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Old 05-03-2020, 09:20   #1
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Why my engines draw much amps?

I have a great battery charger (Pronautic 50) that shows how to treat a flooded battery well. It shows positive amps when sustaining at 13.4v and when conditioning at 14.5v.

When I start my engines (stbd does the house bank), I see the alternator voltage go to 14v, but the amps go negative 15a. So, there must be something eating the current. Yes, everything else is off and yes the heaters cycle off.

Help? I have 1998 mechanical style Cummins 6BTA-370.
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Old 05-03-2020, 09:29   #2
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Re: Why my engines draw much amps?

Is it only when you fire up, then goes away fairly quickly?

Your starter is a big amp draw item. Also if you taking this -15A reading from the analog amp meter on the engine panel, would question the pinpoint accuracy of these meters as these are typically only reliable for ballpark measurements.
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Old 05-03-2020, 10:03   #3
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Re: Why my engines draw much amps?

Where are you measuring g this negative current from?
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Old 05-03-2020, 10:13   #4
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Re: Why my engines draw much amps?

Maybe the ammeter is hooked up backwards
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Old 05-03-2020, 11:03   #5
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Re: Why my engines draw much amps?

Our 2001 Cummins 6BTA 330 hp draws lots of amps (have not measured how many, but voltage drops quite noticeably) while the grid heater is on. It's on and off until the engine warms up a bit.
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Old 05-03-2020, 19:57   #6
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Re: Why my engines draw much amps?

Thanks all. It's a constant negative (out of battery) current. It's not the starter. It's not the heaters, because I see them cycle on and off.

The point of measurement might an issue. The meter is on the main panel midships. I think it gets voltage and current back aft.

My batteries don't die after a long run, so maybe it's OK.
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Old 05-03-2020, 20:12   #7
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Re: Why my engines draw much amps?

Buy or borrow a clamp-on ammeter and start verifying the current flow in individual cables. Should be fairly easy to find the guilty party. And while you are at it, make at least a gross wiring diagram for your boat. It's a nuisance to do, but will save you countless hours in the future.

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Old 06-03-2020, 07:06   #8
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Re: Why my engines draw much amps?

Disconnect the grounds returning to the battery one at a time to find the current hog.
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Old 06-03-2020, 09:12   #9
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Re: Why my engines draw much amps?

Thanks again.

I don't understand how a clamp on DC meter works. Without a changing magnetic field, does it still work? I thought the meter had to be in-line. Can you suggest a model to buy?

I don't get how disconnecting the ground at the battery reveals something.
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Old 06-03-2020, 09:14   #10
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Re: Why my engines draw much amps?

PS - I get the ground test now. Pull the ground on equipment.
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Old 06-03-2020, 10:04   #11
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Re: Why my engines draw much amps?

As a previous poster mentioned, find the shunt that the gauge reads from. The shunt will only measure the current passing that wire. If your alternator is putting out 14v, and you have similar at the battery, while you may be using current somewhere your batteries CANNOT be discharging as the voltage is greater than the resting voltage of pretty much any battery. My bet based on available information is that you're measuring the current of a specific circuit, not the entire system.
While I don't have a cummins, my engine room blower and various other things use almost 10 amps when everything is running. Squirrel blower fans can be pretty big current draws if they move alot of air.
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Old 06-03-2020, 10:39   #12
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Re: Why my engines draw much amps?

Quote:
Originally Posted by GeneM View Post
Thanks again.

I don't understand how a clamp on DC meter works. Without a changing magnetic field, does it still work? I thought the meter had to be in-line. Can you suggest a model to buy?

I don't get how disconnecting the ground at the battery reveals something.
How it measures DC current:

A wire carrying DC current creates a static magnetic field that would not be there except for the current. A DC clamp on meter has a magnetic (opening) ring that has a magnetizing coil and a Hall Effect sensor that measures the magnetic field across one of the gaps in the ring. Before making a measurement, current is passed through the coil until the sensor measures zero in both direction so this coil current represents the zero offset for any permanent field in the ring.

After placing it around the DC conductor the coil is adjusted until the magnetic force in the gap is again brought to zero. The change in the amount of current it took in the coil now corresponds to the current flowing in the wire (multiplied by the number of turns in the coil).

How disconnecting ground (or positive) connections at the battery works:

You are watching the ammeter that was showing an unexpected load on the battery. You check the effect on the reading as you remove circuits one at a time and when you see the current drop - - BINGO that is the culprit.

If you are watching a voltmeter that is indicating a steady drop due to a bogus load, it will be much more difficult to detect the culprit. Theoretically as you tap each load on/off/on/off you look for slight corresponding oscillations in the voltage.
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Old 06-03-2020, 13:44   #13
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Re: Why my engines draw much amps?

You do realize that when your engine is running, the alternator is charging the batteries and you will see a negative current because of this. Current out is displayed as positive and current in is displayed as negative.
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Old 06-03-2020, 16:37   #14
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Re: Why my engines draw much amps?

Thanks all again-2.

Maybe I need an EE degree. I appreciate your smarts. I learned about DC ammeters.

I know where the shunt is, so I'll trace that line to see if it's seeing the alternator.

Again, the battery charger shows positive amps when it's charging, so I assumed positive is input to the battery.

Suddy-Greg said the alternator will make negative amps when charging. If that's true, I'll have to do some noodeling.
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Old 06-03-2020, 17:00   #15
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Re: Why my engines draw much amps?

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Originally Posted by NewMoon View Post
Our 2001 Cummins 6BTA 330 hp draws lots of amps (have not measured how many, but voltage drops quite noticeably) while the grid heater is on. It's on and off until the engine warms up a bit.

Read this, if you have an intake air heater, my Duramax for example did, they draw huge amounts of power, but of course donít when the engine warms up a bit.

Find out if your engine has either an intake air heater, or some cycle their glow plugs after starting for a short while.

Newer, more modern engines may have these features, I believe itís to make a cold Diesel idle in a more civilized manner and not smoke etc., and may even be required to meet new emissions, I donít know.
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