AndyW
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| posted on 22/2/14 at 05:18 PM |
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Battery voltage on tick over
Hi
As part of my winter mods I have fitted a new alternator. When I had the car running today, the digi dash shows the voltage as 15v. It does not go
above this and only drops to 14.9 to 14.8 with full lights on.
Is this over charging or acceptable? The battery has been on a charger/maintainer and shows fully charged and ok health wise.
Thanks
Andy
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theprisioner
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| posted on 22/2/14 at 05:37 PM |
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My battery voltage monitor gives:
Red/Green flash >15.2v
Green 13.2V - 15.2V
Yellow 11.8V - 13.2V
Yell Flash 11.5V - 11.8V
Red 11.2V - 11.5V
Red flashing <11.2V
anything other than Green and Yellow is bad news
At rest Volts no battery connected 12.4V anything less than that and you are putting in less than you are taking out I guess. Should be green most of
the time. That makes your reading normal I guess.
http://sylvabuild.blogspot.com/
http://austin7special.blogspot.co.uk/
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mark chandler
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| posted on 22/2/14 at 07:02 PM |
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Sounds a bit high, you could also benefit by fitting a larger pulley if it never drops at idle so save a couple of HP
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Smoking Frog
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| posted on 22/2/14 at 07:40 PM |
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Sounds about right. You could always check with another meter.
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britishtrident
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| posted on 22/2/14 at 08:01 PM |
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Too. high 15 volts will drastically shorten the life of bulbs in the system, nothing to do with pulley size voltage is controlled by the regulator.
14.8 or even 14.9 would be fine.
It could be just an instrumentation error, do a sanity check with another meter measuring directly across the battery.
It could also be the battery is overcharged by your float charging, try leaving the side lights on for 15 minutes resting the battery overnight and
re-testing.
At current ambient temperatures the overnight off charge off no load voltage should be about 12.5 volts.
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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coyoteboy
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| posted on 23/2/14 at 08:09 AM |
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I'd say much over 14v was over charging From my experience, the only times I've seen charge levels like that is when using an old school
open output transformer to float a battery for days. All my tin topsa are regulated to 14/14.1v at high revs. As mentioned it's nothing to do
with the pulley speed, it is down to the regulator. Does your new alt have a sense line? More modern alternators account for voltage drop in the
windings by running a "zero" current sense line back to the battery terminal, if that is missing the reg could be attempting to Max out
its capability as it thinks the battv is zero.
As BT says, confirm with a decent meter at the battery posts and the alternator contacts both at idle and with the engine off after a bit of a load
and rest.
FWIW you should not float charge a 12v battery over 2.25v/cell For more than a couple of days max or you induce damage on the positive plates.
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theprisioner
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| posted on 23/2/14 at 09:17 AM |
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I must disagree it depends on the type of alternator. If the alternator gets feedback from the ECU then the charging voltages can be much higher than
even 15V and that depends on the type of battery (cadmium I believe) and the temperature. If you disconnect the link to the ecu then the alternator
reverts to a normal alternator 14.5V max. You need to know what charging system you have?
http://sylvabuild.blogspot.com/
http://austin7special.blogspot.co.uk/
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Paul Turner
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| posted on 23/2/14 at 09:33 AM |
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Over the 25 years I have had sevens alternator voltage falls pretty much into 2 camps. The Lucas ACR charges at about 13.8 volts whereas pretty much
everything else charges at 14.3 volts. My current small Denso off a 1989 Daihatsu charges at 14.4 volts at engine start, once everything has heated up
and the battery is restored back to full charge it settles at 14.2 volts.
Voltages of near 15 volts are common on a lot of modern cars but the manufacturers fit special batteries (Calcium?) to cope.
If your alternator kit came form GBH beware, I had 3 and all failed within 20 miles. I was not happy, gave up and got a refund.
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mark chandler
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| posted on 23/2/14 at 09:40 AM |
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I did not say the pulley would affect the charging voltage, but if you are getting full charge at idle then it's spinning faster than is needed
as you do not need to be charging until you get to maybe 1500rpm.
As such you could fit a larger alternator pulley slowing it down relative to engine speed, any power saving on the crank with ancillaries translates
to more HP at the wheels.
Regards Mark
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coyoteboy
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| posted on 23/2/14 at 03:25 PM |
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If you're worried about the power sapped by an alternator at full load you can't have many to spare, even a full 2.2kw aalt (the likes of
those off a 5 series bmw with full elec pack!) at full load only takes ~3hp, and load will depend primarily on battery voltage as a locost will have
bugger all other draws in comparison. But it does indeed waste fuel to some degree.
The prisoner, any charging > 15v would seriously shorten the life of most passive components like lamps as said above. The feedback from the ECU is
normally used to Reduce the load on the alt by dropping the exciter voltage, there would be no point upping the charge voltage - it achieves nothing
if the alt is sized to produce sufficient current in the first place (all a higher charge voltage does a is cause decomposition of the electrolyte?)
What would it be trying to achieve by increasing the voltage?
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AndyW
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| posted on 23/2/14 at 03:47 PM |
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OK, so I have left the charger/maintainer off over night and the battery sits at 12.5v.
Start it up and the battery light stays on and only goes off if I rev the engine. This then seems to start the charging. I have tested it with a multi
meter rather than the dashboard volt reading and it still shows a steady 15v at the battery.
If I put on the lights it does drop to 14.5v ish.
I really need to get this sorted as soon as possible.
So, does anyone have a definitive answer as to is 15v too much?
Does any one have any suggestions as to why the alt light stays on until I rev it? The alternator is the same voltage and amp rating as the one I took
off and the connections are all the same.
Any more help appreciated.
Thanks
Edited to add, I'm running a standard ECU and it has no control on the alternator.
[Edited on 23/2/14 by AndyW]
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theprisioner
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| posted on 23/2/14 at 03:50 PM |
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Ok for simple lead acid systems like this probably fitted to a 7esk with no ECU feedback.
However watch out for modern systems they can and are designed to generate quite high voltages:
http://www.vehicle-electrics.co.uk/ford%20smart%20charge%20alternator.php
I apparently have one of those on my kit!!!
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http://austin7special.blogspot.co.uk/
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AndyW
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| posted on 23/2/14 at 04:19 PM |
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quote:
Originally posted by theprisioner
Ok for simple lead acid systems like this probably fitted to a 7esk with no ECU feedback.
However watch out for modern systems they can and are designed to generate quite high voltages:
http://www.vehicle-electrics.co.uk/ford%20smart%20charge%20alternator.php
I apparently have one of those on my kit!!!
not running the standard ford alternator, just a bog standard jobbie....
Shall I be concerned or will it be ok. I'm a bit worried now that I'm going to fry something
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theprisioner
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| posted on 23/2/14 at 06:05 PM |
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It looks like you have something wrong with your alternator. However two things I can think of:
* Verify on a good quality analog meter, the spikes and things from an alternator etc get counted on a DVM and analog meters filter them out because
they are mechanical.
* Even in a low tech alternator has temperature compensation. Try this again when the weather gets warmer or a heated garage.
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http://austin7special.blogspot.co.uk/
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AndyW
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| posted on 24/2/14 at 01:02 PM |
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going to pull the alternator and have it tested, can't risk running it with a fault. I will post up results when they happen.
[Edited on 24/2/14 by AndyW]
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