Starter Problem or Batteries? 2011 Itasca Meridian 34Y

[KYBlue]

I have a class A with Cummins diesel. Recently my starter was turning over too slowly to start the engine. I have 2 950 CCA chassis batteries and 4 12 volt house batteries. When I engaged the boost button on the dashboard, the starter easily started the engine. We pulled the 2 starter batteries and did a load test which they failed. I bought and installed 2 new 950 CCA batteries from a company that only sells batteries. The new batteries would not turn the engine fast enough to start and the boost button had to be used. Same as before. I did a load test on the new batteries and they seem fine. I will take them back today and have the seller check them in case I am missing something.
Is it possible that I have a loose cable connection somewhere or a failing starter motor? Was I mistaken to think that if the boost from the house batteries could start the engine that my starter and cable connections were not the problem?

 

[Morich]

I would start with the basics of getting good voltage to the starter. You likely have good voltage at the batteries, so I might check for bad cable connections to get that voltage to the starter. Lots of high tech ways to do that but I like to stick to the simple X voltage sent through Y resistance will come out with Z!
So I go for checking the voltage on the battery post, not the clamps first, then compare it to the voltage you get at the big battery cable on the starter. You don't have to do the math of the XYZ stuff!
If you have X at the battery posts and don't get near the same at the starter, there is a problem causing high resistance somewhere between those two points.
I ease my mind by first trying to make sure I'm working on the correct problem before trying to fix it!
The most common problem on RV is corrosion and that does sound like what you have, so I would want to make sure the simple simple stuff is not the problem, way before tough things like changing a starter.

Also a big one may be a dirty ground cable connection. So while at the battery, check the resistance from some good solid metal to the negative post of the battery! It should be near zero if the cable to ground is good! Easy to miss looking at the bus bar which is often down and behind the batteries to keep it hidden! The negative cable goes direct to ground so the resistance should be very low if things are good and clean!

Explanation for why the boost helps is that old XYZ stuff. You are making X higher, so you can get Z higher even when Y is still the problem! If you were dealing with a hose with a kink in it, you are turning up the faucet to get more water through the kink!

But that's all just theory until you find out if the hose has a kink in it!

 

[KYBlue]

Thanks, Richard. Good analogy. I'm 77 and don't do much crawling around under a motorhome any more but I know some folks who can. Will check it out after Christmas and report the outcome.

 

[be happy]

I had a similar experience with my 07 Meridian. Two years back I though I was having a battery problem with the starter batteries. They would turn the starter over sometimes and other times not so much. I did replace the two batteries and it sort of helped. By that I mean the starter would turn over a little bit faster.
Now to this past spring, the batteries were ok, but it would take many turning of the key to start the motor. It was to the point I did not want to turn motor off. Sometimes it would start right off and others it may take a few turning of the key to make very thing work. I had to take the coach in for a state inspection this fall and my mechanic informed me the starter was failing and needed to be replaced. Since the replacement no problems, not saying thats your problem but something to think about.

 

[Waterbug]

I would start with the basics of getting good voltage to the starter. You likely have good voltage at the batteries, so I might check for bad cable connections to get that voltage to the starter. Lots of high tech ways to do that but I like to stick to the simple X voltage sent through Y resistance will come out with Z!
So I go for checking the voltage on the battery post, not the clamps first, then compare it to the voltage you get at the big battery cable on the starter. You don't have to do the math of the XYZ stuff!
If you have X at the battery posts and don't get near the same at the starter, there is a problem causing high resistance somewhere between those two points.
I ease my mind by first trying to make sure I'm working on the correct problem before trying to fix it!
The most common problem on RV is corrosion and that does sound like what you have, so I would want to make sure the simple simple stuff is not the problem, way before tough things like changing a starter.

Also a big one may be a dirty ground cable connection. So while at the battery, check the resistance from some good solid metal to the negative post of the battery! It should be near zero if the cable to ground is good! Easy to miss looking at the bus bar which is often down and behind the batteries to keep it hidden! The negative cable goes direct to ground so the resistance should be very low if things are good and clean!

Explanation for why the boost helps is that old XYZ stuff. You are making X higher, so you can get Z higher even when Y is still the problem! If you were dealing with a hose with a kink in it, you are turning up the faucet to get more water through the kink!

But that's all just theory until you find out if the hose has a kink in it!

Reading near equal voltage at the battery post and starter solenoid terminal does not eliminate corrosion or a bad cable as the problem. There will be no voltage drop unless you are passing current. (E=RI). Using the hose analogy, if you put a pressure guage on a faucet and on the end of a kinked hose, they will read nearly the same if there is no water flow.

 

[Morich]

Lots of theories but when the simple stuff works, I stay simple!

 

[Waterbug]

Lots of theories but when the simple stuff works, I stay simple!

Ohm's law is not a theory. It is a law of physics. The land line telephone system runs off of 45 volts DC run thru miles of 24 guage single strand wire. It is 45 volts DC leaving the phone company central office and 45 volts DC at your phone jack. That is because there is no current flow.

 

[klook]

Ohm's law is not a theory. It is a law of physics. The land line telephone system runs off of 45 volts DC run thru miles of 24 guage single strand wire. It is 45 volts DC leaving the phone company central office and 45 volts DC at your phone jack. That is because there is no current flow.

Hence it would not do any work, like spin a starter. People are deceived by the volt meter at times.