Load testing a power supply? (switcher)

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Hi;
I searched the forum and could not find an answer to this, so here it goes.......

A little while back, I fabricated a little load-bank for testing my linear power supplies after rebuild. It is basically a 1 ohm resistor that I connect to the p/s to see how it performs. I have used this on A/R's and Midways and it has always worked perfectly, until now.

I am trying to test an Atari switching p/s using this rig but each and every time it goes into overload and shuts down. I tried using just a light bulb and it still shouts down.

It must have something to do with the p/s being a switcher vs. A linear but my lack of an EE degree prevents me from understanding why.

Is there any way to safely load a switcher out of the cab, (not hooked up to a board)?

Thanks in advance.
Jeff
 
Hi;
I searched the forum and could not find an answer to this, so here it goes.......

A little while back, I fabricated a little load-bank for testing my linear power supplies after rebuild. It is basically a 1 ohm resistor that I connect to the p/s to see how it performs. I have used this on A/R's and Midways and it has always worked perfectly, until now.

I am trying to test an Atari switching p/s using this rig but each and every time it goes into overload and shuts down. I tried using just a light bulb and it still shouts down.

It must have something to do with the p/s being a switcher vs. A linear but my lack of an EE degree prevents me from understanding why.

Is there any way to safely load a switcher out of the cab, (not hooked up to a board)?

Thanks in advance.
Jeff


1 ohm sounds way low!! I have a rig for switchers that works fine, but I'll have to go check the value.
I'm not sure linear's need a load, usually they bleed power off through a Zener or regulator.
 
Thanks, I would appreciate that..

I cannot test the +5vdc on the Midway linear p/s without a load, just does not work and some A/R's are the same, they do not regulate properly without a load. Then on the other hand, some do work without a load. I just put them all on the bank to be sure they can supply what they are supposed to.

I used Ohms law to determine that a 1 ohm resistor should place a 5A load on the +5vdc supply.

Jeff
 
On the +5 volt dc line I just use a 6.3 light bulb. It will only load a little bit and will not load the full 5 amps but it will give you a steady voltage for adjustments and testing.
 
Are you sure it's going into overload, and not OVP/UVP due to lack of a load? Not all switchers use 5V as the reference, some use 3.3V or 12V and there's always some exotic ones out there.

As a rule of thumb, a good dummy load for testing switchers is twice the voltage in ohms. This will give you 500mA, enough for the power supply to self-regulate but not enough to make your average resistor spontaneously combust.

Now use Joule's law (P=IE) to determine that the 1 ohm resistor had better be capable of handling 25 watts.

And a resistor that can take 25 watts is a pretty frickin' big resistor. We're talking half an inch in diameter with a welded on heatsink. Oh, and it gets hot enough to burn skin in seconds.
 
And a resistor that can take 25 watts is a pretty frickin' big resistor. We're talking half an inch in diameter with a welded on heatsink. Oh, and it gets hot enough to burn skin in seconds.

25W, Bah! Peanuts!
We often load test 5V, 100A switchers at full load at work. We use a length metal pallet strapping wrapped back and forth between ceramic posts. Four fans blowing on it... still glows red hot like a big oven heating element.

With the switcher in this thread -- original poster needs to make sure the power supply cannot be loaded asymetrically. Such as only 5V loaded when 12V or other supplies also need a load. Not uncommon.

Ed
 
Hi;
I am sure that it is going into overload, it does not output at all without a load on it.

He is the rig I fabricated to load test the P/S,'s:
(see attachment)

I tried a bulb and that as well put it into overload, I am thinking towards anything with a "short" kills the output......... This must be a "switcher" idiosyncrasy....

Jeff
 

Attachments

  • LoadBank.jpg
    LoadBank.jpg
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DO NOT FORGET!

ARs have those pesky "sense" connections and they have to be connected for the board to be able to properly regulate the output. (Unless you did some kind of mod to it...)

RJ
 
The problem I am having is load testing the +5vdc output on the Atari switching power supply.....
 
25W, Bah! Peanuts!
We often load test 5V, 100A switchers at full load at work. We use a length metal pallet strapping wrapped back and forth between ceramic posts. Four fans blowing on it... still glows red hot like a big oven heating element.

Now this.....I'd like to see a picture of:D

Edward
 
1 ohm sounds way low!! I have a rig for switchers that works fine, but I'll have to go check the value.
I'm not sure linear's need a load, usually they bleed power off through a Zener or regulator.

The Atari Switcher needs a load on the +5vdc or it just keeps clicking away.
With the load bank I made for the linear or even the coin door bulb hooked up, it goes into overload and shuts down.

There must be something I am missing with regards to testing a switching P/S under load, some other component that must need to be in series??

Jeff
 
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