Line voltage regulator?

[HoldTheOnions]

Hi, I am trying to figure how to regulate line voltage, e.g. from 120 to 60v, but I think I am searching for the wrong thing because I can't find anything that does that, everything I can find has to do with low voltage regulation.

For example, I have a 4 amp motor with a dimmer switch that I have set to draw 1-2 amps depending, but whenever someone does something on the same circuit, e.g. turn on the tv, then my motor speed slows down.  I want it to not do that for cheap.

Thanks for any help.  :-)

[Galaxyrise]

Try looking for a "line conditioner" or "power conditioner" that specifically mentions brownout protection

[Seekonk]

Does your motor have brushes?  Universal motors can run on DC so a DC speed control can work.  Define cheap because nothing is as cheap as a light dimmer,  Those were never intended to be speed controls.  It might work a little better if you attach a lamp to the motor.

[HoldTheOnions]

Hi, thanks for the replies, but a conditioner is pretty expensive and they can't adjust the output voltage, at least the ones I've seen.  I have also tried a speed controller, but it has the same issue, which is if the input voltage drops then the output voltage drops as well, I am assuming because it just stepping down with resistors and not regulating to anything.

I see simple circuits to take a 12v and regulate to a constant 5v output, and that's what I need, but one for 120 to 60 and one for 120 to 90 or so.  Maybe I can't find it because it doesn't exist or my thought process is all wrong.

Anyway, thanks again!

[ovnr]

But it sounds like you're trying to regulate line voltage - that is, AC. And there is no simple way to do that - the closest would be a variac.

Again, check if you actually have an universal motor (brushed motor) - you can probably control it fairly easily if that is the case. If not, you're pretty much screwed if you don't want to spend a fair bit of money.

(Also, non-universal motors aren't generally controllable by varying their voltage.)

[Phaedrus]

Line voltage is AC. The 12V to 5V circuits are for DC, they won't work. For clarity you should say "120VAC" when referring the line voltage, not 120V

It sounds like what you want is a "Variac", or variable transformer. It's the only thing that will drop down AC voltage the way you want. Unfortunately they're rather pricey if you need more than 50W or so, and most are geared toward stepping between 115VAC and 230VAC.

[AlfBaz]

One way to regulate AC is with saturable reactors, 2 of them also known as magnetic amplifiers.
Unfortunate I don't know of any cheap off the shelf solution to your problem, shame the dimmer is open loop.

Scroll down to saturable reactor here to get an idea of how it works http://www.allaboutcircuits.com/vol_2/chpt_9/7.html

[ejeffrey]

What kind of motor is it?

How much is the speed varying?

How much do you need to regulate the speed, relative to the free-running speed when just connected to the line (no dimmer)?

How accurately do you need the speed regulation?

How cheap do you need it to be?

A 4 amp motor at 120 VAC is 2/3 HP.  The _vast_ majority of line-operated motors of that size are AC induction motors.  That means their primary method of speed control is frequency, not voltage.  If you are using a dimmer to reduce the duty cycle until it slows down, it will definitely behave 'odd', with dramatic changes in speed with small changes in load or supply voltage. A variable frequency drive is the right way to control such a motor.  They are more expensive than dimmers, but it is the only reasonable solution if you indeed have an AC induction motor.  There will still be some variation of speed with load, and a bit of variation with line voltage.  If you really need accurate speed control you need a synchronous motor or a tachometer and a feedback circuit.

[HoldTheOnions]

It's a $30 Stinger shop vac that I am using to power my fluid bed coffee roaster.  It pretty much doesn't suck, so I can't recommend for a shop vac, but it will blow 2 lbs of green coffee without breaking a sweat :-)  I was hoping to build a circuit for $10 or so, but apparently that isn't possible.  I think the best solution is to spend $40 on an electronic temperature control, which will be considerably cheaper than regulating the line.  I didn't want to go that route, but with a house full of people I am finding it impossible to maintain temps analogly. 

I do have an old psu and 12/120 transformer in the bin, so I also contemplated combining the 12v outs and connecting to the  transformer and then to the dimmer.  The psu can deliver 22 amps on the 12v, which is more wattage than I need, so if it doesn't blow up, seems like that would give me regulated power as well?

[ovnr]

Eeeh. Please do not build anything line-connected yourself without a clear understanding of how dangerous it is, and why what you're saying doesn't make sense.


Anyway: You have a vacuum cleaner. It, very likely, has an universal motor. So you can just go buy an oversized dimmer for it - that's what adjustable vacuums do. Here is a horrible chinese one - be aware that exposed parts may be live, and it may need more cooling than it actually has.

Note: you must get one that's sufficiently powerful - a lighting dimmer is not going to cut it, and will just generate magic smoke.

[Seekonk]

Just go on ebay and find yourself a 90V DC half to one horsepower speed control. 

[ejeffrey]

You can also regulate the flow by using a flow impedance.  That doesn't require any electrical work, and could be done quite simply and cheaply.  Are you try to adjust the flow rate over a constant-power heater to regulate the temperature?  If so, I would just put the dimmer on the heating element instead of the motor.  Set the flow rate to something reasonable and adjust the power to hit your desired temperature.

[HoldTheOnions]

Thanks for the replies, I got it sorted.

[ovnr]

Thanks for the replies, I got it sorted.

You know, this sort of reply bugs me. It's of course great that you got it working to your liking, but I much prefer it when people share what they did to solve their problem, so that people who find the thread at a later time can benefit from it too.

I've lost count of how many Q&A threads I've found when looking for solutions that end with "Well I solved it" and no further information. Argh. Nothing personal, of course - it's just really prevalent.