Setting constant current output on Digimess SM3040/HY3040 and similar PSUs?

Thread Starter

Irving

Joined Jan 30, 2016
2,979
Calling all SM3040 owners: how do you set a constant current output on these PSUs?

Before I tear what little hair I have out or worse, disembowel the PSU, someone please tell me I'm not going mad. On all other PSU I have, you short the output with a DMM and turn up the current limit until the s/c current is your desired constant current. Then you remove the short and turn up the output voltage to above your desired compliance voltage.

But if I do that on my SM3040 the output current into the short never goes above about 350mA. Is this normal or is it faulty?

If I connect it to an electronic load and dial in, say, 20A, on the load then if the current limit is set just a little higher it outputs 20A at the desired voltage but if the demand goes higher rather than current limiting, the voltage just dies completely.
 

Thread Starter

Irving

Joined Jan 30, 2016
2,979
I am not able to download the data sheet from the link you provided.
Have you read the manual?
Ummm, there wasn't a link AFAIK. The 'manual' contains no (useful) information.

The relevant section says:

"3.6 Output voltage and output current
The output voltage is adjusted to the desired value using both the Coarse and Fine Voltage controls. The output current level is adjusted to the desired value using both the Coarse and Fine Current controls. If the output current exceeds the set current value the power supply will limit the output current to the set value."

Which sort of implies it should work as I expected...
 

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KeithWalker

Joined Jul 10, 2017
2,453
Yes, it does imply that it should work as you expected. If you are sure that the compliance voltage was set high enough for the load you are using, then the supply must be faulty.
 

KeithWalker

Joined Jul 10, 2017
2,453
Is there a spec sheet in the manual? If so, does it mention any special limitations on output voltage and current? It appears to be going into over-current shut-down.
 

Thread Starter

Irving

Joined Jan 30, 2016
2,979
Is there a spec sheet in the manual? If so, does it mention any special limitations on output voltage and current? It appears to be going into over-current shut-down.
No more than I already posted.

The current limit is based on the voltage drop across a current shunt at approx 1.865mV per amp. If i dial-in, say, 5A on my electronic load and then turn down the current limit until the volts start to drop - its an incredibly fine line - then i can drop demand to 4.99A and the voltage recovers, but as I increase demand and the voltage decreases, the current limits drops off, its nowhere near constant, and its virtually impossible to select a specific limit.
 
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