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2018 Sunseeker 2400W MBS
Join Date: Jan 2017
Posts: 80
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RV Generator Problem – NO CRANK! (LONG, But Hopefully Helpful…)
Okay, I’d originally crafted together this post to seek the guidance & assistance of my fellow MBS owners regarding a curious problem we suddenly started having with the Cummins Onan QG 3600 LP propane generator on our 2018 Sunseeker 2400W (Mercedes Sprinter Chassis). It’s always been super reliable since the day we bought it, but on the way home from our last trip it suddenly wouldn’t start and, in fact, wouldn’t even crank over. No noise, no click, no nothing! Uh-oh, NOT good with a very HOT summer ahead of us…
Well, we got home okay and just for grins I tried it again and it cranked right up. Well that’s good, but also BAD I thought, because now it’s an “intermittent” electrical problem that will be that much harder to track down and fix. In my previous world of military aviation, our mechanics would always sign off that kind of pilot complaint as “CND” (Could Not Duplicate, ha)! Of course, I couldn’t blame them because I was both a pilot AND a maintenance officer – and sometimes the truth hurts. If they applied power to the aircraft after landing and the problem didn’t present itself, then it must not be a problem anymore, right??
Ah, short answer is NO. They just couldn’t FIX it if they couldn’t OBSERVE the problem, so I just kept trying over the next week or two to see if I could repeat the NO CRANK condition. Luckily, I didn’t have to wait long as the very next day with the coach just sitting in place, it would not crank (from either the remote switch inside OR the start switch mounted directly on the generator). So, for the benefit of others who have had (or probably WILL have in the future) some kind of electrical gremlin as this, I’m going to give you a synopsis of the troubleshooting logic I applied to successfully SOLVE this problem myself.
Okay, here was my thinking…
-- MBS Chassis Battery Only 1.5 Yrs Old & Voltage Tested Good at 12.8v, so NOT the Issue
-- MBS Chassis Alternator Output Tested Good at 14+ Volts, so NOT the Issue
-- Upgraded 200A LiFePO4 (Lithium) House Battery Only 2.5 Yrs Old & Voltage Tested Good at 14.5v, so NOT the Problem
-- Initially Suspected a Potential Issue with the Lithium Battery’s Internal BMS (Battery Management System), or Possibly Something Related to the BCC (Battery Control Center in the Stepwell) or the Li-225 Battery Isolator I’d Installed when Switching to Lithium, but Decided to Save Those for Later (Hoping to Find Something Simpler, ha!)
-- Continued Testing Random No Start Condition Over a Period of Days to Narrow Down Cause and Finally Discovered a Potential Anomaly – One Day It Just Cranked for a Second & then Quit. Al 12v DC Circuits in Coach Worked Fine, But When I Measured Voltage at the Generator Starter Solenoid it was WAY Too Low (Only 2.6 Instead of 12+)! Hmmm…
-- Checked All Battery Voltages Again & They Were Fully Charged, But Solenoid Voltage Was UNSTABLE, Slowly Creeping Up & Down Between 1.2v – 10.1v
-- At First, Based on Many Forum Posts About Lithium Batteries Not Living Long When Called Upon to Provide Heavy Generator Cranking Amps, I Thought Maybe my Lithium Battery (or More Likely it’s Internal BMS) Was Failing & No Longer Able to Deliver the Req’d Power
-- To Check this Theory, I Started the MBS Diesel Engine to Provide Some Extra Charging Current and, Whaddya Know – the Generator STARTED Fine!
-- So, Now I’m Thinking I Probably Need a New Lithium Battery – UGH!
-- Sure Enough, Even Though my Lossigy LiFePO4 Battery Offers a Healthy 5-Yr Warranty, They Also Explicitly Warn Against Extended Use as Starter Batteries.
-- Well, Wasn’t Sure How that Warranty Claim Would Go (Ha!), so Continued Researching & Found Most Onan Generators “May” Require Up to 450 CCA in Extreme Cases, But More Typically Only Pull Something Like 200-250 CCA, Which My Battery Says It Should Easily Handle for Short Periods of Time
-- Just for Kicks, Tried Starting the Generator Again the Next Day WITH Engine Running and Got Another NO CRANK (with Only 1.2v Showing at the Solenoid)! Tried a 2nd Time with Shore Power Connected and 60A Converter Charging the House Battery and Same Thing – NO START! So, the Battery Boost Theory Was No Longer Holding Water and Something Else Must be at Fault.
-- Well, Duh, You Electrical Wizards Out There Must be Screaming Out Loud by Now, Saying, “When Are You Gonna Check for a Bad Power Cable to the Generator???”
-- Uh, Excuse Me, But I Forgot to Tell You I’d Already Gotten Under the Coach & Traced the 12v Positive Cable from the Starter Solenoid Back to the BCC Where It Gets Its Power and Found Nothing Obvious. Also Looked for Any In-Line Fuses or the Little “Self Resetting” DC Circuit Breakers That Might Have Been at Fault – Nothing Obvious Found… (Note: I DID Find ONE DC Circuit Breaker Inside the BCC, But It Was Labeled “Converter” and a Continuity Check Showed It to be Good Anyway) Also Pulled the Generator Control Board to Check the Multi-Pin Connector Going into the Board as Well as the Two Ground Lugs Underneath. Gave All the Above a Liberal Dosing of De-Oxit Just for Insurance
-- So, Pulling My Last Few Old Gray Hairs Out of my Head, I’m Left Wondering WHY I’m Only Getting a Miserable Little 1.3v to the Positive Side of that Starter Solenoid?? Could it Possibly be Something Inside the Lithium BMS, the BCC, or the Li-225 BIM Itself…
-- Well, I Must Admit NOT Really Knowing, But I DID Still Have a Fully-Charged Deep Cycle Lead Acid Battery on Hand so, Just to Rule Out Anything “Lithium-Related,” I Swapped the Lead Acid Battery Back In and Noted NO CHANGE – Generator Would Still NOT Start!! So, That Rules Out Lithium Issues, ha!
-- Now I’m Finally Convinced – There Simply MUST be a Problem Somewhere Within That Heavy Gauge 12v Positive Cable Between the BCC and the Generator Solenoid. I’M NOT QUITTING TIL I FIND THE PROBLEM!!!
-- For Safety’s Sake, I Disconnected ALL Power from ALL Batteries (Chassis AND House) and, Oh BTW, Also Learned the Generator Solenoid Was Getting It’s 12v Positive Power from the MBS Lead Acid Chassis Battery Anyway (NOT the Lithium House Battery), So All That Time Fretting Over “Lithium” Issues was a Giant Waste of Time, Ha!
-- Realizing the Positive Cable MUST be Loose, Corroded, or Shorted Somewhere Along Its Path, I Painstakingly Crawled Around Underneath the Coach and RETRACED It Once Again from Solenoid to BCC. Trust Me, This WAS a Bit Painful for my 69 Year Old Aching Back, as the Cable Was Encased in Plastic Sheathing with About 20 Other Wires of All Colors Under the Rainbow. When I Finally Got All the Way Forward to the Battery Compartment Under the Entry Stairwell, Things Turned Messy… For the Last 2-Feet of Cable Run, Everything Going into the BCC Area was Fully Encased in at Least 4-6 Inches of Heavy Age-Hardened Spray Foam Insulation - Ugh!
-- Not to be Deterred, I Grabbed my Handy Gasket Scraper Tool and Proceeded to Remove EVERYTHING in My Way. I WANT TO SEE THE TERMINATION POINT!
-- Finally, EUREKA! There, at the End of the Rainbow, I FOUND the Problem! The 12v Positive Cable at the BCC Lug had Vibrated LOOSE and was NOT Making Good Reliable Contact. I Could Easily Move it by Hand, as it Had Been Installed at the Factory WITHOUT a Lock Washer. Once Discovered Under All the Spray Foam, it was an Easy Matter to Clean Things Up with Some Sandpaper, Install a Lock-Washer, Tighten It Back Up Again, and then Reapply Some More Spray Foam to Protect It from the Elements. MISSION ACCOMPLISHED – It’s Miller Time!
Bottom Line – Yes, it was painfully frustrating and tried my patience immensely. However, in the end, it wasn’t anything overly complicated OR expensive to fix. Anyone with basic hand tools, some common sense, a rudimentary understanding of 12v electrical systems, a good multimeter, and access to this Forum and/or some good YouTube videos as a tutorial could have figured this out and fixed it themselves, like I did.
Hope this gives a bit of encouragement to my fellow Forest River owners out there so they may realize that many of the typical maintenance problems we run into while enjoying our RVs are just NOT that difficult to fix ourselves. None of us are too old to learn a few new skills in life, especially with the advent of YouTube video tutorials and Forums like this to help us along.
Come on, hit the road and ENJOY life out there in your RV – don’t waste your valuable time and money taking it to the dealer for every little loose screw or loose wire! Most of this stuff isn’t rocket science – YOU can do it!!
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At the tender age of almost 70, I've learned the hard way that life is HARD... but it's even harder if you're just not very bright and FAIL to learn from your mistakes...
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