[star_aqua]

Originally Posted by Samir Taheer

If its the 24V system i can totally understand the 2nd battery.

SL500 is a 24v system.

[esteem_lover]

All our buses & trucks too have 2 batteries, wonder why ? Do they also have a 24V system ?

[Samir Taheer]

Originally Posted by amitk26

Samir 2nd battery is installed to run ICE as in the example zen. The assumption is that you do not run full load 100% time but peak load requirement is high.

So you're saying the ICE is run off the 2nd Battery?

I understand that if your using 60% of the alternators capacity then the other 40% charges the battery. Yes?

But if i understand you right - In the Zen - You're using the alternator to charge both batteries and you're using the 2nd battery to power the ice?

Suman - I didnt reply to your earlier post. Yes i was speaking from personal experience, because all the SUV's and some cars i owned in the past have had 2 batteries as stock.

[amitk26]

Originally Posted by suman

Amit & all others - can someone please explain the stock second battery in the SUVs & the Merc? Lets leave the non-stock ones out of it for the time being? It would help us understand better

I do not own Merc or the said luxary SUV so not in authoritative position to say this but there are only 2 possibilities let me assume few things and then owners can clarify and pick applicable possibility.

Possibility 1 : 24 Volt system ( less likely due to below reasons)

Highly unlikely design choice because this would mean that off the shelf available 12 V gadgetry meant for cars ( Phone chargers , laptop chargers , Stories) can not be directly used in such high end vehicle and customers will not kindly take frayed up devices. As Car electrical are DC system DC - DC step down at every point is also not feasible design choice.

Possibility 2 : 12 V system with lot of peak load requirements.

This is quite possible , Lift Kits , Tyre inflators , built in electrical gizmos etc.
All these systems are not used 100% of times so it does not make sense to fit in a bigger alternator with high current ratings.
A more economic design choice is to fit in a bigger battery which can keep on charging 95% of time and power the peak current requiremnt at 5% times. This is same as aftermarket zen requirement.

Why 2nd battery because fitting 2 65 Amp 12 V standard battery is more economical then a specialized 130 Amp 12V battery not mass produced.

[amitk26]

Originally Posted by Samir Taheer

So you're saying the ICE is run off the 2nd Battery?

I understand that if your using 60% of the alternators capacity then the other 40% charges the battery. Yes?

But if i understand you right - In the Zen - You're using the alternator to charge both batteries and you're using the 2nd battery to power the ice?

Suman - I didnt reply to your earlier post. Yes i was speaking from personal experience, because all the SUV's and some cars i owned in the past have had 2 batteries as stock.

Samir it does not really matter ICE from which battery physically 1st or 2nd because the 2 batteries and Alternator are connected in parallel ,

This is analogous to connect two 750 Liters syntax water tank at roof top of house instead of single 1500 liters , If the 2 tanks are placed at same height
and connected in parallel to plumbing you can not really say from which one water is coming out at a given moment as both will get empty at same rate. IF you compare this system with a single 750 Liters water tank then water will last twice as long or you can open more taps in parallel with same flow rate.

[gigy]

Sorry to floks who have taken the half knowledge thing to themselves but it was for those giving opinins rather than facts. since this discussion is on technical side please be technically sound rather than giving opinions.
Opinions are good for ICE.
By the way,I dont have full knowledge, I am still learning but what i know and sure of i am posting, i dont want to give opinions.
I am not involving cars like BMW, Mercs etc which don't even need a key to be inserted to start, obviously those are not going to start without a battery to power up all the electronic logics. newer cars now also are too complicated to run without battery.
unless there is a battery available sensor a car will run on alternator alone till the current demand don't exceed its capacity. one of my car also has two battery but its purpose is different. some SUV starter are 24v system needed to crank the heavy diesel engine so will have two battery,they run in parallel once car is started or remain in series if its a 24v system. the alternator is charging both of them. some have it because the space available cannot accommodate a large battery in one place. these are exceptions.

[Samir Taheer]

Thanks Amit, I understand what your saying - The Argument on here earlier is that the Battery plays no role in powering Electricals/Electronics and its all provided by the alternator - hence why do we need 2 batteries or bigger capacity batteries and not just allow the alternator to play its role?

[gigy]

If you look at the specification of engine in those SVU with two batteries you will see most of them are powerful than our local trucks. diesel engine is based on compression ignition, so the starter has to be real powerful. to reduce heavy current the voltage is doubled.

[headers]

Originally Posted by Crazy_Eddy

headers, I have a carb esteem so I guess that should technically be pretty close to your Gypsy. A few days back, I had a fuel pump issue and after hours of senseless cranking by the Maruti chaps the battery was kinda dead. Since they were lazy to go pull out their jumper cables, they just swapped the battery with a charged one, started the engine and while it was running they disconnected the battery and re-inserted the old one again; all this while the engine ran fine.

As per your query about a battery 'completing' the circuit.. its not so, since the battery is connected in parallel.

I agree sir, the engine will run for a few minutes, but not keep running always..

I agree about the battery being in parallel too. But in most cars, one cant run the car with the battery "NOT" being there. Its OK to have a dead battery once the car is started as the alternator takes care!

Originally Posted by mail4loys

Few months back while i was driving to Chennai from Cuddalore, my Ikon conked-off and refused to start when we were at Tindivanam toll gate. We push started the car and drove till chennai and directly went to Amron battery shop, the service guys checked the battery and declared it dead with zero charge. Changed to a new batter and the Car started normally. After that incident i thought the car ran on alternator as the battery was completely dead!

This is proof of my statement above!

Originally Posted by anupmathur

We're all here to share and learn. So let us not make this a slanging match!

Yes Sir, we sure are, lets ignore the boys and carry on with our discussions.

I would like you to try removing your battery physically from your car and drive around for say 20 kms or so. Can you sir?

Thanks

[headers]

Originally Posted by gigy

If you look at the specification of engine in those SVU with two batteries you will see most of them are powerful than our local trucks. diesel engine is based on compression ignition, so the starter has to be real powerful. to reduce heavy current the voltage is doubled.

Hi gigy,

Yeah, but modern diesel engines have geared starters to reduce the current consumption as also the load on the electrical system.

Dont want to go into that at this moment as we could start a separate thread later!

[suman]

Originally Posted by gigy

I am not involving cars like BMW, Mercs etc which don't even need a key to be inserted to start, obviously those are not going to start without a battery to power up all the electronic logics. newer cars now also are too complicated to run without battery.

So which cars are we talking about here? I've seen this disclaimer on quite a few opinions on this thread so are we just here or what? Which cars is this "can run without battery" theory applicable to? That is what the "half knowledge" types probably want to know........

Originally Posted by headers

Yes Sir, we sure are, lets ignore the boys and carry on with our discussions.

I would like you to try removing your battery physically from your car and drive around for say 20 kms or so. Can you sir?

Thanks

Vikram, please be specific - do you want Anup to try this with his WagonR (Petrol) or Scorpio (Diesel)?

[headers]

Originally Posted by suman

Vikram, please be specific - do you want Anup to try this with his WagonR (Petrol) or Scorpio (Diesel)?

The Wagon R [petrol] is the choice suman. We know about diesel cars and their superior abilities..lets not get there!

[gigy]

baleno, old esteem&zen, palio 1.2, tata siera runs without battery once started. i dont own other cars.
user experience here includes ford ikon, fiat uno, old mahindra jeep, OHC and gypsy
Can you tell me how is "battery not there" detected in modern cars. even i want to improve my half knowledge.
This thread will have to made vehicle specific to make a single statement.

[suman]

Originally Posted by gigy

This thread will have to made vehicle specific to make a single statement.

You have finally hit the nail on the head.

[gigy]

everyone has posted about failed battery, i have experienced failed alternator. the headlights were going dim, then no horn, display lights went dim, switched of ac and headlights managed to reach a safe place as it was night. let the alternator cool down. after a hour with minumum electrical load reached home. next day the electrician told me its a failed rectifier unit. car was started and less than a minute the alternator was boiling hot.
To generalize it if battery failed you can continue, don't shut engine, keep only stock load on,switching of AC is recommended.
If alternator failed stop as soon as possible in a safe place else the car is going to stop till the battery gives way.
If its a exotic and luxury one which can sense the ripple disturbance in DC line and sense dead battery, you anyway don't have a option, it will decide to shut down.