Author Topic: Alternator questions  (Read 2518 times)

roymil

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Alternator questions
« on: September 22, 2023, 02:23:10 »
Hello, I had purchased a Bosch AL69X some months ago and just today was preparing it to install it and had some questions about the differences in wiring this new internally regulated alternator with the original wiring harness in my original W113-280SL.   

I was wondering if I just need to jumper the D+ from the old harness to the AL69X and if its ok to just disconnect and float the DF & D- lines to the old external regulator which wont be needed now.   I want to keep it installed for originality but have had bad luck with these old regulators failing.  The B+ connection is obvious but not sure if it would be good to also run a parallel heavy ground cable to the battery, or nearby chassis bolt as well.

Your posting today is strangely perfect for me on the same day I go looking for answers, describing what sounds like a good solution for my situation but I didn't see this sub-harness on your new website. 

I'd like to find out more about it.   I had already replaced the wiring from my battery to starter and up to the original alternator but that was with the 35A system in mind.  Now I need the 80A from the AL69X to power my auxiliary cooling fan and also my electric oil pump which could together draw 30+ amps when both run together, as is very possible in hot conditions...which of course is even worse for the copper wire since it becomes more resistive at high temps.  So I am very concerned about having heavy enough copper lines from the alternator over to the battery and the junction for these new accessories which lives near the battery.

I'd appreciate any advice and more info about your sub-harness, cost, time to deliver, etc.   Thank you for providing your knowledge and services to SL113.

Best, Mark
Mark Miller
1968 280SL
Rode in his pagoda's first mile.

rwmastel

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Re: Electrical gremlins
« Reply #1 on: September 22, 2023, 02:34:57 »
Mark,
Can you copy/paste this post into a new thread in the electrical forum?  This is the commercial advertising forum where Leo is promoting his website, not really meant for a diagnosis or troubleshooting discussion.  Thanks!
Rodd

Did you search the forum before asking?
2017 C43 AMG
2006 Wrangler Rubicon
1966 230SL auto "Italian"

Peter van Es

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Re: Alternator questions
« Reply #2 on: September 22, 2023, 08:14:37 »
Done...
1970 280SL. System Admin of the site. Please do not mail or PM me questions on Pagoda's... I'm not likely to know the answer.  Please post on the forum instead!

lpeterssen

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Re: Alternator questions
« Reply #3 on: September 22, 2023, 13:55:34 »
Dear Mark Miller

Excellent question, and I am glad to help.

You have to connect to the AL69X internally regulated alternator the large thick cable “Bat+” to the large screw and nut post on the back of it.

Leave, as you indicate on your post, the “D-“ brown cable and the “DF” black cable disconnected from: a) the alternator and, b) original external voltage regulator.

Connect the THIN  “D+” cable which is RED/blue to the small charge light port on the back of NEW ALTERNATOR.

Important notice
==========

Your new alternator has larger capacity than original pagoda alternator. That is 80A vs. 35A.  THEREFORE…..
YOU HAVE TO INCREASE the section of the cables coming out of the ALTERNATOR with 80A.

My quick fix suggestion and correct from technical point of view is to:


1. Buy about 6 feet of new marine grade cable in size AWG-8 (has 10 mm2 section). RED
2. RUN a new T30 cable with above section from the alternator to the JUNCTION BOX that is in the right fender lower part.  This 10mm2 section cable will run in parallel to original harness to increase capacity in 50A.
3. REPLACE original harness section from JUNCTION BOX to STARTER.  In that way the excess energy produced by this alternator will go straight to T30 (bat+) terminal at starter, and from that point energy will travel directly to BATERY.

DOING what suggested above will give you peace of mind a that harness will not fry with new alternator capacity.

Best regards
Leonardo Peterssen
« Last Edit: September 22, 2023, 14:50:14 by lpeterssen »

roymil

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Re: Alternator questions
« Reply #4 on: September 22, 2023, 17:42:58 »
Thanks Leonardo,
This all makes sense except I don't seem to have any junction box on my right lower fender.   It appears the B+ wire goes directly from the alternator all the way back to under the dash, I assume to the headlight and ignition switches.   I do have the small two terminal block attached to the edge of the oil pan in which one larger terminal ties the heavy wire from the starter to another heavy wire up to the alternator.  These are the two new 8AWG wires I had already replaced a while ago when I thought I was only dealing with 35A max system.   Now with the AL69X, I am thinking they are insufficient to move 80A, especially when hot.  My AWG charts show 8 gauge is only suitable to 65 amps at room temp, and I want to be conservative here.   The other, smaller terminal by the oil pan is for the starter solenoid activation wire so no change needed on it.

So, to address your point , I will figure out how to run an additional parallel 8AWG red wire all the way back to the underdash termination points as well as add additional 8AWG wires in parallel from the alternator down to the oil pan terminal and back over to the starter solenoid.  From there back to the battery seems fine with the very large cable.

Also, I noticed that the new alternator case has minimal contact area for grounding with the way it mounts, looser than the old original alternator, so I am also considering adding a heavier ground strap from one of the AL69X rear case screws which has enough exposed threads for a terminal lug and routing that to the nearest designated exposed chassis ground, I think there's one under the intake manifold may be good.  This should reduce any ground voltage drops to the battery in the highest current scenarios.

appreciate any feedback and thanks for your help!   -Mark
Mark Miller
1968 280SL
Rode in his pagoda's first mile.

lpeterssen

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Re: Alternator questions
« Reply #5 on: September 22, 2023, 19:05:59 »
Exactly

That small terminal block on the oil pan side is the junction box I was referring to.

Run that additional cable I suggest from
Your new alternator to that terminal block. And from
There also run a new cable awg 8 to your starter BAT+ post

Best regards
Lp

lpeterssen

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Re: Alternator questions
« Reply #6 on: September 22, 2023, 19:12:41 »
Dear Mark

To run a new cable from
The alternator to the main light switch is a good idea, because the original one should be compromised due to cracked insulation. 

The energy consumption in that segment is not higher if your car is still original. So you will change it only because wear of its external jacket.   AWG10 is enough for that. (Section 5mm2)

Best regards
Leonardo Peterssen

lpeterssen

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Re: Alternator questions
« Reply #7 on: September 23, 2023, 21:30:28 »
Here attached an interesting capacity chart which correlates distances to the max current capacity a wire can have

Best regards
Lp

lpeterssen

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Re: Alternator questions
« Reply #8 on: September 23, 2023, 21:32:40 »
Sorry internet connection is terrible today

Will upload file tomorrow

lpeterssen

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Re: Alternator questions
« Reply #9 on: September 24, 2023, 15:11:47 »
Here the table I promised yesterday

roymil

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Re: Alternator questions
« Reply #10 on: September 25, 2023, 02:12:56 »
thanks for the chart.  I think that just confirms again the need for greater than 8AWG for the larger alternator.   Good point about not necessarily needing more copper back to the dash light switch but I will inspect those wires to be sure the insulation is OK.   I'm actually reducing the current in that line by setting up relays near the lights to reduce voltage drops and get them a bit brighter.  I'll be routing direct from alternator for those and so the dash switch will carry much smaller current now.
Mark Miller
1968 280SL
Rode in his pagoda's first mile.

lpeterssen

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Re: Alternator questions
« Reply #11 on: September 25, 2023, 10:10:31 »
Dear Mark

You mentioned something interesting.  Dimmed headlights.  That is caused always, in my experience, by defective ground post.  Do not add those relays to the headlights, they are not necessary.  Check first the quality of the ground going to each headlight.  Those take ground next to the radiator lower mounts on each side.  Disconnect ground and sand surface, polish terminals, add some carbon conductive grease on them.

If your car has been painted many times, those grounding points are not doing correctly it’s function.

Best regards
L.peterssen