wiring led household bulbs - parallel of series

[DN_Boy]

Hi, looking for some advice. I'm doing a DIY project for a vanity mirror, with bulbs along the top of it. Each bulb is 7w.

I've got some 5 port wago connectors, and have wired it with the live, neutral and earth from the plug connecting into individual Wagos.

Then each bulb holder has a wire running from the Wago to the associated port on the holder. So a live, neutral and earth wire connects to the individual Wago connectors.

All tucked away in a choc box.

Hope that makes sense.

My questions then...

1) I believe the LEDs are wired in parallel not series as the connect to the wago, and not daisy chained to each other?

2) Do i need to be concerned with thermal runaway if the are wired in parallel or is it not a concern with these small led bulbs?

3) If its not correct, could you suggest how i should wire them.

thanks

DN

 

[telectrix]

how many LEDs. and what voltage are they? are they GU10s?

 

[DN_Boy]

they are standard b22 bayonet bulbs. Voltage is stated as 220-240v . In total 4 bulbs connected to the one plug with a 3a fuse.

cant post a link, but this is them of the BQ website.

diall-b22-1521lm-led-classic-light-bulb/1324552_BQ.prd

 

[telectrix]

230V lamps must be wired in parallel so as you get 230V across each.

 

[Baker1988]

Was going to say the same thing as tele above. In series you loose voltage over the loads so you wouldn't get 230V over all lights. Wire in parallel.

 

[DN_Boy]

thanks for the confirmation.

 

[dmxtothemax]

QUOTE - [ My questions then...

1) I believe the LEDs are wired in parallel not series as the connect to the wago, and not daisy chained to each other?

2) Do i need to be concerned with thermal runaway if the are wired in parallel or is it not a concern with these small led bulbs?

3) If its not correct, could you suggest how i should wire them.

thanks

DN ]

1 - Series arrangements are only used with low voltage LED elements,
you most likely have LEDS with built in power supply
These are used on higher voltages like Mains power.
In your situation they would be " Parallel arrangement " only.

2 - Thermal runaway is not a problem with LEDS.
It is only a problem with poorly designed amplifiers.

3 - Mains rated LED lamps are wired Parallel.

 

[DN_Boy]

Point 2 - it is / can be an issue in parallel circuits hence my concern. Quite commonly discussed. I assume because each LEd has a built in driver rather than sharing a driver across multiple LED's chips then protection is built into the household LED bulbs.

How LEDs become overdriven
Even if the LEDs are all from the same production batch and sequentially manufactured, the Vf of individual LEDs still has a ±20% tolerance. The tolerances mean that the total forward voltage for each string can be very different and therefore the current mismatch significant (see Fig. 2).




Fig. 2. Real life situation
In a test using identical SMD LEDs from a single production batch and using 1 Ohm resistors to help balance out the forward voltages, the currents flowing in each string were measured to be 306mA and 394mA. The LED driver was still doing its job of correctly limiting the current to 700mA, but the over‐current flowing through the second string was seriously overdriving the LEDs.
Worse, as the LEDs started to get warm, the combined forward voltage of the higher current string started to decrease. This increased the imbalance and more current started to flow through the already over‐driven string. The current through the other string of LEDs reduced as the constant current driver compensated, so they started to cool down and their forward voltage increased.

The net result was thermal runaway with the majority of current flowing through one string only, even though the LEDs were mounted on a large metal heat sink. The test was stopped when the current imbalance was 600mA to 100mA. Obviously, if this situation was allowed to continue, the over‐driven string would eventually fail and then the entire 700mA would flow through the remaining intact string and destroy that as well.