Alfa Romeo Forums banner

1 - 14 of 14 Posts

·
Registered
Joined
·
134 Posts
Discussion Starter #1
Hi All,

I've reviewed a number of alternator related threads but was not able to find when an alternator upgrade was performed on an S4 what exactly did people upgrade to in terms of alternator manufacture part number and was it stock swap, i.e. no mods required and if mods were required what was required.

Basically, my spider has the stock 65 amp alternator and I'm looking to upgrade to at least 85 amp but would prefer something around 100 amps.

Thanks in advance for any feedback.
Bob
 

·
Administrator
Joined
·
17,050 Posts
Why do you need 100 amps?

If everything is up to par the stock alternator should handle all normal electrical loads. If anything is not up to par (loose, corroded connections or for example), adding more amperage won't make up for the problems.
 

·
Registered
Joined
·
134 Posts
Discussion Starter #3
I've always read and have to say observed that the charging system is marginal. From everything I've read the alternator rating of 65 amps would be at max or near max alternator RPM. Assuming the designers designed it correctly this is probably at high engine RPMs. I don't run the car that hard so expect the alternator is producing something less than max, probably in the 30-40 amp range.

Well with A/C, fans, lights I suspect it is struggling to keep up as with each of these being switched on the voltage on the dash multimeter although inaccurate is showing relative decreases in voltage with each thing that is turned on which also implies system is struggling.

I understand that at idle the system probably cannot supply what is needed but at higher than idle, 2-3k rpm although better it still appears to be marginal.

This in conjunction with upgraded headlights, going to Halogen H4 bulbs, I suspect the current load will be higher than the current sealed beams that are currently installed on the car.

Bob
 

·
Registered
Joined
·
820 Posts
I've always read and have to say observed that the charging system is marginal. From everything I've read the alternator rating of 65 amps would be at max or near max alternator RPM. Assuming the designers designed it correctly this is probably at high engine RPMs. I don't run the car that hard so expect the alternator is producing something less than max, probably in the 30-40 amp range.

Well with A/C, fans, lights I suspect it is struggling to keep up as with each of these being switched on the voltage on the dash multimeter although inaccurate is showing relative decreases in voltage with each thing that is turned on which also implies system is struggling.

I understand that at idle the system probably cannot supply what is needed but at higher than idle, 2-3k rpm although better it still appears to be marginal.

This in conjunction with upgraded headlights, going to Halogen H4 bulbs, I suspect the current load will be higher than the current sealed beams that are currently installed on the car.

Bob
there are a lot of " i suppose " and " i guess" and "maybe if's " in your theory. i would simply suggest that since it is not a " known issue " after 20 years that it is more than likely not an issue at all and second, if you want the answer, just hook up a volt meter to it and turn everything on and see if it drops to less than 13 volts at max load at anything above idle and if so, which revs. if its 12.2 at idle, thats all thats necessary. anything above idle would mean its more than adequate.
 

·
Premium Member
Joined
·
14,028 Posts
From everything I've read the alternator rating of 65 amps would be at max or near max alternator RPM.
The rpm vs Current curve is not linear. Your alternator spins at higher rpm than your engine because it has a smaller pulley. Typically you will have about 80% of full output current when the engine is at 2000 rpm and almost 100% at 3000 rpm.

If your total lighting load is 180 watts that is only 15 amps. Everything else uses less current. Plus you have a lot of battery capacity to handle peaks, like when you use your turn signals. 65 amps should be fine unless you have a 500 watt stereo running at 100%.
 

·
But Mad North-Northwest
Joined
·
10,528 Posts
Yeah, my S4 seems to have trouble keeping up electrically when a lot of stuff is turned on. I've done quite a bit of troubleshooting with a multimeter, and at least on my car there seems to be quite a bit of voltage drop in the ignition switch. That is, the switch itself: all the other wiring people point to (wire from alt to junction box, for example) was fine.

It's annoying but not enough for me to have done something about it. Given that voltage drop may be the problem, it's unclear to me whether a bigger alternator would help too much or whether there would be more benefit from an ignition relay or something.

If you do try a bigger alternator, report back with your findings.
 

·
Super Moderator
Joined
·
10,623 Posts
65 watts should be fine unless you have a 500 watt stereo running at 100%.
Gubi said:
Given that voltage drop may be the problem, it's unclear to me whether a bigger alternator would help too much or whether there would be more benefit from an ignition relay or something.
Those two quotes summarize my thinking pretty well. It would be nice if alfarobert could solve his problem by just installing a bigger alternator, but I too am skeptical that will accomplish much. Voltage drop, rather than insufficient current, is probably the issue.

I play with 70's era BMW's, as well as Alfas - there is a lot of commonality in how they are built and the components they use. But one thing that BMW did differently was to install a "load shedding relay"; this heavy-duty relay is turned on by the ignition switch, and handles all the heavy-current loads. Adding something like this to an Alfa might be a better solution to the problem of voltage drop across old/oxidized components.
 

·
Premium Member
Joined
·
14,028 Posts
Adding something like this to an Alfa might be a better solution to the problem of voltage drop across old/oxidized components.
It also reduces the probability that a family member will flatten the battery by leaving the heater blower or turn signals on.
 

·
Registered
Joined
·
372 Posts
Hi All,

I've reviewed a number of alternator related threads but was not able to find when an alternator upgrade was performed on an S4 what exactly did people upgrade to in terms of alternator manufacture part number and was it stock swap, i.e. no mods required and if mods were required what was required.

Basically, my spider has the stock 65 amp alternator and I'm looking to upgrade to at least 85 amp but would prefer something around 100 amps.

Thanks in advance for any feedback.
Bob
When my alt started squealing at high rpms last week (dry bearing), I swapped my 55amp S3 alt for a rebuilt from BNR who has an Ebay store. It came with a pulley and fan attached and was rebuilt to make 80 amps. It bolted on and whether I "needed" it or not, it was delivered in two days and looks to be rebuilt well. My battery/alt lamp glows noticeably less at idle with my electric fan, wipers, high beams, radio, AC and heater fans going and not at all above idle.
It was $160 shipped and has a 1 yr exchange warranty compared to $230 plus shipping for a 55 amp with 6 months warranty from the Alfa supplier I usually try to support.
FWIW
 

·
Super Moderator
Joined
·
10,623 Posts
When my alt started squealing at high rpms last week (dry bearing), I swapped my 55amp S3 alt for a rebuilt from BNR
Glad to hear that the new alternator solved your problem. But keep in mind that your issue was a squealing bearing and perhaps a failure to charge at low RPM's, not insufficient maximum capacity. BNR's prices are so low that an alternator with a capacity of 80 amps costs about the same as one that maxes out at 55 amps. But that isn't to say that you will ever use those extra 25 amps.
 

·
But Mad North-Northwest
Joined
·
10,528 Posts
Note that they went to a larger alternator on the S4: per the service manual it's 70A. One would think that would be sufficient, but Mongo dunno.
 

·
Registered
Joined
·
372 Posts
Glad to hear that the new alternator solved your problem. But keep in mind that your issue was a squealing bearing and perhaps a failure to charge at low RPM's, not insufficient maximum capacity. BNR's prices are so low that an alternator with a capacity of 80 amps costs about the same as one that maxes out at 55 amps. But that isn't to say that you will ever use those extra 25 amps.
Thanks,

I agree, and that bearing was the reason I replaced it, but given no real downside to the extra capacity, and the lower cost, and easier install with the pulley included, and the fast shipping, ... it was a no-brainer.

The 55 amp'er never let me down, even after the electric fan conversion. I don't know how close to system max output it was running--closer than now. The annoying light glow is common and that going away was icing on the cake.
 

·
Registered
Joined
·
549 Posts
Here, this is 70 amps - its also on amazon prime for $72. I went with this one as the BMW alternators do not fit on the alfa without major modifications.


Quality-Built 14395 Premium Alternator - Remanufactured

http://www.amazon.com/gp/product/B000ES8L40/ref=oh_aui_search_detailpage?ie=UTF8&psc=1


The real issue is having heavy electrics on the S2 style externally regulated alternator - which is what I had. That alt puts out only 30 watts and can't even keep up with an aftermarket stereo (with no external amp) at full volume.
 

·
Registered
Joined
·
3,724 Posts
I think the stock alternators have enough amps, if yours is dropping volts just test for drops. It's a 20 year old alternator, maybe it just needs a rebuild.
 
1 - 14 of 14 Posts
Top