Transformer Amps in / Amps out for LED lighting, lamps running very hot

Thread Starter

ABC21

Joined Jan 2, 2019
7
Hello

Forgive my lack of knowledge, if someone could help me with a very basic problem.

I have 12 LED lamps that require 25v DC, the transformers that they are supplied with (all 12 of them) have an output of 25v @ 0.7A.

I have purchased a transformer that is rated as below:-
Power: 350 W
Frequency: 50-60 Hz
Intensity Level: 16.4 A
Output: 24v DC (this has a regulator for + or - 1v so I have adjusted it to 25v)

The description on the website is as below:-
This 24V Power Supply is ideal for connecting indoor lighting system that cannot be used by being connected directly to the mains.
It transforms mains alternate current to 24V direct current.
It has a 350W nominal power, however it's recommended that it only be used for permanent loads of up to 280W. Its output current is 14.6A.
It has a regulator that allows us to adjust the voltage output from 20V (minimum) to 25V (maximum).

The problem I have is the Lamps are running much hotter than if I use the original transformer.
Do I need to step down the amps (if so how), or have I simply purchased the wrong transformer.
Again sorry if this is a stupid error or question, help would be appreciated.

If I have missed some information out please ask / let me know.

Many Thanks
 

Thread Starter

ABC21

Joined Jan 2, 2019
7
Have you tried turning down the voltage? With the right voltage the lamps will draw the current they were designed to draw.
Hi, thanks for the reply.
That's what I thought that the lamps would only draw the current that they required, the voltage from the original transformer is 25v, and the new transformer is putting out 25v, any idea why they would be running hotter?, Am I missing something?.
 
Are the supplied "transformers" designed for LED's? Did you actually measure the voltage. LED's are better when they are driven by a constant current supply. LED "transformers" typically have a range of voltage operation.
 

BobTPH

Joined Jun 5, 2013
2,136
Agree with KISS. The supplied drivers are probably constant current drivers with a 25V max compliance voltage. If that is the case, you cannot simply parallel the 12 lights on a single constant voltage supply.

Bob
 

MisterBill2

Joined Jan 23, 2018
4,562
Turning down the voltage to avoid destroying all of the LEDs is a good start.Next, connect one of those original supplies to one set of LEDs and measure the voltage. Probably it will be a lot less than 25 volts. Also, the original supply may not be filtered, meaning that the LEDs only get full voltage for less than half of the cycle. THAT will reduce the power and the heating a whole lot. So your supply with a well filtered output will be delivering a lot more power in that case, which will cause a lot more heating but not appear quite a bright. Sorry about the bad news.
 

Thread Starter

ABC21

Joined Jan 2, 2019
7
Agree with KISS. The supplied drivers are probably constant current drivers with a 25V max compliance voltage. If that is the case, you cannot simply parallel the 12 lights on a single constant voltage supply.

Bob
Hello

Thanks for the advice, I was not aware that the LED's required a specific driver (looking through eBay I now realise these drivers/transformers exist).
As explained earlier I have 12 lamps all requiring 0.7A @ 25v.
I have run these all in parallel to the transformer I have purchased (I realise the transformer is wrong).
Do I need to buy 12 LED specific transformers and wire them up individually or can I buy a bigger driver/transformer and wire them up in parallel?
If anyone could advise a suitable one to purchase through eBay this would help me.

Before someone says why don't I use the supplied transformers, the reason is because they are all on individual sockets.
I need to set them up onsite at an exhibition, some have UK plugs some have Schuko plugs and 12 of them into several extension leads with Schuko to UK adapters is both messy and time consuming to setup and break down.

Again thanks for the advise and help, it is much appreciated.
 

MisterBill2

Joined Jan 23, 2018
4,562
Presuming that all of the sets of lights are the same, one driver with adequate capacity should work well. It may even be that the transformer that you have could work if a suitable driver is available to go between transformer and LEDs. Of course, that is presuming that the drivers are constant voltage types, and that each set of lights has the same requirements. A very simple test would be to adjust the supply that you have down as far as it goes and see if the LEDs are close to the original brightness. It may be that some additional resistance in series would be needed. But first, measure the voltage across one set with one original driver so that there is a reference available. And it might possibly work to have two strings in series across the new power supply, but that is just a guess on my part, just an easy thing to try.
 
Last edited:

ebeowulf17

Joined Aug 12, 2014
2,965
Hello

Thanks for the advice, I was not aware that the LED's required a specific driver (looking through eBay I now realise these drivers/transformers exist).
As explained earlier I have 12 lamps all requiring 0.7A @ 25v.
I have run these all in parallel to the transformer I have purchased (I realise the transformer is wrong).
Do I need to buy 12 LED specific transformers and wire them up individually or can I buy a bigger driver/transformer and wire them up in parallel?
If anyone could advise a suitable one to purchase through eBay this would help me.

Before someone says why don't I use the supplied transformers, the reason is because they are all on individual sockets.
I need to set them up onsite at an exhibition, some have UK plugs some have Schuko plugs and 12 of them into several extension leads with Schuko to UK adapters is both messy and time consuming to setup and break down.

Again thanks for the advise and help, it is much appreciated.
Re-read posts 4-7 and do some measurements. Without knowing whether your original power supplies are constant-voltage or constant-current, we can't give you good advice.

As suggested above, rewire at least one of your light fixtures with their original power supplies and measure the output voltage of the supply while the light is lit (in other words, measure the voltage across the light itself while it's running.)

The voltage you find there may tell us a lot. If it's significantly below 25V, it's probably a constant current supply which regulates its voltage down as needed to maintain a specific current flow through the LEDs. In that case you wouldn't think of it as a 25V power supply, but rather a constant current supply such can deliver up to 25V as needed. If you've got constant current supplies now, there isn't an easy way to replace them all with one supply.

On the other hand, if you find 25V across the LED while it's lit, that would imply that you are dealing with constant voltage supplies, and you should be able to substitute a single shared supply - then we'd need to get back to the heating mystery.

Do some tests and let us know what voltages you measure.
 

MisterBill2

Joined Jan 23, 2018
4,562
Now there is a BIG QUESTION that has popped up in my mind: Are the original devices actually transformers???? Or is a block item being called a transformer and actually it is a whole power supply package? That is the thing that is not clear right now. Resetting the purchased DC supply to a lower voltage might be all that is needed. It may also be that adding a series resistor, possibly one for each set, will be needed. A series resistor is certainly an effective way of setting the current, despite being a bit less efficient than a good switcher device. Efficiency is not always the major need in some applications. This may be one of them.
 

Thread Starter

ABC21

Joined Jan 2, 2019
7
Now there is a BIG QUESTION that has popped up in my mind: Are the original devices actually transformers???? Or is a block item being called a transformer and actually it is a whole power supply package? That is the thing that is not clear right now. Resetting the purchased DC supply to a lower voltage might be all that is needed. It may also be that adding a series resistor, possibly one for each set, will be needed. A series resistor is certainly an effective way of setting the current, despite being a bit less efficient than a good switcher device. Efficiency is not always the major need in some applications. This may be one of them.
Are the existing devices actually transformers?
Sorry don't know the answer or how to tell if it is or not, it is a sealed unit.

All the LED lamps are exactly the same make size/shape.

The Existing (supplied) Transformer output is:-
NO LOAD = 26.4v fluctuating to 26.6 volts every second or so.
Under Load = 25.4v fluctuating to 25.6 volts every second or so.

I have adjusted the volts down on the new power supply output is now:-
NO LOAD = 22.7v (no fluctuation)
Under Load = 21.7v (no fluctuation).
The lamps are still running hot, much hotter than if I run one of the lamps on its own using the supplied "power supply".

Does the above information shed any light on my issue?

Thanks again.
 
Last edited:

MisterBill2

Joined Jan 23, 2018
4,562
I am guessing that it is a constant voltage but with a much shorter duty cycle. that has been a great way to get a higher level of brightness without using so much power. It should be quite possible to duplicate that with a series switching transistor and a dual 555 duty cycle generator. The first 555 generates the tri-wave and the second one works like a comparator to generate the duty cycle, based on the switching reference voltage. Then a small NPN transistor to drive the 0 amp switching transistor. It does not need to be that high a frequency, either.
 

Thread Starter

ABC21

Joined Jan 2, 2019
7
I am guessing that it is a constant voltage but with a much shorter duty cycle. that has been a great way to get a higher level of brightness without using so much power. It should be quite possible to duplicate that with a series switching transistor and a dual 555 duty cycle generator. The first 555 generates the tri-wave and the second one works like a comparator to generate the duty cycle, based on the switching reference voltage. Then a small NPN transistor to drive the 0 amp switching transistor. It does not need to be that high a frequency, either.
Hello - OK so this has gone over my head somewhat.

Can someone point me in the right direction (Amazon or eBay Preferably) so I can buy the correct unit, I have found a 555 duty cycle generator <on this link> although they all appear to be rated 5 to 15v input and I am running at 25v.

I have found this one that appears to have a LCD read out on <on this link> although this appears to have a load output of <Signal load capacity: the output current can be about 5 ~ 30ma>, I assume I am correct that 12 x 0.7a = 8.4a so far too much load for this, or is my calculation wrong, and far too little for just 1 LED?

I assume if I purchase/find the correct 555 board, I wire 1 in at the output from my transformer and then have all 12 x 0.7a lamps connected in parallel to this (or do I need to purchase 12 boards?).

I'm also a little bit lost on the NPN transistor part.

I am running out of time to resolve this before my exhibition, is it possible to just purchase another transformer that is designed for LED's will this just work correctly out of the box, as this is a quick and easy solution for me. Again can someone suggest a link, I need a 25v transformer (needs to work 110v - 240v input), have an output suitable for 12 x 0.7a LED's (and I am assuming with a 555 duty regulator built in, (I assume I am correct in reading up about this that it cycles the current supplied on and off only supplying about half the constant current)).

Or should I just give up for now?

Slightly frustrated, although I appreciate the input, its good to learn, especially on a running project. - Thanks everyone
 

AlbertHall

Joined Jun 4, 2014
8,818
Before someone says why don't I use the supplied transformers, the reason is because they are all on individual sockets.
I need to set them up onsite at an exhibition, some have UK plugs some have Schuko plugs and 12 of them into several extension leads with Schuko to UK adapters is both messy and time consuming to setup and break down.
Or should I just give up for now?
Using the original supplies would give good confidence that it would all work as intended even if it is a bit ugly. It may be time to bite the bullet and get the adaptors and extension cables needed.
 

MisterBill2

Joined Jan 23, 2018
4,562
Sorry, I am not that advanced, I only have a simple volt / resistance meter.
To check for an AC signal, to see if it is a PWM arrangement, set your meter to the AC mode and see what voltage you get. If it is much above zero then you have a PWM driver. It may work to use one of those LED driver supplies as the PWM driver of a big power transistor to control the output of your high current DC power supply that you purchased. You would only need a single resistor to limit the base current. That will be simple, although you would need a heat sink for the big transistor. Somebody with drawing ability could produce the drawing for you, I hope.
 

AlbertHall

Joined Jun 4, 2014
8,818
To check for an AC signal, to see if it is a PWM arrangement, set your meter to the AC mode and see what voltage you get. If it is much above zero then you have a PWM driver.
This is assuming that the AC ranges are capacitor coupled and many are not, therefore AC volts ranges will indicate a reading for a DC input.
 
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