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Multifunction Basic Power Supply Test Line 3523
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Multifunction Basic Power Supply Test Line 3523

by jweed on Fri Dec 18, 2020 6:43 pm

I just received the Multifunction Basic Power Supply Test Line 3523. I purchased it with the intent of using it for test leads on my DMM. Lady Ada mentions using it with a DMM in the product video. I was surprised to discover that with absolutely nothing attached (except my DMM), the resistance reads 40K Ohms. I opened the little inline box and discovered a circuit boad with three 20K resistors on it. Two of them in series across the input. I'm not sure what the resistors are for. Current limiting?

Seems to me this item is ONLY for power supplies. It's not for DMMs. Perhaps I should have realized that. I added it to my order at the last moment and didn't look carefully (only $5).

I think the Adafruit marketing people should be more specific and say "NOT FOR DMM USE" where it can't be missed. The video should be edited accordingly. Besides mentioning use with DMMs, it also says the green and white clips have an unknown use. Please figure out what they are for and tell us. In the video Lady Ada suggests that she might open the little box to show us the PCB inside, but doesn't. I wish she had. She would have seen the resistors and realized there's more to it than meets the eye. Even if I had purchased it for power supply use, I still would have wanted to know about the internal resistors. Now that I think about it, the advice in the product description about cutting the confusing wires off should have been a red flag.

I'm not looking for a refund. I modified the circuit board and cut wires to make it OK for my purpose. The photo I added is the unmodified PCB.
IMG_2445.JPG
As-shipped 3523 PCB showing three 20K resistors
IMG_2445.JPG (99.88 KiB) Viewed 457 times

jweed
 
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Re: Multifunction Basic Power Supply Test Line 3523

by adafruit_support_mike on Fri Dec 25, 2020 4:54 pm

The two 20ks between the positive and negative leads are probably for power supplies with switching regulators. The simplest versions of those go badly out of regulation if they don't have at least some current load. I'm not sure what the third resistor is for.

You're right that it deserves mention on the product page. I'll let the folks who handle the shop know. Thanks!

adafruit_support_mike
 
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Please be positive and constructive with your questions and comments.