Voltage Drop while driving

[SloPoke]

I have a 2006 Cummins ISL400 in my motorhome. While driving up from Rio Grande Valley to Albuquerque last week, I noticed that the Voltage reading on both my analog gauge on the dash and my silverleaf computer showed that the voltage started at 13.4v and slowly dropped to 12.8v during each day’s travel. Had it into a diesel repair shop here in Albuquerque today and had the charging system tested. The voltage at the chassis batteries from the alternator was 13.6 Vdc, which is what it should be. Next, they load tested the chassis batteries and they passed. On the way back to where I am staying, the gauges were jumping around from 12.8v to 13.0v. Has anyone experienced or heard about this before?
Thank You for your input.

[Craig36]

I have a 2007 Kountry Star on a Spartan chassis with the same engine.

I have experienced the same thing, but never had testing done. I suspect it is a voltage regulator cycling on and off, but that is just a guess.

I'll be interested to follow your thread to see if others observed the same thing.

[96 Wideglide]

13.4 seems low to me. I'm used to see'ing 14.0V while I'm driveing. Maybe alternator??

[Piker]

The gauge jumping around could be just a loose connection somewhere to the gauge itself?

It could also be the isolator relay delay. It senses the voltage from the chassis charging system and ties in the house batteries if the voltage is adequate. This helps to prevent overloading the alternator if there is a large draw on it from lights, accessories, etc. What condition are your house batteries? If they are not in good condition they could be overloading the isolator relay, which will then cycle on and off to prevent overloading the alternator. You could also have a bad connection at the relay itself, causing the isolator to sense the incorrect voltage, thus causing it to cycle constantly. I had this issue myself.

As far as trusting the gage for what the actual system voltage is... accuracy at the gage will depend on the quality of wiring and connections to the gage from the alternator/batteries. If the wires are too long for their size, or if there are corroded connection or fuses, you will get lower than expected readings at the gage... also possibly erratic readings.

I too think 13.6 is a little low, but probably still acceptable. I get 14.2 at the alternator on our rig.

-cheers

[twinboat]

Did the check the belt and idler for proper tension ?

[gatorcq]

Originally Posted by twinboat

Did the check the belt and idler for proper tension ?

One belt, spring tension idler. If loose belts a few other items would be having issue.

Normal voltage read is anywhere from 12.7 to 15, based on the need and RPM Built in voltage regulator inside the alternator.

[pbensen]

The ambient temperature as well as the SOC of the batteries are variables on the charge voltage. I have a digital volt meter readout on my trailer brake controller in my van that I routinely monitor . I notice that when it is hot outside the charge voltage is around ~13.9v. When it is colder outside I see higher charge voltages; ~14.7v.

[b17drvr]

If it’s cold out, the grid heater will cycle on and off and that will drop the voltage.

[theoldwizard]

This is NORMAL ! All modern engines have "smart" alternator that charge the starting battery just enough to replace the energy used to start the engine. I have discussed this multiple time before. At 12.8V the starting battery is not going to discharge.

What this does mean is that you will NOT recharge your house batteries unless you have a DC-DC battery charger. Also discussed previously.

Originally Posted by gatorcq

Normal voltage read is anywhere from 12.7 to 15, based on the need and RPM Built in voltage regulator inside the alternator.

100% correct ! (Although voltage output of the alternator is typically controlled by the PCM not the regulator.)

[twinboat]

Originally Posted by theoldwizard

This is NORMAL ! All modern engines have "smart" alternator that charge the starting battery just enough to replace the energy used to start the engine. I have discussed this multiple time before. At 12.8V the starting battery is not going to discharge.

What this does mean is that you will NOT recharge your house batteries unless you have a DC-DC battery charger. Also discussed previously.


100% correct ! (Although voltage output of the alternator is typically controlled by the PCM not the regulator.)

That's not the case in a 2006, motor home, diesel engine package.

Your claim may be true for new, small, gas saving, vehicles that are searching for the most MPG numbers, but not in the truck engine market.

I have a 2017, E450 chassis and it runs the electrical system at 13+ volts all of the time.
It has a fairly simple isolation/combining " BIM " device that re-charges my house batteries fine.

[theoldwizard]

Originally Posted by twinboat

I have a 2017, E450 chassis and it runs the electrical system at 13+ volts all of the time. It has a fairly simple isolation/combining " BIM " device that re-charges my house batteries fine.

This still far from "optimal" for re-charging a 200+ Ah battery bank (two 6V GC2 gold cart batteries) that are down below 80% state of charge !

This video is made by Sterling Power, a European company, the maker of DC-DC charging systems. DC charging is still DC charging on either side of the Atlantic.

Skip to to the "meat" of the discussion 8:31 - 9:30. The black meter is showing current INTO the house batteries. They did change the wire size from about 14 AWG to about 2 AWG (6 AWG would have probably been adequate). The current to the house batteries went from <10A to >90A !

[twinboat]

Originally Posted by theoldwizard

This still far from "optimal" for re-charging a 200+ Ah battery bank (two 6V GC2 gold cart batteries) that are down below 80% state of charge !

This video is made by Sterling Power, a European company, the maker of DC-DC charging systems. DC charging is still DC charging on either side of the Atlantic.

Skip to to the "meat" of the discussion 8:31 - 9:30. The black meter is showing current INTO the house batteries. They did change the wire size from about 14 AWG to about 2 AWG (6 AWG would have probably been adequate). The current to the house batteries went from <10A to >90A !

I know about the Sterling product line.

Driving down the road may not be the optimal charging routine but it works.

The point is, MH alternators have voltage regulators and are not set to 12.7 volts.

[Ray,IN]

Originally Posted by twinboat

Did the check the belt and idler for proper tension ?

MackWrench pointed this out in a different thread. This u-tube video confirms your reply.

https://www.youtube.com/watch?v=h8pQ...ature=youtu.be

[skypilot_1]

Originally Posted by b17drvr

If it’s cold out, the grid heater will cycle on and off and that will drop the voltage.

After engine start, the intake air heater should not be on if working normally. If intake temp above 60'f it should not come on during starting as well. just sayn