I am trying to improve some labs we do in a school environment.

I need to get something that will put a useless but real load on an electric motor that has a C-face

We currently have two labs where the students configure, hook up and drive a three phase motor - one with a VFD - another with a Soft Starter.

Problem is there's no load on the motor - thus limiting my ability to show off the cool things these devices can do

Not having much luck finding a good solution to how to load up these motors. A bell housing, a coupling, and a thing would be perfect. I just need to find the thing.

Any and all help greatly appreciated in advance.

If I've posted this in the wrong place, my apologies.

Dennis

 

One method is to use as heavy a flywheel as possible, these can often be obtained from scrap Treadmills.
The 2hp - 3hp belt motor has them.
They even have a V-belt groove on them.

 

One method is to use as heavy a flywheel as possible, these can often be obtained from scrap Treadmills.
The 2hp - 3hp belt motor has them.
They even have a V-belt groove on them.

Thanks for the suggestion Max. Unfortunately, I was looking for something that would be capable of providing a constant load while not being overly wild for a lab station table top.

 

That's a tremendous amount of HEAT that must be Generated, and then Dissipated.

A practical "Power-Absorber" would be a combination of
a Heavy-Flywheel and a Propeller in a 55-gallon-Drum full of Water,
because the Water can easily absorb a lot of HEAT.

A huge ~48-inch-Industrial-Exhaust-Fan would also make an excellent Dummy-Load,
because it has a lot of inertia, plus a exponentially increasing Load.
.
.
.

 

That's a tremendous amount of HEAT that must be Generated, and then Dissipated.

A practical "Power-Absorber" would be a combination of
a Heavy-Flywheel and a Propeller in a 55-gallon-Drum full of Water,
because the Water can easily absorb a lot of HEAT.

A huge ~48-inch-Industrial-Exhaust-Fan would also make an excellent Dummy-Load,
because it has a lot of inertia, plus a exponentially increasing Load.
.
.
.

Thanks for the idea LowQCab. I was hoping for a solution that would fit on a 2' deep by 5' wide lab bench. I was thinking a generator and a blow dryer?

 

Thanks for the idea LowQCab. I was hoping for a solution that would fit on a 2' deep by 5' wide lab bench. I was thinking a generator and a blow dryer?

A generator and an electric load will work, and can be further used to demonstrate conversion losses since you won't get out nearly as much electrical power as you put in.

Another idea is a pump that pumps water through an orifice. The pump, the fluid, and the orifice are all going to get hot since they are absorbing all the power from the motor and not doing work with it. Hydraulic pumps and valves can get hot enough to confiscate the skin off your fingers if you touch them.

Who is your audience? Little kids? Adults?

 

A generator and an electric load will work, and can be further used to demonstrate conversion losses since you won't get out nearly as much electrical power as you put in.

Another idea is a pump that pumps water through an orifice. The pump, the fluid, and the orifice are all going to get hot since they are absorbing all the power from the motor and not doing work with it. Hydraulic pumps and valves can get hot enough to confiscate the skin off your fingers if you touch them.

Who is your audience? Little kids? Adults?

Thanks for the idea strantor. My students are all adults. Ten to a class. Everybody gets a lab station and each one has a Motor, VFD, and Soft Starter.

 

The simple load will be a small hydraulic pump with a variable relief valve. Certainly heat will be generated, no question thee. That means only short demonstrations. Add a temperature display to the reservoir and a thermal shut down switch like a real hydraulic system.

 

Thanks for the idea Bill. Simple system, easy to control the load. Downside - oh what a mess could be made.

Just some quick numbers.
1 kWhr = 3412 BTUs
1 HP = .746 kw
So 1 hp hr = 2545 BTUs

A little over 3 gallons of water weighs 25.45 lbs

So 2545 BTUs/25.45 lbs = 100 BTUs/lb = 100 F rise in one hour

So closing down on the valve till the 1hp motor was running at full amps should give me 20-30 minutes of time without melting a 5 gallon industrial pail.

Or go for gold – use peanut oil instead and a 5 gallon stainless pot. Heat the oil to 400F and throw in a small turkey. 3 mins per pound are we’re there.

I should probably try that one outside. Our labs are kind of nice

Anybody else got an idea?

Thanks again,

Dennis

 

I designed a hot oil pressure surge test stand to abuse hose assemblies with quite hot oil, I think it was 250 degrees F. Pressure spikes rising to a few hundred PSI several times a minute. The oil was heated by pumping it thru an orifice, with a 5HP pump. it was able to hold the temperature withing +/- 2 degrees F . The customers loved the machine, ran it 3 shifts constantly and wore it out in five years. So they sent it back for a rebuild and ordered a second one as well. That showed ho well pumping and losses can heat oil.

 

There's always the tried and true, stupid simple prony brake. Probably the world's first and longest lasting (still used) Dynamometer technology.

 

The prony brake is indeed still around and it is still a valid tool. Rather cumbersome in larger versions as well. And potentially a hazard for both heat and wear particles. BUT cheap and easy.

 

Thanks for the tip about the prony brake. I think it would quickly get out of control in terms of size and weight. Biggest issue is I would need a bed plate. Something that mounts on a c-face bell housing really would be the way to go. I've been looking for a generator but not having any luck. Will continue the search.

Anybody else got an idea?

Thanks again to everyone for the ideas,

Dennis

 

The school lab I taught had a DC generator as a load, and its output was connected to a bunch of incandescent lamps. The setup included both AC and DC instrumentation, such that conversion efficiency could be demonstrated, as others have mentioned.

 

Biggest issue is I would need a bed plate. Something that mounts on a c-face bell housing really would be the way to go.

Not a prony brake but you can get c-face mount disc brakes.
An air-operated version could present an adjustable load via an air regulator.
https://www.nexengroup.com/power-transmission/friction-clutch-brakes
There are also magnetic particle brakes controlled by electric current.
https://ogura-clutch.com/products-by-type.php?type=09
I've also found that gearboxes full of sand and seawater instead of oil make pretty good brakes.

 

You could, as an alternative to a "C-faced hydraulic pump" and a bit of plumbing, also use a "C-faced" medium power rated servo motor as a generator load. In fact, an induction motor with some DC applied to the windings can also serve as a load, although heating will be an issue. In fact, a "just plain DC" motor will also work as a generator and it could serve as a load. The issue with any of these loads will be measuring the torque required to turn it. That would lead to an adapter extension attached to the C-face mount. Still all very possible.

 

You could, as an alternative to a "C-faced hydraulic pump" and a bit of plumbing, also use a "C-faced" medium power rated servo motor as a generator load. In fact, an induction motor with some DC applied to the windings can also serve as a load, although heating will be an issue. In fact, a "just plain DC" motor will also work as a generator and it could serve as a load. The issue with any of these loads will be measuring the torque required to turn it. That would lead to an adapter extension attached to the C-face mount. Still all very possible.

Yeah, why didn't I think of that? I gave my daughter an old AC servo motor, a transformer, rectifier and big capacitor to use as a hand-crank generator for a science fair project. It worked great! Two motors, one induction and the other permanent magnet, with same bolt pattern could be coupled shaft-to-shaft and bolted together with threaded rod. Four lengths of pipe cut to precisely the same length could be used as standoffs for the threaded rod to pass through, to mitigate shaft misalignment.

TS never mentioned any need to measure torque, I think he just wants a way to place a load on the motor. It was probably my talk of a prony brake dyno which created the pretense of needing to measure torque, so disregarding that your idea should work great!

 

I would go a bit better than pipe sections for the spacers, but certainly adequately squared pipe ends could work. Cut with a band-saw and the faced-off with an end mill, so that all four are the same length. 15 minutes in the machine sop, including setup!