Multiple HP Power Supplies in Parallel

[algerdes]

"Don't ..." seems to be a word people use a lot, not only around their children, but also around here when it comes to use multiple power supplies.  There comes a time when "Don't" doesn't cut it!

I'm mounting 3 HP HSTNS-PL18 power supplies in one cabinet, then connecting all three together in a bus/parallel setup.  All 12vdc power (vdc +) will come from one bus bar and all 12vdc negatives (vdc -) to another.

I know that this has been done with the larger Meanwells, and in HP server racks where these very units are combined.  The Meanwells don't require it, but ... I am trying to figure out if the HP PS units require a common control line.  If so, which of the connections on the back of the PS gets connected to each?

If you have used multiple HP Server PS units, in a bus/parallel, did you have a third line connected between each PS?

Thanks in Advance!

ALG

[k6ccc]

My biggest question is why?  What is your use case where you need to parallel them?

As a general rule of thumb, DC power supplies don't operate well in parallel unless they are specifically designed to do so and are operated properly to do so.  These server supplies are designed for it, but I have no specific information on doing so.

My pixel tree has four 5V 70A supplies, but each of them feeds one half of a F16v3 or Expansion card or the power injection for the same strings.  The DC output from each of the four supplies is not paralleled.

[algerdes]

In the earliest days in this hobby when Pixels (of all types) came on board, many of us wanted to be able to treat the power like this.  Unfortunately the small (300 + watt) units were not capable of redundancy.  So, we suffer with the individual units.

We have done this with large Meanwell power supplies with wonderful results.  (I believe Dan does it with parts of his large display.)  It is the cost of the big boys that is prohibitive.  These server supplies are just the ticket for price, and being redundant capable.

By using enough supplies in parallel, with a spare part of the setup (I would call it "hot", but designation usually means it is ready to be put in, not already in and sharing some of the load), when one supply takes a vacation, the others keep the show going.

By making a "large battery", we don't worry about having two non-redundant supplies fighting with each other - even if by accident.  All the controllers, remotes, etc., draw from a single source.

With the ever increasing pixel counts in props, moving up to a redundant supply system only makes sense.

My question is about these smaller 750 watt units.  The backplane of the servers they are usually connected to has a bus for the V+, a bus for the V-, a control wire (turn on, turn off - usually the whole server), and a "power light" for each of the PS units.  We open the case, look at the lights and can tell if a power supply is operational or not.  If we have a PS down, we simply pull it, replace it, go about our business. The unknown here is that some redundant PSs use a signal line to advise the other PS units as to the current level of the bus.  Not sure if these 750s use  it, or if I can just connect them.  (I'm still trying to find better specs on the 750s.)


If no one has done it and can pass along their findings, then when I get my next shipment of PS units (10 more on the way), I'll just try it and see if I need to turn the smoke removal fans on, or not.

[walterfsnow]

A common topology employed to increase output power is to connect the outputs of two or more supplies in parallel. But why do you want to do that?

[JonD]

Not sure the redundancy is going to be near as valuable as you are hoping.  If a power supply goes out on a HPE server, the lights on the front of the server will turn red indicating a problem, it will email you a message informing you of the outage, and if you open the remote management page there will be errors all over the page.  Not sure how you are planning to recreate this with your light show?

Let's say a power supply does in fact die and it protects you from the outage.  How will you know there has been a failure?  Are you going to take a multi-meter out to your controllers every night to test for failures?  Chances are you won't know about the failure until the second one goes out and the show is down. 

[rayster]

So you are making a mega power supply! What is the longest run of power cable and what size wire are you using? Remember the smaller the wire the more voltage drop you will get. Also the smaller the wire the less amperage it can handle, 18 ga under 10 amps and 10 ga is only 30 amps.

Also the more power supplies you add to get more current the more chance of blowing the whole thing up if you get a short circuit any where.

How are you powering it on the A\C side of the power supply? So a 750 Watt supply needs about 7 amps on the A\C side so on a 20 amp outlet you can get 2 power supplies run at full output and maybe 3 not running full output. Also you can not turn it all on at once due to inrush current.

Just some food for thought. That is why most people run many power supplies closer to the props to keep the low voltage cable runs short.

[jnealand]

What you may be missing is that Al does a big display in a city park.  This is not a residential display.

[algerdes]

Wow.  Didn't expect to find this thread re-visited.

The tests (and desires) were indeed intending to come up with "power boxes" that would contain multiple power supplies, with the idea of keeping the costs down per unit as compared to the large supplies offered by vendors such as Meanwell. 

Our best chance was the HP Server power supplies commonly used in multiples within the computer server case.   We tried up to three supplies in parallel to bring it up to 750 watt x 3 = 2,250 watts.  This one "mega-supply" would be enough to drive a whole area.  By keeping the draw down to the equivalent of two supplies, the third would be involved evenly up to a failure of one of the three of them, and then the other two would keep the show up until the third could be replaced.  

Two things happened. 
1) We found that we could afford the larger units, that were built specifically for the job. 
2) Our display changed!  I'm only doing animated lights in a section of the park, and that display is much smaller than before.

This year my display is using just 9 controllers (down from 20+), is centered in a single area (well within distance of a common power point.)  [The rest of the park is "static" using AC props.]  The need for redundant power is almost negated by the change.  Currently, my display is about the same size as a large home display.  (Maybe a bit larger, but not by much.)

Parallel power supplies are still in my mind.  They have just been put on the back burner.  If I get all the new props built this summer, perhaps I'll return to them - if I can find more.  

[JonD]

From my experience, most technical people do not have the self-discipline to monitor this type of redundancy.  If you don't have alarms bells screaming failure/fix me... you need a person that loves to create a list of all their other lists watching over this.  If you don't catch the first failure and the second power supply fails, you could in fact have the remaining power supplies running a lot of lights in a significant brown out situation.  I fear this will not end well for you.

If you had two power supplies... each able to run all the lights and one fails, the other would have enough power to keep everything running.  If the second died, the lights would just go off.  There are systems with more than two power supplies, but when that is the case there is always safety in place that will shut everything down if not enough power.  I did not see you mention that feature above.  What you suggested above seems like a very bad idea to me, regardless of the size of your show.

You know your situation better than I.  Just want to make sure you have considered this scenario and have accounted for it.

[algerdes]

Duplicating the monitoring hardware/firmware that exists in the HP server would definitely be something to think of. Two things from that environment would be nice to have: 1) The alarm circuitry to let us know when one was not acting correctly; 2) The automatic shutdown of a malfunctioning power supply. 



The BIG CAVEAT is the need to use power supplies that are made to be connected in parallel.  In earlier tests, and doing it to see just what would happen, we watched a couple of generic PS units fight to stay "in sync" with each other.  It ended up in one of them meeting a premature death, and the second (in our mind) becoming unstable enough to warrant NOT using it in the display.  (It is sitting on the top shelf of my workshop.)

Our tests showed great promise in using multiples.  It was our needs that changed.

FYI - There is at least one member of our community that has a HUGE power bank running his show.  (Got the idea from him.)  Multiple 1200+ units, all connected together and then fed through a substantial power line network.  At the time it was our desire to use smaller, less expensive and more available PS units that prompted our research.
 

[JonD]

The alarm would be nice, but even if it caught a failure right away, it would not be impossible to have two power supplies go out at the same time later.  You could probably find a third party device that would shut everything off when the power gets too low.  If so, that would add to the costs you are trying to avoid.  Without a low voltage safety in place, I would either just replace the power supplies as they go bad, or only use them in tandem at half power.  Otherwise, your risking a large amount of lights to a brown out.