Exploring Lithium batteries

The batteries in Changabang predate my ownership. At best, they must date from before the RdR 2018, probably 6 months before that. In other words, they are at least 6 years old. That’s pushing it for what they are I think:

• House batteries: three 105 Amps flooded sealed lead acid batteries.
• Starting battery: I don’t know for sure, but likely 70 Amps, which is what the old manual for the Volvo Penta D1-30 required 20 years ago. I think the chemistry is Calcium. I’d need to remove it to confirm.

The engine starts just fine on the battery, with no sputtering. I can’t find a similar battery for sale so I’m not sure what this is TBH. It also means that I have no idea if these require some sort of maintenance. That said, there are plenty of choices to replace it.

The battery monitoring system in place is not working correctly though so I am not sure how much capacity is left in the house bank. They have been used offshore for at least 2 months. It’s hard to say how much is left in them.

All the above to say that replacing the batteries has been on my mind. And that means that there may be an opportunity to change chemistry and explore LiFePO4 batteries. And this got me in a few rabbit holes, soul searching. Hence this post to help me organize my thoughts!

Before I dig in further, I’ll lead with a few words about charging capabilities on CaB.

Charge!

On CaB we have the following sources of electricity:

• The 115 Amps alternator: a Mitsubishi a3tr0093am. This requires the engine to run, which requires fuel. This charges both starting and house banks.
• The shore power charger: a Cristec CPS3 12 V / 25 A. This requires … shore power! This charges both starting and house banks.
• The Watt & Sea Cruising 300 hydrogenerators and their converters, which are only connected to the house batteries. This requires that the boat moves. At 5 kts we can get 9 Amps with the big prop. And when we move very slowly, the boat may be mostly flat and we may be able to get both working together to help in those situations.
• A bunch of 100 W or so solar panels and a Victron BlueSolar charge controller MPPT 75 | 15, which is only connected to the house batteries. This requires … sun!

Use cases

Ok, so the first thing is to figure out what my use cases are for batteries.

Of course, there’s the engine starter battery. But there’s more to this because this battery may die, hence the house battery must be able to at least a few times start the engine. And, similarly, the house battery may die and the starter battery must be able to step in to drive all the boat’s systems.

Next is to define how I would use the house bank. This bank drives everything on the boat except the engine starter, so let’s clarify how I plan to use the boat:

1. The boat is just sitting in port most of the time.
2. I’m doing afternoon sails.
3. I’m going offshore for an offshore race.
4. I’m going offshore for a RTW attempt.

Sitting in port

All that matters here is that the batteries are kept charged up and not left to discharge for a long time. “A long time” means different things for different chemistry. For lead acid, if I was not to do anything with the boat for more than 6 weeks, I would want a charger to keep them floating or top them up regularly (which is what I do now with the shore power charger). For LiFePO4 my understanding is that the discharge rate is so low that it doesn’t matter (it is recommended to charge them before storing them for a long period, e.g. 3+ months). If we combine chemistries then we are facing two different charging profiles.

Afternoon sails

The starting battery is used twice (to leave the dock and return), maybe a few more times. I’m motoring likely 30 minutes in total, maybe more. The hope there is that the 115 Amps alternator will run enough to top up the starting battery.

Then we sail for something like 4-8 hours, drawing something like 5 Amps from the battery (a good guess), for a total of 40 Amps. Let’s round that up to 50 Amps, which is about 15% of the battery bank. Again the alternator will feed some back in but what I am also doing every so often is plugging the batteries on the shore charger to top them back up.

The bottom line is that these events do not require charging while at sea and the batteries can be topped up in port. If anything fails then it’s not a big deal because we can get back in port safely, even if that means finding a downwind slip/side-tie to sail in, should we not be able to start the engine. Worst case: one could call a tow boat.

Offshore race

Here we need to consider the return trip as well. Sailing to Hawaii is about 1.5 weeks and sailing back is about 2.5 weeks. The key assumption is how we can approach redundancy. In other words, I feel like we only need one backup plan, not 3 or 4 as would be needed when sailing non-stop RTW.

In a race, the engine should not be used, except on an exception basis:

1. An MOB recovery or anything else that requires the engine.
2. All charging options fail and that leaves us with the engine to charge the house batteries. In fact, the backup charging plan is probably the engine (and a solar panel maybe).

Also, we should be in movement all the time, so the hydrogenerators can be used to top up the batteries.

RTW

Here we do want multiple solutions to charge the batteries and we need multiple solutions should the starting bank or the house bank fail. This is a more serious conversation but one that can easily be solved with a spare house battery, a spare starting battery (or a jump starter), and three charging solutions already onboard (engine, solar, HG). So I won’t consider this use case too much for now.

LiFePO4 issues

Considering an upgrade to LiFePO4 here are the issues I see:

• Considering cost it’s best to not use a LiFePO4 battery for the starting bank. This means that we will have two different battery chemistries, each with its own charging profile. This in turn likely means that charging devices can only be allocated to one type of battery, not both as some are currently. This needs to be explored to confirm that’s possible without too much change to the electrical system on CaB.
• To address the need for a backup to the starting bank to start the engine, a house bank must be able to start the engine several times without suffering serious damage that would affect its ability to serve as a house bank. Many LiFePO4 manufacturers explicitly state to not use their battery to start engines. Some support starting gasoline engines. An alternative solution to explore is a jump starter.
• Charging from the alternator is a problem with LiFePO4, as the alternator can suffer serious damage under certain circumstances.

A proposed solution

Here’s a proposal that I think would work:

• Keep the starting battery.
• Find a solution to connect the alternator and the shore power charger to only the starting battery. This may not be as easy as it seems as I think that everything is going to be a bus bar today.
• Replace the three house batteries with one LiFePO4 battery of 100 Ah or more, with an integrated BlueTooth BMS.

And here’s how things would go for each use case above:

1. In port and afternoon sails: as I do now, keep the starting battery topped up by using the shore power every so often. Use a solar panel to slowly charge up the LiFePO4 battery when not in use. Alternatively, use a simple charger to top up the battery while putting the boat away or preparing it before leaving.
2. Offshore racing: as I do now, use the hydrogenerators to charge the house battery. Every week, start the engine and charge the starting battery using the alternator. If the starting battery fails then have a jump starter to start the engine. If the house battery fails then swap in the starting battery. For this reason, it may be best to replace the current one with a larger dual-purpose one, assuming it can be fitted in the small space.
3. RTW sailing: same as above but replacing the 100 Ah battery with a larger one and with the addition of a spare LiFePO4 battery and a spare starting battery (in addition to the jump starter).

The weaknesses in the above are:

1. I don’t have a battery monitor on the starting battery. This could be partially solved with a voltmeter indicator.
2. I can’t use the alternator to charge the LiFePO4 battery (well I could but then I could run into problems). This can be partially solved with a DC-DC charger in between the starting battery and the LiFePO4 battery.
3. There’s only one house battery and if it shuts down for some reason (BMS intervention for example) then the boat would be without electricity. An option could be to use multiple LiFePO4 batteries.

Budget

Essentially the bare minimum approach here only requires purchasing a LiFePO4 battery. The prices vary wildly; with budget ones in the $250 range (LiTime), mid-range in the $400 range (SOK marine grade 100 Ah), and premium going all the way beyond $1000. Improvements include a diesel engine jump starter ($100?), a DC-DC charger ($300), and an additional LiFePO4 battery.

What’s next?

Validate the current wiring and see what’s possible. My guess is that there is a bus bar for charging to which both systems are connected. If that is then it would be a matter of creating a separate bus bar to charge the house bank. The alternator and shore charger would remain in place. The hydrogenerators and solar panels would go to the new bus bar. And possibly a DC-DC charger would be setup in between both bus bars.