paralleling 2 35 amp linear power supplies

[357]

would 2 400V 95A diodes work from each positive lead to the load?
Like this?

 

[unit_399]

Yes. Remember the diodes will drop the output voltage by 0.7V. I would add a LARGE electrolytic cap across the output where it enters the load. A 1 Farad stereo cap will work good.

- 399

 

[nomadradio]

This one-piece dual diode has the cathodes wired together on the mounting flange. Feed each power supply's output to one of the two anode screws. Output is from the mount flange.

https://www.ebay.com/itm/ON-Semiconductor-400A-100V-Schottky-Barrier-Rectifier-Module-Diode-MBRP400100CT/201102209180?ssPageName=STRK:MEBIDX:IT&_trksid=p2060353.m1438.l2649

It will need a heat sink. If you bolt it directly to an aluminum heat sink, you'll need to insulate the heat sink where it's supported.

The rating is overkill, but the price is pretty good. And the smaller 100-Amp and 200-Amp parts are not that much cheaper on Fleabay.

73

 

[Tallman]

You will need to adjust each power supply separately and get them with in.03 volts of each other before attaching them to the diodes. The diode that nomad recommends is perfect for this application because they are Schottky diodes which will give a .2 voltage drop when conducting. That's why the diode mod on cb's works so well, .2 versus .6 voltage drop.

That is the method that Megawatt power supplies runs two 400 watt supplies. It works because I have two 36 amp units that have set up like that 5 years with no problems.

 

[nomadradio]

Switchmode supplies have a big advantage when it comes to putting them in parallel for more current. The output of a switchmode supply IS a diode feeding a filter capacitor. No need for an external diode to combine switchmode supplies in parallel. Just tie them together.

But a linear-regulated supply has bipolar power transistors feeding the output. The danger is that if one of the parallel supplies drops its output voltage, the output of the other supply or supplies will now be feeding back into that one.

This is, in effect, reverse polarity being applied to those transistors. Risky business. The combining diodes will prevent reverse current flow.

The other risk is that if the crowbar (overvoltage protect) feature gets triggered in one of the parallel linear supplies it will now be sucking the full current of more than one power supply. Tends to smoke that circuit. Combining diodes also prevent this risk.

73

 

[Tallman]

1) Switchmode supplies have a big advantage when it comes to putting them in parallel for more current. The output of a switchmode supply IS a diode feeding a filter capacitor. No need for an external diode to combine switchmode supplies in parallel. Just tie them together.

2) But a linear-regulated supply has bipolar power transistors feeding the output. The danger is that if one of the parallel supplies drops its output voltage, the output of the other supply or supplies will now be feeding back into that one.

3) This is, in effect, reverse polarity being applied to those transistors. Risky business. The combining diodes will prevent reverse current flow.

4) The other risk is that if the crowbar (overvoltage protect) feature gets triggered in one of the parallel linear supplies it will now be sucking the full current of more than one power supply. Tends to smoke that circuit. Combining diodes also prevent this risk.

1) Not all switchmodes can just be hooked up. The MegaWatt 50 amps can be but not the 30 or 36 amp. The regulation circuits will interfere with each out until one or the other burn up.

2) Won't feed back through a diode. That would be a reverse bias on the diode and the barrier region would widen and prevent conduction.

3)You said it:"The combining diodes will prevent reverse current flow." That's totally true.

4) If the crowbar circuit triggers there is something that has failed all ready. If one supply drops out for what ever reason the combining diodes will prevent one supply feeding back into the other, The voltage would sage and not trigger the crowbar circuit.
You said it:"Combining diodes also prevent this risk"

 

[357]

Thanks for the replies.
That dual diode is a bargain...thanks

 

[2RT307]

I ran twin Iota power supplies in parallel for several years with no issues. They are both switching (DLS-45), and 45 amps each.

73,
Brett