I bought SPD4323X and have some complaints about it:
- fan noise annoys me. It's not the airflow, the fan itself emits annoying buzz. I had the same problem with SDS2000X+ where I replaced it with Noctua. But I think that one is variable speed, so that might be more involved. Did anybody changed the fan in their unit?
- when entering value from keypad it goes into modal-like where no buttons work except for keypad, knob button (which confirms value), knob turn and arrow keys (which cancel entry). You cannot turn the channels off and not even Home cancels entry! I think instead that pressing any button not on keypad should: cancel entry, and perform whatever normal action that button does.
- it has buttons for individual channels, so there's really no good reason to allow arrow keys to switch input focus between channels. Instead of that left/right arrow could function as voltage/current button respectively.
- maximum voltage setpoints are 6.06/32.32/32.32/6.06. But in CH2/CH3 series mode for some reason it has 60 V limit. Obviously if you connect them externally you can get 64.64 V.
- main screen doesn't show configured OVP/OCP values at all
- I'm not sure what's the purpose of OVP. If it's for DUT that feeds voltage back into supply, well, I don't think it will be affected by turning off supply source that has lower voltage, and thus doesn't feed any current anyway. If it's meant as protection in case of user fat-fingering the voltage, it's totally unsuitable as it doesn't clamp the setpoint and trips only when that voltage is actually exceeded, and takes long time to do anything about it.
- voltage and current readings are not averaged, just point samples. If you have load that aliases with display update rate you might get totally bogus reading. What's worse is that also applies to CC/CV indicator! You might have load that in pulses hits CC and not see anything on the display. Lack of averaging might be excusable, but when control loop hits CC/CV it should be latched and ensured that at least one display frame shows changed state.
- OCP/OVP reaction jitter seems all over the place. It usually trips in 10ms-50ms, but I have seen even 300ms occasionally. I think it's on the UI thread... It's also sampled, so you might have pulsed load that aliases with OCP sampling that will never trigger.
- when in bonded CH2/CH3 mode it's not consistent which values it displays. CH2 shows combined values from both channels, but CH3 shows CH3 only.
- when in CH2/CH3 bonded mode OVP/OCP values still apply to individual channels. If it trips on CH2 it will turn both channels off. If it trips on CH3 that will cause shrieking continous beep, but will NOT turn anything off.
- as others mentioned, current limit in CH2/CH3 series mode is wacky. It sets voltage limits of each channel to half of the setpoint, current limit on CH2 to setpoint, and current limit on CH3 to setpoint + 0.1. I suspect they did that because if you set current limits exactly the same voltage ratios of both channels will drift randomly, so this is their "fix". But now if both channels are in CC the channel with lower limit (CH2) will be progressively driven lower and lower, eventually going into negative, clamping at -0.75 V. (I guess there's reverse protection diode). As all the current current flows through diode the (correct) limit set there is ineffective, and all that's left is the limit on CH3, which is 0.1 A higher than the user intended. And the combined voltage display (in CH2 block) now reads ~0.75 V too high, because ADC doesn't measure negative voltage that is on CH2.
(I think the dirty fix they need to do is to subtract 0.1 A (or less, 5 mA would be plenty enough) from second channel limit instead of adding it. In some cases this might make current limit too low, but at least it won't exceed configured current. Proper fix probably would be to add extra relay that adds some feedback path between CH2 and CH3 that biases output voltages to be equal).
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