Alternator output on Volvo 2020

[Dawn Chorus]

Hi All,
I'm having some charging issues with my Bav34 that has a Volvo 2020 fitted.  I'm pretty sure its the original alternator and engine from new in 2001.  Can anyone advise what the alternator output should be at say 2000 revs?  Mine varies massively from about 9amps down to 2.5amps.  All help gratefully received.

Steve

[sy_Anniina]

Alternator output is a function of multiple variables. Low revs reduces output, but the maun driver is the demand: full or almost full battery will not accept much current.

Any standard alternator of that erä should output tens of amps (40-80) to empty battery or other high load. I tested my new 100A alternator on MD22 at 2000rpm by having a 1kw inverter load plus bowthruster at the same time.

BR

Tommi
SY Anniina

[symphony2]

The alternator is rated at 55A but you will never see that. As suggested its output at any given time is determined by the acceptance rate of your batteries and their state of charge. The maximum charge rate for ordinary lead acid batteries is around 20% of capacity when fully discharged but it falls as the SOC rises and by 80% could be as low as 5% slowly falling to 1%. So with a 100Ah battery working in the normal 50-100% SOC range you are unlikely to see more than 10A for short periods. I expect your 34 has a 75Ah start battery that is almost always fully charged and 2*100Ah house batteries. If you start with near 100% SOC and use, say 40Ah overnight (down to 80% SOC) when you start the engine it will likely show 15A for a short period as it charges the engine battery and house together, then switch to house only and fall to 5-8A and then less than 2A as you get near full.

So probably nothing wrong with what you are seeing. Engine revs are largely irrelevant as the alternator will meet these sorts of demands at low rpm. If you want to keep track of your batteries and charging/usage, suggest you fit a battery monitor.