Tenma 72-10495 possible Korad KD3005 varient - Page 1
Forum section: electronics / beginners

author: Jimmy6616
author_rank: Newbie
timestamp: April 24, 2023, 12:03:47 pm
content: Hi oh knowledgeable peopleI have the dual 5A supply from Tenma (Farnell) Looks like 2 Korad's together with a link cable for serial\parallel operationOne side went faulty, after removing the vertical board behind the LCD, the large open coil had disintegrated , the 1N5408 in parallel had blown and also a 330uf Cap looked a bit bloated. I replaced the items and powered it up. All works except the current measurement and display are way off so something else must be amiss. If i set to say 2.5A @ 17V, I get 17V @ 3.14A but the display shows current draw @ 0.035AIve searched for circuit diagrams and on this forum for a similar issue but to no availAny pointers that would help ?

author: Andy Watson
author_rank: Super Contributor
timestamp: April 24, 2023, 12:17:50 pm
content: Quote from: Jimmy6616 on April 24, 2023, 12:03:47 pm"Large coil" ? Was this actually an inductive coil or was it a coil of resistive wire, i.e. the current shunt? You presummably have an identical "coil" on the working channel - do you have facility to measure its resistance - it will likely be sub-ohm in value.

author: Jimmy6616
author_rank: Newbie
timestamp: April 24, 2023, 12:42:48 pm
content: Andy , an open coil 1mm dia wire , 8 turns , id 6.5mm set 21mm above the pcb. I made a new one

author: Andy Watson
author_rank: Super Contributor
timestamp: April 24, 2023, 12:50:26 pm
content: I can't find the schematics (they're on this forum - somewhere), so I can't confirm what the components should be, however, what I'm suggesting is that the coil is unlikely to be an inductor. It is more likely to be a resistor that has been coiled-up to save space.

author: Jimmy6616
author_rank: Newbie
timestamp: April 24, 2023, 12:54:53 pm
content: This is the coil in parallel with a diode if it helps

author: Jimmy6616
author_rank: Newbie
timestamp: April 24, 2023, 02:31:24 pm
content: This is the pcb out of the psu

author: radiolistener
author_rank: Super Contributor
timestamp: April 24, 2023, 11:10:35 pm
content: this is not the coil, this is the shunt resistor which is used to measure current. But since it has such geometry it has some inductance.I'm not sure about your clone, but here is korad schematics, so may be it will be the same.

author: Jwillis
author_rank: Super Contributor
timestamp: April 24, 2023, 11:20:07 pm
content: It has a designation R2A manganin wire current shunt ? Has an extremely low temperature coefficient. Meaning its resistance changes very little with temperature. Can handle a lot of current before break down.Unless the manufacturer cheaped out and used copper wire. You never know for sure sometimes.

author: DaneLaw
author_rank: Frequent Contributor
timestamp: April 25, 2023, 01:16:57 am
content: Korad inside pictures and videos, but its the Korad KA3003P and the Korad KD3005P so not the same.I mostly use them for lazing various wavelengths/ diodes and testing drivers..https://imgur.com/gallery/B7ZOQ3J

author: Jimmy6616
author_rank: Newbie
timestamp: April 25, 2023, 05:52:20 am
content: As I made this shunt from 1mm copper wire and the psu is both showing the wrong current and also the output does not match the set current what are my options ?

author: Andy Watson
author_rank: Super Contributor
timestamp: April 25, 2023, 09:02:34 am
content: Replace it with the appropriate resistance. It appears to be 0.1, 5W. You can check the resistance in your working channel.

author: Jimmy6616
author_rank: Newbie
timestamp: April 25, 2023, 09:07:33 am
content: Thank you . So if locate a 0.1ohm 5W resistor, does it have to be a high precision or wire wound etc

author: mawyatt
author_rank: Super Contributor
timestamp: April 25, 2023, 02:29:01 pm
content: Quote from: Jwillis on April 24, 2023, 11:20:07 pmRecall that manganin wire was difficult to solder, if so then this shunt would need some sort of crimp to the PCB or a crimp sleeve which is solderable. If it's just copper then it would have a high positive TC (~0.4%/C), so likely some alloy or combination to achieve a lower TC and be solderable, otherwise it would have horrible performance.Best,

author: Jimmy6616
author_rank: Newbie
timestamp: April 25, 2023, 02:49:27 pm
content: Thank you for the feedback