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flyers
September 13th, 2007, 10:15 AM
Hi guys,

I'm designing a control panel system and one of the require from customer is to have parallel (2 units) power supply (24V DC) for the control panel & PLC as well.

There is one incoming 230V AC to the 2 units of power supply (230V AC to 24V DC). Each 24V DC power supply output will energize a relay & a pilot lamp (24V DC). in the event if any of the 24V DC power supply is faulted the relay wiil be de-energize and send an OFF signal to the PLC DI and the pilot lamp for that particular power supply will also be OFF.

My concern is do we need to put a diode after the power supply output, after the relay & pilot lamp so there is no current flow backward? Or izzit possible/advisible to do so?

I'm not sure what problem will I be facing, please advise me....thanks a lot.

jtn
September 13th, 2007, 10:48 AM
You can by power supplies already designed to be used in parallel. Attached is a manual for Idecs that have some models that can be used parallel. I believe Sola makes some also.

panic mode
September 13th, 2007, 11:26 AM
i read the question few times and i still don't know what exactly you want to do.post circuit...

Mickey
September 13th, 2007, 11:32 AM
Another source:

http://www.acopian.com/redundant-power-supplies.html

Ken Moore
September 13th, 2007, 01:01 PM
I use the off the shelf item from Sola-heavy duty. The Sola power supplies also have a status contact built in, no need for a relay.

Ken Moore
September 13th, 2007, 01:03 PM
I use the off the shelf item from Sola-heavy duty. The Sola SDN power supplies also have a status contact built in, no need for a relay.

http://www.solaheviduty.com/products/powersupplies/sdnpred.htm

keithkyll
September 13th, 2007, 01:22 PM
The output internal to a SMPS supply is transformer winding - diode - cap. The problem is the regulator circuit. Most likely, the higher voltage SMPS would drive, while the other would go into shutdown.
If both were linears, they might oscillate with each other.

As suggested, the supplies neeed to be designed for this. The diode idea is safer (no question about supply design) and may be cheaper depending on how much labor is involved in wiring.
Add diodes and set both supplies for 24.7 or so. That will provide isolation, and eliminate any questions.

Supplies with a status output may prove to be the best solution.

Gerry
September 13th, 2007, 04:58 PM
If the power supplies are not designed for parallel operation, then definitely isolate them with diodes. Just make sure the diodes can handle the current involved and they have adequate heat sinking.

BobB
September 13th, 2007, 05:04 PM
I combine switchmodes all the time throughg bridge rectifiers to give redundancy of 24VDC supply. Easy and reliable. Mount the rectifiers directly on the cubicle mounting plate.

keithkyll
September 13th, 2007, 05:19 PM
Great Idea. I had visions of diodes soldered inline and didn't like it. A 25 amp or larger bridge will have a mounting hole in the middle, and .25" blade connections. Much better and cleaner.

John Gaunt
September 13th, 2007, 07:11 PM
Using a bridge rectifier is a good idea. I have used diodes in the past bolted through an aluminium heat sink for this purpose.

It is a good idea to independantly adjust each power supply so that their output voltages match and they will then share the load fairly equally. Remember that there will be a small voltage drop through the diodes so make the voltage adjustments with the diodes in the circuit.

bikerdude
September 13th, 2007, 08:49 PM
Hi,
Interesting idea using the bridge rectifier. Does anyone have a schematic I can look at?
Thanks BD

bernie_carlton
September 13th, 2007, 09:03 PM
Apply the outputs of the two power supplies at "PS1" and "PS2". Take the output where indicated. The other two diodes aren't used.

http://www.plctalk.net/qanda/uploads/Bridge.JPG

bikerdude
September 13th, 2007, 09:14 PM
Guys,

Thanks, another great tool for my tool box!
BD

flyers
September 15th, 2007, 09:27 PM
Hi guys,

Thanks for all the replies and info given, it's a great help for me.
I've spoke to the end user, since they are Taiwan based, thus they prefer to use Meanwell brand power supply (all other panles are using this brand, non redundant).
so, i've browse the meanwell website and I found out that this might be suitable for me;
http://www.meanwellusa.com/search/DR-RDN20/DR-RDN20-spec.pdf

But the site does not have 2 different incoming (230V AC), so we are connecting one 230VAC to 2 Meanwell power supply and parallel it's 24V DC output.

According to some of the info given by the gurus here, I need a diode to eliminate backflow when one power supply is down. But if i'm using this kind of Meanwell redundant power supply, do I still need to have a diode there?

Hope to hear from you guys again. Thanks.

rsdoran
September 16th, 2007, 09:12 AM
Not sure what you are asking. The unit you linked to is a redundancy module i.e. you can connect 2 power supplies to it and have one output, if either power supply fails the associated relay will drop out. No need to add diodes, they are incorporated as shown in this pic.


http://www.plctalk.net/qanda/uploads/pwsredundancy.jpg

flyers
September 20th, 2007, 09:56 PM
Not sure what you are asking. The unit you linked to is a redundancy module i.e. you can connect 2 power supplies to it and have one output, if either power supply fails the associated relay will drop out. No need to add diodes, they are incorporated as shown in this pic.


http://www.plctalk.net/qanda/uploads/pwsredundancy.jpg

Sorry my mistake, I taught this DR-RDN20 required two units to do redundant feature. It's actually a unit with built-in DIODE for redundancy feature. I can use 2 normal meanwell power supply and connect a diode & relay (for alarm) in each output to do the same job, but it's not a proper method.
So I think we'll have to settle with the common model, S-320-24 http://www.meanwell.com/search/S-320/default.htm .

Below is my design, any comments from you guys?

http://www.plctalk.net/qanda/uploads/s320.jpg

BobB
September 20th, 2007, 10:19 PM
I can use 2 normal meanwell power supply and connect a diode & relay (for alarm) in each output to do the same job, but it's not a proper method.
Why? I do it all the time - it works and is very reliable. Probably a lot more inexspensive also. Have not seen the Meanwell units in Ozz at all.

Calistodwt
September 21st, 2007, 12:15 AM
You can either make up your own diode blocking units or else use the simpler option and purchase the redundancy module DR-RDN20 which is essentially a diode blocking unit. On your proposed system you will have redundancy for power supply failure only, which is ok if you are not concerned with the mains power failure for which you have no redundancy. If redundancy is required on mains power then install a small UPS on one ofthe supplies.

pw3
September 21st, 2007, 08:14 AM
Moore Industries makes a dual/redundant 24vdc power supply, I believe rated up to 3A. It uses two conventional xfmr/cap type circuits (versus switching) and has alarm contacts. They cost about $700e and are very stoutly made. If this is of interest to you I can locate the p/n as I don't believe they list this model on their website.

Also, Phoenix Contact makes a din-mounted diode block (as described in previous blogs) specifically for connecting two DC supplies in a parallel/redundant config.

flyers
September 21st, 2007, 12:07 PM
Moore Industries makes a dual/redundant 24vdc power supply, I believe rated up to 3A. It uses two conventional xfmr/cap type circuits (versus switching) and has alarm contacts. They cost about $700e and are very stoutly made. If this is of interest to you I can locate the p/n as I don't believe they list this model on their website.

Also, Phoenix Contact makes a din-mounted diode block (as described in previous blogs) specifically for connecting two DC supplies in a parallel/redundant config.

Hi,

Meanwell has a din mounted diode block as well, the DR-RDN20 is a 20A diode block by meanwell. Other option is using a 3rd party diode, i'm using SKKE 81/08 diode.

BTW, does anyone know how to check the efficiency or power factor of this diode?
http://www.semikron.com/internet/ds.jsp?file=800.html

Thanks a lot.

Alan Case
September 22nd, 2007, 01:49 AM
Hi Bob.
Meanwell power supplies are here. I see quite a few of them. Quite a good little unit.
Regards Alan Case

fayaz ps
September 22nd, 2007, 02:04 AM
i need a star delta starter logic diagram



Hi guys,

I'm designing a control panel system and one of the require from customer is to have parallel (2 units) power supply (24V DC) for the control panel & PLC as well.

There is one incoming 230V AC to the 2 units of power supply (230V AC to 24V DC). Each 24V DC power supply output will energize a relay & a pilot lamp (24V DC). in the event if any of the 24V DC power supply is faulted the relay wiil be de-energize and send an OFF signal to the PLC DI and the pilot lamp for that particular power supply will also be OFF.

My concern is do we need to put a diode after the power supply output, after the relay & pilot lamp so there is no current flow backward? Or izzit possible/advisible to do so?

I'm not sure what problem will I be facing, please advise me....thanks a lot.

thanhbinhvtvn
November 14th, 2011, 09:57 PM
Hi Flyer,
What type of diodes you choose for redundant parallel power supply and their technical data (rating current, voltage etc.)

iant
November 14th, 2011, 10:03 PM
Welcome to the Site.
This is a very old Post 2007
Diode current ratings and Voltages are dependent on your requirements.
I would recommend that you consider the total line current as should one fail the other supply needs to supply twice the load.
the only other consideration is the dissipation of heat.

John Gaunt
November 15th, 2011, 04:35 PM
Yes this is a very old post but following this post we now use Meanwell diode units rather than building our own diode unit.
We sometimes use others but mostly use the Meanwell power supplies also.

BobB
November 15th, 2011, 04:44 PM
I use a standard bridge rectifier for combining the battery supplies - usually 40 amp as they have metal cases. I then use Meanwell 24/24VDC power supplies to feed the PLC etcetera. I do not groung the negative output from the switch modes but let the 24VDC float - maintains isolation that way.