LED Bulb in Boot causing Battery drain!

[Sam McGoo]

I thought this worth posting as I know a lot of people here, like me, change all their bulbs to LED as one of the first mods to update the car's appearance a bit.
Until recently I'd never actually been unable to start my car due to a flat battery, but did have a feeling something was draining it slowly see here - My previous thread on battery drain

After actually suffering a flat battery twice in a month and assuming the battery is fairly old as I've had the car over two years and it was a genuine Maserati battery, I've just had it replaced today, with thanks to Matt at SportsItallia, as I happened to be in the area today and he had plenty in stock.

Anyway, on my return home I decided to plug in my Launch X431 pro mini to clear any codes stored from the battery going flat yesterday, and there was one still active - a fault with the boot light. Further investigation and putting my phone in the boot filming while I shut the lid, revealed that my boot light didn't turn off!
I swapped it for a new LED bulb and the same happened again. These were good quality Philips x-tream LED T10 bulbs.
I've swapped it for the standard bulb and it now goes off when I close the boot lid and fault code has cleared.

I know an LED is low power consumption, but if on 24/7 it'll obviously use a bit. Also, the bulb holder was quite warm, so must have been consuming. (not scorching like it is with a normal bulb though lol.

So for those with an LED bulb in the boot and a camera phone, probably worth checking.

 

[Zep]

A lot of solid state relays need a minimum resistance to work, sounds like in this case your LED bulbs don't have enough and so the SSR isn't working. You could add a resistor in series and it will probably start working. or get a high resistance LED.

 

[Steve4200]

All systems built for Filament Lamps detect Lamp Failure in one of two ways :-

1. A very small current is passed through the lamp by the controlling ECU when Lights OFF. Detects Open Circuit.

2. The controlling ECU expects the correct current based on lamp wattage when Lights OFF as Method 1 and Lights ON. Detects Open Circuit/Poor Connection and incorrect Lamp Wattage.

The later is the modern method.

Regards

 

[conaero]

In our experience, fitting LED bulbs to the exterior lighting causes a blown bulb error for the reasons above.

 

[Dman666]

Fitted LED side repeaters,number plate lights and boot light and never had any warning or issues,did have a battery drain because the rubber boot handle was disconnect slightly inside from plastic switch and was staying open.

 

[Sam McGoo]

Fitted LED side repeaters,number plate lights and boot light and never had any warning or issues,did have a battery drain because the rubber boot handle was disconnect slightly inside from plastic switch and was staying open.

I did exactly the same on my GT-S and didn't knowingly have any issues either. As Zep said probably depends on the resistance of the LEDs used.
This is on my GT Sport, but just to add that this doesn't show up any warnings, lights etc....Only when interrogated with the computer did it show up a problem.

And only by leaving my phone in there and closing the boot, was I able to see that it was still on.

 

[jet_noise]

A lot of solid state relays need a minimum resistance to work, sounds like in this case your LED bulbs don't have enough and so the SSR isn't working. You could add a resistor in series and it will probably start working. or get a high resistance LED.

Your solution is the wrong way round IMHO
To get a minimum resistance across the lamp you need to a parallel resistor or have a low(er) resistance LED

At the risk of mansplaining ...
...it's complicated by the highly non-ohmic characteristic of filament lamps. Particularly that their off (cold) resistance is very low. If there are any features of drive devices (as you suggest) or lamp failure interrogation means (or anything else*) that rely on this then it can be troublesome to get right.

*Engineering war story - the car digital clocks (remember them) backlight with which I was involved in the '80s were dimmed when the vehicle lights were on. We used the low resistance of the sidelights (to -ve) when off as the -ve to the backlight to ensure full brightness.
Except for Honda who would not be convinced that this cost effective means was without unknown disadvantages.

 

[Zep]

Your solution is the wrong way round IMHO
To get a minimum resistance across the lamp you need to a parallel resistor or have a low(er) resistance LED

At the risk of mansplaining ...
...it's complicated by the highly non-ohmic characteristic of filament lamps. Particularly that their off (cold) resistance is very low. If there are any features of drive devices (as you suggest) or lamp failure interrogation means (or anything else*) that rely on this then it can be troublesome to get right.

*Engineering war story - the car digital clocks (remember them) backlight with which I was involved in the '80s were dimmed when the vehicle lights were on. We used the low resistance of the sidelights (to -ve) when off as the -ve to the backlight to ensure full brightness.
Except for Honda who would not be convinced that this cost effective means was without unknown disadvantages.

My reasoning was that I have previously had to introduce resistance in series to allow correct switching of LEDs. My understanding is LEDs are also non-ohmic, but have a lower peak resistance - is that right? Given that the issue here is a change of state of the bulbs from 'on' (higher resistance for incandescent as you say) to 'off' (there should be no current flowing), I assume the issue is around current leakage keeping the LED lit?

As for build failure warnings, I guess there are two ways of determining failure of an incandescent bulb, one is the resistance, very high when the filament is broken or abnormally low current consumption, which is why switching to LEDs can cause an issue?

Do feel free to continue explaining as I enjoy learning about this stuff. Mansplaining is unnecessary, I'm not a woman

 

[jet_noise]

I'm using mansplaining in a gender non-specific way Sort of the modern equivalent of teaching one's grandmother.

LEDs are (more or less) not ohmic at all rather than just being non-linear. A typical equivalent circuit is a voltage source of about 2V in series with a very small resistor. i.e. as soon as you hit it with 2V the current becomes very large. You can make it work (i.e. limit the current) at higher voltages by providing some series resistance. Further if more than one LED is needed you can connect several in series. And even more can be used by combining parallel groups of series LEDs and resistors.
Using resistors to limit current is cheap but at some point, for brightest lamps e.g. headlights, I might expect there to be an active power supply to translate supply to LED voltages. There would be so much loss in the resistor that it would become too large, hot & expensive.
That last is engineering opinion, not application knowledge, I don't have experience of LEDs beyond instrument lighting. And that was 25 years ago!

Leakage current keeping an LED lit.
LEDs (can) produce light at a far lower current than filament lamps. Hence their greater efficiency - more light for less current. In a system designed for filament lamps an LED (can) produces some light at the leakage current, a filament lamp won't.
i.e. the current is there regardless so changing lamps should make no difference to battery drain when off, it's just that you can see it with LEDs whereas you can't with filaments.

Introducing resistance to allow correct switching.
I assume this means to ensure that they do turn off. This works as you say but I'm mildly surprised that the on output is not significantly affected.

Sam says, however, that the lampholder is warm. Leakage current would not be enough to do this IMHO. I suggest that the lamp detection system is too (or not sufficiently) bright (pun intended). It sees the load as taking too little current when on and the algorithm ignores the boot switch and leaves the lamp on until such time as the load returns to normal.
The lampholder is not as warm as it would be with a filament lamp due to the lower current taken by the LED.

I would further suggest that the boot lamp is one of the lowest current loads on which failure detection works. So there's not as much leeway as there would be for other loads to discriminate between present/not present. Which is why it affects this lamp alone.
If the load is increased (lower resistance) then the issue might go away. Which may defeat some of the reasons to change to an LED!
It may be beyond Sam's skills/desires to mess around with vehicle wiring to make this work.

 

[Zep]

I'm using mansplaining in a gender non-specific way

That’s good, as I identify as a garden rake

Thanks for the lesson And I agree, in this case the juice isn’t worth the squeeze, better to stick with standard.

 

[Gazcw]

the juice isn’t worth the squeeze

That the missus favourite line!