landyacht318
Near a large body of water
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I have become a ventilation Nazi and have 9 muffin style computer fans keeping my B van at or below ambient temperatures and keeping my fridge as efficient as possible.
Recently I found this mac daddy fan which includes a speed control.
mac daddy muffin fan
It moves more air for less noise and amperage draw than my current roof exhaust fan. The external speed control rheostat seems real simple. Pictures are available in the above link.
My question is: will this Fan draw the same amperage no matter what the speed control is set to, as one friend claims?
I have a Vector multi voltage ciggy style plug (for my MP3 player) and an experiment showed Different amperage draws for each voltage setting when powering one of my fans, as expected.
Is there a major difference in the operation of these two speed control (voltage control) devices?
I've been told by electricians that using a dimmer switch on your AC lights in your home will use the same amount of electricity no matter what the setting. Is this true? DC and AC?
Somebody enlighten me, please.
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wa8yxm
Wherever I happen to park
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Joined: 07/04/2006
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Fan motors will change amprage as voltage changes,,, However predicting the change is kind of tough, and it's non-linear The only way to be sure is to stick a meter in the line and play with it.
As for AC lights and a dimmer.. I have never tested it but I believe that they do indeed reduce current draw as voltage is reduced (As you dim them), however again it is NOT linear
The catch is that the common dimmers work by rapidly turning the bulb off and on, this can INCREASE current during the "on" part (While of course cutting it to zero during the off part) again, meter it to be sure A Kill-A-Watt meter is real handy for testing AC stuff
Nothin adds excitment like something that is none of your business
John is Near Kenwood TS-2000 housed in a 2005 Damon Intruder 377
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landyacht318
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Thanks for the info.
I did notice in my experiment with the multi voltage Vector plug that the draw was not linear. The draw was less than .1 amp at 6 volts(6.32 volts) and .6 amps at 12(11.76volts).
When I bypass the Vector and get a full 12.8 or more volts the draw increases to .7 amps.
The fan I did the experiment with claims to move 106 cfm and draws .38 amps @ 12 volts. It is louder than a fan that lists a 43db noise level.
I've no way to test the cfm but the amp draw is way off.
If the mac daddy fan performs as advertised it will really be a case of more for less.
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sixpack98
Texas
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Joined: 06/29/2006
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It depends on the type of voltage control being used. If it is a simple rheostat the current will stay about the same (at constant speed). The wattage will remain the same since the rheostat and fan are in series. What changes is the voltage dropped over the rheostat and fan. Not very efficient.
If its an electronic speed control the wattage will decrease as the voltage decreases since the electronic speed control is very efficient and has a pretty much constant drop across the device.
The following is an example of a very efficient temperature controlled variable speed controller. About $4.00 to build. It uses a thermistor to control a power MOSFET. The thermistor changes resistance relative to heat and controls the output voltage of the MOSFET. At fan shut off the current draw is about 2ma. The chief advantage is the fan speed changes as the temperature changes and approaches steady speed once it settles in. The trim pot sets the speed controller start temperature.
I found this circuit was found on a power PC web site and I modified it to meet the environment of an RV. Radio Shack has the parts except some don't carry the thermistor but it can be found at any electronic supply or on the web.
* This post was
edited 08/29/08 04:02pm by sixpack98 *
Mark and Dawn
2006 HR Endeavor
40 PET
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landyacht318
Near a large body of water
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I finally got around to purchasing the fan I posted a link to above.
It is as advertised. The speed control does go from low to high in just half it's range of movement, but not a big deal.
It seems to draw about .1 amps as minimum speed and slightly over .4 amps at full speed.
It is a large improvement over the fans it replaced.
I say fans as I had 2 counter rotating fans. The second lower rpm fan significantly increased the output of the primary loud high RPM fan. At night I'd turn off the loud fan and the blades would still be pushed from the secondary. 2 fans inline that are not counter rotating are worthless. Loud and move less air than 1.
When I add this lower RPM fan to the new fan the increase in flow is slight to non existent at full speed and markedly louder.
The wires running from the speed control to the fan are about 5 feet long so I extended it a few feet.
If your looking to increase your ventilation I highly recommend this fan. Moves a lot of air for little amp draw and takes up little space.
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