I have a ribbon of LEDs running off from the mains through a DC 12v converter thing that puts out 1.5amps.

This has worked fine but I decided to add a second ribbon of LEDs from the same adapter. All is fine for about 30 minutes and then the lights go out for about 10 seconds before turning on again for about 20 seconds and the repeating this until I get bored and turn them off.

Do I just need a higher amp adapter?

The ribbons both state 2 amps but the first was fine on 1.5 amp. I can find 1.5 and 3.0 amp versions but not a 2 amp version. Will 3 amps kill the LEDs?

The lights are in a sauna so get hot but the adapter is low down and behind a wall panel so doesn’t get that hot. Not sure if that is relevant .

And my first Google after posting this thread has found a 2amp transformer!

Will that be enough for both ribbons, each of which specified wanting 2amp feed, or should I go bigger?

In a sauna you say?

I’ll ring ahead to A&E.

Always read these threads… you just never know which one is going to be the last. you might be ok but then again 😯

Are they in series? Go for the 3A.

They are in parallel and started blinking after 27 minutes. Just found a sight that says you can over power without harm but under powering can cause issues.

I agree with your recommendation of 3amp, thank.

Heat would have been my first suggestion. We had a problem with a transformer overheating then the lights would go out. You can try a higher power one as that will run less hot for same lights. I am sure the transformer should be vented really and the wall of a sauna will still get pretty hot surely ?

Just found a sight that says you can over power without harm but under powering can cause issues.

Yeah. The theory goes that they’ll draw what they need, rather than the transformer “over-powering”.

If they are 12v and 2A that means the resistance is 6 ohms.
Resistances in parallel will reduce the total resistance and increase the current. 2 x 6 ohm resistances in parallel give 3 ohms total resistance. I=V/R thus 12/3 = 4amps.

If the strip has been shortened the power requirement will be less, that’s why it works with a 1.5A power supply.

You might get away with 3A if the second string is shortened.

(not all LED strings may be cut capable of being cut short though).

Rich.

Our kitchen lights are two 5m LED strips in parallel, and they need a 50W 12v supply to keep them happy. The LED strips themselves are something like 35W combined, but I over specced the supply a bit so it lasts longer.

If they are 12v and 2A that means the resistance is 6 ohms.

That’s not how LEDs work… they are non-ohmic

That’s not how LEDs work… they are non-ohmic

I didn’t realise that. Thanks! (Genuinely). It’s good to learn something.

Rich.

EDIT:
properbikeco, out of interest, what would the likely current characteristics be then with the addition of another string in parallel or is it not possible to easily predict?

Rich.

what would the likely current characteristics be then with the addition of another string in parallel or is it not possible to easily predict?

Current required will double.

Electricity now? Jesus wept… 😉

I will whack in the more powerful options.

Sauna heat at the base of a sauna really isn’t an issue. Beers stays cool on the floor while at 40-50 degrees on the raise bench. Transformer at the floor level.

The regulator in the PSU is probably overheating and self-protecting. Each strip draws circa 2A, though may operate on 1.5A (TBH they probably round the power figures up). You should therefore use a 12V 4A transformer to provide enough power.

The only reason this would not work is if the LED strip expects to work with a specific transformer which was matched to that exact model of LED strip and controlled the output in a specific way.

Just to check, post the model number of the LED strips so we can verify before you purchase.

NB, fires in saunas are easy to start and spread extremely fast, I suggest you soak-test before you install and be sure your connections are very secure after installation.

That’s not how LEDs work… they are non-ohmic

But the resistors in the strip are, presumably? You don’t just wire bare LEDs up to a supply and stand back, unless you like darkness.

LEDs being semi conductors so their resistance drops as their temperature increases. This means they are prone to thermal runaway if not driven correctly. Flourecent tubes also do this, and pencil leads.

Most consumer LEDs have internal current control. This includs the light strips, they have iccle switch mode power supply chips on them. So all you need to do is supply them with a stable (12v) voltage, the current rating on the supply is its max rating so best to make sure this is well above the load you are putting on it, especially if in a demanding environment.

If wiring up discrete LEDs then you need to worry about having a constant current supply to drive the LED correctly, e.g. a 700mA supply chip for a typical cree/luxeon LED.

Although I have also wired up bare LEDs to a supply, this provides illumination and works OK as long as the LED can cope with the maximum voltage that a freshly charged battery can kick out.