Diesel start batteries
My Fleetwood Discovery uses two 950 cca batteries. While checking the batteries current draw I noticed when I turn the ign. key on there is minimal current draw (o.5 dca) but after starting the engine...
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Clamp ammeters are great, but you need to know which way the current is flowing.
Clamp the meter jaws around the cable and ensure that the jaws are closed.
Turn on a load, eg headlights, and note whether or not the display has a "-" in front of the current reading. If possible fit the meter so that it shows a "-".
Turn the load off and start the engine.
If the display had "-" with the load and now doesn't, then the alternator is charging the battery.
Be aware that some engines have air heater elements that may draw more current than the alternator can supply at idle.
The alternator charge current will be high after starting and will gradually reduce as the battery recharges.
You also need to check the voltage.
Clamp the meter jaws around the cable and ensure that the jaws are closed.
Turn on a load, eg headlights, and note whether or not the display has a "-" in front of the current reading. If possible fit the meter so that it shows a "-".
Turn the load off and start the engine.
If the display had "-" with the load and now doesn't, then the alternator is charging the battery.
Be aware that some engines have air heater elements that may draw more current than the alternator can supply at idle.
The alternator charge current will be high after starting and will gradually reduce as the battery recharges.
You also need to check the voltage.
