T1N Voltage Issue, on the road help

Pasieka

Member
Never remove the battery cable with the engine running. The resulting voltage spike can destroy electronics. Better to just use a volt meter, as that will detect under and overcharge.
That's probably true... especially on German cars.

You would think zenner diodes and other industry standard methods of circuit design would be present to correct for and anticipate user error.

Sent from my SM-N950U using Tapatalk
 
Last edited:

Midwestdrifter

Engineer In Residence
American cars use Bosch alternators too. I personally saw a Chevy truck die from a battery cable breaking and the alt spiking. It has to do with physics, not your ridiculous "German car" reasoning. The alternators are digitally monitored, the reality is that the field current can only change so fast.
 

Pasieka

Member
American cars use Bosch alternators too. I personally saw a Chevy truck die from a battery cable breaking and the alt spiking. It has to do with physics, not your ridiculous "German car" reasoning. The alternators are digitally monitored, the reality is that the field current can only change so fast.
The physics, reaaaalllllllyyy, please, explain.

Sent from my SM-N950U using Tapatalk
 

Aqua Puttana

Poly - Thread Finder
The physics, reaaaalllllllyyy, please, explain.

Sent from my SM-N950U using Tapatalk
The physics of parts failure.

In my many decades of electrical maintenance I have never seen electricity fail. I have repaired many mechanical failures to restore system operation.

I think that you should visit the Danger Zone. You'll probably find it comfortable and you may like it there.

:cheers: vic
 

autostaretx

Erratic Member
The physics, reaaaalllllllyyy, please, explain.
Let's start by quoting the (in this case 2006) Sprinter Owner's Manual (page 266): (emphasis added)
Do not loosen or remove the battery terminal
clamps while the engine is running or the key is in
the ignition lock as this could damage electrical or
electronic equipment beyond repair. All electrical
consumers must be switched off.
As for the physics, the battery is an energy storage device which also serves (as a mental model) as a capacitor ... voltage spikes elsewhere in the wiring are (very) effectively "eaten" (surpressed) by the battery... high voltages serve to charge it, drop-outs are fought by the battery supplying the "missing" voltage/current. The alternator really has to *work* to haul the battery voltage up to the 14.x charging level. Disconnecting the battery mid-flight very definitely removes that "capacitive" protection.

When you suddenly disconnect the battery, the alternator and any inductive load (wiper and fan motors, relay coils) will suffer a voltage drop (or rise, as soon as the alternator system notices and can respond to, the drop-out) .... that's called dV/dT (or dI/dT for currents) in electronics-speak. That rapid change is equivalent to what happens in a gasoline car's ignition coil: rapid disconnect (ignition points opening) creates a very short dT (in the denominator) hence very high resulting voltage or current (depending upon capacitance or inductance of the chunk of the circuit you're looking at).

Look at the relay choices MB uses throughout the Sprinter ... many (but not all) have resistors (or diodes) bridging their coils to *fight* ("snub") those dI/dT effects... without them the collapsing magnetic fields can generate voltages far in excess of "12v".

The alternator's coil is similar, and bigger ... although the regulator will *try* to control it, it does take a noticeable amount of *time* (from sensitive electronics' point of view) to react to sudden changes. (there's a reason a coil's inductance is also called "reluctance").

The Sprinter has many distributed sources of inductance more than happy to supply unwanted voltages, and damn few distributed capacitors to soak them up.

Disconnecting the battery while running is very definitely an "old school" technique (i used to do it to 1960s VWs and Porsches) ... but the fly-by-wire Sprinter ain't old school.

--dick
 
Last edited:

Luke.Drifter

New member
Reminds me of a 100-degree day in Spokane last June. Luckily O'Reilly had a 150A alt in stock and a shady parking lot. The Domino's across the street kept the family fed while I performed some unplanned maintenance.
I can't remember if I thanked him, but Vic's alternator change-out write-up saved me quite a bit of time (allowing me to return a few tools to the O'Reilly by closing time on a Sunday).
Alt change-out.JPG
Down-and-dirty.JPG
 

alexk243

KulAdventure
Reminds me of a 100-degree day in Spokane last June. Luckily O'Reilly had a 150A alt in stock and a shady parking lot. The Domino's across the street kept the family fed while I performed some unplanned maintenance.
I can't remember if I thanked him, but Vic's alternator change-out write-up saved me quite a bit of time (allowing me to return a few tools to the O'Reilly by closing time on a Sunday).
View attachment 99189
View attachment 99190
Nice! Luckily our sprinters are high enough of the ground to do the repairs without a lift/jack.

KulAdventures.net
 

Top Bottom