How to parallel two power supply

[jetblack750il]

Hi, how to sync 2 unit of switching type power supply with the output of 24V 8A for both.

Any ready plug n play module out in the market? Im not a electronic guy.

Thanks for helping,
Lionel

 

[RadioRon]

Some power supply manufacturers make supplies that use several switching converters at one time to service a single load. I'm referring to a type that is referred to as N+1 redundant. In this type of supply there might be multiple switcher modules, usually one more than is needed to provide the overall load current. This is done so that if one module were to fail, the others can carry on at full rated load.

Here is an example:
**broken link removed**
Note the description of model SEC-40BRM as one example.

 

[jetblack750il]

How to parallel two power supply?

Thanks Ron,

But I already have 2 unit of power supply , can I do anything to what I've now from 2unit of 24V 8A to 1unit of 24V 16A ?

Maybe with a custom make power control system or something else?


Thanks
Lionel

 

[tonigau]

Lionel,
Paralleling switchmode converters for higher current is not straight forward. as with any voltage regulated source, the highest voltage will supply all or most of the load current while the other just idles. It is possible though with carefull adjustment of output voltage & placing a low resistance power resistor in the +out lead of each supply to achieve improved current share capability.
But there are tradoffs such as response time (ability of converter(s) to react to changes in load current) , wasted energy in the resistors.
You won't get double the current but maybe 175% depending upon resistors used & how accurate the converters current share.
This is could work but depends what the load is.
Also the 2 converters may drift in output voltage(eg with temperature/age).
Selecting the resistors is a tradeoff between current share balance, power dissipation in the resistors & tolerable response time.


There are some IC's to implement current sharing between converter outputs, more complex than the resistor aproach & again there are tradoffs, but if the load is not critical then should not be a problem.

If you were to place 0.1 ohm resistors on each converter +output, & assuming 7A current from each converter then the resistor will drop 0.7V & waste 4.9W each. This is not a recommended value of resistance but give you a starting point. it could depend how accurate the converters can be adjusted (most switchmode converters have output trim adjustment.).
I would use 2 x 50W aluminium housed(eg: Arcol) resistors mounted on metal plate.

Measure the voltage across each resistor to guage the current sharing of the 2 converters.

Also keep the wiring balanced as well.

Note also if your switchmode converter has a spec of 8A & you wish to draw 8A from it. This spec might be at 25 degC. & at its rated voltage (eg: if you trim up to compensate for volt drop across resistors the total power output might be exceeded.
eg 8x24V =92W, 8x25.4V = 203.2W

Pulling full rated power from a power supply all the time will likely reduce its life considerably but this can depend on the specific unit & how well it has been designed.
In our industry power supplies are used up to 30% to 50% of rated capacity to maintain reliability mainly.
Resistors we use up to 40% of rated wattage. eg For 4W power we use a 10W minimum resistor.

Toni G .au

 

[carmusic]

yes you can do it using specific IC and mosfet take a look at this chip i have made it with several units

Linear Technology - LTC4357 - Positive High Voltage Ideal Diode Controller LTC4357 LTC4357IDCB#TRMPBF LTC4357CMS8#PBF LTC4357IMS8#PBF LTC4357IDCB#PBF LTC4357CDCB#TRMPBF LTC4357CMS8#TRPBF LTC4357CDCB#PBF LTC4357IMS8#TRPBF LTC4357CDCB#TRPBF LTC4357IDCB

 

[jetblack750il]

Thanks Toni,

I only need 24V 10A for my application , maybe I can save some money by not buying a new higher power unit.

Or spent a little on it and learn.

Will you please show me how to wire up in drawing? I know Im not good at it.

Thanks
Lionel

 

[jetblack750il]

Hi Carmusic,

Thanks for helping, can you assemble all item needed and ship it to me in Singapore? How much it cost?


Lionel

 

[Leftyretro]

We use to do something similar all the time for control panels in a oil refinery. Typically most of the instrumentation controls used 24vdc.

If the panel required say 8 amps of power we would install two 10 amp 24vdc power supplies. We would diode isolate each supply to a common 24vdc fused output strip for all the individual load circuits.

We did this for redundancy rather then to add the current capacity of the two supplies together. If one power supply failed then the other would still be able to handle 100% of the load. We would also wire 24vdc relay coils to each of the power supplies output (before their isolation diode) so as to generate an alarm contact in case either supply did go down.

We learned early on that one can't depend on redundancy in design if you can't detect a loss of redundancy.

 

[carmusic]

no sorry i cannot assemble them since i use those ic on pcb assembly that already have power supply on it

 

[tonigau]

Will you please show me how to wire up in drawing? I know Im not good at it.

Lionel, sorry for delayed reply.
See attached drawing...

Edit:
If you cant open the pic in explorer, right clik & "save as"

 

[john1]

Blank picture

 

[tonigau]

Blank picture

If you cant open the pic in explorer, right clik & "save as"

The link is not blank its, just the thumb image. it happens with .gif images for some reason.

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Lionel,


I should have mentioned:

This scheme still may not work satisfactorily if the trim adjustment is too coarse, but you will have to test this your self.
Also test the working at a lower current say 8A or less so that 1 converter is not going into current limit while setting up.
A condition that may exist when paralleling converters for extra current is where 1 converter is running in current limit & the other converter supplies remainder of load. This is not ideal.
Let us know how you get on, I need to implement a scheme similar to this for some new installations soon but at a much lower voltage.