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Alternator output voltage

 
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Porver9two4  



Joined: 23 Jan 2004
Posts: 100
Location: United Kingdom

PostPosted: Thu Dec 07, 2017 2:26 am    Post subject: Alternator output voltage Reply with quote

Does anyone know what the standard alternator output in Volts is for a 2.0 NA? I know the alternator is rated at 75 Amps and would assume it should be producing between 13 and 14.5V, but mine seems to be reading low....
At first I suspected the gauge, but having now had a meter on it I am only getting about 13.2V with no load and that drops to a measly 12.3 with the lights and blower on. I can't believe that is right and suspect I may have an issue brewing..... finding the issue may be more of a challenge though as the alternator appears to be working correctly, just producing low volts.
It has just had a new starter motor / alternator wiring loom as the old one was completely and utterly corroded to death, so I know that part of the wiring is sound.
Could it be an earthing issue? I can't recall where the main engine earth is off the top of my head....
The alternator is a Bosch 035903015M / 0120469551.
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nikobbell  



Joined: 29 Nov 2017
Posts: 13
Location: chicago, illinois

PostPosted: Thu Dec 07, 2017 6:34 am    Post subject: Reply with quote

not sure about standard output. I had the same problem and took the alternator out and had it tested. Major pain. It was fine. So I just ran another ground from the back of the alternator to a bolt on the shock tower and voila.. it's throwing 13.83 at idle. Around 132 with lights and blower on. The ground may be your problem. Check your belt too, may be slipping if it's old and worn. since I had it out i changed the rubber bushing that mounts the alternator to the block, the belt and the voltage regulator brushes on back of the alternator. hope it helps.
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staticsan  



Joined: 19 Jan 2009
Posts: 444
Location: Sydney, Australia

PostPosted: Sat Dec 09, 2017 12:45 pm    Post subject: Reply with quote

I've been down the road of alternator not charging. I feel your pain.

The main ground strap from the block to the body is over near the coil.

Standard voltage on original alternator is 13.5V or so. It should drop only under load and if it thinks the battery is charged.

However, 13.5V won't charge batteries with newer chemistry; they want 14.5V. I had four roadside servicemen point this out and two auto-electricians disagree until I bought and installed one of Ideola's alternators and all charging problems went away.

Wade.
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Porver9two4  



Joined: 23 Jan 2004
Posts: 100
Location: United Kingdom

PostPosted: Tue Dec 12, 2017 10:37 pm    Post subject: Reply with quote

Ahhhh..... interesting.
Maybe I will check my outputs again and double check the earths. If standard voltage is only 13.5V or so, I am probably not far off that and maybe there is nothing wrong with my alternator after all.
What alternator upgrade options are there? Any updated alternators off other brands / models that can be easily swapped on?
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staticsan  



Joined: 19 Jan 2009
Posts: 444
Location: Sydney, Australia

PostPosted: Fri Dec 22, 2017 8:10 pm    Post subject: Reply with quote

I bought this: http://garage.ideola.com/prod-ElectricsUpgrades.html#OEM

Wade.
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nikobbell  



Joined: 29 Nov 2017
Posts: 13
Location: chicago, illinois

PostPosted: Sun May 27, 2018 6:01 pm    Post subject: voltage Reply with quote

not my experience at all. 13.8 is more than enough to charge my brand new battery. 13.2 under heavy load. probably unlike most people here i drove the car every single day this chicago winter and it started every day without issue.
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musicalannette  



Joined: 21 Feb 2012
Posts: 412
Location: UK

PostPosted: Mon Jun 04, 2018 9:22 am    Post subject: alternator/starter harness Reply with quote

tbh a very weak point on he 924 is the starter/alternator wire.
admittedly an earth fault is also quite likely.
I would imagine on a charged battery that starts the car easily you should be getting around 13.7 volts or better.

there are quite a lot of earth connections for the gauges under the passenger dash of a rhd car. there an a couple of terminal connectors that are circular, the car gets condensation there if its outside and causes a contact resistance.

if the charge light is out measure voltage at the alternator not the battery.

the wires that runs from the alternator/starter runs VERY close to the exhaust and it is covered by a PTFE heat protected sleeve. At a bend he wires can melt inside or be aged and can either short or have increased resistance.

TBH it is the on piece that PORSCHE didn't and couldn't test as ageing and heat problems take many years to develop a fault most likely on a curve in the wiring at the back of the the engine or near the exhaust manifold where the wires bend . If it shorts inside the heashield the whole lot melts.

What is a good idea is to replace the wires with something that is really designed for withstanding heat. You want P.T.F.E covered wire for all the things inside the heatshield(that's made of P.T.F.E. thin wall tube).
Its not cheap but its the best available. More likely to be found in aerospace/space/defence. Especially if you like it in a desert or are miles from anywhere and a breakdown is to be avoided.
Hope it isn't that or your sake but it IS worth the weekend and multiple tens of pounds it will cost to replace it if you intend to keep the car. IT IS MORE LIKELY TO GO THAN THE ALTERNATOR although at this age car that could also be at fault.

It is the one place that I know of the Porsche 924 team knew there was a problem and skimped as they fitted a heatshield when they should have fitted better wire. But anticipating weathering and ageing and internal resistance and a heat build-up and a curve 30 or 40 years own the line and a 100 or 200 dollar increase in price tag maybe the sort of decision that had to be juggled. I would be interested to know if they fitted that type of wire to the LE Mans cars?

Hope this helps or a least makes you think and allows you to dodge a problem in your own time before I happens. The last thing you want is to fix it to have another fault appear . I don't know if Ideola does a PTFE harness? It would make sense if he did, It would be fit and forget.

I do remember the cars own gauge (voltmeter) earth being a problem when I first got t running and was highlighted when all the lights and heated rear window and blower were on. Make sure your checking the voltage with a handheld meter. if your wires are ok then your ether loading the alternator too much (taking too much power) in which case your alternator will get hot. Your loosing voltage down the wires and getting a voltage drop to he battery from the alternator (because the wires are too thin or corroded probably) or the field wire from the battery to the alternator could have a volts drop or the alternator itself be at fault. Either with windings, slip rings/brushes or a regulator. You might have belt slippage but you would probably hear that, just run the car max electrical load (lights on, heated screen on, blowe on etc and spray a bit of water at the belt with a household sprayer and see if it squeeks. I doubt it would be that but the tensioner can relax over time as I think its rubber bushed.
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