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My shop fan says DO NOT use with a speed control.I would like to use a speed control, and run the fan at a slower speed. Is this bad for the motor?Will the motor windings get too hot?Is this unsafe?I might use this speed control, which says do not use on a brushless type motor. I believe my fan is an AC induction type electric motor. This might not even work with my fan?
Last edited by jonnymacuser; 09-20-2020 at 12:16 PM.
Reply:your asking a question you already answered..the fan says dont use one and the controllers say dont use on a brushless motor..how much more info do you want that says its a BAD idea??? most likley if you do it will burn up the motor and get so hot a fire could start in the windings...it looks like your fan has a high and low speed setting..if thats not good buy another fan..
Reply:Pretty much like using a toaster around water. Even if it was safe, would I really want saturated toast?
Reply:My shop fan says DO NOT use with a speed control. - Don'tI would like to use a speed control, and run the fan at a slower speed. -WhyIs this bad for the motor? - YesWill the motor windings get too hot? - Yes Is this unsafe? - Yes (only from the standpoint of you failing to heed the directions/warnings)The fan will overheat fairly quickly , which will cause the one time overcurrent protection to fail. It is a tiny fuse soldered into the winding requiring disassembly to repair. Why not use a small $20 box fan instead , it would be far simpler if you wanted less air flow. Its a hundred dollar fan why ruin it , you might need it for something else later. Why do you want to slow down a High Velocity Fan, it already has 2 speeds ?HTHAirco 250 ac/dc Heliwelder Square waveMiller Synchrowave 180 sdMiller Econo Twin HFLincoln 210 MPDayton 225 ac/dcVictor torchesSnap-On YA-212Lotos Cut60D
Reply:I've used those controllers. Big differance in cheap vs more expensive. That maybe a brushless fan and won't work a controller. An alternative would be to make a two foot extension cord with a 20 amp diode inline. Should make the fall run half speed. I don't know how efficient it will be on the motor. It would be worth a try
Reply:
Originally Posted by Insaneride
I've used those controllers. Big differance in cheap vs more expensive. That maybe a brushless fan and won't work a controller. An alternative would be to make a two foot extension cord with a 20 amp diode inline. Should make the fall run half speed. I don't know how efficient it will be on the motor. It would be worth a try
Reply:
Originally Posted by Insaneride
I've used those controllers. Big differance in cheap vs more expensive. That maybe a brushless fan and won't work a controller. An alternative would be to make a two foot extension cord with a 20 amp diode inline. Should make the fall run half speed. I don't know how efficient it will be on the motor. It would be worth a try
Reply:
Originally Posted by Hobbytime
thats the same thing as a speed controller except you just cut the speed in half rather than have variable... you are cutting the amount of power going to the motor..so it will over heat the same and possibly burn up..poof..
Reply:
Originally Posted by ronsii
I think a lot of the 'issues'
come into play when you compound the 'electronics' (in fan)on top of more 'electronics' (in speed controller) most of those speed controllers use an SCR or TRIAC to 'chop' the power on the downside of the sine wave curve... so while you are 'cutting' power from the fan motor you are not really lowering the peak voltage going to it... but you are lowering the RMS voltage to it... and if the fan already counts on full RMS voltage to make the electronics do thir thing once you affect that then bad things will happen
I have not seen the latest/greatest chinese offerings in their fan motors but have worked on the older ones... they had an actual two speed motor so you could run a speed controller on the full speed set of windings... or at least I did without problems
Reply:It's a 2 speed high velocity fan. Live with it or get a different fan. This is like buying a tapped voltage Mig machine and wanting to make it a variable voltage. If you want variable, get variable.
Reply:
Originally Posted by albrightree
Why not use a small $20 box fan instead , it would be far simpler if you wanted less air flow.
Reply:
Originally Posted by Hobbytime
thats the same thing as a speed controller except you just cut the speed in half rather than have variable... you are cutting the amount of power going to the motor..so it will over heat the same and possibly burn up..poof..
Reply:
Originally Posted by Insaneride
I don't know Hobbytime, I think a diode inline would be more like switching the fan off and on 60 times a second. ronsi gave a brief explanation of the scr controller. I will add that the scr can be triggered during the positive cycle and the negative. It seems to me that an scr should be able to control that fan. I looked up data sheets for the diodes in my pic. One is 40 amp. The other is hi voltage low amps. I think I have a ceiling fan (brushless motor) somewhere. I'll give it a try and let you know how it works. I see no reason why it should not work other than cooling the motor.
Reply:
Originally Posted by Hobbytime
yeah, im not 100% sure a diode would work or not, but the diode in laymen terms slows down the current flow( they have other uses too)..so it may also depend on the quality of the motor if it has built in safteys for low voltage to avoid damage to the motor or just let it burn up...by reducing voltage or flow the fan may struggle to get started and burn up trying to get to full RPM...give it a try and see what happens...
Reply:
Originally Posted by ronsii
LOL!!!!! you just used the words 'quality' and safety' in the same sentence when talking about a chinese motor LOL!!!!!!!!!!
Reply:A DC motor will take more circuitry (and money) to control it then if you just bought an AC motor and used your cheap speed switch. You are trying to defeat the basic laws of DC electronics.
Reply:I use a 2-speed, 24" whole house fan mounted in the ceiling...https://www.homedepot.com/p/Master-F...S24M/100018252MillerMatic 252, HTP 221 w/cooler, Hypertherm PM45, Lincoln IdealArc 250 AC/DC"I'd like to believe as many true things and as few false things as possible"
Reply:Get one of the bigassfans, they move any amount of air you need moved!!! and they're quieter than pretty much any other way of moving air
HD, lowes and just about everyone else sells them.https://www.lowes.com/pl/Big-***-fan...ent=4294389884
Reply:If you put a diode in AC circuit you create DC. A cheap AC fan motor may not run on DC.
Reply:
Originally Posted by danielplace
If you put a diode in AC circuit you create DC. A cheap AC fan motor may not run on DC.
Reply:
Originally Posted by Insaneride
Wrong. You do not get DC. You get one half the power of AC. You could filter with a cap and use a full wave bridge (4 diodes) to get DC but a single diode is going to supply half cycle of 50 or 60 Hz. Look it up.
Reply:Ok so it's 60 Hz DC. It still is fluctuating from zero to half wave peak AC no? In all fareness to danielplace, a diode and capacitor could make it DC with a whole lot of ripple and only for light loads of milliamperes. I've built several power supply's from scratch and repaired a few and have been shocked by a few. I've even used a diode and transformer to switch a solenoid that didn't mind half wave positive cycle only but it was still switching from peak to zero at 60Hz. One power supply in a guitar amp that I repaired shocked the snot out of me after the caps were discharged. The choke had a warning label to discharge but I never thought a coil could store current when power was off. Apparently a magnetized coil can hold a charge. I used my cap discharger to bleed off the stored current. Caps store voltage, coil stores current if it's magnetized. I forget who (member here) schooled me about that. Voltage leads current in a coil and current leads volts in a cap.
Reply:
Originally Posted by Insaneride
Ok so it's 60 Hz DC. It still is fluctuating from zero to half wave peak AC no? In all fareness to danielplace, a diode and capacitor could make it DC with a whole lot of ripple and only for light loads of milliamperes. I've built several power supply's from scratch and repaired a few and have been shocked by a few. I've even used a diode and transformer to switch a solenoid that didn't mind half wave positive cycle only but it was still switching from peak to zero at 60Hz. One power supply in a guitar amp that I repaired shocked the snot out of me after the caps were discharged. The choke had a warning label to discharge but I never thought a coil could store current when power was off. Apparently a magnetized coil can hold a charge. I used my cap discharged to bleed off the stored current. Caps store voltage, coil stores current if it's magnetized. I forget who (member here) schooled me about that. Voltage leads current in a coil and current leads volts in a cap.
Reply:I think of mains AC as a push/pull. The positive is is like the push and the negative is like the pull. Half wave of AC could be push or pull depending on polarity. If you chop or pulse DC you get a frequency. It's not really DC anymore because it's running at a frequency. It's alternating from off to on at frequency. DC is always on. Pulsing gives it a frequency and can then be put thru a transformer. DC won't work thru transformers. I believe inverter supply's use this technology to step up DC but I'm not abreast of the latest tech. They were originally called DC to DC converters. When you chop or pulse DC, you can then run it thru a transformer to step it up. If you chop it into a hi frequency , you can decrease size of transformer and step up the volts. The old camera flash circuits work that way. A 1.5 volt AA battery can be stepped up and stored in caps to get 250 volts. Flash tubes ( xenon) work well with hi voltage. EG&G perfected this technology for hi speed photography and big azz light house lamps. DC is always on. AC alternates on to off. AC can also go on to off to negative on to off. If it has a frequency, it's not DC.Here's a pic of half wave AC circuit and waveform. You could instal a cap to to get a crude but exceptable DC with ripple. The cap maintains volts during the off cycle.Second pic is same circuit with cap and rippled DC. True clean DC is a nice flat line but everyone already knows that.The problem with using a diode to slow the fan down is, it woul be missing either push or pull ( polarity) and would have difficulty starting. A push or pull by hand or air blast would get it started and then the push or pull would keep it running. I think the SCR controller the op showed would actually work on his fan. I noticed using those SCRs is you need to start out with full speed then back off to desired speed for some if not all motors. Trying to start at slow speed is hard on the motor. IMO.
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Reply:
Originally Posted by Insaneride
Wrong. You do not get DC. You get one half the power of AC. You could filter with a cap and use a full wave bridge (4 diodes) to get DC but a single diode is going to supply half cycle of 50 or 60 Hz. Look it up.
Originally Posted by danielplace
Your right some wouldn't consider pulsating DC as DC at all. It is still direct current by definition albeit pulsating DC. It isn't the more pure DC you get from a 4 diode rectifier but it is DC.
Reply:
Originally Posted by danielplace
Your right some wouldn't consider pulsating DC as DC at all. It is still direct current by definition albeit pulsating DC. It isn't the more pure DC you get from a 4 diode rectifier but it is DC.
Reply:I won't get into the electronics theory argument, but I do have some experience with 2 speed v.s. variable speed exhaust fans in a hog barn, not exactly like your ceiling fans but hear me out. When our barn was first built, only 2 speeds were available and were "relatively" cheap for the time. Over the years people decided they needed more accurate control of the temperature so they went to variable speeds. What I noticed was that the motors were more expensive, the thermostats to control them were a lot more expensive ( I was picking up 2 speed controls for $30, the variable speeds were $250 ) and the variable speed controls they were selling us didn't last as long. What I noticed in the barn was that during cold winter days, a lot of the fans would shut right off to contain the heat. Anywhere heat was being contained, it would trip a thermostat to run close to half speed. In other words, most of the time the fan would either run fast or slow or not at all.... the same thing it was doing with the 2 speeds, but for a lot more money. I'm not sure you're going to gain much going to a variable speed as opposed to a 2 speed. I kept one 18" fan in my shop for exhausting welding fumes with the intention of running it slow to limit heat loss. After about 3 mins. I came to the conclusion that slow speeds were doing nothing to exhaust the fumes and that there was no point in running it anywhere but full tilt. Just my 2 cents. If your fan isn't working right, make sure the blades are clean or you lose efficiency, and make sure you have fresh air intakes that can keep up to it or nothing will leave the shop.Last edited by whtbaron; 11-06-2020 at 11:48 PM.250 amp Miller DialArc AC/DC StickF-225 amp Forney AC Stick230 amp Sears AC StickLincoln 180C MIGVictor Medalist 350 O/ACut 50 PlasmaLes
Reply:Well..... even with a full wave bridge network on an incoming AC 120/240/480/etc...50hz/60hz/20hz...etc... line you're still gonna have PULSATING DC coming off the output
don't believe me... throw a scope on er' and let me know what you find out
Reply:
Originally Posted by Insaneride
Well that's debatable. Pulsed DC isn't DC anymore because it's alternating or pulsating between square wave on and square wave off. It's alternating at a frequency I measured in Hz and can be used with a transformer. DC won't work in a transformer. It gets blocked after a time constant or something like that. Square wave alternating isn't like the sine wave AC that Tesla discovered and developed for us and what we think of and were taught but square wave does have a frequency same as sawtooth and sine wave and is alternating. I believe that is the technology behind inverters and has an advantage over 60 Hz AC as the transformers can be designed less cumbersome for more power using higher frequencies from square wave. Aircraft and tanks use 400 Hz for lighter smaller transformers. Higher frequencies can shrink transformers even more but switching DC to square wave is more practical using transistors than generating a sine wave for same purpose. At least that's what I think. |
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发表于 2021-9-1 23:17:40