Power supplies in Parallel??

[stumper1]

My dumb question of the day...

A friend asked me if it would be OK to run 2 Boss PSA-120 power supplies in parallel.  He just happens to have a spare female power supply jack on the end of his daisy chain cable that is not being used - he also has a spare PSA-120.  He has several pedals chained together but rarely uses more than 2-3 at a time.  Thinking that in the rare occasion he may want to run ALL his pedals at once he would overload the power supply he called me with this question.  I told him to buy a One-Spot.  He said" yeah but, I allready have 2 good power supplies".

With all I understand about this (which ain't a lot!!) I think it should work just fine.  Still, my common sense tells me it's just not a good idea...

Anyone?

Thanks,
Deric

[brett]

Hi.  It's sometimes not a good idea to use power supplies in parallel.  Sometimes one will take more of the load than the other.  But in this case, you are gonna power some pedals from PS1 and some others from PS2.  That's completely OK as far as I know.
cheers

[Paul Perry (Frostwave)]

Brett's right, what you are doing is not running the supplies in parallel, you are just usig them simultaneously to run different gear.
Connecting the output of two or more supplies together (like, two 1A supplies to make a 2A suppy) is ALWAYS a **VERY BAD** thing to do.

[stumper1]

Well...........I was talking about hooking them together.  He has a Boss TU-2 tuner pedal.  One PSA goes into this.  He uses a One-Spot daisy chain cable out of the tuner to other pedals.  The One-Spot cable has an unused female connector at the other end.  He wanted to plug the other PSA into that - so, he would essentially have a PSA-120 plugged into each end of the daisy chain cable.  My first thought is "that can't be good!".  Then he asked "why?"

So I guess my question is..."why?".

Thanks,
Deric

[SaBer]

The two power supplies can't have the exact same voltage. This (minor) difference in voltage will cause one supply to try to make current flow through the other. I have no idea how the situation will resolve in practise, but this is what I think will happen in theory...

[Fp-www.Tonepad.com]

If he wants to split the load to each of the power supplies he may as well cut the daisy chain!

If it ain't broken don't fix it.

Fp

[(doug harrison)]

I tried something like this once with a 9V battery and a rated 9V DC wall wart. I wired an LED in series with the battery, my theory being that if the battery dropped any voltage, it would light up the LED, right? Ok, with only the battery connected to the pedal, the pedal worked and the LED lit up. With the wall wart added in parallel to the battery, the pedal worked, but the LED stayed dim. I measured 0 V across the LED.   I left it connected for about ten minutes, but nothing blew up, got hot, smoked, or smelled bad.

Maybe it's worth another experiment, just to see how far it'll go before something blows (or not).

Next time I'll reverse the LED.

Maybe this would be good if you are using rechargebale batteries in your pedals.

[niftydog]

chances are he won't overload the supply, unless he's got some really hungry pedals there.

Best is to buy a second daisy chain and use both supplies independently.

It is possible to run supplies in parallel, but to do it correctly is not a trivial exercise.

[Hal]

wait, what is the differance between this and running the two secondaries in a transformer in parallel?

[Paul Perry (Frostwave)]

wait, what is the differance between this and running the two secondaries in a transformer in parallel?

The difference is, if the two secondaries are wound identically on the same core, then they are pretty near perfectly matched. Plus the internal resistance of the two windings helps a bit to even the current draw. Trying this trick with absolutely identical transformers might be ok... but, in general, parallel connect5ion of unmatched power supplies (and especially regulated power supplies!! can lead to tears.