AC Variable Load Controller (photo)

[Dave B]

This is my AC variable load controller based on 2 LM3914 LED Driver ICs. It is basically an adjustable bargraph AC volt meter that monitors the AC output direct from my alternator. From the output of the LEDs I can switch on 2 different solid state relays (or any number) at any level of output independently which will remain on for as long as the LED (AC selected output) remains lit. I plan to pre-heat water, no batteries. My single phase, single disk,  unslotted silcon laminate stator Volvo type axial alternator outputs approx. 100 VAC @ 400 rpm from my 12' 3 blade rotor. I am currently experimenting with different hot water heating elements and switching levels including no load at start up and hysterisis. Updates to follow, so far this functions exactly as planned.  Dave B.  

[Old F]

Dave

I take it that you are using two separate circuits  one with LEDs  and one with out .

And the one with out you are taping the points where the LEDs would have been for your set point.

Is this right ?

 I have been playing with some thing similar  for DC.

Oh and I like your old school  bread board lay out.  :  )

Old F

[domwild]

Dave,

Thanks for that. Have you posted the circuit for this one before? If not, pls do so if it is not too much bother. I suppose you will want to automate the switching process. I take it the load is off in a no wind situation to get the mill started. 12' is four meters, this is a large diameter prop no doubt. The RPM must be low.

Keep up the good work.

dominic

[srnoth]

Hey Dave,

Nice Work. Would it be possible for you to post somemore information on the circuit, if its not too much trouble.

Cheers,

Stephen.

[Ungrounded Lightning Rod]

If those glowbar resistors are dissipating any significant amount of power I'd mount them away from the board and lose the nylon tiewraps.  They get HOT.  Wood ignites at 451 degrees and smoking nylon is stinky and toxic.

Say a couple terminal strips and the resistors supported away from everything else on their leads, with lots of nice air around them.

[Dave B]

Thanks for the comments and suggestions. Yes, the power resistors you see can get quite warm if running full bore for 10 minutes or so straight (equivelent to 30+ MPH wind) but this is still well within their power rating even if constant. The mounting is temporary with either heat sinks to follow or "open air" as mentioned just to be over cautious. The AC from the alternator is being rectified and then the DC is being dropped down through the power resistors to the level adjustment pot that controls the base input to the LM3914's. Toggle switches select the LED(s) at which the solid state relays will be triggered. A DC wall wort provides the LED voltage and the solid state relay input is parralleled across the selected LED(s). I'll get some schematics sketched when I have time. A search on LM3914 will show the  exact circuit except for adding the solid state relays to the LED outputs. Comments and suggestions always welcome. Thank you, Dave B.

[wooferhound]

There is information on a circuit simular to this one in this story...

http://www.fieldlines.com/story/2004/11/19/21229/573

[Ungrounded Lightning Rod]

I believe the power rating for the resistors assumes they have air all around them rather than having one side tight to a surface.

You'll notice that they are usually made to stand off from the board when used with a PC board, and are often connected to their own terminal strips to insure they don't cook the board or the connection to it.

[Dave B]

Again, thanks for the tip on the power resistors. I have tested this circuit at 120 VAC direct line voltage and both relays triggered switching a total  of 20 A  or 2400 watts. At this voltage the resistors get quite warm and the relays remain luke warm at best (they are rated at 30 A each) My furling limits my alternator to approx. 100 VAC and so is highly unlikely that it would ever reach 120 VAC to begin with. If by chance it did it would never remain at this level for the extended period of time I have tested it at 120 VAC. I am a firm believer in over kill and even though as is the math figures all to be well below highest safe limits and testing proves this out I will be mounting the resistors open air and even possibly bumping up to higher power ratings. Lots of other fun stuff may be going into this design also such as auto load shutdown in case of power failure and or battery backup. This is just too much fun.  Dave B.