120A alternator upgrade

**steveG** · 18th January 2013, 09:02 AM

Originally Posted by drivesafe

Hi Steve and because you are running a winch, go for the thickest cable you can fit.

The thinest cable you can safely use with a 120 amp alternator is 4B&S ( 20mm2 )

The thicker you go, the less voltage drop you will have while winching.

As far as the size of the stud on the alternator goes, you can use any size cable eye terminal and if there is a restriction because of a limited clearance area on the back of the alternator, you can always file the edges of a larger terminal down till it fits.

The size of the fuse will be governed by the thickness of the cable, for example, 4B&S ( 20mm2 ) = 120 amp fuse, 3B&S ( 25mm2 ) 150 amp fuse, and 2B&S ( 32mm2 ) = 200 amp fuse.

Don't forget that you will probably need to up size your earth cables.

Good point about the earth cable. I upgraded it from the tiny one that was there from the original V8 setup - pretty sure its now 50mm2 but will double check.

I've got 70mm2 cable from the battery to the winch, and the solenoid is in the engine bay just behind the headlight. I'm going to connect the alternator output to that as it seems to make sense to a) connect it back to the battery via large existing cable, and b) have it feeding as directly as possible to the winch.

I still need to sketch it all out and make sure I'm not doing something stupid circuit-wise but seems to make sense so far.

Steve

**steveG** · 17th March 2013, 08:53 PM

I fitted the new alternator today.

Here's a couple of notes that might be useful to others:

Pulley offset is different to the original alternator.
Original alternator is 44.2mm from inside of forward alternator mounting foot to centerline of belt
Replacement is 48.8mm so pulley sits further forward.
I had to remove ~4.5mm from the rear of the pulley boss and put an extra thick washer/spacer under the pulley nut to compensate for the removed material. Pulley is cast iron FWIW.
The battery light on the dash won't light up unless you have the alternator output connected to your battery supply. Its probably the same for every alternator, but I only found it out today (after wasting a heap of time wondering why it wasn't working).
The adjustment lug on the new unit is a bit further around, so you may have to modify the adjustment arm. Mine was a bit of a mis-match anyway having an original Stage1 alternator, and a truck mount bracket to put the alternator in a higher position - so needed modifying.

Steve

**flagg** · 23rd June 2013, 08:47 PM

Originally Posted by steveG

[LIST=1][*]Pulley offset is different to the original alternator.
Original alternator is 44.2mm from inside of forward alternator mounting foot to centerline of belt
Replacement is 48.8mm so pulley sits further forward.
I had to remove ~4.5mm from the rear of the pulley boss and put an extra thick washer/spacer under the pulley nut to compensate for the removed material. Pulley is cast iron FWIW.

Hey Steve thinking I may go down this route. I can't quite picture what you mean about re-aligning the pulley.. will it be obvious once I have it in front of me?

Originally Posted by drivesafe

The thinest cable you can safely use with a 120 amp alternator is 4B&S ( 20mm2 )

The thicker you go, the less voltage drop you will have while winching.

The cable I have from the alt is about 5-6mm across. I"m not sure how to identify what is 4B&S or 20mm2... is what I have enough?

**steveG** · 23rd June 2013, 09:08 PM

Originally Posted by flagg

Hey Steve thinking I may go down this route. I can't quite picture what you mean about re-aligning the pulley.. will it be obvious once I have it in front of me?

The cable I have from the alt is about 5-6mm across. I"m not sure how to identify what is 4B&S or 20mm2... is what I have enough?

Yes - it will be obvious once you have the alternator in front of you. Essentially you need to move the pulley rearwards to align it with the crank and water pump pulleys, so machine some off the back of the pulley boss, and put a thick washer under the nut to compensate for the removed material (so the nut doesn't bind on the shaft).

You need cable that's got about 6mm diam copper in it. If the 5-6mm you've got includes the insulation its too thin.

Steve

**MLD** · 27th June 2013, 06:21 PM

Originally Posted by steveG

I've got 70mm2 cable from the battery to the winch, and the solenoid is in the engine bay just behind the headlight. I'm going to connect the alternator output to that as it seems to make sense to a) connect it back to the battery via large existing cable, and b) have it feeding as directly as possible to the winch.

Steve

I'm no auto electrician but i'm sure i read somewhere that it was not wise to connect the winch to the alternator without passing through the battery. The rationale applies to all loads.

I'm curious of the thoughts from Drivesafe and any other auto-sparky out there to that set up. To my lay mind it stands to reason otherwise the auto makers would run loads off the alternator without passing through the battery.

cheers MLD

**steveG** · 27th June 2013, 09:02 PM

Originally Posted by MLD

I'm no auto electrician but i'm sure i read somewhere that it was not wise to connect the winch to the alternator without passing through the battery. The rationale applies to all loads.

I'm curious of the thoughts from Drivesafe and any other auto-sparky out there to that set up. To my lay mind it stands to reason otherwise the auto makers would run loads off the alternator without passing through the battery.

cheers MLD

You can't pass current through the battery to a winch - the battery effectively hangs off the side of the circuit like a reservoir in parallel with the alternator.
Your alternator will never supply a winch by itself. The battery(s) will be assisting as the winch draws more current than the alternator can supply - therefore the voltage drops below battery voltage and the battery feeds back into the circuit.

Maybe what you've read is that it isn't a good idea to hook up a separate alternator straight to a winch with no battery in the circuit. I could see that not being a good thing.

Steve

**swivelrat** · 27th June 2013, 09:25 PM

G'day,

my 95 130 tdi alt decided to throw in the towel the other day, a MM 127-65 which had a good innings all considering. I read quite a few blogs on replacement options and it looked like I would be best tracking down a 100 amper off a disco. I rang a few joints, couldn't find a bosch model to suit but found a mob doing Merelli Magnetti's. A 65amp was $127 and the 120amp was a whopping $485. So I did the sums to work out an average load required and worst case. With everything going flat out, plus fridges etc, 65 amp chits it in. So I'll the $350 for the starter when it goes.

On a different note, Im more interested in battery preservation. Say if dropped the batteries to a very low voltage, my understanding is that its important to charge the battery steadily and not to subject it to shock treatment so to speak with 120amps up front, but Im keen to be proven wrong here????

**steveG** · 28th June 2013, 07:08 AM

Originally Posted by swivelrat

G'day,

my 95 130 tdi alt decided to throw in the towel the other day, a MM 127-65 which had a good innings all considering. I read quite a few blogs on replacement options and it looked like I would be best tracking down a 100 amper off a disco. I rang a few joints, couldn't find a bosch model to suit but found a mob doing Merelli Magnetti's. A 65amp was $127 and the 120amp was a whopping $485. So I did the sums to work out an average load required and worst case. With everything going flat out, plus fridges etc, 65 amp chits it in. So I'll the $350 for the starter when it goes.

On a different note, Im more interested in battery preservation. Say if dropped the batteries to a very low voltage, my understanding is that its important to charge the battery steadily and not to subject it to shock treatment so to speak with 120amps up front, but Im keen to be proven wrong here????

If you've got multiple batteries and are draining them I think you might need to take another look at your sums if you think 65A will handle it. How much have you allowed for battery charging in your calcs? What type of batteries?
Best thing for batteries is not to drain them down too low.
Have a look at the specs for most deep cycle or AGM batteries (you don't usually find any charts for purely crank batteries). Draining to 80% remaining they will do LOTS of cycles, 50% its significantly less and if you are draining them to 10% you might be down to less than 100 cycles.
While some batteries don't like high charge rates, the likes of AGM are happy with it.
If its going to take you 20hours to recharge a deeply discharged battery then you won't be fully charged the next night so you have less capacity and will draw it down even further.

IMO, best thing is plenty of battery capacity so you don't discharge them too deeply, batteries that will take high charge rates, and an alternator with plenty of capacity to provide the charging. If you're going to camp for extended periods without running the engine (ie more than a night or two) you probably need to consider another source of charging (portable charger or solar).

Steve

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