Superflow Sf110

[jsmith]

I am in the UK and 240 volt. Would I be able to use an american 110 volt Sf110? On the superflow website it says that the unit is 120v AC or DC 15A (240v 8A optional). Would I be able to use the unit with a transformer or would it pull too much current?

Thanks in advance.

[bruce]

Why not ask the people at Superflow? They sure would be able to give you the best advice on their product lines.

[DaveMcLain]

I agree, I think I would talk with the folks at Superflow. Wide open, the 110 will draw about 15 amps at 110 volts ac. I've got the motor controller on my bench so it slows down the motors according to what's needed to keep the depression that's needed for the test constant.

Running on 50Hz there in Europe will change the speed of the motors, it will slow them down somewhat I think that'll drop the capacity of the bench slightly but I don't believe it'll hurt much..

[Ellis]

I am in Australia.I have a SF 110 which was made to suit 240v.

[jsmith]

for sale?

[Rick360]

A properly sized transformer to drop 240 to 120VAC should work fine.

I don't think that 50Hz would have an effect on the motor speed. Vacuum motors are universal motors with brushes and run very high rpm (>20,000) without the relationship to frequency that a typical induction motor has.

Rick

[DaveMcLain]

That's very interesting and something I had not thought about, the fact that they are "universal" style motors. That means on a home built flowbench it would be possible to control the speed of the motors and thus the depression with a light dimmer, right? Can you run a universal motor off of a triac style dimmer or would you need to use a Variac to lower the voltage and slow the rpm?

[Rick360]

Universal motors run great with a triac type speed controller. I have one I built for my Makita die grinder. Most light dimmers aren't made for the amperage that a vacuum motor needs. Most vacuum motors will pull ~10amps (120v). If you have several vacuum motors,(my bench has 6) then you would be looking at some pretty stout triacs or one for each motor. Audie Technologies sells a depression controller for flowbenchs which controls the motors in this manner. I am planning on building one for my bench by next Winter.

Rick

[84-1074663779]

Rick, if you are going to build your own high power motor speed controller from scratch, use back to back SCRs not triacs. Getting triacs to turn off at the mains zero crossing points can be difficult with a complex load like a motor.

For most of us, a variac is a simple and robust way to control motor speed, without all the problems of exploding electronic motor speed controllers.

As a retired power electronics engineer I have been through all this before myself, and wish to save you guys from a lot of expensive trouble.

[DaveMcLain]

Don't triacs also make lots of harmonic distortion on the AC waveform? Does this cause any harm to the motors? I've got a pretty stout variac so that might be fun to experiment with. I've also got some heavy duty triac light dimmers that will handle high wattage we'll have to give this a try..

Thanks for the info..

[84-1074663779]

Yes Dave, the triacs work by turning on the full mains voltage at a suitable trigger point on each half mains cycle, and allowing that cycle to power the load up to the next mains zero crossing. The triac is then supposed to turn off until the next trigger point is reached.

That will not hurt the motor, after all the motor commutator does pretty much the same thing.

The main problem with triac light dimmers when driving motors is that they quite often refuse to turn off at the end of each half mains cycle. The triac then suddenly goes to maximum output power and you lose control. Another difficulty is the very high voltages that can be generated by the motor commutator, can destroy your triac.

Light dimmers are designed for driving filament lamp loads not motors. A simple resistive filament load is pretty triac friendly. When the mains voltage drops to zero every half cycle, so does the current and it turns off. The triac also does not receive any high voltage spikes back from a lamp load.

Think about what happens with an automotive ignition coil when the points open, the power does not gracefully fall to zero. The stored inductive energy can generate massive voltages. A motor load can do a similar thing and destroy your triac.

Commercial power tools often have inbuilt triac motor speed control units, so it is definitely possible. These units are specially protected for motor applications and are quite different to simple lamp dimmers. A very high power lamp dimmer might work, or might not work very well, or may just unexpectedly go *pop*. As very large commercial lamp dimmers are not exactly cheap, it is not worth blowing up several to discover all this for yourself. If you already have one, give it a go, it may even work, but don't be too surprised if it goes bang.

The better solution would be to buy a suitably large secondhand variac. These are fairly cheap secondhand, readily available, and are guaranteed to work reliably with your motors, and will last a lifetime.