I'm converting an old atx power supply into a bench power supply for some tinkering with a laptop motherboard as well as a few other future projects and read that I needed a 10 Ohm 10 Watt "sandblock" resistor. I did some searching and haven't been able to find much about them besides the alternate name of "power resistor". Could someone explain the difference between and power or sandblock resistor and a regular resistor?
Power resistors are usually rated for a much higher power than regular resistors.
ie. You can get a power resistor that can handle 5W or 10W, but regular resistors often are rated for 1/4W or 1/2W
That, and not all power supplies need this. This resistor merely puts a fake load on the power supply so the power supply thinks its connected to a computer. I've used many power supplies that worked fine without
So.. find one, but before you buy it, test your power supply....btw, I used my power supply to power a car audio amplifier driving a 10" sub and was able to drive the sub much harder than I should have before the power supply tripped and reset.
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So-called "sandblock" resistors are simply wire-wound resistors encased in a cement or sand block shell. This is a less expensive alternative to encasing the wire-wound element in a (usually hollow) ceramic shell. A 10 Ω, 10 W, sandblock resistor will work as well as any other resistor of comparable resistance and power rating at DC and low-frequency AC, but most power resistors, unless specially manufactured, have inherent inductance that adds inductive reactance to their resistance at higher AC frequencies, such as radio frequencies. Unless you are trying to use the resistor as a "dummy load" for an RF transmitter, you are free to use whichever style is available. Sometimes you can find these with an aluminum case with mounting tabs around the sand block, which is handy for mounting to a heat sink.
I did some tests lastnight and as it is now the power supply will not turn on. However it works fine when connected to my broken pc motherboard. I attempted to cross the green switch wire and a black ground wire, also attempted to use a regular resistor both 330 Ω and 100 Ω between a red wire and black wire. Even with both of these done at the same time the atx does nothing when turned on.
While doing this I had my multimeter connected to a ground and red to see if any voltage was being generated... and got nothing.
While doing this I had my multimeter connected to a ground and red to see if any voltage was being generated... and got nothing.
Check some of the other pins.
http://pinouts.ru/Power/atxpower_pinout.shtml
Check here for details... but there should be a standby voltage present when the power supply is off.
When the supply turns on check the PWR_OK pin (usually grey) and also check the 12V line (Yellow).
*The power supply fan should instantly turn on when the PS_ON pin is pulled low. (Attached to black)
If the fan does not come on, or even flicker, you may not have a proper connection between the green and black wire. (If I want to reuse the supply in a PC again when I am done, I usually just bend and slip a paper-clip into the end of the cable. This is only a very very short term solution though and must be done with care)
Have you checked the standby wire?
It should have a voltage regardless.
Does the PSU have a power switch on the back?
Does the PSU have an LED indicator that lights when it's plugged in?
It is plugged in right?..
Sorry for the basic questions, I have never had a PSU not work for me before and I currently have 3 scattered about the house.
No problem, bring on the basic questions.
Have I checked the standby wire?
- No, was unaware of it. I don't recall a grey wire but I wasn't looking for it, will do so when I get home this evening.
Does the PSU have a power switch?
- Yes, I've been using it.
Does the PSU have an LED indicator that lights up when its plugged in?
- No, there are no led indication lights on it.
It is plugged in right?
- Didn't know it needed to be... kidding... yes it is plugged into the same outlet it was plugged into when it was running my now dead desktop.
Have I checked the standby wire?
- No, was unaware of it. I don't recall a grey wire but I wasn't looking for it, will do so when I get home this evening.
Does the PSU have a power switch?
- Yes, I've been using it.
Does the PSU have an LED indicator that lights up when its plugged in?
- No, there are no led indication lights on it.
It is plugged in right?
- Didn't know it needed to be... kidding... yes it is plugged into the same outlet it was plugged into when it was running my now dead desktop.
haha, Thank you for indulging me.
Using a 100 and 330 Ω in parallel will give you 77Ω which will draw 65mA from the power supply.
If this is indeed a problem with the PSU not detecting a load on the 5V line, you will need to add a bigger load to it. The 10Ω resistor will draw half an amp... Perhaps you have an electric motor in the house you could use? Some people have actually 'made' their own resistor by wrapping wire around a stick... it got very hot, but actually worked as a low value resistor. The longer the wire, the higher the resistance.
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Why not use a light bulb, It has the added advantage of helping you see what you are doing
Adam
Adam
I thought about that... but isn't the resistance of a lightbulb about 100Ω ?Why not use a light bulb, It has the added advantage of helping you see what you are doing
Adam
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Depends on the light bulb.
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