Using both 6 x 6V Flooded Acid and New LiFePo4 in a unique way

[Captain DJ]

Like many boaters, I am drawn to solutions for power that do not require starting up the Genset. I have an older 34 Cheoy Lee Pilothouse that has an Onan 7.5kW Genset, 6- Interstate 6V deep cycle batteries, and 2-8D starting batteries (one for each FL 120). I have recently added 2- 200 Amp Hour LiFePo4 batteries and 4- 100 watt solar panels and an MPPT charge controller.

Here are some of my systems integration issues:

Alternators should NOT charge Lithium without adding an external voltage regulator with a temperature sensor and the ability to change the charging profile dedicated to the Lithium bank.

The MasterVolt- Mass Combi - Inverter Charger (12-2500) would need reprogramming to tweak the charge profile to approximately what the new lithium bank requires.

A PC and serial port would be required to alter the MasterVolt (pre-lithium) parameters.

The MPPT Solar Charge Controller (and my backup MPPT unit) both have Lithium pre-programmed profiles, so that is easy.

Temporary Solutions (for this cruising season, at least):

I believe in KISS approaches and I want to keep both banks, isolated, but switchable. Here is that plan.

Keep the six deep cycle flooded acid connected to Inverter and Alternators as they exist now, no reprogramming is required.

Keep the two Lithium connected to the MPPT charge controller and only charge via solar.

Use the flooded acid when cruising, or at shore power, then after we are on the anchor or mooring ball for say 24-48 hrs and flooded house bank gets down to say 50-60% SOC, then switch to LiFePo4 batteries for inverter functions to give us a day or three extra, pending how much sun is present at the time.

We hardly ever stay in one place for more than 3 or 5 days, so using flooded acid just after a 6-10 hr cruise and then switching to lithium as a Plan B on extended stays should work for our needs this year.

Am I missing something critical?

Have any of you tried a hybrid/two-tiered house bank approach with totally separate charge input modes?

This seems like the easiest way for me to get 2-5 days out of the systems for charging (i.e. alternators & inverter/charger for flooded and separate solar for lithium) but have never heard anyone else using both quite like this.

If finances were better, maybe new alternators with external regulators and new inverter charger with lithium profile options could allow me to simply ditch the flooded acid technology for everything except my starting bank. But sadly I am trying to get the best and longest house bank usage for the smallest investment in funds and time required to acquire and install and learn newer charge input devices.

Ideas?

Ultimately I want to get rid of the over-sized 7.5kW Genset and replace it with (already acquired on the cheap) 1 cylinder Kubota setup to run a high output 12 v alternator, to fill in the gaps on strings of cloudy/rainy days in Fall when solar in PNW will probably not keep us up, at least with only 4-100 watt panels. This could be like our Webasto furnace, rarely used, but nice to know it is there if needed. And it would be extra economical compared to the Onan.

Thanks in advance for your input.

 

[twistedtree]

A couple of thoughts….

The only issue I see with your battery management plan is that I think it exacerbates the time that your lead batteries are in a partial state of charge, and the degree of resultant sulfating. I think you would be better off using the LFP bank first, and when exhausted, switch to the lead bank. For shorter stays you wouldn’t need to drain the lead at all, and for longer stays the lead will be at a reduced SOC for less time before recharging.

On your generators, just keep in mind that recharging your batteries will take the same amount of energy regardless of which generator is being used, and both generators will consume the same amount of fuel to produce that energy. There will be slight differences based on the efficiency of the different engines, generator ends, and power conversion, but I think it will be small. There is no great magic in a small DC generator vs a large AC generator. If there were, you can be sure boats would widely use them, but they don’t. And no, it’s not because of an oil company and engine company conspiracy. It’s because of a physics conspiracy. The bastard is out to get us at every turn.

 

[Captain DJ]

Thanks, Twisted Tree,

As far as day-to-day usage I agree, the Lithium house bank should be used first and foremost.
I was not super clear because I was attempting being "concise" but with a boat named "Ramble On" it is just not in my core programming.

I have a nice battery box/step in the forward stateroom that houses the deep cycle flooded acid batteries and is 2 feet from the inverter/charger and about 3 ft to alternators. Originally I was going to do away with these 6 batteries leaving just enough space for the two new 200 amp-hour lithiums to take their place with added bus bars and fuse bar, nice and neat.

But, when considering using both banks, lithium bank and Flooded Acid bank (one at a time). Just after cruising the SOC on the Flooded Acid bank should be near 100%, at least 95%. The LiFePo4s will now be in the engine room and at 100% SOC. My real plan was to swap over to lithium after 3-4 hrs after getting good and settled in a new harbor. This will allow me to have the Flooded Acid bank deep cycles at 85-95% SOC reserved as backup, so after two or more cloudy days we can use them if we are not ready to get going again.
Giving time for engine room cooling and post cruise ER check.

I know now the way I phrased it originally was misleading of my intentions. Sorry about that.

Regarding the small displacement 1 cylinder Kubota using the exact same quantity of fuel as the 7.5kW Onan is bewildering me. I think the same diesel to kW or watt hour or amperes hours conversions are the same either way. I can get my head around that. But, and I am not arguing, just pondering:

Doesn't a larger and older Genset, grossly underloaded, making 120 volt to convert via charger (15-20% loss in conversion from 120v AC to 12 V DC) simply use a lot more fuel than a tiny 1 cylinder that is doing about 85% of it's continuous duty rating to JUST generate 12 V DC.

It is like using a Smartcar to transport two skinny people around town instead of a Hummer pulling a trailer, no? Both vehicles are transporting the same weight of passengers across the exact same terrain, yet one is "just big enough" and is designed specifically for such a task, while the other can do THAT task, plus oh so much more.

Hard to get my head around it. Thanks for your insights.

 

[twistedtree]

Thanks, Twisted Tree,

As far as day-to-day usage I agree, the Lithium house bank should be used first and foremost.
I was not super clear because I was attempting being "concise" but with a boat named "Ramble On" it is just not in my core programming.

I have a nice battery box/step in the forward stateroom that houses the deep cycle flooded acid batteries and is 2 feet from the inverter/charger and about 3 ft to alternators. Originally I was going to do away with these 6 batteries leaving just enough space for the two new 200 amp-hour lithiums to take their place with added bus bars and fuse bar, nice and neat.

But, when considering using both banks, lithium bank and Flooded Acid bank (one at a time). Just after cruising the SOC on the Flooded Acid bank should be near 100%, at least 95%. The LiFePo4s will now be in the engine room and at 100% SOC. My real plan was to swap over to lithium after 3-4 hrs after getting good and settled in a new harbor. This will allow me to have the Flooded Acid bank deep cycles at 85-95% SOC reserved as backup, so after two or more cloudy days we can use them if we are not ready to get going again.
Giving time for engine room cooling and post cruise ER check.

I know now the way I phrased it originally was misleading of my intentions. Sorry about that.

Regarding the small displacement 1 cylinder Kubota using the exact same quantity of fuel as the 7.5kW Onan is bewildering me. I think the same diesel to kW or watt hour or amperes hours conversions are the same either way. I can get my head around that. But, and I am not arguing, just pondering:

Doesn't a larger and older Genset, grossly underloaded, making 120 volt to convert via charger (15-20% loss in conversion from 120v AC to 12 V DC) simply use a lot more fuel than a tiny 1 cylinder that is doing about 85% of it's continuous duty rating to JUST generate 12 V DC.

It is like using a Smartcar to transport two skinny people around town instead of a Hummer pulling a trailer, no? Both vehicles are transporting the same weight of passengers across the exact same terrain, yet one is "just big enough" and is designed specifically for such a task, while the other can do THAT task, plus oh so much more.

Hard to get my head around it. Thanks for your insights.

My guess is that you would see at most a 10% difference.

As a first measure, a diesel consumes fuel proportional to the load. It is not proportional to the size or capacity of the engine. Now engine size does come into play, especially if very much larger or very much smaller. But it’s a second order factor. Also, larger diesels tend to be more efficient than smaller ones, assuming they are loaded at a reasonable level.

A car is different because the work is all in accelerating and moving the vehicle around. The passengers are a small side effect because their weight is a relatively small portion of the overall weight.

Also, a gas engine’s fuel consumption is much less proportional to load. So there is benefit to using a smaller engine. That’s primarily why the same car with a smaller engine will get better mileage than one with a larger engine. But diesels aren’t like that, or at least a lot less so.

 

[Bacchus]

Captain DJ
"If finances were better, maybe new alternators with external regulators and new inverter charger with lithium profile options could allow me to simply ditch the flooded acid technology for everything except my starting bank. But sadly I am trying to get the best and longest house bank usage for the smallest investment in funds and time required to acquire and install and learn newer charge input devices. "

Have you looked at whether your existing alts can be modified for external regulators? If possible that may be a lot more economical.

 

[Marco Flamingo]

No comment on the generator use as I already yanked mine out and can now skip over that part of any post.

I am assuming that you're switching from LA to Lith is not by way of a 1-2-both switch. The "both" could be a problem even for a few moments.

I have been looking at various combination issues as well. I now have a Lith battery that is dedicated to induction stovetop use and was looking at various ways to keep it charged. One was by way of a DC to DC charger that has a Lith specific charging profile. The most common use for the DC/DC charger has the "start" battery charged sufficient such that the "house" battery begins to charge. I actually think the opposite would work for me. My "start" battery is plenty big for +20 starts (and has it's own monitor). My Lith "stove" battery is the one that might cut my time at anchorage short.

 

[Captain DJ]

Thanks Don,
I am looking into adding external voltage regulators and temperature sensors to my Delco Alternators. Thinking of doing what I did on my Grand Banks 42 Classic, set one to the charging needs/parameters of the start bank and the other for the house bank. In this scenario I would likely have to not only switch battery source inputs before the inverter but post the house bank alternator. This would allow me to either A: set if for Lithium or B: set if for the 6V flooded in series and parallel. This or a DC to DC transfer charger would allow me to just send the alternator on Starboard to a Lithium Profile and let that bank charge the flooded reserve bank via DC to DC charger. Thus keeping the Port alternator always set to attend the needs of 8 D flooded Starting Bank.

 

[Captain DJ]

Thanks Marco,

I did think of that.
"I am assuming that you're switching from LA to Lith is not by way of a 1-2-both switch. The "both" could be a problem even for a few moments."

I made sure it was optioned 1 or 2, NEVER Both. or OFF.
It took looking at a lot of switches to find the Blue Seas one for 1 or 2 or OFF (without both).

I think this DC to DC charger might work best
https://www.amazon.com/Victron-Ener...id=1661019432&sprefix=dc+to+dc,aps,755&sr=8-4

Good recommendation, Thanks

I just mentioned the DC to DC charger as part of my solution when Don made the astute observation/recommendation of changing at least one of my alternators to have an external regulator and temperature control sensor.

Your link : DC to DC charger that has a Lith specific charging profile.
was both helpful and affordable.