AGM BATTERY CHARGING - ALTERNATOR VOLTAGE BOOSTER

Unless members start realizing their COPs went out and their fuel economy has seemed off since running the Alt-S diode then it really doesn't matter, I just felt compelled and a responsibility to share this info.

 

It does apply there buddy.

 

Going off these maps @ 2100 rpm, if the Alt-S diode is giving a .5v bump and the alternator is putting out 14.64 volts, the ECM thinks the voltage is 14.14 correct? So the ECM is expecting the COPs to have a dwell of 2ms but since they're actually receiving 14.64v they will have a shorter dwell than 2ms; the result being the ECM will fire the COPs for too long.
The same will be for the injectors, they will have a shorter dwell than the ECM thinks and will fire the injectors too long.

 

Probably splitting hairs on this one

 

I haven't read all of this thread, but I think I'm catching on to what you're trying to say here. The problem is, the ECU doesn't reference the Alt-S circuit for voltage. The ECU monitors voltage from the 20amp EFI fuse which is directly off the battery.

 

That's great news, but raises the question in my head 'why have the Alt-S circuit then?'. I would think the voltage would be the same throughout the system, maybe that's why they did away with that circuit in the 3rd Gens.

 

I've been tracking battery voltage off two different sources for some time. So if what I am gathering what you wrote correctly, then you are saying that at any given moment the PCM is actually pulling half a volt less than the actual charging system voltage correct?

 

The IC Regulator in the alternator monitors both battery and stator voltages and depending on the measured voltages, the IC regulator will adjust the amount of rotor field current to control alternator output. What you're doing here is spoofing the the battery voltage, but to the IC Regulator to "spoof" it into more output, not the ECU. The ECU just monitors and adjusts based on actual battery voltage.

IC Regulators can be mounted both internal or external to the alternator. 2nd Gens uses an internal regulator 3rd Gens use an external.

 

What the ECU/PCM actually sees at the ECU/PCM plug will vary of course from actual battery voltage, but not because of anything to with diodes being used to bump charging voltages. It's due to the condition of the wiring, connectors, terminals between that plug and the battery. In some trucks there might be enough resistance to drop 0.5v, some more, some less. But the moral of the story is there will be some (which is expected).

But yes, actual ECU voltage at the ECU can and likely will be a little bit less than charging voltage at the battery.

Simple test for you with HPTuners, is add the PID for ECU voltage, start a log and bring the laptop under the hood or someplace with line of sight to the battery. and put a multimeter on the battery while the vehicle is idling. Your voltage delta will obvious comparing the two.

 

This isn't even going to the ECM, just the regulator People on here were talking about protecting the ECM with adding the fuse back, I assumed that as a fact. The fuse is protecting the regulator, the ECM isn't being spoofed at all. I'm standing down now.

 

All good man!

 

My voltage variance between PCM and battery voltage is anywhere between .4 to .5 volts so that definitely coincides with what you mentioned. I sort of figured the PCM saw less voltage than what was actual battery but it is good to see those thoughts re-affirmed by you.

 

https://invertersrus.com/product/victron-buckboost/

Not a cheap solution by any means but one that covers all the bases.

 

Hey guys, thanks for the awesome thread and all the research,

Do I have to use an AGM battery with this mod? I am not sure what battery I have and it's raining out.

Voltage on my head unit dropped into the low 13's, have a few amps and a couple subs. The voltage used to hang around 13.8 with A/C on and music blaring. The alt is now charging 13.5-.6 at idle and battery static is 12.9. I figured the alt is crapping out and found this thread. Was looking into a high output alt but this is way cheaper. Will keep an eye on alt and see what it does next couple days

thanks

 

Are you reading that at idle? With all the audio equipment drawing quite a bit of power your alternator doesn't really put much power out during idle. Now bring the rpm to 1500-2000rpm and the voltage reading will probably come up. But I would also verify with a multimeter at the battery because the accuracy of the head unit and the possible voltage drop from the all the wiring will give you an off reading. If you have a standard battery then 13.5v at 2000rpm then that is normal. If you run that diode you will likely over-voltage the battery causing it to swell and possibly leak or blow up worse case.

ONLY do this if you have an AGM battery. DO NOT do this if you have a standard battery, it can be dangerous.

 

I just got around to adding the diode and my idle charge voltage is 14.2v. Is this still too low?

 

14.2 is technically lower than spec for a Northstar AGM I think, but I wouldn't sweat it.

I bought the fused diode from Australia when upgrading to AGM last year.

On cold startup the charge voltage will initially climb up to 14.4V. But for normal (warmed up) driving the steady state charge voltage is only 14.0V. I checked it even at the battery. Guess I should have got the adjustable version?

But still my battery kicks ass. I can run my fridge all night, plus the stereo and lights for several hours at camp. Cranks right up in the morning, even if I ran the battery into the 11V range. I carry a little lithium battery jump starter as a contingency, so I feel zero need to consider a dual battery setup, or any of the other wildly complicated TW battery upgrades. (At least until my core support gives out--I drive like an ass hole in the desert.)

Someday I plan to make my own fused voltage booster to plug into this circuit position, using a bandgap referenced voltage regulator instead of a diode. But I don't feel like that's an urgent problem I need to solve right now. If you have an AGM, put a diode in the alternator sense fuse slot (preferably a fused one) to boost your voltage, and you will be in pretty good shape.

 

I found a 130amp alternator that works for my 2TR-FE. Relevant here because it's a newer style with hairpin regulators, which opens up possibilities of swapping to a regulator with higher output. I have found a regulator with a 14.5v setpoint that should be pnp and another with 14.8v setpoint but will require a conversion harness. I just installed it today with success, reading a 0.3v drop at the battery from the advertised voltage setpoint. I will be doing a writeup on it when it's said and done, will post the link in this thread.

 

Excellent!!! Do Post Info Please!!!

 

Well done.