I have always used the boost switch in starting our coach because using the chassis batteries (2) alone it seemed to labor a bit before starting. At first, I suspected something might be wrong with the batteries, however, both are only about 2 years old and gave a good load test at MOT earlier this year. While having our fuel lines changed at MOT I asked Keith to evaluate this problem. He checked the batteries again and thought they were OK, but he did suggest cleaning the "bus" connections where all the engine cables attach to the chassis battery cables (on the frame behind the chassis batteries). It took him a while to get it apart since the bolts were seized and had to be cut off. The result (see attached) is that the engine now starts as it should without the boost. Evidently, the corroded bus (am I using the right term?) added significant resistance to the starting circuit. I am posting this since I was unaware of these connections and perhaps others are too.
These are power posts or studs. Good ones will have a nut (wrench fitting) at the bottom of the post. You probably will need a thin tappet wrench for this. Then the outer nut will be easier to remove.
Many have actually added a pair of bus bars, one for plus, one for minus. Each battery is connected to the bus bars. Starter motor cables go directly to the starter motor. Another set of cables connects to the power posts. A switch in the negative cable to the power post is a good idea. A shunt after the switch lets you monitor the start battery condition. You need to use big current capable bus bars. BEP Marine Pro Installer 650 Amp, 3-Stud Heavy Duty Bus Bar (https://baymarinesupply.com/wiring/wire/bep-marine-bus-bar-3-stud-650-amp.html).
This one has a bottom nut,
Blue Sea 2002 PowerPost terminal (https://baymarinesupply.com/wiring/wire/blue-sea-5-16-powerpost.html)
This one does not, just don't over tighten.
BEP Marinco Pro Installer 50V, Single Stud (https://baymarinesupply.com/wiring/wire/bep-marine-single-stud.html)
All of these studs and bus bars are long enough to connect three lugs (the recommended maximum number).
Do you have a recommendation for a shunt? I found this one mentioned on youtube:
ttps://www.go2marine.com/Blue-Sea-Systems-DC-Current-Analog-Meter-Shunts_2?gclid=EAIaIQobChMIxe-_1puV5QIVhJ6fCh0DKAIMEAQYBCABEgLQovD_BwE
I like Victron components. The Victron BMV battery monitor comes with a shunt, temperature sensor and is Bluetooth capable. One without bluetooth is a bit cheaper, you have to look at the monitor.
Victron BMV-712 Smart Battery Monitor with Built-In Bluetooth (https://baymarinesupply.com/electrical/battery-monitors/victron-bmv-712-smart-battery-monitor-with-bluetooth.html)
Victron BMV-702 Temperature Sensor (https://baymarinesupply.com/electrical/battery-monitors/victron-bmv-702-temperture-sensor.html)
The BMV 700 keeps track of the battery in the same way, less money, no temp monitoring.
Victron BMV-700 Battery Monitor (https://baymarinesupply.com/electrical/battery-monitors/victron-bmv-700-battery-monitor.html)
They might be a bit cheaper elsewhere but there is a discount at Bay Marine for the Forum community. Call and place your order and ask for a Forum discount. And they will actually help if you have questions.
The shunts are rated for 500 amps continuous and up to 1500 short term (like starting).
Adding a switch to the negative side lets you disconnect the start batteries easily.
BlueSea make a good one. Blue Sea Systems model 9003E Marine Battery Switch (https://baymarinesupply.com/wiring/switches/blue-sea-e-series-9003e-battery-switch-on-off-red.html)
So does BEP Marinco. BEP Marinco Pro Installer EZ-Mount On/Off Battery Switch (https://baymarinesupply.com/wiring/switches/bep-marinco-pro-installer-ez-mount-on-off-battery-switch.html)
These are rated about the same, use 4/0 cable to achieve maximum capability.
Make sure everything is clean and shiny when connecting cables and components. Enhace conductivity and keep the corrosion and oxidation at bay with a terminal grease. One little tub will last a lifetime (for most of us).
NO-OX-ID "A Special" Conductive Terminal Grease (https://baymarinesupply.com/wiring/switches/no-ox-id-a-special.html)
If you need cables Bay Marine will make them in any size and length to order.
Custom 4/0 gauge marine battery cable (https://baymarinesupply.com/wiring/custom-battery-cables/custom-0000-gauge-marine-battery-cable.html)
Roger,think he may mean the grounding cables that are grounded to the frame,mine are secured by a bolt thru the frame,George
do you mean the positive or negative cables?
If all connections are nice and clean, you should NEVER need the boost switch unless a battery problem, etc. I have posted several times about the boost switch being a crutch and masking a starting system problem. Yours is a prime example of a fault in the starting system making the boost switch necessary. If the Cummins factory says an engine will require X amps to start, then your start battery capacity should be that much will a little more for a hard winter and cable loss. No increased capacity will allow it to turn over or start any faster. What happens is that one day when the house batteries may be low and you have high resistance somewhere in the starting cables, you are stuck.
How many time on this forum has a member been stuck where the coach would not start? Lots! Almost every time, cleaning the battery posts, terminals has instantly cured the problem. Good to know where each cable goes and what it connects with so the connections can be cleaned if necessary. Not a bad idea to run an extra ground cable directly to a ground point close to the batteries. Vibration and corrosion are the most common cause of problems.
Pierce
John44... The pic of the terminals is not the best so I can understand the confusion. There are two terminals, both isolated from the frame. One is for the positive terminals of the chassis batteries and all the cables connected to it. The other is for the negative cable from the starting battery and all the cables connected to it. I know where the frame ground is located since John Haygarth and I cleaned it when I visited him in BC last summer. On my coach, it is on the cross-frame member near the hydraulic pump side.
I've attached a "before" cleaning pic that shows the terminals better and how dirty they were.
George
Looks like those examples Roger had would work,would definitely redo them.
George, Swap the positive or negative cable to the other battery. Better life for your batteries and more usable power.
George this was Dons solution
Charging System project (https://www.foreforums.com/index.php?topic=34545.msg318742#msg318742)
Isn't his negative coming off the rear battery on the right side and the positive coming off the front battery on the left side the correct way for a setup?
A closer look at the picture on a bigger screen and George H's battery connections look right.