LoneHort
Member
yes thanks for a great write up.
270ah DIY LiFePO4 build
- Thread starter Poey50
- Start date
Poey50
Well-known member
Thank you for the generous comments.
One more photo. I couldn't find any reason to leave the Plastik 70 conformal coating in the spray-can so have added several more coats, including to the sides (but not, of course, the terminal contacts). It seems to have helped the scrim tape to adhere better to itself and the cells. It all has a rather reassuring plasticy look.
One more photo. I couldn't find any reason to leave the Plastik 70 conformal coating in the spray-can so have added several more coats, including to the sides (but not, of course, the terminal contacts). It seems to have helped the scrim tape to adhere better to itself and the cells. It all has a rather reassuring plasticy look.
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pcatterall
Well-known member
Very useful write up, got a bit lost in some places so would have to read several times. and will not be undertaking similar in my shed ( but perhaps a kit?)
Returning to capacity you say "This is roughly the size of an 80ah lead acid. The usable capacity is around that of 5 x 100ah lead acid batteries" Does this mean 500 ah or their 'useable' ah (say 250ah)
In any case your package effectively is 1/5th the weight and size of conventional lead acid.
What sort of costs would a package of this size cost on the 'retail/marine market'?
Returning to capacity you say "This is roughly the size of an 80ah lead acid. The usable capacity is around that of 5 x 100ah lead acid batteries" Does this mean 500 ah or their 'useable' ah (say 250ah)
In any case your package effectively is 1/5th the weight and size of conventional lead acid.
What sort of costs would a package of this size cost on the 'retail/marine market'?
Poey50
Well-known member
Do feel free to ask any questions on sections that are not clear.
As regards capacity, the LFP pack has 270ah capacity. All of that is theoretically usable but it is not wise to do so on a regular basis if you want a long life from the battery. As a rule of thumb LFP is generally reckoned to have about twice the usable capacity of lead acid for a given nominated capacity size. Obviously there are a number of variables in all that but the difference is going to be most significant for those cycling their batteries daily when, because of the long absorption stage of lead acid, it may not be possible to get back to more than 80-85% state of charge.
Morgan's Cloud (Attainable Adventure Cruising) tend to have a scientific view on these matters and on their spreadsheet for auditing power needs on boats I see that they use a factor of 2.33 for LFP compared to lead acid. So by their calculation my 270ah is equivalent to 630ah of lead acid. I'm not taking all that too seriously, I'm just glad to have plenty of capacity in a comparative small space with no need at all to ever get it back to full charge to avoid the dreaded sulphation.
Your question about comparing this to a commercial option is an interesting one as it is not easy to answer. As said at the beginning of the thread there is no drop-in replacement option for LFP that meets the Nordkyn 5 principles for marine use. The only option that would do that, as far as I am aware, is an integrated system from Victron which would be, I guess maybe three times the cost. By most measures DIY LFP is, arguably, both more suitable for boats and considerably less expensive. You could match the capacity with say a 300ah LFP drop-in from Quality Source for £1800 but it it decides to shut down then there is no communicating with it.
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Mikedefieslife
Member
Hmmm. I paid $904 for the exact same cells and bars including shipping to Spain. 
Poey50
Well-known member
Hmmm. I paid $904 for the exact same cells and bars including shipping to Spain.
I think you are a year or two ahead of me? Is that right? Prices are dropping all the time and I don't think R J Energy are now the cheapest. The hot deal these days seems to be the 280ah cells from Xuba Electronics.
TernVI
Well-known member
Is that inc VAT and import duty?Hmmm. I paid $904 for the exact same cells and bars including shipping to Spain.
I think prices will drop further.
Poey50
Well-known member
Assuming that is 'delivered cost' and that the cost of delivery to any part of Europe from China is roughly the same, that would represent around a 15% drop in costs since Mikedefieslife bought his.
Poey50
Well-known member
Thank you.
I've designed it to fit in to one leg of the moulded 'L'-shaped battery box of our boat. This will be securely fixed down so a fake battery box isn't needed for protection. The big life-shortener for LFP is heat (whether caused by fast charging, fast discharging, high ambient temperature or, worst of all, overcharging) so it is important to have good air-flow around the pack. I will be installing a thermostatically operated fan through the other leg of my battery box to circulate air from cooler spaces around the moulded box.
It's interesting to me that Victron use a heavy case for their LFP batteries even though only part of the battery management system and none of the relays are in the case. There is something about the brand 'battery' whereby we can't imagine them without that familiar cased look. But if you cut the top off a Victron (no-one would do this!) you will find a set of plastic cased prismatic Winston cells with cell boards similar to mine (see link). The case offers some support but that could easily be provided in other ways. I think what the blue case says is 'I'm a Victron battery" even at the expense of poorer heat dissipation.
Inside a Victron LiFePO4 Battery
Notice all those good air channels between the Winstons all made redundant by the case. But if people knew that there were Winstons in the case they might consider just buying them separately and DIY it. So ... keep the blue plastic coming!
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vas
Well-known member
Thanks for the writeup, I guess there are 24v installations as well 8cells vs 4, any catches you know of? Ie are all controller boards suitable?
Final q, how do you define high discharge? Running a 80A@24v load is acceptable or not fe?
Final q, how do you define high discharge? Running a 80A@24v load is acceptable or not fe?
Poey50
Well-known member
24 volts is no problem. That particular BMS is expandable up to 255 cells so 8S would definitely be no problem. All BMSs would cover 24v.
The longest life comes from low discharge and charge what is sometimes called 'fractional C use' (with C = capacity of the battery) which is anyway typical of marine use. I've tested my 270 ah battery with a 90amp load and the temperature only rose by 3 degrees above ambient. That is a 0.3C discharge which is sometimes mentioned as a good limit for long life. It would be regularly charging and / or discharging at 1C or above that could shorten life expectancy through heat. By and large LFP thrives in the same temperatures as humans do.
Temperature and longevity discussed here.
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Mikedefieslife
Member
Bought mine a year ago. That is delivered cost to La Linea. About 8-9 days from China they landed in Germany where they took 2 days to be delivered to Spain.
Heat has been mentioned in the thread. I think for typical boat usage this isn't going to be a big problem. If you have an electric motor as an engine that is another matter. My maximum continuous load is about 90a (electric water heater). I seldom draw much more than 25a at a time, and that would be with the watermaker running in addition to the usual appliances. Ambient temps here are around 31c. 32c in my saloon, and 31c in the battery compartment. The highest temps I've seen so far when loaded is 35c. Normal daily range is more like 32-34c.
Without water cooling they will never be below ambient, so one just has to accept that like any other chemistry, they lifespan might be a little shorter than is regularly kept at 25c.
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Poey50
Well-known member
I was about to say that is a like-for-like drop in costs of 15% but seeing the delivery time it sounds like yours came by air. Mine was a 35 + days delivery by sea.
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Mikedefieslife
Member
Aha, you're right.
For 4pcs 3.2v 271ah LiFePO4 Cell’s, USD165/pcs, sub total USD660
For 4pcs Copper connector with M6 screw, USD8
Shipping fee to door: USD236
Delivery time: 5-7days
Sub Total USD904 + 5% for paypal fees
For 4pcs 3.2v 271ah LiFePO4 Cell’s, USD165/pcs, sub total USD660
For 4pcs Copper connector with M6 screw, USD8
Shipping fee to door: USD236
Delivery time: 5-7days
Sub Total USD904 + 5% for paypal fees
Poey50
Well-known member
My equivalent cell price was 620 USD so, in fact, only a 6% drop in a year.
JohnGC
Active member
Thank you for this write-up and for the links. There is a lot of information , I have begun absorbing it.
I have one observation and one question.
The plastic layer you used to insulate the heater dissipation sheet from the cells might be improved by using this https://uk.farnell.com/bergquist/q3ac-300mmx300mm-sheet/q-pad-3-005-12-x12-sheet/dp/681465
Although if it is only a thin sheet it won't make enough difference to justify the cost.
You plan to use a charge regime between 25% and 85% (or thereabouts). How will manage that? I guess the 85% can be set by the charger maximum voltage and the 25% can be monitored manually . Or do you have something more elaborate in mind?
I have one observation and one question.
The plastic layer you used to insulate the heater dissipation sheet from the cells might be improved by using this https://uk.farnell.com/bergquist/q3ac-300mmx300mm-sheet/q-pad-3-005-12-x12-sheet/dp/681465
Although if it is only a thin sheet it won't make enough difference to justify the cost.
You plan to use a charge regime between 25% and 85% (or thereabouts). How will manage that? I guess the 85% can be set by the charger maximum voltage and the 25% can be monitored manually . Or do you have something more elaborate in mind?
Poey50
Well-known member
Thanks for the interesting suggestion -- just to be clear that is a sheet that insulates but has good thermal conduction properties?
A good question about how to manage the upper and lower charging targets. It may be possible to set the upper state of charge through setting the upper voltage limit making use of the increase in voltage at the upper knee and setting all chargers to finish at that voltage. But you can see from the curve below that 85% is still on a relatively flat section so SOC might be hard to pinpoint with end voltage.
These don't need to be precise as there is no danger of damage to the cells (unlike if charging to 100% or discharging to 0%).
So I will probably use the relay on my Victron BMV712 to sound an alarm to remind me to end charging. It's not critical if I forget as the charging sources will stop around 90-95% (I need to experiment) and of course, the final backstop is the high voltage disconnect of the BMS but I don't want to rely on that.
For the lower limit I think I'll alarm on 20% and again there is the low voltage disconnect as a backstop.
All this is probably going to be clearer when I've done some sea trials.
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JohnGC
Active member
Thanks for the interesting suggestion -- just to be clear that is a sheet that insulates but has good thermal conduction properties?
A good question about how to manage the upper and lower charging targets. It may be possible to set the upper state of charge through setting the upper voltage limit making use of the increase in voltage at the upper knee and setting all chargers to finish at that voltage. But you can see from the curves below that 85% is still on a relatively flat section so SOC might be hard to pinpoint with end voltage.
These don't need to be precise as there is no danger of damage to the cells (unlike if charging to 100% or discharging to 0%).
So I will use the relay on my Victron BMV712 to sound an alarm to remind me to end charging. It's not critical if I forget as the charging sources will stop around 90-95% (I need to experiment) and of course, the final backstop is the high voltage disconnect of the BMS but I don't want to rely on that.
For the lower limit I think I'll alarm on 20% and again there is the low voltage disconnect as a backstop.
All this is probably going to be clearer when I've done some sea trials.
The sheet material is most often used in small pieces to electrically isolate devices such as MOSFETs from heatsinks. It's used instead of mica insulators and thermal grease. Because it can be compressed, it is able to conform to the surface irregularities and so transfer the heat better, this was the function done previously by the grease. Different thicknesses give different levels of voltage isolation. As you see it's also available in larger sheets; it can be easily cut. But if your plastic sheet is thin, you won't gain a lot by using it.
For the SOC limits, it is the life expectancy of the cells I was thinking of rather than the safety. I'll be very interested in your observations once you begin to use the battery in anger.
I'm considering LiFePO4 for our new (to us) boat. It already has a lot of Mastervolt kit and I could just drop in a Mastervolt LiFePO4 in place of the AGM, but that would be a lot more expensive than DIY version which is something I would enjoy doing. Time will tell.
Poey50
Well-known member
It really is a satisfying project. Let us know how it goes.
