Two voltage source in Parallel

If even all will be well you won't get a double amperage. It's a very dangerous and counterproductive idea.

You might be able to get 2 DC supplies to work safely in parallel, but with extreme caution. If the outputs of the two supplies aren't exactly the same voltage, it's possible that power supply #1 would not only feed current into the load but also feed current backwards into power supply #2. PS 1 would go into overcurrent and possibly fry, and the fate of PS 2 would depend on what it actually was! Also, if the ripples of the two supplies were out of phase, the two supplies could both feed excessive current and see backwards current, at different times in the AC input cycle!

Adding an extra regulating stage (with an ouptut voltage vs output current characteristic that you know well) to the output of each individual supply might be a good way to go. Or it may just be more trouble than it's worth and you're better off buying a bigger supply.

the easy way to do this is to place a low value resistor of .05 ohms in series with each power supply. This will cost a little but will also add some self balancing to it.

Adjust the set point as close together as possible and use a common voltage refence point. 2-3 feet of wire in the reference line to each unit will held.

A better way would be to split up the load, and drive each half with a different supply. If you must combine them, then make sure each one is set to the same voltage, and that both have low ripple under load. As a precaution, I would connect a forward biased rectifier to each output. Make sure the rectifiers are rated at 10 amps. You may need them on a heat sink. Good luck.

Yours was the first good answer I read going from the top.

A GA too....

A further point of interest:-

One should always make sure that not only the two voltages unloaded/loaded are as near as possible the same but that the other "characteristics" of both supplies are the same!!! This best served by using two identical (in this case PC Power) supplies...... this ensures that they "track" best together from no load to full load.

One can use slightly dissimilar supplies, but the series resistor will need to be much larger (in an attempt to make both charateristics similar) and then the output will tend to drop more as the load increases.....

I don't like the idea of connecting them in parallel, it most likely will not work properly, but if you have to try the series diodes and resistors, that seems like a good way to go. If the supplies are the same make, hopefully they will have similar voltage set points and things won't go awry.

Connecting them in series would probably be fine!

It's probably more trouble than it's worth, but you could series the supplies to get 24V then use a switchmode regulator to convert it back to the original 12V voltage at double the amps (although with maybe 10% losses).

Connecting 2 power supplies in parrallel will ALWAYS get you in trouble (sooner or later), unless you add a "serious" electronic circuit to keep both voltages exactly the same.

You talk about 12V, 10A... two times ... that's a total power of 240 Watts ... 240 Watts can do some SERIOUS damage...

Best idea (already stated a few times in this thread) : split up the load, or get ONE power supply that can handle your load.

You must have informations by the power supply factory. there is some power supply, it is possible to make them in parallel and the others is prohibited. see the data sheet of this power supply, it's the only solution you have.

Hi Fireball,

We parallel dc supplies all the time. What you need to know, but probably wont be able to find out, is what happens in the event that either of the supplies sees a load greater than the specified load. Most, but not all SMPSs are short circuit proof. If they are that type and they go into a current limit mode rather than a crowbar shutdown mode then sharing will work fine even if they have widely differing characteristics. However if they are run like this on a permanent basis you may find the lifespan of the unit that is flat out will be shortened. This will depend on the safety margin level built in by the manufacturer.

The advice to add diodes to the outputs is wise, unless you have the schematics and can see that the outputs cannot be backfed.

One word of caution, House sheep mentions the phasing of the ripple as a source of problems. We haven't found that to be troublesome but we have found supplies whose regulation goes off track when a "pulsey" load is connected. If you do this then go slow and check what happens as the load comes on. We put a pwm fixed voltage regulator onto a dc system to cut down the 28.5V seen on a 24V battery when on charge to reduce the number of halogens burning out. The result was the charger went mad and put out about 33V, cooking the batteries!

Lastly, I would strongly advise against trying any tricks with putting the supplies in series as, in the case of a short circuit, you end up with the units in reverse parallel with the result that one unit will smoke, terminally! (Been there, done that, still got the smoke stains on the ceiling!)

Best of luck

Chas

Do a search on "Redundant Power Supplies" to see solutions which intentionally connect DC power supplies together as a backup system. Because they are separated by heavy duty diodes, one power supply will contribute current until its output voltage drops below the other, due to the load.

The real purpose is to keep the circuit alive if one power supply fails. Still, it is advisable to have a current limiting circuit breaker on each supply. Placing more load on a power supply than it is intended to carry is a sure recipe for disaster if there are no provisions for automatic disconnect. Also, you should use DC circuit breakers.

It will be a disaster to connect both in parallel, without checking the actual waveform.

if the amplitude and timing matches, with grt precaution you can try for that, BUT with sufficient fusing.

Hi Francis,

Your concerns about phaseing are unfounded.

It is DC and everyone has already agreed that the situation would be safer with diodes to be sure nothing can backfeed. What kind of problem do you think will occur?

regards

Chas

Regards!

It is a common practice to use two or more Power-Sources like [Batteries; Power-Supplies; Generators; Transformers etc even prime-movers in transport] in parallel & Series & there is NO-DANGER if all the requirements are met. Some are:

1. Power-Sharing [according to individual power-rating VA/W ratings]

2. Reverse power-Feed

In case one source fails. Faulty unit shut-down & Isolated;

By-passed in series combination & Opened in parallel setup.

3. Frequency Synchronisation

4. Voltage level

etc etc

In parallel Voltage-Level is of utmost Important in both AC & DC sources while

"Frequency Synchronisation" is as much necessary.

In Series it is the current-rating which is necessary

or

the load not more than the lowest-current-rated supply's can be drawn from series set-up

I have seen 2/3 Railway Engines in Pakistan on "Quetta"; a hilly station; line & even in

plains to move longer trains.

I had been using Dual-Power Supplies by RS-UK & Farnells which can be connected in series to add voltage range & in parallel to add current capacity.

Almost all the major Manufacturers /Vendors supply such units & all electronics & related setups use such units.

Kind regards

Provided both supplies have isolating diodes to protect them against being backfed, there should be no problems. The outputs will have to be boosted/adjusted slightly to take out any diode losses.

I recently built an Elektor SMPS design from 2003, which is basically two power supplies (on the same PCB) running in parallel!!! It works perfectly!!

Regards!

Correct.

Please see my post #15 para 2.

Happy to know your successful design of Dual-SMPS.

Will you make a little modification for connecting in Series.

Although all the design parameters seem to be similar, yet if you

take some pain to measure difference in load sharing, you will have a deeper

in-sight of compos tolerances' effects.

Regards.

if we connect two 12v soureces, net (total) voltage willbe 12v because voltage is same in parallel