Need help with voltage control circuit

[drjeseuss]

Likely overthinking again, but I can't figure a good way to control voltage.  In a solar or wind setup (wind especially) there will be a variance in volts through the day.  I'd like to add a bit of circuit to help this.  If my batteries are 12v and the power output of the mill is greater than 12v then it follows a normal charging circuit.  But if the volts are less than 12v, it gets diverted through a doubler, then to the charger (I know my amps will drop from this, but at least it's still doing more than dumping power away).  I know how to do the doubler, the charger, etc, but can't for the life of me figure a way to choose a path based on <12v or >12v.  I'm sure I've overthought this, and I'll bet it's been discussed all over, but I've been scouring for hours and can't seem to find just what I'm seeking.  Thanks in advance for the help.

[DamonHD]

Hi,

Have a look at the circuit here:

http://www.earth.org.uk/wind-power-pilot-autumn-2007.html#MotorWind

The idea is that the cap-based doubler should be able to extract some of the small energy available at low wind speeds and does nothing much at all after normal cut-in.

For a decent turbine you'd need big caps, but you can try out the idea (I haven't tested this variant yet) with any old cheap stuff you have to hand.  You could guess at a good cap size by matching the cap reactance to the coil resistance at the AC frequency from each coil when the wind speed is just below normal cut-in, ie when you want the doubling.

No 'switching' needed.

I repeat: I haven't tested this circuit yet myself.

Rgds

Damon

[commanda]

Should read this thread.

http://www.fieldlines.com/story/2006/3/17/185646/194

Amanda

[ZooT]

I'm tripping a SPST relay with a zener diode, and that turns a 150 watt car heater on and off.....

Wonder if you could trip a SPDT relay with a 12v zener diode and make that "<12 or >12" switch?

[drjeseuss]

Great ideas.  I've been inspired, not to be greedy, but to be efficient.  As most of my work on this so far has been at a highly experimental level (that's code for hobby/A.D.D. fix/...) I'm trying to get the most out of a micro sized system.  My wind generaotr is a 4 phase stepper.  I've got each phase pair routed through a bridge rectifier.  This gives me 2 seperate, but roughly equal outputs.  I've been mulling over weather to connect them in series to boost volts, or to connect in parallel to capture combined amps once I exceed my minimum.  I didn't want to waste on the high speed/high energy end, nor did I want to loose all energy produced below threshold.

  I must say the relay idea sounds simple enough to work.  I like it.  I think I could use a DPDT relay that, when triggered, would switch the mill output from a regular charging path to a double then charge path, or back again.

  I'm thinking of using a PicAxe chip to control much of my process, primarilly for logging purposes, but this would enable me to do some easy computing to flip the switch.  The PicAxe will be monitoring volts, amps, SOC, mill RPM, windspeed.  Using these factors, it would be easy to if-then a result.  This way it could even decide weather a voltage doubling would get it over the threshold or not.  If not, don't bother doubling.  Also, it could decide when (after a few calculations and tests I'll know when) to drop the doubling circuit to allow the RPMs to rise in a stronger wind thus resulting in the needed volts, and at improved amps.

On another note, in my bridge (GBL005) I believe I remember seeing that it loses 1vDC on the output (similar to the 1N4001).  Anyone had experience with this chip?  Sounds like I might be better off making on from schottky diodes.  Anyone?

[ghurd]

Have you checked the output into a battery at different RPMs and both configurations yet?

There is a very real possibility any gain with the relay circuit would be used up by the relay coil current.

I would be surprised if it breaks 100ma, amazed if it breaks 125ma.

The 1V drop of the bridge is nothing significant with most steppers. There is usually plenty of voltage. The current is limited by the resistance.

At 50 to 100ma the data sheet shows about 0.7V per leg.

Schottkys may help a little, mostly because they are fast. I never noticed any difference.

Schottkys may gain a whole volt, but don't expect the current to rise much at all.

"Threshold" on steppers is usually at very low RPMs.  Steppers can get away with it, but in efficient windmills it leads to stall.

Until the tests into a battery are done, my bet is you are chasing a problem that doesn't exist.

G-

[drjeseuss]

I see your point yet again.  I'm starting to think you're my conscience of sorts...  the voice of reason anyway.  While I'm thinking of saving volts in my bridge, I fail to think of volt/current loss in a relay circuit.  Go figure.  I'll have to do some bread boarding I think before I move on.  Thanks again ghurd.

[ghurd]

If you want to try stepper'S', I suggest building bridges on perf board,

connect 4' wires for the battery and 6~8' wires for the inputs, all terminated with insulated mini gator clips.

Plan on 5 input wires because 5-wire steppers seem most common.

It will save a lot of effort if you start testing every stepper from every printer, etc you can find.

Lets the motor be tested with a drill or with blades out in the wind.

Like this that Roger uses.  

I left out the blocking diode (the single diode) because it serves no purpose.

I left out the cap too, but it can help a little tiny bit.

Might help some to use 3A Schottkys, because they are faster (not much more money). 3A because you will want to short it for fun and some steppers will break 1A Isc.

Big fun in those little motors!

G-