Lost connection: House battery to Converter (SOLVED)

[WesternHorizon]

Boondocking way out west.

1995 Tioga Montara Class C on Ford F350 chassis, 460 V-8. Upgraded to BestConverter Ultra III in 2014.

Inverter chirping in the afternoon from low voltage, so started Onan generator. 14.4 volts on meter, later dropped to 13.9. Around this time the fan in the converter started pulsing low / higher. I thought this was because the battery was charged.

Turned off the Onan and everything went black.

Checked converter bottom 30A fuses (unscrew lower compartment). If fuses removed while Onan is on, lights go out. Implies power converter is the only source of 12 VDC.

Fan does not come on, implying the battery is not putting any load on the charger.

Turned off Onan and checked supply line from house battery. Less than one volt (dropping slowly because of backfeed from power converter.)

Key symptom: Converter no longer has a connection to the house battery, either to charge it or get power from it.

Yet battery is charged and starts the generator through the heavy cable.

Chassis manual shows “Modified vehicle power feeds” 50A fuse in Power Distribution Box. Pulled this with difficulty: OK.

Key diagnostic question: What has changed?

Wrote everything down, ran Honda EU2000i overnight to power furnace and most importantly the VPAP machine.

The problem is now fixed. Can anyone diagnose it based on the clues above?

[WesternHorizon]

"You ask what changed.. You pulled (with difficulty) the fuse and I assume put it back. in the process you scraped the contacts (Blades)"

I was unclear about this part. That fuse had nothing to do with the problem. Not sure it is even used for anything. But good tips on intermittent fuses. Thank you.

[YC_1]

Have voltmeter, will travel. Even when traveling in a friends RV I take a voltmeter and alligator clips. It has saved me many times as well as others.

[wa8yxm]

WesternHorizon wrote:

Chassis manual shows “Modified vehicle power feeds” 50A fuse in Power Distribution Box. Pulled this with difficulty: OK.above?

You ask what changed.. You pulled (with difficulty) the fuse and I assume put it back. in the process you scraped the contacts (Blades) clean and restored contat.. Alt-The fuse may be bad in a way that allows it to opperate intermederate (I do not have the time to explain that but a bad connection internally vibrates into an out of contact) I do not think this is common with BLADE type fuses (E LIke ATC) but it is with some others... More likely corrosion erased by pulling and inserting.

[WesternHorizon]

Old-Biscuit wrote:
Battery POS cable to converter In-Line CB tripped

Bingo!

Next morning noticed that there is a red 10AWG cable coming up from below and possibly from the rear of the vehicle. It connects to the bottom lug of a component on the firewall. Could this be the supply line to the converter?

With generator running, this showed 13.6 volts. Could this be backfeed from the converter, trying to charge the house battery?

With generator off, this showed 0 volts. Bingo?

The top lug showed 11.6 volts with and without the generator on. I suspected this was the undercharged house battery.

I very carefully wrapped a jumper of wire between the two terminals. And on came the lights!

So, what changed? This circuit breaker wore out over 23 years. I Googled and found one

Modified Reset Circuit Breaker

Glad I had electrical tools along so I could diagnose this problem. Almost did not bring them but figured there might be a problem with the dirt bike. Would have lost days going in to the city.

Good fun being self-sufficient out in the boondocks.

[MrWizard]

My generator is connected the engine battery

I need to track down the cable and change that

Yes my Onan starts with house batteries disconnected

[Old-Biscuit]

Battery POS cable to converter In-Line CB tripped