Limit desk fan
 

I got this fan a couple weeks ago at a radio rally . Sold as non working.The seller had said it’s not safe to use as it had all sticky goo coming out the motor. Infact all it is the gromet turning to goo .
The fan works fine and I’m going to put a nice new 3 core cotton flex on it.
Now the problem it doesn’t work on the low speed. It has a coil to drop the voltage and it’s open circuit.
It runs nicely at 150 volts on my variac so I’m looking for some help on options to lower the voltage.there must be a more modern way of reducing the voltage.
I could put a dimmer switch in line but I’m sure some of you good people will come up with a better option. The fan is 90w load.
Andy

Re: Limit desk fan
 

I'd have thought a little onboard dimmer module (motor rated of course!) would've been the ideal way, if you can get it to fit.
Some lab beaker stirrers we used to repair had dimmer-style speed controls (universal motor) and ISTR they were fussy about the triac contained, DV/DT triggering and all that..but a purpose dimmer, somtimes sold as a 'drill speed controller' will be suitably designed. PS..some dimmer controls might make the motor buzz annoyingly, though a small motor should be ok IMHO

https://www.ukelectricalsupplies.com...ive-dimmer.htm

Re: Limit desk fan
 

I'm not familiar with the coil arrangement. Does it only have two wires?

Re: Limit desk fan
 

I'd be inclined to pull the coil (series choke) apart and attempt to rewind it. Once you've found out roughly what gauge wire was used, a simple fill the space winding should work OK. If it's just in series with the mains to the motor and the winding can take the current, there's little chance of any problem if it's not quite right. If the fan's too slow, just remove turns......

You might get away with a suitable capacitor but be very wary of any resonance at 50Hz if you try it.

Re: Limit desk fan
 

It's a reactor type speed control. It creates a phase shift that alters the speed of the motor. Most fans today use AC capacitors. Ceiling fans use two or three caps for speed control.
Dave, US radcoll1, a little rusty on my AC math. :shrug:

Re: Limit desk fan
 

The Xpelair Taurus desk fans (80's age) we used to fix by the hundred used in the sewing rooms of the UK's garment industry in the early 1990's had either switched windings with buttons on the base for the basic ones, or the luxury ones were continuously variable speed with a triac controller. The chinese generic ones that came in later years used either switched windings or switched capacitors, but you need a decent sized base to accomodate all that, those 18in fans had big bases :D

Re: Limit desk fan
 

At Vent Axia, we abandoned triac speed control because of the ‘buzzy’ acoustic noise problem. Speed control was by inductors or auto transformer, but I find series capacitors just as effective. I’d start by trying 1or 2 uF.

Martin

Re: Limit desk fan
 

Thanks everyone for your suggestions. I think I will try all 3 options and see what’s most likely to work. Andy

Re: Limit desk fan
 

I have used a fluorescent lamp choke to reduce the speed of a desk fan.
IIRC it was an Expelair Taurus as pictured in a previous post, with a failed semiconductor speed control.

I simply used the choke and a three position switch to give OFF/LOW/FULL speed control.

Re: Limit desk fan
 

Well the wire was so fine on the transformer so I didn’t go that route so in the end I went for the capacitor option . 1.5 MF did the trick.
For some reason the switch operated in the neutral,that’s not ideal so now it’s altered to switch the live. I replaced the horrible black rubber flex for some nice 3 core cotton covered
Thanks everyone for your help and suggestions Andy

Re: Limit desk fan
 

dont forget to add a discharge resistor! ;D

Re: Limit desk fan
 

I hadn’t thought about that . Thanks for reminding me .Can you recommend a value Andy

Re: Limit desk fan
 

Anything of a few hundred kΩ will be fine; just watch the power dissipation (which is just V*I, and I=V/R; you can do it in one step as P=V**2/R). A 470kΩ resistor would be dissipating about 0.11W, if the motor went short and left the full 230V across the R||C network.

Re: Limit desk fan
 

Thanks Julie . I will get on with that in the next day or so Andy