220V DC Motor startup current and speed control

Hi Guys

Showing my lack of knowledge in some areas here, but - I’m helping my son build a potter’s wheel and we’re using a 220V dc motor from a running machine which will be speed controlled by one of these:

Speed Controller

Has anyone here used one of these controllers? What method does it use to control speed - is it pwm?

The motor is rated at 200W, so do you think a 3A fuse on the 220v ac input will be ok? I don’t know how to calculate what the startup current is likely to be but is it likely to exceed the fuse rating if the supply is switched on while the speed controller potentiometer is set to maximum speed?

If it is, other than not doing that (!), I could find a way of introducing a soft start circuit, but if the speed controller uses pwm, and if the soft start also uses pwm, will it work?

AC or DC motor?

If AC motor, and that controller is for AC motors, and the 220V is typical for AC mains, so I assume you have an AC motor: that’s phase cutting. To say it very crude: that’s the AC version of PWM.

The motor is rated 200W, that’s <1A, startup current will be higher but a standard (slow type) 3A fuse won’t blow instantly if the current is more than that.

Thanks wvmarle, but it is a DC motor.

We were originally planning to use the control system from the static running machine, but it had, separate from the AC/DC converter circuitry, a separate display board with touch sensitive switches which had a built in 10 minute timer we couldn't program away. It was just far too complex for a simple speed control, hence we decided just to use the motor and the speed controller in the link.

What makes you think an AC power controller will work with a DC motor?

I believe it's time for you to stop right here. 220V AC can kill. 220V DC is truly deadly.

The speed controller I referenced is a DC motor controller. The controller has an AC input but DC controllable output.
Operating Voltage: AC 220V 50hz
Control motor Power: 0~500 W
Output DC Voltage: DC 0~220 V Adjustable
Over Current protection:Yes
Short circuit protection:Yes
Word Explanation:
P1 P2 :connected as emergency stop
M+ M-: Motor + Motor -(DC Output)
AC AC: 220 AC Input
Scope of application: Apply to <500W DC motor
Installation method: Panel screws installation
Size(LWH): 100 x 60 x 110 mm

OK, didn’t read it that carefully.
Specs seem to match just fine.
Other than that - there doesn’t seem to be much use of this kind of voltage/power in the Arduino world, so not likely anyone in here actually tried it out.

It’s not PWM, those controller are phase angle fired SCR’s.

A fuse will not prevent damage to the SCR’s, they will fail shorted well before a fuse will clear, unless the fuse is a true I^2T device which would cost more than the drive itself. You could and should use whatever fuse was in the treadmill to protect the wiring but the bottom line is that you cannot save a solid state device from failure with a common fuse.

A proper motor drive would have an in-built acceleration/deceleration ramp that prevents startup and shutdown at full speed. Case in point was the original treadmill. You get what you pay for. Honestly, what do you expect for 15 quid and free shipping? It’s a dirt cheap Chinese design and yes, it's a fragile piece of crap. Even the seller admits it’s crap and tells you not to turn it on at full speed.


I think for the cost the controller will be fine. It will at least get you going. After sometime using it you will find out what happens when you don't start the motor at "0" commanded. Or perhaps you are unhappy with the stability etc. and want to upgrade, Perhaps it will do fine for you application.

I don't see how it can damage the motor (as long as its fused, doesn't need to be fast to protect the motor).

As stated previously, the operation of this controller is simple. Consider a regular phase control dimmer (pre CFL/LED). Convert the output to DC (rectifier and maybe some filtering, maybe not).

That's why it is so inexpensive.

I've worked on those machines, and the phase angle controlled SCR's seem to work fine.

Go for it.


Thanks for all the input guys.

Considering the (relative) low cost of this unit, I decided it was worth giving it a try and have ordered one.
I don't think the startup current will turn out to be an issue because it turns out that it will be highly unlikely that this motor will ever be run at anything like full speed. Even if it was, and the controller left at full speed setting, the motor is rated 200W and this controller up to 500W. The a.c. input will be fused at 3A so I think the only thing I'd need to be concerned about would be the mechanical loading on the motor mountings due to the startup torque. That's a different subject and has been well catered for!

Oh yeah - regarding it being made in China, so were the original electronics from the running machine :slight_smile:

Thanks again!

When it comes to components, there’s a big price gap between “domestic” (aka “made in China”) and “imported” when you look on marketplaces like Taobao. The “imported” ones can easily cost 3-5 times the “domestic” versions. I’m quite sure that there’s also a big quality difference between the two.

This accounts for a.o. the popular BT136-600 TRIAC. For a simple light dimmer a domestic version would most likely work just fine. For the 600W AC controller I built a while back it was a no-brainer to go for the more expensive imported part (which was still fairly cheap). Same for the X2 safety capacitors: about 10x the price for an imported, branded product, but at least you can be sure it’s going to do the job.

Nowadays everything is built in China, and the assembly itself is usually done quite well. It’s the components that are used that really make the difference. Lots of excellent products are built there - those are usually sold under well known Western brand names. Lots of crap is built there as well - usually sold unbranded, meaning price is the only thing they can use to differentiate themselves with the competition…

The power supply you’re looking at is probably populated with domestic grade components. I’d expect 200W to be safe, after all it’s less than 1A, but wouldn’t want to push it to the 500W limit. Mind that startup current is a multiple of running current, which is why you should always turn down the knob before starting up.

For devices with a significant initial inrush current use a slow-blow fuse - remember a fuse is basically
to protect the wiring, not the circuit (it will help protect motor and transformer windings as that is just wiring).

Semiconductors blow much quicker than any fuse wire....

NTC thermistors are often used to limit inrush current - they work well.


NTC thermistors are often used to limit inrush current - they work well.

I'd expect a PTC to work better for that.

Nope - wrong way round.

These gadgets start off high resistance when cold, then as current flows and they warm up their resistance drops. I'd call that NTC.... they run pretty hot.

eg EPCOS make them, and typically have a >50:1 change in resistance between cold and at rated current.

I've used them in many products.

Some big power tools such as ( eg) 9" angle grinders use them in series with the supply to reduce the big 'kick' on starting without significantly reducing full power. They're typically rated around 2kW.

They call it 'soft start' and it takes a few seconds to reach full speed, as against a mighty kick which tries to tear the tool out of your hands if fitted with a heavy grinding disk. A nice feature.


Ah, got it.

I thought it'd be meant to limit the current by increasing resistance when the current is too high, heating up the part. Like a self-resetting fuse.