Saturday, Jan 23, 2016 at 11:19
Serioulsy I don't know where you are getting this information of older alternators having anything other than a 13.8 volt nominal charging voltage.
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For as long as I can remember the nominal charge voltage on automotive systems has been 13.8 volts ...... yeh and there is paperwork and other information for days to confirm this.
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I've been arround cars and their electrical systems since the late seventies ...... I am a technician & I can read a multimeter ...... have always read around 13.8 Volts at the battery terminals and at the alternator, until I started seeing reasonably recent vehicels and recent replacement alternators. ..... weirdo euro cars don't count.
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Testiment to this fact is my 03 hilux ...... quite soon after I baught it I fitted a digital voltmeter ...... and that meter read 13.8 Volts all day once the battery was up to charge. ...... Because of the age of the vehicle I changed both the starter and the alternator in the interests of reliability ...... now the up to charge voltage reads 14.2 ish volts ..... which agrees with the documention that comes with the alternator. ...... not only do the instruments confirm this ..... there has been a slight bit more willing ness of the vehicle to crank.
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Having lived with screw top batteries in cars for a few decades ..... I can tell you they DO lose fluid and faster than many people want to be bothered about. ...... serioulsy .... tell me how many people
check the fluid level in their own batteries.
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It is also a
well known and documented fact in the battery business, that 13.8 volts was chosen as the nominal charge voltage because it was the best compromise between rapidity of charge and fluid loss ..... increase the charge voltage above that and fluid loss increases ...... there are graphs and stuff if you can be bothered looking.
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Now back to screw top batteries and modern technology.
A few decades back we saw little other than screw top batteries in cars ....... and those batteries represented the basic, pretty much undeveloped technology.
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Bottom of the market screw top batteries still are much the same as those basic batteries ........ lots of people when they replace a cranking battery are looking for the cheapest option ..... and this is what they get. ....... if you baught a used car ...... this is probably what you got.
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Moving to modern technology ........ quite some time ago it was discovererd that by adding certain other metals to the lead in the plates and changing the composition of the electrolite by adding other chemicals to the simple acid ..... gassing and fluid loss could be considerably reduced ....... to such a point the battery could be sealed. ... this gave us all the sealed battery technologies, " sealed maintenence free", "unspillable batteries", "starved electrolite", "gell" and when the marketing people got hold of it AGM.
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These same metalic and chemical changes, made to reduce gassing, also increased battery life, strorage capacity, and pretty much every other property of the battery.
As you move up the market from the basic battery, more of these metalic and chemical changes will come into play ..... Ya cheapest screw top batteries will be ya basic technology, move up the market and screw top batteries will have some of these improvements....... continue on up and more of this newer technolgy comes into play till we arrive at the top end "AGM" product.
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In any given situation a modern top of the range screw top battery will require considerably less maintenence than a basic battery ...... due entirely to reduced gassing and fluid loss ..due to these changes.
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It is very likley that in the upper part of the screw top market, those batteries will tolerate the slightly higher charge voltages ........ but regardless the fluid loss in any screw top battery will be higher with higher charge voltages ..... its just an unavoidable fact.
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As far as temperature ......
well a lot of us don't live in the south, so even in winter the battery will be warm because mostly they are mounted under bonnet ...... in summer under bonnet battery temperatures will reasonably be in the 40 to 50C + range.
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As far as temperature compensation in alternators ....... in the warmer pats of the country, that will be pretty much irrelivent, because under bonnet, both the alternator and the battery will be hot enough that any temperature compensation will have the voltage wound back to the minimum nominal charging voltage
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The reason why I caution about higher charge voltages and screw top batteries is .... because most people who buy a replacement screw top battery buy on price ....... so are very likley to buy a basic unimproved battery.
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As for me and my recommendation ..... I will never buy another screw top battery, because they are just bad value ....... then there is the maintenence and the unavoidable acid leakage.
Since changing over to exclusivly sealed batteries, I have no problems with corrosion on battery terminals and have not needed to top up a car battery.
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All the sealed batteries will tolerate a higher charge voltage ..... some will require it.
Hence the existance of booser diodes and the like.
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cheers
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