dual power supplies

[bluebird]

I seem to be searching for power supplies a lot lately. I'm too busy/lazy to build them right now.

I needed a +/-20V supply. I found two Lambda regulated 20V supplies and plan on connecting them for +/-.

is there any danger in linking two individual supplies like this?

[theoverstayer]

dude

[bluebird]

J butta,

Each supply has negative, positive AND ground with negative and positive sense tabs. I have the - connected to the + of the other supply. That point will be the center tap (common) for the +20 and -20.

So your saying ALSO connect the two grounds?

it seems I shoud connect the ground tap to negative on one box and positive on the other at the center tap point.

both supplys are in little metal chassis boxes. I've mounted those in a bigger rack box.

Should the center tap or the gound be fastened to the main chassis?

[SSLtech]

Okay here's the scoop as I see it:

On both supplies, connect the + sense to the + out, and the - sense to the - out.

Connect the + of one supply to the - of the other supply. This is the center tap.

The Grounds are almost certainly chassis grounds. These can be checked by simply ohm-testing them to the case.

Assuming they are to the case, you have a choice. You can either connect them to the center "0V" point, or leave them floating. Remember, if you geound them at the center tap "0V" point and then feed other units which have any connection to ground, you're setting up a loop. -If you're powering a unit that has no connection to electrical ground, this is a way to do it.

A better way is to run seperate ground and 0V wires. Instead of 3 wires with +18V, 0V and -18V, run four, with +18, 0V, -18 and a seperate ground. Grounding at a single, central point will allow flexibility inb things like a console installation. If you're using one set of PSUs to power half a dozen different boxed DIY projects, staring the ground and the 0V at the PSU will work well as a single point... but take a tip and DO NOT ground 0V at the destination units, or you can have fun chasing loops down later!

How's that baby coming along Bluebird?

Keith

[SSLtech]

wait... I wasn't suggersting wiring them in parallel... From Bluebird's post i understood them to be wired in series... which was what I was describing. (though apparently unsuccessfully! :grin: )

In fact if you ever do want to parallel supplies (for redudndancy/broadcast or whatever reason) make sure you use diodes to stop the two PSU outputs picking a fight with each other!

Keith

[NewYorkDave]

Absolutely. The output of one supply looks like a short to the output of the other supply; never run them directly paralleled.

Using diodes is a common approach for "main/backup" systems where you want one or the other supply (but not both) to source all the current at any given time. Whichever supply is providing the higher output voltage will source all the current. The diodes form a simple OR gate.

[SSLtech]

A diode and a small resistor (0-point-something ohms) high-wattage can allow you to share current... along with some careful calibration. This is how it works in the SSL shared/switchover systems.

Keith

[bluebird]

Hey Keith,

The baby is is still growing. It will come in a month. I'm completely blown away with human life at this moment....and it happens all the time, I mean, Wil just had twins... :shock:

Ok the ground is chassis ground so I'll just leave those floating as I have another Power One +/-12 in the same box. so all the chassis will be grounded to the box and the 0V point of the two Lambdas AND the Power One will be strapped to the chassis at one point...

Console PS's suck....

I'm beginning to think this ADM is going to sound bad. its build wonerfully with the best possible parts, but the circuits seem to be designed badly.


thanks,
Ian