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Old 28-08-2016, 10:17   #1
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12v speed control for Guest 900 fan

I've got 4 Guest 900 oscillating cabin fans. They move a ton of air but are also as loud as a tropical storm. I can't find any accessory switches that will allow me to slow them down a little, anyone have some suggestions on where to find a speed control device? Trying to sleep with these things blowing on you ain't happenin'.
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Old 28-08-2016, 10:20   #2
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Re: 12v speed control for Guest 900 fan

Google is your friend.
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Old 28-08-2016, 14:18   #3
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Re: 12v speed control for Guest 900 fan

Yeah, I googled the bejeezus out of it and after many hours over several weeks I fogot what I was looking for. But i got some nice LED lights on the way, a new main traveler, a new goose neck and I've been offered several million dollars from a bank in Nairobi and several other small countries. People seem to leave money laying around everywhere.
But i still can't find that speed control.
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Old 28-08-2016, 14:40   #4
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Re: 12v speed control for Guest 900 fan

This should do the trick. Scroll down for the fan speed control.

RV Lighting - 12v DC Dimmer Switch
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Old 29-08-2016, 09:29   #5
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Re: 12v speed control for Guest 900 fan

Quote:
Originally Posted by SSgtPitt View Post
Yeah, I googled the bejeezus out of it and after many hours over several weeks I fogot what I was looking for.
[... ]
But i still can't find that speed control.

Too funny and rings a few bells!

As Steve suggests, there are products out there, my guess is they use pulse width modulation (PWM) to turn the 12V on and off at a frequency where humans cannot see the flickering anymore. The ratio between on and off then gives the brightness of the lamps or the speed of the motor.

A motor also creates voltage pulses whenever you turn it off and hence the controller needs to be able to handle that. Well, and other nearby devices on that bus.

Also, keep in mind that PWM can also create radio interference for you and everyone in the vicinity, so be aware if you hear hissing noises, squealing or if your emails don't get through the HF radio anymore while any of those devices is active.
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Old 29-08-2016, 13:09   #6
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Re: 12v speed control for Guest 900 fan

It may start to hum if you use a dimmer switch.
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Old 29-08-2016, 13:30   #7
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Re: 12v speed control for Guest 900 fan

You need a rheostat. They were common for heater fans on vintage cars. Maybe google that. The last one I bought NAPA auto had a universal type. Not sure if they still do or not as it's ben a while.
Adapting it may be another thing entirely, but the NAPA ones are very robust, probably overkill for a modern fan.


Later: wow, they've gotten pricey and not sure if they still include the bracket or not. Ebay may be your friend. https://www.napaonline.com/napa/en/p/SPP172513/
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Old 29-08-2016, 17:24   #8
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Re: 12v speed control for Guest 900 fan

You guys are all crazy!

A dimmer IS a rheostat and is a potentiometer and it wont work. Light dimmers can only change the voltage and hence they only can work in LIGHTING or non-motor applications. Electric motors get adjusted by changes to their frequency and remember dimmers only handle changes to voltage and not frequency. You are SOL.

Whats needed is a frequency controller such as a variable power switch on an electric drill. Im facing the same problem right now trying to add variable power to a car polisher that spins too fast in the ON position, the only position it has. Yesterday I spent the day going to electric parts shops and could not find a frequency controller. I was thinking about salvaging a variable switch from an old drill motor or maybe just throwing this polisher away.

Your only real option is to scavenge a multiposition switch from an old fan or keep looking for such a switch online. A light dimmer switch will likely ruin the motor as well as not giving you the variable result you want until it does quit. The dimmer will likely start burning and stinking. You want the potential for a fire?

If you do find a frequency controller switch, please come back in the thread and post the result. Thanks!
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Old 29-08-2016, 17:48   #9
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Re: 12v speed control for Guest 900 fan

Some people love to complicate things. You need a PWM controller, $12 on Amazon, delivered next day. A dimmer would not work and it would waste energy. Make sure that the amp rating on the controller exceeds your fan amperage.

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Old 29-08-2016, 17:57   #10
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Re: 12v speed control for Guest 900 fan

PWM devices can, indeed, cause RF interference. A simple rheostat will work fine. You just need to get one with a power rating appropriate to the load. For example (very simplified, but ...) if your 12-volt fan draws a nominal 2 amps, then the load is about 25 watts, so you need a rheostat rated for 25 watts (actually less, but WTH.) Furthermore (also simplified) 12v and 2A means 6 ohms, so you want a rheostat in the range of say 0 - 10 or 20 (ish) ohms. More is OK, but likely you will find that 6-8 ohms works nicely. Alternately, try some fixed resistors in that range (and power rating) and find the one that you are happiest with and just use it. I control my fans with hi/lo speed using fixed resistors this way. For your particular fans remember V=IR, P=IV and figure your requirements from this.
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Old 29-08-2016, 19:23   #11
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Re: 12v speed control for Guest 900 fan

Quote:
Originally Posted by CharlesV View Post
You guys are all crazy!

A dimmer IS a rheostat and is a potentiometer and it wont work. Light dimmers can only change the voltage and hence they only can work in LIGHTING or non-motor applications. Electric motors get adjusted by changes to their frequency and remember dimmers only handle changes to voltage and not frequency. You are SOL.

Whats needed is a frequency controller such as a variable power switch on an electric drill. Im facing the same problem right now trying to add variable power to a car polisher that spins too fast in the ON position, the only position it has. Yesterday I spent the day going to electric parts shops and could not find a frequency controller. I was thinking about salvaging a variable switch from an old drill motor or maybe just throwing this polisher away.

Your only real option is to scavenge a multiposition switch from an old fan or keep looking for such a switch online. A light dimmer switch will likely ruin the motor as well as not giving you the variable result you want until it does quit. The dimmer will likely start burning and stinking. You want the potential for a fire?

If you do find a frequency controller switch, please come back in the thread and post the result. Thanks!
Sorry but you don't know what you are talking about. A rheostat works great on a DC motor. Maybe you are thinking AC. As I said earlier, they were standard issue on heater fans in trucks in the 40's and 50's etc. They are usually ceramic bodies as the energy not going to the motor is being used up as heat.
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Old 29-08-2016, 22:20   #12
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Re: 12v speed control for Guest 900 fan

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Old 29-08-2016, 23:28   #13
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Re: 12v speed control for Guest 900 fan

Cheapest way to do it is Ebay search for these things
DC 12V 8A LED Light Protect Strip Dimmer Adjustable Brightness Controller New HT
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Old 09-09-2016, 11:22   #14
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Re: 12v speed control for Guest 900 fan

I use PWm motor speed controllers And LED dimmers to control brushless computer fans.

The LED dimmer has a 13khz pulse and makes the fan Whine annoyingly when it is slowed down. So much so I can't use it for this purpose.

The PWM motor speed controller is 21KHZ and I cannot hear it whining, although Fido probably can. Not sure if a brushed motor fan would act the same, but all my future PWm motor speed controllers will be 21khz or higher in the future.

I also have some Ciggy plug style universal voltage controllers that can handle 2 amps output, and can output 3v, 4.5v, 6v, 9v and 12v. No whine. These throttle fan speeds nicely too in those 5 detentes, and have proven durable over 3+ years of service. Only issue with my version is the design can allow one to tweak the unit sideways in 12v receptacle and short out and blow the fuse to the receptacle. Some heatshrink covering all but the spring loaded nipple prevents the issue entirely. I've only loaded mine with a fan that can consume 1 amp at 12vdc. a 92 MM vantec tornado I put on a gooseneck on a 2" spring clamp.

https://www.amazon.com/CyberPower-CP...ZVQBP2S0WFF16X
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Old 09-09-2016, 12:39   #15
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Re: 12v speed control for Guest 900 fan

Use a 12v light bulb in series. Start with 5watt. Then try a 10 etc.
when you have the speed you want. You're done. Just cover it in putty or some other thing so the light doesn't keep you awake. It's just a resistor.
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