LED Tape Lights - Can I wire in parallel ?

[andyblackman]

I'm planning of using 5 x 1 metre lengths of LED tape lighting to illuminate our front steps.

I've got this tape from TLC Direct:
https://www.tlc-direct.co.uk/Products/SK153726.html

I'm now wondering if I must daisy-chain the 5 lengths in serial, or whether I can wire them in parallel ?

View media item 92647
I'm using a transformer and photocell switch (also from TLC) so that the lights come on during the hours of darkness.

Any help or advice is much appreciated...[/img]

 

[jj4091]

Have you read the instructions https://www.tlc-direct.co.uk/Technical/DataSheets/Skytronic/SK153723_Instructions.pdf pdf on the page of your link?

 

[Taylortwocities]

Have you read the instructions https://www.tlc-direct.co.uk/Technical/DataSheets/Skytronic/SK153723_Instructions.pdf pdf on the page of your link?

Including this bit:
If you are unsure about anything please have the tape installed by a competent installer

 

[RF Lighting]

They will be fine in parallel, but you may have issues making you connections to the strip water proof.

 

[bernardgreen]

They can be connected in parallel, in fact this would give more even illumination as there would be less voltage drop. Ensure polarity is correct

 

[ban-all-sheds]

this would give more even illumination as there would be less voltage drop.

Does it not use a constant-current driver, then?

(No - I admit it - I have not looked at the blurb)

 

[bernardgreen]

No constant current driver, just a few diodes in series with a resistor, and this is repeated along the strip.

 

[ban-all-sheds]

That's a bit poo.

 

[EFLImpudence]

How could they be connected in series?

 

[bernardgreen]

I am looking at LED lighting for a friend to replace several small and unreliable halogen capsules. Bare with me as I evaluate these as a possible option.

https://www.tlc-direct.co.uk/Technical/DataSheets/Skytronic/SK153723_Instructions.pdf

•Number of LEDs - 60/m
•Cut intervals - 5cm ( = 50 mm )
•LED spacing - 16mm
Hence 3 LEDs per cut interval

A string of 3 LEDs and a resistor per cut interval in series between the power rails. ( Or 3 LEDs and a current source for a better quality of manufacture ) every 5 cm, 20 Strings per metre

•Current - 300mA/m

Hence 15 mA per string.

Volt drop per diode depends on grade min 2.9 to max 3.5

So about 3 volts across the resistor with 15 mA = 45 mW per resistor

20 x 45 = 900 mW in the 20 resistors per metre

12 volts across the string with 15 mA = 180 mW per string

20 x 180 = 3600 mW per metre

Which matches the stated wattage per metre.

•Power consumption per metre - 3.6W/m

Conclusion. The LEDs rated at 40 mA normal (absolute max 60 mA ) are being run at 15 mA so may not be as bright as they could be, but at the lower current the life span of the LED should be longer.

 

[JohnW2]

How could they be connected in series?

There may be a language problem here.

The strips' (with two conductors running along their 'edges' are designed to be wired 'in series' ('end-to-end'), with the pair of one conductors of one strip wired to the pair in the next strip (and no joining together of the conductors at the end of the run), with a 'constant' voltage source. As bernard has said, that means that each diode(s) are being fed with a constant voltage (give or take any VD along the strip), and therefore must each have their own resistor or other current-limiting something - i.e. the LED+resistor groups are all in parallel across the supply, even though the 'strips' are 'in series' ('end-to-end').

The actual LEDs could only be run in series if there were a constant current source. There would then be just a single conductor serving the LEDs in series, with a return conductor from the last one to the other side of the constant-current source. One problem with that approach is that it would probably be difficult to design a constant current source which was efficient across a wide range of numbers of LEDs (hence output voltages required) - in particular, most simple constant-current sources would become very inefficient when driving just a small number of LEDs (hence low voltage output). Another issue is a safety-related one. With LEDs in series, you can't have more than about 20 in series before one gets to 'potentially dangerous' voltages (>50V) coming out of the constant-current supply, which would have all sorts of implications.

Kind Regards, John

 

[JohnW2]

That's a bit poo.

It might sound it - but see what I've just written to EFLI.

In particular, these strips have 60 LEDs per metre, and can be used up to 5 metres (i.e. 300 LEDs). If those 300 LEDs were in series at, say, 2.5V per LED, you'd need about 750V volts out of the constant-current source - which would be frightening, and certainly not practical. Even for 1 metre, you'd need 150V. Certainly not 'ELV'.

To keep it down to ELV, one would need very many constant-current sources, each supplying a very small length of strip (with LEDs in series within that bit of strip) - which would be likely to lead to a (very expensive) mess.

Kind Regards, John

 

[EFLImpudence]

Thanks for reply.

However, as the lights are made similar to 'diagram 1' they cannot be connnected as in 'diagram 2'.

 

[JohnW2]

Thanks for reply. However, as the lights are made similar to 'diagram 1' they cannot be connnected as in 'diagram 2'.

As I saidat the start, I think it's a matter of language again. In the OP's everyday English, 'in series' meant that the strips were arranged 'end-to end' (rather than 'side-by-side', aka 'in parallel).

Within the strips the LEDs (presumably plus resistors) are obviously in parallel (in both the everyday and electrical senses). Those strips can be connected 'end-to-end' or 'side-by-side' - which becomes 'in series' and 'in parallel' respectively in everyday terminolgy - but, of course, in electrical terms both are 'in parallel'.

Kind Regards, John

 

[ban-all-sheds]

Bare with me

I'm tolerant and open-minded about that sort of thing, but please don't take it personally if I say I'd rather not.