Sooo, the tinkerer in me came up with this crazy idea:
Since Dremel and clone tools use universal electric motors, along with most drills I believe, a hack can be made to increase the tool power output if we can afford to feed it via a “supercharger” stage: a bridge rectifier plus a handful of μF worth of 400/450V electrolitic capacitors (I'm on 230VAC mains). Universal motors use dual winding stators sandwiching a brushed rotor and work either with AC or DC.
If your tool is single speed (full blast), this applies directly. If not, and you want to have variable speed/power, you need an AC triac based speed controller with good power rating like the generic ones I've got on eBay (2000W speed controller, based on BTA16 triac), because the speed controller is to feed the supercharger stage, and then the tool's internal regulator should be bypassed (piece of cake).
I've set the trafo straight at 230VAC because obviously we're not using a “classic gearbox” (transformer). Other significant parameters: load at 330Ω (my tool is rated for 160W at 230VAC, since W = V² / R, R = V² / W), “filter” (booster) capacitor value 500μF.
Since the tool already used a (bypassed too small unreliable) triac/diac AC based speed controller, the average voltage curve value is valid for a direct comparison vs the 160W/230VAC rating (triac/diac triggered controllers lose the first ≈7° of the pulse slope on 230VAC because of 28V diac triggering).
Am I inferring correctly an average of ≈300V input in these 330Ω motor windings with a bridge rectifier plus 500μF capacitor stage supercharger?
Would this mean an increase of up to more than 30% (300/230V) in rpm and (!) a smidge above 70% in power output (272+W)?
Quite substantial, colleagues.
Please, don't go overboard with something using this idea… LoL!
Know what? I've scavenged a couple of old PC power supplies, and found 4 × 2A05 rectifier diodes plus 2 × 330μF 200V and 2 × 680μF 200V electrolitic caps (505μF on 2S2P assembly). Of course they're a tad hulky, especially the fat 330μF ones (well above 10 year old PSU). However…
Playing with mains is serious sh1te, so I'll make sure I can build a more or less well sealed box for the supercharger stage. I'll also be using scavenged AMP Mate-N-Lok connectors for interconnection, and the cables in them are only rated for up to 300V (!). Fortunately, the caps would get auto-discharged upon switch off or mains cable unplugging.
We'll see.
Stay tuned!
GO GO 270W Derpmel!!!
Cheers ^:)
Originally posted on Mon, 04/10/2017 - 13:39; lil fixup.
My first question would be: How do the cutting tools hold up to that high speed. Cutting discs for angle grinders and saw blades for circular saws are rated up to a specific speed. That is why it is unadvisable to use a circular saw blade on an angle grinder. The saw blade might just shatter to piece from the amount of force that gets on the blade from spinning.
2nd thing is do actually get more torque out of the motor? I highly doubt it but if you actually do how will the rest of tool hold up to the extra force?
I would increase the amperage not the voltage its more usable to have more torque. You need to think about things like the gearing and bearings they will over heat with to much RPM.
Gears usually heat more then the engine.
This will work if you increase the voltage you will get more power from the engine guaranteed. Increasing the amperage will give you more torque so more cutting power it wont stall in other words.
dekozn, these tools' engines are relatively small, and their accessories also usually small in diameter, so usually no problems. Of course, it is your responsibility to keep your tool's rpm under the maximum allowed for its attached accessory.
With regards to the increase in torque, bear no doubt. The winding's DC resistance is constant, and although we should be speaking of impedance here, at least for the same rpm and/or load the way current and voltage scale should be about linearly proportional. DC motors work this way as far as I know, these ones aren't much different. That's the reason I estimate such overall raise in power output, although for obvious reasons, such increase shouldn't be used continuously to prevent an early engine failure. To put it simple, if we are increasing rpm by a factor of 300/230 (voltage increase), let's be wary while, at the very least, using the last “quarter” of turn in the gas handle. ;-)
everydaysurvivalgear, the only stuff I can do is to increase the voltage, and that is done in this way because we're increasing the overall voltage at the motor's windings through setting some caps in parallel with the windings, caps which retain and discharge energy while the AC wave “returns” to 0. If you try to stall the electric motor, torque will increase dramatically along with the reduction in rpm, up to a peak point (maximum power, V × I = rpm × τ), also indicating a reduction in the motor windings impedance because of effects in its magnetic field. This is as far as I understand this; maybe HKJ or some other expert could elaborate further.
Well, for now I'll pass on doing this. While I am rebuilding the speed controller box for it to use an AMP Mate-N-Lok connector, definitively there's no additional space in the tool case's innards for a much bigger controller box.
The idea would work for sure, though.
2 DOGS, variacs seem über-kewl, their price not that much, though. And by the way, Popular Science web designers, probably along with many other related morons behind, deserve to be shot. It's one of those stupid pages which do the web formatting for you, so if you're on a small screen (they infer that by the quotient of your screen resolution and dpi values), you end up with jackassly zoomed in contents (images, text) with no way to zoom out, and if you're on landscape mode the dumbass-made onscreen squatter bars get ludicrously big to fLIck up the scene even more.
kiriba-ru, the motor uproar is caused by the AC wave cutoff caused by the diac triggering. I know this for the fact that I've directly connected the tool's motor to mains and it runs surprisingly smooth.
It’s some of my battery powered tools that I find underpowered(usually by nimh or nicad cells) and those are the ones I’d want to upgrade. I’ve done so with a 3 3/8” 12V saw. The Dremel I’d prefer to keep as is at 7.2V. My 18V kit has plenty of power but certain tools drain the batteries much more quickly than others. I don’t want the added weight of two-battery versions but at least they are getting around to using newer, higher capacity cells in the tool packs, most used high drain 1.5 Ahr cells but now are going to 2-2.5 Ahrs.
Of course, even if the nominal voltage wasn't increased, for me there's little doubt those NiCads couldn't even dream of remotely delivering half of the current the new pack can without breaking much sweat. Additionally the staggeringly improved capacity allows the operator to do a lot of work with a single shot.
Batteries seem to be one of the expensive parts of a tool, thus high quality li-ion packs may be hard to find inside cheap toys. If enough space is available inside the battery tray… dream on! For the above tool, doubling both voltage and current delivery could be done with a 4S2P pack of HE2s/VTC5s and 2 × 30A BMSs in parallel, but that would probably mean motor meltdown LoL!
if you run the motor at too high of speed the failure mode is throwing the windings out of the armature.
done that to some drone motors myself.
thought the bearings seized but an autopsy showed winding failure.
I believe I can understand the potential causes for all sorts of failures. Electric motors tend to be simple, efficient and reliable, some of them can tolerate a lot of abuse.
Ended up rebuilding the speed controller box with an AMP Mate-N-Lok connector. Working nicely. The tool heats up enough when drilling holes on metal and other hard work, maybe it's better to have left it at stock power.
Next project in queue: inexpensive hair clipper high power li-ion conversion. From 2S AA Ni-MH to 2P 14500 (TrustFire IMR14500) with 15A BMS.
