snotbottom Posted July 20, 2023 Share Posted July 20, 2023 Enclosures for a bare variac, to obtain the correct values mounted (amps) i need a steel plate 300 x 300mm , mounted is 1.4 amps , unmounted is 1 amp, so even unmounted I should be OK , what have you guys done for enclosures? And did you earth the panel if mounted on steel? I dont want to heath robinson this. Link to comment Share on other sites More sharing options...
snotbottom Posted July 20, 2023 Author Share Posted July 20, 2023 So I tried it out unmounted, it worked, however the RUCK fan didnt do much until the variac was at around 50 percent then it took off, so to start the fan requires a lot of voltage, Im thinking because its old the fans external start capacitor might be leaky , any ideas? I can swap out the capacitor for a few quid and see, I take it RUCK fan motors are brushless? Link to comment Share on other sites More sharing options...
snotbottom Posted July 20, 2023 Author Share Posted July 20, 2023 I think the fan capacitor is shot, I got the fan to its lowest speed and let it run for a while, I could hear the cap making noise, what I didnt see was the cap making light crackling sounds also caused sparks at the variacs bush which burnt the winding, it still works Ok at anything above the minimum voltage to start the fan but its not ideal. Any suggestions before I go buying a new cap? Link to comment Share on other sites More sharing options...
Seasick Steve Posted July 20, 2023 Share Posted July 20, 2023 (edited) @snotbottom 6 hours ago, snotbottom said: So I tried it out unmounted, it worked, however the RUCK fan didnt do much until the variac was at around 50 percent then it took off, so to start the fan requires a lot of voltage, Im thinking because its old the fans external start capacitor might be leaky , any ideas? I can swap out the capacitor for a few quid and see, I take it RUCK fan motors are brushless? As far as I'm aware, you shouldn't lower the variac to below 45% as most fans will stall below that and can get damaged. There's a variac thread somewhere on here with lots of info. E2a Here's the thread Edited July 20, 2023 by Seasick Steve Link to comment Share on other sites More sharing options...
snotbottom Posted July 20, 2023 Author Share Posted July 20, 2023 15 minutes ago, Seasick Steve said: @snotbottom As far as I'm aware, you shouldn't lower the variac to below 45% as most fans will stall below that and can get damaged. There's a variac thread somewhere on here with lots of info. E2a Here's the thread Thanks man, From doing some reading I have found that the type of motor also dictates how the variac performs, so if it has a start capacitor then until the cap sees the minimal voltage to operate the fan wont work, its like a bottle neck, In my case the cap wont function until it sees enough voltage to run the fan at a fair rate of knots, so I cant run it down to whisper quiet. I might look at different cap values and see if I can find one that starts the fan at a lower voltage. The dimmer switch I used before caused hum but the cap got the voltage it needed, a dimmer switch effectivly switches the fan on and off really fast which makes it very effective but also causes hum, reducing the voltage via a variac has a different negative effect, I'm gonna keep reading up on this. induction motor - How well does a Variac work for fan speed control? - Electrical Engineering Stack Exchange Link to comment Share on other sites More sharing options...
Seasick Steve Posted July 21, 2023 Share Posted July 21, 2023 39 minutes ago, snotbottom said: the type of motor also dictates how the variac performs Yeah, it depends on fan type I think. I have a box fan which I run off a variac, which I built after reading/following that thread I linked in last post. There's lots of info about how they control the fans voltage wise re the motor type. Link to comment Share on other sites More sharing options...
Themadhippy Posted July 21, 2023 Share Posted July 21, 2023 Id go for a time delay relay that bypasses the variac for a second or 2 to let the motor start. 1 Link to comment Share on other sites More sharing options...
snotbottom Posted July 21, 2023 Author Share Posted July 21, 2023 35 minutes ago, Themadhippy said: Id go for a time delay relay that bypasses the variac for a second or 2 to let the motor start. You mean give it full voltage then back it off? It wont matter, the start capacitor will still only work at minimal voltage then shut off, I need to lower this start voltage and the only way to do it is change the values of the capacitor.. Link to comment Share on other sites More sharing options...
Themadhippy Posted July 21, 2023 Share Posted July 21, 2023 Quote the start capacitor will still only work at minimal voltage then shut off no,the capacitor causes a phase shift on 1 winding to get rotation started ,once the motors almost upto speed a centrifugal switch opens and switches off the capacitor and start winding Link to comment Share on other sites More sharing options...
snotbottom Posted July 21, 2023 Author Share Posted July 21, 2023 7 hours ago, Themadhippy said: no,the capacitor causes a phase shift on 1 winding to get rotation started ,once the motors almost upto speed a centrifugal switch opens and switches off the capacitor and start winding So does the phase shift in effect give more voltage? The frequency remains the same? Or does the frequency change with shorter period? Would removing the cap altogether give a lower start speed as the voltage from the variac increases? My understanding is the cap acts as a buffer on startup? Link to comment Share on other sites More sharing options...
Themadhippy Posted July 21, 2023 Share Posted July 21, 2023 Quote So does the phase shift in effect give more voltage no,the phase shift delays the current to one winding to form a rotating magnetic field Link to comment Share on other sites More sharing options...
snotbottom Posted July 22, 2023 Author Share Posted July 22, 2023 I see , so removing it would cause problems at startup? Link to comment Share on other sites More sharing options...
Themadhippy Posted July 22, 2023 Share Posted July 22, 2023 Quote so removing it would cause problems at startup? yep,it wont start,it will just sit there vibrating Link to comment Share on other sites More sharing options...
snotbottom Posted July 25, 2023 Author Share Posted July 25, 2023 On 22/07/2023 at 6:41 PM, Themadhippy said: yep,it wont start,it will just sit there vibrating Thanks man, it is what it is I guess. Link to comment Share on other sites More sharing options...
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