Car Battery help needed.....please

The change to 42v systems doesn't have much to do with the alternator being unable to cope. I beleive it's to reduce the current required to operate all the motors in new cars (windows, seats, doors...).

They never do. In the City and Guilds, you're taught that an alternator only ever charges to around 80%.

It'll fast charge to 80%, after that it trickle so slowly it'l probably only get there if you're driving a truck...

It's a *very* poorly designed car whose alternator can't cope with the total load. That means the car could cut out with a battery fault or low even when running.

Eh? Are you saying batteries of today have a different way of measuring capacity other than amp/hours? And modern cars aren't noted for having larger capacity batteries in the main.

The quiescent load on a battery is irrelevant as regards the technology. If anything, modern batteries are damaged more by being run flat.

And if 'older' technology wasn't suitable for high loads and fast re-charging how come it was the zenith of battery electric vehicles?

I wouldn't have thought shutting down an alarm system much use, would you? Better simply not to fit it.

Multiple battery systems are an old idea - things like ambulances and motor homes have used them for years. The idea is to keep the 'starting' one separate from the accessories one, where those accessories are much used with the engine not running.

Higher voltage systems save weight on cabling etc over 12 volt ones - and increasingly important might save money too with the escalating costs of copper. It also makes the design of a combined starter/generator which is part of the flywheel more practical. Why cars have stuck with 12 volts for so long I've no idea. It makes no sense.

If you do attempt to charge a lead acid to a true 100% of capacity, it will gas very freely towards the end of this charge. Modern designs simply aren't up to coping with this.

Dave Plowman (News) ( snipped-for-privacy@davenoise.co.uk) gurgled happily, sounding much like they were saying :

Are you anywhere near a branch of Manbat?

I recently bought a battery from their Bristol branch and their price (=A350 for a Type 072) and service was top notch - they even took my old one away. As well as making their own 'Numax' brand (which I believe came out top in an AutoExpress test) they actually make a lot of the Varta range in the UK.

Mathew

I've never seen an alternator stop at 13.6V 14.2 is the norm always has been

Most cars were 6V years ago and some VW used 6 V right up to the early 70's.

Then that means according to you that virtually every car is poorly designed. Sit down with a workshop manual for any car of your choice, add the total electrical load of everything that *could* be on at once and then compare it with the alternator peak output. You will find that the alternator output will *not* balance the full load, or even get close to it.

Bear in mind that at or just above idle speed, the alternator output is

*much* lower than peak.

The HFS on Ford vehicles is managed by the ECU for this very reason. If the battery voltage gets too low for continued vehicle operation, the HFS is switched off.

The battery survives by virtue of the fact that for a reasonable percentage of time, there is a much smaller load.

Ampere hours is only one way a battery is sized for car applications. Cold cranking amps is another.

The way modern batteries are constructed, with complex shapes for the plates, more reliable intercell connections and many more factors make batteries far more durable than in the past. I stand by my statement absolutely; batteries made to sixties standards would simply not give good service in a modern car.

If you want to get more detail, the Varta site is quite informative.

Are you saying that the sixties was the zenith of battery powered vehicles? If so, I think you need to do a little research!

Battery powered vehicles of the past, and of now, use totally different designs. Yes, they may have used lead/acid technology, but that's about all. They are/were more like so-called leisure batteries. IOW, designed for complete charge/discharge cycles, with periods of time left in a totally discharged state. This is something batteries for cars do not tolerate.

I've no idea. You would have to address your question at VAG and others that use this technique.

The whole idea of multiple batteries on modern vehicles is *not* to seperate them! The way they were used in the past doesn't relate to their use now.

VW's Touareg, for example, uses the ECU to determine which battery or combination of batteries to use at startup. Just a description of the strategy runs to a couple of pages! This is in spite of some models being fitted with a water cooled alternator driven by a two-speed gearbox capable of 300A peak output!

Because by and large, it provides an adequate system in the most cost-effective way?

Chris

Both mine do. I had one once that wouldn't. A Rover P6 3500. It was a right royal pain in the arse. I put a bigger alternator on it.

Of course you can be more intelligent on how they are shared, but the principle is the same. Otherwise you might as well just fit a larger one.

It needs a 300 amp alternator which can't cope with the entire accessory load? Do tell what they are...

The message from Chris Whelan contains these words:

Front and rear screen heaters, lights, blowers, plus all the other things that are drawing current all the time and I very much doubt my Moandeo's keeping the battery charged! That's why the screen heaters have timers.

An alternator with a maximum output of 75amps is not that uncommon. Are you saying that all the ancilliarys on at the same time consume more than that? No way. Mike.

I suspect it's more to do with the stop start treatment that many cars receive these days, rather than the alternator can't cope with them all on at the same time. For cars that do a lot of m/way work, I can't see the alternator being unable to charge the battery, even with all the ancilliaries on. Wipers, lights, a/c, heated screens, blowers etc. Mike.

Have you ever sat down and added them up?

A HFS takes more than half of that on its own...

Chris

No, they are *not* the same! As you said, multiple batteries on old vehicles were used to *seperate* main and accessory functions. Modern multi-battery vehicles *share* those functions intelligently. In that respect you could consider them as opposing systems!

Why not look at VW's site? Included are such things as full electrical tailgate closing...

Chris

...and on vehicles using silver calcium batteries, 14.6v.

Chris