[ElonSkum]

For the last 2 months, the cabin light bulb, a halogen bulb, has been blowing out. Have had 3 replacements in the last 3 months. Would go for an LED this time, but want to fix the problem before I make the upgrade.

The fuse remains alright, just the bulb keeps blowing out.

Any suggestions where I should start my diagnosis from?

[mvadg]

Originally Posted by ElonSkum

Any suggestions where I should start my diagnosis from?

I don't know how to put it in the context of a Hyundai, but this was a problem with my Kinetic Honda and the dealer told me to check and replace the regulator. Replacement of the "regulator" fixed the problem of the headlight bulb blowing - I replaced 3 in quick succession before getting it diagnosed.

I am sure there is an equivalent rectifier or other component in your Hyundai that needs to be checked. I would also do it before the faulty component destroyed something much more expensive.

[ElonSkum]

Originally Posted by mvadg

I don't know how to put it in the context ....

Thanks for the reply. I really appreciate.

But, I feel the power distribution in a car would be more nuanced than that of a two-wheeler.

I might be wrong, but my educated guess says that the power to the lamps in a car either comes straight off the battery or is a rectified DC from the alternator, whereas in a scooterette, it might be just a regulated AC power fed directly to the lamps. But, still a point to ponder nonetheless.



My central locking has been giving me grief as well. So, your suggestion has set my mind thinking.

[mvadg]

Originally Posted by ElonSkum

Thanks for the reply. I really appreciate.

...My central locking has been giving me grief as well. So, your suggestion has set my mind thinking.

Basically the same in both the 2-wheeler and 4-wheeler in this case. In fact I did a bit of Googling and found this:

https://boodmo.com/catalog/4202-alte...8-hyundai-i20/
and this:
https://www.carparts.com/blog/a-shor...rging-systems/

Those high voltages might burn out something more expensive like an ECU (hopefully they have additional protection). So you'd better hurry.

[saket77]

Grab a volt meter and check the voltage in the cabin light holder. Both with engine off and on, and one with slight revs too. Shouldn’t cross 14.4 volts.

Regards.

[ElonSkum]

Originally Posted by mvadg

https://www.carparts.com/blog/a-shor...rging-systems/

Thanks for this article. Brief and succinct. So, it's still done the way it has been for decades. I used to think with CAN bus and all, the charging and all that would be more sophisticated. May be the electronics would be.

Originally Posted by saket77

Grab a volt meter and check the voltage in the cabin light holder. Both with engine off and on, and one with slight revs too. Shouldn’t cross 14.4 volts.

Regards.

Thanks for the tip. That's what I plan to do. But, never occurred about the revving thing. On a motorcycle I might have, but never occurred doing that in a car.

[saket77]

Originally Posted by ElonSkum

Thanks for the tip. That's what I plan to do. But, never occurred about the revving thing. On a motorcycle I might have, but never occurred doing that in a car.

Revving the engine is important. You can also measure at the battery terminal. At idle, voltage should be around 13.8V. Rev your engine and the alternator regulator should upper cap the volts to 14.4 to max 14.5V. If the voltage surges over this, even in spikes then the regulator is faulty.
Else check for loose connection in the cabin light unit.

Regards.

[ElonSkum]

Originally Posted by saket77

Revving the engine is important. You can also measure at the battery terminal. At idle, voltage should be around 13.8V. Rev your engine and the alternator regulator should upper cap the volts to 14.4 to max 14.5V. If the voltage surges over this, even in spikes then the regulator is faulty.
Else check for loose connection in the cabin light unit.

Regards.

Now, that was the kind of tip I was looking for. Thanks a lot.

[Mr.Boss]

Originally Posted by ElonSkum

For the last 2 months, the cabin light bulb

Add the missing details like Car make, model, year, any modifications in the electrical system (recently or in past)

Voltage regulator (as already suggested by others) could be an cause, but that should affect other electrical parts as well. I don't think we will encounter a high rev condition with door open (for cabin lamp to switch ON, unless it is kept ON intentionally while driving) and I doubt a faulty door switch. Check this as well

[ElonSkum]

Originally Posted by Mr.Boss

Add the missing details like Car make, model, year, any modifications in the electrical system (recently or in past)

It's a 2010 Hyundai i20 Sportz Petrol.

I can't seem to find any way to edit previous posts here on TBHP.


So, I checked the voltages yesterday. And, now I have so many more questions.

1. First checked the battery, with engine off, idle and revving. Ranged between 12-14.4VDC. 12 with engine off, dipping to around 10 when cranking the ignition and maxing out at ~ 14.4 with engine revving. So, all good there.

2. Now checked the readings in the cabin lamp socket. Ranged between 12-14.4VDC with off, idle and revving. I must have taken these readings around 4-5 times with pauses of 5-10 mins in between, inside the garage and again, after I had gotten the car out in the yard.

Curiously, the reading once did spike to around 18~20VDC for a half a minute or so. I tried replicating the error again, but in vain. I am not sure whether the strange reading was due to my fault - I was fiddling with current readings as well, while testing a cheap 1A COB LED hooked to the cabin lamp socket. Do note that I have one of those ,ubiquitous, cheap Chinese, yellow DMM, DT830D.

I made another observation, that the DMM when set to AC voltage, does give out readings!!.So, the power to the lamps in my car is just regulated, not rectified? Just the way it is in my 2005 Pulsar 180. Showed around 30VAC. A perfect scaling factor of 60%. Time to get a good true RMS DMM or a good analog meter.

Is my analysis correct? Power to the lamps in my car is just regulated, not rectified?

Another question, may be deserves a

[mvadg]

Originally Posted by Mr.Boss

Add the missing details like Car make, model, year, any modifications in the electrical system (recently or in past)

I don't think we will encounter a high rev condition with door open (for cabin lamp to switch ON, unless it is kept ON intentionally while driving) and I doubt a faulty door switch. Check this as well

You have a point there Mr.Boss! I think the OP should replace the cabin bulb with a good quality bulb, preferably from a different brand. Also avoid touching the glass of the bulb, even though cabin bulbs are unlikely to be halogen lamps.

[ElonSkum]

Originally Posted by mvadg

You have a point there Mr.Boss! I think the OP should replace the cabin bulb with a good quality bulb, preferably from a different brand. Also avoid touching the glass of the bulb, even though cabin bulbs are unlikely to be halogen lamps.

It's a 42mm tube type halogen bulb.

Are there good brands, selling such tube type halogen bulbs? I can't seem to find any online. My driver got them all from the local market. Aftermarket replacements are all the same garbage IMO. He has thrown away the blown stock bulb. I will check for brand markings on the luggage lamp, which is still the stock.

[SreeT]

Originally Posted by ElonSkum

Do note that I have one of those ,ubiquitous, cheap Chinese, yellow DMM, DT830D.

I made another observation, that the DMM when set to AC voltage, does give out readings!!.So, the power to the lamps in my car is just regulated, not rectified? Just the way it is in my 2005 Pulsar 180. Showed around 30VAC. A perfect scaling factor of 60%. Time to get a good true RMS DMM or a good analog meter.

Is my analysis correct? Power to the lamps in my car is just regulated, not rectified?

I too have a cheap meter like yours and the same thing happens to me as well. These cheap meters don't 'filter out' if that makes sense the DC voltage when measuring AC voltages with it, so it gives you a false reading. Try measuring the voltage at the battery when the car is off to confirm this. 'DC rejection' is the technical term for it I believe.

Also these cheap LED replacement lights can mess with the voltage measured by the regulator in the alternator and cause problems.

It can just be that one of the earth connections is bad so I'd check those first before replacing the alternator. AFAIK on a normal car, there's alternator - engine block via the alternator support, engine block - chassis via a thick wire (usually via gearbox) and battery to chassis via a thick wire. The connections to the chassis usually go bad.

[ElonSkum]

Originally Posted by SreeT

I too have a cheap meter like yours and the same thing happens to me as well.....

Thanks for all the info. Almost forgot about the missing cabin lamp. Been driving without one for the last one month. Need to fix it this weekend.