New Products Flash Sale
Thread Tools
Old Aug 26, 2015, 05:03 PM
marableg is offline
Find More Posts by marableg
Registered User
United States, PA, Philadelphia
Joined Feb 2015
7 Posts
Discussion
Dell NPS-750BB A - float the dc ground

Hello everyone,

I just received two of these power supplies (NPS-750BB A). Does anyone know how to float the dc ground in order to use them in parallel?
marableg is offline Find More Posts by marableg
Reply With Quote
Sign up now
to remove ads between posts
Old Aug 27, 2015, 12:58 AM
jj604 is offline
Find More Posts by jj604
ancora imparo
jj604's Avatar
Melbourne, Australia
Joined Jul 2005
8,222 Posts
You don't need to float the DC ground to use them in parallel.

Do you mean you want to use them in series? To produce 24Volts.
jj604 is offline Find More Posts by jj604
Reply With Quote
Old Aug 27, 2015, 07:28 AM
marableg is offline
Find More Posts by marableg
Registered User
United States, PA, Philadelphia
Joined Feb 2015
7 Posts
Yes. I mean in series to produce 24V. Sorry about the error.
marableg is offline Find More Posts by marableg
Reply With Quote
Old Yesterday, 04:35 AM
Jason50 is offline
Find More Posts by Jason50
Registered User
Joined May 2013
290 Posts
I've been replacing the two M3 screws behind the main output connector with nylon ones. Washers between the board and the case at that location, also nylon compete the job. To actually do this you will need to remove the cover and then the cooling fan. Make sure you test that the negative DC terminal and the case are isolated before using.

As with any mains powered device if you are not sure about what you are doing don't attempt this.
Jason50 is offline Find More Posts by Jason50
Reply With Quote
Old Yesterday, 01:44 PM
ggcrandall1 is online now
Find More Posts by ggcrandall1
Registered User
ggcrandall1's Avatar
USA, GA, Marietta
Joined Aug 2005
7,209 Posts
Quote:
Originally Posted by Jason50 View Post
I've been replacing the two M3 screws behind the main output connector with nylon ones. Washers between the board and the case at that location, also nylon compete the job. To actually do this you will need to remove the cover and then the cooling fan. Make sure you test that the negative DC terminal and the case are isolated before using.

As with any mains powered device if you are not sure about what you are doing don't attempt this.
Additional information. Only float the ground on the 12V to 24V power supply. After making the series connection check the grounds with an ohm meter before applying power.

Some insulation across the output terminals to prevent something from contact them would be in order too.

Glen
ggcrandall1 is online now Find More Posts by ggcrandall1
Reply With Quote
Old Today, 02:19 AM
marableg is offline
Find More Posts by marableg
Registered User
United States, PA, Philadelphia
Joined Feb 2015
7 Posts
Ok. I replaced the two M3 screws with nylon ones and added nylon washers to the top and bottom of the board. Checked for continuity and I now have no continuity between the -12V and the case.
marableg is offline Find More Posts by marableg
Reply With Quote
Old Today, 03:59 AM
Jason50 is offline
Find More Posts by Jason50
Registered User
Joined May 2013
290 Posts
Once it's back together it's good to go. As already mentioned , use that one as the "high" side. With the other units DC still grounded if anything does go wrong you still have the mains earth protection.

Once you have all the connections sorted, hot melt glue works well to insulate everything. It's also easy to get off again if need be.
Jason50 is offline Find More Posts by Jason50
Reply With Quote
Old Today, 05:55 AM
ggcrandall1 is online now
Find More Posts by ggcrandall1
Registered User
ggcrandall1's Avatar
USA, GA, Marietta
Joined Aug 2005
7,209 Posts
Sanity check? Your picture shows no continuity between the chassis and a green wire.
Is that wire the mains ground? If so I am confused. I thought that the mains ground to chassis should still be in tact. I thought only the -12V to mains ground should be isolated.

Can someone clarify? Have I misinterpreted the picture. Am I incorrect in my understanding of the correct way to isolate the -12V?

Glen
ggcrandall1 is online now Find More Posts by ggcrandall1
Reply With Quote


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
For Sale Modified Dell NPS-700AB power Supplies with 4mm bullets TechBill Aircraft - Electric - Batteries & Chargers (FS/W) 7 Aug 22, 2015 11:34 PM
Question Have Dell NPS-700AB - Charger? vexter0944 Batteries and Chargers 4 Oct 15, 2014 12:42 PM
Discussion Question on NPS-700AB Dell power supply output Rich in ILM Batteries and Chargers 1 Mar 02, 2014 02:31 PM
Discussion Dell NPS-700AB power supply arrived broken htuong95 Batteries and Chargers 3 Oct 02, 2013 12:42 AM
Discussion NPS-700AB Dell 2850 PS ericm7030 Batteries and Chargers 0 Mar 04, 2011 06:07 AM