90 Amps load test at alternator post

[Sodo]

I just did this test.

I was reading another thread: (In for a penny, in for a pound) and suggested the member do this test.
Then thought maybe I should see how my van responds before suggesting it to someone else.

So here's the test. You can see there are a few places that volts can be lost.
I did not expect to find anything wrong on my van, it's not misbehaving at all.
Maybe nothing is wrong?
But 2 volts is a LOT of lost volts.
I will find where the volts are lost.

The lobsterclaw ammeter shows the load-tester pulling 90.5 Amps from the alternator post.

Somewhere between the battery, and the direct 4ga to chassis, 90.5 amps load causes voltage to drop from 12.5v to 10.4v, a 2.1volt drop.

My van has a new, oversized 3ga cable from the alternator to the starter post.
From the starter post to the battery, is the 1990 fat cable 10.5 feet long.

My newish, upsized cable,
3AWG from alternator to starter post (2021?) (by the numbers) should be responsible for only about 0.12v of the loss.

I will find the reason for this 2.1v loss!

==================

I have a 130A Tribeca alternator.
So does this mean......
that driving home Sunday eve after a few days camped

IF:

very hungry LiFePO4 battery (50A Renogy DC-DC charger),
a hungry start battery (25A?),
400W headlights aburnin' (30A)

---->50A+25A+30A = 105A....

Does this test suggest I'd have only (~14.5 - 2.1 =) 12.4 volts to charge the start battery?
OK....the start battery would NOT suck 25A if there's not 14.5v available.
But I bet the DC charger would boost 12.4v to suck 50A for the LiFePO, letting loose some amps sometime AFTER it regained a full charge the start battery.
(what a HOG!)

This makes me want an ammeter on my alternator cable.
_________________


'90 Westy EJ25, NEW oil rings (!) 2Peloquins, 3knobs, SyncroShop pressure-oiled pinion-bearing & GT mainshaft, filtered, cooled gearbox.
'87 Tintop, EJ25, cooled filtered (original) gearbox
....KTMs, GasGas, SPOT mtb

All Vanagons should do this:
Add direct starter-to-chassis cable THEN delete ground strap at front transaxle mount.
The best time to do this mod was in 2010. The second best time is TODAY.
If your starter is slow, this is MORE important.

[harvgwen]

Are you saying that you are losing 2V while cranking your engine? If so, that sounds like a fairly reasonable number. If you check the voltage across your 2 battery terminals while cranking the engine, you may find that you actually haven’t got much of a voltage drop at all between the battery and the starter. The battery cannot maintain 12.5V with a heavy draw coming from it.
_________________
1986 Westfalia Vanagon, 2.2 Subaru
Okanagan Valley, British Columbia

[Sodo]

Not cranking.
It's losing 2volts at the alternator post - while holding "the button" down on the load tester.

========= EDIT =========
OK Harv! YES I knew something was wrong here.
I was enamored by the thought of "not cranking"
and missed a step!

FIRST I need to test the battery to find the voltage the battery can sustain with a 90A draw.
If it drops 2v right at the battery, then 2.1v back at the alternator is not significant.

But I'll still do the voltage drop tests of each leg just to solidify this procedure in my mind.
======================

The load is similar to a starter load (90A) but quieter and more consistent.
If the starter had an intermittent problem, that additional fault would add confusion to the diagnosis.

This tester produces a known consistent load.
I like this method better than cranking.

Does anyone know the "wire gauge" and length of the fat battery cable?
VW upsized them over the years.
_________________


'90 Westy EJ25, NEW oil rings (!) 2Peloquins, 3knobs, SyncroShop pressure-oiled pinion-bearing & GT mainshaft, filtered, cooled gearbox.
'87 Tintop, EJ25, cooled filtered (original) gearbox
....KTMs, GasGas, SPOT mtb

All Vanagons should do this:
Add direct starter-to-chassis cable THEN delete ground strap at front transaxle mount.
The best time to do this mod was in 2010. The second best time is TODAY.
If your starter is slow, this is MORE important.

[telford dorr]

If you're getting a 2 volt drop with the load connected directly to the alternator, then there are two possibilities:

1) if the engine was running, the alternator couldn't supply 90 amps at the speed it was turning, so the alternator voltage dropped and could not be made up by current from the battery, due to wiring resistance from the alternator to the battery, and/or battery condition.

2) the voltage drop is at the connections between the load and the alternator and/or ground - especially if the voltmeter is in the load device. (90 amps is a lot of current, so it wouldn't take much connection resistance to drop 2 volts [2 volts / 90 amps = 0.022 ohms between both connections, to be exact]. To avoid this problem, use a separate voltmeter (directly connected to the alternator, not to the load clips) to make the measurement.
_________________
'71 panel, now with FI
'Experience' is the ability to recognize a mistake when you're making it again - Franklin P. Jones
In theory, theory works in practice; in practice, it doesn't - William T. Harbaugh
When you're dead, you don't know you're dead. The pain is only felt by others.
Same thing happens when you're stupid. - Philippe Geluck
More VW electrical at http://telforddorr.com/ (available 9am to 9pm PST)

[DanHoug]

[MarkWard]

I have a similar load box from long ago. Take yours and connect it to the battery posts directly to apply the load with your amp meter on the alternator cable. Report your findings.

[Ahwahnee]

I suspect that 'toaster' you're connecting to the electrics is drawing down the voltage.

[Sodo]

The cart jumped ahead of the horse right out of the gate but I'm still enamored by "testing without cranking".
That the toaster produces a draw appx same as a starter (90A) is a beautiful thing.

[DanHoug]

[PDXWesty]

What RPM was the load test done under? I would suspect you need to be at 3000 RPM to produce enough current at higher loads.
_________________
89 Westy 2.1 Auto

[Sodo]

[fxr]

[E1]

Knowing how attentive you are to these cables and connections, I’m curious what the battery’s actual CCA might show on a load tester — for it to be losing nearly two volts to just to run the tester… that almost can’t be.

Or maybe your tester’s gone bad…
_________________
If ever twice as rich, we’re gettin’ a double-wide
’84 “Westfailure”/2.1 Digijet/5.43 Ring & Pinion/Peloquin/D-rated BFG KO2s

AI has spoken to further illiteracy, to steal, to cheat, and to replace humans
The caveman’s first question to the headhunter: “Hey, you got any coffee?”

[harvgwen]

I still think that drawing 90A will cause the battery voltage itself to sag to the tune of 2V, and that there isn’t really a lot of Voltage drop at all. The way I think this should be tested is to apply the same 90A load, but this time measure the voltage at the battery itself.
_________________
1986 Westfalia Vanagon, 2.2 Subaru
Okanagan Valley, British Columbia

[PDXWesty]

[fxr]

[crazyvwvanman]

That battery load tester EXPECTS the battery voltage to drop when you switch it on.
That is how it works!
It measures the strength of a battery, by measuring the how much the battery voltage sags under its load.
Then you find the colored zone on the meter face that matches the factory cranking amp rating of the battery and see where the needle points with respect to that colored zone.
The larger the battery the less expected voltage drop when the switch is held on.
A smaller battery is expected to sag to a lower voltage and still be considered GOOD.

His photos are too fuzzy to see the cranking amp numbers in the green zones.

Mark

[Ahwahnee]

[Sodo]

Keep in mind I'm doing this on a van that exhibits absolutely NO starter deficiency.

I'd do it on a van that HAS a starter deficiency,
but nobody I know has starter trouble.
I only READ about them on the internets (currently).

I have to CAUSE trouble.
Maybe I'll be lucky enough in the future to have an actual starter problem.

( dutifully following the tool's instructions to the T )
Using 100A battery load tester (actually 90A) on the bare battery it shows 1.6v drop.
That suggests my wiring has 2.1v - 1.6v = 0.5v drop.

0.5v / 12.5v = 4% ......hmmmmm
I HEAR 2% is the acceptable number,
so I'm gonna take 4% as 2% too MUCH...
and git after it!

I'll go thru the 'circuit' methodically with a voltmeter and this "special tool" to find where that "lost 0.5v" is hiding.

Getting a little wild here.....
beyond the limits of the tool's design....
but well within it's capabilities (as a simple 90A resistor).

Probably should test Vdrop between each wire segment (across each connection).
_________________


'90 Westy EJ25, NEW oil rings (!) 2Peloquins, 3knobs, SyncroShop pressure-oiled pinion-bearing & GT mainshaft, filtered, cooled gearbox.
'87 Tintop, EJ25, cooled filtered (original) gearbox
....KTMs, GasGas, SPOT mtb

All Vanagons should do this:
Add direct starter-to-chassis cable THEN delete ground strap at front transaxle mount.
The best time to do this mod was in 2010. The second best time is TODAY.
If your starter is slow, this is MORE important.

[harvgwen]

There’s certainly no harm chasing this, and I know you’ll keep us all in the loop, so this will be a good learning experience for all of us. I’m not an electrical expert, but my suspicion is that your van is fine. I don’t know if 2% is a good number or not. If 2% is a good number on a “standard” vehicle with the battery near the starter, it may be an optimistic number for our vans with a long cable from the battery to the starter. Also, I’ve felt that the said cable is a little on the thin side for what it does, which will also contribute to a voltage loss, as will the fact that it’s (probably?) a 40 year old cable.
Again, I’m not an electrical expert. I will be eagerly following this thread.
_________________
1986 Westfalia Vanagon, 2.2 Subaru
Okanagan Valley, British Columbia