Alternator Upgrade SF forester ej20

Dedman

Dedman

Forum Member
Joined
Dec 3, 2012
Messages
766
Location
Perth Western Australia
Car Year
1999
Car Model
Forester
Transmission
5MT
Hi all

I am looking to upgrade my alternator and was wondering what larger output alternators (current one is only 70A) from other Subarus or other vehicles that I would be able to replace my one with without to much effort.

If anyone else had done an alternator conversion I would love to hear about it.

With my dual battery system, upgraded headlights and winch my existing alternator just doesn't cut it

Cheers
 
Gidday Dedman

70A should be absolutely fine. The bigger the battery capacity, the less grunt needed from the charging system, IME ... That's a whopping 840W at 12V, and 1008W at 14.4V!

The SG non-turbo Foresters have a 90A alternator (Turbo = 110A). So has SWMBO's SH. Both of these cars have four headlights running 55+60W each side when on high beam - 230W total draw.

The battery isolation circuitry should prevent both batteries hitting up the alternator at the same time.

Just a few thoughts. No point spending money that you don't have to, then you have more available for the other important things in life.
 
Ratbag said:
The battery isolation circuitry should prevent both batteries hitting up the alternator at the same time.
Click to expand...

A simple isolator connects / disconnects the aux battery. When it connects, both batteries are drawing from the alternator until the main battery drops to a predetermined voltage.

The 90 amp alternators in my Foz (1 x Aux) and Triton (2 x Aux) works well. The Foz has a simple Matson isolator whereas the Triton has a CTEK 250S.
 
Thanks for the replies. It could just be that my alternator is getting a bit old from all mud and other crap that goes through it. I just found it strange that after a hour and a half drive it had only brought the battery voltage up to 13.8V (well actually it dropped from 14.3 at the start of the drive (after the isolator had already kicked in) to 13.8 by the end of the drive. And that was with the AUX batter being close to fully charged already....
More amps for winching can never go astray.

Also last night I was driving (aux battery at 12.2V before starting) and headlights on the alternator was only getting the voltage up to 13.2V at 3000rpm and only 12.6 at idle which seemed a bit low. I did have (low beam head light on which draw 200W)

Also I am interested in rewireing the alternator directly to the start battery then running the lead to the fuse box off the aux battery. Is there any problem with this when the isolator has not kicked in yet? I am not sure how the voltage regulator or the dash charging warning light works. Is there likely to be an issue with the alternator output going to a different battery than the one that is supplying the fuse box/everything else?

Lastly would an SG alternator just be a bolt in job?

Cheer
Dedman
 
I don't know but the fanbelt part no. are different between the ej20-ej25. I've got 12.9 at idle and just on 14 when charged, and 14.4 when charging whch drops to 14v with headlights uhf stereo a/c and spotlights on at 2800-3000rpm. with everything underload at idle drops to 12.5~ ime ledacid batterys only charge to 13v when full, but need about 2.5v over 12v to charge fully. given this is from expirience with lighting systems and UPS systems not car batts but the chemistry the same I'm pretty sure.

What is the voltage switch over on the isolator set at? 13.8 after 30-40min is only a touch low.
 
I'd highly recommend doing this. I looked it up at work and matched up a few that would fit as a direct bolt on.
The best you'll get for the price is a 2007 2.5l Outback Manual alternator. It puts out 110amps. Otherwise 90amp ones from SG Foresters and Outbacks (99-03) are adequate. But you are right that the 70amp SF one isn't, I have found it inadequate a few times.
 
Cut in is 13.2V cut out is 12.7

taza said:
I'd highly recommend doing this. I looked it up at work and matched up a few that would fit as a direct bolt on.
The best you'll get for the price is a 2007 2.5l Outback Manual alternator. It puts out 110amps.
Click to expand...

Thanks heaps for the info Taza, I really appreciate it. Is the 2007 outback the only model that will fit or are there other years that should as well?
 
Apparently later model alternators are computer controlled? :shrug:

So wont work (regulate) on an earlier Subies :(

Taza, can you confirm this with your auto elec mates :poke:
 
NachaLuva said:
Apparently later model alternators are computer controlled? :shrug:

So wont work (regulate) on an earlier Subies :(
Click to expand...

Nachaluva do you know which years are the later models? Do you have a link to where you are getting this info. Would love to do some reading on it.
 
NachaLuva said:
I called about this
https://www.ebay.com.au/itm/SUBARU-...=AU_Car_Parts_Accessories&hash=item2a27e2dbdc

& they told me it was computer controlled. Apparently thats what the "C" in "LSC" on the label means
Click to expand...

From what I can gather from the internet you can put a LSC alternator into a 2 pin alternator, possibly without any modifications. The C pin seems to be so the computer can turn the alternator off whilst starting to make life easier for the starter. I think that the alternator will run normally and will self regulate voltage if the C pin is not connected or is connected to a voltage but havent worked out which one yet.... If I manage to work it out I will post more.
 
idw said:
Thanks Kevin, how do you find the matson for performance?
Click to expand...

Very good. I have had one on the Forester for 9 years and never a problem. I got the newer model with the override switch for the Triton and ran it for a couple of years until I decided to go with the CTEK. The latest one now sits in my sons Landrover 90 series.
 
So I just went and had a look at my alternator (which I probably should have done yesterday before consulting the internet) and my current alternator has the plug marked as LSC. The C pin does not have a wire going to it so I guess that answers that question. It would appear that LSC alternator is the same as a 2 pin alternator if the C pin is not connected to anything.

The internet seems to also imply that the S pin is a sensing pin that provides feedback to the alternator so it know what voltage the system is at. It is fed from the fuse box (instead of directly from the alternators output terminal) so that any voltage drop along the alternators output wire is compensated for.

For the way I want to wire up my dual battery system (fuse box feed coming straight from the aux battery and alternator output going to the start battery directly) I am going to need to make a new sense wire connection directly to the start battery or the alternator will not get the correct feedback voltage (meaning it will generate as high a voltage as it can) when the dual battery isolator has the two batteries disconnected.

On a side note: im pretty sure you can easily hack the alternators output (if you want to boost system voltage for some reason) by using a voltage divider to supply a slightly smaller fraction of the battery voltage to the alternators S pin so that the alternator outputs a higher voltage to compensate for it.
 
Here is a good read about how alternators work and what the pins are;

https://wilbo666.pbworks.com/w/page/39441708/Toyota%20Alternators#AlternatorRegulatorSTerminal

Its for Toyota so it is not exactly applicable to Subaru's but it is still good info.

Apparently Toyota alternators have an Ignition wire instead of the computer wire to turn them on and off (the alternator is off until power is supplied via the ignition wire) where as Subaru alternators are self exciting (no idea how that works) so have a computer wire that is used to switch them on and off or partially on which is controlled on more modern models by the ecu.
This control is in addition to the alternators internal voltage regulator meaning the alternator will run fine in an older vehicle and wont over charge batteries.
All the computer control does is allow the ecu to get the alternator to charge batteries at different rates based on temperature and also turn it on and off to help with starting and save fuel.

I think I may have worked out why my battery voltage is a bit low and possibly why it decreases with longer drives.
When wiring my dual battery system up I extended the lead to the fuse box. In doing this I have unknowingly extended the alternator sense wire away from the battery.
I measured the voltage in the fuse box with the engine running it sure enough is 14.4-14.5V however when the two big batteries in my car are charging, drawing heaps of current the voltage drop between the fuse box and the batteries is 0.5V or more meaning the batteries always see under 14V.
I am guessing as the engine bay heats up a bit on longer drives then the resistance of my extra wire increases causing a further decrease in voltage at the batteries.

Soon I will make my own alternator output cable directly to the start battery as well as a connection to the 'S' pin of the alternator as a direct (but separate) connection to the start battery. That way I will have maximum power and voltage available at the main battery that there is possible for there to be.

I might still look into an alternator upgrade as well because I am always paranoid that if I stall it when winching hard there will be no juice left to start the engine again and the 70A is somewhat marginal at times anyway.
 
taza said:
I'd highly recommend doing this. I looked it up at work and matched up a few that would fit as a direct bolt on.
The best you'll get for the price is a 2007 2.5l Outback Manual alternator. It puts out 110amps. Otherwise 90amp ones from SG Foresters and Outbacks (99-03) are adequate. But you are right that the 70amp SF one isn't, I have found it inadequate a few times.
Click to expand...

Got a pn for the 110 amp Outback alternator you mention above?
 
The C pin is control. Later model subarus, generally obd2 + use 3 wire plugs do be able to switch the alternator on and off.

I am pretty sure you can use any alternator that fits on the plug. It just means the computer wont be controlling it so it will run all the time as your standard one does. Don't quote me on this, this is why I recommend a gen 3 outback alternator. 95A is a good upgrade without putting to much load on the engine., and I know for a fact it works fine.

Another note on alternators is you cant go from 3 wire two two wire alternators/ wiring on a car with factory 3 wire. The car will throw a check engine light. Was one aspect I had to address when putting an 04 wrx engine with 3 wire into my 2 wire gen 3 outback, I couldn't use the standard alternator wiring from the fuse box.
 
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