Protection Diode for HP6033a in battery charging application, questions  - Page 1
Forum section: electronics / projects

author: valley001
author_rank: Frequent Contributor
timestamp: March 04, 2021, 05:38:26 pm
content: Hello all,I have a HP6033a here that I bought an repaired to use for top balancing large lithium cells. I have 30SQ045 Schottky diodes to use to prevent reverse current in the event of line power loss. My assumption was that the diode should be placed between the positive PS output and battery, with the volt sense lead mounted between the diode and battery so the PSU can compensate for the voltage drop of the leads AND diode and ultimately deliver accurate voltage to the cells.Then I found this from keysight. Although it is not the same power supply I wonder if this would apply to my older model. If it must be installed this way, how would one have an accurate voltage delivered to the load? I know it could be compensated for manually but I like the cleaner approach of having the PS adjust automatically for the diode voltage drop. I don't trust myself to manually compensate by setting voltage higher than the target voltage, I worry that it may overshoot and then over charge the cells.https://blogs.keysight.com/blogs/tech/bench.entry.html/2020/08/25/why_do_i_need_toadd-9g1S.htmlWould my method of having the sense leads placed between the diode and load risk damage to the sense circuits in the event of power loss? I welcome any feedback on this.

author: oPossum
author_rank: Super Contributor
timestamp: March 04, 2021, 05:59:36 pm
content: There are typically resistors between the power supply output and sense input to ensure the power supply will operate properly without any connection to the sense terminals. If you have the sense input connected to the battery and the power supply's output is lower than the battery then there may be enough current flow through those resistors to damage them. The 6033A service manual shows that the resistors between out and sense are 1k 1/4 watt.

author: valley001
author_rank: Frequent Contributor
timestamp: March 04, 2021, 06:07:38 pm
content: Quote from: oPossum on March 04, 2021, 05:59:36 pmSo the sense lead must be connected before the diode to protect everything. IIRC according to the manual the sense leads handle "a few milliamperes" so could I put a small fuse between the sense and battery? Would that suffice in theory?

author: valley001
author_rank: Frequent Contributor
timestamp: March 05, 2021, 11:14:18 pm
content: So I ran the PS charging 3.4v @15 amps and the diode gets HOT! I measured 93 Celsius before I shut it down, now rethinking the diode thing or perhaps I need to add a heat sink (if there is one in this package?)Its weird that there isn't a normally open relay or something to interrupt the supply if power is lost, rather than use a diode.

author: t1d
author_rank: Super Contributor
timestamp: March 06, 2021, 02:21:40 am
content: Using a MOSFET for reverse polarity protection makes for a neat circuit. It can be configured highside with a P channel, or lowside with a N channel. No pesky diode voltage drop and maybe a better solution for the amps. Circuits can be googled. Hope that helps.