Uprated alternator

#1
Hi, my alternator is playing up, not charging at low revs etc, I now have an uprated one to fit ( 65 amps) question is can i just fit this one without doing any damage to the car.
any advise would be great , regards Steve.
 

GRTV8

Well-Known Member
#2
My alt was doing the same .The unit was actually a very good one. Talking to an auto sparky about alternative alternators ,he suggested I get mine refurbished.
Cost less than a new one [often Chinese ] and uprated too.
 
#3
if it's a straight swap eg bolts /connections then fitting higher rated alternator isn't an issue as it will only output power as needed to battery and system as needed. much like any other alternator in fact. They all have built in current and voltage controllers. so you can get alternators with different ratings. issue only being if if alternator connections are different and we are using more than standard power drain? eg adding in other things on wiring circuits so we need to update wiring and fuses .eg high energy spotlights combined with moonbeam lights..
 
#4
Thanks to both, my present alternator is a standard 18 acr, it has been to a auto electrician who checked it out and said it was fine. but when put back on the car would only charge with the engine running at about 1000 revs, any thing less and it was very hit and miss, ( any lights etc on and its a waste of time)
The replacement has exactly the same fittings and plug, so i will swap it over at the weekend.

Many thanks Steve.
 

PeterZRH

Well-Known Member
#5
I did this and wrote it up. It depends on whether you have an 11AC or later ACR type. The 11AC will obviously be wired differently and the 12v output will likely need to be doubled up to get to the terminal post on the floor. You can do this directly or route a second feed via the starter motor. The connector block on later models has 2 wires making this easy.
 

SydneyRoverP6B

Well-Known Member
Staff member
#6
Hi, my alternator is playing up, not charging at low revs etc, I now have an uprated one to fit ( 65 amps) question is can i just fit this one without doing any damage to the car.
any advise would be great , regards Steve.
Hi Steve,

With no lights etc on, your ammeter should be over the null position at idle, say 600rpm. With lights on, there will be a discharge registering, which is normal for the 18ACR.

Ron.
 

roverp480

Active Member
#7
Fitting a higher rated alternator wont necessarily alter its output much at lower revs. as it will be only spinning at the same speed as the one removed . Your 18ACR would appear to be working correctly .
 
#8
I had the same problem with my car, it turned out that it had been fitted with an alternator from a Ford, which had a larger pulley, meaning that it wasn't spinnng as quickly.
 

PeterZRH

Well-Known Member
#9
Fitting a higher rated alternator wont necessarily alter its output much at lower revs. as it will be only spinning at the same speed as the one removed . Your 18ACR would appear to be working correctly .
Modern ones tend to be better at low speeds as they used different power diodes with a low forward voltage drop.
 

colnerov

Well-Known Member
#10
I had the same problem with my car, it turned out that it had been fitted with an alternator from a Ford, which had a larger pulley, meaning that it wasn't spinnng as quickly.
Hi, Yes with the advent of the Ford XR3i people were chasing them around at high revs, because they could, and they were getting subsequent alternator problems. The solution was larger pulleys to bring down the alternator speeds down.

Colin
 
#11
Now fitted, simple plug and play, car happily ticking over at 600 rpm, lights on, heater fan running, well pleased with that, but only time will tell I suppose.
 

roverp480

Active Member
#13
Sounds good, understand how less voltage drop on modern diodes could make a big difference, presume that's why early alternators were battery sensed
 
#14
Not sure of the make or model, but did a few checks this morning, when running its charging the battery at 14.5 volts, the ignition light stays off at normal idle speed, coil is nice and cool, but not happy as to how hot the alternator is getting, i know it is producing electric power etc , question is should they get hot to the touch??
 

SydneyRoverP6B

Well-Known Member
Staff member
#15
Not sure of the make or model, but did a few checks this morning, when running its charging the battery at 14.5 volts, the ignition light stays off at normal idle speed, coil is nice and cool, but not happy as to how hot the alternator is getting, i know it is producing electric power etc , question is should they get hot to the touch??
I was thinking that it may have been an uprated 18ACR rather than a replacement. The alternator will always become hot with use, and certainly touching it will be a brief affair. Always remember that you never get something for nothing, there is always a price to pay. Your new alternator has the ability to deliver more current than the original 18ACR. This is particularly obvious at low rpm when you have accessories switched on and there is no discharge showing on the ammeter. With a greater current delivery capability at low rpm, there will be more heat generated. The alternator does not deliver more current that what is required, so as a hypothetical example, if all your accessories draw 42 amps of current from the battery, the alternator will return 42 amps back to the battery. The primary difference is that your replacement can deliver more current at lower rpm, and that should help to improve the life of your battery. You could also fit additional accessories if you wished thereby taking the total current required beyond what your the 18ACR is capable of delivering, but provided that total requirement is less than what your replacement alternator can manage, you won't have any issues.

Ron.
 
#16
Ron, many many thanks for that comprehensive answer, I am very pleased with the performance of the alternator, my concern was how hot it was getting, I had never given it a thought on previous cars, it was only because I touched this one by accident that I noticed the heat.
No name on this one, its more compact than the original and has a smaller pulley.
Regard Steve.
 

jp928

Active Member
#17
Porsche 928s have a 2.5" air duct from the wheel arch (behind a shield) feeding a shroud on the alternator to cool it. There is a bend in the duct to prevent water being inducted. If you have a modern car with an OBD-II connector, its instructive to display volts and watch the value change - on my Subaru I see 14.7V at startup, gradually dropping back to 14.1-14.3V when the battery is full. I wouldnt worry about 14.5V , unless it stayed there for longer periods.

Black hose goes under the 'chassis' rail into engine bay to special cover on rear of alternator.
 
#18
New pulley is probably the reason its now charging at idle. You should check that the new pulley is still in alignment with the others so your fanbelt isn't bending. Auto sparkies are notorious for forgetting to check belt alignment when they replace alternators.
M
 
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