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Tenma 72-8695 2 x 32v 3A + 5V @ 2A mini-review / teardown

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Bored@Work:

--- Quote from: mariush on September 26, 2012, 10:18:28 pm ---I know about ohm's law.

--- End quote ---

Then apply it.

ejeffrey:

--- Quote from: mariush on September 26, 2012, 10:18:28 pm ---Well, I assumed that if I limit the fan to 0.1 A when it normally uses 0.15A, the power supply would simply remain at 12v 0.1A and the fan would spin slower... like how it is if I were to connect the fan to a bunch of batteries that are almost depleted... the batteries would still show 12v yet unable to give a lot of  current.

--- End quote ---

Not to be a dick, but you just have a very basic misunderstanding of current and voltage here.  Pretend the "fan" is just a resistor of 80 ohm (it isn't, but that is close enough to demonstrate this point), and try to figure out what happens when you connect a power supply or battery with a 100 milliamp current limit.

mariush:
I understand now. I = V / R 

If the fan is the constant resistance then the only way the current can be limited is by reducing the voltage.

Thanks for reminding me.

T4P:

--- Quote from: mariush on September 26, 2012, 08:38:18 pm ---Below 0.1A, it's really hard to adjust. I'd say at about 0.07-0.08 A, the relay inside triggers and decouples the power supply.

--- End quote ---
That's not good. A power supply should CC down to 0v and not just suddenly decouple the PSU

mariush:
Well, it's a regular 10k potentiometer, so it probably just jumps from 0 ohm to what would be 0.08 A . You know the way regular pots work, I'd have to be very, very precise in adjusting - about 300 degrees are equivalent to 3.4 A

If I  replace it with a 5 turn or a 10 turn pot, it will probably work just fine. I might just do that when i place the next farnell order in a week or so.

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