Rigol DP832 PSU stupid question - Page 1
Forum section: electronics / testgear

author: do9zzz
author_rank: Newbie
timestamp: December 10, 2014, 02:06:23 am
content: Hello together,I'm thinking about buying a new bench PSU. On of the candidates is the Rigol DP832.But there is one question about it:The documentation says, it is not allowed to paralel all three outputs together.One of my requirements would be to have an CC controlled output of 3-5v @ 8A. In the case of the DP832 this would mean to parallel all outputs.Since channel two and three share a common ground a serial connection is prohibited of course. But I can't find any reason why not to parallel them to achieve the higher output current needed. Sure there would be no tracking between ch. 2 and 3 but I can live with this.Maybe someone in here can brighten up my limited mind on this topic?Regards,Alex

author: ovnr
author_rank: Frequent Contributor
timestamp: December 10, 2014, 02:58:15 am
content: I have no direct experience with the DP832, but if the specs and/or documentation say to not do something... don't do it. Really.Especially don't buy it with the intention of doing something you've been expressly told not to do. There are other power supplies on the market.

author: Gall
author_rank: Frequent Contributor
timestamp: December 10, 2014, 01:30:22 pm
content: The parallel connection is prohibited because of the principle how the voltage is regulated. Two regulators in parallel cannot have exactly the same voltage if they're not specially designed for such a connection. This means, the two feedback circuits will be in conflict, which most likely will lead to one of the outputs will take the whole load alone.

author: do9zzz
author_rank: Newbie
timestamp: December 10, 2014, 03:39:33 pm
content: Hello Gall,okay I understandI didn't know that both channels (2 and 3) are supplied by the same transformer tap (implemented by your answer). My thought was that the common ground is the the only connection between this channels. In this case it makes sense not to parallel these outputs to avoid the regulators working against each other.Does anyone else have another information on this topic?Thanks a lot,Alex

author: broderp
author_rank: Regular Contributor
timestamp: April 16, 2015, 12:07:58 am
content: I also have the same basic question and am looking for some definitive answer.If GALL's rational is true, then this would mean that even though I can hook up 3 separate loads with a total of 9A, hooking this supply up safely will only yield a max of 6A thru CH1 & 2 as one should never parallel CH3 with the other two.Am I understanding this correctly?I had hoped that even though CH23 & 3 share the same PCB in the bottom of the case as well as a common ground (why?) they could be utilized in such a fashion that you can tap the total 6A power they offer.

author: rs20
author_rank: Super Contributor
timestamp: April 16, 2015, 12:18:43 am
content: Quote from: Gall on December 10, 2014, 01:30:22 pm"Conflict"? What conflict??If you pull up to 3A from the supply, one output may take the whole load alone, yes. This is fine, because every supply is rated for 3A.If you pull between 3A and 6A, that one output goes into CC mode at 3A, and the next supply starts taking on the difference. Still fine.Above 6A, two of the supplies are most likely in CC mode (in my experience, based on how your wiring is arranged since the accuracy of the outputs is superior to the drop caused by 3A). Still fine. Sure, the three supplies are "in disagreement" as to whether the output is the correct voltage or not, but you get your 9A at about 5V, and every supply is within its own spec.In other words, the 9A output arrangement described by the OP is perfectly legitimate, and I've done it several times with my DP832. I have no idea why the manual says not to do it; I can't help but wonder if it's to prevent ham-fisted users feeding 30V from channel 1 into the 5V-only channel 3 and destroying it. That's probably a good enough reason to say not to do it in the manual, but not a relevant reason to a remotely competent user.