[T3] Electrical questions

Mon Aug 24 19:45:41 PDT 2015

Sean,

That's an heroic bit of work you've done on this system, with a whole 
lot of voltage drop data, but I don't see much that I'd find fault 
with. My main thoughts are that if the starter cranks nicely, then 
the battery and it's state of charge must be okay. None of your 
voltage drops sound unusual; they're actually pretty good for a 6 V 
system.

I'm not a fan of polishing all the connections, simply because 
connections that LOOK dirty are seldom a problem. Connections that 
are actually loose ARE a problem, so I support tightening them 
carefully. The key to any good electrical connection is that it forms 
what's called a "gastight" connection where there are places where 
the 2 metal parts are so tight together that air can't get in and 
cause oxidation. Those important connections are all in places that 
we CAN'T see, so the dirty parts that we CAN see are irrelevant. 
Nevertheless, cleaning doesn't hurt anything, although I'm concerned 
about sanding, as that may leave behind grit embedded in the brass, 
or leave scratches in the brass that let air in. Of course you then 
need to get everything put back together properly.

The one voltage you got that bothered me was the 7.5 V from the 
generator at some point. That's too high; you should see 7.1-7.2 V, 
measured at the battery or B+ terminal while driving. Sustained 7.5 V 
will damage the battery. Anything measured at idle is meaningless, 
because the generator isn't doing anything then. You seem to 
understand this, because you were careful to mention that you got the 
7.5 V measurement just above cutout. If you measured it at somewhat 
higher rpm you might have gotten a slightly lower and better number. 
There tends to be a bit of a "hump" in the voltage where the 
regulator just begins to regulate. I tell people to look for the 
"plateau" in the voltage, where it levels off under good regulation.

I suspect that there was some other starting problem that got you 
started down this path, but, for the most part, your charging system 
sounds like it is doing okay. The reduced voltage with the headlights 
on seems a bit high, and that may be a problem, especially with 
halogens, which are quite intolerant of low voltage (hence the 
relays.) You sourced the relay power directly from the battery, 
right?

For the record, I'm currently working on a solid state voltage 
regulator that I can adapt to either 6 or 12 V systems. If this 
works, it should last forever and give much better regulation. 
Getting a solid state solution for the 50 A cutout is challenging, 
but I think I have a reasonably priced solution. I haven't tested 
anything yet; so far this is all in the thinking stage: nothing in 
testing, let alone production.

My plan is to install my solid state regulator circuit inside genuine 
Bosch VR boxes. That would make them look original, while also giving 
original mounting and connections. I would sell them on an exchange 
basis. I have a large pile of dead Type 3 Bosch 12-Volt VRs, but only 
one 6 V VR. If any of you have a few dead 6 V Bosch Type 3 6-Volt VRs 
lying around, please save them for me. I'll give you a break on a 
solid state version when they are ready.

Jim

On 24 Aug 2015 at 17:33, Sean Bartnik wrote:

> Hi all,
> This is a cross-post from the Samba but I wanted to get a read on this from the great minds here.
> 
> Just as a bit of background, not long ago I put in Cibie H4 55W/60W halogen headlights with relays.  Over the last few months I suspect the battery had become slightly discharged just from a lot of short-trip city driving.  Last time I measured anything it was showing about 6.13V which is a bit low.  The other day I drove to my office parking garage to aim the new headlights.  Left engine idling while aiming them, then took a drive for ~20 min to run an errand.  Came out of the shop and the Eggcrate wouldnTMt start.  It was cranking fine but no sign of ignition.  I did not have a meter with me to check voltage at coil terminal 15 while cranking but I was guessing that the idling while aiming the headlights might have put my battery below where it needed to be.
> 
> Luckily I was parked somewhere I could push-start the car myself, which I did and it fired right up.  Once I made it home I put the battery on the charger and it did indeed need a charge.
> 
> Today I decided to poke around and do some voltage drop testing.  And here´s where we get into the Samba post:
> I´d love to get some input on these findings:
> 
> -------------------------
> 
> Spent some time today checking out the electrical system to make sure everything was in order, and trying to eliminate or reduce some previously measured voltage drops.
> 
> So today with fully charged battery (6.28V) I measured voltage drop from the + terminal of the battery to:
> 
> *With ignition off*
> Voltage Regulator B+ terminal: 0.00V
> Lug on fuse box were the B+ wire comes in: 0.00V
> 
> *With ignition switched on*
> Voltage regulator B+ terminal: 0.03V
> Headlight switch terminal 30 in from VR: 0.09V
> Headlight switch terminal 30 out to fuse box: 0.10V
> Fuse box terminal 30 in: 0.28V
> At fuse box terminal for 15 wire from ig. switch: 0.29V
> At fuse box terminal for 15 wire to coil: 0.30V
> At coil terminal 15: 0.56V.
> 
> So I was losing over half a volt from battery to coil with ignition on.  This may have been my starting problem the other day as the battery was slightly discharged (6.13V) to start with before idling with headlights on to set the aim. When cranking the voltage at coil terminal 15 could have easily dropped to below 4.8V and no sparky.
> 
> So I pulled the fusebox down and started poking around, finally decided to hell with it and pulled the whole fusebox out.  Hit everything in the fusebox with De-Oxit.  Measured resistance across the bus bars that join certain neighboring fuses, 0 ohms.  Put fuses in and measured resistance across the fuses.  0 ohms.
> 
> Hit some of the wire terminals hanging in the car with De-Oxit.  Some of them were a bit loose on their spades so I tightened them up with pliers.  Also pulled the headlight switch and hit those terminals with De-Oxit.  Notably the terminals for the big red wires to headlight switch and from headlight switch to fuse box were a little loose.  Clamped them down a bit.  
> 
> Pulled the coil and cleaned up terminals 15 and 1 with sandpaper and De-Oxit.  Clamped the terminal 15 wire down a bit too as it was somewhat loose.
> 
> Measured the resistance of the coil wire from fusebox to the engine compartment and it was only 0.3 ohms.  For reference, my meter reads 0.2 ohms when you connect the two meter leads together. Ol' Crispy is pretty non-crispy in my car, thankfully.
> 
> Put the fuse box back together, didn't leave out any wires and everything seems to work.  This time I measured voltage drop from battery + as follows (ignition ON):
> @ Fuse box where 30 comes in from H/L switch: 0.11V (was 0.28V)
> @ fuse box where blk wire comes in from ig. switch: 0.15V (was 0.29V)
> @ fuse box where blk wire goes to coil: 0.15V (was 0.30V)
> @ coil: 0.33V (was 0.56V).
> 
> So clearly things are better now.  Can anyone with experience advise as to whether these are reasonable voltage drops?
> 
> Then I connected my meter to D+ terminal on voltage regulator and the other lead to battery ground.  Fired up the engine and not long after generator cut-in, I was showing a good 7.5V on this lead not too far above idle.  
> 
> However when I switched my meter over to terminal B+ on the VR, I was getting around 6.5V at idle up to about 7.01V at max speed.  With headlights on that dropped to around 6.75V at max speed.
> 
> I would love to see 7.5V out of the voltage regulator.  Is there a good reason why I shouldn't attempt to make that adjustment?  I worry that I don't fully understand the relationship between charging voltage and charging current and therefore I'm hesitant to mess with it without fully understanding it.
> 
> -----
> 
> Thanks!
> -Sean
> ´65 Squareback (formerly Keith Park´s)
> 
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-- 
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Jim Adney, jadney at vwtype3.org
Madison, Wisconsin, USA
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