Dump Control relay

[Walter]

A wind turbine dump controller can switch the turbine output between the battery pack and the dump resistor with a SPDT relay. Alternatively it can switch the dump resistor in parallel with the battery pack with an SPST switch.

Aside from the cost of the relay is one method more effective than the other?

[ghurd]

Calculate the values of the required dump resistor.

Without knowing the voltage, everything else is a bad guess.

The only way to know the voltage is to connect the dump load to a known voltage,

and the only known voltage is the battery voltage.

I left out my normal spew about evil relays being crap in controllers.

G-

[DanB]

I would not divert power from the wind turbine to a resistor to 'dump' - better is to have a controller that looks at battery voltage and dumps power directly from the batteries.  Either sort of relay should work, but be very careful if you use a relay ~ it's a lot of current and if the voltage is high (especially a 48V system) a normal relay may not work at all.  When they open they may draw an arc which will quickly burn up the relay.  Solid state is probably a better way to go ~ or if you have a very basic system like I do, a mercury contactor may work.  I don't trust normal relays to hold up in this situation though (I've had bad luck).

[Ungrounded Lightning Rod]

Think of the battery as a reservoir behind a dam.

Think of the dump load as opening a spillway to lower the water level.

Why divert the incoming river when you can just spill the excess water?

(And if power comes in FASTER than a dump load can dump it and the batteries overcharge a bit, the dump load can pull the overcharge off after the fact.  If you divert, rather than just dump, an undersized dump load means a runaway mill which may then self-destruct.)

[fabricator]

Now that is about the simplest way I have ever seen that explained, if I can understand it it has to be simple.

[Walter]

That's a pretty good analogy.

As for "Why divert the incoming river when you can just spill the excess water?" that's the question before us. Is it better to disconnect the pack and spill into a resistor or is it better to parallel the pack with a resistor and bleed off the surplus.

In the first case if the dump load is undersized then the batteries will overcharge for the duration. Over a lengthy period with strong wind and no other load on the battery pack the batteries will boil off water.

In the second case if the dump load is undersized then the turbine will over speed.

so maybe it would be best to disconnect the turbine and apply a short to its terminals.

[Ungrounded Lightning Rod]

Doing things that disconnect the turbine introduce additional points of failure that could lead to an unloaded turbine running away.  (If you feel you must short out the turbine in a windstorm you can do it upstream of the rectifier or blocking diode without disconnecting it from the battery.)

Leaving things hooked up and dumping as fast as you can means the turbine still sees the battery voltage as a load and its speed is limited by this.  Meanwhile the battery's charge current is the turbine's output current minus the dump current.  You normally size the dump load (or the sum of the multi-stage dump loads) LARGER than the turbine's long-term safe current.  So you will only see overcharging for more than a few seconds at a time if the turbine isn't furling properly and is about to burn out.  So you needn't worry about significant excess water loss from gassing.  Meanwhile a failed dump load just means you have to add water more often and/or annoy your neighbors with bright yard lights until it's fixed, not a scrapped mill.

Remember the KISS principle and keep it simple.  In this case (as usually happens) the simple design does the right thing and doesn't introduce nontrivial problems that need patching.

[Walter]

Thanks Rod, that makes good sense.

[TomW]

Rod[

I like this quote myself, kind of sums up "K.I.S.S."

Perfection is achieved, not when there is nothing more to add, but when there is nothing left to take away and achieve the desired results.

Tom

[soisay]

Should there be a little buzzing from the controoler while its dumping ?

Ihave the propper Ohmite resistors setup .

The buzzing is just audable.

P.

[DamonHD]

Or even:

"Everything should always be made as simple as possible, but not simpler." -- Albert Einstein

Rgds

Damon

[Ungrounded Lightning Rod]

Also known as "Einstein's Razor" and my favorite slogan on the KISS principle.

(The full form of the original Einstein quote, before it was summarized and generalized from physics theory to engineering and most other endeavors, is:  "It can scarcely be denied that the supreme goal of all theory is to make the irreducible basic elements as simple and as few as possible without having to surrender the adequate representation of a single datum of experience."

Then somebody applied the KISS principle to the verbiage, thank God!  B-)  )

[Ungrounded Lightning Rod]

What kind of controller do you have and where is it hooked up (across the battery or upstream of the rectifier)?  Are you using wire-wound resistors, especially the ones that are like heater coils on a ceramic form?

If you've got a significant high-speed variation in the dump load current (such as when using a pulse-width controller or dumping on the AC side of the rectifier, this produces a varying magnetic field that can shake the components of the resistor, creating vibration and noise.  (Like hum in a transformer, for the same reason.)  If it's barely audible you're probably fine.

But if you're dumping at the battery and you don't have a pulse-width dump controller, you might want to check your battery for something that would raise its resistance and show excessive ripple from the genny's charge current:  Loose or corroded connections, low water, sulfation, or long wires (sharing charge or load current) from the place where the dump controller is hooked up to the battery.

[soisay]

Thanks for the help. My resistor setup is from this web site a few weeks ago .Its eight resistors six of them 0.5 ohm two 1 home all are 300 w. Thats two sets of 3 and the other 2 one ohme at the end .

3 phase to the rectifier then DC to the batteries then from the batteries to the controoler from there to the Ohmite resistors. I had to bend my ear to find wich exactly was causing the buzzing , its the controoler. The resistors get hot but not enough to smoke or change colour. Connections are all solid bolted ring connectors with six square wire. The controoler is a tristar C60. Any ideas what the little buzzing could be.

P.

[Ungrounded Lightning Rod]

Sounds like it's some kind of switching controller.  Buzz is probably the turns of an inductor being vibrated.

Since it's working right and the sound is minor I wouldn't worry about it.

[David HK]

Forget relays.

Some well inteded advice if you require it, is to purchase a "ghurd" controller.

Also, read this article and it may help to explain more about your requirements.

http://www.fieldlines.com/story/2009/10/7/201054/947

Ghurd is a frequent contributor to this forum.

Good luck.

David in HK

[scoraigwind]

Pulse width modulation (PWM) controllers like the Xantrex C-series and the Morningstar Tristar ones will always make a buzzing noise when working (especially the heaters will buzz) and so it is nothing to worry about.  If it annoys you then you might prefer to use a controller that switches the load in and out more slowly, maybe with a relay.

Dumping straight off the windmill often stalls it (in low winds anyway), so it slows right down.  This may or may not be a good thing depending whether you are trying to heat water or just waste power.  Most people dump off the battery and leave the windmill connected to the battery.  This may cycle the battery a bit but it doesn't mind shallow cycling like that.

[soisay]

Thanks for that Scoraigwind ,as its just a little buzzing I'll leave it .It is dumping from the batteries side. Iwas wondering if anyone had the same little buzzing while its dumping . Thanks.

P.

[imsmooth]

You can look at this http://www.mindchallenger.com/wind/wgpage16.html controller.  It used an IGBT or MOSFET.  So far it has been very reliable

All you need to do is change the diodes to set the threshold to your voltage.  In this schematic it is set to 230v.  You would want it to be something a little above your battery voltage.  You would also have to change the voltage regulator.  This one, which is meant for grid-tie, needs a robust voltage range to run the ICs, and needs to generate voltages for the ICs over a wide range.  If you are using a battery, you don't need the resistors going to the 18v regulator chip.