Hi guys, I'm trying to rig a speed controller to a professional (read: ridiculously fast) blender, that was given as a present, so that it can be used for normal tasks and not send everything flying all over the kitchen. There are also numerous reports of the motor burning out after a year or so because it basically runs too fast.

I did Physics A-Level but to be honest can't remember a blind thing about it, my brother is an electronic engineer but he lives in Singapore.... I'm willing to hack the thing to pieces (read: have already) as it's basically useless at the minute with the speed it runs at.

The motor is marked with 'DC 230V' which I'm assuming is for the motor itself and not the power supply. There are other numbers on it but they mean nothing to me or Google (D712-3523-01CN; HS06023B; Class H; TRAHSMPBL007; 1009) The device overall is rated at 500w. From searching around the closest I have come to what might possibly work is this:

http://www.ebay.co.uk/itm/AC220V-In...ial_Automation_Control_ET&hash=item25807e3b37

My budget is as low as possible.

Whaddaya reckon? Will I kill myself/burn the house down? I'm not fussed about the first but would rather not leave my partner with all the hassle of sorting out the insurance.

Thanks

Jack

 

Or this (looks basically the same) http://www.ebay.co.uk/itm/Input-AC2...al_Components_Supplies_ET&hash=item20d5b075b5

 

Originally large blenders had a mechanical type arrangement for Universal motor speed control, now most are Triac control. I would be surprised if it were not a Universal motor, which the majority have.
But if a professional model actually marked DC, then it could be a bit more sophisticated and have a DC motor?
A universal motor (AC/DC) actually operates in a runaway fashion and rely's on the load to restrict the max rpm.
Max.

 

Sorry, I didn't meant truly professional, just a high end company (dualit) and really expensive. It's a stick blender, not a large bowl based one.

The motor connects to two points labeled +ve and -ve so I'm assuming that means it is in fact a DC motor. Looks very similar to this.

All I can find is conflicting advice on whether I could do this just using a resistor or if I actually need PWM control. I don't mind either way but I don't want to waste my money on getting both. Should I just go for a PWM controller and see if it works, or is there something I'm missing?

 

Yes, I would opt for DC for sure, (although a universal runs on either) but is field/armature series connected.
You could experiment with a decent DC source to see what the desired voltage/rpm would be.
Automotive battery for a start or a small gell-cell.
OR measure the existing DC to see what the minimum is, if variable?
Max.

 

All I can find is conflicting advice on whether I could do this just using a resistor or if I actually need PWM control.

The resistor approach is not a good idea, in my opinion. You might find a combination that works, but the resistor will dissipate a LOT of heat, potentially as much as the blender motor is using, and therefore would need to be rated to 500W or so and would be expensive. You could use something like a lightbulb instead but that doesn't sound like a solution.

Also, the torque of the motor is reduced by the resistor approach, whereas PWM can slow the motor without as much torque reduction. PWM will give you fine control over speed and is more power efficient. There are reasons that PWM is so widely used for this.

The question is whether your particular motor is compatible with PWM control. I think that's highly likely but it'd be nice to hear from a DC motor expert, to learn if there is much risk that it wouldn't work.

 

If it anything like the one in the pic, it could well be made by Johnson Co, they produce a lot of these small motors for portable hand tools and small appliances, they are usually abundant on the surplus market.
They are popular with model makers.
If like the above motors, there should not be a problem running off of a PWM source.
Max.

 

Thanks a lot for the advice. The blender already has a basic speed control on it but it is incredibly narrow, perhaps this is a limitation of the motor and I won't be able to get it any slower. But I've just googled 'DC motor PWM incompatible' and couldn't find anything to suggest it wouldn't work. http://www.ebay.co.uk/itm/Input-AC2...al_Components_Supplies_ET&hash=item20d5b075b5 looks like a likely bet.

 

There are some simple ones for $2.00 ebay 330968404957 to test it.
I doubt it is running direct off of recitfied mains?
I would confirm the voltage across the motor at full rpm to get an idea what range you need?
Max.

 

It's a mains powered blender but I have no idea what rectified mains is. I'm in the UK so mains power is 240v AC. I tried opening up the circuitry between the mains connection and the motor but it started feeling like it might break. This is as far as I got:

Motor connection side:

https://dl.dropboxusercontent.com/u/5722395/2013-07-27 16.29.53.jpg

Mains connection side:

https://dl.dropboxusercontent.com/u/5722395/2013-07-27 16.44.35.jpg


And this is a picture of the motor itself:

https://dl.dropboxusercontent.com/u/5722395/2013-07-27 16.31.02.jpg

Feeling a bit out of my depth. My previous kitchen hack just involved wiring up a thermostatic controller to an extension lead.

Thank you for your patience!

 

I got in! Does this give any useful info on what might work?

https://dl.dropboxusercontent.com/u/5722395/2013-07-27 17.03.03.jpg
https://dl.dropboxusercontent.com/u/5722395/2013-07-27 17.03.16.jpg
https://dl.dropboxusercontent.com/u/5722395/2013-07-27 17.03.43.jpg

 

So it is a 230vdc motor.
Probably a simple controller as the post I showed on ebay, they can be had for up to 230v, but Not sure if they would give you any better range than you already have?
With limited electronics, which yours seems to have, I would guess it has a Triac operating into a bridge rectifier and the output of the bridge to the motor, these are known as simple phase angle controllers, you don't need the large capacitor often used in PWM.
Just guessing though.
(that looks like a Johnson Part number on the motor)?
Is there a part on the large semi with the silver tab at the top in the centre pic?
Max.

 

bta12-600b

Google says it is a Triac

 

Is that teeter-totter thing in the middle a kind of tilt switch, to prevent operation if the blender is not level?

 

No it's to prevent the full-speed and the variable-speed buttons being pushed simultaneously

I cant seem to find a controller rated for 230v other than the one I posted earlier.

 

Do you have a small 240/120v transformer handy? around 100va?
It would more than likely run off of this, if you wanted the higher speed you could just plug into the 240.
Put the same outlet on the 120v TXFMR.
Max.

 

Afraid not. Would something like this do http://www.amazon.co.uk/Stepdown-24...74954417&sr=8-3&keywords=stepdown+transformer ? Only problem is the motor is supposed to be 500W, how much would that matter?

 

It would be worth a shot, the motor is rated for 500w when ran on its rated voltage, the variable speed is going to vary the mean voltage and hence current anyway.
The unknown is whether the 120v is going to make much difference to the control circuit.
The main Triac is most likely not going to be affected, and I suspect the simple phase angle control circuit that it appears to be, the lower voltage could well work.
If it works, it might be the cleanest way?
You don't know anyone with a 120v source to try it on?
Max.

 

Just to confirm, would the PWM controller not be worth investigating for lower speeds? I could bypass the existing circuitry and get some help from better-skilled people than myself. Ideally I'd like to be able to run it as slow as possible as well as as fast as it currently goes.

If the PWM is a bad idea then I'll see if I can find someone with a stepdown transformer. I don't know anyone right off the bat.

Thanks so much for your help!

 

You could try the PWM, you may get better control, but you will either have to gut the existing one or bypass it completely somehow.
If the TXFMR works it would be cleaner and less invasive?
Max.