How long would it take for an interior light to flatten a battery?

[JamesH]

I guess I am pessimistic by nature...

Last night i hopped in the Defender and realised the interior light was left on the last time I went in there to find something. In the carport there is a movement sensor light so I did not notice I left it on. Anyway I came back to drive it at least 24 hours later, probably 36 and I realised my mistake.

I thought, lucky I have the 2nd battery which is manually isolated but I turned on the ignition and the lights came on fine, (the interior light had been still bright when I switched it off). Try to turn it over and yes it was a little reluctant but basically it fired up OK.

So instead of going "phew, that was lucky" I'm now wondering if there is something wrong with my isolator switch and it had been draining both batteries but I still had enough to start.

I would have thought 24hrs plus of interior light would flatten a single battery. What do you think?

[100I]

Not sure how much/how long an interior light would drain, but when you reconnect your aux battery the poor battery will suck your good one down til they roughly equalise, and of course the worse your main is the lower the aux will be pulled down.
On that note if you were in the whoop whoop and you knew ahead of time that the main was very flat, the best course of action would be to remove it and fit the (presumeably good) 2nd battery in it's place rather than reconnect the two (whether via solenoid systems etc or jumper leads).

[V8Hybrid]

The interior light usually takes about 24hrs to drain the battery enough to have enough umph the turn the stater over (especially diesels).

[waynep]

******WARNING SCIENCE CONTENT ******** ;):angel:

Ok so your typical interior light is what, 10 Watts ?
I = P/V
So at arbitary 12.5 volts it draws 10/12.5 = 0.8 amps - so lets say an amp with safety factor. If you have say, a 55 Amp/Hour battery, it should technically burn for 55 hours. ( 1 amp for 55 hours )

However your battery will probably drop below the threshhold voltage/capacity needed to turn the starter motor in about half that time, so lets say the interior light should be able to be left on for 27 hours without compromising your starting ability. This tallies with the practical experience mentioned above.

This is assuming of course the bulb/battery ratings as quoted above, ( you can work out the numbers for your situation ), you have a good battery, and there's no other load on the battery ( eg fridges, phone chargers etc )

[JamesH]

Not sure how much/how long an interior light would drain, but when you reconnect your aux battery the poor battery will suck your good one down til they roughly equalise, and of course the worse your main is the lower the aux will be pulled down.
On that note if you were in the whoop whoop and you knew ahead of time that the main was very flat, the best course of action would be to remove it and fit the (presumeably good) 2nd battery in it's place rather than reconnect the two (whether via solenoid systems etc or jumper leads).

Thanks Dan. I had been told about this but I thought it would not be an issue if the car had been started and was barreling down the road. The batteries were equalised/ing but if the alternator was doing its job they'd both charge up in time. I also understood that the equalisation was not an instantaneous thing.

But I know little about the matters.

[100I]

Thanks Dan. I had been told about this but I thought it would not be an issue if the car had been started and was barreling down the road. The batteries were equalised/ing but if the alternator was doing its job they'd both charge up in time. I also understood that the equalisation was not an instantaneous thing.

But I know little about the matters.

Not if it's been started, I'm saying if you know you have a flat start battery, it's something to be wary of.
Say if you are at the bottom of a gully and you have only one shot at starting it, if you hook the batteries up in paralell, you now have two 1/2 flat batteries, neither strong enough to crank.
Know wha ah mean?

[JDNSW]

The interior light is probably 6w not 10, and may even be less. How long you can leave it on will depend on how good your battery is, and how easy it is to start your engine. I know from experience that in my Citroen, it won't last a long weekend, but will a normal weekend. The County, I don't know, but I can tell you it won't run the UHF for a week. Could be a good argument for fitting an LED bulb in your interior light?

John

[waynep]

Could be a good argument for fitting an LED bulb in your interior light?

John

Yep you can buy them in the same form factor ( festoon ) as the incandescent. They would draw maybe less than 1/10th the current of the traditional bulb.

[ladas]

Yep you can buy them in the same form factor ( festoon ) as the incandescent. They would draw maybe less than 1/10th the current of the traditional bulb.

And I do beleive that Inc sells them on this forum via the markets section !

[RonMcGr]

And I do beleive that Inc sells them on this forum via the markets section !

Well, in a Disco, the light goes on when you open the door and then off about 5 minutes later if the door is not shut.

My mates old Statesman Caprice looses battery power in a few hours with a door open. 15 lights turn on when you open the door :eek:

[VladTepes]

Yep - it handily illuminates all the broken bits for you !

[Utemad]

Could be a good argument for fitting an LED bulb in your interior light?

I've got these in mine. Should also make the covers last longer.

They are bloody bright though. If someone is sitting in the middle rear seat and you open the door at night the middle row light (Disco1) will blind them.

[mox]

Regarding LEDs for interior lights, don't know enough about them to comment. However I do like the interior light bright enough to be able to read things at times. On my Defender have bent the globe holding terminals so they take an 18 watt globe instead of standard 10 watt and left the cover off. Regard it as just an unnecessary thing that causes trouble, reducing the light intensity and would probably melt anyway. eg As some taillights are prone to with more powerful globes intended for indicators or stoplights that are okay for intermittent use are run continuously.
Regarding batteries, I normally run 86's, which are slightly bigger than the standard one and commonly used in tractors and trucks. Takes a long time to flatten a good one from the interior light. Fortunately my 300Tdi starts very easily and using the glowplugs makes it quicker still. Can get away with using 86 batteries too old and sick to start tractors.

[numpty]

Don't know about all Defenders, but in our Td5, if you leave the door open, the interior light goes out after 8 mins.

If the batteries are manually isolated, I can't see the flatter battery discharging the good battery, as everything operates from the battery selected, and at all times is isolated from the other, unless of course the manual switch is switched to Both.

[Tote]

A handy trick for starting diesels that need to be heated before starting (not usually modern LRs) is to tip a kettle of hot water over the glow plugs before attempting to start with a low battery. This prevents the glow plugs from draining the last of the charge from the battery if you crank it as soon as you turn the key on.
A trick learnt with old farm hiluxes with dodgy batteries.
Direct Injection diesels such as TDI /TD5 usually will start without glow plugs anyway.

Regards,
Tote

[Aaron IIA]

I don't know what tipping hot water on the glow plugs will achieve. Do they have a temperature sensor in them, and the hot water will turns them off, hence saving power? But this will not significantly warm the engine, in order to ease starting. Diesels need heat in order to start, and if you are low on power, you could carefully try lighting a small fire underneath the engine. The heat warms the oil so that the engine will turn over quicker, and the heat buildup will aid starting. Alternatively, just warm the inlet manifold, so warmed air is drawn into the engine. Old Bedfrod diesel engines had a heater plug in the inlet manifold, and none in the engine. If you can push/hill start it, this will turn the engine over faster, and start it quicker.
Aaron.

[Utemad]

Well, in a Disco, the light goes on when you open the door and then off about 5 minutes later if the door is not shut.


Don't know about all Defenders, but in our Td5, if you leave the door open, the interior light goes out after 8 mins.

Not if you slide the interior light to ON while you are sitting in it. Only if it is on DOOR.

[Tote]

I don't know what tipping hot water on the glow plugs will achieve. Do they have a temperature sensor in them, and the hot water will turns them off, hence saving power? But this will not significantly warm the engine, in order to ease starting. Diesels need heat in order to start, and if you are low on power, you could carefully try lighting a small fire underneath the engine. The heat warms the oil so that the engine will turn over quicker, and the heat buildup will aid starting. Alternatively, just warm the inlet manifold, so warmed air is drawn into the engine. Old Bedfrod diesel engines had a heater plug in the inlet manifold, and none in the engine. If you can push/hill start it, this will turn the engine over faster, and start it quicker.
Aaron.

Glow plugs don't warm the engine, the warm the fuel that is about to be injected into the cylinders. The hot water heats the injectors enough that the diesel ignites when the engine is first cranked.

Regards,
Tote

[Captain_Rightfoot]

Don't know about all Defenders, but in our Td5, if you leave the door open, the interior light goes out after 8 mins.

If the batteries are manually isolated, I can't see the flatter battery discharging the good battery, as everything operates from the battery selected, and at all times is isolated from the other, unless of course the manual switch is switched to Both.

I've managed to out smart this by switching it to ON in the back and leaving the car for a week. :angel::angel: I swear I've never seen a battery as flat as the primary one after that... :D:D

[Aaron IIA]

Warming the injectors will probably help to start a cold engine. But in my 2.25D, the glouw plugs heat the inside of the pre-combustion chamber. But I suppose the glow plug heating element would also heat the tip of the injector.
Aaron.