Battery chemistry choice for the non-lithium battery in the system.

[GILow]

I’m sure this has been asked already, but I’m having trouble finding the discussion. If someone can point me in the right direction I’d be grateful.

But on the off-chance it hasn’t been discussed, here goes:

The new boat (44 foot mono) has a 24 volt, 304 AH LiFePO4 main battery bank. This bank powers just a pair of 240V inverters for the all electric galley. It also receives charge from the 900W of solar. (The solar may be increased later if needed, but I’m hopeful that 900 W will do.)

The rest of the boat runs on 12 volts and my intention is to have a single 12v battery that powers everything including the engine. This battery will be charged by a pair of Victron Orion 70 amp chargers, from the 24 volt bank.

My logic for this setup comes from a few thoughts over time, the key concern being that I don’t want a BMS failure to leave us in the dark at a critical moment. With this setup I can immediately start the engine if the BMS fails and get somewhere I can fix the problem. I can also swing the solar across to the 12 v battery easily enough if power is needed for a longer time.

So, with this in mind, I’m thinking “what sort of 12 v battery?” The main loads for the battery in this situation would be starting the engine and powering the windlass. The house loads are otherwise trivial. The battery itself can live in a perfect battery world, maintaining 100 % charge at all times thanks to the big 24 volt bank. This seems to suggest an AGM? But is there something better?

Thoughts?

Matt

[Wotname]

Originally Posted by GILow

I’m sure this has been asked already, but I’m having trouble finding the discussion. If someone can point me in the right direction I’d be grateful.

But on the off-chance it hasn’t been discussed, here goes:

The new boat (44 foot mono) has a 24 volt, 304 AH LiFePO4 main battery bank. This bank powers just a pair of 240V inverters for the all electric galley. It also receives charge from the 900W of solar. (The solar may be increased later if needed, but I’m hopeful that 900 W will do.)

The rest of the boat runs on 12 volts and my intention is to have a single 12v battery that powers everything including the engine. This battery will be charged by a pair of Victron Orion 70 amp chargers, from the 24 volt bank.

My logic for this setup comes from a few thoughts over time, the key concern being that I don’t want a BMS failure to leave us in the dark at a critical moment. With this setup I can immediately start the engine if the BMS fails and get somewhere I can fix the problem. I can also swing the solar across to the 12 v battery easily enough if power is needed for a longer time.

So, with this in mind, I’m thinking “what sort of 12 v battery?” The main loads for the battery in this situation would be starting the engine and powering the windlass. The house loads are otherwise trivial. The battery itself can live in a perfect battery world, maintaining 100 % charge at all times thanks to the big 24 volt bank. This seems to suggest an AGM? But is there something better?

Thoughts?

Matt

If I am understand the question correctly, you only need a 12V battery with enough CCA to start the engine but don't need anything big in the capacity etc. All the day to day 12V loads will be provided from the 24V, 304 AH LiFePO4 main battery bank by the pair of Victron Orion 70 chargers which should be big enough to drive the 12V windlass especially as there is presumably no engine fitted alternator in the system.

Seems like an AGM is overkill as any sort maintenance free LA with a decent CCA will do the job but nothing wrong with going to an AGM, just a few more $.

I like the concept!

[Wotname]

Of course, once the 24V battery fails (BMS etc), you will have SFA (capacity wise) available 12V boat system. So the engine alternator will be needed to power the boat when there is no sun.

Doesn't change the 12V chemistry question though!

[GILow]

Yes, the capacity of the 12 volt battery, in theory, only needs to be pretty small. But then, if the litihium bank becomes unavailable a bit of storage capacity in the 12 volt system will be nice to have.

As for the thinking around the AGM, I was thinking that would be the lowest maintenance option? Also I’m wanting to get a fair bit of current out of what is a small battery, such as for the windlass. I feel like FLA will fail both the low maintenance and high current demands.

Matt

[CarlF]

AGM's are the obvious choice since the AGM's biggest drawback - partial state of charge sulfation (PSOC) won't be a concern since they will always be at 100% charge.

AGM's also can't spill acid so don't have to be in a leakproof case.

[Wotname]

Originally Posted by GILow

.........
As for the thinking around the AGM, I was thinking that would be the lowest maintenance option? Also I’m wanting to get a fair bit of current out of what is a small battery, such as for the windlass. I feel like FLA will fail both the low maintenance and high current demands.

Matt

Agree that FLA will fail the low maintenance / current demands. That leaves a maintenance free (semi-sealed) LA battery or a AGM.

The windlass should not be an issue, if you are using a pair of Victron Orion 70 amp chargers. It is unlikely the windlass would demand 140A continuous and any intermittent high current will be less than the CCA of start battery anyhow.

The only significant load requirement for the 12V battery will be the starter motor so the battery needs to be sized for the engine's CCA requirement. Capacity is largely a non issue but cranking amps will be the number to look at.

A maintenance free (semi-sealed LA) start battery will be cheaper than a AGM but the lower self discharge of an AGM might be important (occasionally).

Your proposed setup is very little different to that of a RV or a power boat.

[SOLAR SUPPORT]

Originally Posted by GILow

I’m sure this has been asked already, but I’m having trouble finding the discussion. If someone can point me in the right direction I’d be grateful.

But on the off-chance it hasn’t been discussed, here goes:

The new boat (44 foot mono) has a 24 volt, 304 AH LiFePO4 main battery bank. This bank powers just a pair of 240V inverters for the all electric galley. It also receives charge from the 900W of solar. (The solar may be increased later if needed, but I’m hopeful that 900 W will do.)

The rest of the boat runs on 12 volts and my intention is to have a single 12v battery that powers everything including the engine. This battery will be charged by a pair of Victron Orion 70 amp chargers, from the 24 volt bank.

My logic for this setup comes from a few thoughts over time, the key concern being that I don’t want a BMS failure to leave us in the dark at a critical moment. With this setup I can immediately start the engine if the BMS fails and get somewhere I can fix the problem. I can also swing the solar across to the 12 v battery easily enough if power is needed for a longer time.

So, with this in mind, I’m thinking “what sort of 12 v battery?” The main loads for the battery in this situation would be starting the engine and powering the windlass. The house loads are otherwise trivial. The battery itself can live in a perfect battery world, maintaining 100 % charge at all times thanks to the big 24 volt bank. This seems to suggest an AGM? But is there something better?

Thoughts?

Matt

The energy of the 304Ah@24V, 7.2KWh LFP bank can meet your daily energy consumption depending on the use of kitchen stoves and other 220V consuming devices, depending on the number of people living on the boat. If there is no deficiency here, I think you can leave the 24V system as it is. If you have excess energy in the 24 V LFP bank, you may consider transferring it to 12V batteries. Solar energy capacity also seems sufficient. It is more logical to consider adding a separate 12V bank that can start the windlass, bow thruster? and the engine when necessary. The engine and windlass can work with the existing LA battery bank, but you want to support them with another small capacity battery bank to avoid problems in case the LA batteries are discharged. Considering removing your LA battery completely? Small capacities are possible with LTO battery solutions. It is possible to operate all 12V systems that require high current with LTO and charge them using an alternator. Since BMS is not used with LTO, there are no HVC and LTC risks. You only need to protect your alternator against overcharging current with a modest DCDC device. You can solve the cell balance of LTO by using active balancer with 5A capacity.

[GILow]

Originally Posted by CarlF

AGM's are the obvious choice since the AGM's biggest drawback - partial state of charge sulfation (PSOC) won't be a concern since they will always be at 100% charge.

AGM's also can't spill acid so don't have to be in a leakproof case.

Yes, this pretty much summarises my thinking so far. But still wondering if there’s another chemistry to consider or some downside (aside from coast, as Wottie notes) I should be aware of.

[GILow]

Originally Posted by Wotname

Agree that FLA will fail the low maintenance / current demands. That leaves a maintenance free (semi-sealed) LA battery or a AGM.

The windlass should not be an issue, if you are using a pair of Victron Orion 70 amp chargers. It is unlikely the windlass would demand 140A continuous and any intermittent high current will be less than the CCA of start battery anyhow.

The only significant load requirement for the 12V battery will be the starter motor so the battery needs to be sized for the engine's CCA requirement. Capacity is largely a non issue but cranking amps will be the number to look at.

A maintenance free (semi-sealed LA) start battery will be cheaper than a AGM but the lower self discharge of an AGM might be important (occasionally).

Your proposed setup is very little different to that of a RV or a power boat.

Remember, if the BMS on the lithium bank dies I will lose the boost from the Orions. Hence I’m thinking I need something that can handle a lot of current. Most single FLAs I’ve met have struggled with sustained windlass loads. (Part of my early and somewhat painful learning about boat electrics.)

[Wotname]

Originally Posted by GILow

Remember, if the BMS on the lithium bank dies I will lose the boost from the Orions. Hence I’m thinking I need something that can handle a lot of current. Most single FLAs I’ve met have struggled with sustained windlass loads. (Part of my early and somewhat painful learning about boat electrics.)

I think you might be confusing deep cycle technology with high current (high CCA) start technology. What size is the proposed alternator? It should provide the lion's share of the windlass requirements.

Traditionally the issue with start battery technology is small AH and low cycles. As far as I understand your proposed set up, neither of these issues are a concern. All you want is enough CCA to start the engine; at which point, the alternator is supplying the 12V loads (including the windlass).

However if you want a high current, reasonable capacity and good cycling, then the Optima Yellow Top Spiral AGM (D31) is the way to go. 900CCA & 75AH.

The only difference between the D31A (auto) and D31M (marine) is the colour (yellow v blue) and the terminals lugs (the blue marine one has lugs and bolts).

The Optima D31 is suggested for thrusters.

[CaptainRivet]

Originally Posted by SOLAR SUPPORT

The energy of the 304Ah@24V, 7.2KWh LFP bank can meet your daily energy consumption depending on the use of kitchen stoves and other 220V consuming devices,u depending on the number of people living on the boat. If there is no deficiency here, I think you can leave the 24V system as it is. If you have excess energy in the 24 V LFP bank, you may consider transferring it to 12V batteries. Solar energy capacity also seems sufficient. It is more logical to consider adding a separate 12V bank that can start the windlass, bow thruster? and the engine when necessary. The engine and windlass can work with the existing LA battery bank, but you want to support them with another small capacity battery bank to avoid problems in case the LA batteries are discharged. Considering removing your LA battery completely? Small capacities are possible with LTO battery solutions. It is possible to operate all 12V systems that require high current with LTO and charge them using an alternator. Since BMS is not used with LTO, there are no HVC and LTC risks. You only need to protect your alternator against overcharging current with a modest DCDC device. You can solve the cell balance of LTO by using active balancer with 5A capacity.

2nd vote for LTO Yinglong cells, perfect chemistry for your use case and exactly my plan to when switch 2x12V 3000W multi to 2x 24/3500 Studer XTM and reconfigure the 4P4s LFP 1088AH/12V to 2p8S 24V/544AH. Rest of cat is 12V.

only starter 1p6S in 30A would be ok, you wanna use it additionally as backup battery 2x1p6S with 30 or 40AH LTO cells would be the way to go. So in worst case you reconfigure the LTO to 1p11S for 24V and can even run your inverters.
Use one or 2 Victron 24/12 DC2DC converters (no need for expensive charger) with remote and a Victron BMV 712 battery monitor for LTO that cuts the converter with its relay output when LTO reaches 14,4V. Advantage if you eg in emergency take the LTO as LFP replacement in 1p11S the 12V equipment can still run of the 24/12 converter which I assume you already have anyhow. Or how does the 12V equipment runs of the 24V bank?

[GILow]

Originally Posted by Wotname

I think you might be confusing deep cycle technology with high current (high CCA) start technology. What size is the proposed alternator? It should provide the lion's share of the windlass requirements.

Traditionally the issue with start battery technology is small AH and low cycles. As far as I understand your proposed set up, neither of these issues are a concern. All you want is enough CCA to start the engine; at which point, the alternator is supplying the 12V loads (including the windlass).

However if you want a high current, reasonable capacity and good cycling, then the Optima Yellow Top Spiral AGM (D31) is the way to go. 900CCA & 75AH.

The only difference between the D31A (auto) and D31M (marine) is the colour (yellow v blue) and the terminals lugs (the blue marine one has lugs and bolts).

The Optima D31 is suggested for thrusters.

I’ll check out the Optimas, thank you.

Alternator is supposedly 120 amp, but since it has a single V belt I’m taking that number with enough salt to make a heart surgeon gibber.

Ideally the battery would be able to run the windlass without the engine. Another level of fallback. Probably unnecessary, but hey, a fella can dream.

[GILow]

As for the LTO cells… no thanks. Another BMS based system is not what I am looking for. I want something a bit more robust for the 12 volt battery.

[s/v Jedi]

Originally Posted by GILow

As for the LTO cells… no thanks. Another BMS based system is not what I am looking for. I want something a bit more robust for the 12 volt battery.

Are Odyssey TPPL AGM batteries available where you are? It’s what I have.

Also, the 70A Orion isn’t a smart unit, i.e. not a charger, just a power supply. I am using two 30A smart Orion’s in parallel.

[Wotname]

Originally Posted by GILow

I’ll check out the Optimas, thank you.
......

All else being equal, the lead purity and the mass of lead determine number of cycles and the capacity.

The market leaders are (IMHO) Optima Spiral (yellow/blue top) and Odyssey Extreme with perhaps Lifeline on the podium.

Both Optima and Odyssey claim to have the purist lead so it's a fair bet they are close to equal first on that score.

Odyssey weight much more than the Optima for the same cubic footprint so they certainly have more capacity that the Optima. This is due to the 'wasted' space of the circular (spiral) design of the Optima. If you compare apples with apples as far as number of AH used per cycle, then Odyssey will last longer simply because each cycle is a smaller DOD. But naturally they cost more 'cause they have more lead.

For a given space (cubic footprint), the Odyssey gives the most bang (CCA/Capacity) with the Optima in second place.

For a given dollar per bang, they are even stevens.

For best bang per buck, something like an Aussie/NZ Century AGM will be in front. Certainly not as good as the podium finishers (re CCA/capacity/number of cycles) but way cheaper (due to lower quality and less mass of lead).