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PinkPig
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Joined: 05 Aug 2004
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Location: Southampton, UK
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 Posted: Mon Jan 04, 2021 21:46 Post subject: Alternator output. 15.5v too high? |
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So, while I wait for new batteries to arrive I've checked the old ones. One won't hold charge for more than a few hours. The other seems okay on 13v, but definitely not new performance.
What I did also check was the alternator output as the batteries are only six years old and wondered if it had been overcharging and cooked the battery.
Difficult to tell. Just running the one good battery the measurement at the battery is 15.5volts
I've done some research and found that some Japanese alternators do run up to 15v+ when presented with a flat battery, but at the same time I'm wondering if the 15.5v is a duff regulator, and that had fried the battery.
New lockdown means I can't take it in for testing.
Going to charge the good battery on a charger then check again to see if the alt output is lower
Any tips on further testing I can do?
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The PINK PIG!
1988 Delica L300 Star Wagon 2.5TD 5sp Manual.
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A never ending camper/restoration project
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| Posted: Mon Jan 04, 2021 21:46 Post subject: Google Ads keep this community free to join! |
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andyman
Joined: 08 Dec 2012
Posts: 5602
Location: Penrith
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| Posted: Wed Jan 06, 2021 0:57 Post subject: |
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Must say, 15.5v sounds a bit high. Most authorities I have seen reckon on a maximum charging or alternator output rate of 14.4 - 14.8v for short periods when the battery has been severely depleted eg by significant cranking in cold weather, dropping within a few minutes to the 13s. A battery already damaged, with lowered charge capacity cannot accept such a high charge rate, and will be further damaged (fried/cooked) if it continues to be exposed to such rates, and indeed, that is what the voltage regulator is supposed to do, ie, reduce the alternator output as the battery gains charge. Think of it like the ball-cock in a cistern; as the water level rises, the flow from the valve reduces until an equilibrium is established. With a good battery, that equilibrium is maintained at around 12.8 volts. If a battery cannot accept the excess charge (energy) and store it, it will be manifested as heat, boiling away the electrolyte, and buckling the plates.
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Fostlongstrider
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Location: Hedon, East Yorks
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| Posted: Wed Jan 06, 2021 11:53 Post subject: |
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You could have a faulty diode pack in the alternator which is not letting the voltage regulate.
Highest it should go with a low battery is 14.7 volts and it should reduce down to 12.6 volts as the battery charges.
It's possible the battery internal resistance is low and this would also allow a higher alternator voltage to occur.
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Ian.
All the best from the East Riding of Yorkshire.
'93 L300 Super Exceed Corse Gray over Grace Silver.Auto.
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PinkPig
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| Posted: Sat Jan 09, 2021 0:17 Post subject: |
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Hi,
We'll I've found a local place to test and refurb a spare alternator I had in the shed and let me know the bench test outputs. I'll get it back next week.
Having read the workshop bible. I should be seeing a charge voltage of around 14.5v depending on the temperature but no more than 15.4v at -20C and it is about +2C at the moment.
So either the regulator it shot, or, one more test to do it the sensor cable is broken so the alt doesn't have a reference voltage.
However, also fully charged one battery, and watched the voltage from cold (glow plugs etc) and it sat about 12v first glow, then around 13v on the secondary glow cycles.
The straight up to 15.5 - 15.8v idling.
I'll test the sensor cable next, but think I'm going to be knuckle scraping in the freezing cold.
Not bad though - last time the current alternator was returned was 2005!
And my spare is a 90amp and came off the mystery machine...so must be brilliant!
Output table:
https://photos.app.goo.gl/CQ5zpFFKkkZBTg5v8
_________________
The PINK PIG!
1988 Delica L300 Star Wagon 2.5TD 5sp Manual.
Instagram: https://www.instagram.com/__PinkPig___/
A never ending camper/restoration project
Project 1 - Pop-top camper conversion 2011-2015
Project 2 - Campervan the sequel - 2016 restoration, welding, respray, new interior, vertical pop... |
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Deker
Joined: 08 Mar 2008
Posts: 3833
Location: Borehamwood
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| Posted: Sat Jan 09, 2021 21:31 Post subject: |
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| Fostlongstrider wrote: |
It's possible the battery internal resistance is low and this would also allow a higher alternator voltage to occur. |
Should that be battery internal resistance is high 
Mr D |
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Fostlongstrider
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| Posted: Thu Jan 14, 2021 12:14 Post subject: |
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If battery resistance is high voltage will be reduced!!
Could try measuring the current flow but that requires either disconnecting the battery to put an ammeter in series or a special clamp on ammeter that reads DC.
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Ian.
All the best from the East Riding of Yorkshire.
'93 L300 Super Exceed Corse Gray over Grace Silver.Auto.
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Deker
Joined: 08 Mar 2008
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Location: Borehamwood
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| Posted: Thu Jan 14, 2021 22:04 Post subject: |
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| Fostlongstrider wrote: |
1) If battery resistance is high voltage will be reduced!!
2) Could try measuring the current flow,
but that requires either disconnecting the battery to put an ammeter in series or a special clamp on ammeter that reads DC. |
1) Correct: If Battery resistance is High, engine not running, will show low volts.
However, with engine running, Alternator will "See" Low volts - Therefore the alternator will try to "make up" the difference. And "pump out" higher voltage.
2) clamp on ammeter that reads DC: I have two, one Analogue, one Digital.
HTH
Mr D |
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Fostlongstrider
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| Posted: Fri Jan 15, 2021 9:43 Post subject: |
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That's correct.
Shows what retirement and this lockdown does to the old grey matter.
Getting my V = IR mixed up.
Of course with engine running the alternator will try and compensate for low voltage using the reference voltage.
Could always connect a known good battery to the vehicle and check the voltage again.
If the voltage is still high there is something amiss with the alternator.
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Ian.
All the best from the East Riding of Yorkshire.
'93 L300 Super Exceed Corse Gray over Grace Silver.Auto.
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PinkPig
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Joined: 05 Aug 2004
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Location: Southampton, UK
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| Posted: Fri Jan 15, 2021 19:19 Post subject: |
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Hi,
Thanks guys.
I've got my spare alternator back, bench tested and working fine, and a couple of new batteries so will go out and play in the cold this weekend.
Will check the sense wire first is showing battery voltage. Apparently common for people to take in alternators to fix, then find nothing wrong.
Without the sense it will run at full voltage (about 15.8v on the spare alternator) as it is trying to charge a battery it sees as completely flat 0v.
I've had a very dodgy cables and connectors in the loom that have degraded over the years and needing replacing.
If the sense is okay then I'll try the new batteries and measure again (although I fully charged the one good old battery out of the pair and ran it up alone and it still showed 15.5+ volts)
Then if it is definitely a bad alternator...the knuckles will get scraped!
_________________
The PINK PIG!
1988 Delica L300 Star Wagon 2.5TD 5sp Manual.
Instagram: https://www.instagram.com/__PinkPig___/
A never ending camper/restoration project
Project 1 - Pop-top camper conversion 2011-2015
Project 2 - Campervan the sequel - 2016 restoration, welding, respray, new interior, vertical pop... |
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Deker
Joined: 08 Mar 2008
Posts: 3833
Location: Borehamwood
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| Posted: Fri Jan 15, 2021 20:39 Post subject: |
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Ian: Thanks for your reply on Fri Jan 15, 2021 9:43
Hopefully, our readers may glean and understand information from your posts
Wed Jan 06, 2021 - - - Thu Jan 14, 12:14
And my post Thu Jan 14, 2021 22:04
Unfortunately PP may not be equipped to carry out a current (Amps) reading from alternator to battery,
at his reading of 15.5+ volts.
To me, a current reading on the stated voltage, would help me to understanding what is occurring.
P.S. Your Grey matter is not as Grey/old as mine 
Mr D |
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PinkPig
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andyman
Joined: 08 Dec 2012
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Location: Penrith
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| Posted: Sat Jan 23, 2021 16:03 Post subject: |
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As long as you know that there is no likelihood of intermittent reconnection (ie can disconnect at one end), it may be simpler to just put in a whole new wire connecting where needed. Then tag it, so you know what it is next time you are in there!
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Andy C L300 Super Exceed - over 100 smiles per gallon! |
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Deker
Joined: 08 Mar 2008
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Location: Borehamwood
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| Posted: Sat Jan 23, 2021 18:46 Post subject: |
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| PinkPig wrote: |
A fused cable which is handily carrying 12v straight from the battery that I can tap into.
I seem to be replacing the loom piecemeal as well.
Time for a cuppa to study some wiring diagrams, then give up and bodge something... |
If you are tapping a wire to feed the Alternator -
Be sure that any 12v wire you tap into switches OFF with the IG. switch OFF.
Mr D |
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PinkPig
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Location: Southampton, UK
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PinkPig
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Location: Southampton, UK
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PinkPig
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Location: Southampton, UK
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PinkPig
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| Posted: Sun Jan 31, 2021 18:06 Post subject: |
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So, just to finish this thread off (it's been very cold and very wet so haven't had chance to get anything done).
Cut the Sense cable to take a voltage off it and there was nothing with ignition off and occasionally 0.1v with the engine running and me wiggling the loom. Still can find a break so must be the conector plug. So then introduced battery voltage into the cable and instantly the ~15.8v charge voltage dropped to around ~13.8v or there abouts.
Then it started raining again!
So just need to go back and make the temporary fix permanent, fused, tied into the loom etc.
Maybe next weekend, not like its going anywhere!
_________________
The PINK PIG!
1988 Delica L300 Star Wagon 2.5TD 5sp Manual.
Instagram: https://www.instagram.com/__PinkPig___/
A never ending camper/restoration project
Project 1 - Pop-top camper conversion 2011-2015
Project 2 - Campervan the sequel - 2016 restoration, welding, respray, new interior, vertical pop... |
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andyman
Joined: 08 Dec 2012
Posts: 5602
Location: Penrith
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| Posted: Sun Jan 31, 2021 20:09 Post subject: |
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At least you know where the problem is now. I'm slowly doing de-rusting, repairs and painting under the front end of mine while there's nothing else happening. Numb fingers from sub-zero temperatures limit the amount of time I spend under there before a hot cuppa and bad TV lure me away. But as you say, no rush.
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PinkPig
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Location: Southampton, UK
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Fostlongstrider
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| Posted: Tue Feb 02, 2021 12:24 Post subject: |
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Glad to hear you seem to have found the problem.
_________________
Ian.
All the best from the East Riding of Yorkshire.
'93 L300 Super Exceed Corse Gray over Grace Silver.Auto.
Flying Brick Supporter. |
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