Charging sources for LiFePo Battery?

[smokey73]

Seeing what @Maine Sail has shown on his How-To site I have a question about what source to charge the Lithium House Battery.

I will be using the Stock 80 A Alternator to charge the Start Battery.
I will have a Victron XS 50A DC to DC charger set to the correct voltage for Lithium Battery.

I have a 100A Solar Panel with an MPPT controller for keeping the batteries charged on a mooring
I have a ProNatic 50A Shore Charger

Rod's simple diagram shows the Solar and Inverter/Charger directly charging the Lithium Battery and the Alternator charing the Start Battery with a plug in Victron charger available to charge the Start Battery. I understand charging the Start Battery from the Alternator with the Victron DC to DC charger between the Start Battery and House Battery so that is not a point of discussion here.

Since there is a Victron XS DC to DC charger between the Start Battery and the House Battery that can be customized to a profile for the Lithium Battery, regardless of the profile of the charging source, what would be the problem if all the charging sources, (ProNautic 50 Shore Charger, Solar MPPT, and Alternator) where set for the FLA Battery profile charging the Start Battery and just letting the Victron DC to DC Charger handle all the charge loads to the LiFePo House Battery? What am I missing?

Your thoughts on this would be appreciated, especially @Maine Sail since he created the simplified diagram.

 

[Maine Sail]

Seeing what @Maine Sail has shown on his How-To site I have a question about what source to charge the Lithium House Battery.

I will be using the Stock 80 A Alternator to charge the Start Battery.
I will have a Victron XS 50A DC to DC charger set to the correct voltage for Lithium Battery.

I have a 100A Solar Panel with an MPPT controller for keeping the batteries charged on a mooring
I have a ProNatic 50A Shore Charger

Rod's simple diagram shows the Solar and Inverter/Charger directly charging the Lithium Battery and the Alternator charing the Start Battery with a plug in Victron charger available to charge the Start Battery. I understand charging the Start Battery from the Alternator with the Victron DC to DC charger between the Start Battery and House Battery so that is not a point of discussion here.

Since there is a Victron XS DC to DC charger between the Start Battery and the House Battery that can be customized to a profile for the Lithium Battery, regardless of the profile of the charging source, what would be the problem if all the charging sources, (ProNautic 50 Shore Charger, Solar MPPT, and Alternator) where set for the FLA Battery profile charging the Start Battery and just letting the Victron DC to DC Charger handle all the charge loads to the LiFePo House Battery? What am I missing?

Your thoughts on this would be appreciated, especially @Maine Sail since he created the simplified diagram.

Yes but the Orion will pull more than 50A from the charger & solar so, when on shore power you will need to limit Orion current. Best to feed solar & pronautic to LFP and use ignition excite for the orion/alternator and use a small IP65 to keep start batt charged.

 

[dlochner]

Off the top of my head, the first thought is reduced charging efficiency especially with the Solar panel. The Orion will need to draw more than 50a to produce 50a.

And as I type this I see Rod has beat me to the punch.

 

[jssailem]

I try to think about the problem from the point of usage and available power input.

Sources of power at:

• Mooring or Anchorage: Solar source. Connect to Boat power storage LiFePO4 battery. When full, it spills over to the Start battery using the Victron DC - DC.
• Marina dock Shore source: Connect to Boat power storage LiFePO4 battery. When full spills over to the Start battery using the Victron DC - DC.
• Auxiliary Engine Start Battery source: Connect the Engine Alternator to the Start battery. You consume a bit of energy at the start, then it is replenished. While the engine is running, when the Start battery is full spills over to the LiFePO4 battery using the Victron DC - DC.

You will want bidirectional charging between the two battery groups (House - Start).

Victron does not make a bidirectional charger. Their solution is to install two Orion XS chargers — one wired start → house (your current plan) and a second one wired house → start for maintenance/trickle charging.

Sterling Power does make bidirectional DC -DC chargers.
Sterling dc-dc-chargers

 

[smokey73]

@Maine Sail Difficulty is that my boat is on a mooring, not tied to the dock. I don't have any place to plug in the Victron IP67 charger to make sure the start battery stays charged. I've had several diesel cars and as long as there aren't any parasitic loads, the battery stays charged between starts. I don't know if that is the case for a marine application or if I need a trickle charger on the start battery. I don't have an inverter/charger, just an charger. I could buy a small 12 V powered inverter like you can buy for a car and hook up a trickle charger to the start battery. Would that work or is there something wrong with that logic?

@jssailem I'm not sure how you'd wired so the "spill over" as you refer it would occur at the right voltage from the house battery to the start battery considering the voltage settings for the LiFePo House battery is lower than the typical charge settings for the FLA start battery.

 

[dlochner]

@Maine Sail Difficulty is that my boat is on a mooring, not tied to the dock. I don't have any place to plug in the Victron IP67 charger to make sure the start battery stays charged. I've had several diesel cars and as long as there aren't any parasitic loads, the battery stays charged between starts. I don't know if that is the case for a marine application or if I need a trickle charger on the start battery. I don't have an inverter/charger, just an charger. I could buy a small 12 V powered inverter like you can buy for a car and hook up a trickle charger to the start battery. Would that work or is there something wrong with that logic?

@jssailem I'm not sure how you'd wired so the "spill over" as you refer it would occur at the right voltage from the house battery to the start battery considering the voltage settings for the LiFePo House battery is lower than the typical charge settings for the FLA start battery.

A small diesel takes very little power to start, it does take a lot of power for a very short time, however if you do the math it is only 1ah or 2ah. Assuming the battery begins with a full charge, it only takes a few minutes to return the battery to 100% SOC. In your design with the alternator charging the start battery and supplying power to the DC-DC the alternator's power will be shared between the DC-DC charger and the battery. As the battery approaches fully charged, more of the power flows through the DC-DC charger and ultimately the house battery. There is nothing particularly magical about this process and it can be defined with some simple algebra.

Assuming the boat is used with some frequency and the diesel is run battery should be fine. It will certainly take more than a couple of weeks to drop to low to not start the diesel. One thing you could do is add a shunt and ammeter to the start battery circuit to monitor the battery's SOC. The Victron BMV-712 will do this and is not too expensive. With the monitor you will know the battery's charge state.

The short answer to your questions, no you do not need a trickle charger to keep the start battery charged, so long as the battery is in good condition and not too old and the boat is used frequently. Since the boat is on a mooring, the charger only comes into play when the boat is in a marina and at a dock. Being on a mooring, the worst thing you could do is sail on and off the mooring without running the diesel.

 

[Maine Sail]

@Maine Sail Difficulty is that my boat is on a mooring, not tied to the dock. I don't have any place to plug in the Victron IP67 charger to make sure the start battery stays charged. I've had several diesel cars and as long as there aren't any parasitic loads, the battery stays charged between starts. I don't know if that is the case for a marine application or if I need a trickle charger on the start battery. I don't have an inverter/charger, just an charger. I could buy a small 12 V powered inverter like you can buy for a car and hook up a trickle charger to the start battery. Would that work or is there something wrong with that logic?

@jssailem I'm not sure how you'd wired so the "spill over" as you refer it would occur at the right voltage from the house battery to the start battery considering the voltage settings for the LiFePo House battery is lower than the typical charge settings for the FLA start battery.

As long as start has a on/off switch, and no parasitic loads bypass it, your start batt can sit there for months with no worries..If you are really worried a small 20W panel for start works too.

 

[smokey73]

@dlochner and @Maine Sail Thanks for the response. As I thought about it and my previous experience with diesel cars, there is no specific need for charging other than from the generator for most conditions. I will carefully check that there are no parasitic loads. It does have an on off switch. I'll get a Victron IP67 "plug in"charger for the occasional need to top off the start battery when hooked up to shore power as suggested by Rod. No need to complicate it. Again, thanks for your feedback.

 

[Johann]

@dlochner and @Maine Sail I'll get a Victron IP67 "plug in"charger for the occasional need to top off the start battery when hooked up to shore power as suggested by Rod.

If it were me I would opt for the Orion TR Smart 12/12-18 DC-DC to keep the start battery charged from the LFP house. So while on the mooring the MPPT charges LFP house, and the Orion 12/12-18 floats the lead start battery from the LFP house. While motoring, the Hitachi 80A charges the lead start battery, and the Orion XS 50A charges the LFP house.

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[marcham]

All good points above.

Assuming you have an AGM start battery, you only need to charge it once a month. This can be done with the engine (alternator) or with the 120V AC charger.

We also spend the summer (about 3 months a year) on the hook/mooring ball. In our case, we have all charge sources going to the main consumer: the house batt (solar, alternator, inverter/charger). A dc -dc charger goes from the house to the start batt ONLY when the engine is running (tied to the ignition circuit). We also have a 120V AC 7 Amp charger to keep the start batt topped off over the winter months at the dock. This charger is on the circuit fed by the inverter charger (Victron 3000/120), so in an emergency while on the hook, I can also charge the start batt from the house batt using the inverter and the AC charger.

For your setup, if you don't want to start the engine to charge the start batt, you could connect the 120V AC charger to the inverter/charger and use that to charge the start batt. About60 minutes once a month will keep it full. AGM batts loose about 2-3% charge per month, not a big deal. They can sit for 3-5 months without a top up charge without damage. Otherwise, running the engine for 30-45 minutes a month will keep it full (assuming you are not also charging the house batt from the alternator).

I wouldn't recommend 2 dc-dc chargers, operating in different directions, as if not very well controlled, could cause a parasetic drain.

 

[Johann]

For your setup, if you don't want to start the engine to charge the start batt, you could connect the 120V AC charger to the inverter/charger and use that to charge the start batt. About60 minutes once a month will keep it full. AGM batts loose about 2-3% charge per month, not a big deal. They can sit for 3-5 months without a top up charge without damage. Otherwise, running the engine for 30-45 minutes a month will keep it full (assuming you are not also charging the house batt from the alternator).

I wouldn't recommend 2 dc-dc chargers, operating in different directions, as if not very well controlled, could cause a parasetic drain.

The OP doesn’t currently have an inverter, otherwise the AC charger would work. As far as the two DC-DC chargers they do need to be programmed correctly, but the same would be true with one DC-DC and one AC charger in opposite directions. In this case it is simple… the Orion XS is ignition activated, and the Orion TR would have a minimum input voltage set near the 100% SOC resting voltage of the LFP house bank.

One advantage of the dual DC-DC vs a dedicated inverter for an AC charger is the lower standby power draw from the DC-DC charger.

 

[jssailem]

Pages 16 through 20 of the Victron manual discusses the details of setting the charger up to provide a bidirectional charge to the batteries using 2 Victron Orion XS chargers.
The setup involves:

• Output configuration for FLA:
  • Output current: Limits the maximum output current.
    The value can be adjusted between 1 A and 70 A in 0.1 A increments.
  • 
    
  • Battery settings: Allows to change the battery settings in order to adjust the absorption voltage, float voltage, and others to fit the battery being charged; see the Charger mode - Battery settings [17] section for details.
  • 
    
  • The charger has built-in presets (via VictronConnect app) for lead-acid batteries, including Flooded/FLA. You can select a FLA preset or customize absorption (~14.4–14.8V typical for FLA), float (~13.5–13.8V), and other parameters like adaptive absorption time, equalization (if needed), and temperature compensation. Follow your specific FLA battery manufacturer's recommendations.
• Input from LiFePO4:
  • Input voltage lock-out: Allows the choice between two thresholds, one to set the lock-out value and another for the restart value. Normally, a minimum difference of 0.5 V is recommended for proper operation. The protection can still be disabled if desired by the user. For more information about the input voltage lock-out, please read the Engine shutdown detection [13] section.
  • The input voltage range is 9–17V, which easily covers a healthy 12V LiFePO4 bank (typically ~13–14.6V when charging or resting higher). The wide range and buck-boost design handle voltage variations well.
• Input voltage lock-out and engine shutdown detection:
  • This function can be adjusted (or disabled) to prevent unwanted draining of the LiFePO4 when it's not the "source" you intend, or to only activate under certain conditions. Set the lock-out/restart thresholds appropriately (e.g., defaults are around 12.5V lock-out / 12.8V restart in charger mode).
  • You can set this function to trigger the Start Battery to charge the LFP battery when the engine is running (or stop when the engine is off).

The Victron Orion XS charger is a clever tool. You can also use switches in the circuit to provide a manual override if desired.

 

[marcham]

Ack the lack of inverter onboard.

I stand by the fact that setting up by-directional DC-DC charging is complex, there are multiple use cases that must be considered and the devices must correctly configured (possibly with ignition interlock), the system must also be extensively tested in multiple scenarios to avoid faults.

If on a mooring with solar charging the house batt (powers fridge, bilge pumps, etc...), It would be simpler to just use an AC charger to top off the start battery once a month, or start the engine once a month. If there is no installed inverter onboard, a portable 200W inverter would do the trick, to support a 7-10 A ac charger.

Sure, the dual dc-dc or bi-directional XS 50 would be ideal in this scenario, but it requires complexity in configuration. It also will likely result in a constant 0.8 - 1 A draw on the house battery. Is the house storage size and solar capacity up to the task? The start AGM does not need a constant float charge, except if stored for 4 months or more....

if starting the engine monthly, run it at 1200 RPM for 20-30 minutes to let it get to temp and recharge the start batt.

 

[Johann]

Ack the lack of inverter onboard.

I stand by the fact that setting up by-directional DC-DC charging is complex, there are multiple use cases that must be considered and the devices must correctly configured (possibly with ignition interlock), the system must also be extensively tested in multiple scenarios to avoid faults.

If on a mooring with solar charging the house batt (powers fridge, bilge pumps, etc...), It would be simpler to just use an AC charger to top off the start battery once a month, or start the engine once a month. If there is no installed inverter onboard, a portable 200W inverter would do the trick, to support a 7-10 A ac charger.

Sure, the dual dc-dc or bi-directional XS 50 would be ideal in this scenario, but it requires complexity in configuration. It also will likely result in a constant 0.8 - 1 A draw on the house battery. Is the house storage size and solar capacity up to the task? The start AGM does not need a constant float charge, except if stored for 4 months or more....

if starting the engine monthly, run it at 1200 RPM for 20-30 minutes to let it get to temp and recharge the start batt.

Agree on your assessment… but you can reduce the constant draw on the house down to 0.08A with the proper input voltage setting… or 0A if the DC-DC is switched off.

 

[...3TacksontheWater]

Waffle House came with a group 27 lead acid battery. It weighed a ton. That battery was quickly replaced by a LiFePO4 to save weight. The new battery is charged by a 35W solar panel that hangs straight down off of the starboard pushpit top rail. It is always at full charge and I’ve only once used the navigation lights and then, the deck light to secure the docking and clean up chores. I actually hung out for a few hours more with all of the lights on after my chores to drain the battery. Next time I got to the boat the battery was again fully charged. This is with a 35 W solar panel that does not face the sun directly.

Recently, I decided to swap out my 6HP Tohatsu (a great and perfectly sized engine) with a Mercury 9.9 with electric start and most importantly, with the gear shift embedded in the throttle so I never need to take my eyes off of the slip during my docking approach. Prevailing winds coupled with power boaters making their way to their launch ramp and, a possible current pushing me into the dock during windy days make docking a bit tricky. To start the new engine, I plan to use a 440 CCA AGM motorcycle battery. Between the larger engine with a starter and the AGM cranking battery, I’ve now given back my original weight savings but, the benefit of better control of forward and reverse during docking is well worth the weight penalty.

I already have two 12V quick disconnect plugs installed in the cockpit for my solar panel to charge the LiFiPO4 and all I plan to do is occasionally set the controller to AGM and then swap the connections between the ”House” LiFePO4 battery and the new AGM “Starting“ battery. Respectfully, I think we sometimes overthink things. I know I do. Depending on how much you sail, simply adding a smaller solar panel or even just switching your existing solar panel over to charging the start battery while sailing will be all that you need to do. Once you return to your mooring, swap the solar panel to return the battery to charging the house battery. I hope this helps.

George