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Old 02-27-2019, 09:27 PM   #1
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Cummins 6bta low volt alarm

Hi,
First time posting. Have just purchased a fly bridge cruiser with 2 Cummins 6btaís. This site was invaluable getting everyoneís options on the engines prior to buying the boat.

The starboard engine low volt light/alarm sometimes comes on after starting and remains on for up to 20 seconds. The voltage output on the gauge appears low and jumps up when the light/alarm stops. We have checked the battery voltage and immediately after start with a multimeter and it would appear that the alternator IS pumping out sufficient power. At this stage it would appear to be a false indication. Any ideas?
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Old 02-27-2019, 09:34 PM   #2
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Thoughts from a non electrician:
? Initial alternator belt slippage that resolves.
? Battery condition, especially immediately after start drain.

And more importantly, welcome aboard!
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Old 02-27-2019, 09:41 PM   #3
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Thoughts from a non electrician:
? Initial alternator belt slippage that resolves.
? Battery condition, especially immediately after start drain.

And more importantly, welcome aboard!
Thanks for the reply BruceK.
As for the alternator belt slippage, we have tested the batteryís with a multimeter immediately after start and whilst the alarm is sounding. The multimeter was indicating 13V and 8amps flowing into the battery which I would have thought would rule out belt slippage.
The previous owner told us the batteryís were pretty old and not holding charge well. We changed the batteries and it has happened both before and after we replaced them.

Cheers.
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Old 02-27-2019, 09:53 PM   #4
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Some 6bta have intake air heaters, they cycle on after a start and can drag volts down.
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Old 02-27-2019, 10:42 PM   #5
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I would guess it is the intake heater. It has a 10 amp fuse that if you remove it and the issue goes away you have solved the problem. Go to :
https://www.sbmar.com/
and read up on it.
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Old 02-27-2019, 10:56 PM   #6
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Here is the actual article:

https://www.sbmar.com/articles/elect...eater-circuit/
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Old 02-28-2019, 03:26 AM   #7
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Thanks to all.

I found a reference somewhere else that the heater only operates when the ambient temperature is below 59F. Iíve had the alarm come on briefly when the temperature has exceeded 85F so Iím not sure the heater would be operating.

After doing a search online Iíve discovered a lot of other guys with these engines turn the key but wait 10 seconds before engaging the starter to allow the heater to turn on and off. This is something I had not been doing. Maybe Iíll give that a go.

Cheers.
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Old 02-28-2019, 06:45 AM   #8
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I think the heater cycles on any time you turn the key on even with ambient at 85F, but with engine cool. Turns on for like 10sec, then cycles off. Once you hit starter, it cycles on and off until engine warms up some, or it exceeds about 1100 rpm.

Lots of folks disconnect them as they are not really needed unless boating below freezing.
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Old 02-28-2019, 06:49 AM   #9
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Quote:
Originally Posted by caltexvb View Post
After doing a search online I’ve discovered a lot of other guys with these engines turn the key but wait 10 seconds before engaging the starter to allow the heater to turn on and off. This is something I had not been doing. Maybe I’ll give that a go.

I almost do that. Not quite 10 seconds, I think; mostly I just wait 'til the batteries begin to return to normal voltage, after initial voltage draw (from the heaters)... then start. The heater cycles are clearly visible on our voltmeters...

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Old 02-28-2019, 06:53 AM   #10
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My guess would be intake heater too, and I would also guess the circuit that turns it on has a fault, likely the temperature sensor. I think you could live with this issue forever, it won't hurt anything.
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Old 02-28-2019, 06:56 AM   #11
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Next time Iím on the boat will have a look to see if they are fitted with air intake heaters. Still scratching my head as to why the voltage at the batteries was reading over 13V while the low volt alarm was going off.
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Old 02-28-2019, 07:50 AM   #12
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My Cummins 6BT isn't particularly accurate reporting voltage. I did clean up the instrument cluster grounds, there were a LOT of terminals that daisy chain the ground. Some cumulative drop will cause problems, but it's not necessarily indicative of a real problem, just some funkiness in the gauge clusters. Check out the ground path and the molded plugs, make sure connections are all good. Compare voltages at the engine vs the gauges.
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Old 02-28-2019, 09:09 AM   #13
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I am not sure it is so much of a low "voltage" alarm as it is a low "amperage" alarm. I know the gauge reads volts. But 8 amps right after a start is quite low. I have amp readouts on both of my engines and they get right up there after a start....60-70...and then settle around 20-25 depending on what "appliances" you have running. One alternator seems to by the master and it kicks the other one off when not needed so that is a total of 20-25 amps. So maybe 8 amps per engine is not too far off but after the start it definitely takes a dip.
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Old 02-28-2019, 08:40 PM   #14
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The previous owner told us to start the starboard engine first which runs off a dedicated cranking battery then start the port engine which runs off 2 house/cranking duel purpose batteries. After discussing the low voltage issue with the mechanic (who also maintained the boat for the previous owner) he said to start the port first because of the way these boat a wired (Bertram Caribbean 35.) I wonder if that could somehow be the issue.
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Old 03-02-2019, 10:26 AM   #15
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The air or "grid heater" is either a box heater just before the turbo air intake, or in my case with a jacket water after cooler (JWAC) 6BTA, located under the JWAC. After I start the engine, I'll push up to 1,000 RPM for the few minutes it takes to warm the air intake. At that RPM, there's usually enough voltage coming off the alternator to keep the voltage from cycling.



The electrical components on these grid heaters are a problem. The ECM and contactors can fail (mine shorted out last season), and replacement components are about $500. I'll be removing all ECM components and install a fused push button momentary ON/OFF switch on the console, and wire directly to the grid heater terminals.



There is a temperature actuator in the components (58 degrees sounds right), and unless it's really cold, the engine will start without a pre-heating cycle. I have a block heater on my 6BTA and that's enough to start the engine in cold weather without a pre-heater (assumes you're plugged into shore power). Tony Athens of Seaboard recommends removing air and block heaters (problematic), and use an external oil pan heater if your operating in cold temperatures.
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Old 03-02-2019, 04:15 PM   #16
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If Iíve read the manual correctly, this box should contain the air heater. There are no wires running to it so Iíd assume there is no heater fitted. That should rule out the heater as the source of the low voltage alarm.
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Old 03-02-2019, 04:51 PM   #17
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Self exciting alternator taking its time to come on charge?


So long as it consistently goes away... how far down the priority list does it slip?
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Old 03-02-2019, 05:44 PM   #18
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If Iíve read the manual correctly, this box should contain the air heater. There are no wires running to it so Iíd assume there is no heater fitted. That should rule out the heater as the source of the low voltage alarm.
There are terminals on the other side of the box. make sure no wires there. If none, you are correct, heater not the issue.
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Old 03-02-2019, 05:46 PM   #19
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One time when the alarm occurred we idled the engine up to about 1200RPM and the alarm continued to sound for about 10 seconds. Would have thought that would have got the alternator on line straight away.

It always goes away so I guess itís just something weíll have to live with.

Yeah ran my hand around all sides of the box. No wires.
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Old 03-02-2019, 05:52 PM   #20
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When alarm comes in, go around engine and alt and batts with a voltmeter and see what the readings are. Normal is 13.8-14.2Vdc.
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