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 Post subject: Uprated Alternator
PostPosted: Tue Jun 30, 2020 10:21 am 
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Joined: Sat Feb 18, 2012 11:43 am
Posts: 93
Location: Shaftesbury
Hi All

In my 1500 when I am running with main beam on and overdrive engaged shows its charging at 13.4v (I have a digital volt meter fitted to), Overdrive disengaged it goes up to 13.5V.

When running without lights on it shows 14.1V

If I uprated the alternator to a 65amp one for example would this increase the rate of charge when running with lights etc on to be a more stable 14 plus volts?

Just wondering if it worth doing. Battery never seems to discharge.

Cheers

Nigel

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Track day Sprint for track fun....
1500TC for summer everyday use....
VW Touran for winter and family everyday use...


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 Post subject: Re: Uprated Alternator
PostPosted: Tue Jun 30, 2020 12:21 pm 
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Joined: Mon Nov 07, 2011 9:57 am
Posts: 652
Location: Dorset
Possibly. Have you tried measuring diectly at the alternator between the housing and the output? If it's noticably higher there you might have some dodgy connections/cables/grounds causing some drop.


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 Post subject: Re: Uprated Alternator
PostPosted: Tue Jun 30, 2020 1:07 pm 
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TDC Cheshire Area Organiser

Joined: Wed May 17, 2017 5:28 pm
Posts: 1057
Location: NANTWICH.
Hi Nigel, if it ain't broke, don't fix it!! If you are not having problems i would leave well alone as some of these new alternator's are not that good.

Tony.

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 Post subject: Re: Uprated Alternator
PostPosted: Tue Jun 30, 2020 3:59 pm 
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Joined: Tue Oct 15, 2019 8:00 pm
Posts: 129
I agree with Tony, if it ain't broke don't fix it. Depending on where your voltmeter is wired in you are more than likely seeing the effects of volts drop along cables and across less than perfect wiring connections. If that is the case then fitting a higher output capability alternator will do nothing to cure it.

Not sure what alternator you have fitted currently (pun intended :) ) but if it is the standard 17ACR which I think outputs around 36amps then

full beam headlights 20 amps (maximum of 4 x 60W = 240W or approx 20 amps)
sidelights 3 amps (6 x 5W = 30W or approx 3 amps)
Ignition 4 amps
O/Drive Solenoid 1 amp (maybe a little more)

Total 28 amps

Still leaves 8 amps headroom. Not a lot, but unless you do loads of driving in the dark and wet (rain = wipers & blower) and/or also do loads of very short journeys with lots of stops and starts, then that should be plenty even allowing for recharging the battery after starting the car. (Assume starter takes 400A for 10 seconds = 1.1A/H from the battery, so battery needs about 1.5A charging for an hour, in reality it gets 10's of amps for the first few seconds after the car has started so most is recovered fairly quickly and the rest trickles in on the journey.)

It is only necessary to fit a larger alternator when you start fitting power hungry accessories. A common one is an electric fan - these can easily "pull" in excess of 20 amps - but they don't usually run all the time, so again depending on how you use the care an standard alternator can cope. My Landy 110 2.5 Turbo Diesel has its original 45 amp alternator and it is fitted with twin kenlowes and I tow a large trailer at night - never had an issue with a flat battery - and it kills them on starting needing glowplugs for 15 seconds before starting at 80A and massive starting current.

One last point when fitting higher output alternators to old cars - the original design and wiring, terminals and connections was for a 36 amps alternator. Simply swapping for one with nearly twice the output risks putting excess current down "tired" wiring that wasn't designed to cope when new let alone when it is a bit tired, result - at best warmer wiring! So if you do swap for a higher output alternator you should carry out a thorough check of the wiring.

Roger

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1975 Sprint Man O/D in Honeysuckle Yellow
1971 Stag Auto White

Too many cars, too little time!


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 Post subject: Re: Uprated Alternator
PostPosted: Tue Jun 30, 2020 7:02 pm 
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Joined: Tue Sep 19, 2006 4:50 pm
Posts: 2245
I fitted these on my Dolomite and Spitfire when I needed to replace them; https://www.ebay.co.uk/itm/172388880931

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 Post subject: Re: Uprated Alternator
PostPosted: Wed Jul 01, 2020 10:37 am 
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TDC Member

Joined: Sat Feb 18, 2012 11:43 am
Posts: 93
Location: Shaftesbury
Thanks All

I agree I think I will leave well alone for now, works ok with no battery discharge.

I run back from work on late shift, it’s about a 30 min drive mostly on full beam... (Dorset Darkness!)... and battery always shows 12.4v in in the morning.

As always this forum always provides excellent advice :D

_________________
Track day Sprint for track fun....
1500TC for summer everyday use....
VW Touran for winter and family everyday use...


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 Post subject: Re: Uprated Alternator
PostPosted: Wed Jul 01, 2020 12:23 pm 
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Joined: Tue Oct 15, 2019 8:00 pm
Posts: 129
Quote:
Thanks All

I agree I think I will leave well alone for now, works ok with no battery discharge.

I run back from work on late shift, it’s about a 30 min drive mostly on full beam... (Dorset Darkness!)... and battery always shows 12.4v in in the morning.

As always this forum always provides excellent advice :D
Sounds ideal to me !!

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1975 Sprint Man O/D in Honeysuckle Yellow
1971 Stag Auto White

Too many cars, too little time!


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