I just repaired a blown Behringer EP2500 amp I bought for $25 (the circuitry is an exact copy of the QSC RMX 2450) and I'm working on final adjustment in accordance with the QSC service manual. The bias is dialed in, but in order to set the positive and negative current limits I need a 2 ohm resistive load rated for 1200W. Before spending $60+ on four of these does anyone have a cheaper idea?
My first idea was to use a space heater, but all of mine have fans (inductive). I have a 12V car battery tester but it's only 0.1 ohms.
My first idea was to use a space heater, but all of mine have fans (inductive). I have a 12V car battery tester but it's only 0.1 ohms.
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Electric stove elements...try to find them in recycle or junk yards.
Keep them cool and the resistance will not change too much.
Keep them cool and the resistance will not change too much.
wander down the hardware store with a multimeter and measure the resistance of whatever water heater elements etc they may have?
Braking resistors off Ebay? although these will probably still end up costing $60 or so and usually need heat-sinks to achieve full power....
Braking resistors off Ebay? although these will probably still end up costing $60 or so and usually need heat-sinks to achieve full power....
Oil filled convection space heater? The ones that look like a portable steam radiator from yesteryear...
Hi,
Your talking around 50V and 25A. FWIW resistors can generally
take about 10 times the long term power short term. So if
you use a test signal with a high peak to average ratio you
can adjust the limits on a scope with a lower power load.
FWIW I'd use 1R to set the current limits, rather than
2R. You'd only need one, rather than four, sine wave.
rgds, sreten.
Your talking around 50V and 25A. FWIW resistors can generally
take about 10 times the long term power short term. So if
you use a test signal with a high peak to average ratio you
can adjust the limits on a scope with a lower power load.
FWIW I'd use 1R to set the current limits, rather than
2R. You'd only need one, rather than four, sine wave.
rgds, sreten.
Heat pumps have electrical heater strips for when the outside temperature becomes too cold for the heat pump to work well. We used to connect those in series and parallel to make dummy loads of any wattage we needed.
Dubwoofer,
One has to be careful here. In the end you may obtain a 2 ohm load of say 5% accuracy. With that low a value, what is the contribution of the terminals, internal conductors, connections? Exactly where must this 2 ohm be maintained?
Not trying to split hairs (though that is precisely what needs to be done here!), but apart from the desired load resistance you may need to consider these other factors. Merely 0,1 ohm elsewhere is already 5% of the load value.
(How to check such a low value? Not with an ordinary dvm resistance reading. Better to chase a fat current through it and measure the voltage across the resistance. Ohms readings are normally not as accurate as d.c. voltage readings.)
One has to be careful here. In the end you may obtain a 2 ohm load of say 5% accuracy. With that low a value, what is the contribution of the terminals, internal conductors, connections? Exactly where must this 2 ohm be maintained?
Not trying to split hairs (though that is precisely what needs to be done here!), but apart from the desired load resistance you may need to consider these other factors. Merely 0,1 ohm elsewhere is already 5% of the load value.
(How to check such a low value? Not with an ordinary dvm resistance reading. Better to chase a fat current through it and measure the voltage across the resistance. Ohms readings are normally not as accurate as d.c. voltage readings.)
I've gotten 5 ohm 225 watt Dale log resistors for $5 each +$20 freight from apexelectronic.com. They are out now, probably. electronicsurplus.com also sometimes has things. Takes a 130 W soldering iron to heat the 10 ga wire required. I mount the logs on a metal plate with a tab cut out and bent up to hold them up off the coffee table I use to work on. I cut the metal plate out of a PC case. 4 1/2" grinders with a slitting disk are handy to cut sheet metal. Use safety glasses and top grain leather gloves..
I would use stainless iron fencing wire, cut to length to make up your resistance load. Placed in a bucket of water to keep them coll.
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