Rigol DP832 Output Capacitor Limitations

Summary

This blog details a hindrance with the Rigol DP832 power supply outputs when used for purposes such as characterising digital inputs, circuit reaction times or external power supply transient performance to name handful.

Rigol DP832

DP832 'Gotcha'
The Rigol DP832 is a good mid-range power supply sporting an easy to use interface to suit the hobbyist and options such as remote communications and power cycling to cater for some professional applications. For engineers familiar with power supply interruption testing, as defined in EN61496-1, the Rigol DP832 can be setup, with some fiddling, to assist with compliance tests.

It was the power cycling feature on the DP832 that was to be used for testing the PLC input design, however after the first few power cycles some unexpected measurements were observed. The configurable PLC input section circuit is shown below.

PLC Input Section

The power On captures shown below illustrate the difference between using the Rigol On/Off power button and the second capture shown the response using an external switch with the Rigol power button set to On.

Power ON Delay using Rigol Power Button

Power ON Delay using External Switch - Rigol Power ON

The delay in powering the circuit Off was also easily visible on the scope.

Power OFF Delay using Rigol Power Button

Power OFF Delay using External Switch - Rigol Power ON

Output Capacitance
Looking at the captures from the scope this appeared to be output capacitance. I recalled that Dave Jones from EEVBlog had torn down the DP832 several years ago; the output capacitors where found in EEVBlog #511; credit and many thanks to Dave Jones saving me the teardown.

The output capacitors appeared to be 1000uF electrolytics, which would explain the delayed switching performance.

EEVBlog #511 DP832 Output Capacitors - 2 Channels

EEVBlog #511 DP832 Output Capacitors - 1 Channel

Output Solution
As a temporary solution to testing, a relay was added. Channel one performed the relay coil switching and Channel two was left powered with the output connected to a Normally Open relay contact. The switching response was did not have the effect of the capacitor charge time although some relay contact bounce was evident.

Rigol DP832 with standard banana plugs

Summary

This is more an 'instructables' rather than a blog post and relates to the undersized banana post holes on older model DP832 power supplies.

Rigol DP832

Undersized Binding Post - Early Models

Although I had been using the Rigol DP832 for some time, there only recently became a requirement to upgrade the leads used with the power supply. There has been an issue with the early model DP832 binding posts which had been mentioned on a number of forums such as the EEVBlog.

It should be noted that the newer DP832 models (second half 2017 builds and possibly earlier) have the larger 4mm sized internal hole in the binding posts.

Binding Post Drilling
Armed with a 4mm drill bit in the drill, the first binding post was carefully brought into a state of banana compatibility.

DP832 drilling binding posts

After the first binding post was drilled and the metal shavings removed, a new banana plug was tested - snug fit! Disclaimer - Modify the binding posts at your own risk. This posts shows how the binding posts were modified on my Rigol DP832.

DP832 new banana plug test

Using the 4mm bit results in a fit for the banana plug which is tight and my preference when handling anything power related. A 4.1mm bit was not tried however this was mentioned in the EEVBlog forum.

DP832 with newly drilled binding posts

The depth to drill the binding post is somewhat dependent on the original hole depth. 

DP832 binding post hole depth

On average the depth of the hole in the DP832 binding posts that were drilled was between 16-18mm. It should be noted the exposed metal section of a standard banana plug is approximately 18mm, however contact with the banana plug is achieved in the first 12mm of the banana plug only.