Technical Electrical/Electronic Question

[Shoaldrafter]

All,

I normally reside over on O'Day Owners Forum, but am making a double entry post over here also:

I routinely point folks to archives on questions. I asked our archives several questions using search function provided. I did not use internet search of our archives yet.

Here is question: I have a fan speed control. It is old and does not function well. It is 'rheostat' type. I checked West Marine Catalog and Defender and could not find new version.

I was asking where to look when computer engineer suggested solid state device. However, he was microprossor designer and not a sail boat or boat person. He was unable to point me in direction of marine suitable device.

Searching the internet I have NOT found any device to vary cabin fan speed on boats. There has to be something out there but this old guy is not searching in right places.

I would also want to apply this to cabin lights and maybe other things.

I am not even aware of best short caption to define this question. This is a good Sunday in winter question, yes?

And certainly feel free to shoot back snide remarks, as long as they contain some relevant info.

Ed K

 

[Maine Sail]

All,

I normally reside over on O'Day Owners Forum, but am making a double entry post over here also:

I routinely point folks to archives on questions. I asked our archives several questions using search function provided. I did not use internet search of our archives yet.

Here is question: I have a fan speed control. It is old and does not function well. It is 'rheostat' type. I checked West Marine Catalog and Defender and could not find new version.

I was asking where to look when computer engineer suggested solid state device. However, he was microprossor designer and not a sail boat or boat person. He was unable to point me in direction of marine suitable device.

Searching the internet I have NOT found any device to vary cabin fan speed on boats. There has to be something out there but this old guy is not searching in right places.

I would also want to apply this to cabin lights and maybe other things.

I am not even aware of best short caption to define this question. This is a good Sunday in winter question, yes?

And certainly feel free to shoot back snide remarks, as long as they contain some relevant info.

Ed K

Ed,

For lighting Blue Seas makes some dimmer devices sold by amp draw. They are pricey though as DC dimming is not as easy as AC dimming. The newer digital style DC dimemrs are pulse width modulated to control output. The newer ones will work with both LED and incandescent bulbs.

As for cabin fans you'd probably spend less money to just buy a new 12V fan that has three speeds. You could also build your own rheostat. Pre-made ones for 12V are getting hard to find as most are moving over to PWM type dimmers.. You can pick up inexpensive fans at a truck stop or Wal*Mart or spend more money on a Hella or Bora fan. The cheapies are harder to find with three speeds but they are out there. We use the Bora Caframo fans on-board and love them..

Digital Dimmer 12V / 12A

 

[Sumner]

....... You can pick up inexpensive fans at a truck stop or Wal*Mart or spend more money on a Hella or Bora fan. The cheapies are harder to find with three speeds but they are out there. We use the Bora Caframo fans on-board and love them..

Digital Dimmer 12V / 12A

We also love the Caframo fans....

....it was hard to part with the money for the first one, but then easy to spend the money on the second one.

I can't believe how much air they move on so little amperage. Way more effecient than the 'truck-stop' fans I've bought in the past. Also the built in timers save even more electricity. We go to sleep at night with the fan on low and with the 2 hour timer on and it clicks off by itself 2 hours later while we are asleep, saving electricity. If we wake up and are hot just ...

...push the button for another 2,4,6 or 8 hours.

http://purplesagetradingpost.com/sumner/macgregor2/inside-31.html

Like MS said spend the money on a good fan and not the controller if possible,

Sum

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[kenn]

MS and Sumner have, as usual, given great advice.

From a technical standpoint, it actually isn't significantly harder to 'dim' DC as compared to AC... there's just less demand for it. But there's some stuff out there.

Depending on the total current draw of your fans, I would be quite tempted to try one of these 8 Amp LED dimmers. I would probably add a reversed diode and a capacitor across the fan to minimize any generated hash and to protect the dimmer from reverse EMF from the fan motor.

Actually, some more ebaying for "12v dc motor controller" turned up some more beefy controllers, intended for motors. Obviously these aren't necessarily 'marinized' for life on a boat. I would consider spraying the boards with a lacquer or electrical protectant to better resist the sea air.

 

[Shoaldrafter]

Guys,

I keep reading. The replies help some.

Ed K

 

[RAD]

Copied from the Oday site:

Heres what you need providing the fan draws less than 6 amps.....easy and cheap
http://www.ebay.com/itm/PWM-DC-Motor...item3a6d641546

here's another site to cover both fan and light

http://www.pca.com/newproducts/12vdimmer.cfm

 

[Steve Dion]

Here is a source for 12vdc rheostats. I don't know if this fits the bill or not, but it is worth checking out.

http://www.buycheapr.com/us/result.jsp?ga=us9&q=12v+dc+dimmer

 

[Don12364]

KISS

Lovely old fashioned simple circuitry - free of electronickery.
Search e-Bay for 'Wirewound Variable resistor' and look at the range of 25 watt devices on sale for approx $5+shipping.
If it is only a small cabin fan, you will need to look at the wattage rating on the fan label and divide this by 12 volts to know the amperage it will draw - or measure it using a meter.
Then, divide 25 watts by the current squared and this will give the approximate resistance you will need.
It is not an exact science but, if in doubt, purchase several wirewound fixed resistors and try each in series to find the resistor that gives the slowest fan speed you are likely to need.
See:-
http://www.ebay.com/sch/i.html?_nkw=wirewound+variable+resistor&_sacat=0&_odkw=wirewound+potentiometer&_osacat=0&_trksid=p3286.c0.m270.l1313

 

[Shoaldrafter]

Thank you Donalex

Lovely old fashioned simple circuitry - free of electronickery.
Search e-Bay for 'Wirewound Variable resistor' and look at the range of 25 watt devices on sale for approx $5+shipping.
If it is only a small cabin fan, you will need to look at the wattage rating on the fan label and divide this by 12 volts to know the amperage it will draw - or measure it using a meter.
Then, divide 25 watts by the current squared and this will give the approximate resistance you will need.
It is not an exact science but, if in doubt, purchase several wirewound fixed resistors and try each in series to find the resistor that gives the slowest fan speed you are likely to need.
See:-
http://www.ebay.com/sch/i.html?_nkw=wirewound+variable+resistor&_sacat=0&_odkw=wirewound+potentiometer&_osacat=0&_trksid=p3286.c0.m270.l1313http://www.ebay.com/sch/i.html?_nkw...iometer&_osacat=0&_trksid=p3286.c0.m270.l1313http://www.ebay.com/sch/i.html?_nkw...iometer&_osacat=0&_trksid=p3286.c0.m270.l1313

- - - - // - - - -

Donalex,

Thank you and all who contributed. There was a time that I knew the formula and could figure out the current, watts, etc., however a voice told me just ask on internet rather than look for some old notebook.

As to 'Wirewound Variable resistor' versus solid state, I may just get one of each to test. If solid state would substitue then we would eliminate point of corrosion issues, yes?

Now I know what PWM - pulse width moduation - means and it just might work. (http://www.aaroncake.net/circuits/motorcon.asp)

And I have been forwarded comments from others, such as this reference:

http://www.alliedelec.com/variable-resistors/potentiometers/?dsNav=N:4294966716-4294965370

It seems even old type 'Wirewound Variable resistors' that have been water sealed are around when you get some directions which log to look under.

This thread offers some good comments, advice and references for those interested.

Ed K

 

[txjim]

Just remember that, although simple, the rheostat will burn power as it forms a divider with the motor to reduce speed. A PWM controller will greatly improve the efficiency of the fan system with the possible side effect of introducing switching noise into your electrical system.