[Repair] Current reading error with DSN-VC288 (100V 10A Voltmeter Ammeter)

[danon.spy]

Hi DIYer,

I have come across this issue. When I tried to make a power supply using some cheap DC to DC converter and a volt+amp meter, the current meter show an error as in the pictures. It show stable ~15.5A even with or without load. I don't know what have I did 

When I shorted the little current shunt with the LM358 opamp (pin 2 or 3 or 4), it seems to fix the issue. But I don't know if I permanently do that, would it destroy that meter? Will it have any negative effect?

Images (click on image for original size):

[danon.spy]

 

[BrankoMN]

https://www.ittsb.eu/forum/index.php?topic=1351.0

[danon.spy]

https://www.ittsb.eu/forum/index.php?topic=1351.0

Thank you so much for that link.
I am reading this and test on my meter with the RESET trick, will update for the result. 

[jorgemef]

After some fighting with a latest one from AliExpress I concluded:
Best linearity is achieved by using external supply.
If using same supply leave ground from voltage plug floating else will add a lot offset impossible to compensate with potenciometer.
The best linearity I achieved was by incrementally regulating the potenciometer and reset the module to compensate offset for potenciometer setting unloaded. I used same power supply so with 10ma I read 8ma and with 1,5A I read 1,53A. With external supply I achieved 10mA as 10mA and 5A as 5,01A.
I opted for same supply as is enough for my needs and didn't wanted to buy another transformer just to power it up as I am using two independent units in a same power supply to have independent rails. Have small switching PSU Wich I could use but they introduce EMI in the output through the amperimeter.

[jorgemef]

Hello.

Any bether unit that fits same layout or suggested seller that sell a good version of this meter?
Unfortunately one of my units broke during reset. Not sure if is because I reseted with it on, but had done it before without problems. This time microcontroller and LDO let magic smoke out. I was powering them with 28V. Maybe was too much.

Will look for a new unit to fit to my almost finished dual rail power supply. If I can find something better than my crippled version will go for it. 

Cheers,
Jorge

[BrankoMN]

Try this https://www.aliexpress.com/item/1005003786622190.html?spm=a2g0o.order_list.0.0.21ef1802VVJUFk and read carefully product description. Here is a description of how to set it up https://youtu.be/NxnhyCE43Vc . I bought one and it works great.

[xavier60]

I wish the display refresh was really 300ms as advertised instead of really being 1000ms.
Those 4 digit meters have auto-zeroing on the current meter, so the reading is very stable.

[smd_hunter]

Best linearity is achieved by using external supply.
If using same supply leave ground from voltage plug floating else will add a lot offset impossible to compensate with potenciometer.

Thanks for the idea Jorge! I have two DC-DC source modules with segment display to see voltage and current, one of them has a lm358, the other one does not. The one with the op-amp differs the current as it happens to the OP. When I get home I will do some tests.