Technical query arising from the demise of my 405 battery this am.
I have always bought the largest good quality battery that is recommended for any car I have (for example fitting a 44AH instead of the stock 38AH one) or fitting one for diesel instead of the one required for petrol. My theory has been that for the small extra cost it may give that extra power you need if the interior lights have been on. I have also always thought that it should last longer, as it would never be discharged and kept topped up by the alternator.
A few months ago, on a technical site, I read the advice that you should not fit a large battery, as it would not "cycle" as it was partially discharged and then fully recharged after starting the car. It said that the larger battery would be prone to sulphurisation and failure.
Views anyone?
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What you read is true.
Also, if battery is too great a capacity for the alternator, the alternator will be forever 'chasing its tail' and not manage to completely charge the battery on shorter runs. Thus, upgrading battery capacity should be matched by upgrading alternator output capacity.
With most modern cars the stock battery should be more than adequate - unless you have a fault somewhere making the car difficult to start (e.g. low comp. or duff glowplugs on a Diesel).
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What you read is true. Also, if battery is too great a capacity for the alternator, the alternator will be forever \'chasing its tail\' and not manage to completely charge the battery on shorter runs. Thus, upgrading battery capacity should be matched by upgrading alternator output capacity. With most modern cars the stock battery should be more than adequate - unless you have a fault somewhere making the car difficult to start (e.g. low comp. or duff glowplugs on a Diesel).
Thank you Aprilia
I will away to the local motor factors when the rain and sleet stop. I spent a few minutes in the rain getting the good battery off my 309 diesel (untaxed at present) and onto my 405 this morning. Wish I hadn\'t bothered now!
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Everyone closed but Halfords, so I will leave the big battery in a while.
I have been thinking about "not manage to completely charge the battery on shorter runs". Starting the car should take about the same amount of current whatever the battery. Let's say, in round figures 500 coulombs. The alternator would have to effectively replace the same current whatever the size of the battery, wouldn't it? Therefore no increase in alternator capacity required?
I thought the need for ever increasing alternator capacity was not to enable modern cars to have their batteries recharged quicker but to enable the battery to be recharged at the same rate whilst the alternator supplies the air conditioning, ICC equipment, windows, front and rear screen heaters etc at the same time. In diesels, of course, it enables the heater plugs to continue to operate whilst you drive down the road for the first half-mile or so.
I am taking your advice about the battery anyway(45AH seems about right) as the vehicle probably has a limited life anyway. I will keep the old one to enable the final trip to the scrapyard. Bush going in rear axle, causing slight scrub of rear tyre, and my local gurus say fit a whole secondhand axle. This will exceed vehicle worth at next MOT
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Rear axle radius arms worn out on high mileage 405's is a common death-knell of them.
Fitting a second-hand axle is the most cost-effective way out of it usually.
--
groups.msn.com/honestjohn/problems.msnw?Page=1 - Pictures say a thousand words.....
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Still passed the MOT, despite me asking the tester to double check. Not worn enough for a failure or to make tyre wear too expensive. I suppose at 193k miles (with all suspension, springs, joints etc original) I can't be too disappointed!
I did fancy a 406 diesel estate as a replacement, but there seems a lot of problems compared with the 405
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Crinkly,
My 405 went to 251k with knock-knee-d trailing arms and a blowing head gasket.
The emissions on mine got progressively better each year, according to the MOT. At that rate, the exhaust could have been cleaner than the intake after a certain time...
So you should still be able to get some miles out out of your machine!
Cheers
rg
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Crinkly Dave. Mpdern Lead Acid batteries are not designed as deep cycle types as Aprilia was refering to so your contrait will be a purely physical one. The amount of energy used by yhe starter is easily replace by the alternator no matter what the capacity of the battery. Deisel heavy duty batteries are designed for greater cold cranking amps and have a lower internal resistance at the cost of materials. Regards Peter
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Just read that, sorry about the typo's
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I will go with Peter D on this. I personally would go for the Heavy duty diesel version, if it will fit, the lower internal resistance and capacity may just make it live an extra winter (or 2) or get you out of trouble when the car starts to be difficult. Worth paying an extra 20%.
pmh (was peter)
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Yes, I would go for the highest spec one which will fit (usually the diesel)
Starter batteries are designed to provide large current for a short period of time, and then take a charge quickly.
Leisure batteries are 'deep cycle' and are used in caravans, invalid carriages, golf carts, forklifts etc... these are designed to run flat and be recharged overnight.
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pmh
Yes, I see no problem with using a larger battery, and I've done just what you suggest on a few previous cars without problem. Given that we're talking about capacity differences of perhaps 20 to 40 Ah, the average alternator (50A plus these days) should still cope with a part discharged battery given any sort of reasonable run. I have had no problems even on cars with dynamos, never mind alternators. As you say, the larger battery has that bit in reserve for the winter, or period of time parked up. Not only do most diesel variants use larger batteries, but often petrol vehicles destined for cold climates use them too, so it's hardly likely to be a problem.
Regards
john S
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My preference is the Bosch Silver range. Peter
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Aprilia is right the battery installed should never be at a higher rate than alternator can charge.The reason being if so installed as has been said.I think I mentioned this before.Once engine started the alternator.take`s over supply to all circuit`s.But if battery is still low will carry on trying to recharge battery and keep other circuit`s going at the same time.It is not possible for the alternator to keep up supply and will burn out.
In diesels, of course, it enables the heater plugs to continue to operate whilst you drive down the road for the first half-mile or so.<<
The heater plugs only work when you first switch on ignition/remotely open car/do not stay on
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Thank you troops
As I suspected, views were about evenly split
Went out this morning to buy the cheapest one I could, and finished up with an 065 for £35, with a 3 year guarantee (the dealer is long established, and has replaced batteries for mates after nearly 3 years without arguement. Supposedly Crompton, but unlabelled. Halfords wanted £47 for a 44AH one, £54 for a calcium one (but could not explain the technology) and £75 for a heavy duty one.
I will start shopping around for a secondhand axle, but enthusiasm for things mechanical is waning.
Thanks again.
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An alternators capacity is chosen to ensure it can supply the entire needs of the electical load worse case and still leave room for a few amps or so for topping the battery. There is no relationship between the battery and the alternator other then the 14.25 volts or that is limites by the alternator regulator to avoid overcharging. The only sensible limit is the physical space on your battery tray. Regards Peter
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I beg to differ, but in the PSA XUD's at least, the glowplugs stay on for quite a while after the engine has started.
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In my experience it is better to put a bigger battery on than the original.All this "alternator will not take it" is rubbish.
On my old Sierra I put the battery for a diesel transit on, it lasted for ages and always charged itself without a problem.
My John Deere 6400 tractor came with a 110 Ahr battery.On really cold mornings it would not start the tractor, so I put a 154 Ahr one on six years ago and it starts straight away now.
So my advice on this matter is "big is best"
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Aprilia is right the battery installed should never be at a higher rate than alternator can charge.The reason being if so installed as has been said .I think I mentioned this before.Once engine started the alternator.take`s over supply to all circuit`s.But if battery is still low will carry on trying to recharge battery and keep other circuit`s going at the same time.It is not possible for the alternator to keep up supply and will burn out.
I disagree, it is not possible for the size of the battery to burn out an alternator.
To start a car, a number of joules of energy will be discharged from the battery,, the alternator's job is to replace this energy lost from the battery. The energy coming in and going back is not dependant upon the total capacity of the battery..
In diesels, of course, it enables the heater plugs to continue to operate whilst you drive down the road for the first half-mile or so.<<
The heater plugs only work when you first switch on ignition/remotely open car/do not stay on.
Many, if not most modern diesels have 'afterglow', or post heating, whereby the glowplugs stay on for up to three minutes after starting, this reduces cold-knocking, particulate emmissions, and improves driveability.
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I agree with both of ST's comments but would go even further in the second instance. Some BERU glow plugs were designed over 20 years ago to automatically operate whenever the cylinder gas temperature needs increasing, which can be a long time after starting in some instances.
For example, I could envisage post-heating being useful after running downhill for an extended time, i.e. with fuel shut-off but full air flow through the cylinders (there being no air throttle on a conventional diesel engine). This could occur many miles into a journey, not just at the start, and the benefits would include reduced emissions, etc., exactly as ST said.
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