dummy load problem,please help

[snake]

hi firends,i built a 400 watt wind gen and i really need a dummy load.i want to build 1 myself,please can you help me?thanks

[Janne]

If you want to make one yourself, you might want to consider wire wire wound resistor.. For 12V thin steel wire works well.

Another good source for wire are broken electric heaters, you won't need long sections of the ni-cr wire that's in there for proper resistance.

[wooferhound]

400 watts, but What Voltage will your system run at ?

[TomW]

I didn't catch this early enough to change it before it got comments.

Not to hammer on you, snake.

I think you are confusing a dump load with a dummy load?  

Confusing terms abound in this hobby. Might I suggest we we use dump load from here on?

We had a go with guide wires vs. guy wires awhile back but that got squared away.

It probably does not matter in the context here but future researchers are likely to miss this discussion due to different term for the dump load.

We did use dummy loads for testing transmitters in my RF days so there is such a thing as a dummy load.

The thing we use on battery banks dumps excess power as heat thus a dump load.

Just seemed worth mentioning in the mess of terms related to this hobby lots of folks struggle with understanding them.

Another option for a dump load I have used is broken kiln element nichrome wire from pottery kilns.

They are only useful to the potters in full lengths. You likely only need a few inches so one that has failed is a good source from someones junk.

You would need Ohms Law and or Watts law to calculate the resistance of the dump load. Start with battery volts and maximum input possible and work from that. for calculations on a 12 volt bank I would use 14.4 volts and it always makes sense to oversize the dump load power handling to be sure it can handle all the source can shove into it.

Good luck with it.

Tom

[snake]

thank you for your reply tom.in fact i have been mistaken,its dump load for wind generators.so ,some more ideas if possible please.thanks

[electrondady1]

what about a toaster?

mine says 1400 watts

they have that same wire inside.

[ghurd]

Capt Slog made his own from an AC heater.

http://www.fieldlines.com/story/2007/8/30/8538/81113

G-

[Electron Pump]

  I made one from four, 55 watt, 12v automotive spotlight bulbs. I believe the package mine came in said 12.8v.

  My situation is a little different than most. I have a manual switching system not a charge controller.

[wooferhound]

The Human Charge Controller !?

[wooferhound]

snake

you are expecting 400 watts from your wind generator

400. w divided by 12 volts cut-in equals  33.33 amps
     
400. w divided by 14.6 volts full Charge equals  27.4 amps
     
     

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

12. v 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

[Ungrounded Lightning Rod]

Yes, you don't want to use lamps for an automatic dump load system.

 - They have a low "off" resistance so they have a large surge on turn-on (though not as bad as a motor).  This is hard on the switching transistor or relaty, which has to be 'way oversize.

 - They have a relatively short lifetime (while other resistors last for many years) and when they burn out you probably won't notice, leaving you with your battery unprotected or inadequately protected against overcharge.

[Ungrounded Lightning Rod]

It's a dump load if it is to get rid of extra power to avoid/cure overcharging of the battery (or something similar) or make opportunistic use of extra power (like for water heating) when the wind is giving you more than you can use normally.

It would be proper to call it a "dummy load" if you were using it to load down an otherwise unloaded mill during testing.  But these mills are normally used as windchargers and a rectifier-battery load has a voltage-current curve drastically different from a resistor OR a temperture-sensitive resistor like a lamp.  So testing is normally done with a battery (maybe with an added dump load if the testing will run long enough to risk overcharging it), rather than with a dummy load.  That's why you don't hear about dummy loads much on the board.

Now if you were building a mill strictly to power a resistive load, testing it with a dummy load WOULD be appropriate.  (Though you'd probably test it with the REAL load...)

[snake]

tell me something friends,if i take a 10mm aluminium wire,i make a coil,connect it as dump load,adding a fan to cool the coil,dont you think it would be ok?

[ghurd]

A 10mm diameter AL wire?  Less than a mile long?

I think we call that a "dead short".

Need a long wire, with a small diameter.  Then Ohm's Law, and Watt's Law to find out how many watts per inch or cm or whatever.

Resistance charts for AL wire are on the internet.

G-

[snake]

its better to buy 2 ceramic car heater of 200w each for dump load i think.woud that be ok?

[snake]

a toaster is rated at 120v or 240v,then how it works?

[ghurd]

Some people use them.  They work.  Do not expect them to use the power they say they use, they tend to use less power.

I recall someone saying they do not last as long as you would hope.

G-