Hybrid Battery Bank Idea

[hzcruiser]

Originally Posted by john61ct

Ideal IMO is one big Main bank plus a smaller Reserve for mission-critical backup.

To me there is no real reason to treat batteries in banks, I mentioned them because they are physically in the same location: one VRLA in the foc'sle for the windlass, three in the bilge, one in the wheelhouse and the LFPs are in the salon under the settee next to the starter batts and 2000W inverter.

The long-term goal is to have a system that tells the skipper which batt is the least efficient in terms of Ah in vs Ah out. Together with the batt capacity it's then an easy decision which one to replace first. I don't want to replace the whole lot in one hit but rather phase them out whenever I can get an attractive (as in price and preformance) replacement. It's also easier on the budget.

Originally Posted by john61ct

Which is LFP vs lead for purpose of this topic is as per owner's budget and preference.

Well said.

[hzcruiser]

Originally Posted by valhalla360

If lithium prices come down like some claim (I'm a bit skeptical but hey...) this is at best an interim solution. Once lithium are cost competitive, there is pretty much nothing to gain from lead acid and a change to full lithium will make more sense.

Someone on this forum crunched some numbers and showed that LFPs are more expensive to buy but significantly cheaper in the long run given their usable capacity and number of cycles. (Link anyone?)

And given that my back is not getting much better in the forseeable future I'd vote for the much lighter LFPs. For testing, I bought four 140Ah cells and they were like child's play to get onto the boat and installed. Eventually I need to get rid of the old 70Ah Marathon VRLAs... not looking forward to that as they are 30kg (65lb) each.

[valhalla360]

Originally Posted by hzcruiser

Someone on this forum crunched some numbers and showed that LFPs are more expensive to buy but significantly cheaper in the long run given their usable capacity and number of cycles. (Link anyone?)

And given that my back is not getting much better in the forseeable future I'd vote for the much lighter LFPs. For testing, I bought four 140Ah cells and they were like child's play to get onto the boat and installed. Eventually I need to get rid of the old 70Ah Marathon VRLAs... not looking forward to that as they are 30kg (65lb) each.

This is a side issue.

If you believe lithium is cheaper, it makes more sense to go pure lithium.
If you believe lead acid is cheaper, it makes more sense to go pure lead acid.

I just can't see a situation where it makes cost and/or complexity advantage to do a hybrid system.

[john61ct]

Originally Posted by hzcruiser

To me there is no real reason to treat batteries in banks

Well there is, and it is very real. Batteries kept separate will have much lower total capacity, efficiency and longevity, plus total higher costs than combined into one bank. The more batteries, the more pronounced the difference.

If you properly design the system and care for a quality bank it should last well over a decade. Yes higher cost at one time but overall much lower cost per year.

And certainly much lower care & attention, greater reliability than what your talking about.

If that is not compelling for you then your boat so be it, but at least be fully informed in making the decision.

[john61ct]

Originally Posted by hellosailor

And by the time you've engineered in a way to prevent loads from eating at the Li battery while it is connected to charge the Pb bank

Why would it be a problem for the LFP bank to carry other loads while topping off the lead?

[Dockhead]

Originally Posted by valhalla360

This is a side issue.

If you believe lithium is cheaper, it makes more sense to go pure lithium.
If you believe lead acid is cheaper, it makes more sense to go pure lead acid.

I just can't see a situation where it makes cost and/or complexity advantage to do a hybrid system.

Well, it's an objective question which will have an objective answer. Which I don't know

I don't know if lithium can be cheaper for anyone, but if it is, it will be first cheaper for those who are truly off grid and not running generators much and using a lot of power.

Lead acid is definitely cheaper for someone like me with my present pattern of cruising, where I don't discharge them deeply all that often, and don't have a problem giving them a finishing charge at least once or twice a week.

I can imagine that a hybrid bank could be cheaper and better for someone in between. It will greatly increase the efficiency and extent the life of a lead acid bank for the price of a small LiFePo battery and control system.

I also really like the idea someone above had of using the LiFePo battery to replace a thruster or windlass bank. If you have a separate bank for this anyway, then the whole proposition looks very different. Then all you need is the B2B charger.

[seandepagnier]

Originally Posted by john61ct

Peukert means the lowest number of banks will be most efficient, greatest total capacity.

This "law" doesn't apply to lithium, and more capacity means more self-discharge. Depending on battery type, there is actually an optimal capacity for efficiency where more or less capacity is worse for a specific use.

An intelligent battery controller could combine many batteries of different types to yield the full capacity at the best possible efficiency and life span.

This would be very useful even for pure lithium batteries, as the cells are individually monitored and can be individually replaced.

[john61ct]

Originally Posted by boat_alexandra

This "law" doesn't apply to lithium.

I don't think he was talking about a boat with LFP only. It is a very important consideration for lead.

Originally Posted by boat_alexandra

An intelligent battery controller could combine many batteries of different types to yield the full capacity at the best possible efficiency and life span.

Since it is a hypothetical device, of course it "could".

If it ever becomes real, we'll find out if any benefits are worth the added cost and complexity.

Originally Posted by boat_alexandra

This would be very useful even for pure lithium batteries, as the cells are individually monitored and can be individually replaced

LFP BMS (are supposed to) do this now.

Many LFP users are skeptical that they add value over their cost and complexity for House bank usage.

In any case all this has nothing to do with the main concept that is this threads' topic.

[TheThunderbird]

I love DH idea:-)

My genny charges 10A 220V bulk, then 8-5A Absorption,and 4-3...A..,2A floating:-)


I stop it at 3-4A:-)
If I could have then a Li B to charge...:-) I could reach a 99% SOC

I will consider practical implementation (B disconnection, and?)

My chargers have 3 output lines, lower V seen, is chosen... manual operations needed?

[valhalla360]

Originally Posted by Dockhead

Well, it's an objective question which will have an objective answer. Which I don't know

I can imagine that a hybrid bank could be cheaper and better for someone in between. It will greatly increase the efficiency and extent the life of a lead acid bank for the price of a small LiFePo battery and control system.

I don't question that it's a valid question but when doing a quick look at the numbers, I think it doesn't hold up.

Can you share the numbers on the situation where it would be more efficient than simply adding a few more amp-hrs of standard lead acid? (let's ignore a pure lithium for the moment as it's a separate question).

If you read my example, adding 200ah to a 1000ah bank would negate most of the issues without the complications of a hybrid system.

Given the common situation of having a solar array (or wind generator) to do the top up (even at high latitudes). Just do the bulk charging in the mornings and let the solar finish it at a slow rate rather than adding complications.

[Dockhead]

Originally Posted by valhalla360

I don't question that it's a valid question but when doing a quick look at the numbers, I think it doesn't hold up.

Can you share the numbers on the situation where it would be more efficient than simply adding a few more amp-hrs of standard lead acid? (let's ignore a pure lithium for the moment as it's a separate question).

If you read my example, adding 200ah to a 1000ah bank would negate most of the issues without the complications of a hybrid system.

Given the common situation of having a solar array (or wind generator) to do the top up (even at high latitudes). Just do the bulk charging in the mornings and let the solar finish it at a slow rate rather than adding complications.

Anyone who is getting a good finishing charge from solar will never need this idea.

For those charging with generators for whom the finishing charge is a problem, it could be useful. Increasing the size of the bank will only make the finishing charge even harder.

Whether the complexity is worth it to anyone whatsoever-- I have no idea.

[john61ct]

If solar-only, this idea gets the lead bank to full every cycle, basically extends the long tail past sunset.

In theory not needed if running the genny in the morning, but sometimes we miscalculate, or we thought it was going to be sunny all day but the clouds rolled in, or usage turned out to be higher than anticipated e.g. kids aboard, turned up the tunes, keep opening the drinks fridge all day.

Originally Posted by valhalla360

Can you share the numbers on the situation where it would be more efficient than simply adding a few more amp-hrs of standard lead acid? (let's ignore a pure lithium for the moment as it's a separate question).

If you read my example, adding 200ah to a 1000ah bank would negate most of the issues without the complications of a hybrid system.

The problem being addressed here is preventing PSOC abuse, helping to ensure that the lead bank gets to 100% Full every day.

Going to a larger bank does nothing for that goal, just ensures shallower DoD - which is great, just a solution to a different problem.

[valhalla360]

Originally Posted by john61ct

If solar-only, this idea gets the lead bank to full every cycle, basically extends the long tail past sunset.

In theory not needed if running the genny in the morning, but sometimes we miscalculate, or we thought it was going to be sunny all day but the clouds rolled in, or usage turned out to be higher than anticipated e.g. kids aboard, turned up the tunes, keep opening the drinks fridge all day.

The problem being addressed here is preventing PSOC abuse, helping to ensure that the lead bank gets to 100% Full every day.

Going to a larger bank does nothing for that goal, just ensures shallower DoD - which is great, just a solution to a different problem.

Assuming the batteries get up to 90% most days and every week or two they get up to 100%, I wouldn't really consider that abuse and it won't make much difference in life expectancy.

Worst case if twice a year you do hit a few cloudy/high usage weeks, the extra couple gallons per year you burn to do the final top up is still going to be simpler and cheaper.

Given the typical cruising boat usage, I just see it as an exceptionally rare cruiser who could benefit from this. Short of winter in the arctic, even in the north, solar can be used to top up after a morning burst with the engine charging. If you are really going to be in the arctic cruising in the winter, a wind generator may be in order to effectively do the same thing.

I'm still not seeing a good use case for this plan.

[TheThunderbird]

It is sad that many fight a new idea on the personal ground of evidence that is distant from the suggested assumptions.

Thank you, DH.

Anyone planning for a cautious and selective (for many a reasons...) phasing-in of the Li technology should consider your idea.

[john61ct]

Yes no one claimed widespread need or even common use cases for the idea beyond the examples clearly stated.

This idea would be very low incremental cost if you belief in a Reserve/dedicated Starter anyway and maybe have no interest in using dino juice for charging.

But the OP is explicitly flagged as a thought experiment only for the technically curious.

Originally Posted by valhalla360

Assuming the batteries get up to 90% most days and every week or two they get up to 100%, I wouldn't really consider that abuse and it won't make much difference in life expectancy

I 100% disagree, most strongly.

Yes a grey area, no hard lines susceptible to easy data collection.

But for my own install work, any less than half the cycles is extreme PSOC abuse, and even missing 100% more than once a week would have a significant impact on longevity assuming everything else is good.

Sure just buy cheap GCs every few years no problem

But a big expensive bank, worth the effort to get to Full every day.