HP 66332A Output Off but still loading source - Page 1
Forum section: electronics / testgear

author: rommac100
author_rank: Newbie
timestamp: March 01, 2023, 05:57:13 am
content: Not sure if this a just a limitation of the PSU but for whatever reason my HP 66332A (well two of them) exhibits this issue where the output can be set off but will still draw current from a source. It is voltage dependent on the source so 20V source will equate to about 20mA current draw and 1V source is somewhere around 1 mA. Not sure what the issue could be immediately but any assistance would be appreciated.

author: Berni
author_rank: Super Contributor
timestamp: March 01, 2023, 06:27:21 am
content: Id need to go check on mine. But it sounds normal.But in general it is typical for most PSUs to have some loading on the output when it is disabled. Some of it is because most of the sensing circuitry is still connected. But commonly they are loaded down on purpose to help discharge the output capacitors, since otherwise the output voltage might remain present for a good while after being turned off.Some rare PSUs even actively pull down the output. I have a big 4 channel rack mount HP system PSU that pulls down the output using full rated output current.(Tho forgot if it does that in disabling or just programing to 0V output). The one you have does that at the set current for the channel, so it is pretty useful as a electronic load too.(I mostly just use it for that, since it is a pretty annoying PSU to use)

author: J-R
author_rank: Super Contributor
timestamp: March 01, 2023, 06:47:06 am
content: I just checked mine and it does not do this. There is an initial current flow spike when the other PSU is set to 20V, but it drops to zero after a few seconds. End result current flow is below 0.001mA. I'm confident the spike is due to charging the 66332A's output capacitance (there are two settings for this value).Just to double-check, you actually have the output disabled, and are not just setting the voltage/current to zero?

author: J-R
author_rank: Super Contributor
timestamp: March 01, 2023, 07:00:37 am
content: Tinkered some more and it looks like my 66332A is a completely open circuit when the output is disabled, and I can hear the relays. The current flow was from the other power supply's output capacitance, not the 66332A's.

author: Swainster
author_rank: Frequent Contributor
timestamp: March 01, 2023, 07:25:20 am
content: I have a couple of 66311Bs and they both do this - when the ouput is disabled they pull down with about the equivalent of a 330R resistor. This is different to programming 0V, when they pull down with pretty much the full capability of the down programmer (doesn't follow the current limit setting).edit: My units don't have the relay option - perhaps this makes a difference?

author: J-R
author_rank: Super Contributor
timestamp: March 01, 2023, 08:08:18 am
content: OK, sorry, that explains it, I have "Option 760: Output disconnect relays". I see Keysight's official options page calls it "DC isolation and polarity reversal relay". User manual states "Units with option 760 have isolation and polarity reversal relays connected to the output and sense terminals."

author: Berni
author_rank: Super Contributor
timestamp: March 01, 2023, 10:33:49 am
content: Ah yeah that would explain it. Mine doesn't have the relay option.

author: rommac100
author_rank: Newbie
timestamp: March 01, 2023, 04:23:44 pm
content: Ah okay that makes sense that the option 760 would allow for a complete disconnect from the circuit (neither of my units have this option). I was planning on using these power supplies for charge and discharge cycling while also doing some long term no load monitoring of some 18650 cells. I assume having a relay would prevent this long term monitoring so I might just need another multimeter to do the long term voltage measurements.

author: alm
author_rank: Super Contributor
timestamp: March 01, 2023, 04:51:02 pm
content: Quote from: rommac100 on March 01, 2023, 04:23:44 pmCheck the service manual for what the option entails. It would not surprise me if option 760 just entails soldering in a few relays and passives, and changing some jumpers. But I didn't check.Be careful hooking up those cells directly to a power supply without external protection like series diodes. If the power supply loses power, or if a voltage spike trips the overvoltage crowbar, that could result in the cells destroying the power supply. The longer you have them hooked up, the higher the chance of something like a power cut. Keep in mind that these batteries can have hundreds of amps of short-circuit current in a sufficiently low impedance load. Although I believe these supplies have an internal fuse in the crowbar circuit that might mitigate this problem. But in general I prefer to use battery charges to charge cells, and use battery simulators like this to simulate a battery.

author: Berni
author_rank: Super Contributor
timestamp: March 01, 2023, 07:53:51 pm
content: Last time i had to cycle batteries i combined a programmable PSU and programmable electronic load to do the job. The PSU had a diode in series, so that the battery couldn't discharge back into the PSU. I did actually blow up a PSU as part of that setup, but not because of the setup, it was just a cheep chinese piece of crap PSU that didn't have the cooling to keep up (despite having a fan and running it bellow max specs) so it blew its pass transistor, resulting in a but if a hairy situation but luckily i was dealing with lead acid.. lithium would have exploded. Got the money back for that PSU from Farnell since it was literally weeks old.Tho i don't see why this instrument couldn't do all of it. As long as you put a fuse in series with the battery and place the battery in a metal bucket, it should be fine.If you want to do long term monitoring on cells then you need a DMM with high impedance mode since even the input resistance of a multimeter can affect the battery over a long enugh period.