How evil is it use a big Zener as a turbine dump load?

[DamonHD]

...is it evil to use (say) a 15V Zener of continuous Watt rating much higher than the wind source maximum power both as a kind of passive 'dump' load for excess energy and to remove spikes much larger than the 12V system nominal to avoid damaging other things?  (I know that the battery should act as a filter, but I feel warmer inside nuking spikes ASAP, and one day this might accidentally get disconnected from the battery.)

How much less evil would it be to use (if available) say a 14.3V or 13.5V or lower Zener instead to guarantee that even a full battery could not be 'overcharged'?  There would be another reverse-blocking diode after the Zener on the way to battery so that only the turbine current can find its way to the Zener.

I'm assuming that even for a gel SLA, with a maximum turbine charge current of << C/100, that I don't really need much regulation at all and I won't damage the battery: opinions please?

Rgds

Damon

[wooferhound]

Or maybe even Zener Overspeed Protection

[Nando]

Damon:

to make a HIGH power Zener to limit the power, it not difficult, and the problem is the dissipation of the clamped power.

The dump controller is a Zener, basically, which is more effective and can be varied to allow a battery profile as you may need it.

You can dissipate such power via high power resistors which stand high current and high temperatures much better and easier than semiconductors.

The proper dump controller should be one operating at high frequency with a much higher capabilities than the maximum capacity of the power source to warrant proper battery charging profile and protection for it.

Nando

[DamonHD]

Remember that this is a very very small secondary power source, so I could clamp it to (say) 13.xV to look after the battery and just provide a small charge when the battery is really low.

If the power source were a little larger then I'd look at G's circuit (or my variation) first, and beyond that I'd want a real multi-stage controller!

But for this tiny C/400 current, will a big Zener mainly to kill spikes and any surprise blasts of wind with a full battery, be OK?

Rgds

Damon

[Flux]

You could use a zener, the scheme was used at one time for motorcycle charging systems.

You will not really have a decent choice of voltage, it is most unlikely that a standard voltage unit will be exactly what you want. You can easily make the equivalent of a variable voltage zener using a TL43c shunt regulator chip and a power transistor then you can set it to any voltage you want. It then becomes nothing more than a linear dump regulator. You could include a resistor to dump a fair proportion of the power rather than dump it all in semiconductors.

I am not sure how much trouble it is worth taking with very tiny systems. If you have to use them in remote places then you need to keep things fairly automatic and if they are generally floated and for backup then a constant voltage dump is fine. If you are trying to extract much useful energy from a tiny system then you probably need something a little more sophisticated to get a better charge efficiency from 80% upwards.

Flux

[DamonHD]

Thanks.

I am doing this in large part to get some familiarity with turbines, and to have something I can use to automatically log 'usable wind' on my turf.  (One thing that this is going to drive other than a tiny charge into my SLA is an optoisolator so that I can see how many 'wind-minutes' I get each day...

So, if I get (say) 50% energy efficiency that will be fine for now.

Thanks,

Damon

[ZooT]

Could that resistor be a small 12v ceramic car heater element?

[ZooT]

I suppose I should elaborate a bit more hoping to get better answers.....as I'm really interested in this too

I've been reading over at redrock and over at chemelec's site....and everything that I've read so far says that these simple shunts short out solar panels once the battery is up to the voltage set by the circuit.(zener voltage+ tranistor + any additional diodes piggybacked to the zener)

If one were to add a resistor between the emitter of the power transistor and the ground wouldn't that serve as a dump load rather than shorting out the solar panel or in this case wind turbine?

The redrock simple shunt has a resistor located between the positive lead and the collector of the power transistor.

Is the resistor in that circuit a simple dump load?

[DamonHD]

You don't need to dump solar PV at all AFAIK: you can just 'let go' safely and it isn't going to run away like a turbine, though you are wasting the available energy.  That's what my Morningstar controller does for example.

I'm just treatning my Zener as a back-stop spike-killer and dump-load for my tiny turbine if something goes wrong (eg a connection opens up somewhere).  See http://www.earth.org.uk/wind-power-pilot-autumn-2007.html

Rgds

Damon

[ghurd]

I've done it with similarly sized (~1W) windmills, and smaller batteries.  1.3 and 7AH SLAs.

Used 2, 5W Zeners in series, 6.2 and 8.2V.  Paralleled with a Schottky blocking diode and the battery.

Worked fine... as far as I could tell.  The battery stayed near but below 14V. That was all I wanted!

G-

[DamonHD]

What were you using the 1W mills for, if I may ask?

(Yes, on reflection, a voltage a little lower than 15V would be better, but the shop that I was standing in didn't have one at that power rating!)

Rgds

Damon

[DamonHD]

All irrelevant today since windspeed is <2mph!  B^>

[ghurd]

"Proof of Concept", LOL.  Just for fun.  Stepper motors.  Playing with blades, etc.  Charge AAs, or a drill battery. Charge a 12V 7AH, then use an inverter to charge the cell phones. Stuff like that.

Wind here today won't blow smoke away.

G-

[ZooT]

I only mentioned the PV's because both circuits are intended for PV's, and the designers of the circuits say they're not suitable for wind turbines...why?...because they create a short circuit.......which they state is safe for PV's......but not for a wind turbine

So....what if they didn't create a short circuit?

If a zener diode by itself will act as a  spike-killer and dump-load wouldn't an amplified zener do the same?

Flux mentioned using a big resistor to dissipate the current rather than dissipating it in the semiconductor(zener).

So if I'm reading this correctly you want to place a big zener between the positive and negative leads of your wind turbine to act as a dump load/spike killer.

The zener rating determines when the short is created and the current is dissipated by the zener in your description.

The zener "is" the dumpload.

Flux said that adding a resistor to that might make the zener run cooler and live a bit longer.

So now we've got a zener and a big resistor between positive and negative.

The zener trips at it's rated voltage and current passes through it and is dissipated by the resistor.

Is this correct?

One article says that an amplified zener is just a "big" zener and can be used as such with the only real difference being that the current is dissipated by the power transistor rather than the zener itself, which only triggers the transistor. And the transistor can be heatsinked, so now the transistor "is" the dumpload...

Is this correct?

OK......so can we add a resistor to that and use the resistor to dissipate the current?

If so, now the zener is a trigger and the transistor is a switch, and the resistor is now the dumpload......

Heck.....I'm heading to radio shack now, as you folks got me thinking about this yet again (laughing)

I'll let you know if I make some smoke........