DC-DC Charger install with Lifep04 batteries

mrbillfog25 · 01-02-2022, 02:20 PM

Greetings,
I will be installing Lifep04 batteries and a dc-dc charger in my coach. Also installing a new inverter/charger but I'll save those questions for another post. I know there has been a lot of discussion about the best way to install the dc-dc charger but I was thinking I could simply install a battery switch between the Aux start solenoid and the coach battery connection on the battery disconnect relay and then connect the dc-dc charger between the chassis battery and the coach batteries.

The switch would remain OFF to avoid direct alternator charging of the Lifep04 coach batteries. If I needed to "jump" the coach batteries to the chassis battery to start the engine I could turn the switch to ON, depress the momentary boost button on the dash, and start the engine. As soon as the engine is running I would turn the switch back to OFF.I have attached a current and proposed diagram. Any feedback or suggestions would be greatly appreciated!

DavidM · 01-02-2022, 02:37 PM

You are the first person on this and the IRV2 forum to recognize the issues with installing a DC to DC charger. Your proposed installation should work, but unless the switch is closed it will not let the coach's DC system charge the chassis batteries since the DC to DC charger acts like a diode.

Also I am glad you are using a Perko type rotary on/off switch. Others, but not for DC to DC charger installations use knife switches, which I think are ancient from the days of knob and tube AC wiring.

I use the chassis battery charging capability to keep the chassis batteries up while using solar during winter storage. If I installed a DC to DC charger like you propose, I would just keep the switch closed during the winter.

How many amp hours of Lithium batteries do you have? The higher the amp hour capacity of lithium batteries, the more current they will draw if well discharged. If you have just 200 Ahs then first measure the alternator current with the engine idling and the lithium batteries well discharged. You maybe be ok. Others have indicated 40-60 amps which should be ok for most alternators.

One guy with 600 Ahs of new lithiums said his alternator was fried after 6 months. So 200 may be ok, 600 is probably not ok.

David

**creativepart** · 01-02-2022, 03:02 PM

I'm interested in this topic. My AGM house batteries (4-100ah) are 5 years old. Next week I'm planning on giving them a test to determine just how well they are still working. As soon as I see some real degradation I plan on replacing them with LFP batteries - either 4-100ah or 2-200ah.

I've been pondering the whole alternator charging issue and reading up on it. And, at this moment I'm considering just disconnecting the alternator charging on the house batteries. That may be ill-advised but at least it doesn't prevent me from making a change if that choice turns out badly.

My 300w of solar panels do a good job of charging my house batteries now and I could easily add another 100w if need be. And, while we do plenty of camping with shore power, when we do dry-camp I'm not at all adverse to running the generator an hour in the morning and an hour or two in the evening.

So, I'm not sure I have a great need for alternator charging on the house batteries. Especially if I don't have to stay above 50% state of charge.

I like the on/off switch idea in concept, but the simplicity of not having to add new switching appeals to me.

mrbillfog25 · 01-02-2022, 03:05 PM

Wow that was a fast reply. Thanks David!
Great point on not being able to charge the chassis battery from the DC system with the switch off.

I have 200Ahs of lithium I am moving from a fifth wheel to the Winnebago along with the inverter/charger, etc. I plan to install solar as well but that is for another day.
Thanks again for the response and Happy New Year.
Bill

mrbillfog25 · 01-02-2022, 03:17 PM

creativepart, I thought about just disconnecting the alternator charging but I didn't want to lose the capability of "boost" starting the engine if the chassis battery dies.

I understand not making changes that can be easily reversed.
Thank you for the input.
Bill

**creativepart** · 01-02-2022, 03:26 PM

Quote:

Originally Posted by mrbillfog25

creativepart, I thought about just disconnecting the alternator charging but I didn't want to lose the capability of "boost" starting the engine if the chassis battery dies.

Bill, In the 7 year's I've owned two motorhomes and driven over 60,000 miles I've not once ever needed to use the boost switch to start the RV. Accommodating that switch is fairly low on my list.

(Famous last words.)

Morich · 01-02-2022, 04:03 PM

I can agree with doing it either way but I tend to like simple, when I can see a practical way to do it.
Not knowing how hard to acces the batteries may blow this idea but what about simply disconnect the charging from alternator to coach batteris and assume it will not often be needed---but also have a cover plan.

If you can access the two battery systems easy like under a simple flap, etc., how about disconnect the coach charging but be prepped to use a simple strap between the positive poles of each. Since negative is still connected to the frame as normal and only the positve sides connection removed/diconnected, then if/when the emergency did occur onewould have to oepn the flap, connect the strap and start the engine.

The "boost" feature is just a simple way to jump start the engine without getting out but I rarely used it and if I wanted/ needed it once in every few years, I would be okay with just doing a manual connection. Two alligator clips and a foot of # 6 was good enough! Especially since I never used it in the time I owned that particular RV!

jipper · 01-06-2022, 11:27 AM

I installed a similar system in my 2019 Navion.
I installed both the B to B and the jumper circuit with the switch between the boost solenoid and the disconnect relay. This is under the passenger seat in the sprinter and I mounted the switch to the outside of the seat base.
I also added a shutoff switch to the boost solenoid signal wire at the dash switch. This allows me to shut off alternator charging when I wanted to. This is the LR wire at the boost switch.

Jipper
2019 Navion J

bkg · 01-10-2022, 06:33 AM

Quote:

Originally Posted by mrbillfog25

Greetings,
I will be installing Lifep04 batteries and a dc-dc charger in my coach. Also installing a new inverter/charger but I'll save those questions for another post. I know there has been a lot of discussion about the best way to install the dc-dc charger but I was thinking I could simply install a battery switch between the Aux start solenoid and the coach battery connection on the battery disconnect relay and then connect the dc-dc charger between the chassis battery and the coach batteries.

The switch would remain OFF to avoid direct alternator charging of the Lifep04 coach batteries. If I needed to "jump" the coach batteries to the chassis battery to start the engine I could turn the switch to ON, depress the momentary boost button on the dash, and start the engine. As soon as the engine is running I would turn the switch back to OFF.I have attached a current and proposed diagram. Any feedback or suggestions would be greatly appreciated!

The switch is an excellent idea and one that I have considered myself. The issue I have is the charging maintenance of both the chassis and coach batteries. My RV stays parked in my driveway so I have the luxury of keeping my RV plugged in to keep the batteries charge maintained.
I do understand charging maintenance will be less of an issue with Lithium but, this is a concern for more than just charging while in storage. I like the fact that all my coach onboard battery's voltage is maintained; be it through solar, converter, or alternator - it is encouraging to see the display of both chassis and coach batteries voltage at 13.2 volts.

I'm with creativepart that I have little expectancy of ever needing the jump feature but I do depend on the alternator to recharge my coach batteries when we do an overnight stop or when we boondock. I have a compressor refrigerator and according to my Victron meter my coach batteries lose between 60 - 90 amps in a 24-hour period. The Victron has shown me that the alternator is a good bit more efficient at replenishing the batteries versus running the generator to power up the converter/charger.

So, I'm on the wait-it-out plan. My coach batteries are 1-1/2 years-old; technology already has appliances out there to work with alternator and Lithium charging, just not ideal for mixed battery chemistry. Soon enough there will be an array of Lithium starting batteries that will fit most vehicles applications. That's my hold-out, the entire 12-volt system designed with Lithium.

Bobby

lenore · 01-10-2022, 07:12 AM

Yes why not have a switch that goes to both sides {input and output} of Victron DC to DC converter that when turned on bypasses the DC to DC providing temporary jump line for the Boost solenoid.

Q-Branch · 01-10-2022, 05:41 PM

I'm in the midst of a 1000ah Lifep04 upgrade and just installed a pair of Victron DC to DC chargers in parallel. I have an aftermarket high-output alternator installed (from a fire truck) and with the two chargers in parallel, I can "potentially" charge at 60 amps. I to augment the OEM jump-start selenoid with an additional switch. And before anyone says it, yes it's overkill but go big or go home!

gurroz · 01-10-2022, 06:16 PM

My mobile RV tech who is also a heavy truck mechanic is installing my Renogy DC to DC charger this Friday. I will try and post photos. I know he is going to mount it under the dinette bench located by the entry steps. The battery is located under the steps and there is an enclosed box under the bench that is connected to the battery cut-off switch. He thinks it's a logical place to locate it and easy access to run wires.

jimkamery · 01-11-2022, 03:10 PM

When upgrading and installing the DC-DC charger on my 07 Outlook, I was also faced with the same predicament. I am an electrical engineer so I started by taking the attached schematic and making voltage readings with the engine off, with the engine running, and holding down the boost switch. After about an hour I figured that if the Battery mode solenoid didn't energize, the alternator would not charge the coach batteries, but it had to energize through the boost switch in order to "jump" the coach batteries to the engine. I added a SPST 15A toggle switch in line with wire LR and if the switch is off, my DC-DC charger works great. Like Creative Part, I don't anticipate needing the boost function, but I installed the switch just in case it ever happens. I installed the DC input from the DC-DC charger to wire KKF and ground and hooked the output of the charger to wire YEL and ground.

Oakprk · 01-21-2022, 02:27 PM

Quote:

Originally Posted by mrbillfog25

Greetings,
I will be installing Lifep04 batteries and a dc-dc charger in my coach. Also installing a new inverter/charger but I'll save those questions for another post. I know there has been a lot of discussion about the best way to install the dc-dc charger but I was thinking I could simply install a battery switch between the Aux start solenoid and the coach battery connection on the battery disconnect relay and then connect the dc-dc charger between the chassis battery and the coach batteries.

The switch would remain OFF to avoid direct alternator charging of the Lifep04 coach batteries. If I needed to "jump" the coach batteries to the chassis battery to start the engine I could turn the switch to ON, depress the momentary boost button on the dash, and start the engine. As soon as the engine is running I would turn the switch back to OFF.I have attached a current and proposed diagram. Any feedback or suggestions would be greatly appreciated!

You don't show the BIM in your current configuration.

gurroz · 01-21-2022, 05:54 PM

Well, we completed the installation, but I cannot figure out how to add photos to this site. I had a 1000W pure sign inverter at the house that I decided to add at the same time. I went with the Renogy 60 amp model DC to DC charger and used the recommended 80 amp fuse. Both items were installed under the dinette bench by the steps which house the battery. The small red power wire for the DC to DC unit was routed to the solenoid located by the battery. We will run a heavy gauge extension cord from the inverter to charge computer batteries and run the TV when needed. The seat belt cutouts on the bench will finally come in handy. After testing all works as advertised.

lenore · 01-21-2022, 08:15 PM

Quote:

Originally Posted by mrbillfog25

Greetings,
I will be installing Lifep04 batteries and a dc-dc charger in my coach. Also installing a new inverter/charger but I'll save those questions for another post. I know there has been a lot of discussion about the best way to install the dc-dc charger but I was thinking I could simply install a battery switch between the Aux start solenoid and the coach battery connection on the battery disconnect relay and then connect the dc-dc charger between the chassis battery and the coach batteries.

The switch would remain OFF to avoid direct alternator charging of the Lifep04 coach batteries. If I needed to "jump" the coach batteries to the chassis battery to start the engine I could turn the switch to ON, depress the momentary boost button on the dash, and start the engine. As soon as the engine is running I would turn the switch back to OFF.I have attached a current and proposed diagram. Any feedback or suggestions would be greatly appreciated!

This should work perfectly. When the switch is on you will have jump capability. OFF and the DC to DC will be working independently.

**creativepart** · 01-23-2022, 11:32 AM

Quote:

Originally Posted by gurroz

Well, we completed the installation, but I cannot figure out how to add photos to this site.

How to add photos to a post

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