Pyramid PS-8KX 12 volt power supply failure

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  #1  
Old 02-15-15, 10:07 PM
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Pyramid PS-8KX 12 volt power supply failure

I use this unit to supply power to a small 12v sump pump in my front yard. This is probably the 3rd or 4th unit I have replaced over the years. I leave it on all the time and live in Northern California so the pump doesn't get turned on a lot.
For the first time after a failure I got curious and I opened this unit up (I know a little something about 12v automotive systems but am a lightweight about AC.)
OK, here is what I found:
1. The output terminals read 13.89 volts (no load). If I put a load on it ( a small 12v bulb) it does not illuminate and the voltage drops to around 2mv.

So I opened it up, sort-kinda figured out how to connect directly to the output side of the transformer. Tested by connecting just after both the + and - diodes and it reads 11.58 volts. Add the same load at those points and it reads around .270 volts.

So I assume the transformer has failed since I am bypassing everything but the transformer and the diodes.

Now its no big deal to replace the unit as its around (another) 40 bucks. But I am real curious as to why it acts this way. Why would the output side of the transformer show about the right DC voltage until a load is put on it, and then with a load drop to near zero?
 

Last edited by fatfenders; 02-15-15 at 10:28 PM.
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Old 02-15-15, 10:30 PM
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Welcome to the forums.

The Pyramid power supplies are inexpensive and not always reliable. That unit is actually 6A rated.

When you measure the output of a transformer it is AC. Set your meter for AC and that transformer will probably show better than 16vac.

You should use a power supply rated at twice the amperage of the motor. You should probably be using a 10A supply or even a little larger.
 
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Old 02-16-15, 10:51 AM
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Pete,
Thank you for the reply.
 
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