So a while ago i got my hands on a old sewing machine sadly the foot pedal blew up on me and i also noticed that the machine made my fingers tingle (more on that in this old post here: https://sh.itjust.works/post/35395330 ).
After that i didnt touch the thing for a while but now i needed to sew something so i got myself a new motor and pedal for it online.
The motor fits neat to the machine and the pedal works. But after the last time i was a bit afraid to just touch it, decided to better do a voltage check first.
So i grabbed a Multi meter and connected one side to main earth, and the other side to the metal body of the machine.
And apparently there are 30-32V AC on the metal body of the machine :( Then i tested the current and it was 4.1uA.
I did the same thing for the motor spindle an and the results where even worse >.< 173V AC on the spindle and 43uA when i short it to main earth over the multi meter.
Now my question is:
Is this normal?
Is it maybe just some parasitic currents from the Motor windings acting as antenna and inducting voltage into the metal body of the machine?
Will it kill me if i touch it?
Should i ground the machine to earth using a second plug?
Should i isolate the motor from the metal machine body?
Here are some more pictures from my measurements and measurement setup:
I would be pretty wary of using it with that amount of voltage. If the electricity routes through you, it would probably give you more than a good buzz.
Based on the fact that it made your fingers tingle before you replaced the motor, I doubt the new motor or your installation of it is the cause of this issue. You probably have some kind of short inside the machine itself. Best bet is to crack open the machine (when unplugged, obvs). This could be the most dangerous part - make sure you can identify capacitors on the circuit board and find a youtube video about safely discharging them, as capacitors can store dangerous amounts of electrical charge even when the circuit is unplugged, and discharging them accidentally can fuck you up. Then look for obvious loose connections. If you don't see that, you will have to start searching for the short. Set your DMM to measure resistance. Search the motor component with one lead and the rest of the machine's circuit with the other. As long as resistance is a real number, you have a closed circuit and the short is on the circuit the leads are on. When resistance jumps to infinity, you are no longer in a connected circuit, and the short is somewhere else. Often, shorts will read as significant amounts of resistance, as the marginal connection between two components is not enough to allow free-flowing current. Note that this creates a new danger - even if you don't electrocute yourself with the machine during use, it is possible it will catch on fire as electricity running through a marginal short heats up the components. If you are lucky, you can identify the short by noting the leads have non-zero resistance in one spot, but 0 reistance upstream and downstream of that spot. Then you might look real close and see a loose wire or a burn mark. But maybe this is just an expected bit of resistance that was designed into the circuit. It's a bit of an art, takes some patience, and if the solution isn't immediately obvious, there is about a 70% chance you are wasting your time.
Ideally, as the other user said, you would also install a ground during your troubleshooting so you don't electrocute yourself in the future if it happens again.
No such thing in there, this is a very old machine there is no electronics inside the machine. The only electronics is the motor itself (bolted to the outside), and the foot pedal that controls the motor (wires go from mains to pedal to motor, there are no wires going inside the machine).
Depending on the type of motor, it may still have a motor capacitor to help it get started. Certain types of electric motors need a capacitor in order to start safely from a standstill, no matter how old they are. (And such motor capacitors can often be pretty large and dangerous.) And even if you're not opening the motor housing where such a capacitor would probably be located, that capacitor will still be connected to certain electrical leads inside the machine, and touching those leads could expose you to it.
So still a good idea to check.