Doubling LED transformers

[hard-work]

If LED strips need say 40 watt, would doubling up two 25 watt transformers do it? That is 230v in on both and the 12v outlets commoned up.

 

[DetlefSchmitz]

No that would be a daft thing to try.

 

[ban-all-sheds]

If you are referring to electronic transformers, or LED power supplies, that might not work. Check with the maker, or get the right device.

 

[winston1]

If LED strips need say 40 watt, would doubling up two 25 watt transformers do it? That is 230v in on both and the 12v outlets commoned up.

For a start you can't use a transformer on LED strips. LED strips require DC, transformers output AC and will blowup your LED strips.

You need DC power supplies. Doubling up two will likely create circulating currents due to a slight voltage difference on their outputs.

 

[333rocky333]

You need DC power supplies. Doubling up two will likely create circulating currents due to a slight voltage difference on their outputs.

Do you get circulating currents by doubling up DC power suppliers

 

[bernardgreen]

Do you get circulating currents by doubling up DC power supplier

In most cases one of them, the one with the highest output voltage, will provide the majority of the current. A few millivolts difference between output voltages is all that is needed for the current sharing to fail. That said there are DC power supplies designed to operate in parallel mode. Low ohm reistors in series with the outputs will omprove current sharing but at the expense of having to use remote sensing. Taking the control feedback voltage from the load and not at teh piwer supply outputs.

Connecting the outputs of two Switch Mode Power Supply ( SMPS ) modules in parallel is very risky, They are very likely to go unstable and fail to control their output voltages correctly.

 

[333rocky333]

In most cases one of them, the one with the highest output voltage, will provide the majority of the current. A few millivolts difference between output voltages is all that is needed for the current sharing to fail. That said there are DC power supplies designed to operate in parallel mode. Low ohm reistors in series with the outputs will omprove current sharing but at the expense of having to use remote sensing. Taking the control feedback voltage from the load and not at teh piwer supply outputs.

Connecting the outputs of two Switch Mode Power Supply ( SMPS ) modules in parallel is very risky, They are very likely to go unstable and fail to control their output voltages correctly.

Would you call that Circulating Current though

 

[John D v2.0]

If LED strips need say 40 watt, would doubling up two 25 watt transformers do it? That is 230v in on both and the 12v outlets commoned up.

I think I can summarise this thread by saying "no"

 

[ban-all-sheds]

.

 

[ericmark]

I had to do the calculations for two power supplies at university however it all assumes it is a smooth DC supply. As pointed out it is unlikely the DC power supplies bought to power LED light will be smooth enough and I know even with a 12 volt battery charger connecting two outputs together can cause the components to fail, I did it in error and now have a rubbish battery charger as a result.

However to say can't ever be done would be wrong, there seems to be exceptions to every rule, but it would need some method to share load, most likely would be to feed one at one end and other at the other end of the LED strip, in which case may as well run as two independent runs.

So simply not worth the effort, just consider it can't be done.

 

[SFK]

Hard-work
If it is a 40W LED strip that you wish to drive with two 25W drivers, then cut the LED strip in half so you have two lengths needing 20W each..
Then connect one 25W driver to each of the 20W lengths using a length of wire.
SFK

 

[bernardgreen]

However to say can't ever be done would be wrong,

The way to do it with SMPS modules is to interlink the modules such that they take it in turns to switch a "dose" of power to the output.

 

[SimonH2]

Would you call that Circulating Current though

I wouldn't. "Circulating current" implies that there's current flowing out of one supply and into the other which won't be the case.

 

[winston1]

I wouldn't. "Circulating current" implies that there's current flowing out of one supply and into the other which won't be the case.

If the voltages are slightly different it could be the case. But if they have diodes on their output it won't happen.

 

[JohnW2]

If the voltages are slightly different it could be the case. But if they have diodes on their output it won't happen.

Even if they don't literally have 'diodes on their output, there has to be some rectification (with or without subsequent semiconductors) - so I would think it doubtful that there would be a significant 'backwards' path from the output. However, as bernard has said, 'applying a voltage' to the output might possibly play havoc with the regulation (if it is sensing voltage at that output).

Kind Regards, John