ALARMED

Anybody know if you put 2 (24VDC) power supplies in parallel to boost an existing application, and each having different amperage ratings, can damage be done to one or the other? Or do they have to be identical?

Thx.

donniedj

Include a suitable diode to the output of each power supply. By suitable, I mean the correct voltage and current ratings. Then connect the diodes to form 1 cathode output.

Sebi

It possible, but the output amperage only the lower amp*2! (think about Kirchoff law)

Nigel Goodwin

Sorry, I don't understand the reasoning behind that?.

I thought Kirchoff's law was something like - "the current leaving a junction is equal to the sum of the currents entering the junction".

__________________
PIC programmer software, and PIC Tutorials at:
http://www.winpicprog.co.uk

bmcculla

Parralleling power supplies isn't a very good solution. The problem is even with the diodes the load isn't nessesarily shared equaly between the two. Say due to manufacuring tolerances one supply provides 24.1V and the other supplies 24.0V. When the load is put on the 24.1V supply sources the current and beacause it's feedback controlled the voltage doesn't drop at all. So the 24.0V supply doesn't see any load at all(because the node it is connected to through the diode is .1V higher than its output.). This means that the first supply is sourcing all the current.

Its hard to get two supplies working together without acsess to their feedback control (hard to do on a comercial supply).

Brent

Oznog

It may or may not work. Generally a diode is not necessary since a rectifier or regulator already allows current to only go one way.

Now if it's two indentical transformers, you're fine if each has its own full wave bridge. If they're regulated or poorly matched, you've got the trouble Brent describes. One will bear all the load until it's loaded far enough to drop its voltage below the other supply's voltage. That may be enough to overload that supply.

ante

The way to go is using resistors (low value high power) to equalise the current.

Ante :roll:

samcheetah

yes that is kirchoff's current law

it is not a good idea to use two power supplies in parallel operation. because no two power supplies are 100% identical. and when there is no load attatched to the paralleled power supplies the results can be catastrophic. think about it. disconnect the load and then calculate the current that develops in the small internal resistances of the power supplies. a high current will flow from the slightly powerfull supply to the slightly less powerfull supply.

ante

Switch mode PSUs and converters can often be paralleled directly with no problem. This demands that they are both (all) the same. Some modules have a sync connection that controls the “teamwork” between the units. If this is not the case or the units are not equal the resistor solution will work almost every time.

Ante :roll:

Attached Images

psu_par.gif (33.4 KB, 354 views)

ante

Switch mode PSUs and converters can often be paralleled directly with no problem. This demands that they are both (all) the same. Some modules have a sync connection that controls the “teamwork” between the units. If this is not the case or the units are not equal the resistor solution will work almost every time.

Ante :roll:

Attached Images

psu_par_543.gif (33.4 KB, 353 views)