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Tenma 72-10480 Bench PSU - 5mA offset?
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jewelie:
Hi

I've just bought a commonly recommended starter/basic bench Tenma 72-10480 30V 3A Bench PSU direct from CPC Farnell ( https://cpc.farnell.com/tenma/72-10480/power-supply-1ch-30v-3a-adjustable/dp/IN06822 )

In testing, the current reading on the display seems to be offset low by 5mA+, all the way down, e.g.


* 180mA (on PSU) = 185.5mA (on 2 DMMs)
* 90mA (on PSU) = 95.5mA (on 2 DMMs)
* 10mA (on PSU) = 15.1mA (on 2 DMMs)
This is my first bench PSU, I'm struggling to understand which accuracy ref to compare these to in the datasheet ( https://www.farnell.com/datasheets/2241024.pdf ) but I think it might just be within spec? 

I'm a little frustrated with this 5mA offset.

My options, as I see them are-


* If it's actually out of spec, get it replaced.
* User recalibrate it - if this is realistically possible. (Anyone know?)
* Put my big girl knickers on and deal with the fact that it's not quite accurate. (Meh, I bought a bench PSU because I didn't want to keep relying on fudging powering things.)
Thoughts?

- Julie

PS  For reference, I'm a hobbyist with an ancient CS+EE degree, so I messily straddle the line between beginner and not entirely. I'm relatively aware of the dangers of 250V (which is what the "230V" is around here) and tend to be very cautious etc, but I'm also aware that there's soooo much I don't know.
Andy Watson:
Probably option 3, keeping in mind that these units are obviously built down to cost - you're still getting a lot of bang-for-buck if you can live with its foibles.
If you want to explore option 2, search-out details of the Korad KA3003 - the un-  or re-badged version of the Tenma. 

Or there's the second-hand TTi offerings for a similar price - but that's another can of worms :)
mqsaharan:
I think its a nice unit for the price.
Please do perform some basic testing (and may be some intense testing) of the unit before committing to it and if you find anything wrong with it better to get it exchanged under warranty while you can or if you would like you can improve/repair it to your liking.
The early units had some serious problems with the design of output transistor board but I think that has been solved. Check out Dave's videos #315 (last five minutes) and #404 for it. #314 is the teardown video.
Take a look at the following links. These may not be exact models as yours but may give some useful information.
Some people have reported problem with rotary encoder. I don't know if it has been solved. Read the comments as well.



For repair, this also has schematics, calibration procedure:
https://www.eevblog.com/forum/repair/korad-kd3005p-problem-with-current-metter/
ledtester:
fwiw, here are the specifications for the Korad series. The Tenma looks like a rebranded KA3005:

https://static.eleshop.nl/mage/media/downloads/KA3005P_datasheet.pdf

Note the Setup Accuracy and Read Back Temp Coefficient.


J-R:
You could try the calibration steps listed here:
https://www.eevblog.com/forum/testgear/korad-3005p-calibration/

I ran through this on my KA6003P and while I wasn't particularly impressed, it's still reasonable for this class of device I suppose.

Mine is basically 20mV low all the time except for the upper setpoint, which is spot on.  I can adjust that high or low and doesn't seem to matter - it's always 20mV low everywhere else.
For current I was able to reach ~3mA setpoint accuracy and ~1mA readback accuracy.
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