Foretravel Owners' Forum For owners and Fans of Foretravel Motorcoaches September 10, 2025 ...

12v?

January 19, 2021, 05:22:46 pm

chk ofvoltage after 5days-Solar OFF
start 12.3
house 12.5
engine starts right up. let it run 5min
gen start.. lug lug.. kills c8.3 mechanical
oh no... starts right back after my panic
engine  volts b4 start 12.2
house 11.9
alternator at 12.5v after 10mins via dash..
hit boost, start gen normal
bulk charge indicated..

at 20 min engine running, gen running 10min.. alternator at 13.2, dash guage.. digital at 13.4.

1, what is common to cause this
2. clean posts@ battery?
3. Ground? where are they?
thanks in advance!

Quote Selected

Re: 12v?

Reply #1 – January 19, 2021, 06:12:28 pm

When I had my Monaco when the generator was running and I started the Cummins the voltage drop caused by the starter would
kill the generator. You are the other way around and the generator starter shouldn't cause a big enough voltage drop to kill the
Cummins.

Quote Selected

Re: 12v?

Reply #2 – January 19, 2021, 06:45:00 pm

Depends on which battery starts the generator (vs chassis battery which powers the engine fuel solenoid).

Of course also depends on condition of batteries!

Quote Selected

Re: 12v?

Reply #3 – January 19, 2021, 07:05:16 pm

I personally ran our coach off a old almost junk Optima Red top battery and would start the generator every time Effortlessly. When we picked it up. Since we have used MK gel batteries.
Scott

Quote Selected

Re: 12v?

Reply #4 – January 19, 2021, 08:09:56 pm

A voltage reading of 12.3 indicates about 30% discharged. With this state of charge, when you start the main engine, the voltage should be over 14V for a few minutes. Checking the alternator output as well as a load test on each start battery should show where the fault lies. With the start batteries disconnected from each other and then charged, the voltage on each one should be about 12.7 volts the next day. HF has an inexpensive battery condition tester for $19.95 https://www.harborfreight.com/100a-612v-battery-load-tester-61747.html I bought one and find it works well. 12.3 volts at the battery will start the process of sulfation.

Quote:

"There are two types of sulfation: reversible (or soft sulfation), and permanent (or hard sulfation). If a battery is serviced early, reversible sulfation can often be corrected by applying an overcharge to an already fully charged battery in the form of a regulated current of about 200mA. The battery terminal voltage is allowed to rise to between 2.50 and 2.66V/cell (15 and 16V on a 12V mono block) for about 24 hours. Increasing the battery temperature to 50–60°C (122–140°F) during the corrective service further helps in dissolving the crystals."

Pierce

Quote Selected

Re: 12v?

Reply #5 – January 20, 2021, 04:29:15 am

Sounds like batteries again...

Quote Selected