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100 Amp DC Load 24 volt in

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bodgeroger

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Hi Guys, new to this electronics stuff, but i need to build a variable dc load i have built a couple but all have ended in loss of magic smoke.
i am thinking perhaps an infinite number of 2n3055 transistors is not the way to go but i just cannot think how to do this with MOS FETS or IGBITS.

Anybody got any ideas i could try??

tks bodgeroger
 

tcmtech

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You could go with a Massive IGBT block! They can be found on eBay for a reasonable price. This one here would set you back around $50 -$75 on eBay. And it Has a 4100 watt dissipation capacity!

Just make sure your heat sink is big enough! Several square feet with big honkin fins!;) Or water cooled works very well for compact applications.
 

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Willbe

New Member
Already did that.
Iron coat hanger wire has 6x the resistance of copper and can stand this current if you submerse it in water.
No shock danger at 24v.
 

MikeMl

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How long does it have to dissipate 2.4KW?

Water cooled resistors can dissipate KW, especially if you turn the water to steam.
 

bodgeroger

New Member
variable load

Water cooling is out, nice idea but implementing a portable load would be really difficult, now a huge chunk of aluminium with "stonking fins" is good and with the addition of a fan too, well this is the direction to go.

time for dissipation is variable, i have had power supplies being burnt in at 100 amps over the weekend ready for installation Monday morning.

As to the igbit block this is very good and i do have access to some of these but i do not know how to drive them especially with a varying load, I.E. turn the volume control and current goes up or down!!:confused:
 

ronsimpson

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I used car headlights for a load. Two bulbs for 24 volts. I have a bank of bulbs with switches to switch each pair. No heatsink but you can get a sun tan.
 

tcmtech

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Using IGBT's for a variable load is easy you just use a simple pot with one end at the collector and the other at the emitter. The variable goes to the gate.
For unattended running I would highly recommend a thermal switch that would disconnect the collector connection of the pot. If it over heats it will shut it down.
 

MikeMl

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Here is a picture of something that I built years ago. It is a computer-controlled capacity tester for 35Ah lead-acid aircraft batteries. The two big coils on top are "locomotive braking resistors" that I bought from a surplus dealer. They are rated at 1200W each.

I have two of the braking resistors left over from that project. One is 0.069Ω and the other is 0.150Ω., each rated at 1200W in free air. I=24/(0.069+0.150)= 109.6A.

If you can use these, contact me via PM.
 

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bodgeroger

New Member
Hi MikeMI,

Now that is what i had in mind, but i was planing to use the transistors to provide the load, but scanning through a few IGBIT datasheets it looked like they turned on with the meerist sniff of gate voltage, but as if what you say is true then a simple pot would work and point noted about over heating and flames:rolleyes:

anyone want to post a circuit for me??;)

what about thermal stability as the IGBIT gets hotter wont it "runaway"

Roger
 
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