Can I wire 2 smps in parallel for double the ma at the same v out?

[zambo]

Can it be done without death fire smoke and the wailing of children , universe bending in on itself etc? How would one achieve this great feat?

[jasperoosthoek]

Difficult question, depends on how well they are matched. In a perfect world absolutely, in practice maybe. The problem arises when one has a higher voltage than the other. They are designed to source current, not to sink (sink meaning drawing current in the other direction of normal operation).

If you run two resistors from both units to the load then you will probably be fine. Say 0.1 ohm for 1A from each supplyand 0.05 ohm for 2A max etc. That will limit the drop across the resistors to 0.1 volts. You can measure the voltage across the resistors. It should stay equal for big loads and zero for no load.

[zambo]

Sweet! ok my hypothetical is this. 2 1363 smps from taylor electronics. same everything. run each output through a resistor or a diode ( 1n4007) so they cant hurt each other and into a big reservoir cap like a 47uf 400v. from there its typical tube amp ps cap / re / cap etc. this could really work?

[jasperoosthoek]

Oh, I thought you meant the ones found on laptops or chargers for mobile phones...

Don't connect them with diodes to the same cap as you suggested, that way you will never know whether they share the current equally. One might fail and then the other will follow soon.

Instead of connecting the SMPS to the first reservoir cap with diodes, connect them to the cap with a resistor to even out the current between the units. Diodes are not necessary. The cap will avoid any crosstalk between the units. As long as their output voltage is not too different it will work perfectly.

You could also give both supplies their own reservoir cap and connect them to the first shared reservoir cap with a resistor. That will be even better but you will need an extra cap. You can do this with as many units as you like as long as their outputs are similar.

[zambo]

Thanks Jasper! Oh the mayhem I can cause now!

[iccaros]

can someone draw this out, I am having issues picturing what the layout would be..

[zambo]

                ------smps------cap---resistor-
walwart<                                               >----cap---resitor----b+ supply
                -----smps------cap----resistor-


youcould add more resistors and caps etc after the last one for lower voltages etc if you want. reistors can be small value but probably 2 watts at least. to be safe. I guess we could do the ohms law math and figure out how many watts they need to be. I will probably only use a 1 ohm resistor or maybe less.

[phector2004]

Just a thought, can't you use one SMPS to power each half of your circuit? The voltage will be more or less the same, and it keeps things from getting complicated

E.g.
Tubes 1 & 2 --> SMPS 1
Tubes 3 & 4 --> SMPS 2
Heaters --> 12V DC

[zambo]

you can unless your circuit is 2 el84's at 200 volts with a 130ohm cathode resistor

[frequencycentral]

I'm still worried about heterodyning.

[zambo]

wont the caps and resistors kind of make a seperating buffer that stops that? I am goin to try it and post results for sure.

[iccaros]

Just a thought, can't you use one SMPS to power each half of your circuit? The voltage will be more or less the same, and it keeps things from getting complicated

E.g.
Tubes 1 & 2 --> SMPS 1
Tubes 3 & 4 --> SMPS 2
Heaters --> 12V DC

That was my thought..

[iccaros]

                ------smps------cap---resistor-
walwart<                                               >----cap---resitor----b+ supply
                -----smps------cap----resistor-


youcould add more resistors and caps etc after the last one for lower voltages etc if you want. reistors can be small value but probably 2 watts at least. to be safe. I guess we could do the ohms law math and figure out how many watts they need to be. I will probably only use a 1 ohm resistor or maybe less.

so this

[zambo]

that will work but you will keep more voltage if you leave out the resistors right after the smps and before the first caps. Its pretty small voltage drop if you use like a .1 ohm resistor. I havent tried it yet but i have two of them to do it with and when i get some decent 2 watt resistors i will do it. fingers crossed..lol

[iccaros]

I fly to Georgia Tomorrow, after I get back I want to try this.. I'll fix the drawing

[SISKO]

I'm still worried about heterodyning.

+1!

[Cliff Schecht]

Typically you don't want to parallel two switching power supplies unless you can sync the oscillators, otherwise you run into the heterodyning problems like Freq said. Even filtering won't eliminate this problem as switching power supplies pulse the crap out of your supply current-wise. This is where you typically run into crosstalk issues between two SMPSs running of of the same power supply. Even an obscene amount of bypassing won't completely eliminate this problem (high gain would be a big problem with this setup). The only solution without resorting to more elaborate (read: more expensive) measures would be to sync all oscillators if possible.

[zambo]

darnit we need a better smps. thats all there is to it. we need at least 250 to 300 volts and 100ma or better. I just dont know how to design such a beast but it doesnt seem like they are that far off of what exists already. How hard would it be Cliff? I know you have worked a lot on this particular thing.

[iccaros]

darnit we need a better smps. thats all there is to it. we need at least 250 to 300 volts and 100ma or better. I just dont know how to design such a beast but it doesnt seem like they are that far off of what exists already. How hard would it be Cliff? I know you have worked a lot on this particular thing.

See if this will post
http://www.desmith.net/NMdS/Electronics/NixiePSU.html

from the bottom of the page...
What can be seen from these results is that with a small change in component values allowing the use of a bigger inductor and a less lossy FET, we can make the SMPS produce 120+mA with no real problems.

[zambo]

It heterodynes as predicted.....boooooooooo    its a low frequency. not super loud or anything. may be able to squelch it but.......I am thinking better smps is needed. Thanks for all the help though.