Adjusting DC motor shield current trip point

[Maletrain]

About a year ago, I started a thread (which I can't seem to find now) about running an NCE Power Cab with a battery instead of the OEM wall wart.  The need for that got canceled, and I went on to other priorities. But now the that has resurfaced, and I am back on the project.  One response to the old thread was to use a DC motor power shield to protect the Power Cab from over-current.  So, I bought the one recommended and am ready to set it up.  But, the instructions are a bit odd, and contacting the seller with a direct question produced a bot-style response that did not answer it.

So, here is the link to the motor shield I bought https://www.ebay.com/itm/224126511915 , which includes "instructions" for its setup.  To save readers the trouble, here is the part that is making me wonder:

"Current Limit Adjustment:
When the red alarm LED is lighting, eliminate the overcurrent factors, it will automatic reset (automatic mode), or push the Reset Button, reset the power (Manual Mode).
Reset the current limitation pot should as follow:
1. Turn off the power.
2. Adjust the Current Limitation pot until the desired maximum current is reached.
3. Reset the power."

What I am wondering about is that the "instructions" seem to imply that I need to set the current trip point with the power off.  I guess I could trial-and-adjust that setting with the power off as I turn the screw, and then power up to test it, repeatedly until I found the right setting.  But I was expecting to be able to do it with the power on and the current flowing (to some resistor) at the value that I want for the trip setpoint, and turn the screw until it trips.

Does anybody have experience with setting the trip current for this particular unit?

To forestall discussions of other issues, I'll add that I intend to put a fuse between the battery and this device.  I am just looking for something that will act faster than a fuse to limit current to the Power Cab in the event of a short circuit in or beyond the Power Cab.

[mmagliaro]

Well, I don't have any experience with that unit.  But my advice is to adjust it the way you wanted to,
and see how it goes.  Put a load across it where you want it to trip, try adjusting the screw until it just trips.
Then turn it off and on, and see if the setting works as you expect.  They may have devised the circuit so that
it doesn't work right unless you turn it off before every change in the trip point, but that's hard to believe.
And even if they did, you'll soon know, and then you can do it the hard way - switching it off between every adjustment.

[Maletrain]

My concern isn't that it is designed that way - its more about maybe it NOT being designed to avoid being damaged by turning down the pot with the power on. 

I have no idea how the circuit is designed. 

I'll probably try it with the power off a few times, and maybe I'll hit it without too much trouble.  I'll try to start so that it trips when I turn the power on, then edge it up with the power off and retry until it doesn't trip.  The "delay time" pot has a printed symbol that seems to indicate that turning it clockwise increases the delay time, so I will guess that clockwise also increases the trip current, and start with it fully counter-clockwise.

At least they aren't particularly expensive items.

[mmagliaro]

Caution is always a good idea.  But I'd be shocked if the circuit could actually be damaged by adjusting the current limit
while it was on. 
You're right, $6.. wow.  That's amazingly cheap.   I don't think I could buy all the components on that board, plus the board, for less than $20 and that's optimistic.

I did end up building that overcurrent device I showed (like... 6 - 8 months ago?), but instead of a trimmer, I opted for
a 3-position DIP switch.  You select one of 8 possible trip points between 1-5 amp just by setting the switches so people with no
electronics knowledge could set it and use it without having to calibrate it with a test load.

[jagged ben]

I'm also inclined to think you won't damage the unit trying your way.  (At that price, just buy two, anyway.)  But it may just not work.  It could be that the thing is digital enough that it reads the pot on startup and then doesn't respond to changing the pot while powered on.