Alternator upgrade - done! (6 Viewers)

[FrazzledHunter]

I upgraded the factory alternator to a higher amperage unit to support, among other things we want to do, charging a travel trailer under tow.

In another thread titled "Trailer Power" https://forum.ih8mud.com/threads/trailer-power.1317688/ we were talking about powering a travel trailer from the tow vehicle. Among other topics discussed were upgrading the alternator and I said I was going to attempt it. I said I’d post when I got the HD alternator installed.

Well it’s installed and it appears to be working fine. Voltages are a textbook 14V at cold (45F) startup and 13.6V when warmed up. These are the EXACT voltages I observed with the OEM alternator under the same conditions. Yes, I checked the day before!!! The plan is to run with it for a while before our trip in February and update the wiring and add the additional loads when we get back assuming no issues.

The unit went in almost flawlessly but had to have a minor mod which I’ll discuss below.

First off, the guys at M2K were great throughout the whole process of teaching me the ins and outs of alternators to come to the proper decisions for the installation. They worked very hard educating a clueless consumer.

>>>EDIT: M2K is the company behind the name on the alternator "Smart Battery Charger" https://m2kinc.com/

Just as helpful were the techs at No Limit of Baltimore who did the alternator install. VERY FEW shops would have undertaken the job at all much less go the extra mile to mod the alternator to finish the installation. My hat is really off to them and they have really won my respect; they do it all there.
No Limit BMORE - https://www.nolimitbmore.com/

The alternator unit is a M2K 390A made in USA from DENSO parts:
390 Amp - Toyota 3UR-FE (LIN) | SBC - https://smartbatterycharger.net/product/390-amp-toyota-3ur-fe-lin/

Based on discussions with the manufacturer about engine RPM’s at engine idle and our needs it was determined that to get the best performance a 2” diameter pulley should be used instead of the 2.5” regular pulley. This obviously gives more amps at lower RPM's.

A pulley of smaller diameter necessitates a serpentine belt that is just a bit shorter than OEM. The OEM belt length is 2410mm and the one used for the install was 12mm shorter. I’m a fan of Gates belts so I used Gates K080944.
GATES GLOBAL ONLINE CATALOGUE - https://navigates.gates.com/us/p/gates/k080944.html

The mechanic reported that the shorter belt went on and felt just like the OEM belt did when it came off. So far so good! Note it was the M2K guys that recommended the belt length and they were spot-on.

Now for the slightly sketchy part.

The mechanic got the alternator mounted only to find that the plug for the control wire at the end of the wiring harness was too big to fit on to the new alternator and lock. Minor panic ensued until he was able to shave off a bit of the alternator housing with a miniature high speed sanding disk. It took 45 minutes extra shop time to do this but I’m not sweating that; a minor bump in the road. Had we noticed it before the alternator got mounted it wouldn't have warranted mention.

Now some pictures:

OEM alternator looking at the control plug; note the space between the plug and the alternator housing.
The rough edge on the back almost makes it look like the plastic housing was cut at the factory.
It might have been. Who knows.

New M2K alternator on the LC looking at the control plug:

This is the control plug at the end of the wiring harness - won't fit:

 

[TeCKis300]

So awesome. Thanks for sharing this. Been waiting for an alternator upgrade path to be documented on this forum. Too bad I didn't get a chance to upgrade before I had to drop in a replacement. Probably because I've been abusing my OEM alternator with 20A trailer charging + 18A onboard lithium charging + 10A or so of ancillary devices + unknown starter battery deep cycling in camping trips.

I wonder how much utility there is in upgrading to a small pulley on the stock alternator? High output at idle RPM is probably the most stressful scenario for alternators.

 

[tbisaacs]

Woah this is a cool upgrade!

 

[RET2]

OK waiting to see who's going to go gonzo and instal a Premier Power Welder/alternator upgrade?

 

[FrazzledHunter]

So awesome. Thanks for sharing this. Been waiting for an alternator upgrade path to be documented on this forum. Too bad I didn't get a chance to upgrade before I had to drop in a replacement. Probably because I've been abusing my OEM alternator with 20A trailer charging + 18A onboard lithium charging + 10A or so of ancillary devices + unknown starter battery deep cycling in camping trips.

I wonder how much utility there is in upgrading to a small pulley on the stock alternator? High output at idle RPM is probably the most stressful scenario for alternators.

Well I like it when I can give back to the forum that has given me so much!!! Also thanks to you for posting how you did your install as it was looked at by both me and the mechanic. Ultimately the mechanic went out the side above the frame and did not drop the sway bar and go from the bottom as you did. This meant that KDSS didn't have to be messed with. He said he hates doing that LOL!

Your timing was bad as I have an OEM alternator sitting here with 24K miles on it that might have come in handy.
Actually I'll hang on to it just in case this new one blows up.

Regarding high amperage at lower RPMs.
You're 100% right about high loads at low RPM's. The M2K guys explained that it's mainly a cooling issue. The current demand outstrips the alternator's ability to cool itself and if done too much can permanently damage the alternator.

This was a huge topic of discussion between me and M2K. It was borne of me explaining our use case of
packing up from a camping trip with a:

• Yeti 1500X at 10%
• 2nd battery under the hood at 50%
• Future RV with 400Ah of batteries at 20%.

Then starting the LC up and plugging in the RV while sitting at idle at the campsite packing up, then maybe at a dump station and more than likely sitting in traffic.

Worst case total amps estimate would be 90 more or less truck, 25 to the 2nd battery, 40 to the Yeti 1500X and 60+ at the bumper to the RV.

• I want to push up 50A to the RV lithiums and that means 50+ to be available at the rear bumper.
  • The plan is to wire to be capable of 100A
• The RV will have a Victron Orion XS 12/12-50A DC-DC Battery Charger
  • I can lower the amp draw on it if I'm loaded up elsewhere or jack it up if I'm not.

EDIT 3/17/2024: I ultimately couldn't source a Victron Orion XS 12/12-50A so I went with a REDARC BCDC 1250D. It had the added advantage of dual input for solar so I had the dealer divert the ZAMP connector on the trailer from straight to the batteries to the REDARC. This enables me to use any brand of unregulated solar panels (of which I already own) to charge the treiler lithium batteries.

So I found for engine RPMs at idle:

• Cold: 1000-1200 RPM
  • Might be OK but doesn't last.
• Parked warmed up: 700 RPM.
  • This is barely enough
• Idle when warmed up, in drive with the foot on the brake 550 RPM.
  • Not enough

So after passing that along and assuring the M2K guys I didn't plan to race the LC and run the engine up to 12,000 RPM they decided on the smaller pulley.
BTW, they don't do high idle kits. We discussed it. Why waste the gas for the same outcome they asked?

Here's some numbers they gave me regarding engine-alternator RPM's:

• OEM 2.5 in pulley has a 3:1 alternator:engine RPM ratio
• 2 in pulley has a 3.45 alternator:engine RPM ratio

So at the lowest observed RPM the alternator is turning at 3.45x550 or 1890 RPM.
According to the data sheet that's almost 200A!
Just enough.
I hope.

 

[FrazzledHunter]

OK waiting to see who's going to go gonzo and instal a Premier Power Welder/alternator upgrade?

Whoever installs such an upgrade might want to have a look at this:
12V 780 Amps | SBC - https://smartbatterycharger.net/product/12v-780-amps/

I almost went that route.

 

[bloc]

Great Tech...

Regarding high amperage at lower RPMs.
You're 100% right about high loads at low RPM's. The M2K guys explained that it's mainly a cooling issue. The current demand outstrips the alternator's ability to cool itself and if done too much can permanently damage the alternator.

Interesting, I never even thought to ask why idle is harder on them.

 

[FrazzledHunter]

Great Tech...



Interesting, I never even thought to ask why idle is harder on them.

My understanding of their explanation is that the windings must dissipate heat under load anyway.
But if you have the perfect storm of high load and low RPM's it means the heat can't be removed fast enough.
They mentioned an alternator can actually catch fire.

 

[RET2]

Whoever installs such an upgrade might want to have a look at this:
12V 780 Amps | SBC - https://smartbatterycharger.net/product/12v-780-amps/

I almost went that route.

But we 200 owners are gentlemen and not heathen Jeep owners that thrash and catastrophically break their rigs right?

 

[FrazzledHunter]

But we 200 owners are gentlemen and not heathen Jeep owners that thrash and catastrophically break their rigs right?

Well I dunno.
I could STILL add the dual alternators for 390+780 amps for a total of 1170 amps.
I can imagine driving by jeeps and causing the coils in their engine to overheat and explode as I drove past them from the sheer power of the magnetic fields emanating from my LC.
Might be fun.

 

[bloc]

My understanding of their explanation is that the windings must dissipate heat under load anyway.
But if you have the perfect storm of high load and low RPM's it means the heat can't be removed fast enough.
They mentioned an alternator can actually catch fire.

My understanding is also that as temperature in a conductor increases so does the resistance, leading to yet more heat..

So.. positive feedback loop…

 

[FrazzledHunter]

My understanding is also that as temperature in a conductor increases so does the resistance, leading to yet more heat..

So.. positive feedback loop…

Exactly!

 

[mobi-arc]

The change to a smaller pulley is in the "how to make a high output alternator 101" handbook. In order to drive higher amperage, the stator configuration gets changed from Wye to Delta which creates about 20% greater amperage, at the expense of low rpm voltage. So in order to compensate for that cut-in voltage, the pulley diameter is reduced in order to get the alternator to spin faster at any give RPM, but particularly at idle, where the alternator-to-flywheel pulley ratio needs to be gamed in order for the alternator to spin quickly enough to create output. Of course, there are trade-offs...like everything. Additional stress on alternator bearings. Concerns about belt wear when the alternator is loaded. And there's the heat that gets generated at that elevated output which takes its toll on the regulator, rectifier plate, and bearings....is that heat being managed properly and what's that going to do to the longevity of the alternator? Always tradeoffs.

 

[dingoboyexplore]

Was wondering why this never caught on in the offroad world. I started my love for car audio in 2008ish. Doing the Big 3 alternator wiring upgrade and swapping to higher amp alts was very common. Everything back then was rated at 1200rpm for full power output. Youd just rev the engine to that and be able to maintain enough power for the stereo. This was prior to lithium and such. My 98 jetta had a factory 105A alt i believe, maybe even less? I had meangreen alternators rebuild it to 190A which at the time was HUGEEE. Seeing the posted 780A above....ugh that is so nice. I learned all my wiring stuff from youtube back then, a guy called Steve Meade lol.

 

[Moby]

This is great! I did an alt upgrade on my FJ-62 because stock was so bad at idle the headlights would dim. And I was running a stereo system, on board PC, dual batteries, etc. so pretty power hungry compared to stock. Used an oem case and a smaller pulley like here. I don't currently have the need in the 200 but great to know this is an option.

 

[FrazzledHunter]

Was wondering why this never caught on in the offroad world. I started my love for car audio in 2008ish. Doing the Big 3 alternator wiring upgrade and swapping to higher amp alts was very common. Everything back then was rated at 1200rpm for full power output. Youd just rev the engine to that and be able to maintain enough power for the stereo. This was prior to lithium and such. My 98 jetta had a factory 105A alt i believe, maybe even less? I had meangreen alternators rebuild it to 190A which at the time was HUGEEE. Seeing the posted 780A above....ugh that is so nice. I learned all my wiring stuff from youtube back then, a guy called Steve Meade lol.

First of all I sincerely hope that what I have documented will encourage others to copy what I’ve done. All the effort and time I have put in on research will be more than paid off if that happens. Messing with the electronics of an LC/LX is scary. I get it, believe me. I backed out more than once.

So as to why hasn’t this caught on and caught on HERE and why is this so difficult? The short answer is you have to engineer it and figure it out yourself on both on the tow vehicle and on the trailer. Then find someone competent to implement it if you can’t.

TL;DR
I have wanted to do this starting with my 2000 100 series Land Cruiser (RIP) and again with my 2018 200 series since 2020. I have spent literally 2 years trying to find out how to do this and who to hire to do it. The problem is threefold: finding out what hardware will do the job, what hardware is as robust as OEM and finally WHO is willing and able to do the installation. It is the last part, the WHO that proved to be the largest obstacle. I gave up more than once. This time, with an upcoming purchase of an RV with lithium batteries that I wanted to charge while under tow, I really persisted in my search and found a first rate vendor and installer. I got mad LOL!

In the end, what made it all possible was the internet. The internet’s search and communication capability allowed me to learn what I needed about car electronics, alternators and how others are doing the same thing (in Australia) that I wanted to do.

Here are is a list of some anecdotes, conclusions plus some of my own opinions that have evolved based on my long quest:

• Car electronics are complex and expensive in modern cars. I mean REALLY REALLY complex and expensive. The quest for fuel efficiency and gee-whiz electrical stuff has led to electrical components being networked together with LIN and CAN buses. You literally can have window motors communicating with ECU’s. Want your dash to show if your door is open? Want your alternator to tell your ECU to send more voltage to the battery if it’s cold? This led to the complexity.
  • If you order a 3rd party alternator for your 200 series you’ll notice that it specifies a LIN alternator. WTF is LIN? I sure didn’t know. People who build alternators do. People who install them don’t or almost never know. I know now.
  • So if you want to upgrade outside of OEM (not just alternators) you not only do you have to find a component that works, it likely has to sit on a network that also has to work. Care to diagnose all this if it quits working? You’ll potentially bat your head against the wall.
• Liability. So a guy like me calls a shop and wants to install a 3rd party alternator in an $85,000 car. Care to install something that potentially fries all of this? You’re talking thousands of dollars of damage and a HUGE liability for a shop.
• Idiot, stupid, posers in the industry. We have dealerships that literally can’t change the oil. Care to trust something like this to that kind of shop even if they’d do it? My interviews with some so-called high end stereo and electronics shops in my area have devolved into arguments as to why it’s NOT OK to string flooded lead acid, AGM and lithium batteries together under the hood with simple wire. Many shops argued you should do this.
  • This started with my putting in a REDARC BCDC1225D charger for my AGM 2nd battery over 2 years ago.
  • In one shop, I made an appt. to have my 2nd battery wired and the shop had me wait in the waiting room for an hour. Tech came out and told me that the owner wouldn't work on Land Cruisers. He said “Wouldn't touch them with a 10ft pole" and not just for my job. I mean not AT ALL. I kid you not. It got ugly. I called them chickens*** posers that should maybe be working on golf carts in front of a room full of customers. They asked me to leave. Dunno why.
• The RV industry.
  • The American RV industry does not have its act together on this. If you want to feel stupid for weeks talk to an American RV salesman. Nuff’ said.
  • It’s apparently common in Australia to power an RV from the tow vehicle and it’s due to the Australian RV industry having its act together. In Australia, half the problem is solved!
    • It’s no wonder that the ONLY trailer RV I found that came from the factory with a second charging cable designed specifically to be connected to the tow vehicle was an Australian-made Kimberly. Kimberly uses an EcoFlow battery management system that has a connector specifically designed for and labelled “Alternator”.
  • I have talked to the presidents of trailer manufacturers at the Hershey PA RV show about powering/charging their trailer under tow. They say it would be easy to do but just “Get the solar panels” or “Use shore power”. Umm no, I’m packing up camp and driving all night to an off grid campsite. They are seemingly unable to comprehend the problem or see no market in it.
  • I have also been told by the RV sales people regarding tow vehicle charging that “You can’t do that because your alternator can’t do it and that's why we don't do that”. OH REALLY!!!

I could go on but for the sake of everyone’s sanity including my own I won’t.

 

[TeCKis300]

Well I like it when I can give back to the forum that has given me so much!!! Also thanks to you for posting how you did your install as it was looked at by both me and the mechanic. Ultimately the mechanic went out the side above the frame and did not drop the sway bar and go from the bottom as you did. This meant that KDSS didn't have to be messed with. He said he hates doing that LOL!

Your timing was bad as I have an OEM alternator sitting here with 24K miles on it that might have come in handy.
Actually I'll hang on to it just in case this new one blows up.

Regarding high amperage at lower RPMs.
You're 100% right about high loads at low RPM's. The M2K guys explained that it's mainly a cooling issue. The current demand outstrips the alternator's ability to cool itself and if done too much can permanently damage the alternator.

This was a huge topic of discussion between me and M2K. It was borne of me explaining our use case of
packing up from a camping trip with a:

• Yeti 1500X at 10%
• 2nd battery under the hood at 50%
• Future RV with 400Ah of batteries at 20%.

Then starting the LC up and plugging in the RV while sitting at idle at the campsite packing up, then maybe at a dump station and more than likely sitting in traffic.

Worst case total amps estimate would be 90 more or less truck, 25 to the 2nd battery, 40 to the Yeti 1500X and 60+ at the bumper to the RV.

• I want to push up 50A to the RV lithiums and that means 50+ to be available at the rear bumper.
  • The plan is to wire to be capable of 100A
• The RV will have a Victron Orion XS 12/12-50A DC-DC Battery Charger
  • I can lower the amp draw on it if I'm loaded up elsewhere or jack it up if I'm not.

So I found for engine RPMs at idle:

• Cold: 1000-1200 RPM
  • Might be OK but doesn't last.
• Parked warmed up: 700 RPM.
  • This is barely enough
• Idle when warmed up, in drive with the foot on the brake 550 RPM.
  • Not enough

So after passing that along and assuring the M2K guys I didn't plan to race the LC and run the engine up to 12,000 RPM they decided on the smaller pulley.
BTW, they don't do high idle kits. We discussed it. Why waste the gas for the same outcome they asked?

Here's some numbers they gave me regarding engine-alternator RPM's:

• OEM 2.5 in pulley has a 3:1 alternator:engine RPM ratio
• 2 in pulley has a 3.45 alternator:engine RPM ratio

So at the lowest observed RPM the alternator is turning at 3.45x550 or 1890 RPM.
According to the data sheet that's almost 200A!
Just enough.
I hope.

Great info!

I'm still pretty keen on possibly overdriving the stock alternator as a poor mans upgrade. Or mitigation against too much idle load/heat. In the teardown of my 169k mile alternator, the brushes had plenty of life left, commutator was clean, bearings smooth. Probably failed regulator or windings due to loads overtime. I don't believe I need more peak amp output, rather more output support at idle including cooling.

With a stock 2.5" pulley, a 2.25" would be a 11% overdrive, 2" 25% overdrive.
At worse case scenario idle 500 rpm, 11% overdrive would be 555rpm, 25% is 625rpm.
Nominal idle 700 rpm, 11% is 777rpm, 25% is 875 rpm
Engine redline at 6k rpm with stock 3:1 pulley has alternator at 18k rpm. 11% is 20k rpm. 25% is 22.5k rpm.

Looking at the typical alternator output curve, even incremental rpm overdrives can greatly increase performance at idle. This graph also reminds me I'm often idling in the desert temps where underhood heat isn't helping.

Some eyeballing of nominal outputs of a typical 180A alternator with different pulleys
@500rpm stock 2.5" pulley - 28A, 2.25" - 32A, 2" - 45A.
@700rpm stock 2.5" pulley - 90A, 2.25" - 108A, 2" - 135A.

I'm really liking the idea of a 2.25' pulley. I do spend quite a bit of time in the upper RPM bands when towing so this is also trying to respect durability there. Now to source one and a shorter belt.

 

[dingoboyexplore]

First of all I sincerely hope that what I have documented will encourage others to copy what I’ve done. All the effort and time I have put in on research will be more than paid off if that happens. Messing with the electronics of an LC/LX is scary. I get it, believe me. I backed out more than once.

So as to why hasn’t this caught on and caught on HERE and why is this so difficult? The short answer is you have to engineer it and figure it out yourself on both on the tow vehicle and on the trailer. Then find someone competent to implement it if you can’t.

TL;DR
I have wanted to do this starting with my 2000 100 series Land Cruiser (RIP) and again with my 2018 200 series since 2020. I have spent literally 2 years trying to find out how to do this and who to hire to do it. The problem is threefold: finding out what hardware will do the job, what hardware is as robust as OEM and finally WHO is willing and able to do the installation. It is the last part, the WHO that proved to be the largest obstacle. I gave up more than once. This time, with an upcoming purchase of an RV with lithium batteries that I wanted to charge while under tow, I really persisted in my search and found a first rate vendor and installer. I got mad LOL!

In the end, what made it all possible was the internet. The internet’s search and communication capability allowed me to learn what I needed about car electronics, alternators and how others are doing the same thing (in Australia) that I wanted to do.

Here are is a list of some anecdotes, conclusions plus some of my own opinions that have evolved based on my long quest:

• Car electronics are complex and expensive in modern cars. I mean REALLY REALLY complex and expensive. The quest for fuel efficiency and gee-whiz electrical stuff has led to electrical components being networked together with LIN and CAN buses. You literally can have window motors communicating with ECU’s. Want your dash to show if your door is open? Want your alternator to tell your ECU to send more voltage to the battery if it’s cold? This led to the complexity.
  • If you order a 3rd party alternator for your 200 series you’ll notice that it specifies a LIN alternator. WTF is LIN? I sure didn’t know. People who build alternators do. People who install them don’t or almost never know. I know now.
  • So if you want to upgrade outside of OEM (not just alternators) you not only do you have to find a component that works, it likely has to sit on a network that also has to work. Care to diagnose all this if it quits working? You’ll potentially bat your head against the wall.
• Liability. So a guy like me calls a shop and wants to install a 3rd party alternator in an $85,000 car. Care to install something that potentially fries all of this? You’re talking thousands of dollars of damage and a HUGE liability for a shop.
• Idiot, stupid, posers in the industry. We have dealerships that literally can’t change the oil. Care to trust something like this to that kind of shop even if they’d do it? My interviews with some so-called high end stereo and electronics shops in my area have devolved into arguments as to why it’s NOT OK to string flooded lead acid, AGM and lithium batteries together under the hood with simple wire. Many shops argued you should do this.
  • This started with my putting in a REDARC BCDC1225D charger for my AGM 2nd battery over 2 years ago.
  • In one shop, I made an appt. to have my 2nd battery wired and the shop had me wait in the waiting room for an hour. Tech came out and told me that the owner wouldn't work on Land Cruisers. He said “Wouldn't touch them with a 10ft pole" and not just for my job. I mean not AT ALL. I kid you not. It got ugly. I called them chickens*** posers that should maybe be working on golf carts in front of a room full of customers. They asked me to leave. Dunno why.
• The RV industry.
  • The American RV industry does not have its act together on this. If you want to feel stupid for weeks talk to an American RV salesman. Nuff’ said.
  • It’s apparently common in Australia to power an RV from the tow vehicle and it’s due to the Australian RV industry having its act together. In Australia, half the problem is solved!
    • It’s no wonder that the ONLY trailer RV I found that came from the factory with a second charging cable designed specifically to be connected to the tow vehicle was an Australian-made Kimberly. Kimberly uses an EcoFlow battery management system that has a connector specifically designed for and labelled “Alternator”.
  • I have talked to the presidents of trailer manufacturers at the Hershey PA RV show about powering/charging their trailer under tow. They say it would be easy to do but just “Get the solar panels” or “Use shore power”. Umm no, I’m packing up camp and driving all night to an off grid campsite. They are seemingly unable to comprehend the problem or see no market in it.
  • I have also been told by the RV sales people regarding tow vehicle charging that “You can’t do that because your alternator can’t do it and that's why we don't do that”. OH REALLY!!!

I could go on but for the sake of everyone’s sanity including my own I won’t.

That's quite the explanation for what I said. I was speaking in general terms of in the camping community upgrading alternators in vehicles. But I guess you took it personal?

 

[FrazzledHunter]

That's quite the explanation for what I said. I was speaking in general terms of in the camping community upgrading alternators in vehicles. But I guess you took it personal?

No not at all! Your question is a valid one and I 'm glad you asked. The question needs asking.
I was ranting a bit about what I went through which was years of frustration.

There is a real reason why upgrades like this haven't happened and I think I know why. I was actually trying to answer the question LOL! But I went off on a tangent.

My intention was to agree, support and buttress what you said. I guess it might not have come off that way and my sincere apologies if it didn't.

 

[FrazzledHunter]

Great info!

I'm still pretty keen on possibly overdriving the stock alternator as a poor mans upgrade. Or mitigation against too much idle load/heat. In the teardown of my 169k mile alternator, the brushes had plenty of life left, commutator was clean, bearings smooth. Probably failed regulator or windings due to loads overtime. I don't believe I need more peak amp output, rather more output support at idle including cooling.

With a stock 2.5" pulley, a 2.25" would be a 11% overdrive, 2" 25% overdrive.
At worse case scenario idle 500 rpm, 11% overdrive would be 555rpm, 25% is 625rpm.
Nominal idle 700 rpm, 11% is 777rpm, 25% is 875 rpm
Engine redline at 6k rpm with stock 3:1 pulley has alternator at 18k rpm. 11% is 20k rpm. 25% is 22.5k rpm.

Looking at the typical alternator output curve, even incremental rpm overdrives can greatly increase performance at idle. This graph also reminds me I'm often idling in the desert temps where underhood heat isn't helping.

Some eyeballing of nominal outputs of a typical 180A alternator with different pulleys
@500rpm stock 2.5" pulley - 28A, 2.25" - 32A, 2" - 45A.
@700rpm stock 2.5" pulley - 90A, 2.25" - 108A, 2" - 135A.

I'm really liking the idea of a 2.25' pulley. I do spend quite a bit of time in the upper RPM bands when towing so this is also trying to respect durability there. Now to source one and a shorter belt.

View attachment 3519080

Interesting. I just mic'd the pulley from my OEM alternator and came up with:

• 57mm/2.24in at the top of the ribs
• 65mm/2.56in at the outer edge*

So this is now hopefully documented correctly.
I'm not sure which measurement is the correct convention for specifying pulley diameter.

Getting a 2 in. pulley wouldn't have occurred to me before all of this.
But I don't know where to go to get one.
I guess you'd have to match up the spindle width and depth.
There is a thread on smaller pulleys but it's for an 80 series:
Alternator Smaller Pulley - https://forum.ih8mud.com/threads/alternator-smaller-pulley.1238173/

I've never seen actual performance graphs for the OEM alternator.
I should have posted these earlier but here are the performance specs for the M2K alternator.

Note that the specs refer to their standard pulley size.
*In another brochure they state the their pulleys are "5% smaller than the OEM diameter for increased idle output while retaining OEM belt length" and they list that below as 62.53mm.
So I am assuming that pulley measurements are based on the outer rim and would be the 65mm measurement above.
Again, I got a custom 2" pulley from them that required me to get a shorter belt.