Using 240V AC operated power tools with 110V AC input ? - Page 1
Forum section: electronics / beginners

author: vinlove
author_rank: Frequent Contributor
timestamp: November 17, 2021, 06:21:45 pm
content: I guess 240V Mains AC operable tools would slow down in speed (such as rotary tools, like electric saws or drills), when used with 110V AC input into them. But what other effects would it have to the tools? Would they have more torques due to more amp generated according to Ohms Law.And 110V AC input to the power tools wouldn't stress the 240V operable tools in any shape of forms? Correct? The other way around using 240V AC input to 110V AC operable would blow the tools off for sure.

author: bob91343
author_rank: Super Contributor
timestamp: November 17, 2021, 06:47:47 pm
content: Some models would not see enough voltage to run and thus might sit quietly and overheat.

author: TimFox
author_rank: Super Contributor
timestamp: November 17, 2021, 06:50:32 pm
content: If the motor will not turn at all, it develops no back-EMF (stall condition) and draws a large current ("stall current") given by the applied voltage divided by the winding resistance, which is probably not good for the motor.

author: VooDust
author_rank: Regular Contributor
timestamp: November 18, 2021, 01:46:35 pm
content: The tools might work.However, and that's in fact due to Ohm's law, you'd only get 25% of output power which might render a power tool useless.Let's say the tool has a resistance of 20 Ohms. At 220V, 11 Amps of current would flow, resulting in 2'420 Watts of power.At 110V, the resistance of the tool is still the same, so you'd get 5.5 Amps and 605 Watts.So halving the input voltage resulted in one fourth of output power (i. e. quadratic decrease)

author: BeBuLamar
author_rank: Super Contributor
timestamp: November 18, 2021, 01:58:06 pm
content: Since power tools generally have DC motors so they would run but with much less speed and torque also. They don't draw more current either.

author: magic
author_rank: Super Contributor
timestamp: November 18, 2021, 07:26:37 pm
content: Quote from: VooDust on November 18, 2021, 01:46:35 pmThat's only applicable when the motor is stalled, and then its mechanical power output is zero, and torque is proportional to current, i.e. decreases in half, and all the input power is wasted as heat in the windings.

author: james_s
author_rank: Super Contributor
timestamp: November 18, 2021, 07:42:46 pm
content: Motors are not resistors, you can't use Ohms law to calculate the behavior of a motor as if it was a resistor.Most power tools use brushed universal motors, these will run fine on either AC or DC and will usually operate down to 10% or even less of the rated voltage, but they will produce correspondingly less torque. Is there a particular reason you want to do this?

author: vinlove
author_rank: Frequent Contributor
timestamp: November 18, 2021, 08:34:34 pm
content: Quote from: james_s on November 18, 2021, 07:42:46 pmSure. In here we use 240V AC mains, and most power tools are crazily powerful and loud. There are times when they would be more useful running slower and less powerful. If the power tools have speed controls, then yes it is possible to use the control switch to lower the speed and power. But when they are just simple ON/OFF control only, and monstrously powerful and loud, it can be problem, for example, 2000W angle grinder or circular saw.So I was thinking of using half the normal voltage 110V for them, which then will slow down a lot, and run far better for the job, and less loud. But wasn't sure what other effects it might cause to the power tools.I had been running 240V AC vintage HF radios on 110V before, and it used to run very quietly and nicely with less sensitivity and band noise giving quieter pleasing reception on the noisy HF band at nights.

author: vinlove
author_rank: Frequent Contributor
timestamp: November 18, 2021, 08:40:05 pm
content: When I experimented with my VARIAC and the 240V AC vintage tube radio, the lowest voltage it was working reasonably well was about 100V. Below that, it became too quiet to be practical, and at about 75V it just had gone totally deaf.

author: TimFox
author_rank: Super Contributor
timestamp: November 18, 2021, 08:49:14 pm
content: With less than half the rated voltage applied to a tube radio, the heater voltages are far below the useful operating range.Were you to somehow maintain the heater voltages while reducing the plate voltage, the effect might be less strong.

author: james_s
author_rank: Super Contributor
timestamp: November 18, 2021, 09:50:05 pm
content: Well you won't hurt anything running a universal motor at lower voltage, that's essentially how the variable speed controls work in those that have them. Just don't try it with something that has an induction motor, you'll find those in stuff like bench grinders and such.

author: andy3055
author_rank: Super Contributor
timestamp: November 19, 2021, 12:33:33 am
content: Quote from: vinlove on November 18, 2021, 08:34:34 pmAngle grinders and circular saws will need to run at the required speed. If not they will tend to stall and that will be bad.

author: vinlove
author_rank: Frequent Contributor
timestamp: November 19, 2021, 11:12:59 am
content: Quote from: TimFox on November 18, 2021, 08:49:14 pmI wasn't monitoring the plate voltage while doing the testings, but just concentrating the reception and audio from the radio while changing the input voltage. Must admit the vintage transistor radios worked better.

author: vinlove
author_rank: Frequent Contributor
timestamp: November 19, 2021, 11:16:24 am
content: Quote from: andy3055 on November 19, 2021, 12:33:33 amCircular saws will not be good, I can see the point. But For angle grinders, and sanders it sometimes works far better with slower speed, for example, smaller and softer items such as wood, and sharpening knives.

author: vinlove
author_rank: Frequent Contributor
timestamp: November 19, 2021, 11:18:10 am
content: Quote from: james_s on November 18, 2021, 09:50:05 pmWhat difference would induction motors make from other motors? Could you elaborate more on that please? Thanks.

author: tunk
author_rank: Super Contributor
timestamp: November 19, 2021, 01:47:16 pm
content: Out of curiosity, does 50 vs. 60Hz matter?

author: themadhippy
author_rank: Super Contributor
timestamp: November 19, 2021, 02:01:30 pm
content: Quotedepends on the type of motor.an induction motors speed is determined by both the frequency and the number of poles.

author: TimFox
author_rank: Super Contributor
timestamp: November 19, 2021, 02:56:07 pm
content: The number of poles in an induction motor determines the synchronous rotation speed, but the actual rotation speed is always below that (3600 or 1800 rpm typical for 60 Hz).When the rotor is at the synchronous speed, there is no net torque. The usual spec (1750 rpm or so for 60 Hz) is slightly slower, where the torque on the rotor is maximum.Seehttps://www.tlclam.net/synchronous-motor-vs-induction-motor/

author: james_s
author_rank: Super Contributor
timestamp: November 19, 2021, 06:21:35 pm
content: Quote from: vinlove on November 19, 2021, 11:18:10 amMagnetics is not my area of expertise so I'm sure someone else can explain it in more detail, but in essence an induction motor will draw more current as the input voltage falls, so prolonged under-voltage can cause it to overheat and burn out. This is why controlling the speed requires the use of a variable frequency drive rather than adjusting the voltage or using a light dimmer type circuit.Things are complicated somewhat by the fact that there are numerous types of induction motors, some of which behave differently. A shaded pole motor for example such as often used in small fans does actually respond well to varying the voltage, at least within a reasonable range.