Alternator upgrade AC11 to modern A127 type

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PeterZRH

Well-Known Member
Hi folks, anyone want to check my process for swapping these? The newer type have internal regulation (no more relays) and better output at low speeds.

Disclaimer: Use this at your own risk. If your car explodes/catches fire that's your problem not mine.

ISOLATE THE BATTERY

1. Isolate the alternator relay control circuit at the 6RA relay:
Disconnect and make safe the brown wire to C1 from +12V permanent
Disconnect and make safe the white wire to W1 from +12V ignition

2. Disconnect the field control from the 11AC
Disconnect the brown/purple field + control wire
Disconnect the brown/green - control wire

3. Physically replace the 11AC with the A127.
Disconnect the brown +12V battery wire
Disconnect the brown/yellow indicator light wire.
SWAP THE ALTERNATOR
Reconnect the +12V connection
Reconnect the brown/yellow wire that was to AL to the IND terminal

4. Bridge the 3AW Ignition Light relay.
Connect the yellow wire to the brown/yellow wire (inline spade connector should do it).

RECONNECT THE BATTERY
3500-series-1-wiring-alternator-swap.jpg
 
In this vein, is it correct that an 18ACR can be replaced by an A127 without any wiring changes? Except maybe a large output wire on the B+ post?
thanks
 
Further info.

You need:

1. This type of connector - a Lucas/Bosch "B" alternator block 1697627007525.png1697627025048.png

2. The retainer clip! 1697627498966.png

3. The correct wiring. The two big terminals are in fact one and the same output. You can use the existing wiring for one side. I would recommended 2 runs of 8-guage AWG wire. If you look at real world implementations then these are often surprisingly thin - look to be 12 gauge on GM trucks for example! This is because maximum output over short wires is usually OK to be in excess of the rating for short periods of time. In reality your alternator will almost never kick out much more than half its rated output. Most of the time it'll be no more than 10-20amps. When you do your own work I'd recommend you adopt the highest, safest standards as good or better than OEM. Remember wire ratings for a certain gauge are often for a single, copper conductor, not the multi-core flexible type you will be using, which will be less. You can run the second wire to the large terminal on the starter or the terminal block on the floor of some cars, or the shunt on cars with an ammeter - for that you'll need a 1/2" spade which can be tricky to get. the Ring type connectors are easy to find something that will work but obviously make sure the size allows enough transfer contact. Silicone insulate wire is desirable over PVC as it handles heat better. Not essential though.
 
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My alternator is wired to the post of the floor. I glued some insulation around the post to provide a little additional protection from accidental short circuit.

1697627716347.png
 
I made a little "pigtail" on the small connector in the large terminal block so I could attach the original wire to the 3AW without cutting anything....
In fact in all this change, no original wire of connector was cut. This is 100% reversible should anyone yearn for a crappy charging circuit!

1697628244748.png
 
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I isolated the original 11Ac wiring with heat shrink and these are safely tied bac. I chose not to use the original power cable. The thinking for this was that I could use it for an electric power steering pump (it doesn't fit the V8)

1697628342856.png
 
I’ve just completed my switch-over from the 11AC to the A127 and used Peter’s guide for the wiring.
However, Although I now have a good 14.75DC coming out of the alternator, and no warning lamp on at the dash anymore, my Ameter still reds just below centre with everything off, and deflects significantly when I start switching on lights, heater etc. Have I missed something? Should there be a -ve connection or he like at the new alternator as I just used the Lucas plug for the power and lamp as per the guide here…..
looking at my wiring diagram the original 11AC has its heavy brown/white lead at B+ going directly to the Ameter shunt. Even with the Lucas connector used to provide new charging route to the battery via the floor post, surely that B+ connection is best left connected so that the Ameter has an accurate current rate?
 
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Make sure the warning light is connected the bulb hasn’t blown. If either of those are the case the alternator won’t charge.

You mention a measured voltage but nothing on the ammeter? Where are you reading the 14.75v?
 
sdibbers said:
Make sure the warning light is connected the bulb hasn’t blown. If either of those are the case the alternator won’t charge.

You mention a measured voltage but nothing on the ammeter? Where are you reading the 14.75v?
Click to expand...
I may have confused things with how I wrote that…..
so problem started when my ignition switch just flew apart behind the dash. Starter was just racing along and took me a moment to fiddle the key to get it to stop. Replaced the switch and from then on the Alternator was duff and of course ignition lamp on.
replaced the alternator with the A127 type so now have just under 15v coming out of the alternator.
BUT - where before all this my Ameter needle would sit nicely right in the middle of the gauge, now it’s slightly to the -ve. Then even with the car running as I put a load on the electrics I get a marked current drain at the meter. Still no dash lamp on……
 
Roy’snow50+ said:
I may have confused things with how I wrote that…..
so problem started when my ignition switch just flew apart behind the dash. Starter was just racing along and took me a moment to fiddle the key to get it to stop. Replaced the switch and from then on the Alternator was duff and of course ignition lamp on.
replaced the alternator with the A127 type so now have just under 15v coming out of the alternator.
BUT - where before all this my Ameter needle would sit nicely right in the middle of the gauge, now it’s slightly to the -ve. Then even with the car running as I put a load on the electrics I get a marked current drain at the meter. Still no dash lamp on……
Click to expand...
Yep, that's odd. The output of the alternator should be going straight to the battery. I mean the 14.7v isn't a bad thing, that's the output of a healthy alternator.

Is the Ign light on when you turn on the ignition but don't start the car? Also, if you measure across the terminals on the battery with the engine running do you see 14.7v? If so, the charging circuit is acting as it should. It might just be a fault in the ammeter. If, however, the voltage to the battery is staying at a nominal 12v when the engine is at idle. Then its a charging system fault. That could be the alternator, or the ignition switch or something else that hasn't occurred to me yet!
 
sdibbers said:
Yep, that's odd. The output of the alternator should be going straight to the battery. I mean the 14.7v isn't a bad thing, that's the output of a healthy alternator.

Is the Ign light on when you turn on the ignition but don't start the car? Also, if you measure across the terminals on the battery with the engine running do you see 14.7v? If so, the charging circuit is acting as it should. It might just be a fault in the ammeter. If, however, the voltage to the battery is staying at a nominal 12v when the engine is at idle. Then its a charging system fault. That could be the alternator, or the ignition switch or something else that hasn't occurred to me yet!
Click to expand...
Thanks so much for this. I’ll run a few more tests with the meter and drop an update back. Just weird that this little catalogue of faults all started when the ignition lock fell apart. I suspected that in doing so it caused some sort of short that damaged the alternator diodes inside the old 11AC, but now wondering like you say if it could have caused damage elsewhere.
 
Roy’snow50+ said:
Thanks so much for this. I’ll run a few more tests with the meter and drop an update back. Just weird that this little catalogue of faults all started when the ignition lock fell apart. I suspected that in doing so it caused some sort of short that damaged the alternator diodes inside the old 11AC, but now wondering like you say if it could have caused damage elsewhere.
Click to expand...
It could well have. Unfortunately, it takes time to trace these things. I had an AC11 fail on my car a few years ago. It would extinguish the ign light when you started the car, output voltage for the first half hour of driving then a no charging with no warning light. It was fun losing lights, ignition and everything else on the Garden State Parkway in the gloming!
 
If you don't use the orignal alternator output wiring, the ammeter won't register the current from the alternator, but will still register the draw. Mine's the same after following this guide, although I took my feed to the post on the starter motor rather than the post on the floor.

I figured with a 100A alternator, I didn't have to keep my eye on the ammeter to make sure I'm not draining the battery!
 
Baron von Marlon said:
If you don't use the orignal alternator output wiring, the ammeter won't register the current from the alternator, but will still register the draw. Mine's the same after following this guide, although I took my feed to the post on the starter motor rather than the post on the floor.

I figured with a 100A alternator, I didn't have to keep my eye on the ammeter to make sure I'm not draining the battery!
Click to expand...
My car was an S1 so originally didn't have an ammeter. However I fitted the round dial dash because I like it better. I have designed and made a hall effect current sensor based driver for the ammeter. This functions exactly like a clamp meter and requires no cable to be cut - just wrap it around the battery cable. It removes the risk of either the shunt failing or starting a fire. It's actually rated at +/-100amps so could be callibrated for your situation:

www.poweruc.pl

Split core current sensor HSTS21 Rated input ±50A ±100A ±200A ±300A ±400A ±500A ±600A Rated output 2.5V±0.625V

Model：HSTS21 Open loop split core type,Sub-plate mounting type. Detect DC,AC and pulse current. Technical index: Flame resistance：UL94-V0 Operating temperature：-10～+70℃ Storage temperature：-25～+70℃ Bandwidth：DC～25kHz Dielectric strength：2.5KV 50Hz 1min Electric parameters: DOWNLOAD
www.poweruc.pl

1750017164460.png
 
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