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Dual alternator and dual battery in 2018 3500 Longhorn

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Ken45

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I have a 2018 3500 Longhorn diesel with dual 440A alternators, and dual battery. I want to be able to charge my 12V land based battery backup system which I use for powering freezers, fridges, and house gas furnace etc. System works great as long as there is mains 120VAC. During power failures batteries run the load for 2 to 3 days. Currently the batteries charge via AC through a Magnum inverter/charger. For extended power failures the plan is to use a gas generator(120VAC) every few days to charge the batteries through the Magnum. When I run out of gas or can't get any, the RAM could be a great backup.
Getting to the point.... with all that capability in the RAM, I should be able to charge these deep cycle backup batteries, total 832 Amp hours, fairly quickly.
Questions: Point of connection in the truck, does this(photos) look like it would work? Any better suggestions? Ideas? Because the connection is temporary, could I use a booster cable clamp on the top of the battery pos terminal? Thanks!!
Neg connection1.pngPositive connection HAPP1.png
 
I think you'll find you have dual 220A alternators (440A total).

That's what the current offering is and AFAIK has always been for duals on the Cummins. Just a point of clarity.

I would install Andersen connectors.
 
I build van power systems that are sort of like what you are trying to do there.

I am still coming up to speed on the ram truck setup - don't own one yet, but will eventually.

On the van versions, you would not want to do it that way because:
- The starter battery connection is the wrong place to tap in for extended use power draw
- The voltages will not be correct for charging the starter battery ( which is most likely a flooded type ) vs AGM or Li. They are close, but not correct.
- The voltage drop through the wires will be too much

Some vehicles - especially the newer ones, have a shunt that measures how much power is going in / out of the battery. This is fed into the engine computer, and if it goes far off of the measurements, the computer can go crazy. What this means is that pulling power might need to be done using the upfitters guide approach for that specific vehicle vs just what we used to think about doing 25 years ago.

A very common method in vans is to either use a sterling battery to battery charger, which has pros and cons.

Or

Use a method that is often referred to as the "Orton method" - because he has promoted the idea on van forums for years.

Basically you put a 1 or 2 kW inverter in your vehicle - powered off the starter battery.

Run that 120 vac over to your desired battery pack and charge using that power. Dramatically smaller wire, and dramatically better / faster charging, especially toward the end of the charge.

The alternators produce almost nothing at idle RPM, so there needs to be a method to bring the engine rpm up to 1000 - 1200 rpm. Some vehicles have that built in and some do not.

_____________

One of the benefits of using the Orton method, is that it will try to pull out that power even if the battery voltage is a bit low - and sometimes this triggers that engine computer to run the rpm up to charge.

The sterling instead cuts off charging if the battery voltage goes lower than the set points - so it will sometimes do absolutely nothing, especially in vans built after 2017 ( in some brands even 2008 )

The downside of the Orton method, is that the inverter pulls some power ( 20 - 40 watts ) in idle mode, so you have to completely shut it off when not in use.

___________________

A 2 kW inverter will try to pull 200 amps @ 12 volt, so this is nominally a pair of 2 awg or a heavier single wire.

Here is an ampacity chart that is a useful guide for modest distance wire lengths. It would indicate 4/0 ( as in 0000 not 4 awg ) for a single wire use.

www.cerrowire.com

Cerrowire Resources - Ampacity Charts

Ampacity is the maximum current that a conductor can carry continuously under the conditions of use without exceeding its temperature rating. Cerrowire's ampacity chart helps calculate the load requirement for a circuit.
www.cerrowire.com www.cerrowire.com
 
BTW - the cable on the right with red looks like it is properly crimped.

The one more to the left looks like it was done with a hammer crimp and should be replaced if you want to actually pull power from that wire and not overheat.

In general, you want to ground to the body, not the engine for most vehicles. On vans, there are specific factory engineered ground points for attaching a high current ground. Not sure about trucks yet.
 
HarryN said:
BTW - the cable on the right with red looks like it is properly crimped.

The one more to the left looks like it was done with a hammer crimp and should be replaced if you want to actually pull power from that wire and not overheat.

In general, you want to ground to the body, not the engine for most vehicles. On vans, there are specific factory engineered ground points for attaching a high current ground. Not sure about trucks yet.
Click to expand...

Ram builder guides all say body/chassis grounds are only good to 50A.

Everyone here pretty much does DC-DC chargers.

For the 19+ trucks, there's a nicer HAPP rated to 300A with a couple studs available on the + side. Engine grounding is recommended on the - side.

post #7:
Brutal_HO

Thread 'In Cab Power FAQ -- AUX Switch power info -- Chassis power info'

This is a roll-up thread that should answer most if not all questions regarding power availability in the cab.

A lot of the credit for technical detail goes to @Jimmy07 without whose help and guidance much of this info would be hard to assemble.
There are other contributors, you know who you are. If you recognize a photo as one of yours, shoot me a PM and I'll add the credit.

PDC and AUX PDC Fuse worksheet: https://docs.google.com/spreadsheet...ouid=105565244363658163151&rtpof=true&sd=true
or here...
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Brutal_HO said:
Ram builder guides all say body/chassis grounds are only good to 50A.

Everyone here pretty much does DC-DC chargers.

For the 19+ trucks, there's a nicer HAPP rated to 300A with a couple studs available on the + side. Engine grounding is recommended on the - side.

post #7:
Brutal_HO

Thread 'In Cab Power FAQ -- AUX Switch power info -- Chassis power info'

This is a roll-up thread that should answer most if not all questions regarding power availability in the cab.

A lot of the credit for technical detail goes to @Jimmy07 without whose help and guidance much of this info would be hard to assemble.
There are other contributors, you know who you are. If you recognize a photo as one of yours, shoot me a PM and I'll add the credit.

PDC and AUX PDC Fuse worksheet: https://docs.google.com/spreadsheet...ouid=105565244363658163151&rtpof=true&sd=true
or here...
  • Like
  • Love
Click to expand...

Thanks - then would it make the most sense to connect the ( -) right to the alternator(s) mount for a high amp application ?

I guess these don't have a shunt in there ( - ) for engine charge management ?

Will look around to try to find the ram builders guide.
 
The "shunt" is a "fuse" on the + side of the battery.

The IBS (Intelligent Battery Senor) is on the negative side.


Builders guides are now behind a login "paywall" of sorts. No fee, but you have to submit a request for access as a builder/upfitter. I used a fictitious company name I've used before to get samples and my work email address (a large IT company). Once signed up, I just changed the email to my personal account. Can't change the login, but I could change the email.

 
What size is the magnum 120VAC charger?

Since this is a backup to the primary system I’d look into the cheapest option.

Here is the alternator output curve. At idle in a hot engine compartment there are ~ 205A available. Manual fast idle to 1500 rpms and there are ~345A available.

IMG_3726.jpeg
 
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