Bench power supply?

[pmackenzie]

I am would like to get a bench power supply, and would appreciate any links to reasonably priced models. I am thinking 0-20volts, 30 A, but
my budget might force me down to lower amps.
thanks,

Pat MacKenzie

[BMatthews]

I don't have any real options to suggest but I may have an alternative if you're handy with electronics.

Assuming you only want this supply for sporadic use you could use two car or, better yet, deep discharge type batteries in series and then build a regulator circuit. I'd build in a charger circuit at the same time and couple it into the system.

The reason this sort of makes sense is that 30 Amps is a LOT of current and you're going to pay big bucks for such a supply if it has good regulation figures and some safety crowbar or current limit features.

If I was designing something like this I'd make the regulator a two part design. A first stage PWM switching regulator followed by a low pass filter and linear regulator if you need good regulation numbers. Otherwise the PWM and filter may be all you need.

Think of it as a monster ESC..... :D

I did pretty much this arrangement for a motor thrust test stand. It's worked out great but I'm only running 12 volts and the PWM part without the low pass filter.

[pmackenzie]

A good suggestion. Using two car batteries would eliminate the large transformer, rectifier and filter caps. The batteries would see double duty for field charging.
Based on the high prices I have found so far on the web, I will probably end up having to make my own supply. The configuration you describe was what I was thinking of as well, with the addition of current limiting.
I was hoping to find something reasonably priced since there are some other things I want to work on and spare time is a finite resource. You hate to spend a lot of time making something only to find out after that you could have just bought it for about the same price.

Pat MacKenzie

[babblefish]

May I suggest looking for electronic surplus stores? I paid $70 US dollars for a P/S rated at 0-20 volts and 0-50 amps from such a store. Weighs as much as my car, but it works great. Also, look in electronics magazines for ads from surplus stores.

[AndyOne]

I made a supply for powering RTP models back in the 70s, it was about 10 A, 50V and was quite simply achieved by using a Variac fed into a 40V 10 A transformer for isolation/step down/safety then into a large bridge recitfier on a big heatsink. There is also a 10000uF capacitor and a bleed resistor across the output.
A Variac is a mechanically variable auto transformer which allows the output to be varied from 0% to more than 100% of the input voltage.
The whole thing weighs nearly enough to require a two arm lift and its been working as a battery charger, an RPT PSU and a foam cutting bow supply for more than a quarter of a century.
The output voltage will droop a bit with load as there is no active stabilisation but to give a lot of DC and it works well.
All the major parts were second-hand including the 1940 radio case it was built into.
A word of warning don't be tempted to use a Variac without an isolation transformer as it will have a direct connection to the mains, 240 volts in the UK, 110V in the US still not good.

This could be your answer to a cheap large power supply if youre not too worried about stability.

Andy.

[DNA]

http://www.allelectronics.com/cgi-bin/category.cgi?category=480&item=PS-2512&type=store

[pmackenzie]

DNA,
VERY close. Good price. Thanks.
Pat MacKenzie