Mark is porbably going to have more electrical
adventures getting across the Pacific, but the multimeter tests he ran can tell a lot about his system:
Check voltage before, during and after charging
The 'Lights' mentioned are 4 cabin
12.32 volts at 6.59pm
13.30 volts 7.01pm
13.55 volts 7.30pm with lights on 13.38 volts
13.61 volts 7.50pm with lights on 13.44 volts
13.60 volts at 8pm with lights on 13.42 volts
12.77 volts with lights on 12.57 volts
12.68 volts 8.06 after a drain to remove surface charge.
So what is his multimeter saying:
1. His alternator
works, bringing the batteries up to their regulated voltage of 13.6 volts after half an hour's charging
2. The regulator
is likely a single
stage internal type, which maintains the output terminal of the regulator
at 13.6 to 13.8 volts (you can put the multimeter directly on the output terminal to get a more accurate value).
3. The voltage reading at the battery
comes up to 13.55 volts by 730 pm, which is less than the voltage at the alternator
due to the voltage drop through the charging wire. This is the end of the bulk phase of charging, where the batteries are taking the entire potential output of the alternator.
4. The battery
voltage slowly rises from 13.55v at 730 pm to 13.60v at 800 pm during the acceptance phase of the charging cycle. The voltage at the alternator is held constant by the regulator, and the current
going into the batteries slowly drops over time. The small increase in voltage at the battery terminals is because the voltage drop in the wire (and any connections) from the alternator to the battery is decreasing as the charging current
5. The 0.17 volt decrease in battery voltage when the lights are turned on is most likely due to the voltage loss in the wire from the alternator to the battery. The regulator is boosting the alternator output current to compensate for the light load, and the increased current leads to a larger voltage sag from the alternator to the battery. Here the multimeter test is telling us something else--this voltage sag seems too big for the light load(which I assume to be up to 5 amps), and its time for some more work.
First, clean all the connections between the alternator and the battery (both hot side and ground). It may not change things, but it certainly can't hurt and doesnt cost anything. You can also measure the voltage drop across each connection while the battery is being charged at high current--the dirtier connections will have the highest voltage drop.
Second, measure the alternator output terminal voltage to see if it changes when the lights go on. It should in the first half hour of charging, when the alternator is putting out all it can, and its output is shared by the light load and the battery charging load,. However, if you have been charging for more than 45 minutes (well into the acceptance phase where the alternator is controlled by the regulator) and the alternator voltage drops by more than 0.05v when the lights come on, then you have a dodgy regulator.
Finally, determine if the wire from the alternator to the battery is big enough (#4 or lower) for 80 amps. If it is too small, which is a common problem in production and charter
boats, put this on your list for when you get across the pond.
As pointed out in other posts, your battery bank is to small for sustained performance. Every time you discharge and recharge the batteries they are losing capacity. This loss is non-linear, so that 4 discharge cycles which take out 25% of the bank's capacity will cause less capacity loss than 2 discharge cycles which take out 50%. Thus, to nurse your batteries across the Pacific, you are better off charging for 1/2 hour every 6 hours, than charging for an hour every 12 hours, or especially 2 hours every 24 hours. Discharge batteries also suphate with time, and since you don't have the capacity for equalizing the batteries, the more frequent charging regime will also help with that problem.
One final comment--while you are in the initial bulk phase (alternator maxed out), the battery voltage and the charging current will vary with engine rpm
. The battery voltage will gradually be going up anyway, but you will probably be able to see a higher voltage as you bring the engine rpm
up. With practice you will find a 'sweet spot' probably between 1000 and 1500 rpm where the engine is smooth, the alternator output is a high percentage of maximum, and you aren't burning too much fuel
. The engine gurus are going to jump in and tell you that running at a fast idle is not good for the engine, but you won't wear it out in a few hundred hours, and you can put in a fancy regulator, bigger batteries, solar panels
, etc. when you get back to the first world.