Cranking ampers. QSM11’s

[Marcelo Sanabria]

Hello everyone!

The following concern might be very basic for many of you, but I have done all I could do with my limited knowledge in mechanics and I’m counting with your expertise in order to solve the issue.

Everytime since I got the boat, my STBD side QSM11 cranking cycle is VERY SLOW during the starting process. The voltage shown at the screen is between 13.1 and 14.1 volts before hitting the push button, but while cranking, it will go down to 8-9 volts or even less (screens turn off so I can’t see the reading). Most of the times it will just start, the screens will come back and everything works just fine, so I just depart to my destination; however, if something comes up after I shut it down (Ex: anchoring/mooring issue), and I need to re-start it, the cranking cycle becomes even SLOWER and the engine just WON’T start, unless I jump it with jumper cables or a booster (I usually connect the cables directly to the starter instead of the battery, so I don’t get to crawl to the side of the engine in a hot engine room of my Viking 45C), by doing so, it will start ok.

In the 12 volt system, I already got all of the cables replaced, the starter is a new one and I tested the battery, which has 1200AMP at 22 degrees (Celsius), 1625AMP at 0 degrees (Celsius) and 1200AMP CCA. 

Now, according to the Cummins QSM11 Data Sheet, the battery shall have 1800AMP at 18 degrees (C) and 2250AMP at 0 degrees (C), so the question is if my problem is cranking amperes related or anything else.

FYI, the boat is located in Puerto Rico, so the minimum temp we’ll get here is above 75(F)/23 (C).

On the other hand, the PORT engine will not give the the same problem, even though the battery has lower Cranking ampers.

Thanks in advance for your imput.

Rgds

Marcelo

Topic

[Marcelo Sanabria]

Hello all!

After taking all measures as recommended, being all in good ranges, and after reading the operation’s manual for QSM11’s, I found out that even though the battery had more than the CCA recommended by Cummins, it had only 280 min of reserve capacity while the recommended value is 480min RC. So I installed a new 8D battery that has 1450 CA and 500min of RC…and problem solved.

[Marcelo Sanabria]

Hello Tony!

As I mentioned, I got all the cables and terminals replaced, but I’ll double check tbe connections.

Also, I will take the measures the coltage at the battery terminal.

By the mean time I’ll do my homework with the link provided.

Thank you very much.

Best rgds

Marcelo

[Marcelo Sanabria]

Thanks Richard, I’ll take the measure of the starter pulling amps.

I only made a load test on the battery of the engine in question, and yes, they are connected in parallel, but I dont see a difference when pushing the parallel switch.

Well, actually I did not install a new starter, I got mine refurbished/rebuilt after a mechanic told me that it was the origin of my problem. The shop told me that the starter was in bad shape and replaced some parts.

Rgds

Marcelo

[Richard Dodson]

Cranking amps

Get a clamp amp meter and measure the amps the starter in question is pulling. There should be a rating on the starter.  When you tested the batteries, did you do a load test and when you did your test, did you test each battery separately, if they are wired in parallel.  Lastly, you mentioned the starter was new, what symptoms were present that required the change? 

[Tony Athens]

Marcelo, 

From your post, to me it is obvious you have one or more bad or high-resistant connections in the battery starting circuit on the suspect engine. Could be a  NEG or POS cable of both. Plus the voltage you are most likely looking at is not really  the voltage you should be looking at………… 

Until you are measuring direct BATTERY TERMINAL VOLTAGE, you really do not know what is going on.   

Read this

https://www.sbmar.com/articles/installing-digital-volt-meters-dvm-boat/  

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