M400 & high resistance IGN1 > Splice > Voltage regulator > ...

[PMUT]

Hi All,

we have an 1981 Vogue on the Dodge M400 chassis and had the issue, that the voltage out of the alternator was under load quite too high.
With blower unit turned on we had an voltage of 15,5volts at the battery terminals.

After digging around, I have found out, that the FLD terminal on the alternator had only 11.5 volts at this point.
I have searched for the issue, bypassed the ignition switch, cleaned al contacts on the battery and starter solenoid, bypassed the ammeter in the dash, but still have an voltage drop between ign1 and the voltage regulator line (all seems related to one splice).

Yesterday I have put in an relay, to bypass the ignition switch completely for ign1, which has reduce the voltage drop to round about 0,6volts under a load of 15 amps, which means the alternator will add these 0,6v on top of the normal output.

Now some questions:

- I think it is a common problem -or?
- I would like to know what others have done
- and also if there is a better way to reduce the resistance.

I have not found the related splice until now and also not the related wire.
My next step would be to replace the wire from ignition to the central splice in the picture attached, but how to find them without opening the complete wire harness?



Any hints?


All the best, stay save and merry Christmas

Ulrich

[DaveVA78Chieftain]

As these rigs age, oddball problems surface.  I have not heard of it being a common problem.  While I do not have a Winnebago anymore, if I recall correctly, that splice is located at the top aft end of the engine, passenger side, by the Transmission dip stick under lots of electrical tape.  The common problem area is the half moon connector at the base of the steering wheel which has the major B+ cable for power going to the ignition switch.

[PMUT]

Thanks Dave!

I might have found the splice as you have described it near the voltage regulator wrapped and in a stupid position.
The half moon connector was also completely melted and the copper wires were annealed completely. I have replaced these connections, and have also bypassed the ignition lock with an relays.
I have also managed to feed in a new cable at J10K-18RE, which has reduced the voltage drop in the range of the splice further.
Next step was to put the blower of the cabin heater on a separated relays and cable, which has now at the end fixed all my high alternator voltage issues.

[Oz]

Good to hear! 

   

[RJZeiler21]

I'm having a problem somewhat similar to the original poster's, wondered if anyone might have any tips for me...

I have a 1976 Winnebago Brave on a Dodge M300 chassis with a 440 engine, and the voltage at the battery (checked with a multimeter at the battery posts) is showing about 15.5V with the engine idling, lights/accessories OFF. I replaced the voltage regulator, which had no effect, so then I followed the charging system troubleshooting guide at Dave's Place (http://dave78chieftain.com/Charging_TS.html). From this, I verified that battery voltage (about 12.4V) was present at the ballast resistor red input connector with IG ON. Then, if I leave the red connector disconnected from the ballast resistor (and IG ON still), the full battery voltage was present at the two voltage regulator connector pins, and the two field pin connectors on the alternator. But, if I connect the ballast resistor red connector, then the voltage regulator and alternator field pin connectors are only getting about 11.5V. Is this behavior expected, or is there something on the output side of the ballast resistor that is causing additional resistance in the VR circuit?

I confirmed that my VR is grounded, showing about 4ohms resistance between the regulator case and the RV chassis. My ballast resistor seems to be good, with about 5.5ohms on one side and 1.6ohms on the other. I replaced the connectors at the steering column base already. I've seen the Dodge relay fix for overcharging, but want to avoid that if it's possible to find my real root cause.

Any thoughts on next steps? My ideas are confirming engine/transmission ground straps (anyone know where these are bolted from the factory?), and maybe adding one to reduce the resistance between the VR and chassis ground. Then, have an auto parts store test the alternator for me. Anything I'm missing?

[DaveVA78Chieftain]

Then, if I leave the red connector disconnected from the ballast resistor (and IG ON still), the full battery voltage was present at the two voltage regulator connector pins, and the two field pin connectors on the alternator. But, if I connect the ballast resistor red connector, then the voltage regulator and alternator field pin connectors are only getting about 11.5V.

When a DC circuit is effectively "open" (no current flowing through it), the full potential of the battery is seen at all points in the circuit (12.4VDC in your case).  When you reconnected the red ballast connector, current could then flow which resulted in a voltage drop of 0.9VDC at the VR pins (12.4 - 0.9 = 11.5VDC) which is greater than .5VDC.  There is a bad connection (high resistance) somewhere in the "supply path" between the battery B+ -> Starter Relay -> Ignition Switch -> main solder junction.  The VR sees a low system voltage (11.5VDC) therefore the regulator increases the alternator output to 15.5VDC in order to compensate for the low system voltage. You will simply have to use the chassis wiring diagrams to walk down the "Ign 1" circuit path (with ballast resistor connected) from the battery -> Starter Relay -> ign sw -> to the VR until you find the point where there is excess voltage loss (high resistance).

Please note that the VR does note simply increase field voltage.  It actually chops the signal into pulses of varying lengths via the ground path.

Please note that the ammeter shown on my TS diagram is an external one added for Trouble Shooting.  For 73 and later chassis' (3 round gauge panel), the in dash ammeter is no longer directly in the circuit path as it was changed to a shunt type meter where a section of the wiring harness between the alternator B+ and the starter relay acts as the shunt.

[RJZeiler21]

Dave, thanks for that advice. Sorry it's taken awhile for a response; I had several other things taken apart on the engine and couldn't get back to troubleshooting the charging system until I could get the engine reassembled.

Anyway, based on the advice above, I started checking voltage drop through the IG 1 circuit. This is what I found:

Starter relay to ignition switch connector: 0.14V drop
Ignition switch input to ignition switch output: 0.23V drop
Ignition switch output to ballast resistor: 0.45V drop

Understanding this, I replaced the ignition switch and ran a new wire from the ignition switch output down to the primary solder junction, to feed the ballast, VR, etc. After this, I cold tested the circuit, and now saw 11.8V at the ballast resistor with IG on. Since that was almost within 0.5V of my nominal battery voltage of 12.4V, I figured it would at least get me under 15.0V charging, and I could troubleshoot further later on.

Boy was I wrong! I started it up today and watched the voltage steadily climb up to 17.3V at the battery. It's almost like the voltage is completely unregulated, so I swapped back to my old VR, but saw the exact same result. Any ideas on why this is happening now?