I bought this battery

Ouch! An expensive mistake!

Unfortunately come across this only too often!!!

My origional lr battery died 2 yr ago i thought i was doing good by buying a bigger ah rating but the cca was too low. all the heaters and electrics took its toll over winter and left the alternator catching up. Luckily it was a new alternator and got a replacement under warranty

Indeed, and please don’t think i was pointing the finger or casting aspirations sir! Merely pointing out a mistake that many have made and in reading here... Will maybe stop the same mistake being made by some others Kris

Ha i knew there was no finger pointing. I was just elaborating on my mistakes and i am an avid diy mechanic and it beat me lol. I thought id researched enough but obviously not

Cool

If it's any consolation, the 2007 alternators were problematic anyway - a disproportionately high number seem to have failed.

I thought that when the car is running, the alternator should be powering everything anyway, so not entirely clear to me why an under-rated battery would put an excessive load on the alternator.....

The battery is for powering accessories when the engine is off & for starting the engine. After that point the alternator power everything - and recharges the battery for next time.

Can someone explain why a lower rated battery causes a heavier load on the alternator - I've not heard that one before - I just assumed a lower battery would struggle to actually start the car in the cold etc.

Supply and demand. When under full load the battery struggled to maintain all the demand. The ecu tells the alternator to supply more power and this strain caused the alternator to give up the ghost. Allways started first thing tho. I was told after fitting a new alternator that there needs to be an ecu update from landrover so that was done aswell

That's my point - I still don't understand - maybe I'm just being thick.....

Under full load - the load should be supplied by the alternator - the battery shouldn't play a part once the car is running should it ?

The alternator has to recharge the battery for the effort of starting - but that amount would be the same regardless of battery size.

Im no expert on batteries/alternators Alistair but i think your barking up the wrong tree sir

The battery supplies all the power and is refilled by the alternator which in turn is commanded by the ECU... If the battery is not upto spec, the alternator will be given the wrong commands by the ECU and nothing flows correctly! Over time something has to give! Usually the under achieving battery & or the problematic alternator...

good luck with the battery sale Kris..  ... - .- -.




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Thanks stan
Should be of use as an upgrade to non se vogues.

I still don't completely understand, but I dod manage to find a write-up that explains that the alternator needs the load of the battery charging or it can can get overly excited & burn out diodes - so I guess if the battery isn't providing enough load, then that has a similar effect.

I'm interested as my boat was fitted with dual batteries by a previous owner - I also fitted dual batteries to a Jeep I used to own, without much thought.

I'm hoping that you can have a 'bigger' battery without issues......

Sorry for the thread hijack & good luck with the sale

We allways need more power in some form

Cam-Tech-Craig wrote:

Im no expert on batteries/alternators Alistair but i think your barking up the wrong tree sir

The battery supplies all the power and is refilled by the alternator which in turn is commanded by the ECU... If the battery is not upto spec, the alternator will be given the wrong commands by the ECU and nothing flows correctly! Over time something has to give! Usually the under achieving battery & or the problematic alternator...

Electrikery doesn't quite work like that the battery and alternator are connected together so both would be supplying power at the same time. If there is a big load then the system voltage will drop. The ECU detects this (specific to modern cars, older ones have much more simplistic methods) and provides some current to the alternator which "amplifies" it with mechanical power. Where exactly this power goes depends on the resistance of various parts of the circuitry.

Usually the alternator is connected to the battery and stuff goes out from there because the battery acts as a giant smoothing capacitor to smooth out the rectified sinewave produced by the alternator.

I need to do a post mortem on my defunct alternator but I suspect the diode pack has gone. They're probably just a bit underrated for the car, not liking running so hard for so long. The fact its so enclosed as well certainly doesn't help because that can drastically reduce the MTBF (mean time between failures). Some components I've seen can see their MBTF cut in half by a 5℃ rose above their maximum temperature.

The 830A rating of the battery has nothing to do with running the vehicle. It imply means that it can deliver 830A for 30 seconds at 0℉ (Fahrenheit not Celsius) without dropping below 10.5V. However batteries with large starting currents typically don't like continual discharge which is likely what affects the lifetime in this scenario. Smaller batteries typically have smaller ratings for both.

The original batteries from JLR are actually hybrids which aim to be both (starter and leisure batteries) which is what's suited to the RR with all its electrical systems. The Vartas are primarily a starter battery.

Sorry Craig wasn't meant to be a jibe, just alternator and how they work are one of my bug bears. Ed