Latched Circuit required for heavy load 400V to 600V. - Page 1
Forum section: electronics / beginners

author: Xen.Cloete
author_rank: Newbie
timestamp: May 17, 2019, 05:13:15 am
content: Dear fellow members,I have been searching for some time now and have not found what I am looking for... and I am totally rusted in electronics. So let me get to it.The project: (Woodworking Assisted Gadgets)Circuit to receive electronic signal 3V3 or 5V (This could be a receiver Gate motor circuit with the output) to latch circuit to ON position switching a PhotoTriac (with snubber circuit) which drives a heavy load. The heavy load in this case is a Woodworking dust collector machine, rated at 3HP.Restrictions:1 No Micro controller to be used. Albeit, Ardiuno or any other2 Minimal parts to save costs.3 Overall project must be affordable4 No relays due to power load restrictions unless I can be convinced and the parts are easily availablePower requirements:I don't want to purchase a power supply similar to that of laptops. Makes this too expensive again.Here is a circuit that I would like to use to power others circuit designed above. Image below and here is the linkhttps://randomnerdtutorials.com/esp8266-hi-link-hlk-pm03/I have attached images below since the editor cannot include the imagesPower ESP8266 with HLK-PM03 Converter | Random Nerd TutorialsI am looking for a latched circuit that can assist me with the switching On and Off of a Dust collection motor. I will attach a link below from youTube to give an example of what I require.https://youtu.be/xVZb31TCdZEI would appreciate any help.Thanks

author: Zero999
author_rank: Super Contributor
timestamp: May 17, 2019, 07:45:34 am
content: Mains on a perfboard is not a good idea. There might not be sufficient creepage distance between the mains and DC sides.A latching relay circuit is the usual way to do this, but you said you don't want relays.Presumably you have a permanent 3.3V to 5V power supply available?The easiest solution would be to use a bistable. One can be made from such as the 74HC(T)74 or 4013, some logic gates, a 555 timer or a couple of transistors.https://electronicsclub.info/555bistable.htmhttps://en.wikipedia.org/wiki/Flip-flop_(electronics)https://assets.nexperia.com/documents/data-sheet/74HC_HCT74.pdfhttp://www.ti.com/lit/ds/symlink/cd4013b.pdf

author: Xen.Cloete
author_rank: Newbie
timestamp: May 17, 2019, 08:01:38 am
content: Thank you I will go do some more reading and homework.

author: Ian.M
author_rank: Super Contributor
timestamp: May 17, 2019, 09:47:46 am
content: Quote from: Zero999 on May 17, 2019, 07:45:34 amTo expand on that: You want at least 4mm distance with no copper pads between any part of the mains circuits and the low voltage circuits Strip copper pads off totally to get it. On 0.1" strip or matrix board, stripping two adjacent tracks or pads gets you 5mm clearance. If you are using expensive double sided FR4 matrix board, beware of copper left in plated through holes!*DON'T* try to use cheap EBAY matrix board - the pads are too fragile and drop off if you look at them wrong - not a good thing if it is holding a component lead with mains voltage on it.Personally, I'd bite the bullet and buy a screw terminal solid state relay rated for motor loads. It provides all the safety isolation you need and avoids mains on perfboard. Its not going to be cheap, as a 3HP motor in 230V countries has a running current of nearly 10A, and a locked rotor current of typically ten times that, so will pull a 100A surge at startup.If you do try to 'home-brew' the SSR, you'll need a TRIAC that can handle that 100A surge, and you'll need to heatsink it as even 1V drop at 10A is 10W, a lot of dissipation. That gets into a whole other world of problems maintaining safe creepage distances between the TRIAC pins and a grounded heatsink.The alternative you have already rejected is a motor control contactor with a 12V or 24V DC rated coil. Yes they are big, clunky and power hungry and not particularly cheap, but they'll do the job reliably for tens of thousands of operation cycles, with negligible risk of failing shorted ON. If its got auxiliary contacts, you can use them to latch on the coil power to make the contactor self-latching. Then you've only got the issue of controlling the 12V or 24V contactor coil with 3.3V or 5V logic signals, which at least doesn't have the safety issues of directly controlling mains. Don't forget to suppress the back-EMF spike from the contactor coil with an anti-parallel diode across it so it doesn't kill your logic interface circuit. As you need it to release quickly, put a resistor approx. equal to the DC coil resistance directly in series with the diode. That will limit the spike to approx double the supply voltage.