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Bryan1

Guru

Joined: 22/02/2006
Location: Australia
Posts: 1211

Posted: 03:41am 09 Nov 2008

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Hiya Guy's,
Well with summer coming on my original dumpload wasn't cutting the mustard as it only drew 8 amps and my main battery bank was going over voltage.

. Anyway yesterday I decided to make a new dumpload and the first attmpt was disaster.

The ohm load measured 0.24 ohms and I didnt get upto the shed early enough this morning and the fet on RossW's controller board was toast.

The Version 1 Dumpload

The next pic was taken just after I finished connecting everything up. The dumpload was sitting on 24.5 degrees which was the temperature in the shed. The guages on the left are for the main bank and I had 250 watts of PV going in, the guages on the right are for my backup bank which spends it's life on float.

The next pic was taken about 10 minutes after the dumpload started kicking in, the new fet was switching nicely and as shown it didnt take long for the dumpload to get to 74 degrees.

. The fet was getting warm so I put a decent heatsink on and the white former in the middle stayed cool as

. Time will tell but hopefully I got everything right and this dumpload will see me out.

I managed to get the ohm load down to 1.5 ohm's so as I get the dumpload to kickin @ 28 volts thats about 18 amps of load.

Edit: This pic was taken 1 hour after and I did see 150C but when I took the pic the temp dropped.

Now I really need to start thinking about piping that dumpload down to my house array. This week I'll go see what some 16mm figure 8 cable is worth. Even if I use smaller cable I intend to get my solar batch heater made and the extra power will go into a resistive load in the centre tube of the tank.

Cheers Bryan

Edited by Bryan1 2008-11-10

eirbyte

Newbie

Joined: 19/11/2008
Location: Ireland
Posts: 16

Posted: 10:21am 30 Nov 2008

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Hi Bryan what are the details of your dumpload it looks like alloy plate but what are the rods and the wire I want to make one for 50-60a at 24v for my new turbine.

All the best Jimmy

Education isn't everything; for a start it isn't an elephant.
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Bryan1

Guru

Joined: 22/02/2006
Location: Australia
Posts: 1211

Posted: 07:21am 01 Dec 2008

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G'day Jimmy,
The dumpload is basically a 240 volt mains water heater element and I unwound the nichrome wire from the former. The 2 bars are bussbars and by simply winding a few turns on each bussbar I checked the ohm's with my fluke 865 dmm, with each pass over the ohm's go down acoording to ohm's law and I was aiming for 1 ohm but ended up with about 1.5 ohms which is good enough to cover my RE input. The backing plate is a sheet of 3mm ali and the connecter on the lower left is bakealite so it gave good isolation between the bolts.

For your system to dump 60 amps @ 24 volts you should aim for 0.4-0.56 ohms.

For a dumpload this is a real easy one to make but ensure both bussbars are isolated and the wiring can be easily seen in the photo's above.

Have fun making one but do remember to check that everything is in order and ISOLATED or murphy will pop his head up and let the sparks fly. Just remember 24 volts @ 60 amps is 1.4 Kw so be carefull in every aspect.

Cheers Bryan

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