LiFeP04 Charging Question

[kwb78]

The challenge of making the 2 batteries share load and charging evenly is removed and make wiring simpler.

When you wire two batteries together in parallel, you should take the positive from one battery and the negative from the other. That means the current passes through the both the positive and negative interconnections and should discharge the batteries equally. Like this:



If you do it with the load connected to one battery, with the others in a string from that you will get unequal discharge due to the resistance of the interconnecting cables. The battery nearest the load will discharge more than the other.

Connected as above, there should be no problem with equal charging or discharging and they will self balance.

 

[Daverw]

Not sure how you can easily do this with 4 x 3.6 v in 4S battery packs and bms for each battery

 

[geem]

a. I would take option 1 and fit a second small charger for the engine start battery.
b. Why fit 2 x 100Ah batteries and not 1 x 200 Ah battery. The challenge of making the 2 batteries share load and charging evenly is removed and make wiring simpler.
c. A good battery monitor like the Victron BMV 702 gives you a really good indication of state of charge and is well worth the money.

Two batteries is the ultimate set up. If a BMS faults for whatever reason, it will leave you with 50% of your capacity to keep things running. Balance between two lithium batteries not much of an issue.
The best wiring arrangement for lithium is to run equal length wires to a fuse then isolator for each battery. From each isolator, run the wires to negative and positive busbars.

 

[kwb78]

Not sure how you can easily do this with 4 x 3.6 v in 4S battery packs and bms for each battery

You just treat them as two separate batteries of 4 cells and let the BMS sort each one out. The balance of cells within each battery is important, but the balance between the two batteries doesn't really matter that much. If wired as I showed, they will stay in balance anyway since as soon as one battery's voltage drops below the other the balance of current drawn from each one will change to match.

 

[lustyd]

When you wire two batteries together in parallel, you should take the positive from one battery and the negative from the other. That means the current passes through the both the positive and negative interconnections and should discharge the batteries equally. Like this:

View attachment 175562

If you do it with the load connected to one battery, with the others in a string from that you will get unequal discharge due to the resistance of the interconnecting cables. The battery nearest the load will discharge more than the other.

Connected as above, there should be no problem with equal charging or discharging and they will self balance.

Generally with lithium people are using equal length cables and a busbar rather than this that we’d have done with lead. Whether it’s worth the faff is debatable but seems the way the crowd is going.

 

[geem]

Generally with lithium people are using equal length cables and a busbar rather than this that we’d have done with lead. Whether it’s worth the faff is debatable but seems the way the crowd is going.

I think the driver for seperate, equal length cables comes out of the recommendation to fuse each battery separately and use individual battery isolators. Once you adopt this approach, it lends itself to the use of busbars as well. It makes for a better install in my opinion as you can isolate an individual battery whist keeping the system alive. This may be useful if you had to fix a bad connection, swap a BMS, change a fuse, etc or if you were dealing with a lithium battery that may have failed and you want to isolate for safety reasons.

 

[Neeves]

Continuing my probing

If you are not going to discharge the Lithium down to 20% capacity, why lithium? Lithium is expensive, even if getting cheaper, and if you are happy with a max discharge of 50% - then why not stick with Lead. I know that lithium is lighter - but on a cruising yacht that is not such a big deal - unless you race the yacht (and have my weight fetish). If you do have a weight fetish - then down sizing the rode offers much more advantage than swapping to Lithium (though swapping to a lighter rode is not cheap either).

If part of the grand strategy is to reduce the reliance on gas (in fact remove gas completely), for the galley, then 200 amps of Lithium with not be enough, you will get down to near 20% capacity easily and 200 watts of solar needs a rethink - again its too small. As this thread indicates changing to Lithium is not particularly complex but does need some thought (and there is an enviable resource here keeping us neophytes on the straight and narrow). But its not as simple as swapping batteries (which you can do easily and cheaply with Lead).

If you are only going to use the yacht for weekends, no problems, but even using the yacht for a fortnight you are going to have days of little sun and the 30 amp B2B is really going to struggle to replenish the batteries. Furthermore with only 200 watts of solar you will reply more on the alternator - which means running the engines. (Well it will not struggle but take a long time) - and if you are sailing some of the 30 amp will be swallowed up by the AP and to a lesser extent the fridge - and will you have a de-salinator?

So assuming the concept is a fortright 'off grid' and replacing gas - you will need the same resource as any live aboard - and the liveaboards who post here don't rely on 200amps of battery and 200 watts of solar.

If I may ask the questions - why are you going lithium? what is the grand strategy for use of the yacht and where?

We have 200 amps of a Lithium with a built in, inaccessible) BMS (the strategy is to replace). Its all effectively a terrestrial power station and we can cope with the fridge and evening meal - but not much more. 3 days of overcast skies, which does happen (even in Sydney) and we can draw down to 20% easily and 300 watts of fixed solar struggles to replenish. I have not decided on how much Lithium we need for fully off grid, 400 amps seems a lot but I suspect we should think 600 amps and at least double the solar.

Jonathan

 

[geem]

Continuing my probing

If you are not going to discharge the Lithium down to 20% capacity, why lithium? Lithium is expensive, even if getting cheaper, and if you are happy with a max discharge of 50% - then why not stick with Lead. I know that lithium is lighter - but on a cruising yacht that is not such a big deal - unless you race the yacht (and have my weight fetish). If you do have a weight fetish - then down sizing the rode offers much more advantage than swapping to Lithium (though swapping to a lighter rode is not cheap either).

If part of the grand strategy is to reduce the reliance on gas (in fact remove gas completely), for the galley, then 200 amps of Lithium with not be enough, you will get down to near 20% capacity easily and 200 watts of solar needs a rethink - again its too small. As this thread indicates changing to Lithium is not particularly complex but does need some thought (and there is an enviable resource here keeping us neophytes on the straight and narrow). But its not as simple as swapping batteries (which you can do easily and cheaply with Lead).

If you are only going to use the yacht for weekends, no problems, but even using the yacht for a fortnight you are going to have days of little sun and the 30 amp B2B is really going to struggle to replenish the batteries. Furthermore with only 200 watts of solar you will reply more on the alternator - which means running the engines. (Well it will not struggle but take a long time) - and if you are sailing some of the 30 amp will be swallowed up by the AP and to a lesser extent the fridge - and will you have a de-salinator?

So assuming the concept is a fortright 'off grid' and replacing gas - you will need the same resource as any live aboard - and the liveaboards who post here don't rely on 200amps of battery and 200 watts of solar.

If I may ask the questions - why are you going lithium? what is the grand strategy for use of the yacht and where?

We have 200 amps of a Lithium with a built in, inaccessible) BMS (the strategy is to replace). Its all effectively a terrestrial power station and we can cope with the fridge and evening meal - but not much more. 3 days of overcast skies, which does happen (even in Sydney) and we can draw down to 20% easily and 300 watts of fixed solar struggles to replenish. I have not decided on how much Lithium we need for fully off grid, 400 amps seems a lot but I suspect we should think 600 amps and at least double the solar.

Jonathan

It's so cheap to build lithium now, it comparable with lead. I can build a 105Ah 12v lithium battery for £240. Not cheap compared to a lead 105Ah battery but it will last many more years doing vastly more cycles and have an equivalent capacity, assuming you only drop the lead battery to 50% of about 170Ah assuming you don't drop below 20%. This battery would use grade A cells and a quality Bluetooth bms and active balancer.
Not having to get the battery to 100% charged in a regular basis is a huge benefit. Not having to sit in absorbtion for hours means you can bang in more power from your solar in bulk. It's no longer a cheap prospect going for lead, even on the smaller basic sailboat if you take into account the life expectancy of lead. I know you can always find somebody who says their lead batteries last 12 years or what ever, but most lead batteries do not last that long. The idea of having your lithium battery for 15 or 20 years is now a realistic prospect, assuming you don't buy the cheapest lithium you can find

 

[Neeves]

It's so cheap to build lithium now, it comparable with lead. I can build a 105Ah 12v lithium battery for £240. Not cheap compared to a lead 105Ah battery but it will last many more years doing vastly more cycles and have an equivalent capacity, assuming you only drop the lead battery to 50% of about 170Ah assuming you don't drop below 20%. This battery would use grade A cells and a quality Bluetooth bms and active balancer.
Not having to get the battery to 100% charged in a regular basis is a huge benefit. Not having to sit in absorbtion for hours means you can bang in more power from your solar in bulk. It's no longer a cheap prospect going for lead, even on the smaller basic sailboat if you take into account the life expectancy of lead. I know you can always find somebody who says their lead batteries last 12 years or what ever, but most lead batteries do not last that long. The idea of having your lithium battery for 15 or 20 years is now a realistic prospect, assuming you don't buy the cheapest lithium you can find

Geem,

I know, I know and I'm a supporter of Lithium.

But. most people, who post here, are not buying new yachts. Their Lead batteries may need replacing but all the bits and prieces that they have to charge, manage and use the Lead is now no longer needed - resale value - peanuts.

For lithium they need new batteries, maybe cheaper than they were but still more expensive than lead. Many people don't think of the life cycle of their batteries but might having nagging fears that battery technology will leave them as a dinosaur and/or that buyers might be unsure of Lithium. - you only need to read these threads to see that some people are not converts (for a variety of reasons)

So - they need a new battery charging system. They need, possibly, a new monitoring system, they need new kit - induction hot plate (that they never knew they needed) AC wiring and if they are really unlucky new, induction compatible saucepans. Then, because they are fully qualified Lawyers, or yachtsmen - but are unsure about electrical installations - so need to pay an electrician....

None of this is major but the costs add up.

Jonathan

 

[NBs]

Geem,

I know, I know and I'm a supporter of Lithium.

But. most people, who post here, are not buying new yachts. Their Lead batteries may need replacing but all the bits and prieces that they have to charge, manage and use the Lead is now no longer needed - resale value - peanuts.

For lithium they need new batteries, maybe cheaper than they were but still more expensive than lead. Many people don't think of the life cycle of their batteries but might having nagging fears that battery technology will leave them as a dinosaur and/or that buyers might be unsure of Lithium. - you only need to read these threads to see that some people are not converts (for a variety of reasons)

So - they need a new battery charging system. They need, possibly, a new monitoring system, they need new kit - induction hot plate (that they never knew they needed) AC wiring and if they are really unlucky new, induction compatible saucepans. Then, because they are fully qualified Lawyers, or yachtsmen - but are unsure about electrical installations - so need to pay an electrician....

None of this is major but the costs add up.

Jonathan

Geem,

I know, I know and I'm a supporter of Lithium.

But. most people, who post here, are not buying new yachts. Their Lead batteries may need replacing but all the bits and prieces that they have to charge, manage and use the Lead is now no longer needed - resale value - peanuts.

For lithium they need new batteries, maybe cheaper than they were but still more expensive than lead. Many people don't think of the life cycle of their batteries but might having nagging fears that battery technology will leave them as a dinosaur and/or that buyers might be unsure of Lithium. - you only need to read these threads to see that some people are not converts (for a variety of reasons)

So - they need a new battery charging system. They need, possibly, a new monitoring system, they need new kit - induction hot plate (that they never knew they needed) AC wiring and if they are really unlucky new, induction compatible saucepans. Then, because they are fully qualified Lawyers, or yachtsmen - but are unsure about electrical installations - so need to pay an electrician....

None of this is major but the costs add up.

Jonathan

You're right, the budget is much more than the batteries, you can easily double your budget with everything else and if you still use a professional installer man, the budget can stretch drastically.

that's a lot of money vs lead acid batteries. I can say lead acid batteries can be durable, my life line AGM batteries lasted 15 years and hadn't died yet when I switched to lifepo4 cheap batteries without the blue thoot feature because I have other interests on the boat than watching the batteries soul life, how do people get along with lead acid batteries without an app?

 

[GHA]

You're right, the budget is much more than the batteries, you can easily double your budget with everything else

Depends. Not as black & white as you make it sound. If you have victron smartshunt & solar regulators & mains charger which has LiFePo4 profile like the popular procharge ultra you're mostly there. Just need a B2B if you want to use the alternator. Spend time onboard with solar you'd want the victron combination anyway so you don't kill your lead acid by undercharging.
Not spending lots time on solar there's not so much point switching to LiFePo4 anyway.

 

[Daverw]

The cost can be kept manageable with careful planning, as I’ve updated electrical stuff over the last 4 yrs I’ve made sure all is to be part of the final solution, along the way has made better use of the current agms, given me remote monitoring and remote control of system, also allowed integration of tank levels and temperature monititoring that I never thought I would use but now all the time. Oversizing battery cables also helps. Buying stuff over time when deals come saves loads as it seems the battery’s are the thing that is dropping in price so good to be the last part.

 

[B27]

For a sailing boat in the UK, one of the advantages of Lithium would be the ability to charge at a high rate, to get maximum benefit from a short period of motoring. A 30A DC/DC doesn't seem optimum.
Drop-in LifePO4 batteries generally have low max current ratings so may not be ideal for high current loads like thrusters or windlasses (which I don't have!), but more critically, they may not actually fulfil the role of back-up engine start?

 

[GHA]

For a sailing boat in the UK, one of the advantages of Lithium would be the ability to charge at a high rate, to get maximum benefit from a short period of motoring. A 30A DC/DC doesn't seem optimum.
Drop-in LifePO4 batteries generally have low max current ratings so may not be ideal for high current loads like thrusters or windlasses (which I don't have!), but more critically, they may not actually fulfil the role of back-up engine start?

though you'll overheat your alternator quickly pumping out full current without hammering the wallet upgrading.....

 

[ctva]

Continuing my probing

... If you do have a weight fetish - then down sizing the rode offers much more advantage than swapping to Lithium (though swapping to a lighter rode is not cheap either)...

Ohh err misses.... Is this the lounge?

And who said you could bring anchors in to this thread...

Otherwise, thanks for the input. At this point in our sailing we will be going out for a month or two and when I looked at replacing the three lead batteries, it just made sence with our usage and situation to change. Partly convenience, extra power and long term cost savings. We do not have any of the liveaboard toys, watermaker, electric windlass (but this will be added at some point off the domestic side) and the auto pilot is only used for changing sails or eating or in flat calms. Our main use is the fridge / freeezer which is on 24/7 and small electronics and nav stuff. All cooking is gas.

I think the driver for seperate, equal length cables comes out of the recommendation to fuse each battery separately and use individual battery isolators. Once you adopt this approach, it lends itself to the use of busbars as well. It makes for a better install in my opinion as you can isolate an individual battery whist keeping the system alive. This may be useful if you had to fix a bad connection, swap a BMS, change a fuse, etc or if you were dealing with a lithium battery that may have failed and you want to isolate for safety reasons....

I know you can always find somebody who says their lead batteries last 12 years or what ever...

I didn't mention that when I was looking at this the other month, I noticed that my enging battery is dated July 2012!!! Still works fine and I hadn't noticed any issues. It will be replaced with one of the 2016 domestic ones.

As to your not on the wiring, do you have a link to somewhere to detail that as I want to make sure I'm adopting best (practical) practice?

Thanks all.

 

[Neeves]

Some issues are

People have a yacht that they use for day or over a weekend. And then maybe for their annual holiday.

Some people change their yacht as people do their cars.

 

[Tranona]

I didn't mention that when I was looking at this the other month, I noticed that my enging battery is dated July 2012!!! Still works fine and I hadn't noticed any issues. It will be replaced with one of the 2016 domestic ones.

Yes, engine batteries have an easy life if used just for starting the engine. Even better if you fit one of the high power batteries such as a Red Flash. The one that came with my new Morgan in 2003 lasted 19 years with a similar usage pattern to a sailing yacht. Expensive though and maybe a better choice is one of the new AGMs for stop start cars. My 2017 Ford is still on its original battery even though most of its use is short run urban journeys so lots of starts.

 

[B27]

though you'll overheat your alternator quickly pumping out full current without hammering the wallet upgrading.....

Indeed. Like most small boats, mine has a dumb alternator which simply tries to supply a voltage with a bit of 'source resistance' and maybe a bit of temperature compensation. Smarter alternators starter appearing in cars about 20 years ago.

The most important thing is being able to start the engine.
Adding complication which might compromise that needs proper care IMHO.

 

[geem]

Yes, engine batteries have an easy life if used just for starting the engine. Even better if you fit one of the high power batteries such as a Red Flash. The one that came with my new Morgan in 2003 lasted 19 years with a similar usage pattern to a sailing yacht. Expensive though and maybe a better choice is one of the new AGMs for stop start cars. My 2017 Ford is still on its original battery even though most of its use is short run urban journeys so lots of starts.

It may not be an issue in the UK bit from my experience, Heat kills lead very quickly. We typically get 3 to 4 years out of an engine battery here. My generator stop start AGM battery is kept on float most of the time. If I disengage the dc/dv for a day or two, it's struggling to start the tiny twin cylinder perkins. It's only 3 years old. My previous engine batteries lasted 4 years. I also seem to get good life out of car batteries in the UK by comparison

 

[Neeves]

Ohh err misses.... Is this the lounge?

And who said you could bring anchors in to this thread...

Otherwise, thanks for the input. At this point in our sailing we will be going out for a month or two and when I looked at replacing the three lead batteries, it just made sence with our usage and situation to change. Partly convenience, extra power and long term cost savings. We do not have any of the liveaboard toys, watermaker, electric windlass (but this will be added at some point off the domestic side) and the auto pilot is only used for changing sails or eating or in flat calms. Our main use is the fridge / freeezer which is on 24/7 and small electronics and nav stuff. All cooking is gas.


I didn't mention that when I was looking at this the other month, I noticed that my enging battery is dated July 2012!!! Still works fine and I hadn't noticed any issues. It will be replaced with one of the 2016 domestic ones.

As to your not on the wiring, do you have a link to somewhere to detail that as I want to make sure I'm adopting best (practical) practice?

Thanks all.

A reason amongst many to swap to Lithium is that you can lighten your battery bank (by crudely) 50%. And a 200amp Lead battery is seriously heavy. If saving weight is a focus then using smaller chain offers greater savings in weight, but like (and this was a point) Lithium there are hidden costs.

My view is - costs have nothing to do with me, I don't know the size of your wallet. I just like to mention all aspects, not just highlight the advantages - and leave you (and your partner) to sort out the financial implications.

I'm not flush but am able to afford Lithium as a 'big boys' toy - maybe I'm lucky (I don't know as I don't have male playmates). Actually I know I'm lucky But I do know how much all the bits cost. I have offset the costs as we have wired my toy to our galley (or in reality) to the kitchen and roughly we cook for free - except after 2 or 3 days of overcast skies. Today we had breakfast and dinner - cooked for free, we were out for lunch (at a show within which was a big Lithium display).

This has made me think - considering the numbers of people who underutilise the Lithium bank on their yacht, the excess could be 'bought' by the marina and passed into the grid. But maybe power is cheaper, in say, the UK and not using and getting a return on the investment is not worth the effort.

Now if all these floating, under-utilised, micro power stations could be a source of income or credits - the equations all change.

and CTVA

There is nothing stopping you having a lead house bank (which also starts the engine etc) as well as a lithium house bank. If your 'old' Lead is good enough to start the engine, replacing the geriatric one - why not have 2 house banks?

I am a parsimonious Scot.

Jonathan