Power Supply Question

[taybrynn]

That looks way too dangerous for me.

I'll probably just hot glue over the unused connections or just put em in a baggie or something.

[CaptKirk]

Where is your spirit of adventure?


"I wonder what happens if I touch here...."  

[chrisatpsu]

With good regulation in the ATX power supplies it is unlikely the different rails would be far enough apart in voltage to matter much, right?

but what about PSU's that have totally different ratings for amperage on the different 12v rails...

[rm357]

Without knowing the internal circuitry, connecting two or more 12v rails together is a bad idea. A dfference of only 0.1 volts across a short circuit can result in a lot of amps and a release of nasty smelling magic smoke.

Voltage = current * resistance

Solve for current and you get current = voltage / resistance.

On a good supply, the short circuit protection should kick in and turn thepower supply off.
RM

[CaptKirk]

Ah- very different rated rails would probably be an issue.  Most PS I see have the 12V rails rated the same or close.  For example Looking at an Enhance that claims two 12V rails, one is 15A and one is 16A which I'd bet is "close enough" but would need to be seriously tested in a safe way to see if something "bad" happens if you tie them together.

My rational is that people put 12V batteries in series ALL THE TIME (RV power, solar systems, electric fork lifts, goldf carts) and I can guarantee they are not all the same current and those do NOT blow up.

Kirk

[RJ]

Since the hub does all the needed things to make the ps work why not leave alone so when if you have a problem the warrenty is in tack and you can get it replaced. Just tie wrap the cables up.

RJ

[rm357]

My rational is that people put 12V batteries in series ALL THE TIME (RV power, solar systems, electric fork lifts, goldf carts) and I can guarantee they are not all the same current and those do NOT blow up.
----------------

Actually hooking the 12v rails together is like hooking batteries in parallel - which you can usually get away with as long as one of them does not short out when it fails. Also, the internal resistance in a battery to current flowing backwards through it provides some additional protection. If you start mixing types and brands of batteries and/or old ones with new ones you are more likely to see the stronger batteries discharging themselves through the weaker ones...

RM
PS - hooking power supplies in series would be even worse. If both supplies are "grounded", you would be tying one of the power supply outputs directly to ground!!

[tbone321]

Batteries do not regulate their voltage so connecting them in parallel does not cause one of them to sink current and the other to boost output to maintain their set voltage.  However, if you hook a 6V and a 12V battery in parallel you may not like the result.

[TheBanker]

From what I understand that they are doing is putting all the different feeds together, these are not necessarly different rails.  To get rid of all the wires and maximize the amps by using a combination of all the wires which results in one larger wire to carry more amps.  I will be playing around with the 4 400watt power supplies I bought for 10 bucks each.  I wouldn't do it with more expensive ones.  They have two 12v out puts that I would need to be able to combine to make these little puppies worth it.  We shall see.

[RJ]

I will say this one more time and then the users can do as they like. It will be their problem to deal with if they do not listen.

Use a single rail 12v supply rated above your maximum power requirement. If you do different and have issues make sure you look in the mirror for your problems if you have them.

 The lab supply being looked at would normal be used on a bench for a amp or two of supply. That is a little different than loading it to near full load power hundreds or thousands of dollars worth of stuff.


RJ

[TheBanker]

I will say this one more time and then the users can do as they like. It will be their problem to deal with if they do not listen.

Use a single rail 12v supply rated above your maximum power requirement. If you do different and have issues make sure you look in the mirror for your problems if you have them.

 The lab supply being looked at would normal be used on a bench for a amp or two of supply. That is a little different than loading it to near full load power hundreds or thousands of dollars worth of stuff.


RJ

As a typical hard headed dude, I think what I am hearing is, "TheBanker your an idiot and I am telling you not to do this, it is not good".  I think I might be actually starting to get the message.  Most times I just need to know the "why", which seems to be stated above on the amp issue and the load.  " The lab supply being looked at would normal be used on a bench for a amp or two of supply. That is a little different than loading it to near full load power hundreds or thousands of dollars worth of stuff."

[Trepidati0n]

Nope...RJ isn't calling you an idiot.  What RJ is trying to do making sure that the most amount of people have the most amount of success with nominal amount of effort.  That is what he has done so well.   It isn't that he is being mean or stuborn...it is that from a support point of view he is one man.  Therefore by having a very simple but strict set of rules most things will tend to work right and when they don't, he knows where to begin looking.  If everyone did everything their way and he was expected to support it, his neighborhood liquor store would be emptied out.  

Think of it this way.  Imagine a family w/ 6 kids.  Do you think the parents do every whim their kids have and prepare custom food for them for every meal?  I think RJ should be very proud of what he has done and has done a pretty good job of handling this "family".  I am for sure...thankful.

Now those of us with significant experience in electronics may "deviate" from norm.  But that is because we understand the risks/requirements and will not burden RJ with our choices.

[Rainlover]

Now those of us with significant experience in electronics may "deviate" from norm.  But that is because we understand the risks/requirements and will not burden RJ with our choices.

And those of us without any experience in electronics have all the information we need to make blinky/flashy.

John

[CaptKirk]

Since the hub does all the needed things to make the ps work why not leave alone so when if you have a problem the warrenty is in tack and you can get it replaced. Just tie wrap the cables up.

RJ

Agreed, however I think the issue people are having is finding an affordable solution to do that.  A single 12v railed high amp ATX supply is difficult to find without causing wallet issues.  Multiple rail supplies are more common and more affordable and lower amp cheapo supplies are easiest to get yet.  It seems people are hoping to be able to use multiple rail or multiple cheapo supplies.  It sounds like that may be unadvised as it has not been tested and potentially could cause a bigger issue.  But what if it does work, safely and reliably?  That would give people a much more affordable solution!  If you COULD take two similar supplies with 16A on 12V and get a reliable 25-30 amps combined, that would be fantastic.  Will it work?  I don't know.  Is it advisable now- NO WAY, but we will not find out unless we try.  I for one will be using a 100amp single 12v rail (I think) per your recommendations.  I will be very curious to see if dual rail supplies work as a backup to that PS!

 

[Trepidati0n]

The problem is people are trying to "fix" something even before they have it.  While it is all fun and good to be excited about an idea, throwing it out without some serious effort behind it can cause significant mis-understanding, especially to those who are not well versed in those technologies get involved.  The typical results are disapointment and hurt feelings.

Two points of note:

1.  RJ has already cut the power supply cost in half by using a PC supply instead of an industrial 12V supply.  By this alone it should be evident he has worked this issue (and probably still working it).

2. If you plan on fully using a HUB..you will have nearly $1700 of hardware.  Trying to save $50 off the price of a supply shoudn't be your biggest worry at this point.