Weak / Slow Initial Cranking

[Monaco CS45]

Good afternoon.  Nick & Tonya DiMarino from Littleton, NC here.  We appreciate this forum and allowing us to be a part of it.  We are recently semi retired, purchased a pre-DEF motorhome of our dreams about a year ago.  It is a Monaco Commander 45 Signature.  Excellent condition inside and out with all the luxuries of home.  Our toad is a 2013 Jeep Wrangler purchased as a package deal.  It is our first DP, but we have been camping our whole lives from a Coleman pop up to our last onw which was a 38' gas Newmar Kountry Coach prior to this.   We took our coach cross country nearly 15,000 miles last fall and have made numerous smaller trips since.  Our Monaco is a dream Coach in near flawless condition and we are thrilled with it, but I do have a few kwirks to work out like any RV.  I have been watching posts in this forum for a few months now and have really enjoyed reading experiences and hearing ideas.  I have used many of the ideas to much success. 

I have had what seems like "weak" chassis battery bank since I bought the MH.  When I first turn the key it seems very weak and the engine barely turns over.  If I continue to hold the key in the start position for just a few seconds it will usually begin to turn over, it gets faster / stronger and typically lights right off.  I was getting an oil change & filter at Loves and had them replace the batteries even thought the old ones (2019 date code) load tested just fine.  To my surprise it is exactly the same with new batteries.  This weekend I had to jump start it, as the batteries were down to only 10.5 volts.  I keep my motorhome plugged in and inside a garage while at home.  I religiously water my house batteries and keep them clean.  I keep corrosion off and use inhibitor on chassis and house batteries.  From reading this forum I realized that my stock Magnum inverter didn't charge the chassis batteries, so I installed the maintainer which I keep plugged into the Engine heater receptacle and left turned on while the coach is not being used.  It is stored inside a garage when not being used and is also fairly climate controlled (no extremes anyway). I cannot figure what is draining my chassis battery or why it would be weak when cranking at first.   I am no self proclaimed "mechanic", but I am a do it yourselfer with a good deal of God given common sense.  Could anyone offer me any ideas on what could be the cause of this?  I feel like it is highly unlikely that its the starter because it only has 50,000 miles on the coach, BUT it was weak starting even with brand new batteries.....  However if it were the starter itself then that doesn't explain why my chassis battery bank would tend to drop (drain) down even while connected to a maintainer. I do not see corrosion or any obvious problem when i visually inspect.  I do not want to be a parts replacer.  Your help and expertise is much appreciated!  Incidentally I am not used to using forums, this is my first.  I tried to check using the search features to ensure I am not asking a duplicate question / topic so if I am, it is not intentional.  

[Old Dog]

The 2 Group 31 batteries are hardy up to the task if you have the bigger 525hp Cummins. I installed a 3rd one (really tight fit) and that helped. Are you familiar with the Battery Boost switch function? It ties together both house and starting battery banks, there is a good description in the owners manual. It will eliminate the problem assuming your Big Boy Relay is working correctly. Hope this helps

[vito.a]

Congratulations on such a fine coach.  

Monaco used a large Intellitec relay to connect the house and chassis batteries.  It's called the "Big Boy:.  They are famous for getting carbon buildup inside.  You can either rebuild it, or replace it.  It's located in your rear electrical panel next to the engine (see picture). Be careful working back there as there is a lot of energy in all these batteries.  

Are you using the Boost switch next to the driver when you crank?  Depress it and hold it for 10 seconds then crank the engine.  Note, the Boost switch activates the Big Boy relay so depending on how bad it is this may not work.

Most of us have installed a new gear reduction starter.  It will crank much faster and require less battery power.  

Link: https://www.irv2.com/forums/f123/isx-525-starter-replacement-part-366504.html

Edited September 19, 2022 by vito.a

[Old Dog]

I'd like some more info on the gear reduction starter, specifically for a ISX Cummins if it's not too much trouble. Don't have a lot of faith in the stock one given how hard it has to work to turn this beast over. Thx

1 minute ago, Old Dog said:

I'd like some more info on the gear reduction starter, specifically for a ISX Cummins if it's not too much trouble. Don't have a lot of faith in the stock one given how hard it has to work to turn this beast over. Thx

Never mind, thx for the link

[Rocketman3]

One place to start is to verify the battery maintainer is charging the chassis batteries. After you have been sitting for a while, put a multimeter on the chassis battery. Is the voltage showing what you would expect if the maintainer is running as it should?

good luck!

[Yoaks5]

This is the starter I used Delco Remy 39MT Starter (part # 8200308). It's also a gear reduction starter. The big advantage is it has a rotatable mounting flange. The Denso starters have different part numbers for different flange mounting locations. So just make sure you get the correct one. This one was about $100 more expensive but I was able to pick it up locally and not have to worry about it fitting. 

 

To the op...I would agree with vito.a that your big boy is not working. I cleaned mine once but that only lasts so long so i replaced mine with the Blue Sea ML-ARC. This replaced the big boy and combines both sets of batteries if there is any charge source present (alternator, shore or gen). If you search Blue Sea ML-ARC you'll find all kinds of info on this. 

The big boy is always drawing power when it's engaged. So switching to the blue sea will eventually pay for itself. Especially if you keep your coach plugged all the time at home like I do. 

[Monaco CS45]

I sincerely thank each and every one of you for your help on my weak cranking issue.  I have determined that the Big Boy is not working which explains why my boost button wouldn't help me to start the coach when the chassis batteries were discharged.  Originally I had thought it was due to the low state of charge and that the house batteries couldn't overcome 2 dead batteries.  But I was Wrong!  And I know this thanks to you all and your help on this.  It is such a huge piece of mind to be a part of this group, people are so willing to provide insight and expertise; it can be overwhelming knowing where to start on a motorhome as complicated and sophisticated as this one is.  I have been wondering why I heard the buzzing coming out of the rear electrical box in the engine compartment when I energized the chassis battery switch. Since it quit after a couple seconds I assumed it was normal.  It has been "normal" as long as i owned the coach!   This also explains why my batteries keep getting weak as this Bog Boy is also my battery drain issue.  Again - I thank all of you who helped me out and I only hope I can return the favor to you one day!  

[Tom Cherry]

4 hours ago, Monaco CS45 said:

I sincerely thank each and every one of you for your help on my weak cranking issue.  I have determined that the Big Boy is not working which explains why my boost button wouldn't help me to start the coach when the chassis batteries were discharged.  Originally I had thought it was due to the low state of charge and that the house batteries couldn't overcome 2 dead batteries.  But I was Wrong!  And I know this thanks to you all and your help on this.  It is such a huge piece of mind to be a part of this group, people are so willing to provide insight and expertise; it can be overwhelming knowing where to start on a motorhome as complicated and sophisticated as this one is.  I have been wondering why I heard the buzzing coming out of the rear electrical box in the engine compartment when I energized the chassis battery switch. Since it quit after a couple seconds I assumed it was normal.  It has been "normal" as long as i owned the coach!   This also explains why my batteries keep getting weak as this Bog Boy is also my battery drain issue.  Again - I thank all of you who helped me out and I only hope I can return the favor to you one day!  

You CAN disassemble and clean the Contacts of the BIG BOY.  What I recommend is to have someone hold in the Big Boy while you are back there.  It should go CLUNK.  At that time, you need to measure across the two big terminals.  If you have say 0.05 VDC, you have a pitting problem with the Big Boy's contacts.  Pull it out and disassemble. There are instructions in the FILES for doing that.

Next UP.  The Big Boy is NOT designed to act like a JUMPER CABLE.  It is designed to put a SURFACE Charge on the Chassis Battery from the House. Read the manual on its use.  You are supposed to hold the switch on for maybe a Max of 30 Seconds.  Then wait and do it again.  The Big Boy is only rated at 200 Amps. You need upwards of 1200 AMP.  When you try to start or use it as a Jumper Cable....you really put way too much current through it and the contacts will arc and pit.

In addition, the Big Boy (assuming you have the Intellitec one) is designed to stay ON as long as you need BIRD (both direction) Charging.  There is a control board that turns it ON....if the Chassis needs juice.  It is given 12 VDC THEN....for maybe a few seconds.  THEN that control board drops the voltage to maybe 4 VDC or so (3 - 5 will work).  That then is the HOLDING VOLTAGE.  If you hold it one for more than a minute, the coil heats up.  So, the charge control board hits it to say.  TURN ON.  Then reduces the voltage to a much lower one.  It can stay there forever.....

SO....to test it....Use the Boost Switch to make sure it engages.  That is 12 VDC.  Then measure the voltage drop across the terminals.

NOW....once you have done that, TURN OFF the shore or unplug it.... 50 Amp (will work on 30, but better on 50).  Put a Volt Meter on the Small Terminals.  Will be zero....as there is NO AC for the Inverter.  NOW, have someone turn ON the power (or start the Generator.....AC is AC and the Inverter don't care.  If you watch the volatge on the small terminals (the coil leads) eventually....maybe within a minute or two....you should see 12 VDC and then it drops to the 4 range....  That means it is engaged.....that is also assuming that the Chassis needs charging. 

If the voltage does not come on....or does not drop....then the Control Board is the next stop.  IF it buzzes and you don't hear the CLUNK (it will hum and be warm to the touch), then odds are....you got a BAD coil.  BUT, that would have been evident when you ran the Boost Test.

For the INTERIM.  A single Jumper Cable is your friend.  Tie the Positives on the House and Chassis bank together with a single jumper cable.  That is MORE than big enough to do the charging.  Then you get them back to good charge.  If you have a problem with the Big Boy, you can drive with this....just make sure they clamps are ON TIGHT...as you do NOT want the cables banging loose.  That is all the Big Boy does.  NOW, I have had mine go bad.  It was working....but it quit.  Never figured it out.  I jumped the banks....and let it sit there for maybe 20 minutes.....as it was plugged in.  That gave a surface charge on the Chassis.  BINGO....it started.  I let it run.  I had good voltage.. (no DROP). I was going on a trip.  So I replaced the 5 year old starting batteries anyway.  I later replaced it.  I need to rebuilt it...

Good Luck.  

[Tom Cherry]

On 9/19/2022 at 4:02 PM, vito.a said:

Congratulations on such a fine coach.  

Monaco used a large Intellitec relay to connect the house and chassis batteries.  It's called the "Big Boy:.  They are famous for getting carbon buildup inside.  You can either rebuild it, or replace it.  It's located in your rear electrical panel next to the engine (see picture). Be careful working back there as there is a lot of energy in all these batteries.  

Are you using the Boost switch next to the driver when you crank?  Depress it and hold it for 10 seconds then crank the engine.  Note, the Boost switch activates the Big Boy relay so depending on how bad it is this may not work.

Most of us have installed a new gear reduction starter.  It will crank much faster and require less battery power.  

Link: https://www.irv2.com/forums/f123/isx-525-starter-replacement-part-366504.html

The BIG BOY is rated for 200 Amps.  If your Chassis Batteries are really down or almost dead and you have a good house bank, then you will toast the Big Boy. You will pull upwards of 1200 amps to start.  NOW....the Big Boy is rated for 1200 Amps....with a Max of 30 seconds.  SO BE CAUTIOUS....you CAN burn up the coil as well as the contacts.  I don't push mine and have only had to use it a few times....actually to start the Genny. When I did have the Chassis batteries down....I actually popped on a Jumper cable and then let the Generator run....even though I have 30 amp power.  I let them charge for a while.  Then, hit the starter.  VROOM.

So, Just a caution on the Big Boy.  Repeated hits will only shorten the life.  The key here is HOW does your system work.  I don't know about your system and if you have BIRD charging.  The Poster does....so when in use or on power (in storage), the Big Boy is always ON.  Repeated abuse from starting will shorten the life and then that leads to the issues he has.  Just a CONSERVATIVE Caveat.....each has to do to their MH what they feel is best and is within the rated capacity or design of the components....A simpler and more practical solution.  Use a single Jumper Cable..  From my manual.

Battery Boost Switch:
The Battery Boost switch (located on the driver’s console) engages a heavy-duty solenoid to electrically connect the house batteries to the chassis batteries in the  event the engine will not crank or cranks slowly. The solenoid is designed for short-term high current intermittent use. Engaging the boost solenoid for an extended period will damage the solenoid. (from the Intellitec site.  MAX of 30 Seconds.....at 1200 Amps ....which is about what it takes to start the engine)....so be careful
Jump Starting Using Battery Boost Switch:
With the ignition key off , press and hold the Battery Boost switch for ten seconds. After ten seconds, continue to hold the switch down and turn on the ignition. If voltage is sufficient, try to start the engine.  If the engine fails to crank or does not crank fast enough, discontinue the attempt. Continued attempts will only diminish any remaining surface charge in the chassis battery and end future alternative attempts.
Next, start the generator. This may require using the Battery Boost switch for the generator to start from the engine battery. Once the generator is operating, the electrical combination of the generator and the inverter will charge the batteries.  Allow the generator to run approximately ½ hour before attempting to start the engine.  After ½ hour of generator operation, leave the generator on and hold down the Battery Boost switch for one minute.  Release the switch for one minute, then
press the switch again for one minute.  Alternate this cycle three to five times.  Next, hold the switch down and turn the ignition on . If voltage is sufficient with
the Boost switch held down, try to start the engine. If the engine fails to crank, or fails to crank quickly, the chassis battery may be depleted and the motorhome will require jump-starting or an external charger hooked to the chassis battery.