Charging LifePo4s From the Main Engine -- Class C Motorhome

[Old Islander]

I've replaced the two lead acid house batteries with two 100 amp hour LiFePo4s.

I've changed the main power converter so that when on shore power, the LiFePo4s are charged to 14.6 volts. The solar charge regulator also charges them to 14.6 volts (given enough time and unobstructed sunlight...). But when I'm driving, the Ford chassis charging system won't bring them any higher than 13.6 to 13.8 volts.

I understand it is possible to install a device that will 'step up' the voltage from the alternator, so I get the full charge on these new batteries.

Any advice on how to achieve this will be appreciated...

 

[d23haynes57]

I've replaced the two lead acid house batteries with two 100 amp hour LiFePo4s.

I've changed the main power converter so that when on shore power, the LiFePo4s are charged to 14.6 volts. The solar charge regulator also charges them to 14.6 volts (given enough time and unobstructed sunlight...). But when I'm driving, the Ford chassis charging system won't bring them any higher than 13.6 to 13.8 volts.

I understand it is possible to install a device that will 'step up' the voltage from the alternator, so I get the full charge on these new batteries.

Any advice on how to achieve this will be appreciated...

First step is to check voltage at the alternator and then at the batteries. Next is how much current are the batteries drawing. 13.8 volts is a standard charging voltage for lead acid batteries staying just near or at the gassing voltage. However most common vehicle alternators are now running near 14.1 volts as maintenance free batteries can tolerate that and is better for some AGM. Your LifePos could just be sinking the system down and you need more time for them to finish charging. Also, what other house loads are you running. Alternator charging should never be considered a primary charge source. Do you have shunt meter or other means to monitor current in and out of the battery and monitor state of charge? Yes there are DC to DC chargers but if alternator supply is a limitation, they offer little value in batteries that small. Often, they are used to protect the alternator. Alternaotr, regulator, wiring upgrade probably best route.

 

[Old Islander]

First step is to check voltage at the alternator and then at the batteries. Next is how much current are the batteries drawing. 13.8 volts is a standard charging voltage for lead acid batteries staying just near or at the gassing voltage. However most common vehicle alternators are now running near 14.1 volts as maintenance free batteries can tolerate that and is better for some AGM. Your LifePos could just be sinking the system down and you need more time for them to finish charging. Also, what other house loads are you running. Alternator charging should never be considered a primary charge source. Do you have shunt meter or other means to monitor current in and out of the battery and monitor state of charge? Yes there are DC to DC chargers but if alternator supply is a limitation, they offer little value in batteries that small. Often, they are used to protect the alternator. Alternaotr, regulator, wiring upgrade probably best route.

We've just returned home after a 5 hour drive, from a site where I'd been plugged into shore power, and the LiFePos were fully charged when we left (14.4 volts). They dropped a bit during the drive home (to 13.6V). During the drive, the only draw on them was the 12V fridge. It was a hot day so I expect the draw was near continuous. Typically when we travel, we stay at power serviced sites, and only occasionally at non-serviced (boondocking). We also have two 100 watt panels on the roof which work really well if the site has good sky exposure.

No, I don't have a shunt meter. I'll try to measure the voltage at the alternator and at the batteries. While I'm fairly handy at various RV repairs, I'm not sure the DC to DC charger is something I'd want to tackle on my own. Maybe this is one of those times when I'll get some professional help.

Many thanks for your suggestions...