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Old 02-26-2016, 11:27 AM   #1
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How many amps needed to jump start diesel?

Hi All:

New to RVing (pu the Prism tomorrow if the PDI goes well) and as part of my 'preparing for the worst' decided to buy a jump start powerpack just in case we kill the chassis battery in our noob ignorance.

Wondering, tho, how many amps are needed to kick off the MB diesel engine as they are extremely high compression.

The range of available ones are quite vast and don't want to think I've got enough juice only to figure out I don't when I really need it.

thanks!
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Old 02-26-2016, 08:14 PM   #2
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Best wishes to you and your new Prism. That is one sweet rig.
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Old 02-27-2016, 06:15 AM   #3
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Congrats! It is too bad MBS does not have the "boost" feature for the chassis. I have seen some work arounds on the forums. I installed a trik-L-Charger to keep the chassis battery topped up when I am plugged in or charging the coach with solar. I also carry a set of booster cables. You only need to connect the pos post on the coach to the pos boost post under the hood. The whole system shares the ground.

Good luck w the PDI- Make sure they physically show you how to operate the systems (not just tell you). There is a breaker on the Onan, the plug must be in the outlet in the elect compart etc. There was no owners manual for my 2015 Prism. I downloaded the generic from this forum or from Coachmen. any questions just ask me had mine for a year.
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Old 02-27-2016, 07:12 AM   #4
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The amps required buy the starter very by the engine size/type. We can usually jump them with a 550 amp jump pack if slow cranking. If the batteries are completed flat it takes two 550 jump packs or a big 900 we have in our shop.
Best of luck on the new rig.
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Old 02-27-2016, 07:20 AM   #5
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Congrats! It is too bad MBS does not have the "boost" feature for the chassis. I have seen some work arounds on the forums.
Don't know about the Prism. Do you have a battery control center similar to this one on the Forester/Solera/Sunseeker MBS? If so, all the circuitry, save for a fuse, some wire and a switch - are already in place. This panel is located on the left side of the footwell as you enter from the RV main door. A picture of the cover, which has been removed, is attached.

I'm working on the writeup on how to hook up the existing circuitry to add the boost feature. BTW, this feature IS being installed from the factory on the Dynamax Isata 3 - also now a FR product.
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Old 02-27-2016, 07:29 AM   #6
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If the batteries are stone cold dead they usually need to be charged up before trying to start the engine. If there is enough charge to get a clickety - clikety sound a 550 amp pack should work. On a good day
I have the 12v battery charger cord setup for my Honda EU2000 generator as a backup.
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Old 02-27-2016, 12:59 PM   #7
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Jumpers will reach from the house batteries to the Chassis battery, a bit time consuming to get to the chassis battery. I have never had trouble with the chassis battery running down. There is very little load on it while camping, I keep a couple phones plugged in. In the winter I take it out for a drive every couple months, no problems.
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Old 02-27-2016, 04:50 PM   #8
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When using any form of jump starting (portable pack, second vehicle) after you connect the cables to the vehicle to be started you should try to let its battery charge from the jump source for a few minutes. That will often put enough of a charge in the flat battery so it doesn't need to draw so much across the cables when starting. It would have to be a very large portable pack to be able to provide all the instantaneous starting current on its own.
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Old 02-29-2016, 09:34 AM   #9
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Jumpers will reach from the house batteries to the Chassis battery, a bit time consuming to get to the chassis battery. I have never had trouble with the chassis battery running down. There is very little load on it while camping, I keep a couple phones plugged in. In the winter I take it out for a drive every couple months, no problems.
X2. You won't be wearing down your chassis bat. Just buy one of these and check periodically your batts status ( house and chassis ) LED Auto Car Truck Cigarette Lighter Volt Voltage Meter Monitor Tester 12V 24V | eBay and calibrate it against a known voltage. As an example mine reads point two volts lower than actual charge . Then use this chart battery charge chart - Bing images your good to go. If that still doesn't put you at ease, try scotch!
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Old 02-29-2016, 12:10 PM   #10
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Originally Posted by KatanaPilot View Post
Don't know about the Prism. Do you have a battery control center similar to this one on the Forester/Solera/Sunseeker MBS? If so, all the circuitry, save for a fuse, some wire and a switch - are already in place. This panel is located on the left side of the footwell as you enter from the RV main door. A picture of the cover, which has been removed, is attached.

I'm working on the writeup on how to hook up the existing circuitry to add the boost feature. BTW, this feature IS being installed from the factory on the Dynamax Isata 3 - also now a FR product.
If you don't or didn't want to run the circuit (I did), you could just temporarily jump terminals "ES" and "coach" to close the isolator relay to start it from your coach batteries...you would need a second person or just a short wire with alligator clips.
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