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 the current draw jumps to 25 dc amp and after a few seconds settles between 19 and 20 dc amps. A steady draw of 20 amps appears excessive with nothing on or running except the diesel engine. The alternator shows a steady charge, the block heaters are off, and a battery charger is not connected . Grounds appear to be good. I'm using a clamp-on amp meter in good condition. I would appreciate your advice and/or comments.

Could the clamp on be reading the amperage going back into the batteries? I have a clamp on meter, but must confess that I haven't taken the time to learn how to use it yet.Bill

Trackrig wrote:Could the clamp on be reading the amperage going back into the batteries? I have a clamp on meter, but must confess that I haven't taken the time to learn how to use it yet.BillI think Bob has it. It's been awhile but as I remember it, the clamp around amp meter measures the electromagnetic field generated n the wire by the electrons (electricity) flowing through it. Same theory makes electric motors and transformers possible. I don't think you can tell the direction of the current that way. I think you are seeing the charging current "coming back" from the alternator. I've been out of the electronics field for 21 years but that's my opinion!Jerryps: If we are talking the same device, you don't clamp it on the wire, you clamp it around the wire not touching the wire with the clamps.

Surprised that it does not have a high draw when ignition is on, even before the starter is engaged. The INTAKE MANIFOLD HEATER draws a lot.And the heater can run in cold weather for a few minutes after start up.To minimize voltage drop when starting assuming house battery bank is at or near full charge:Engage "boost/combine" switchStart engineDisengage "boost/combine" switchHard to have too many cranking amps applied to the job.

DC clamp on amp meters will tell you which way the current is flowing. There will be a "-" symbol on the display or not depending on which way it's going. Of course, you have to put the clamp on the right way to know which way that is. The instructions for your meter should tell you all about it.If your measuring the charging current going back into the batteries it doesn't seem unreasonable since they just supplied a lot of power to the glow plugs or grid heater or whatever your engine has and then the starter motor.If you're measuring a current draw from the batteries then something is wrong with your alternator as it should be supplying the draw, not the batteries.

I think Bill has it right. The high amperage is the alternator putting charge back into the starter batteries. After a while, the amperage will drop as the batteries top off.

Diesel start batteries | Good Sam Community

gemert
Explorer
Mar 27, 2014
Trackrig wrote:
Could the clamp on be reading the amperage going back into the batteries? I have a clamp on meter, but must confess that I haven't taken the time to learn how to use it yet.

Bill

I think Bob has it. It's been awhile but as I remember it, the clamp around amp meter measures the electromagnetic field generated n the wire by the electrons (electricity) flowing through it. Same theory makes electric motors and transformers possible. I don't think you can tell the direction of the current that way. I think you are seeing the charging current "coming back" from the alternator. I've been out of the electronics field for 21 years but that's my opinion!
Jerry

ps: If we are talking the same device, you don't clamp it on the wire, you clamp it around the wire not touching the wire with the clamps.
Trackrig
Explorer II
Mar 27, 2014
Could the clamp on be reading the amperage going back into the batteries? I have a clamp on meter, but must confess that I haven't taken the time to learn how to use it yet.

Bill

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