Realistic non-bs comparison of lithium to lead

[john61ct]

LFP is 4x the energy density of lead.

Depending on location, between 3 and 10x the price of quality lead deep cycling.

If your target hull design is OK with carrying 3000lbs of bank rather than 750lbs, then maybe you can save the added cost?

With most mainstream designs you really don't have a choice.

If the EP option will work at all for your limited use case.

[KTP]

Originally Posted by john61ct

LFP is 4x the energy density of lead.

Depending on location, between 3 and 10x the price of quality lead deep cycling.

If your target hull design is OK with carrying 3000lbs of bank rather than 750lbs, then maybe you can save the added cost?

With most mainstream designs you really don't have a choice.

If the EP option will work at all for your limited use case.

I am not quite getting the 4x energy density figure but could be overlooking some things.

LFP was about 110 wh/kg IIRC while lead acid is 40wh/kg, so around 3x, although getting 80% out of a lead acid bank will lead to a short life of a few hundred cycles at best while 80% from a LFP could lead to 2000+ cyles (not sure yet if I believe the 7000 cycle life and no annual degradation)

The Torqeedo stuff though (the new stuff) I think is LFP based (BMW I3 batteries) and is 150wh/kg, which is right at your figure of 4x the energy density of lead acid.

A system with eight of those Torqeedo batteries would have 40kwh available and fit within the weight capacity of of the previous diesel engine and fuel tank. Just a bit expensive right now.

[valhalla360]

Originally Posted by KTP

Well obviously we are going to install the system ourselves (I am a EE). I do get what you are saying, that I could rebuild the diesel myself and know everything was done correctly.

I am not interested in rebuilding diesel engines though. I like tinkering with electrics.

As for getting off a lee shore in a storm, how about either not getting into that situation by being aware of the weather or knowing how to use the sails to get you to a better safer place?

Even with your experience, if we are talking reliability...I would put my money on the rebuilt diesel over you "tinkering" with a one off system.

But if you are doing it because you enjoy tinkering, that's a different ball game. I've "tinkered" building a homemade dingy. It's not as good as a production dingy and when you factor in my labor, probably wasn't making $2hr in savings but it was a fun project. That I totally get.

But if you compare apples to apples, your comment about not trusting a professionally rebuilt engine is just silly hyperbole.

[john61ct]

Originally Posted by KTP

I am not quite getting the 4x energy density figure but could be overlooking some things.

LFP was about 110 wh/kg IIRC while lead acid is 40wh/kg, so around 3x, although getting 80% out of a lead acid bank will lead to a short life of a few hundred cycles at best while 80% from a LFP could lead to 2000+ cyles (not sure yet if I believe the 7000 cycle life and no annual degradation)

The Torqeedo stuff though (the new stuff) I think is LFP based (BMW I3 batteries) and is 150wh/kg, which is right at your figure of 4x the energy density of lead acid.

A system with eight of those Torqeedo batteries would have 40kwh available and fit within the weight capacity of of the previous diesel engine and fuel tank. Just a bit expensive right now.

Getting higher than mfg rated lifetimes from LFP depends on not following their high voltage recommendations, and everything else going right over decades.

BMW i3 use lithium-manganese (LMO) chemistry, apparently blended with NMC, both distant relations to LFP, different voltages and care requirements, higher energy density but a small fraction of lifetime cycles.

If an EP marine vendor provides the pack bundled with BMS and cooling protective systems, fine but check with your insurance. I would not DIY adapt one to using for a House bank, and definitely not for much higher-stress EP, only if professionally designed and installed by the vendor trained techs. Boom bad.

And yes my 4x density ballparking was including the higher usable capacity, but not BMS or other bundled gear.

[Mike Banks]

The one option not mentioned so far--and not even part of the comparison, are alkaline cells. They last many years, are lighter than lead (but larger), can be left flat without sulphating and have a good current draw with low internal resistance.

They are more expensive at the outset--but many remote installations use them as long as it is not really freezing cold.

They really are a viable alternative as long as one can find the room for them--and they are nickel cadmium as a rule, but even the older nickel-iron batteries would work.

I have only ever used flooded cell lead-acid batteries on board, my experience with NiFe and NiCad batteries came from telecommunications. Many mining applications also use them.

Deep cycle lead acid batteries, as well as starting batteries, are extremely heavy and need to be regularly serviced, and because of their massive weight need to be placed appropriately in the hull and usually on or below water line. However, if properly looked after in their own battery locker with easy access, and proper full but not excessive charging, they can last for a few years, even ten or more.

[john61ct]

Sorry but this "alkaline" idea for a big House bank.

Please provide links to what sort of cells you are suggesting are suitable for building a nominal 12V bank between say 300-800AH.

Ideally including pricing, and info / specs about cycle lifetimes vs avg DoD discharge.

I think in X00,000 threads across dozens of forums we'd have come across them before if the were practical for this use case.

[CatNewBee]

buy a Lagoon 420 with electric propulsion, change the LA batteries to LFP and off you go, there is also a 11kW Onan genny on board, when the battery dies. Most of them were unfortunately reverse converted to diesel engines.

[john61ct]

Not unfortunately, but in order to be practical, in most cases out of necessity.

Fine if you're cruising with no schedule, but that's a tiny niche market.