What is TICK wire ?
I assume this is some sort of resistance wire. If so, then you will need to take care over power / temperature rise to dissipate 400W. Maybe a fan or liquid cooling is needed.
I used very low cost / surplus 15ohm/5w WW resistors (64 in total) to make a ~ 300w test load. This needs a large fan to hold a continuous load of 300w
I assume this is some sort of resistance wire. If so, then you will need to take care over power / temperature rise to dissipate 400W. Maybe a fan or liquid cooling is needed.
I used very low cost / surplus 15ohm/5w WW resistors (64 in total) to make a ~ 300w test load. This needs a large fan to hold a continuous load of 300w
I have used a resistor(s) placed in water for this also. Even boiled some.
The water doesn't seem to affect the resistance at 4 Ohms. Just don't add any salt
You should also try to match the reactance of the speaker you are "simulating" as this is an important variable to the amp's operation.
The water doesn't seem to affect the resistance at 4 Ohms. Just don't add any salt You should also try to match the reactance of the speaker you are "simulating" as this is an important variable to the amp's operation.
HeathKit used to sell a 1KW load that was 25pcs of a 2W resistor (25pcs of 100 ohm would give you a 4 ohm load) bussed together in a 5X5 grid and immersed in a 1 gallon can of vegetable oil.
When the can reaches 100*C (this takes a very long time, longer than you would be testing the amplifier) you need to let it cool off (which will also take a long time).
When the can reaches 100*C (this takes a very long time, longer than you would be testing the amplifier) you need to let it cool off (which will also take a long time).
I don't have any imagination. I use the 250W 8R Dale resistors on a big heatsink. Two in parallel for 4R loads. As I recall, they made a 225W 4R resistor in a tubular format. I have a set of those as well. Much cheaper than the 250W jobs.
I remember it cost me $50.00 each to have heatsinks milled flat to mount them on in the late eighties.
-Chris
I remember it cost me $50.00 each to have heatsinks milled flat to mount them on in the late eighties.
-Chris
Tempco is non-trivial. Deriving the cold resistance of a heating element from its power consumption when hot could lead you to guess quite wrong. I strongly suggest measuring the resistance with a DVM when the element is cold, and when it's warm.
In other news, a class-AB amplifier is under most thermal stress at about 40% power, and not at full output, since at 40% the output devices are standing off more of the supply voltage than at max out. If you want to test that, be VERY sure to keep an eye on the amp at all times: I came close to burning up a Carver power amp after a 20 minute run at 40%. It sure did smell funny.
Francois.
In other news, a class-AB amplifier is under most thermal stress at about 40% power, and not at full output, since at 40% the output devices are standing off more of the supply voltage than at max out. If you want to test that, be VERY sure to keep an eye on the amp at all times: I came close to burning up a Carver power amp after a 20 minute run at 40%. It sure did smell funny.
Francois.
The heating element out of a clothes dryer runs around 3 or 4 ohms cold. Given that it's rated for a thousand or more watts, it's not going to change resistance too radically.
20W ceramic resistors are cheap. Series and/or parallel them until you get the desired resistance and wattage.
I'm still not clear on why the thing needs to be tested all the way to clipping. Surely you'll be able to figure out whether it's working way before that. Given that the ratio between the peak and average levels in listening is on the order of 10:1, it should be quite enough to test the thing at 40-50W and leave the rest for peaks.
Grey
20W ceramic resistors are cheap. Series and/or parallel them until you get the desired resistance and wattage.
I'm still not clear on why the thing needs to be tested all the way to clipping. Surely you'll be able to figure out whether it's working way before that. Given that the ratio between the peak and average levels in listening is on the order of 10:1, it should be quite enough to test the thing at 40-50W and leave the rest for peaks.
Grey
Most commercial power amplifiers are not engineered to run at this 40% power point as it is unrepresentative of the musical signal and considerable extra expense and unnecessary.
I am currently working on a 150W MOSFET monoblock and stuck between a nice compact 0.83degC/W and a larger 0.64degC/W heatsink which will dictate the overall size of the unit. Either will absorb the heat from reasonable unclipped programme even into reasonably reactive loads with < 30deg temp rise, and will have a thermal cutout for abusers.
Cheers,
Greg
I am currently working on a 150W MOSFET monoblock and stuck between a nice compact 0.83degC/W and a larger 0.64degC/W heatsink which will dictate the overall size of the unit. Either will absorb the heat from reasonable unclipped programme even into reasonably reactive loads with < 30deg temp rise, and will have a thermal cutout for abusers.
Cheers,
Greg
Try Parts Express , they have some dummy load
4 Ohms 100W, 8 Ohms 100W, 4 Ohms 200W, 8 Ohms 200W.
Don't know if they ship international.
4 Ohms 100W, 8 Ohms 100W, 4 Ohms 200W, 8 Ohms 200W.
Don't know if they ship international.
More seriously 4 1 ohm 300 watt resistors would do it. $20. They ship international, as does Parts Express.
if u don have access to power oscilloscope(check with your university)
then the method can be found at rod elliots site.see the car smps testing procedure and take some tips from it
or else splurge on high power resistances that will increase in cost exponentially jus like caps as the value increases.
then the method can be found at rod elliots site.see the car smps testing procedure and take some tips from it
or else splurge on high power resistances that will increase in cost exponentially jus like caps as the value increases.
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