Consider something like this kit from Apogee. It's linear, has adjustable current limit (i.e. important) and meets your budget, as long as you can live with 3A for the time being. If you go bigger, you can get 5A but you're looking at closer to $300.
You can also keep your eyes open on online auction sites for used industrial equipment like the HP6038A (60V 10A) or the 6Instek GPC-3060D (dual 30V 6A, can be paralleled).
Based on your comments to hex4def6's answer, I understand the following:
- The voltage adjustment works fine (verified with an external voltmeter)
- The voltage indicators are fine (verified with an external voltmeter)
- The supply can drive output current (verified with an external ampermeter + the load resistor gets hot)
- The current indicator is broken (it shows zero current even when an external ampermeter measures non-zero current)
- The current capability reduced
Are these statements correct?
If they are:
It seems like the supply itself is generally Ok, but its current indicator is broken + some reduction in current capability.
In order to indicate the possible root-causes of the issue we need to see a complete schematics. I didn't find your VLS-10M on the web, but I found VLS-35M:
These two are probably the same architecture, just having different number of paralleled pass transistors for driving the current (this one has 8 and delivers 35A intermittent current , while yours should be 2-3 which accounts for 10A).
If it is really the case that internal ampermeter is broken, I see three places where this could happen, without ruining the whole PSU:
RED: The pot used for current scale adjustment or the analog scale itself can be broken
ORANGE: The negative feedback (stabilizing) power resistor which is also used as a shunt for internal ampermeter can be broken
YELLOW: The pass transistor which feeds the above shunt resistor can be broken
Both orange and yellow failures would result in reducing the current capability of your PSU. If the current capability of your PSU is the same as before, I'd say that the issue is either the pot or the analog scale. However, based on your description, it looks like there is some reduction in current capability.
In order to verify this probe the voltage on the shunt resistor - if the voltage changes when you change the output current (by attaching smaller load for example) then both the resistor and the transistor are (probably) fine.
BTW, how comes PSU which is rated for 8A continuous current has 5A fuse?
Hope this helps.
Best Answer
Yes, a bad pot could very well be the issue here. I have a similar unit and I find that I got what I paid for which, unfortunately, is not very much. My voltage display drifts over time so that if I set the output for 3.3V the display will drift up by 2-3 volts over time even though the output itself it pretty stable.
I've purchased a higher quality surplus (HP branded) unit that works much better. You might consider the same thing or try replacing some parts to see if you can get better performance from yours.