the case of home brew only you as the tinkerer can decide.

A proper controller is unlikely to damage your motor. Be careful of running them at very low speeds for excessive time. The alternative of throttling fluid flow with a valve can also cause overloading of a motor, impellor and valve wear due to higher back pressure.

If you want a controller go to a good electronics shop and get a proper controller designed for the job. Even if you wanted to get really techo, little PWM controlled VSD's for single phase motors are very cheap.

 

[Wortgames]

Great info, thanks Scott.

The alternative of throttling fluid flow with a valve can also cause overloading of a motor, impellor and valve wear due to higher back pressure.

Not sure if you are aware of these March pumps in particular, but the impeller is magnetically-coupled to the motor so even a completely blocked output has limited effect on the motor itself. It is apparently the recommended method of flow control.

 

[Yorg]

If you want a controller go to a good electronics shop and get a proper controller designed for the job. Even if you wanted to get really techo, little PWM controlled VSD's for single phase motors are very cheap.
[/quote]


What is a good electronics shop?

 

[tommy cooper]

Great info, thanks Scott.
Not sure if you are aware of these March pumps in particular, but the impeller is magnetically-coupled to the motor so even a completely blocked output has limited effect on the motor itself. It is apparently the recommended method of flow control.

hi guys just a question i thought or was led to beleive the impeller was connected via an axle and the motor it self is mag drive brushless as in other posts and threads ppl talk about the seals on the pumphead and motor.

tc :beer:

 

[Doogiechap]

Hey TC
The impeller is Mag coupled to the motor (verified when I pulled the head off my pump when mounting it to my brewstand) so no axle to impeller to speak of. Just to reinterate a point that has been missing since the refreshing of this thread is that you can definately speed control the pump (either via triac control (dimmer) or better with VSD's). The issue that has kept me and some others from persuing this is the reduction of ventilation of the motor as the fan is directly mounted on the shaft. Less RPM = less airflow = magic smoke escaping .
The manufacturer has advised the flow rate can be regulated to a complete stop via restriction on the OUTPUT side. This suits me fine
An interesting thread.
Cheers
Doug

 

[kook]

http://www.marchpump.com/documents/Part%20...9%20Catalog.pdf

My interpretation of this diagram is the same as what everyone else has stated in the past. The impeller is a sealed unit, driven by a set of magnets attached to the motor axle.