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29th April 2019, 07:49 | #21 |
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ROVER 75 Join Date: Jul 2011
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ok thanks for the info
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29th April 2019, 08:15 | #22 | |
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I think I know where I stand. |
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29th April 2019, 16:13 | #23 | |
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Quote:
9h x 5A = 45Ah, A 'flat' car (typical, not stop start or deep discharge type) battery is typically at 70-80% of full charge when the voltage drops below 10.5v - too low to start the car. 45Ah is over half the capacity of the battery so should be sufficient. kicker here is that the alternator needs enough voltage from the battery for the field coils in the first place, which it won't get from a flat battery - which is the real reason it won't charge on a 450mile run (you won't get 5A spare charging out of it + running the car and it's accessories). 24hrs on a 2A charge, or 12 on a 4/5 Amp charge will be enough. Failing that charge well enough off of the car (i.e. 3-4 hours at 4/5A) to give it enough to work properly and the long run should do the rest.
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29th April 2019, 19:11 | #24 | |
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You've got your percentages and voltage figures wrong as well. The maximum amperage from the alternator well exceeds anything the car accessories can call for. ( possibly twice that required. ) The maximum draw by the alternator ARMATURE is six amps to give an output from the field coils of 110 amps.--- |
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29th April 2019, 21:13 | #25 | |
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75 Contemporary SE Mk II 2004 Man. Sal. CDTi 135ps, FBH on red diesel, WinCE6 DD Join Date: May 2010
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All correct! In addition, putting 45Ah of charge into a battery, will not equal 45Ah of charge available for discharge. A battery is not 100% efficient, nowhere near that. On reflection, I was wrong about the 450 mile / 9 hour run being able to fully charge a flat battery. Ability to put current into a battery, is limited by the battery and the charging voltage available. Charging voltage by the alternator is between 14.1 and 14.4v, no more than the output of most modern chargers rated 3 to 6amps. An alternator will initially put around 20-25 amps of charge into a battery, following starting the engine, but that rate will quite rapidly decline as the battery voltage increases once on charge.
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Harry How To's and items I offer for free, or just to cover the cost of my expenses... http://www.the75andztclub.co.uk/foru...40#post1764540 Fix a poor handbrake; DIY ABS diagnostic unit; Loan of the spanner needed to change the CDT belts; free OBD diagnostics +MAF; Correct Bosch MAF cheap; DVB-T install in an ex-hi-line system; DD install with a HK amp; FBH servicing. I've taken a vow of poverty. To annoy me, send money. |
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29th April 2019, 22:50 | #26 |
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Certainly about a week with an ageing battery, but another odd issue. -
As the available voltage from the battery starts to drop, the side and tail lights come on, even though the switch is off. They go out again as the voltage drops further. Ideas? |
30th April 2019, 07:04 | #27 | |
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Is that not the usual way the 75 indicates to you that the battery is almost flat? I have never understood why it seems to be designed to do this, it just seems so such a strange thing to flash the lights outside, when the driver is in the driving seat. My Ford used to flick its dash dial pointers, which was much more visible to the driver and sensible.
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Harry How To's and items I offer for free, or just to cover the cost of my expenses... http://www.the75andztclub.co.uk/foru...40#post1764540 Fix a poor handbrake; DIY ABS diagnostic unit; Loan of the spanner needed to change the CDT belts; free OBD diagnostics +MAF; Correct Bosch MAF cheap; DVB-T install in an ex-hi-line system; DD install with a HK amp; FBH servicing. I've taken a vow of poverty. To annoy me, send money. |
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30th April 2019, 09:23 | #28 | |
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Quote:
Sorry, got the armature and field coils confused there for a moment. You're still not going to get 6A (at 12v) from a flat battery though. So, no, I don't think you are going to get enough charge (ever) from an alternator running with a flat battery to start with. Who ever said that batteries were 100% efficient? 45Ah to top up 20% of a battery rated at 96Ah is not claiming 100% efficiency! disclaimer: calculations not guaranteed to be accurate as can't be rst to get calculators out and whatnot. your mileage may vary. make your bed and lie in it, what goes around comes around... blah blah blah....
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30th April 2019, 17:35 | #29 | |
This is my second home
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Quote:
No need to shout!
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Harry How To's and items I offer for free, or just to cover the cost of my expenses... http://www.the75andztclub.co.uk/foru...40#post1764540 Fix a poor handbrake; DIY ABS diagnostic unit; Loan of the spanner needed to change the CDT belts; free OBD diagnostics +MAF; Correct Bosch MAF cheap; DVB-T install in an ex-hi-line system; DD install with a HK amp; FBH servicing. I've taken a vow of poverty. To annoy me, send money. |
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2nd May 2019, 21:06 | #30 |
This is my second home
R75 Saloon. Join Date: Feb 2009
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I needed that shouting Harry cos my hearing aid has got a flat battery.--
Perhaps a quick charge from my alternator might provide a cure.----- |
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