Why does my voltage from the DC supply box change on its own?

Question

I have a simple electric motor setup that spins using a simple copper coil rotating around between two metal nuts. The nuts are connected to a DC supply box (on the right) like this:

Sometimes, especially at higher voltages (around 3.0V), the voltage from the box changes on its own (by an amount of ± 0.1V) , and at even higher voltages (maybe around 4.0 or 5.0V, it changes by ± 0.3-0.5V). The box also makes clicking noises like a switch is being turned on and off at higher voltages (something shorting? or maybe a safety circuit? I don't have a manual for this box)

I want to know why:

1. The voltage changes on its own
2. The origin of the clicking sound from the DC supply box

Edit:

The supply box has a light that turns red when the voltage switches on its own, and I think that it is also linked with the clicking sounds.

Do you see how it turns green then red? What does that mean?

Answer 1

Your power supply has settable current limit.

It is set to some value and your load tries to draw more, so the current limit is reached and the supply adjusts the output voltage down in order to keep the current at the set limit.

As the supply needs to internally change between internal transformer taps the relay clicks. Same thing when you adjust the voltage up or down yourself, at some level going up or down a relay will click.

Please dowload the manual for your supply and make yourself familiar with the equipment you are using.

Answer 2

The clicking noise could be an internal relay operating as part of a current limiting system. I suspect your DC supply has a user-settable current limit - what is that set to, and how much current is the DC power supply providing when the clicking noise occurs? If the current limit setting is close to the actual current drawn by the load, then consider increasing the current limit setting - provided the load can handle the extra current.

The voltage change you are seeing may be due to the current limit circuit asserting then de-asserting itself. Suggest putting a volt meter directly at the load to see what the load voltage is doing - even better if you could observe this with a scope.