Jumping the Chassis Batteries - Precautions?

[Mike Groves]

I don't expect to have to use my Jeep to jump the Marquis' Chassis Battery Friday the 30th of October when I return to storage to take it on a drive to Pacific Shores.  But, just in case, what precautions would I take if I actually needed to do so after exhausting the other typical methods of getting the Marquis started?

Mike Groves

[Tom and Pam Brown]

Mike, I had to jump mine as the chassis batteries had only 11.6 volts after a couple of weeks.  I did have to crank my jeep and let it run a couple of minutes.  The coach fired right up.  No harm no foul for me.

[Mike Groves]

Tom,

When you say "crank the jeep" you mean go to a fast idle for a while?  Did someone keep their foot on the gas in the Jeep while you started the coach?  And, most importantly did you use all systems afterward (inverter mainly) with no ill effects?

Mike

[Keith Moffett]

Anytime the chassis batteries are that low, if you jump the chassis batteries either with a seperate vehicle or from the house batteries and then run normaly.  You are putting a major strain on the alternator .  Better to use the emergency start button or tow vehicle to boost the chassis batteries but then fire the generator instead.  Run the generator for 20 minutes and then start the engine. 
I have lost two alternators and this has served me well since.

[Mike Groves]

Keith,

Good idea.  I always start the generator first anyway because its easier to start on a lower battery voltage and easier also if you have to use the coach as well.  But, point well taken, so never jump the coach, just jump the generator if necessary, let it run for a while, then start up the coach.  That has worked for me in the past.

Mike

[Tom and Pam Brown]

No issue with alternator, the chassis batteries were tested and not too low in my opinion.  Generator makes sense as well, we were just late leaving and had to go.

Multiple opinions here as always to choose from...........

[Mike Groves]

Tom,

Given that we have the same model year Marquis, what does your Silverleaf show for chassis battery voltage while underway, and does it jump around or is it pretty much a constant value? 

Thanks,
Mike

[Edward Buker]

While you might get away with jumpering from your car, it is a load that the car alternator and battery was not even remotely designed to handle. There is little risk in jumpering to the motorhome starting bank and running the car engine at fast idle for awhile to get some charge in the motorhome chassis batteries, that should be fine. You have to look at your car battery and alternator and ask yourself was this designed to charge what is equivalent to 4 car batteries while cranking a cold 600+cu inch high compression diesel engine all at the same time?

I would disconnect the car battery + jumper while cranking the Cat engine. Some patience may be needed to bring the chassis batteries up to a starting level of charge. If you can start the generator and get the house system charging then move your jumpers from the car battery to connect the house bank to the chassis bank together. That should give you adequate current in a safer way with wire cabling more designed for the task. This is a good procedure if you do not have a chassis bank charger or if you have an Echo Charger. If you have a Big Boy system the house and chassis banks should automatically be connected together with high current capability once the genset has run for a few minutes.

Your chassis battery bank should be putting out 2000 cold cranking amps for starting and depending on the temperature you may need most all that. At 32 degrees a lead acid battery will only put out 65% of what it will put out at 80 degrees, 40% at zero degrees. Factor that into your plan for charging time, charging will help raise the battery temperature.

Basically look at your options and decide what is the safest way to pull high current capacity for diesel engine starting from what is available to me. Hope this helps.

Later Ed

[Jerry Emert]

OK, I'm a little off the wall as usual but along the same line...you know those small "jump boxes" that they sell now?  About the size of a Cracker Jax box.  My wife has one and has jumped her police car several times on one charge.  She is retired now and after this conversation I'm wondering if you think it might be enough to get the generator started if the batteries are discharged?  Does the generator take a lot more "power" to start it than a 8 cylinder car?  How would you have to do it...unhook the chassis batteries to isolate them so they don't drag down the little jump box?  Will the generator keep running if the batteries are unhooked to hook back up?  Just curious.  Thanks
Jerry

[Lee Welbanks]

As far as I know the generator does not have a alternator to supply power to its control boards and I don't think it will run without a battery supply.

[Joel Ashley]

Jerry, I would think just hooking such a box to the house batteries to start the genset would do the trick.  Until the house bank gets to about 13.4 volts, the BIRD should not let the Big Boy connect the chassis bank in.  Maybe when first hooked in and the BIRD reads a higher voltage, but as the genset plugs heat and it is cranked, dropping the house voltage, I'd think it would isolate the two banks.  Just speculating.

-Joel