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- Опубликовано: 14 окт 2024
- In this video I repair and modify a damaged Carroll & Meynell 10A variac and add in a soft start circuit to reduce the inrush current when the device is first powered up.
/ sdgelectronics
Please visit my home page for further details and the schematic!
Special thanks to Tony Brown from Carrol & Maynell for supplying a replacement part free of charge! #ElectronicsCreators
You should be very proud of that build, Steve, it turned out beautifully. Well done. I was a bit incredulous when you said "microcontroller" until I realized you were doing more than simply inrush limiting. Congrats to you and your wife on Camden's birth! He's adorable, and I see he's already drooling over electronic test equipment -- good lad!
Thanks! Having firmware in the way is certainly NOT the right way to do an "emergency stop" button, and it is massive overkill. He is teething already, so plenty of drool all over!
Congrats on Camden........loves the light......😀
+IanScottJohnston Thanks, yes anything illuminated in fact!
+SDG Electronics Converted any night lights to use some colour changing LED chips yet? Did that for the nephews night light as I got tired of changing the little lamp with the horrid holder. Went with a blue light to match the Sailor Moon ceramic figurine.
+SeanBZA I've still got to finish the LED driver project. Lots of colourful stuff to come!
very cool though I think I wouldnt want the estop dependent on the microcontroller. I'd would want to know it would cut all power no matter what. wire it to kill power to the main contactor.
Nice & complete job there Steve.. Makes my variac inrush mods look a little puny now :)
Congrats on your new Camden alarm clock :)
Cheers friend
John
+orbiter8 (John) Thanks John. He needs calibrating, the timing is all over the place.
+SDG Electronics .. Hahaaa.. LOL
I am actually designing my own bench isolated variable AC power supply. I have two commercial units that I use now with some slight modifications to both but I would like to just make one that has all of the features I want. I decided to use the same resistor method as you, instead of a varistor approach, using a non-inductive power resistor on a seperate heat sink with a thermal switch for overtemp monitor (on the control circuit).
I am using the traditional relay ladder logic design approach where relay contactors are used to switch high currents and control (relay coils) uses low current and the design is dumb with the smarts being a single time delay power relay. I am in the USA with both power and control at 120VAC 60Hz. It is designed like a indusrial control cabinet with DIN rail mounted relays and other connection blocks, safety emergency switch, power push switches, etc.
Design considerations:
I am using a large toroidal power transformer and large variac so I need to have a power resistor during initial power (magnetization current surge) which will be shorted out with the time delay relay. If the supply is in use with power failure the control circuit will drop out and prevent it from automatically powering back up when the power comes back. I am using a GFCI as a primative AC leakage test where I can connect or float the safety groung back to the isolation transformer output (established neutral). I have an AC leakage tester for a tracable leakage test requirement if needed.
Loved your baby in the video. I am happy I watched to the end and did not miss that
Hehe, "To fill the room with ozone", as you do :)
Great project, it turned out very nice indeed :)
Ohhh, and congratz on Camden :D :D
+EcProjects Good way to kill any odours. Thanks!
Glad to have you back again! Congratulations on the newest addition!
Thanks Dino
Had the same problem with my large variac and did a similar solution. Just used a simpler version, using a 24VDC relay to short out the resistor. Did add a 130C thermal fuse in case the relay died open circuit. Added as well a suppressed zero voltmeter, as there was a tap giving 60VAC I was able to use that as power, using a diode rectifier, and then getting a 30VDC rail using a zener then a 723 giving the reference. Meter was simple with recifier and capacitor, and calibrated to show from 60VAC to 360VAC on the remarked scale. Variac goes from 0-340VAC output.
+SeanBZA Very nice. Any pictures?
+SDG Electronics Had some somewhere, but will probably have to open it up and take them again when I get to it. Will send you the link on EEVblog.
Nice job, Steve. Glad to see you're back
Congratulations Steve!
I bought an isolation transformer and a variac some time go now, wired everything up and now only the case is missing. I planned to create a custom case using parts from Schaeffer, but as it turned out, it's certainly not the cheapest solution. I should have bought a used one on ebay as well.
+Pn Junction Yes, they're a little pricey if you make the entire case from machined parts from there. A local metal fabrication place is quite a cheap option.
Congrats on the New Year baby and loved the video.
+Tom OConnor Thanks Tom
Awesome! Great video and congratulations on the little one!
+DoItYourselfMusician Thanks!
Nice video, I did go another way.
It is possible to find isolation+variac in one unit, I found a 3A unit. They are a bit rare and rather expensive, but very useful. The variac used in my unit uses a wheel for the connection to the turns (all the variacs I have seen do that).
I think the carbon brush is a Carroll & Meynell thing
+SDG Electronics I believe the most interesting thing is that you can get variac's with separate mains winding. I do not know how common they are, at one time there was two manufactures in Denmark for the finished unit: B&O and Impo, today there are none (But you can still get them used).
Great video, I also purchased one of the very same variac units from eBay and just like yours it arrived damaged with the knob all smashed and the shaft bent, now I know the makers are so helpful I will see if I can purchase a new shaft and control knob and I will rebuild it as per your project as it looks to be a great unit, I do not have the wire ended mains quick connector on mine as its already fitted with a single 13A socket but I have a 13A plug version of the same quick connector so I can still use the variac in both ways, the PCB looks great although as you say its a massive overkill for this project, how warm does the PSU input voltage dropper resistor get ?, I did worry about its close proximity to the bulk storage capacitor as if its getting very warm it could lead to early drying out of the capacitors, do you have a web site where you can purchase one of these PCB's as I would like to use one on my build ?, all the best, Dave
+david ellis Hi David, the resistor only rises about 5-10°C above ambient at most. The overall current consumption is less than 20mA on the 3.3V supply, so less than 200mW total dissipation in the whole regulator worst case.
If I get time, I can send you a PCB as they sent me the overstock too. My e-mail is on my contact page.
Nice workmanship on that though;DD
Beautiful build; nicely illustrated/explained; slightly uneasy with the concept of software controlled safety switching!. Another observation is that I would always suggest considering the location of any safety switch somewhere very easy to strike in an emergency. On the video this appears slightly 'shrouded' by the quickconnect /upper part of the variac housing since the test system is likely to be placed to the right of the unit due to the orientation of the quickconnect (as per the meter in your testing), thus the operator is likely to be to the right too.
+RDH1024 Absolutely - the stop button was merely a convenience for controlling the output of the variac rather than being an actual "Emergency Stop". Thanks for your comment.
Ah - makes sense. Was wondering as the build was very careful /sold/safe and it's obvious you know what you are doing. Really enjoyed the last few videos of yours, looking forward to more.
I've been looking for 'soft starting' solutions for single phase domestic AC induction motors (ie swimming pool) because I have had issues with them tripping up Inverters that are well withing running specs of the motor, and there is not much on the market. This idea switching in a phat resistor during the start for current limiting seems a great solution. I have a controller ready for monitoring running current and phase angle anyway.
Nicely done.
Fine, thank you. But don't you think that implementing voltage, current, and power reading monitor would not be difficult and would greatly increase the convenience?
Nice, it's not a metal brush, it's a carbon brush ;) Thumbs up :D
Alex
+High Voltage Yep, I mis-spoke - tiredness kicking in...
SDG Electronics Ok
Very Nice, subscribed
For me this solutions looks a bit over-engineered :-)
A complete power supply and serveral extra circuits just to control the inrush current?
I did well with just a 20 Ohm Resistor and an extra switch to bridge the resistor. You even dont need a 100W resistor, 10 - 20 W
will really do as the high current only occurs for some ms :-)
Of course, if you forget the bridging switch and put a heavy load on the variac it will fry your resistor... (it happened to me once :-)
And that's exactly why over engineering the solution is the right thing to do... :D
totally overkill :D a 555, with a relais and a resistance couldnt be enough? :)
How it's called the red device where you plug your wires safetly, by opening the case.
Thanks!
See an earlier comment. It's called a Quicktest connector from Cliff Electronic Components
+SDG Electronics Oh thanks!
Where did you get the Socket&See DIT 400 ?
I think it was CPC, it came as a kit of three items. It's long gone now though - the battery leaked and ruined the PCB.
I've seen that RED AC quick test box in a couple of videos and I wonder if anybody knows where to buy one from?
Cheers!!!
+robfel68 They're made by Cliff Electronic Components: www.cliffuk.co.uk/products/tools/quicktest.htm
Farnell Order Code: 658716
I think CPC sell them cheaper.
+SDG Electronics
Most Kindly Sir.
Thanks.
Which name of your cute baby?