12V din rail power supplies in series for 24V and 12V tap?  - Page 1
Forum section: electronics / beginners

author: V_King
author_rank: Regular Contributor
timestamp: January 24, 2018, 08:25:32 am
content: Hello,I am building a small control system containing 2x 24V water pumps (2.5A max each) and some logic run of 12v.Meanwell is selling these neat little din rail EDR series power supplies and I wonder if I could connect two PSUs 12V 10A in series to feed to pumps and tap off one of them to feed the 12v electronics as per attachment? Meanwell power supplies are isolated and Meanwell documentation says it is ok to use them in series.I really would like to avoid having two different psu and wonder if there could be any issues with such layout?Thanks

author: Paul Moir
author_rank: Frequent Contributor
timestamp: January 24, 2018, 08:36:12 am
content: If by parallel, you mean series as per your diagram then yes, no problem at all.Industrial control is commonly done at 24v, so the 12v control seems a little odd. But I bet you have your reasons.:thumbsup: on the diodes. Good thinking.

author: V_King
author_rank: Regular Contributor
timestamp: January 24, 2018, 08:50:38 am
content: Thanks for reply. Fixed the "spelling", head is not working in the morningI understand that 24V should not be the problem, I am more worried about the 12V tap off as the supplies will be loaded unevenly and not sure whether that will create any problems.The control is just simple 12VDC automotive relay ladder logic. 24VDC relays are expensive.

author: Zero999
author_rank: Super Contributor
timestamp: January 24, 2018, 09:46:59 am
content: Quote from: V_King on January 24, 2018, 08:50:38 amThe tap isn't a problem, so long as the current rating isn't exceeded and that current only flows from the positive to the negative terminal.

author: tszaboo
author_rank: Super Contributor
timestamp: January 24, 2018, 09:57:31 am
content: It looks OK to me. We did similar things with our power supplies, except those were KW+.

author: Damianos
author_rank: Frequent Contributor
timestamp: January 24, 2018, 11:31:22 am
content: I think that you have to check what happens to the system if one of them is overloaded or fails. For example what about the pumps operating at 12V?

author: Zero999
author_rank: Super Contributor
timestamp: January 24, 2018, 11:34:39 am
content: Quote from: Damianos on January 24, 2018, 11:31:22 amThe reverse parallel diodes should guard against that, assuming they have a high enough current rating.

author: Damianos
author_rank: Frequent Contributor
timestamp: January 24, 2018, 01:31:57 pm
content: What can the diodes do, if the pumps are heating, instead of pumping?

author: V_King
author_rank: Regular Contributor
timestamp: January 24, 2018, 02:07:34 pm
content: The power supplies have overcurrent/overvoltage protection and I think if one of the power supplies fails (or turn off due to the overload) I have an open circuit? Am I thinking right? I've got 10A(400A peak) continuous rated diodes (the biggest I could find in axial package).My max peak current should not exceed 5A at 24V and 2A at 12V, so I would think I have enough overhead to avoid overloads. What's more the duty cycles are low - up to 1hour intermittent use every 24 hours period and both pumps would rarely run at the same time. I should have enough redundancy for the application. It is not a heart surgery pumps

author: Zero999
author_rank: Super Contributor
timestamp: January 24, 2018, 02:14:50 pm
content: Quote from: Damianos on January 24, 2018, 01:31:57 pmThe PSU has overcurrent protection and if that's not good enough, then the pump design is faulty. The pumps should have protection against fire, such as a thermal fuse.