DC to DC Charger - Gas Motorhome How To

[Griswald One]

Good Day All,

I am in the process of upgrading my house batteries to LiFePo4 and am considering some of the ancillary equipment that may make the system perform better.

I am adding 2x200Ah Renogy Pro Series batteries. They are in many respects Plug and Play. They give me the longevity I need for our style of use and have a peak load capacity that is up to the task of starting the generator and operating the hydraulics. Renogy included for free in the purchase a shunt and battery monitor, I am not sure if I will include them in my set up since the motorhome already has a an onboard battery monitor (not as good, I know) and the batteries have a bluetooth connection to my phone which provides all the same data the monitor will. In addition my slide configuration will make wiring into the coach living space from the battery bay next to impossible. I will also be adding a disconnect switch to protect the batteries during storage, something I should have done long ago.

My next consideration is a DC to DC Charger to protect the alternator. I am not in a rush on this one as the 210amp alternator is fairly beefy and we are post to post campers so the load will almost always be light. That being said it is still a project I am considering but have had no luck finding installation details for a gas motorhome, at least not any that are written in plain English for those of us who didn't go to College for an Engineering degree. Is it as simple as wiring it in immediately after the battery? Or is there somewhere specific it needs to go. I assume it would not go between the house batteries and the Inverter/Converter as that would impact outflow as well.

If any of you know a video link, particularly one for a gasser on a Ford Chassis, I would love to see it.

Thanks in advance.

[NoviBill]

This photo album has crude diagram of what I removed and what I added to install a DC-DC charger. The charger I bought was 40amp my batteries optimally charge at 20 amps and I have 2 so this should help with battery life and alternator life.

https://www.flickr.com/photos/cdrdwd...77720316645473

The DC-DC charger also acts as a solar charger so I added about 300 watts of solar (foldable panels). When my batteries are full, in theory it will back feed the chassis battery. The one thing I did not include was an emergency starter switch.

*I thought my old BIRD would do this, but the voltages are wrong so it never engages. Something I should follow up on, but will wait until I have a no start :-(

[d23haynes57]

Being a Post to Post camper do you even need alternator charging capability? I can help with the engineering but need more information on your coach. If you had the typical 4 golf cart battery bank that would an approximate >400 A/H set up. Your wiring and contactor was sized to carry that load. If you are not increasing A/H capacity with the 210 A/H alternator you should be good to drop in the Lithium. If you do decide to go with a DC to DC charger you will want to go with 60 amp for the 400 A/H bank. That will put you at a 6 to 7 hour charge rate.

[Griswald One]

Originally Posted by d23haynes57

Being a Post to Post camper do you even need alternator charging capability? I can help with the engineering but need more information on your coach. If you had the typical 4 golf cart battery bank that would an approximate >400 A/H set up. Your wiring and contactor was sized to carry that load. If you are not increasing A/H capacity with the 210 A/H alternator you should be good to drop in the Lithium. If you do decide to go with a DC to DC charger you will want to go with 60 amp for the 400 A/H bank. That will put you at a 6 to 7 hour charge rate.

You are correct we were on the typical 4 battery 6v setup. I think removing the alternator charging would add a level of complication to some of the other systems. The set up on this rig requires alternator charging during all slideout movement and during the deployment of the levelers. I think these Renogy batteries would be up to those tasks on their own... But I am not inclined to mess with system that works.

The 60amp charger is intriguing. Most seem to reference a 30amp so I was not even considering larger.

[Griswald One]

Originally Posted by NoviBill

This photo album has crude diagram of what I removed and what I added to install a DC-DC charger. The charger I bought was 40amp my batteries optimally charge at 20 amps and I have 2 so this should help with battery life and alternator life.

https://www.flickr.com/photos/cdrdwd...77720316645473

The DC-DC charger also acts as a solar charger so I added about 300 watts of solar (foldable panels). When my batteries are full, in theory it will back feed the chassis battery. The one thing I did not include was an emergency starter switch.

*I thought my old BIRD would do this, but the voltages are wrong so it never engages. Something I should follow up on, but will wait until I have a no start :-(

Thanks for the photos, particularity the wiring diagram. I note you installed it after the BIRD... I have seen that term on here several times while I was researching... Would you believe when you google the term BIRD and electrical wiring... All that you get in return is pictures of Birds sitting on wires.

[d23haynes57]

Originally Posted by Griswald One

You are correct we were on the typical 4 battery 6v setup. I think removing the alternator charging would add a level of complication to some of the other systems. The set up on this rig requires alternator charging during all slideout movement and during the deployment of the levelers. I think these Renogy batteries would be up to those tasks on their own... But I am not inclined to mess with system that works.

The 60amp charger is intriguing. Most seem to reference a 30amp so I was not even considering larger.

Especially for a multi battery system you need at least 10 amp charger/100 A/H battery just to ensure the BMS goes into charge mode. With insufficient power the batteries may charge out of sync. If you measure current for charging with your current bank you will see near 100 amp peaks from the alternator. Lithium will typically peak for, 30 to 40 % of total A/H capacity. For a 400 amp bank you will max at 160 amps, reduced by wiring size and other connection resistance. From experience you will probably be around 120 amps.

Now here is a dig! If you need the engine running and the alternator, chassis batteries combined to operate the slide out rooms, the DC to DC charger will disable that capability due to the current limit. Same for chassis battery boost to start the generator.

As for alternator abuse, starting the engine, then adding battery charging, and probably a 180 amp load for hydraulic pump is about as abusive as you can get. If your system can handle that, no problem dropping in the 400 A/H lithium bank.

[Griswald One]

Originally Posted by d23haynes57

Especially for a multi battery system you need at least 10 amp charger/100 A/H battery just to ensure the BMS goes into charge mode. With insufficient power the batteries may charge out of sync. If you measure current for charging with your current bank you will see near 100 amp peaks from the alternator. Lithium will typically peak for, 30 to 40 % of total A/H capacity. For a 400 amp bank you will max at 160 amps, reduced by wiring size and other connection resistance. From experience you will probably be around 120 amps.

Now here is a dig! If you need the engine running and the alternator, chassis batteries combined to operate the slide out rooms, the DC to DC charger will disable that capability due to the current limit. Same for chassis battery boost to start the generator.

As for alternator abuse, starting the engine, then adding battery charging, and probably a 180 amp load for hydraulic pump is about as abusive as you can get. If your system can handle that, no problem dropping in the 400 A/H lithium bank.

Thanks! That all makes perfect sense and saves me the purchase.

[Tony Ramirez]

What # % of Amps does it start to strain the alternator? If I have a 160A(125A@idle) alternator, how big a DC@ DC charger will start to strain the alternator? I would assume it would make a difference if I'm running down the road w no lights on or drive @ night w the headlights on, Right?

[d23haynes57]

What type and size battery bank do you have now and how is engine alternator charging managed? Diode (Duvac) or relay? How is the relay controlled? Ignition switch or automatic voltage control. While you only have 160 amps being a Diesel you probably have Leece Neville or Delco set up which is much more capable than the same amp rated alternators for the gas engines.

If you have the typical 4 golf cart battery set up you already pushing that alternator hard. You can probably see low battery voltage in situations where the alternator is not keeping up. Cable size and length was already designed to provide some current limiting. I would drop in up to the same size Lithium bank and monitor operation.

This battery has become my go to for this application.
https://www.amazon.com/Litime-LiFePO...=Q6J58-sersVpl
The pair will support a 3,000 watt inverter and easily start a Deisel Generator. The BMS is extremely capable including completely turn off charging when the battery is charged. It also works well with AGM charge profiles and the 13.6 open circuit voltage is also ideal for floating AGM batteries.

[Tony Ramirez]

[QUOTE=d23haynes57;6946858]What type and size battery bank do you have now and how is engine alternator charging managed? Diode (Duvac) or relay? How is the relay controlled? Ignition switch or automatic voltage control. While you only have 160 amps being a Diesel you probably have Leece Neville or Delco set up which is much more capable than the same amp rated alternators for the gas engines.

If you have the typical 4 golf cart battery set up you already pushing that alternator hard. You can probably see low battery voltage in situations where the alternator is not keeping up. Cable size and length was already designed to provide some current limiting. I would drop in up to the same size Lithium bank and monitor operation.

Mine is the Delco 160A alternator, I don't know whether it is diode or relay, Ignition or Voltage. Factory it was 4 FLA GCs, it is now 920A LifePO4s.

I have the Victron Orion XS DC2DC Charger which is programmable up to 50A, both input & output. Not knowing how many Amps would strain the alternator, I have it set @ 30As, thinking that should be safe. I wouldn't mind buying that # up though IF I knew it wouldn't strain the alternator.

Thoughts?

[NoviBill]

Originally Posted by Griswald One

Thanks for the photos, particularity the wiring diagram. I note you installed it after the BIRD... I have seen that term on here several times while I was researching... Would you believe when you google the term BIRD and electrical wiring... All that you get in return is pictures of Birds sitting on wires.

My first try was after the BIRD, the BIRD would not engage because the voltage on the LifePo4 was above the full charge state for SLA batteries. So I had to wire around the isolation relay (my DC-DC charge acts as a solid state isolation relay).

Bi-Directional Isolator Relay Delay (BIRD)

Allows the RV when plugged in to shore power to charge the chaises battery

This site states it as a "new approach" so apparently my 2006 FR Lexington is new. https://intellitec.com/bi-directiona...r-relay-delay/

[Deznut]

Griswald see attached - I had to disconnect the battery boost option - dc to dc chargers are not designed to send power two ways ( in ( charging) AND out ( Battery Boost)) I do not have a BIRD in my 2019 Alante 26x ( F-53 chassis built in 2018) hth...
https://www.jaycoowners.com/threads/...2#post-6391754

[d23haynes57]

[QUOTE=Tony Ramirez;6946868]

Originally Posted by d23haynes57

What type and size battery bank do you have now and how is engine alternator charging managed? Diode (Duvac) or relay? How is the relay controlled? Ignition switch or automatic voltage control. While you only have 160 amps being a Diesel you probably have Leece Neville or Delco set up which is much more capable than the same amp rated alternators for the gas engines.

If you have the typical 4 golf cart battery set up you already pushing that alternator hard. You can probably see low battery voltage in situations where the alternator is not keeping up. Cable size and length was already designed to provide some current limiting. I would drop in up to the same size Lithium bank and monitor operation.

Mine is the Delco 160A alternator, I don't know whether it is diode or relay, Ignition or Voltage. Factory it was 4 FLA GCs, it is now 920A LifePO4s.

I have the Victron Orion XS DC2DC Charger which is programmable up to 50A, both input & output. Not knowing how many Amps would strain the alternator, I have it set @ 30As, thinking that should be safe. I wouldn't mind buying that # up though IF I knew it wouldn't strain the alternator.

Thoughts?

For that size battery bank the DC-DC charger is definitely needed for that alternator. Should not be a problem going to 50 amps. Note that as alternator voltage drops the input will go over the setting in order to boost the output voltage. Your original set up was peaking over 100 amps so 50-60 will be good. Note that 50 amps into a 900 A/H bank is still an 18-hour charge rate, reduced by any other loads connected to that bank. I would be looking to upgrade the alternator or rely on more generator charging. Charger or inverter charger would be good at 150 amps. What is your daily consumption? Are you using all of that capacity or is it just in case? Solar?

[Tony Ramirez]

[QUOTE=d23haynes57;6946887]

Originally Posted by Tony Ramirez

For that size battery bank the DC-DC charger is definitely needed for that alternator. Should not be a problem going to 50 amps. Note that as alternator voltage drops the input will go over the setting in order to boost the output voltage. Your original set up was peaking over 100 amps so 50-60 will be good. Note that 50 amps into a 900 A/H bank is still an 18-hour charge rate, reduced by any other loads connected to that bank. I would be looking to upgrade the alternator or rely on more generator charging. Charger or inverter charger would be good at 150 amps. What is your daily consumption? Are you using all of that capacity or is it just in case? Solar?

THANK YOU!

I do have solar, but in winter it's not as productive. I rarely go under 50%, so it's more of a "just in case" scenario. Especially after boondocking w the DW who runs everything like we're at home, & likes the 2 furnaces on. Easier for me to set a an overkill system than to keep saying: "TURN THAT OFF."