Can a 12ga wire crank the Vanagon starter motor?

[Sodo]

Link


Yes it can for a bit .....
but probably not "forever".
_________________


'90 Westy EJ25, NEW oil rings (!) 2Peloquins, 3knobs, SyncroShop pressure-oiled pinion-bearing & GT mainshaft, filtered, cooled gearbox.
'87 Tintop w 47k 53k, '12 SmallCar EJ25, cooled filtered original gearbox
....KTMs, GasGas, SPOT mtb

[DanHoug]

I love the exploration! coupla points...

- I would be more comfortable with an actual amp measurement.

- a short section of wire is not a test. think of the fuse element of a 100 amp fuse common in the clear top Japanese fuses. it ain't much of a conductor and a short section of wire can pass a large current without too much fuss because the resistance is low. now increase your wire length to 10' and test again!

- we've discussed this before but I still maintain, without evidence mind you, that the starter draws far more than 100 amps in many situations. one huge factor is commutator speed and on a cold engine, let's say 0F to include a lot of folks, that starter is turning about half as fast. lots more amperage drawn. until I make some Vanagon starter current measurements, consider this just bloviating about the bush.

- I would like to know the hot resistance of the battery tester. there'll be a dramatic increase in the resistance from cold once the element heats up. could you maybe take a cold resistance and then heat the element red hot and immediately test the hot resistance? then we could do some accurate amperage calculations based on the observed voltage.

keep up the Educational Series!
_________________
-dan
60% of what you find on the internet is wrong, including this post.

'87 Westy & '89 Westy both 2.1 4spd

Past projects can be found at--
www.thefixitworkshop.com

[crazyvwvanman]

Why not use your lobster claw on the jumper and measure the current passing through it during your test?

Mark

[Sodo]

I shoulda put my lobster-claw amp-meter on the wire.
But I've measured that battery-load-tester before....
Thats how I know the 100A battery load tester is actually 90A at 10.5volts.

You say the sttarter draws more than 90A when cold.... makes sense.
We need some 0°F fellers to buy lobster-claw amp-meters & give us some real numbers.

Nevertheless..... 20 seconds at 90A didn't smoke that wire.
Warmth of the insulation was barely detectable.
Are you saying that if I use a 10-foot-long wire,,,,that 10-foot wire will get hotter than the 4-inch wire?
More calories spread over 10-feet makes sense because there's more resistance. But is the wire gonna feel hotter? Or insulation gonna melt sooner?

This all came about because some Facebook feller burned up a 12ga wire and seemingly knowledgeable folks asked if he was trying to start the van with the house-battery (via 12ga wire from his "solenoid").
I thought
"hmmmm I guess thats feasible.....wonder what 90A does to a test-wire...."
And here we are.

I was more interested because a friend was having trouble with his (10 yrs old) gear-reduction starter. He added a jumper (a ground wire) from the brushes-end of the motor,
bypassing the gear reduction cases and internal gears) direct to his (direct-grounded) bellhousing.
And problems ceased immediately (2 or 3 years ago) with that 12ga wire being his savior. See https://youtu.be/5a7cdnEuTA8

[Sodo]

So Mark, does "fusing current" mean that at 235Amps, that 12ga wire would pop like a fuse?

Immediately? Or is there a time-factor?

In many cases, the amperage that melts the insulation is most interesting because the wires then cross, or short to the chassis.
Then it's "fusing current" time.
_________________


'90 Westy EJ25, NEW oil rings (!) 2Peloquins, 3knobs, SyncroShop pressure-oiled pinion-bearing & GT mainshaft, filtered, cooled gearbox.
'87 Tintop w 47k 53k, '12 SmallCar EJ25, cooled filtered original gearbox
....KTMs, GasGas, SPOT mtb

[crazyvwvanman]

That was a 10 second time factor chart.

Yes, that is the amount of time before the cooper breaks.

I deleted it for various reasons but the lack of mention of the 10 seconds was a fatal flaw in the chart.

Mark

[Sodo]

[Sodo]

OK I tested some other conditions with the lobster claw ammeter.
Riveting Samba action, I must say…..

10ft section of 12ga flowed 75 A after 10 seconds.

====. Two 20 second tests with lobster claw ammeter ====

1) Same 4” section of orange 12ga. Started at 89 amps, dropping to 86 amps after 20seconds.

2) 10ft, 12-2 coil of house-wire.
Starting amps was 79Amps, dropping to 74A after 20 seconds

Amperage drops as the resistive element goes from cold to red.
_________________


'90 Westy EJ25, NEW oil rings (!) 2Peloquins, 3knobs, SyncroShop pressure-oiled pinion-bearing & GT mainshaft, filtered, cooled gearbox.
'87 Tintop w 47k 53k, '12 SmallCar EJ25, cooled filtered original gearbox
....KTMs, GasGas, SPOT mtb

[crazyvwvanman]

Thanks for doing the extra tests!

What I was hoping to get at was that you can't just take for granted that your load tester is always a "90 amp load".
So you can't just put it into whatever circuit you like and think that it is making 90 amps flow through that circuit.
You demonstrated that point pretty well.

Mark

[1988M5]

[Sodo]

[crazyvwvanman]

Here is a table with some related info.

https://en.wikibooks.org/wiki/Engineering_Tables/American_Wire_Gauge

Mark

[Sodo]

Interesting, thanks Mark

I whittled that table down to sizes applicable to our vans but it's for solid conductor sizes, not stranded.

You can see that using NEC ampacities is gonna be "safe".
A theoretical case that exceeds an NEC capacity by a few percent is not "flame on".
But why NOT just follow NEC guidelines?

In case anyone is inclined to invoke Preese or Onderdonk wire capacites,
I've included a little info about the fellers,
...........background info which helps a little when slinging buzzwords.

This topic would be more fun if DuncanS was still with us...
Maybe he's reading it somewhere.
_________________


'90 Westy EJ25, NEW oil rings (!) 2Peloquins, 3knobs, SyncroShop pressure-oiled pinion-bearing & GT mainshaft, filtered, cooled gearbox.
'87 Tintop w 47k 53k, '12 SmallCar EJ25, cooled filtered original gearbox
....KTMs, GasGas, SPOT mtb

[DanHoug]

Tom- what was the voltage under load during these tests? i couldn't read the meter needle. pertinent to the discussion, i'll throw some Ohm's Law maths in the mix.
_________________
-dan
60% of what you find on the internet is wrong, including this post.

'87 Westy & '89 Westy both 2.1 4spd

Past projects can be found at--
www.thefixitworkshop.com

[Sodo]

Needles are in motion but here's a snapshot
_________________


'90 Westy EJ25, NEW oil rings (!) 2Peloquins, 3knobs, SyncroShop pressure-oiled pinion-bearing & GT mainshaft, filtered, cooled gearbox.
'87 Tintop w 47k 53k, '12 SmallCar EJ25, cooled filtered original gearbox
....KTMs, GasGas, SPOT mtb

[Wildthings]

12ga wire has about 16 times the resistance of 1/0 wire according to your chart, and assuming you need 8' of wire for the B+ wire on a Vanagon, the voltage drop would be in the order of 1.45 volts at 90 amps. Since the starter will draw more amperage as the voltage drops, the actual voltage drop in the 12 ga wire might be 2+ volts. This would significantly effect the operation of the starter and maybe the fuel injection as well.

The use of a 12ga wire would likely shorten the life of the starter and the battery, along with the B+ wire itself.

VW didn't use 2/0 and 4/0 for the B+ cables for no reason

[Sodo]

NOT proposing changing the big 10-foot-long positive cable to 12ga.

But 12ga could be used on the left side ground wire in this (pre-emptive) aftermarket starter-ground proposal.
The main power-handling ground cable to the chassis should be 4ga if 16".
Or if it's 36" to the original chassis ground bolt hole, should be 2ga.

Pictured is a gear-reduction starter.
Those start out all piss-n-vinegar, right?
Then 5 years later the reduction gearbox is gummed up, dry & black stuff inside from current diverting thru the gears etc.
You have to take it apart and clean it, re-grease, re-establish the case-contact ground-path, reassemble etc.

I wonder if those starters would remain pristine inside if they had a 12ga external COPPER ground.

It HAS to be better than relying upon their daisy-chain of dissimilar metals outdoor connections across the stackup?
_________________


'90 Westy EJ25, NEW oil rings (!) 2Peloquins, 3knobs, SyncroShop pressure-oiled pinion-bearing & GT mainshaft, filtered, cooled gearbox.
'87 Tintop w 47k 53k, '12 SmallCar EJ25, cooled filtered original gearbox
....KTMs, GasGas, SPOT mtb