Need Help with HF Router Speed Control

[phrog]

I just purchased a HF Router Speed Control. Before connecting my router, I plugged a voltmeter into it. At "Full" Setting, it shows 119 volts. On "Variable," for the "L" setting I get 90.0 at low end and 90.1 at high end. For the "M" setting I get 90.2 for the low end and 91.3 for the high end. For the "H" setting I get 91.4 on the low end and 96.5 at the high end. The last 4 volts to achieve the 96.5 is in the last 3 or 4 degrees rotation. It seems that there is not a great spread from 90.0 at one extreme to 96.5 at the other extreme and most is in the very last tweaking of the control knob. Just wondered what others have experienced with this device and should I take it back for an exchange. Thanks.
Richard

[eccentrictinkerer]

The speed control uses phase-angle power control. This means that the power is controlled by turning a triac (or a pair of SCR's) on at some point during each half-cycle of your AC power.

If you call for 50% power the triac turns on half way through each half cycle giving you half power. At 25%, the triac waits until 75% into each half cycle to turn on.

This is the way light dimmers work, also. A router control incorporates a circuit that senses back-EMF to help keep the RPM's up under load (much the way a lawnmower governor works to keep the RPM's constant).

Your voltmeter is reading a very spiky waveform and is really reading peak voltages.

An iron-vane voltmeter or a true RMS voltmeter is the only way to get an accurate reading.

Hook an incandescent lamp up to verify that you're getting a smooth range of control.

[Tom Slick]

Where you thinking it was a variable resistor or reostat? those only work on DC or light bulbs.

as eccentrictinkerer eluded to, it controls the motor speed through modifiying the AC waveform. cheaper multimeters don't like reading modified waveforms.

[RodKirby]

The speed control uses phase-angle power control. This means that the power is controlled by turning a triac (or a pair of SCR's) on at some point during each half-cycle of your AC power.

If you call for 50% power the triac turns on half way through each half cycle giving you half power. At 25%, the triac waits until 75% into each half cycle to turn on.

This is the way light dimmers work, also. A router control incorporates a circuit that senses back-EMF to help keep the RPM's up under load (much the way a lawnmower governor works to keep the RPM's constant).

Your voltmeter is reading a very spiky waveform and is really reading peak voltages.

An iron-vane voltmeter or a true RMS voltmeter is the only way to get an accurate reading.

Hook an incandescent lamp up to verify that you're getting a smooth range of control.

I knew that

[LCHIEN]

I knew that

me, too .


BTW, actually, I cannot think of a single way you could damage your trim router by just plugging it into the peed control and turning it on. The heck with the light bulb.

[eccentrictinkerer]

I knew that

Sorry, TMI, I know. My daughter says that when asked for the time, I tell people how to build a clock!

I spent many, many years working for a company that built SCR/Triac power controls for industry. The most powerful "dimmer" we built was rated at 800 volts - 3000 amps (to heat molten glass by conduction)!

We designed and built all of the power supplies that heat the Cheerio "guns" at General Mills. Each gun has a 7' tall rack of SCR's driving a 3 -phase 440 volt - 600 amp load.

[eccentrictinkerer]

me, too .


BTW, actually, I cannot think of a single way you could damage your trim router by just plugging it into the peed control and turning it on. The heck with the light bulb.

You're exactly right. The light bulb would just give a visual indication of control. Listening to a router spool up is much more fun, IMHO.

My 4 year old grandson loves tools and motors and begs to turn on the big tools. I think we're going to have a lot of safety sessions in the next several years.


(Loring said "peed")

[phrog]

Many thanks to all those who replied. Especially thanks to eccentrictinkerer for his long explanation. I'm not sure I understood all of it but certainly got the gist. Yes, I do have a cheap voltmeter - not into electronics enough (obviously) to justify the cost of an expensive one. You guys are so far over my head that I will just take your word(s) for it and plug in a light bulb. Again, thanks.
Richard
PS Yes, I did notice that Loring said "peed." I think that a control for that would be most useful to anyone with "night" problems - a peed control, yeah, that ought to work.

[John Hunter]

I have a much older model from HF, have been using it for years with a Ryobi 1 1/2 HP router with no problems at all.

[phrog]

I did try the light bulb trick and it dimmed the bulb just as you said it would. I then plugged in the router and it controlled the speed just as you had predicted. Should have tried this to begin with rather than bothering you guys. In any case, thanks to all who replied.
Richard

[Tom Slick]

Just as a side note,
the question of using an external speed controller with a router with an internal speed controller comes up once in awhile. They don't play nicely together because you are hooking two systems together that do the same thing. you are feeding a modified signal into a controller that wants to modify the signal again.
I don't know the nuts and bolts of how it works (I'm sure eccentrictinkerer does!) but I know that electronically they don't play well together.

[eccentrictinkerer]

Just as a side note,
the question of using an external speed controller with a router with an internal speed controller comes up once in awhile. They don't play nicely together because you are hooking two systems together that do the same thing. you are feeding a modified signal into a controller that wants to modify the signal again.
I don't know the nuts and bolts of how it works (I'm sure eccentrictinkerer does!) but I know that electronically they don't play well together.

The internal router speed controller depends on a nice clean sine wave (AC voltage) to do its thing. It uses the zero voltage crossover point to determine when to turn on the triac.

If you give it a chopped up waveform from another controller, it gets really confused. It probably wouldn't hurt anything to try it without a load on the router. It would just sound and run weird, sort of like a lawnmower with a mis-adjusted governor. DAMHIKT