Hi everyone!
First post here after some time lurking (my bad).
Well, I hope to be enough IT here since it's more an electrotechnical matter than pure electronics, but electronics are involved at some point.
I'm working on a bench drill press which I'm recabling and making some improvements which I'm going to list below. In the meanwhile the motor specs are the following (I live in Europe):
230-240V~/50Hz - 550W
Class B - IP20
ȵ: 1450 minˉ¹
Variable speed through pulley: 440-2580RPM
It's a single-phase AC motor which is equipped with two capacitors:
100uF 250VAC 50/60Hz
start cap16uF 450VAC 50/60Hz
run capI know that data is poor, but more in depth info are not available unfortunately.
The motor is powered ON and OFF through a electromagnetic switch from KEDU (KJD20-2), 4pins which cuts Line and Neutral at same time. On the chain,
always in ON state as you plug the cable in the main, there is a device board which sense and display RPMs through a photo diode as soon as the motor is started. There is another switch under the pulleys cover which cuts down the feed if the lid is accidentally opened while motor is running. As last thing there are two laser diodes powered by two AA 1,5V batteries, on/off switch, which draw two lines used as reference guide like many other electrical tools are used to nowadays.
What I've already done is the wirings to lasers from RPM board since the PCB allows that through a low power LDO driver which output 5V (laser diodes accept 3v to 12V) and get rid of batteries; similar machine equipped with laser guide power on laser this way w/o batteries
What I would like to do now is add a switch upstream of the chain since I don't like that the RPM board is always ON while not using the drill and it's constantly humming; so I can leave the plug in while not using the machine
During this long journey started months ago I learned a lot and at some point of this very entertaining project I started to worry about the inductive kickback from the motor while shutting down the machine, so I'm wondering now about the following things:
- Life contacts: prevents contacts of the switches from arcing
- Devices safety: since there are other devices on the chain like the RPM board and the little AC to 12VDC transformer, which I'm planning to add for led light working area and driven ON and OFF by a little switch
- Other things I may not have considered yet and someone is going to point me out eventually...
In the beginning I thought about an
RCD snubber, but I found very hard to design one w/o knowing more about the motor and inductance values; someone suggested me to use a device called Quencharc made by Cornell Dubilier which is an all-in-one package solution, but sold with different ohm values and I don't know what to pick. Another thing to consider in general about a snubber (selfmade or not) could be that more likely I not have enough room to place one.
Later I came across the idea of using a
TVS diode. To make a long story short (lol), according to the rule Vso>=Vrms x 1,56 I need a TVS with standoff voltage of 360V or above. What I can find are TVS with 400Vso but rated for
only 1.5KW, while concerning is that I would easily need more! 6KW? Even more? I don't know.
Found some options from littelfuse but excluding AK series which are very expensive, there are a bunch of alternatives, 5KW but Vso 350V or even 30KW with 360Vso, but I can't find them within EU.
In conclusion, I'm a bit lost now
Sorry for long posting, I hope this didn't come out overhelming but I wanted to give more informations as possible
Every hints, suggestions, new idea, experience or whatever from anyone who wants to help me is really welcomed!
Thank you in advance