why such a high amperage dump load?

[newkidontheblock]

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[Ungrounded Lightning Rod]

Your dump load has to pull enough power to stay ahead of ALL your generation.

Don't have to do it all at once - you can use multiple loads and controllers with slightly different setpoints to ramp up your dump rate.  But if your max load is less than your peak generation your batteries overcharge.  Avoiding that is the whole POINT of dump loads.

Like spillways on a dam, to keep the water from going higher and higher until the dam breaks.

[newkidontheblock]

i have a controller that will switch off of a full charged battery. then switch to a high resistive load, will this work?

[RP]

Is this for wind, solar, hydro...  ?

[Nando]

Again, no enough information, therefore I am going to assume that you have a wind mill.

When the batteries are charged, the charge controller disconnects the battery bank from the wind mill energy, if the wind mill is not stopped producing energy then other decision is needed, to DUMP this energy into something with the capacity to keep that power with its variations within limits, ( 0 to 100 %).

To solve this problem,( assuming that the wind mill is not stopped)a DUMP load or Ballast load is needed and this load has to have the capacity of being variable ( from 0 to 100 %) to absorb all the energy that at any moment the wind mill generates, which is "defined" by the wind velocity.

So, the Ballast controller presents a variable load to the wind mill energy to keep the power generated stable within its capabilities to AVOID either STALLING or ALLOWING high RPM that may destroy the wind mill.

Does this help ?.

Nando

[newkidontheblock]

to russp & nando37 i do not have a wind mill, but i have had some experience with a small wind generator & solar panel charging a battery to operate a remote water well. i thought that wind generators had a furling mechanism to turn the blades out of the wind, at high wind speed.guess i need to read more to understand the systems you are using.

[Spelljammer]

Let's say you design a windmill to handle up to 500 rpms and you want it to furl at 30 mph winds.  And one night the wind is blowing 20 mph and your windmill is turning at 300 rpms.  Your batteries get to 14.4 volts and your charge controller just disconnects the windmill to prevent damage to your batteries from overcharging.  But it doesn't use a dumpload, it just disconnects.  Well now your windmill doesn't have a load on it so it spins up to 600 rpms.  It may or may not damage it.  But then the wind picks up to 29 mph and it still doesn't furl yet but your windmill is going 800 rpms when it starts to fly apart.

Furling is to protect the windmill from damage..but it is set based on the windmill being slowed down because of a load.  Otherwise, if you set the furl speed to a given windspeed while the windmill is not loaded, then you'll never get any real power before it furls.

Dump load is to protect the batteries from overcharging while also keeping the windmill from overspeeding.

[newkidontheblock]

to spelljammer, thanks for the info. how about a rectifier , battery & controller on the tower and a dc electric brake?

[Spelljammer]

Well, you'll have to have a rectifier in the mix...maybe even 6 of them.  It just depends on what type of gen you have.  If you have a dc motor with brushes running as your gen then you will need 1 rectifier.  If you have a 3 phase AC alternator such as the ones people make on this site or even like a car alternator, then you would need 2 diodes per phase.

The generator will put out more voltage as it spins faster.  When it reaches the battery voltage plus any voltage drop across the rectifier then it starts charging.  Like a battery bank at 12.7 volts and a rectifier with .5 volt drop would mean that the generator would start charging the battery bank when it reaches 13.2 volts.  Then the battery voltage will slowly start rising.  That speed is called the "cut in" speed.  If a generator is spinning 200 rpm when it reaches that voltage then you could use some math... 200 rpm divided by 13.2 equals 15.15 rpms per volt.  So at 300 rpms it would try to produce 19.8 volts.  But the battery sucks the voltage down to 12.7 and starts to rise.  The electrical resistance of the stator will dictate how many amps though.

A dc brake...you mean shorting out the positive and negative on the output of the generator, right?  That would work especially on a plain old dc motor.  But the alternators actually send a pulsed DC that can arc across some switches.  Also, what if you short out the gen and the wind is still strong enough to keep spinning the blades?  It would probably burn up the stator.

If you use a high resistive load and low amp draw then it wouldn't be enough to keep the windmill under control speed wise.  If your gen puts out 30 amps, for example, at 30 mph wind and then starts to furl, you will want to make your resistive load draw at least 30 amps.  Because the low amp draw would work in low winds, it doesn't work in the worst case scenario.

Also, imagine that your windmill is trying to put out 50 volts at 28 mph wind and the battery is at 14.4 volts and rising.  Your controller switches to a dump load of 12 volt water heaters.  Now those water heaters are 600 watts each at 12 volts, but now they are using 50 volts.  They quickly heat up using that 2500 watts of power and burn up.  Now you have an open circuit, no load on the windmill, and batteries are full...oops.  Windmill shoots up to 600 rpm and splat.

The better way to do it is to use the dump load controller to run a relay or selenoid switch that connects to the battery bank.  That way you only have a few amps through the controller circuit and a lot more amps coming from the battery through the relay or selenoid switch going to the 12 volt heater element or other load.  And the best part is that the heater element will run at its intended voltage instead of some huge voltage directly off the alternator.

Not sure if this answered your questions or not

[newkidontheblock]

i meant a mechanical, electrical activated brake. that would require a lot of redesign, i know, but to keep spinning when the battery is full seems like a expensive draw back. just trying to help, maybe throw some new ideas in the air.

[elvin1949]

mechanical electric brake,wire's can and do break.

K.I.S.S.

dump into a load and weighted tail furl.

later

elvin