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Zulu Yankee

Electronic Help Please

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Hi all,

 

I need some help from the electronically gifted, a group that I do not include myself in. I built a DC power supply (to use for hotwire cutting).

 

I followed the instructions on the link provided below.

 

http://www.wikihow.com/Convert-a-Computer-ATX-Power-Supply-to-a-Lab-Power-Supply

 

In stead of having several DC poles sticking out of it, I created a switch that would switch between 6V and 12V. I further added a potentiometer (from a light dimmer) to control heat.

 

When I switch it on, I can see the voltage go up and down between 0v and either 6V or 12V respectively, depending on the switch position.

 

However, as soon as I hook it up to the hotwire saw, the voltage drops to 0V across the poles.

 

I also hooked up a 12v lightbulb between the poles. Nothing. Not even a glimmer. When I hook the multimeter up in series, I can see voltage displayed, but 0A.

 

I don't understand. How can it display 12v, but 0A?

 

Any thoughts?

 

ZY


I plan to procrastinate, but not now....

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Hi all,

 

I need some help from the electronically gifted, a group that I do not include myself in. I built a DC power supply (to use for hotwire cutting).

 

I followed the instructions on the link provided below.

 

http://www.wikihow.com/Convert-a-Computer-ATX-Power-Supply-to-a-Lab-Power-Supply

 

In stead of having several DC poles sticking out of it, I created a switch that would switch between 6V and 12V. I further added a potentiometer (from a light dimmer) to control heat.

 

When I switch it on, I can see the voltage go up and down between 0v and either 6V or 12V respectively, depending on the switch position.

 

However, as soon as I hook it up to the hotwire saw, the voltage drops to 0V across the poles.

 

I also hooked up a 12v lightbulb between the poles. Nothing. Not even a glimmer. When I hook the multimeter up in series, I can see voltage displayed, but 0A.

 

I don't understand. How can it display 12v, but 0A?

 

Any thoughts?

 

ZY

 

The real question is does the wire heat up.:confused:


I Canardly contain myself!

Rich :D

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However, as soon as I hook it up to the hotwire saw, the voltage drops to 0V across the poles.

 

I also hooked up a 12v lightbulb between the poles. Nothing. Not even a glimmer. When I hook the multimeter up in series, I can see voltage displayed, but 0A.

 

I don't understand. How can it display 12v, but 0A?

 

ZY

If you are hooking a voltmeter up in series you will absolutely get no current. A voltmeter has a very high impedance, possibly >10Mohm.

 

Unless I have mis-understood you. Could you draw a little picture of how you have the PSU and the meter setup, and whether you are using the mutlimeter as a volt or ammeter (or are you using two multi-meters?).

 

Do you have the 10W resistor on the 5V line ??? You need to draw a load from the 5V or the PSU wont power up properly.

 

You also mention you have a pot installed. Can you tell me where this is installed and how and what wattage it is good for.


Adrian Smart

Cozy IV #1453

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If you are hooking a voltmeter up in series you will absolutely get no current. A voltmeter has a very high impedance, possibly >10Mohm.

 

Unless I have mis-understood you. Could you draw a little picture of how you have the PSU and the meter setup, and whether you are using the mutlimeter as a volt or ammeter (or are you using two multi-meters?).

I had the multimeter, in parallel with the hotwire saw, across the DC poles selected to measure voltage. With the saw unattached, it shows 12v. As soon as I attach the saw, the voltage drops to 0.

 

Then I put the multimeter in serial, selected to measure amps, and got nothing.

 

Lastly, I removed it all and just put a simple lightbulb across the poles, but it does not even glimmer. Nor does it show any current.

 

Do you have the 10W resistor on the 5V line ??? You need to draw a load from the 5V or the PSU wont power up properly.

Yes, I have it on the 5v side and it heats up, so I know that SOME current is being drawn somewhere.

 

You also mention you have a pot installed. Can you tell me where this is installed and how and what wattage it is good for.

I installed it, in parallel, across the DC poles. It is rated for 250W.

 

Do you have an installation like this that works?


I plan to procrastinate, but not now....

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I installed it, in parallel, across the DC poles. It is rated for 250W.

 

Do you have an installation like this that works?

A pot in parallel with the load ??? It should be in series to control to the current to the hot wire saw. Not that this will be effecting the PSU with a small load, unless the pot is set at a low resistance and the PSU is near full load.

 

If you have 12V with no load, but drops to 0V when a load is attached the PSU is probably shutting down with its short circuit protection. What wattage is the 12V globe you are connecting. What wattage is your PSU good for (on the 12V rail only, not total wattage). On the label it will show maximum amps on the 12V rail.

 

Sorry if these seem like simple questions, but i don't know your experience with electrics.

 

Oh, and are you sure the PSU was any good before you modified it ??? I have had heaps of experience with brand new equipment being faulty.


Adrian Smart

Cozy IV #1453

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