Resistors as dump load, is it efficient?

[snake]

hi friends,i built a wind turbine using an ametek 38vdc for a 12v system.i get about 2-3 amps but i dont have a dump load yet.doing my research,i saw that a guy used resistors as dump load.i got resistors of the following capacity:0.35 Ohm 750 Watt edge-wound, high current

load resistor, used in elevator and train electrical brakes.do you think it can work?thanks

[Flux]

Resistors are only efficient as dump loads if you can use the heat. Otherwise dump loads are totally inefficient.

If you can only generate 2-3 amps and you can manage your load effectively a dump load seems a luxury. If you have any decent loads your main problem should be lack of charge.

If it is just a standby battery and you don't have a regular load then you will need a charge controller

Your .75 ohm resistor would be fine for a big set up, it will take 16A. That is a large current to cycle on and off for a little mill charging at 3A. It will work well enough with a pwm controller but for an on off controller you would do better with something with higher resistance that takes about 5A. Probably cycling batteries within the surface charge region doesn't really count as charge /discharge cycles but it would need a fair sized battery to be discharging at 16A.

As long as your battery is 100Ah or more I suspect it will be fine but for a battery sized more reasonably for a 3A machine it may be on the low side.

If you have more than one then you could use them in series and they would be fine. If you ever uprate the charging you could then reconnect them to deal with larger charging currents.

Flux

[wooferhound]

A dump load is designed to Dump the power and heat up a resister so it is not necessary to have an efficient dump load as you are trying to throw away the power as heat. However if you can figure out how to use your dump power to make heat you can use, you will be well on your way to using every bit of power that you are making

you are expecting 400 watts from your wind generator

 400w divided by 12 volts cut-in equals  33.33 amps

 400w divided by 14.6 volts full Charge equals  27.4 amps

so a dump load capable of at least 30 amps will be needed

 12v divided by 30 amps equals .40 ohms

 14.6v divided by 30 amps equals .48 ohms

looks like you are looking for a resistance between .48 and .40 ohms to dump 400 watts. Of course your dump resister will need to be rated over 400 watts or more if you plan to add more capability to your system.

Here is my 2 stage Ghurd dump controller with switches to set the dump amps.

http://www.fieldlines.com/story/2008/7/13/211414/932

[brokengun]

One way you can use that power most efficiently is to heat water. Many people have their dump loads hooked to an electric water heater to supplement water heating.

[boB]

Just remember that as you heat water, the water can get hot enough where you can't heat it up anymore.  If the water heater has a thermal cutout, then when it trips, you don't have a dump load anymore.   At that point, unless you have LOTS of water to heat, you may need real resistor (as you have) that can take the heat.

That's MY 3 cents worth.  (inflation you know)

boB

[Jeff]

Woof

You missed a decimal place. He's only getting 2-3 amps. You do have a really nice controller though!

[ghurd]

I see a bit of a math glitch.

A 0.35 ohm resistor in a 12V system at dumping voltage will be about 41A.

Need a TS-60 controller to handle that resistor.

Both the resistor and TS-60 are overkill for an Ametek style windmill.  Not to mention the wire for 41A.  Sounds expensive to use that resistor.

I believe power resistors are the best dump load for small systems.

They last "forever", unlike light bulbs.

They are cheap, unlike a water heating system that would be fairly silly considering the cost involved to heat water and the amount of hot water a 50W windmill can make with its "extra" power.

Seems a bit inefficient to spend more money (?) than the windmill cost, on an almost microscopic bit of occasional hot water!  That money would be more efficiently spent on a solar panel

The job of the dump load is to burn off the extra power as heat.

Properly sized power resistors are designed to do that.

So I would say power resistors are completely efficient for a 50W system!

G-

[jmk]

 I totally agree with Gurd.