I have heard that the stock alternator on the diesels is undersized and not enough to power the 2 batteries, i was going to upgrade my alternator due to the fact i run lots of things off the batteries. BUT, i have the dual alternator setup. So my question is, did they undersize the dual alternators or is that setup plenty?

 

I would do a 270 3G/6G for the upper and a 200 amp 4G for the lower.

Josh

 

Dual batteries are for high amps at the start up, what last few seconds. Even 40 amp alternator will recharge them in less than 5 minutes in normal conditions.
What exactly are you planning to run? I had 30 amp alternator on my boat and with single battery I was powering microwave oven, coffee maker and lot of other stuff (not necessarily all at the same time).
If you really have lot of accessories you are using with engine off, you need dual battery bank, meaning additional battery hooked up to the system via insulator or battery combiner.
I doubt you will need bigger than 120 amp alternator unless you plan to use it for welding.

 

The FICM needs proper voltage for the circuitry to run cool, etc. A 120A alternator is way too small (IMHO) on every start-up. It puts a strain on the FICM and other components - even with dual batteries. The glow plugs take a ton of current on startup .... up to 200A at startup and then around 10-12A each soon after start-up.

That being said, a two alternator setup will provide plenty of current if they are both functioning properly.

 

Better figure out the strategy for two alternators before you say they will provide lots of current - at startup only one is selected to turn on. The stock single alternator is completely adequate for a stock truck, if you run a big stereo or other appliances you may need more, but not if you are basically stock.

Brian

 

Alternator is not doing anything during start up.
I am still playing with new to me 6l and so far the diagram show that right after start up the truck voltage goes above 15v, what usually is considered overcharge. It starts dropping after about 20 seconds, what I take as the time to recharge the batteries and than stabilize above 14v. Still too high for my taste, but looks that is how Ford engineers want it.

 

So - how quickly does the PCM kick in both alternators ............................ never mind, I see it in section 414-00 -1, after the glow plug system stops cycling. HOWEVER, the one that is kept off is the lower generator (120A) and the upper generator is 140A (which is what should be the minimum amps for a single alternator IMO). In the dual setup, you get 25+% more amperage at startup than the single alternator (I was pretty confident it had higher output than the single).

Again - I disagree with a 110A single alternator being sufficient. The batteries are not at 100% for the majority of their life (among other things).

btw - the 140A alternator will serve as an adequate single alternator (again IMO), but many people have not had good reliability from either the 110A unit or the 140A unit.

edit again - there are those who have put quite a bit of effort showing that the alternator is putting out immediately after start-up. On that topic, I say to just put a clamp-on ammeter on your battery charging cable and measure the amps on start-up. I did one test a long time ago (and so did a few others) that seemed to indicate that current was not flowing immediately after startup. I did not document the test very well at that time, but have no known reason for invalidating it. A few people questioned the results of that test and since then I have done quite a few tests and current is flowing at start-up. My recent testing is with a DCPower alternator and a few friends with 2006 year model trucks and stock (but not the original ones) alternators.

 

For the sake of the facts, I run additional test.
The engine was at 170F from previous driving, so it was warm.
I turned the ignition on and car show 12.8V
During cranking the voltage drop to 12.1v but after start up within 3 seconds it went to 13.5v and after some surging it stabilized at 14.8v at 30 seconds.
After few seconds I turned my headlights and AC with blower at full blast, what lower the voltage to 14v and kept it there. After turning the load off it went back to 14.8 v.
Meaning on my truck I can put max load truck has -right after start and alternator still has enough power to recharge the batteries at 14V.
Can't measure charging amp, but at 14V few seconds after cranking it should be pretty good.

 

I burned out the stock & db 140 amp alternator before buying a large output type.
The stock alternator is way too small for the glow plugs & other engine draws.
I would consider replacing them!

 

Found control module voltage.
It started at 11.9v and doesn't seem to be affected by cranking.
From 11.9v it was steady climbing 50 seconds to 13.2v and stood there till I turned the load on (per above).
The load lower the module voltage to about 12.8v and after taking the load of it gently went up to 13.4v

 

Kayteg1 - I have to admit that you are the first person I have seen that gets 14V+ out of a stock alternator. I would love to know the part number and if it is original. Every 6.0L I have seen sees a significant voltage drop when cranking and for the first bit of time after start-up.

These are more common numbers for stock systems:
<TABLE style="WIDTH: 670pt; BORDER-COLLAPSE: collapse" border=0 cellSpacing=0 cellPadding=0 width=894 x:str><COLGROUP><COL style="WIDTH: 670pt; mso-width-source: userset; mso-width-alt: 31772" width=894><TBODY><TR style="HEIGHT: 13.2pt" height=18><TD style="BORDER-BOTTOM: #d4d0c8; BORDER-LEFT: #d4d0c8; BACKGROUND-COLOR: silver; WIDTH: 670pt; HEIGHT: 13.2pt; BORDER-TOP: #d4d0c8; BORDER-RIGHT: #d4d0c8" class=xl24 height=18 width=894 align=left>Voltage After Resting Overnight......... 12.3 VDC</TD></TR><TR style="HEIGHT: 13.2pt" height=18><TD style="BORDER-BOTTOM: #d4d0c8; BORDER-LEFT: #d4d0c8; BACKGROUND-COLOR: silver; WIDTH: 670pt; HEIGHT: 13.2pt; BORDER-TOP: #d4d0c8; BORDER-RIGHT: #d4d0c8" class=xl24 height=18 width=894 align=left>Voltage During GP Warm-up............... 11.7 VDC</TD></TR><TR style="HEIGHT: 13.2pt" height=18><TD style="BORDER-BOTTOM: #d4d0c8; BORDER-LEFT: #d4d0c8; BACKGROUND-COLOR: silver; WIDTH: 670pt; HEIGHT: 13.2pt; BORDER-TOP: #d4d0c8; BORDER-RIGHT: #d4d0c8" class=xl24 height=18 width=894 align=left>Lowest Voltage during Start-up.......... 11.7 to 11.8 VDC</TD></TR><TR style="HEIGHT: 13.2pt" height=18><TD style="BORDER-BOTTOM: #d4d0c8; BORDER-LEFT: #d4d0c8; BACKGROUND-COLOR: silver; WIDTH: 670pt; HEIGHT: 13.2pt; BORDER-TOP: #d4d0c8; BORDER-RIGHT: #d4d0c8" class=xl24 height=18 width=894 align=left>Voltage after Start-up...... 11.9 VDC</TD></TR><TR style="HEIGHT: 13.2pt" height=18><TD style="BORDER-BOTTOM: #d4d0c8; BORDER-LEFT: #d4d0c8; BACKGROUND-COLOR: silver; WIDTH: 670pt; HEIGHT: 13.2pt; BORDER-TOP: #d4d0c8; BORDER-RIGHT: #d4d0c8" class=xl24 height=18 width=894 align=left>Voltage after a minute or so - at idle.. 13.3 VDC</TD></TR><TR style="HEIGHT: 13.2pt" height=18><TD style="BORDER-BOTTOM: #d4d0c8; BORDER-LEFT: #d4d0c8; BACKGROUND-COLOR: silver; WIDTH: 670pt; HEIGHT: 13.2pt; BORDER-TOP: #d4d0c8; BORDER-RIGHT: #d4d0c8" class=xl24 height=18 width=894 align=left>Voltage at 1500rpm.......................... 13.5 - 13.8 VDC</TD></TR><TR style="HEIGHT: 13.2pt" height=18><TD style="BORDER-BOTTOM: #d4d0c8; BORDER-LEFT: #d4d0c8; BACKGROUND-COLOR: silver; WIDTH: 670pt; HEIGHT: 13.2pt; BORDER-TOP: #d4d0c8; BORDER-RIGHT: #d4d0c8" class=xl24 height=18 width=894 align=left>Voltage after 30 minutes of driving...... 13.6 VDC</TD></TR></TBODY></TABLE>

 

what brand of volt meter are you using? I have a fluke i like the best,
but my ideal & amprobe show slightly different voltages...

 

Post by fulthrottl:


i've done some tests, as i have the DC power xp 270, and it
flat screams... i start up cold in the morning, and friday morning
in HB, CA it was 38F, and the voltage on the dashdaq sits at about
12.7 volts for about 15~20 seconds, then the engine speed picks
up slightly, and the voltage goes up to 14.9 volts, with some millisecond
long spikes above the 15 volt alarm setting i have on the dashdaq.

after it's fully warmed up, the voltage drops a bit to about 14.8 volts.
it STAYS at 14.8 until i shut off the engine.

i've put a fluke ammeter with a detachable display on my main cable
and cranked.... cold, the starter draws a peak of about 775 amps
cranking, then when idling, about 180 amps with the glow plugs
running, dropping to 40 amps or so after warm up.

so, with the OEM alternator, warming up, the batteries are being
DISCHARGED, as the oem alternator is only good for 110 amps.
the charge on the batteries is making up the rest.

and the batteries are never fully charged with the OEM alternator,
as it only has an output of 13.2 volts, which is sufficient to charge
a battery to 25% of a full charge. THATS IT! you never get past
25% charge with the oem alternator. it's worthless.

so the battery drain, shows a a 60-70 amp draw down on the batteries
till the glow plugs switch off. on batteries that are only 25% charged.

this is why your batteries only last a year and a half, and your ficm
burns out... it's trying to pull 48 volts out of an amplifier that is
being fed with 13.2 volts, not 14.8 volts. it can do it, but it pulls more
current doing it, and current makes HEAT, and HEAT is what burns stuff
up.

with the DC power alternator, as soon as the engine is idling, and voltage
goes up to 14.9, the batteries are BEING charged (current flow is going
the other way, the polarity changes on the fluke) and are CHARGING
WHILE THE GLOW PLUGS ARE ON. the DC power is able to carry the full
cold start needs of the engine, and charge at the same time.

the ONLY time there is a discharge on my batteries, is during the
actual crank.

for severe alternator testing, i can boot up the stereo. the amps have
been upgraded, i'm driving the sub with a 1,200 watt alpine, and
the four door speakers with a 600 watt alpine, and at full volume,
the peak loads on the batteries/alternator combination is about 210
amp peak spikes, with an RMS average of 140 amps, playing
allman brothers "firing line" until your ears bleed.

the batteries are still charging with glow plugs and allman brothers
going.

the only way to burn out this alternator would be to short the output
to ground, bypassing the fusible links in the loom.

i'd guess at that point, you's smoke the diodes before you smoked
the winding. it's square drawn copper, in a hairpin winding instead
of a wave winding, and it can take a LOT of heat.....

i'm an electrical contractor by trade, and much of my experience
is in industrial control applications, so i've got 35 years of figuring
out why stuff burns up......

 

If the PCM sees EOT over 131*f then the plugs aren't commanded on for the up-to-120 second cycle. So your truck being warm meant the glow plugs weren't running during your test. But you should post results from a cold start where EOT is less than 131*f so we can compare. See if you can see a spike or voltage increase when the plugs cut out.

 

We'll see tomorrow.