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smps loading

Posted: Sat Oct 21, 2006 5:36 am
by shillyard
I have a power supply I pulled from a 46 inch magnavox. I have tested as far as I can without loading down the secondary winding. I have a variable ac power supply but I need advice on what I can use as a load. I need something that is cheep as this is something I rarely work on.

Posted: Sat Oct 21, 2006 9:11 am
by Chris Smith
Depending on the rated voltage out put, low, med, or Hi, I use a lamp bulb to check for a load.

If you have a huge HV circuit, A spark gap [1/16"] can tell if your producing a voltage, or you can make a voltage divider out of several mega-ohm resistors and place a VOM on just one of them for a voltage reading

Posted: Sat Oct 21, 2006 9:36 am
by shillyard
I don't like the idea of causing an arc to see if there is voltage a resister and meter will do just fine to see if voltage is there but if i remember correctly I would need a resistor wattage of at lest 10 watts. I was thinking a small say 60 watt bulb ? Its been a wile since i have worked on these and I wanted a second opinion.

Posted: Sat Oct 21, 2006 12:25 pm
by Edd
Third Opinion:

Use ‘da lite-‘bub….its right on, at the 130 VDC spec of the derived regulated B+ secondary voltage.

Upon the bringing up of the primary AC voltage , the lamp might slowly vacillate a bit until you get the
voltage on up a bit onwards above the typical 70 VAC latch on threshold.

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73's de Edd
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Posted: Sat Oct 21, 2006 1:49 pm
by shillyard
Thanks Edd. That was exactly the information I was looking for.

Posted: Sat Oct 21, 2006 10:19 pm
by Chris Smith
Unforntunately I dont know your voltage under load.

Low voltage such as 0 to 30 VS..... 120 plus, .....VS 1000 volts plus is all different.

For the HV, I use the simple arc, [small] for the lower voltages [120 and 12v] I use the bulb.

But I do own a a HV probe that can do 50kv easy, which is no more than a plastic wand, and several hundred Mega ohm resistors which I have also built long before i was given one, out of a fiberglass rod and 100 megs resistors. [cheap]

A lot of people think the arc is free running and thus get hysterical about it, ......its not.

It very approved to find a voltage this way as long as your not getting ridiculous about the test. Small gaps.