About AC dimmers/speed controllers (“2000W SCR”, Dremel and etc.)

Off-topic Chatter
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More than a year and half ago I modified my Dremel 395 clone with an external speed controller (bypassed the internal one) attached to its input cable, one of these:

https://www.aliexpress.com/item/Free-Shipping-AC-220V-2000W-SCR-Voltage-Regulator-Dimming-Dimmers-Speed-Controller-Thermostat/32640368025.html

Over time and due to me having to rotate the cable for it to fit inside the case, the connections broke and I had to overhaul the setup. I did it by attaching a connector to the thing, this way no cable rotations were required:

Unfortunately for me I blowed up the enduring SCR I purchased originally while testing the stuff, thus I ordered a new one and replaced it. This second unit only lasted a handnotful of months with very little use (!), I thought I had won a bad unit then and proceeded to order a 3rd unit. Unfortunately, the 3rd unit has lasted less than a mid-80s turbo F1 engine in :facepalm: qualifying setup. Now this smells straight fishy and I am pissed because it takes me a lot of hours to open up the plastic box, replace the part and close it again. I say this smells fishy because it could be that certain people behind the manufacturing of these 2000W speed controllers may be doing something wrong.

Now, with regards to the Dremel 395/MultiPro speed regulator:

Some seller links:

Any relevant feedback with regards to those? The one which came with my tool ended up suffering overheating issues, this was the main reason for me to switch to a bigger, external controller. As you can understand I feel a bit weary with the above “2000W SCR” units.

Cheers fellows

Sun, 01/28/2018 - 05:03

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Hi Barkuti ,

We meet again on the electronic fields.., sorry to hear about your problems , but somehow , this should be the end of the myth that ANY ac dimmers are gone work , no matter what , with any load , resistive or inductive...

Some time ago I'd done the same "mistake".., in fact I tested the same module as your's , for a 1100W stand mount drilling machine , and with the same result :failed module ! I fact I was expected that , especially after I reversed engineered the schematic .( for some info of this , you have a video from Big Clive ,Reverse engineering of a mains power controller. - YouTube )

I ended up with installing an module recovered from a defective vacuum cleaner ( motor shorted )

This china made module is ONLY for resistive loads , as heaters and incandescent lamps , the manufacturer suppose to state this clearly , as many big and trustful companies does for their products .The question is : who is making these ? The answer : nobody knows !!!

But , more than that , checking the the conditions required for the QUALITY of the components used in a 220-240 Volts grid , I had my heart stop for a moment :is a killer module and if I have the power , I'll state this as a criminal act towards consumers !!!...

These said , I'd suggest you to look for a industrial power controller for vacuum cleaners (500-1000W) , as long as your Dremel has about 130W , any will work .

These ,has a truly zero detector , the gate of the triac is optoinsulated from the mains , and the snubber circuit is designated in a RCL grid , to avoid any spikes from the inductive loads . Probably , will be a little pricey (or you can do like me ,recovered one ), but once in place , will do its job with no problems !!!

For sure , you'll be able to find something like this at the repair centers , or ,maybe , you have already a defective vacuum , blender , pump ,kitchen robot , anything that has a variable speed motor... Cheers to you , too !!!

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LoL! We meet again in DIYland cera@1967.

Of course my electronics theory together with my english listening could improve. I've only watched Big Clive's video on the “2000W SCR” briefly and honestly do not really know what's wrong with it when used with inductive loads (Maybe some in parallel with the load diode is missing?). Good to know it at least is adequate for resistive (capacitive?) loads.

I honestly had in mind to attach a rectifier bridge plus some filtering capacitance to boost the average voltage hitting the multitool. This way the motor's inductive transients would have been handled by the filtering capacitor stack, doesn't it?

Now speaking seriously, I've bought one of the above linked variable speed switches for Dremel MultiPro/395. I believe the original one was/is undersized (my tool's motor is 160W anyway), the stuff overheated noticeably (heat coming out of it by the side). Such speed controller also uses a (much smaller) TRIAC, but I hope to enhance the its cooling this time by attaching some tiny homemade copper heatsink to it. Such repair will be fast and hope it endures.

If not, I believe I'll end up buying a better tool to start with: https://www.aliexpress.com/item/HILDA-220V-180W-Variable-Speed-for-Dremel-Rotary-Tool-Electric-Mini-Drill-with-14pcs-Accessories/32849366408.html That looks to have a proper speed controller while still fitting inside my tool's carrying case.

Cheers :-D

4

None of the above improvements you describe will do any good ! Those dimmers are good enough ONLY for resistive loads (no inductive or capacitive , NO !)

The problem with those resides in the fact that an inductive load will make a defazed sinusoids ( current behind voltage ) ,and a capacitive load , the voltage behind current , and the command schematic will heratically "find " a zero to detrigger the triac. As you saw on video , the " command" for the triac ( potentiometer , resistances , capacitor and diac ) is supplied via the motor , and there will be a lot of armonics , generated by the tool ,itself ...This , will be translated in opening and closing of the SCR device not in zero , but somewhere on the sinusoidal cicle .., with a lot of heat generated and finally destruction of the SCR's junctions ( do not forget that the triacs are not guaranteed in all the 4 quadrants !)

That's why the schematics for electric motors includes an IC with the capabilities of command ONLY in zero point , regardless the nature of the load...

Anyway , I'm glad that you found a good replacement for the speed controller , and the idea of an additional heat sink is beneficial .., by the way , did you checked the propeller that should be there for active cooling.., maybe is clogged with dust , or is moving freely on the shaft.., I was just saying...

Wow ... I just opened the link you sent.., cool looking machine , and the price seems to be good . Go for it !

See you around !...

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Mmmkay cera@1967, as far as I understand the main problem lays with the motor's inductive harmonics causing undue TRIAC triggering (mmm, sort of explains why the tool's sound was so nasty). Does this mean the BTA16 inside the box was overheating despite its relatively beefy heatsinking?

The HILDA HLD-180W is also available at Banggood (with a lot of accessories I just do not need or want). It was there I saw this interesting user picture (the sort of stuff worth its weight in credits LoL!):

Another more powerful JD3321C version also available.

Cheers :-)

P.S.: no dust problems inside my tool, I cleaned up everything inside when I bypassed its internal SCR.

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Yeah man , the SOUND is telling you that something is not right , the sinusoids are "ripped" apart (as a tremor ) ..., and the triac was heating , that means that , with the heating , the gate is becoming more and more sensitive at the current needed for triggering.., as an avalanche process !...Visualizing the form of the wave , with an oscilloscope , will show you how distorted this is..! Generally , the triacs are known to have higher gate currents than tyristors , and beeing instable in the 3-rd and 4-th quadrants of the sinusoid wave.

From your picture , the dremel machine seems to have all the good " ingredients" : bear rings on both sides ,easy access for the brushes , big motor , cooling propeller , and in the back side I can see a capacitor of type "X" or "Y" , the ones that suppose to be used with 220 V devices ! Nice ! I think this could be a good investment !

7

I never knew what a quality rotor tool was until I purchased this.
https://www.amazon.com/Proxxon-38481-Professional-Rotary-Tool/dp/B001FWXEO6
I use it attached to my lathe sometimes to do precision milling. I first found out about the tool when my old dremel tool died.
On a mini cnc forum, I read some guys talking about how dremel’s were crap, how they had so much run out, bad bearings, vibration and were weak.
They were all recommending the proxxon 38481. So I bought one about 5 or 6 years ago and I can tell you it is the best money I ever spent on a rotary tool. I recommended this tool before in another thread where I describe it a little better. I know it cost more, but Its an investment in a well made tool. One of the best features is the full wave speed controller, doesn’t bog down at slow speeds.

8

Received the 395 power controller/brush carrier and heatsinked its ST Z9M onboard triac the best I could, there's barely any room left inside.

My clone's engine is indeed a tiny bit bigger, had to open up the carrier's winding feeding reeds a little. The new lever's too short, will have to level out the case above it LoL.

Working smoothly. :-)

Cheers

9

Work complete!

Question to cera@1967 or any other knowledgeable fellow, what makes this power controller sound and work right versus the outboard “2000W SCR”?

Cheers :-)

10

Wow, just bought 5 pairs of carbon brushes and just after replacing the very worn out set in the tool, the speed controller died on me.

As cera@1967 said in the past, this was to be expected.

I am right now wondering if the above mentioned Hilda 180W rotary tool features a God's way speed controller. And not just :???: wondering. If any of you has something worthwhile being said, please do so.

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Barkuti the best money I ever spent on a rotary tool was buying a Proxxon. https://www.amazon.com/Proxxon-38481-Professional-Rotary-Tool/dp/B001FWXEO6
I mentioned it before in this thread, but its a seriously professional tool that will last you for a long time. I know it’s not cheap but built better than any rotary tool I have owned. The full wave speed controller works flawlessly. Full roller bearings in the shaft and motor. If you use a rotary tool for alot of different things, then my vote goes to spending a little more and get the Proxxon. Just my 2 cents :wink:

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Can understand moderator007, I also love quality. Gear like that will have to wait until I fix my mind programs and I can attract general and financial abundance.

In the meantime, bought the 180W Hilda tool with a proper bag. Had to ask for help for such a thing.

:-)

13

I did the same setup when my dremel switch went bad, i also went with a lipo battery, but my question is, when i apply too much pressure when sanding, the voltage regulator starts to beep and the motor stops.
any one know what that could be from?
IMG-1581 hosted at ImgBB — ImgBBrc gliders

14

Smells like some sort of overload protection in the controller; when you increase the pressure when sanding, the engine torque increases and this means more engine input current.

You must somehow limit engine current, or upgrade the speed controller if it is a very annoying problem.

15

yes that makes sense, thanks for the reply,
if i upgrade the speed controller, would i need to up the W on the controller? any idea? or point me to the right direction which ESC i would need to use.
thankyou

16

You are providing too scarce information, this doesn't helps. If you were to carefully lay down your problem's information in a single message, the answer would very likely be already in your hands.

What is W? Wattage? Probably, just probably. This is because controllers are rated for voltage and current.

A suitable controller for your rotary tool must meet both its voltage and current input requirements. There is no problem if the controller exceeds well both, and in fact this is preferable, namely the current requirement if going to buy it from china.

In that photo of yours I just see some battery powered rotary tool (7700?), connected to some sort of high discharge li-ion (?) battery. This has to do with the input voltage requirement. From here I can only guess that the battery is 2S.

Suggestion: If 7700, you could get a nice power boost by using a 3S LiFePO4 battery, which could easily deliver around 9V even under load to the tool. The reason to use LiFePO4 is its flat discharge curve or stable output voltage, which means you won't feel the battery going flat as you discharge it, i.e. full output power until the very end or very close.

17

thanks for the notes, yes i am using a 2s 8.4v 5000mAh lipo battery, and the tool is a very old hand held dremel, the variable switch broke and so i made this, i am familiar with LiFe batteries. I will take your suggestion and give that a try see what happens. thank you

18

dlgglider, according to the available information I've found about the Dremel 7700 (here and there), the stock tool is like a joke toy. The manual I've found @manualslib.es specifies “200mA” as battery capacity, something I could feel to be completely wrong starting with the fact that 200mA specifies a current figure, not a capacity one. In this Dremel 7700 thread @ Parallax forums someone mentions 800mAh; so a small battery. I guess the battery could probably provide 8 to 12A continuous, just probably. With these figures it is easy to guess that the stock battery should not be able to provide 90W continuous in a reliable way. The stock motor, if designed to last, may be rated for that figure or a little bit more.

I am seeing related ads in AliExpress where similar DC motor speed controllers are rated for 2 to 5 A continuous (this or that), which is small. Or this other one, rated for 10A continuous…

If you go with a higher voltage battery, the higher voltage will allow the motor to reach higher rpm; the current input will also increase. I don't exactly know how a DC motor's impedance varies with input voltage, but as far as I know it remains about constant, which means that every increase in input voltage will also cause an increase of input current of the same magnitude. So if you go with an increase in input voltage, don't go overboard or the engine may not handle it (P = V × I).

This ZK-BMG motor governor is rated for 12A continuous and 20A peak. Costs a little bit more, but unduoubtely looks pretty neat. Or you could go with this another one, which meets all the specs you need very well whether you decide to go with a higher voltage battery or not.

As a side note, remember that if using li-ion or LiFe batteries in series without BMS, in case they go flat it is very recommended to charge them at least a little bit just after that, to prevent any chances of leaving a reversed cell in the battery.

19

Barkuti, thank you for the long and informative reply, makes total sense, in fact im using a 3000mAh battery on this now and it must be over dumping and shutting off the unit, it must be a security thing, but looks like i might need a new dremel anyways as it its difficult to hold this one while the battery dangles lol

i also have a voltage checker attached to the balancing lead, this way i know not to take each cell down below 3.2 volts.

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In my opinion and experience cutting off at 3.2V, although no problem, is a tad high, particularly if under load which I guess you don't check.

I've scavenged some 18650 battery packs in the past, succesfully recovering a few cells lying below 2V (1.6 - 1.7 V) in a particular case (Samsung 26C cells out of a 6-cell pack), although I discarded two of them after a self-discharge test of a few weeks. If you were to ask me, I'd tell you that down to 2.5V is completely fine, particularly for quality batteries.

If you want to prolong the life of your li-ion batteries, it's not really about avoiding the lows… it's about avoiding the highs.

If interested, read BU-808: How to Prolong Lithium-based Batteries @ Battery University. Lots of wise information there.

A brand new laptop battery should succesfully deliver hundreds of cycles. However, in practice most of these batteries are kept always fully charged inside the laptop, something which kills them. I know this from experience.