12 V Charging problem

[Norman Martin]

My dash reading shows 13.4 charging from 12 V alternator but checking positive post on back of alternator reads 12.2. Any suggestions what to do?

Norman Martin
2000 XL Country Coach
60408

[PrevostNewbie]

House or Chassis Voltage?

[Norman Martin]

House 12 V system. 24 volt alternator working fine.

Thanks,
Norman

[PrevostNewbie]

is it 12.2 with the engine running?

[Norman Martin]

Yes 12.2 with engine running.

Norman

[PrevostNewbie]

What you are describing is not possible. Batteries without a charge current will not be that high at standing voltage. Are you sure you are diagnosing this correctly? Ignore the gauge for now, what is your House Battery Voltage at the batteries?

[Norman Martin]

House batteries 12.8. plugged in to 50 amp plug.

Norman

[Fratto]

My Thoughts: You may have two issues here....

If the dash gauge is reading 13.4 but the alternator is only reading 12.2 then the gauge is wrong or that gauge is not really reading the 12 volt alternator.

If the 12 volt house batteries do not have any load on them, then 12.2 volts is only 60% of charge assuming they are in fairly good condition. A fully charged no load reading should be closer to 12.7. If there is some load on the batteries then they can read 12.2 while having a higher state of charge due to the voltage drop created by the load.

Lets assume that they are at 12.2 (60%) then the alternator should be sending 13+ to the batteries knowing that they need to be charged.

Measure the house battery voltage at the batteries while plugged in. This will let you know what charge voltage the inverters are providing. Then unplug the bus, wait a few minutes, and measure the battery voltage again preferably with no 12 volt loads on. This should give you a feeling for their state of charge / condition. You will now have also measured the batteries with out the alternator. Then start the bus and measure the voltage at the batteries.

Battery voltage plugged in on the inverter?
Battery voltage not plugged in and resting with no load?
Battery voltage with engine running?

Let us know and we figure out if the alternator is working, voltage regulator is working, you have a bad battery in the bank, etc.

[Norman Martin]

Will do this when I get back home this evening.
Thanks for your help.

Norman