Setting up multiple power supplies in parallel

[danj]

I need to setup 3 PSUs for my 12V pixel megatree and 2 PSUs for my 5V pixel megatree/arches.   Right now, for two of my PSUs that I have specifically tied together at a terminal strip, one PSU is set at 12.19VDC and the other is set at 12.21VDC   I could probably spend a few minutes and tighten these up a bit.   My gut is that once the first PSU hits its capability, the voltage at the terminals will drop and the second PSU will start flowing current into the pixels, so I didn't figure 20mVDC would really make any difference..  I figured I would ask since this is the first time I have needed multiple power supplies.   THANKS

[JonB256]

In the distant past, I have seen "dueling" power supplies where the voltage regulators will start to oscillate the load at a low frequency. It is actually worse when the voltages are set very close to each other. If you have 0.2vdc difference or more, then the higher one will stay in the lead.

Best way to check is to use a voltmeter and monitor the output for stability under load.

Paralleling power supplies like that is generally not done, particularly with inexpensive ones.

[danj]

Thanks Jon.   I am going to try to get to a point where I am running my whole display in my garage next weekend so I can see how everything works together...  I definitely plan to put a meter on the PSUs and see what they are doing.

I am struggling, though, to see how you "wouldn't" share PSUs' outputs in almost any power injection scheme, unless you only supply data via your controller and power up specific elements via only (non-shared/non-parallel) PSUs....    My intended setup (maybe conceptually not so great...) is to power up strips via my controllers' outputs and to power inject where I need to setup strips in series.  Since I am driving 5m strips, I simply planned to power inject everything to make really sure I had good power everywhere..   I appreciate the info.

[gerry]

Hello Dan,

I have two 12V PSUs for my mega tree (each at about 50 % of capacity). These are from Ray Wu. I am running a Pixlite 16 and use each to power one bank . The negatives of each PSU are connected together. (as per a number of posts on ACL).

If power injection is required (for any element in the tree), I will power inject from the same PSU's .(I power inject for other elements , but where I have a single PSU ).

I have been running these off and on for a few months now (with all the strands hanging off my wall inside my house for sequencing and have not seen any problems). There needs to be a common ground ref point , hence the negatives from each are connected together.

[JonB256]

Danj, the difference is that, when power injecting, there is some "load" between injection points. It isn't much of a difference but it will stabilize any tendency for feedback between different supplies.

[Phrog30]

I have a few enclosures with 2 power supplies.  I have both connected at -12.  One power supply feeds the controller.  The other is used for power injection.  I was also told that I would see "dueling", but when I pushed back I was told that it would work.  Well, I have been using this method for a while and so far haven't had any power supply issues or pixel problems. 

Here is info on power injection. http://www.doityourselfchristmas.com/wiki/index.php?title=Power_Injection

At the bottom is a photo showing an acceptable method for two power supplies.  I attached the picture also (this is basically how my setup is, except I only connect my power injection at the ends).  If you look, one power supply feeds the controller which powers the first string.  The second power supply is feeding the 2nd string.  However, in reality, the 1st power supply is feeding the 2nd string as well and the 2nd power supply is feeding the 1st string.  So this would be "dueling".  But, it just isn't.

One thing to note, I have better luck using voltage around 11.8-11.9.  I noticed if I have 12.0, the chips seemed sensitive enough to where they would "glow" red on occasions (not always).  This would happen with only one power supply (before someone says that's a symptom of dueling).  Once I lowered the voltage this glow didn't happen anymore.

James

[danj]

Thanks very very much for your informed feedback!!!  I really appreciate the info. Ok I think I see now--the key is "not" to tie the PSUs together right at the PSUs' outputs...  I will remove the jumpers at the PSUs' outputs.   I didn't realize it was better to be at the lower end of 12VDC; I was purposely setting both a bit above 12VDC.  So I will reset slightly lower than 12VDC as mentioned.

[Phrog30]

The voltage setting is just what I observed. You may get away with 12, or even slightly higher. I mentioned because if you do see a "glow" I would try lowering the voltage first.

Also, it wouldn't be bad to jump the negative side of each power supply right at the terminals. It was depicted in the photos, and I guess I didn't mention it, but mine are connected this way.

[danj]

Thanks James.   I am planning to connect all my -V's to earth ground via my PSUs' earth ground connections, as recommended by SanDevices. I'll take your input regarding voltage level into consideration!

[JonB256]

The "sad" thing about Dueling Power Supplies (I hear banjos )  is that cheaper power supplies will probably never have the problem because their voltage regulators are slower to react. If you spent big bucks for a really nice power supply or use a Server style supply, they are more likely to oscillate with another similar supply.

So, if you are using the <$10 Chinese supplies, I seriously doubt that you will see it.
The >$50 Meanwells might.

[danj]

That is a really interesting point, Jon.   Based on your input and input from others, I will NOT tie the PSUs' outputs together; there is no reason to do that (I just thought it might be a good idea to share across a bus...) and I can configure the PSUs so they each have reasonable loads on them.
I really appreciate your inputs & thoughts on this one.