T4D 80 - ISO Tech PSU

[circuitous]

The sudden shutdown on OCP is interesting.  Thank you for the review.
Can you hook this up to a scope and check for voltage spikes when the output is turned on?
lso, might be worth checking for the same spikes when the unit is switched-on or off (using the mains switch).  I've had PSUs that gave huge spikes when the mains switched on... even with the outputs set to off.

Thanks again!

[bitwelder]

My guess regarding the sudden OCP intervention in parallel mode is that the two linked channels provide each half of the required current, and the OCP actually monitors only the master channel, so if it should trigger e.g. at 2A total current, the limit should be set (with the present firmware bug) at half of that, 1A.

If that is so, the firmware could be probably patched by scaling internally the OCP settings by a factor of 2 but... are we sure that the two channels are *in every condition* providing half of the current each?

[tmm]

My guess regarding the sudden OCP intervention in parallel mode is that the two linked channels provide each half of the required current, and the OCP actually monitors only the master channel, so if it should trigger e.g. at 2A total current, the limit should be set (with the present firmware bug) at half of that, 1A.

If that is so, the firmware could be probably patched by scaling internally the OCP settings by a factor of 2 but... are we sure that the two channels are *in every condition* providing half of the current each?

Martin showed it happening when he set the PSU to 1A OCP and the load at 500mA though, so theoretically each channel should have been loaded around 250mA yet it still shut down. Even if one channel was providing almost all of the current it should have still not shut down but it did.

Assuming each channel is handling half the load when in parallel mode would be dodgy at best because rarely do parallel channels get loaded evenly due to output voltage calibration, voltage drops across relays/wiring that is switched in to connect them in parallel etc. The firmware should be adding the current as measured by each channel's current shunts together, then comparing that to the OCP limit set - that is of course assuming that the OCP is implemented in software rather than dedicated hardware. It does seem to be doing something right because the live current shown on the display appears to be accurate.
I noticed that the load was connected to channel 2 when the testing was done in parallel mode. Is the same problem replicated if the load is connected to the channel 1 output jacks? Also try putting the positive lead on CH2+ and the ground on CH1- and vice versa as that can help load balance on some PSUs.

Also are we sure the Maynuo load doesn't overshoot? This isn't the easiest test on it when the output of the PSU is set to 11V+. When the PSU is off the DC load is trying it's best to be a dead short in order to pull the current it is set to, then the instant the PSU is turned on you get 11V/dead short = lots of current. Try putting a 1ohm power resistor in series with the Maynuo load and measure the voltage across it with a scope. If the DC load is set to 1A the voltage across the resistor shouldn't go above 1V.

[dr_p]

Martin showed it happening when he set the PSU to 1A OCP and the load at 500mA though, so theoretically each channel should have been loaded around 250mA yet it still shut down. Even if one channel was providing almost all of the current it should have still not shut down but it did.

It's not a good idea to start a current limited power supply IN current limit mode. The instantaneous current will most likely overshoot by a lot, more than in the constant voltage case. Both OCP and CC circuitry sense the current overshoot, but by the time the CC lowers output voltage, OCP kick in and disconnects the load.

[MJLorton]

Great conversation gents.

In time..and perhaps once the fix arrives I'll try some more extensive testing (programmed procedure in the Maynuo) and see what the output on a scope shows us as well.