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Topic: Ignition Solenoid/Voltage Drop Confusion (Read 648 times) previous topic - next topic

Ignition Solenoid/Voltage Drop Confusion

Hello all,
I was wondering if anyone has any comments here or ideas what could be going on.
I have a .5+ volt voltage drop between front and rear.  My ignition solenoid looks like the picture.  Not one of the round cole hersee but instead 2 bosch relays.  The large red wire/terminal to the left has power all the time and the 2 relays once the ignition is keyed on. 

Trouble is the voltage drop is before the relays.  And it's affected by things that aren't keyed like the headlights.  It almost has to be either the cable or the terminal wherever it hooks up further back.

Does anyone think the other end of this cable terminates in the storage bay near the big 12v fuses/breakers or back behind the bed on the panel with the boost solenoid?

Thanks for any help!

Re: Ignition Solenoid/Voltage Drop Confusion

Reply #1 –
Quote from: Mark D –
I have a .5+ volt voltage drop between front and rear.
I'm not clear what you mean by "front" and "rear".  Where are you measuring the voltage?  Between what two points?

1993 U280 SE 40' WTBI, Build: 4359
C8.3 300hp, 6-Speed, Exhaust Brake
960 watts on the roof (6 x 160)
Sorento (or BOLT) on a Kar Kaddy SS
"Nature abhors a vacuum"

Re: Ignition Solenoid/Voltage Drop Confusion

Reply #2 –
Quote from: Mark D –
Does anyone think the other end of this cable terminates in the storage bay near the big 12v fuses/breakers or back behind the bed on the panel with the boost solenoid?
Mark,

You don't have to guess the answer to questions like this.  You need to get out the electrical schematics for your coach and figure out the answer.  I know the drawings are complicated, and the lines are pretty small.  Some members take the original drawings to a printing/copy shop and have them blown up to a much larger size.  Makes reading easier.

So, I believe I have the answer to your question.  Look on the B-2126 schematic linked below. If this is correct for your coach, then it contains the answer.  Look at the column of rectangular boxes on the right side of the drawing.  2nd from the bottom is IGN POWER RELAYS.  Those are the ignition solenoids.  Follow wire #430 20R and it ends up at the 90A Auto Reset circuit breaker on the AUX START/ISO PANEL (UNDER BED).

That's your answer.  Or as close as I can come to finding it.

https://www.foreforums.com/index.php?action=media;sa=media;in=3297




1993 U280 SE 40' WTBI, Build: 4359
C8.3 300hp, 6-Speed, Exhaust Brake
960 watts on the roof (6 x 160)
Sorento (or BOLT) on a Kar Kaddy SS
"Nature abhors a vacuum"

Re: Ignition Solenoid/Voltage Drop Confusion

Reply #3 –
Quote from: Chuck & Jeannie –
I'm not clear what you mean by "front" and "rear".  Where are you measuring the voltage?  Between what two points?



I suppose that is confusing.  I mean between the battery voltage at the chassis batteries (rear) and that terminal (front).  With no draw voltage is sitting at 13.5.  When I turn on the ignition and headlights voltage measured up front at the main terminal (before the relays) is more like 12.8. 

Re: Ignition Solenoid/Voltage Drop Confusion

Reply #4 –
Looking at the drawing is definitely a bit confusing.  I do believe though that there are 12v and ground lugs in the rear that need to be cleaned and resnugged.  I'll start chasing after things until I find a culprit.  Thanks for the suggestion!

Re: Ignition Solenoid/Voltage Drop Confusion

Reply #5 –
Quote from: Mark D –
1.  With no draw voltage is sitting at 13.5.
2.  When I turn on the ignition and headlights voltage measured up front at the main terminal (before the relays) is more like 12.8.
1.  Once again - where?  Is this 13.5 volts being measured at the batteries?

2.  If the answer to above is "Yes" then I think you are concerned about a non-problem.  It is a long wire run from the batteries to your dash, so you lose a little voltage in the wires.  Turning on the headlights also turns on the tail lights and clearance lights.  The lights alone could probably account for the voltage drop you are seeing at the "main terminal".  If it was me, I wouldn't worry about it.

Addendum: The red wire terminal connectors at your ignition solenoids look a little crusty.  Wouldn't hurt to clean them up.


1993 U280 SE 40' WTBI, Build: 4359
C8.3 300hp, 6-Speed, Exhaust Brake
960 watts on the roof (6 x 160)
Sorento (or BOLT) on a Kar Kaddy SS
"Nature abhors a vacuum"

Re: Ignition Solenoid/Voltage Drop Confusion

Reply #6 –
Just some quick and dirty analysis...

The 430 wire is 20R ("2 ought" or 00 gauge - Red).

00 copper wire has resistance of .078 ohms / 1000 feet.

Assume 40 feet X 2 ways is 80 feet. 80 / 1000 x .078 = .006 ohms wire resistance in the circuit.

With headlights/clearance lights on and all ignition and transmission ECU loads assume 50 amp load (even higher with dash fan on high, wipers on, etc).

V=IR ... 50 amps x .006 ohms = .3 volt drop. With terminal lug resistance added in from all the connections along the way you can easily have .5 volt loss or more under load.

What you are seeing is normal and expected. As already mentioned, cleaning and re-tightening 23 year old terminal lugs may help some.

This highlights the importance of the alternator functioning correctly and providing full rated voltage under load.
Peter and Tammy Fleming
1991 U300 GV 40 - Sold, owned for 4 years
Downsized to Roadtrek Popular 210 class B

Re: Ignition Solenoid/Voltage Drop Confusion

Reply #7 –
Geeky, 12.8 v indicates a full battery, so don't think you have a problem. 13.5 v is not in the battery, it is the battery charger in float mode, pushing volts with little amps into the battery, and not enough amps to handle the big ignition load and headlight load.

Re: Ignition Solenoid/Voltage Drop Confusion

Reply #8 –
So I have the advanced panel for my Xantrex charger so I can see the exact load.  It is 40 amps with the ignition and headlights on.  I do expect some voltage drop but things just don't seem right.  The voltage seems to sag more and more as I drive and I don't think it's necessarily the alternator's fault.  The gauges read wrong most likely due to ground/voltage potential differential between up front at the gauges and in the rear where the senders are.  There's definitely something to chase down and I think cleaning all the lugs is a good start.

Re: Ignition Solenoid/Voltage Drop Confusion

Reply #9 –
Quote from: Mark D –
The voltage seems to sag more and more as I drive and I don't think it's necessarily the alternator's fault.
Hmm, this sounds suspect. Is your alternator original, and what brand and size is it? Fading voltage as the alternator warms up is a classic symptom of a failing alternator.

To diagnose it further - after driving for some distance (to heat things up) do some load testing. Can you set to high idle or have a buddy assist? With engine reving to say 1000 rpm measure chassis voltage with minimal load, then add headlights, parking lights, and then add dash fan on high. If the alternator voltage starts to fade when hot with these loads you may need to address this.
Peter and Tammy Fleming
1991 U300 GV 40 - Sold, owned for 4 years
Downsized to Roadtrek Popular 210 class B

Re: Ignition Solenoid/Voltage Drop Confusion

Reply #10 –
Mark,

I'm with Peter, I think you may have a rectifier in the alternator that is starting to break down when it heats up. Most likely one of the diodes in the pos. side rectifier.

Mike
Pamela & Mike 97 U 320

"It's not what happens to you, but how you react to it that matters."

Re: Ignition Solenoid/Voltage Drop Confusion

Reply #11 –
Thinking it's time to learn how to rebuild an alternator.  I had it stop producing voltage before but reseating the brushes cured it for over a year.  But I have everything I need to do a full rebuild with bearings and such.  Any suggestions on where to buy the rebuild components?

Re: Ignition Solenoid/Voltage Drop Confusion

Reply #12 –
Mark,
I don't know what " I have everything I need to do a full rebuild with bearings and such" means.

For the OEM LN alternator you will need a Pos.(+) and Neg (-) rectifier, brush box (needs to be one for a DUVAC system), brushes, voltage regulator, front bearing and rear bearing. Now if you have a failing stator or rotor those are available also BUT if those are dead then you will be $$ ahead to buy a replacement. These can be sourced off the net like eBay, amazon, or some online part stores. Seems like in the media section there is a LN part number pdf. somewhere.

Mike
Pamela & Mike 97 U 320

"It's not what happens to you, but how you react to it that matters."

Re: Ignition Solenoid/Voltage Drop Confusion

Reply #13 –
Quote from: Pamela & Mike –
Mark,
I don't know what " I have everything I need to do a full rebuild with bearings and such" means.
Mike

I understand that one.  The OP has the equipment and the know how to replace bearings and brushes.

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