Issues (?) with Keithley 2231A-30-3 DC Power Supply

[Wil_Bloodworth]

I ordered a Keithley 2231A-30-3 DC power supply and it seems like there might be a problem with stability.  Channel one seems fine-ish but channels two and three just seem a bit suspicious.

Channel 2 and 3 don't want to stay on the voltages type in.  If I put 2.0 into channel 2, it will drift down to 1.99.  In order for the screen to stay at 2.0, I have to enter 2.01... see photos below.

Please watch this video on what it's doing and let me know if you think there is an issue I.
https://youtu.be/ECfJka0ihAI







Thoughts?

Thank you,

- Wil

[tooki]

That’s a 10mV discrepancy.

That power supply’s specs list 0.06%+20mV setpoint accuracy and 0.06%+20mV readback accuracy. So even if we ignore the %, that’s up to 40mV discrepancy between setpoint and readback. You’re well, well within spec.

[skander36]

This is not a voltage reference.
For a power source is a very good precission.

[BennoG]

I have the same unit for a couple of months now and I like it.
I only find the display a little dim compared to the meters I have.

I have also written a program to control it from the PC so I can turn every output on and of at will and not all at the same time.

Benno

[Wil_Bloodworth]

Great!  I feel a lot better about the purchase now. Thank you!

- Wil

[J-R]

Great!  I feel a lot better about the purchase now. Thank you!

- Wil

Agreed, 100% this is normal and also it's common in my experience for the setpoint accuracy to be worse than the readback accuracy in real-world use, despite whatever the specs say.  Typically 1 count off from the setpoint or readback can be expected and I'd leave it alone in that case.  If either were ever 3 counts off or worse use that DMM6500 to calibrate it.

However, I wouldn't really describe this supply as being very good if you're wanting accuracy and precision.  It's very easy to find 1mV resolution bench supplies these days, so why not go that route instead?

Also, I know everyone has different use cases and there is also something to be said for brand loyalty, BUT, I do have some concerns with using the Keithley 22xx series as a hobby bench supply.  Not being able to easily enable/disable individual channels and not being able to see the setpoint and readback values at the same time just really jump out at me as negatives.  Are you just needing three independent supplies to set and forget?  Then maybe it is OK.

[Wil_Bloodworth]

However, I wouldn't really describe this supply as being very good if you're wanting accuracy and precision.  It's very easy to find 1mV resolution bench supplies these days, so why not go that route instead?

Also, I know everyone has different use cases and there is also something to be said for brand loyalty, BUT, I do have some concerns with using the Keithley 22xx series as a hobby bench supply.  Not being able to easily enable/disable individual channels and not being able to see the setpoint and readback values at the same time just really jump out at me as negatives.  Are you just needing three independent supplies to set and forget?  Then maybe it is OK.

You pretty much nailed it on the head!  I got, what I thought, was a good deal ($499) on a Keithley power supply so... impulse buy.  And you're exactly right... I bought it because it had Keithley written on it.  Also, the inability to en/disable each channel individually is quite a negative.  Granted... you can enable/disable each channel individually in the menus but it doesn't work like you would think as they're all still tied to the main on/off button.  That said, you can set each channel to 0v really quickly so I guess there's that.  Probably should've just waited... but hey, it's a Keithley right?!

- Wil

[J-R]

Ah yes, the good deal, can't fault that.

Does yours have a serial port or USB?

There are plenty of bench supplies to choose from if your eye ever wanders...

[Wil_Bloodworth]

Does yours have a serial port or USB?

There are plenty of bench supplies to choose from if your eye ever wanders...

Sadly, no USB but it does have a serial port which will do in a pinch.

And my eyes are always wandering!

UPDATE:  After a 2+ hours of warmup time, it is very stable. Channel 2 still shows 2.99v when set to 3v but it's actually dead on 2.99v out so at least the output is matching the screen.  Not a big deal.

- Wil

[Wil_Bloodworth]

I can certainly tell you one thing... this power supply is LOUD!  It is almost like a hair dryer on low.  Seems silly as it's that loud as soon as you turn it on.

- Wil

[BennoG]

The fan is controlled from software, depending on the firmware it is loud or it is quiet.
I have also read reports that it is quiet when new and after a year it is loud as a rack server.

Benno

[Wil_Bloodworth]

The fan is controlled from software, depending on the firmware it is loud or it is quiet.
I have also read reports that it is quiet when new and after a year it is loud as a rack server.

Benno

I might just pop the cover and see if it's just dusty. A good cleaning might help but I doubt that is the issue.  The System Info screen shows Main: 1.03/Aux:1.04 but I haven't checked to see if that is the latest firmware.

- Wil

[J-R]

It seems this is could be a rebranded B&K Precision 9129B: https://www.bkprecision.com/products/signal-generators/9129B
The specs are identical.  The front panel buttons were changed somewhat.

[Wil_Bloodworth]

It seems this is could be a rebranded B&K Precision 9129B: https://www.bkprecision.com/products/signal-generators/9129B
The specs are identical.  The front panel buttons were changed somewhat.

It would not surprise me.  I'm convince Keithley = Keysight = Tektronix = B&K Precision... they all seem to be in bed together so it would not have any problems believing they all got together and are designing the same exact things and rebranding them to different price points.

- Wil

[J-R]

It is somewhat common for some of the big players to rebrand other products especially to fill gaps in their budget offerings, but I wouldn't go full tinfoil hat on this and say they are all "in bed together" or the same company!

For a budget supply, you could consider the following:
https://siglentna.com/power-supplies/spd3303x-spd3303x-e-series-programmable-dc-power-supply/
https://www.rigolna.com/products/dc-power-loads/dp800/
https://www.rigolna.com/products/dc-power-loads/dp900/
The Rigol units are probably the best budget option as they have a healthy amount of equipment in their Clearance Center: https://www.rigolna.com/clearance/ and the DP800 series has a wealth of documented hacks available.  The Siglent SPD3303X-E is also hackable to the SPD3303X.
Do your homework on the hacks to make sure they are still possible and what is involved and the risks are acceptable...

Despite a missing knob, this could also be attractive if you want an A brand:
https://www.ebay.com/itm/186289509024

I picked up a used E36313A from Keysight a couple years back and despite it not being perfect or 100% competing with the budget offerings, I still like it a lot and use it daily.  I also have a E36103A and a E36105A, but honestly those were mistakes I made before getting the E36313A.

[Wil_Bloodworth]

Great recommendations.  Thank you J-R.

- Wil