LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

[Dod42]

Originally Posted by Jman

I wonder if the victron will shutoff your relay at 13.9 as the agm charge voltage goes towards 14.3 and there by never really charging the li pack? This one reason I by-past this simple sounding solution, but maybe I am wrong.


Sent from my iPhone using Cruisers Sailing Forum

I don't think so. The 702 has a voltage sense on the LifePO4 and a separate one on the Starter. The relay is triggered by the LifePO4 bank voltage, there is a seperate trigger for the starter bank, and the charge splitter (Diode Schottky based) should provide voltage separation and even give me a small voltage drop on the charge line bringing the 14.3 down closer to 13.9. Still working on the best place to put the alternator voltage sense line but will play with several options and see which gives me the best results.

[OceanSeaSpray]

The general issue with doing this is that a LFP bank charging to 13.8-14.0V at a relatively high C-rate needs about 30 minutes of absorption time to charge properly. By cutting off at as a voltage limit gets hit, you miss out on this and it actually leaves quite a bit of capacity out of reach.
This is because at high currents a larger fraction of the battery voltage you measure is in fact voltage drop caused by the internal resistance of the cells and doesn't relate to charge.

Here is a little anecdote illustrating this. A couple of weeks ago I was bulk charging 400Ah of new cells (prior to balancing) on a cat with both engines running. We were pushing a conservative 180A for about an hour. All the cells gradually moved up to 3.6V together, at which point we shut down one engine. The current dropped to 90A and all the cells voltages were instantly down to 3.45V: because they were nowhere near charged, even though we had gone all the way to 4 x 3.6=14.4V.
It took over 30 minutes to bring them back up, and then only cell balance issues started to show as we were cutting back the revs not to exceed 3.6V anywhere.
After that it was time to rearrange everything to parallel and balance charge at low current of course.

In applications where cycling is quite significant and the alternator is an important power source, zero absorption time is quite unsatisfactory in terms of performance. Lower C-rates help mitigating this, but not fully.

[Dod42]

Originally Posted by OceanSeaSpray

The general issue with doing this is that a LFP bank charging to 13.8-14.0V at a relatively high C-rate needs about 30 minutes of absorption time to charge properly. By cutting off at as a voltage limit gets hit, you miss out on this and it actually leaves quite a bit of capacity out of reach.
This is because at high currents a larger fraction of the battery voltage you measure is in fact voltage drop caused by the internal resistance of the cells and doesn't relate to charge.

Here is a little anecdote illustrating this. A couple of weeks ago I was bulk charging 400Ah of new cells (prior to balancing) on a cat with both engines running. We were pushing a conservative 180A for about an hour. All the cells gradually moved up to 3.6V together, at which point we shut down one engine. The current dropped to 90A and all the cells voltages were instantly down to 3.45V: because they were nowhere near charged, even though we had gone all the way to 4 x 3.6=14.4V.
It took over 30 minutes to bring them back up, and then only cell balance issues started to show as we were cutting back the revs not to exceed 3.6V anywhere.
After that it was time to rearrange everything to parallel and balance charge at low current of course.

In applications where cycling is quite significant and the alternator is an important power source, zero absorption time is quite unsatisfactory in terms of performance. Lower C-rates help mitigating this, but not fully.

Thanks. The 702 seems to have lots of options on the relay some of which allow for how long before you open and how long to stay closed etc. I'll have a look at a suitable compromise knowing that the BMS HVC relay has my back

[SailRedemption]

I have been looking for an hour now and not finding the thread I found yesterday..

I'm looking for terminal jumpers for lifepo4 batteries. I have copper strips with holes and I saw someone post a picture of what looked like either tin plated copper or stainless steel strip with holes for multiple terminals(so as not to have to stack the connectors).

If anyone can throw me a bone that would be appreciated, I'm offshore so only have my phone to search and it painfully laborous. I have CALB SE180 batteries and the only connectors I found were in ev power and they are un-tinned copper and only connect two terminals.

Sent from my VS986 using Tapatalk

[Gary H]

Hi all,

I've got a question with regards to treating my LiFePO4 cells well to maximize their service life. In addition to protecting the bank with a House Power BMS, I've learned from this thread to not to expose the bank to charging voltages once it is full. To prevent this, I've programmed my Victron battery monitor to cut off charging once the bank is 99% full. (Every so often I monitor the current taper as the bank nears full to make sure that the battery monitor is synced to reality)

My question is at what state of charge I should resume charging? What is better for the cells: fewer cycles to a deeper discharge state or more cycles with less discharge? I'm cruising and living at anchor with solar as my primary power source so ideally I would like to keep the bank topped up when possible.

I've got a 700 Amp hour Balqon bank. I'm charging with a high output Balmar alternator and a Balmar Max Charge MC-614 smart regulator, plus 450 watts of solar and a Blue Sky MPPT controller. My charging voltages are conservative (i.e. Maine Sail's recommendations).

Insights and experiences are appreciated.

[Hoopla]

Hullo all.

In light of the heading of this thread, those “fence sitters” out there might be interested in my eight year journey with LFP.

Firstly as a newbie here I stress my appreciation of the hard yards put into this discussion over many years by so many people here. I’m not someone who just wants to quickly and conveniently vacuum up advise, so please view any questions I might have down the line in that light.

1. My Introduction to LFP

As background I am both a long distance cruiser and racer (crewed and short-handed). I first became interested in LFP eight years ago after following the 2007 Mini Transat Race. This is a single-handed, 4K nm, back to basics navigation and communications, Trans-Atlantic Race in small 21 footers. I think they can carry sat phones for the first time this year!! It is dominated by the French and not for the faint hearted where speeds up to 20k regularly occur. With only 80 odd places available, vigorous pre-qualification is a race by itself. September 2015 is the 20th Anniversary Race if you’re interested.

I take particular interest in the non-French entrants as they are under-dogs in short-handed racing. Therefore in 2007 an American Alex Mevay was of interest, particularly as he had one of these new-fangled lithium battery things powered by solar panel to deal with the significant 2nd crew/autopilot power loads on these small Mini Transat boats. Alex also just happened to be the founder of a new solar company called Genasun!!! By the way Methanol Fuel Cells are ideal for this particular application and are now the principal LFP charge source of choice for these little race boats.

My interest in LFP was pricked again, this time during the round the world races of the 2008/09 Vendee Globe then 2011/12 Volvo Ocean Race, where for instance in the latter Telefonica had a massive 24V 920ah Genasun LFP power supply. This just happened to be set up by CF supporter and core contributor to this thread, OceanPlanet, also an ex-round the world racer. The considerably longer race distance (with extended systems running time) applied to that high battery size resulting from a minimum battery weight rule may have led to an unforeseen consequence. Bruce may correct me here but I am told the very sturdy 2 X 200A 24V alternators feeding that large bank of 24V LFP’s was too much for the 30HP Volvo engine, whereby the engine not the alternators were swapped out in Brazil before race end!!

Doesn’t take long for “innovation trickle-down” from the pro’s and most unlikely of sources like a 21’ race boat to benefit the wider marine community does it.

Anyway I have been following the discussion about LFP on Forums like this for eight years now and I’m only now are in the final stages of deciding whether or not to plunge to incorporate LFP.Why did I wait so long might you ask???...well actually I may have decided a long time ago, I probably just haven’t admitted that yet! The influences on my decision making to date are as follows.

2. LFP Systems and Limited Choice

Whilst I have very good DYI electric and electronic skills I originally didn’t feel confident installing anything other than a “proprietary LFP system”, largely because DYI Electric Vehicle applications while widespread, they had different discharge demands and didn’t have the complexity of multiple charge sources in marine uses, particularly mission critical ones in remote locations. However as the years unfolded the number of “system suppliers” didn’t increase markedly and costs certainly didn’t dramatically plummet as many have predicted and keep predicting. For instance after the market leader Genasun, it took Mastervolt until 2010 and Victron the following year to hit the shelves. The price of all these products has generally remained static in real terms since their release and in Genasun’s case, that’s six or more years ago.

3. LFP System Shortcomings

With education I began noticing more and more shortcomings and started to become uncomfortable withthe approach made by some “system providers”, and more particularly those with a lower price point. In addition some of the features offered like constant cell balancing are consistent with the “fit and forget” approach a “system provider” probably has to try and adopt. However that may not necessarily be a necessity for "FractionalC" use or one you would even want if cost, auto cell balancing circuitry unreliability and DYI repairability in remote locations are issues for you.

Conversely I’m not sure any “system provider” produces a truly “fit and forget” system anyway, particularly in the “on charge/no load arena’. Therefore the operators of LFP need to be all over operational constraints, regardless of the installation approach.

4. DYI LFP V System LFP Cost

I like many didn’t have the luxury of a new build and was retrofitting LFP into a lead acid environment which involves significant LFP “all of system” costs, particularly charging. Unfortunately the costs of dropping in a “system” of choice was more than a bridge or so too far. LFP Battery costs from “System Providers” currently start at approximately a 50% premium, some providers’ batteries come with a much higher premium than that. This ongoing cost premium and difference to DYI has been a significant contributing factor to the extended timing of my decision making.

5. Waiting and Viable Alternatives to LFP

The extended time has definitely caused me to re-think many times over my views about doing a DIY LFP” instead of a “System LFP” install. Except for increased build quality and some product diversity I’m not too sure a lot has or is about to change in the LFP marine market world. In that vein I am also starting to wonder about the true quality of hidden componentry provided by some “System Providers”? For instance maybe the LFP battery chemistry and build quality of some Chinese LFP battery producers may already be equal to, or has even surpassed that of LFP patent holders/originators? I’m sure some of you have an opinion about that subject!

The only other consideration for me has been alternative battery technology starting to come on stream like the Firefly Carbon Foam battery. With the exception of weight and CAR/Actual Capacity, they generally have a lot of similar attributes to LFP but at a lesser cost.

For details go to OceanPlanet’s site and if nothing else read of Nigel Calder’s PSOC use and storage torture test and Maine Sail’s fabulous PSOC tests benchmarked to LFP in the May 2015 edition of Practical Sailor, pretty impressive stuff.

6. Decision Time

I had to do something for while my most recent boat has many features perfect for my application, it’s limited diesel capacity and reliance on same for charging a large AGM battery bank simply isn’t one that can be ignored. For my application upping diesel capacity really wasn’t a solution. So what did I do?

7. Make It Multiple Choice and Chickening Out

Firstly I made the decision a few years ago to start setting up my system with a view to ultimately going LFP or some other battery technology with similar charge/load characteristics, but putting off the final plunge for as long as I could. This was relatively easy as the boat I was working with even though charging sources suited a medium sized bank of “flooded” lead acid, it was fitted out by some genius with 800AH of AGM’s. Changes were immediately necessary regardless, starting with higher capacity BBQ proof alternators.

Optimum and practical charging capacity and demands between quality AGM’s/TPPL’s and LFP’s are similar. Therefore I have not needed to waste any money going about increasing charge capacity with “future proof” LFP friendly < 0.5C charge sources and changing over to a separately switched charge and load bus etc.

Still a lot of hurdles to solve if LFP chosen, particularly my desire to KIS but incorporate some redundancy in the form of an over-sized AGM starting and AGM winch bank that can act as a “limp-home” house bank. This is in the event something unfixable occurring to LFP’s more fragile management circuitry in remote locations.

Apart from getting some AGM/TPPL best methodology out of my brain, the biggest challenge I have met so far is making a choice between Firefly Carbon Foam and LFP and to do that I have to be prepared to abandon using a LFP “system provider” and go with “DYI LFP”. Making the final decision is also hard as Firefly and “DYI LFP” cost difference (ex my labour) per “Usable AH” is not large.

There are currently supply problems with Firefly outside the US so I have decided to delay making the final decision just a little longer. Yes I know…..chicken.

8. Conclusion

Ultimately once I have stopped mucking around I think LFP’s superior “true cost”, flat discharge voltage, PSOC capability and charge acceptance rate per litre of diesel / hours of sun / hydro miles will be the deciders over Firefly’s for me. While “System LFP” has a valuable place, I feel confident now about embarking on a “DYI LFP” install.

Just thinking about those times I have had to motor-sail for extended periods with limited fuel knowing a couple weeks of prior PSOC use has “walked down” already shrinking battery capacity. Then to add insult to injury after the first hour motor-sailing, bulk charging is well and truly over and all that valuable diesel energy is now simply “going to waste” on absorption charging!

Bugger..all the more reason to deep six those AGM’s once and for all. Energy return inefficiency is also the reason I won’t mind taking some DYI $ saved and fork out for excess storage capacity to be able to fully capitilise upon the PSOC capability and high efficiency of LFP’s.

Even with my advanced DYI skills I would not be in a position to consider “DYI LFP” without having first invested a lot of time/years with investigation and planning, not to mention reading the valuable contributions on this thread and others. Forums like this have enabled DYI participants to leverage off the availability of LFP batteries from those challenging traditional LFP patent/supply monopolies or constraints. The resultant is the practical application of LFP technology for marine use is no longer in the hands of a few to distribute and price outside the reach of many. Thank you all for that.

I hope this has helped some “fence sitters”. I do have some questions but I will post those separately in due course.

Hoopla

[offpist]

We have so much power available we cook our food primarily on induction plates. The Mastervolt Combo Duo Ultra has no problem handling it, even in "boost" mode.

[darylat8750]

Originally Posted by Hoopla

Hullo all.

In light of the heading of this thread, those “fence sitters” out there might be interested in my eight year journey with LFP.

Firstly as a newbie here I stress my appreciation of the hard yards put into this discussion over many years by so many people here. I’m not someone who just wants to quickly and conveniently vacuum up advise, so please view any questions I might have down the line in that light.

1. My Introduction to LFP

As background I am both a long distance cruiser and racer (crewed and short-handed). I first became interested in LFP eight years ago after following the 2007 Mini Transat Race. This is a single-handed, 4K nm, back to basics navigation and communications, Trans-Atlantic Race in small 21 footers. I think they can carry sat phones for the first time this year!! It is dominated by the French and not for the faint hearted where speeds up to 20k regularly occur. With only 80 odd places available, vigorous pre-qualification is a race by itself. September 2015 is the 20th Anniversary Race if you’re interested.

I take particular interest in the non-French entrants as they are under-dogs in short-handed racing. Therefore in 2007 an American Alex Mevay was of interest, particularly as he had one of these new-fangled lithium battery things powered by solar panel to deal with the significant 2nd crew/autopilot power loads on these small Mini Transat boats. Alex also just happened to be the founder of a new solar company called Genasun!!! By the way Methanol Fuel Cells are ideal for this particular application and are now the principal LFP charge source of choice for these little race boats.

My interest in LFP was pricked again, this time during the round the world races of the 2008/09 Vendee Globe then 2011/12 Volvo Ocean Race, where for instance in the latter Telefonica had a massive 24V 920ah Genasun LFP power supply. This just happened to be set up by CF supporter and core contributor to this thread, OceanPlanet, also an ex-round the world racer. The considerably longer race distance (with extended systems running time) applied to that high battery size resulting from a minimum battery weight rule may have led to an unforeseen consequence. Bruce may correct me here but I am told the very sturdy 2 X 200A 24V alternators feeding that large bank of 24V LFP’s was too much for the 30HP Volvo engine, whereby the engine not the alternators were swapped out in Brazil before race end!!

Doesn’t take long for “innovation trickle-down” from the pro’s and most unlikely of sources like a 21’ race boat to benefit the wider marine community does it.

Anyway I have been following the discussion about LFP on Forums like this for eight years now and I’m only now are in the final stages of deciding whether or not to plunge to incorporate LFP.Why did I wait so long might you ask???...well actually I may have decided a long time ago, I probably just haven’t admitted that yet! The influences on my decision making to date are as follows.

2. LFP Systems and Limited Choice

Whilst I have very good DYI electric and electronic skills I originally didn’t feel confident installing anything other than a “proprietary LFP system”, largely because DYI Electric Vehicle applications while widespread, they had different discharge demands and didn’t have the complexity of multiple charge sources in marine uses, particularly mission critical ones in remote locations. However as the years unfolded the number of “system suppliers” didn’t increase markedly and costs certainly didn’t dramatically plummet as many have predicted and keep predicting. For instance after the market leader Genasun, it took Mastervolt until 2010 and Victron the following year to hit the shelves. The price of all these products has generally remained static in real terms since their release and in Genasun’s case, that’s six or more years ago.

3. LFP System Shortcomings

With education I began noticing more and more shortcomings and started to become uncomfortable withthe approach made by some “system providers”, and more particularly those with a lower price point. In addition some of the features offered like constant cell balancing are consistent with the “fit and forget” approach a “system provider” probably has to try and adopt. However that may not necessarily be a necessity for "FractionalC" use or one you would even want if cost, auto cell balancing circuitry unreliability and DYI repairability in remote locations are issues for you.

Conversely I’m not sure any “system provider” produces a truly “fit and forget” system anyway, particularly in the “on charge/no load arena’. Therefore the operators of LFP need to be all over operational constraints, regardless of the installation approach.

4. DYI LFP V System LFP Cost

I like many didn’t have the luxury of a new build and was retrofitting LFP into a lead acid environment which involves significant LFP “all of system” costs, particularly charging. Unfortunately the costs of dropping in a “system” of choice was more than a bridge or so too far. LFP Battery costs from “System Providers” currently start at approximately a 50% premium, some providers’ batteries come with a much higher premium than that. This ongoing cost premium and difference to DYI has been a significant contributing factor to the extended timing of my decision making.

5. Waiting and Viable Alternatives to LFP

The extended time has definitely caused me to re-think many times over my views about doing a DIY LFP” instead of a “System LFP” install. Except for increased build quality and some product diversity I’m not too sure a lot has or is about to change in the LFP marine market world. In that vein I am also starting to wonder about the true quality of hidden componentry provided by some “System Providers”? For instance maybe the LFP battery chemistry and build quality of some Chinese LFP battery producers may already be equal to, or has even surpassed that of LFP patent holders/originators? I’m sure some of you have an opinion about that subject!

The only other consideration for me has been alternative battery technology starting to come on stream like the Firefly Carbon Foam battery. With the exception of weight and CAR/Actual Capacity, they generally have a lot of similar attributes to LFP but at a lesser cost.

For details go to OceanPlanet’s site and if nothing else read of Nigel Calder’s PSOC use and storage torture test and Maine Sail’s fabulous PSOC tests benchmarked to LFP in the May 2015 edition of Practical Sailor, pretty impressive stuff.

6. Decision Time

I had to do something for while my most recent boat has many features perfect for my application, it’s limited diesel capacity and reliance on same for charging a large AGM battery bank simply isn’t one that can be ignored. For my application upping diesel capacity really wasn’t a solution. So what did I do?

7. Make It Multiple Choice and Chickening Out

Firstly I made the decision a few years ago to start setting up my system with a view to ultimately going LFP or some other battery technology with similar charge/load characteristics, but putting off the final plunge for as long as I could. This was relatively easy as the boat I was working with even though charging sources suited a medium sized bank of “flooded” lead acid, it was fitted out by some genius with 800AH of AGM’s. Changes were immediately necessary regardless, starting with higher capacity BBQ proof alternators.

Optimum and practical charging capacity and demands between quality AGM’s/TPPL’s and LFP’s are similar. Therefore I have not needed to waste any money going about increasing charge capacity with “future proof” LFP friendly < 0.5C charge sources and changing over to a separately switched charge and load bus etc.

Still a lot of hurdles to solve if LFP chosen, particularly my desire to KIS but incorporate some redundancy in the form of an over-sized AGM starting and AGM winch bank that can act as a “limp-home” house bank. This is in the event something unfixable occurring to LFP’s more fragile management circuitry in remote locations.

Apart from getting some AGM/TPPL best methodology out of my brain, the biggest challenge I have met so far is making a choice between Firefly Carbon Foam and LFP and to do that I have to be prepared to abandon using a LFP “system provider” and go with “DYI LFP”. Making the final decision is also hard as Firefly and “DYI LFP” cost difference (ex my labour) per “Usable AH” is not large.

There are currently supply problems with Firefly outside the US so I have decided to delay making the final decision just a little longer. Yes I know…..chicken.

8. Conclusion

Ultimately once I have stopped mucking around I think LFP’s superior “true cost”, flat discharge voltage, PSOC capability and charge acceptance rate per litre of diesel / hours of sun / hydro miles will be the deciders over Firefly’s for me. While “System LFP” has a valuable place, I feel confident now about embarking on a “DYI LFP” install.

Just thinking about those times I have had to motor-sail for extended periods with limited fuel knowing a couple weeks of prior PSOC use has “walked down” already shrinking battery capacity. Then to add insult to injury after the first hour motor-sailing, bulk charging is well and truly over and all that valuable diesel energy is now simply “going to waste” on absorption charging!

Bugger..all the more reason to deep six those AGM’s once and for all. Energy return inefficiency is also the reason I won’t mind taking some DYI $ saved and fork out for excess storage capacity to be able to fully capitilise upon the PSOC capability and high efficiency of LFP’s.

Even with my advanced DYI skills I would not be in a position to consider “DYI LFP” without having first invested a lot of time/years with investigation and planning, not to mention reading the valuable contributions on this thread and others. Forums like this have enabled DYI participants to leverage off the availability of LFP batteries from those challenging traditional LFP patent/supply monopolies or constraints. The resultant is the practical application of LFP technology for marine use is no longer in the hands of a few to distribute and price outside the reach of many. Thank you all for that.

I hope this has helped some “fence sitters”. I do have some questions but I will post those separately in due course.

Hoopla

Wow! I have less experience than you but this sums up my position very well. Then add the possibility of solar to top off the last 20% or so and the older tech is still viable if weight is not critical. The carbon foam lead acid option sounds very promising.... but... Typical sources seem to be back ordered several months and still they are WAY more expensive than FLA golf cart batteries.

[Hoopla]

darylat8750 it is my opinion that the decision to go LFP over lead acid whether it is a DIY or System Install is a pretty easy one to make. Assuming your battery storage is adequately sized and in good condition, you’re a regular boat user BUT you find there is a significant “imbalance” between battery charging and load/storage, then going LFP is a no brainer.

For some people like offpist with a desire for electric cooking it might be high loads that are causing that imbalance. In my case a bit of both. I have a significant charging constraint with low diesel capacity/supply (despite other charging means) with extended and remote voyaging. While my loads are not high now, they will increase over time such as retro-fitting powered sheet winches to preserve short-handed capacity as I get older etc.

Firefly Carbon Foam is certainly an attractive proposition, but they are not in the hunt compared to LFP’s Charge Acceptance Rate/Actual Capacity and real cost. That said, there is probably no better option out there than Firefly’s for someone who wants a “drop in” more “PSOC user-friendly” and “cheaper real cost” alternative to AGM/TPPL’s, but without incurring the more costly and technical demands of LFP.


Got to get off my butt and finish putting my LFP arrangement to paper.

[darylat8750]

Originally Posted by Hoopla

darylat8750 it is my opinion that the decision to go LFP over lead acid whether it is a DIY or System Install is a pretty easy one to make. Assuming your battery storage is adequately sized and in good condition, you’re a regular boat user BUT you find there is a significant “imbalance” between battery charging and load/storage, then going LFP is a no brainer.

For some people like offpist with a desire for electric cooking it might be high loads that are causing that imbalance. In my case a bit of both. I have a significant charging constraint with low diesel capacity/supply (despite other charging means) with extended and remote voyaging. While my loads are not high now, they will increase over time such as retro-fitting powered sheet winches to preserve short-handed capacity as I get older etc.

Firefly Carbon Foam is certainly an attractive proposition, but they are not in the hunt compared to LFP’s Charge Acceptance Rate/Actual Capacity and real cost. That said, there is probably no better option out there than Firefly’s for someone who wants a “drop in” more “PSOC user-friendly” and “cheaper real cost” alternative to AGM/TPPL’s, but without incurring the more costly and technical demands of LFP.


Got to get off my butt and finish putting my LFP arrangement to paper.

A real issue for me is the problem of no float charging. My eventual goal is to charge primarily with solar. I think a 400 amp 12v LFP would be fine if I knew I would start every evening with 300 amps available. (I am an energy hog. I know. We all do what we need to when She Who Must Be Obeyed needs comforts.) I do have a genset and if I had to start it once a week or so that would be fine with me as I'll need it to do laundry anyway. I'm really temped to try it with 400 amps but if I wind up having to double the LFP bank or run the genset everyday there will be more investment in cells than makes sense to me. Also still scratching out solar panel schemes and if an abundance of solar power is available to do some real good on overcast days maybe the 400amp battery will do....... Still vacillating too much to make a decision.

[sv.antea]

Quick question. Victron BMV-702 battery monitor claims to have a programable relay that can be used to turn things on or off. I can find no information on how to connect to it. One quick installation guides points to the ethernet like plug on the back of the instrument and says something like "relay connections" so maybe it is two of those plugs 8 contacts, but which one? Please advise.

[Hoopla]

darylat8750 looks as though it is just you and me. I think you might be expecting too much of LFP and misunderstand the concept of float charging as it applies to LA and LFP.

LEP isn’t the magic pudding. If your using 300 ah per day that means nearly all the usable capacity of a 400ah nominal LFP bank is being turned over every 24 hours. If solar is your preferred charge source that necessitates a large solar farm with efficient orientation and regulator numbers. Notwithstanding having that charging capacity, your still left with no contingency storage for cloudy days. Clearly 400ah is not near enough capacity for 300ah/day use irrespective of battery chemistry.

Capacity

You’re making a mistake trying to use LFP’s increased usable capacity to artificially slice costs at the expense of practical capacity. If you want to make a proper financial comparison with LA first select a practical LA usable capacity. In your case let us say it’s 600ah of usable capacity. That gives you more than one days capacity and some charging contingency. At twice the daily usage it is still relatively small compared many who prefer usable capacity between four and six times daily usage when utilising solar as the prime charging source.

Therefore for 600ah actual you will need at best a 1200ah bank of LA to achieve that. The equivalent to 600ah in usable capacity with LFP is no more than a 800ah nominal LFP bank. Don’t forget to include in your LA V LFP cost comparison the need for a lot more solar to keep that 1200ah LA bank charged compared to the LFP 800ah bank as well as the multiple LA purchases to get to the same cycle life of LFP. I realise there is an enormous world-wide variance however 30ah per day per 100w solar panel is a reasonable guestimate I think for a good well placed panel. I hope you have a large boat, that is a lot of solar!!

Note: If I have misunderstood your reference to solar and no “float” charging with LFP ignore what I have said as follows.

I know it is difficult but you need to get some LA concepts out of your head when looking at LFP. Firstly solar charges no differently than other charge sources, be it at Bulk, Absorption or Float Stages. The battery chemistry and its SOC ultimately determines how a charger charges and at what rate, not the charger regulator except for pressure or voltage. The lower charge rate of solar is simply a factor of available panel area compared to the higher capacity on offer from DCDC alternators or ACDC chargers.

LA Float Charging

LA Float Charge is the concept of preserving the life of a LA battery by countering self-discharge after being fully charged with a constant lower voltage charge that is preferably temperature compensated. Float Charge commencing signifies when a LA battery is fully charged, therefore instead of calling it Float Charge, it could be called “100% SOC Completed” for LA batteries.

100% SOC can be defined for instance on AGM batteries when they are accepting a charge 0.5% or less of overall capacity . In your 1200ah LA hypothetical case that is 0.005x1200 = 6 amps. Solar is excellent for this Float and the preceding Absorption Stage. That is why small solar panels, while having limited charge capacity, are so good for dealing with “tail end charging” or the Low Charge, Long Absorption and Float Charge times of intermittently used large AGM banks. Returning them very regularly to 100% SOC slows down sulphation and preserves their life.

LFP Float Charging

LFP doesn’t need or in fact like a constant Float Charge. It is better left to self-discharge at say 60% SOC not 100% SOC if not being used. Discussion about LFP Float Voltage can get muddied as LFP prefers full discharge/charge cycles rather than partial discharge/charge cycles to the extent they are both treated the same in terms of life cycle. Providing there is sufficient capacity this leads people to prefer full discharge/charge cycles, not PSOC.

Some people therefore treat Float Voltage as the voltage drop that triggers recommencing of charging after a full 80% DOD cycle. Maine Sail has a very good term. He prefers to call it “Drop Voltage” where charging is turned off (or treated as turned off if a low charge source like solar is being used) at the end of Bulk/Absorption Charging at say 13.8V until the LFP bank hits 80% DOD or say 13.1V and charging current from larger sources is engaged again.

However charge sources on boats are often “take it or lose” be it solar, wind, hydro or alternator(s) from motor-sailing when the wind drops. This makes full discharge/charge cycles sometimes impractical in favour of PSOC usage. The jury is out I believe on quantifying the impact of PSOC usage for FractionalC applications like boats, however it doesn’t appear to be an issue.

Conclusion

Apart from very large systems, solar’s deficiency is being able to “quickly” take advantage of the high Charge Acceptance Rate (CAR) of AGM’s (up until the Absorption Stage) and more so LFP’s. It simply counters this deficiency by time or charging all the time during daylight hours. With no moving parts this is probably the best long life “switch on and forget” charge source.

I don’t have enough experience with solar as a prime charge source or know what opportunities and constraints exist with your application, particularly vessel usage to make further and proper comment. However it seems to me that where solar is the prime charge source, and loads are high, then to properly take advantage of LFP’s high CAR, it has to be a relatively large and efficient solar system in relation to daily load, both which are often hard to achieve on a lot of vessels.

[klaus53123]

Hi Folks,

looks like I have a problem with one of my cells.

Just a few informations:

cells have never been charged higher than 3,47 V (usually charge is switched off when all cells have reached 3,45 Volt, however some cells might be a bit higher when the lowest reaches 3,45V). Charging mainly executed with solar. Cell voltage measured at the poles via BMS.

Cells have never been discharged below 60% DOD.

Today I wanted to hook up my electric water heater (draws about 120A) and after few seconds one cell (cell 3) dropped to 2,7V and BMS switched off. After a few seconds that cell, like all the others showed 3,3xx V. All cells are fully loaded (SOC around 98%).

Any suggestions what to do? Cells have approx 44 cycles so they are new!.

Now with a -6A load on the cells the voltages reads

Cell1: 3.336
Cell2: 3.331
Cell3: 3.297
Cell4: 3.333

Many thanks

Klaus

[Hoopla]

Originally Posted by sv.antea

Quick question. Victron BMV-702 battery monitor claims to have a programable relay that can be used to turn things on or off. I can find no information on how to connect to it. One quick installation guides points to the ethernet like plug on the back of the instrument and says something like "relay connections" so maybe it is two of those plugs 8 contacts, but which one? Please advise.

sv. antea the BMV 702 Monitor has 3 sockets. The RJ12 socket links monitor and shunt using UTP cable. The 4 pin socket is a VE-Direct data socket for other Victron equipment. The one you want is the green 2 pin socket which controls a relay. Manual is available for download from Victron, though from memory I don't think they ever had pics of monitor or installation in the manual, only on the quick instal. Manual does have suggestions on LFP settings.

Cheers

[hellosailor]

Hello Klaus. I am not the expert here, but would suspect the problem is either a defective cell, or a high resistance (thin, loose, or simply not good clean contact) to that one cell. Under low loads, there will be little voltage drop. But a high resistance connection would cause more significant voltage drops under high load.


If the physical connections to that cell seem to be good, the same as to the other cells, then it might be necessary to have that one cell returned or replaced under warranty, for an internal defect. I'd contact the maker and see what they suggest and offer.