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voltage specs twin 91 454

S

slauder

Regular Contributor
Gauge reads low at 12 thru 13.5. Disconnected from shore power (inverter/charge) and used a good voltage meter on batteries. Both banks were 13.4. Started both engines and tested at 1000 rpm and found 14.3. Is this a valid test? Should I be off the chargers for a while first? Am I within specs? I have to test the output at the console gauge next.
 
Those voltages look OK. It is best to let a lead acid battery "equalize" a few hours with no load, no charge for a number of hours before the open circuit voltage test. That test really is good for finding near dead cells, not as a capacity test. Also use a hygrometer if these are flooded, serviceable batteries.
 
Scott: what is your "real" question? Are you concerned about the batteries' capacity or the condition of the alternators?

In either case, a more complete test would involve measuring both the current and the voltage, usually with a load tester involved.
 
Alternators. I know how to test batteries with my cheapo load tester. Its a heater coil and a gauge. How to test load for alternators?
 
Thorough Alternator test - use a load tester across a fully charged battery. Details should be in the service manual. Basic scheme is to raise the engine RPM (maybe ~ 3K RPM) and adjust load tester (carbon pile) until alternator's rated output current is delivered. Check voltage at battery terminals. If the voltage is high enough and the current output in spec, then the alternator provides its rated power capacity. If either the V or the I is low, unsatisfactory operation is almost guaranteed.
 
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