- Volvo Penta
(Mitsubishi) 115amp alternator
, internally regulated, N-type
- External voltage sense wired to the house battery
- House Batteries
: 4 Grp 31 AGMs (105amp-hr each, 420 amp-hr total) - only 2 months old, no deep discharges, fully charged almost daily with solar
power, good efficiency.
output appears low and/or not apprpriately responsive to battery
House bank fully charged, engine running, no house loads
- battery monitor
= 14.2 volts, charge rate 2.0 amps
House bank fully charged, engine running, 10 amp house load
- battery monitor
= 13.95 amps, charge rate negative
After allowing the house bank to discharge for 2 days (live aboard), the battery monitor with no loads showed 12.5 volts and 67% SOC, (-140 amp-hrs)
House bank at 67% SOC, engine running, no house loads
- battery monitor = 13.15 volts, charge rate 38.2 amps
House bank at 67% SOC, engine running, 22 amp house load
- battery monitor = 12.90 volts, charge rate 20.0 amps
1. Shouldn't the alternator produce (and the batteries
accept) more than 38.2 amps (9.55 amps each) at 67% SOC?
2. When the house loads are increased, and the battery voltage drops, why doesn't the alternator increase its output, especially when it's not working very hard?
3. Does this point more to an alternator problem (poor voltage regulation? bad diode?), or something else entirely?
- Before collecting the data, I verified the basic function of the voltage regulator
at various engine speeds, and I checked the external voltage sense by running the engine with the voltage sense wire connected to both sides of the isolation diode (the alternator increased its voltage to compensate for the .7 volt loss across the diode).
- I cleaned and checked connections. I verified minimal voltage drop across the circuit, and the battery monitor voltage matched my meter readings (diode voltage drop aside),
- Before collecting data, I re-routed the alternator output directly to the house battery side of the isolation diode to eliminate this variable.
- After fully charging
the batteries for 48 hours I disconnected the solar panels
, wind generator
, and shore power
- There were no signs of belt slippage, and the engine / alternator did not even get hot during the following tests. "Engine running" means enough rpm
to maximize alternator output.