ckris
Well-Known Member
Works the same way in a sailing boat! Scales up and down pretty well....
Domestic batteries replacement
- Thread starter Nina Lucia
- Start date
Poey50
Well-Known Member
Let us know how you get on. One thing to bear in mind - if you haven't already - is to monitor the health of the lead acid. LFP should last a lot longer than the lead acid so the LA should go first. The LFP will disguise the failure of the LA including up to the point where it pours its considerable power into the dying LA. A temperature sensor on the LA might be useful.
ckris
Well-Known Member
Yes, it is funny the paradigm shift where you start to worry about protecting the more expensive lead acid!
I am confident it will live a long and happy life spent on float charge most of the time.
Why do you think the lifepo4 it will pour considerable power into a dying LA? How is it any different to having two LA in parallel with one dying first?
ckris
Well-Known Member
While this is a point of reference worth thinking about, this is a US standard that is not universally adopted....and not even in the abyc yet.
Nina Lucia
Well-Known Member
Now when I gave you all the information, you moved on to anchors, by the way Rockna or…?
ckris
Well-Known Member
Supplier was Life Batteries. Key bms parameter is pack under/over voltage protection set ar 12v and 14v.
This cycles between ~10% to 90% soc and will cut out before alternator reaches 14.2v standard regulated setting, so long motors do not overcharge.
Why do you say "misleadingly" attractive? I know it might not work for all set ups and you need to check a few things but in many cases it will work perfectly and be a robust, effective and simple way to get benefits of lifepo4.
Poey50
Well-Known Member
It is already in the ISO.
geem
Well-Known Member
The ISO standard is likely to follow the ABYC standard. The white paper becomes the standard. Thats how it works. If you choose to ignore best practise you risk future insurance problems. Your installation is not considered good practise. You assume the BMS will never fail. It's electronic and there are few actually built to withstand the marine environment specifically. A good installation will consider the what ifs? Class T fusing is readily available in the UK. I bought some a month ago.
There is no such thing as lithium drop in replacement
Poey50
Well-Known Member
With a pair (for example) of lead acid they are likely to deteriorate at a similar rate and the loss of capacity will become obvious over time. If one cell shorts and effectively become a 10 volt battery this is already not great news if the pair are on charge as the heat will build.
With a pair consisting of LFP and lead acid the deterioration of the lead acid will be masked by the LFP (as said). At 3.65 volts per cell a fully charged LFP with low internal resistance could stand at 14.6 volts (I know you are using a lower figure) and so the higher voltage and lower resistance is a step up from the equivalent lead acid pair. For any but the lowest state of LFP charge the voltage of LFP is higher. As above the worst situation is when the hybrid pair are on charge.
When I used all lead acid I had a simple heat sensor on each battery and would do a quick check when charging. There are plenty on eBay for little money.
It would be my understanding that if lightly used the lead acid would be mostly held at a low float setting (around 13.2 volts) and would be in lead-acid heaven and could lead a very long life. The concerns are for deeper discharging when - on a sailboat at least - it may be difficult to return often enough to 100% to avoid sulfation. Many sailors already kill their lead acid batteries through chronic under-charging. To have LFP taking charging priority certainly wouldn't improve their situation. As said, if it were me, I'd be monitoring the lead acid health periodically.
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Poey50
Well-Known Member
It is already in the ISO - ISO/TS 23625:2022. You have to pay 160 euros for it but it is likely to be the same as the 2021 preview available here.
https://cdn.standards.iteh.ai/samples/76438/9f817478349b4f4f8770642cb1748902/ISO-TS-23625-2021.pdf
It's 4.9. "In normal operation, different battery chemistries should not be connected in parallel or in series."
Poey50
Well-Known Member
Sensible settings - I'd heard that Life Batteries do that.
"Misleadingly attractive" since I doubt that the downsides are well known. Personally I think the best LFP system for the DIY installer is the dual bus system (it's what Victron use on their mega-costly systems) in which charge and load circuits are separated and the BMS uses external relays so large current never flows through the BMS. I think the best lead-acid / LFP hybrid system using drop-ins is the one now promoted by Morgan's Cloud in which all vital loads continue to be powered by lead acid and the nice-to-haves are powered by LFP. the lead acid being maintained by charging by a B2B from the LFP. It's a low-risk system making use of the benefits of both chemistries but never paralleling them.
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ckris
Well-Known Member
I thought we were talking about t class fuses in the standards, is that in iso?
Poey50
Well-Known Member
6.9 deals with the amperage interrupt capacity of fuses. It simply makes clear that AIC capacity of the fusing must be adequate for the LFP but allows individual fuses on LFP in parallel battery banks. That means for example that MRBF fuses on each battery may be able to share the total AIC of the bank. A single mega-fuse or ANL or MRBF would not meet the AIC requirement. For a single main fuse only the Class T (at 20,000 amps AIC) would do, so effectively that is the only option. I believe the ABYC will specify Class-T but, either way, Class-T will in most cases be required.
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ckris
Well-Known Member
OK, so what is the short circuit current of 100ah lifepo4 v 100ah agm?
Genuine question, it is a while ago since I googled this and remember the huge class t interrupt current but could never find anything definitive to put this into context of a small lifepo4 compared to same size agm....
Poey50
Well-Known Member
I can't quote an exact figure but when I looked into it three years ago when designing my system, the Bluesea MRBF didn't give enough AIC headroom for my 270 ah pack so I went Class-T. I also remember that the MRBF considerably exceeded either the ANL or mega fuse but I can't find those figures. With your set-up using a 100ah LFP, I think you would be OK with MRBF. Cheaper, smaller to fit and widely available.
migs
Well-Known Member
Here are some recent thoughts on fusing; this is from the DIY solar power forum:
Does anyone have insight into changes coming in the ABYC (American Boat and Yacht Council) wiring standard?
I was recently told by a Victron Ambassador that the ABYC is going to change their spec to allow MRBF fuses on single LiFePO4 batteries but still require Class T for multiple batteries in parallel. The implication is that 10KVA AIC is sufficient for single batteries but when LiFePO4 batteries are in parallel, a higher AIC is needed.
Can anyone confirm this? If so, can you provide any studies or background that this decision is based on?
Then there is this research: http://pe.org.pl/articles/2017/5/13.pdf which concludes that the prospective short circuit current (PSSC) for an LFP battery is around 6C. i.e. 600A for a 100Ah cell and so well within the 6kA rating of an ANL fuse.
Also, this calculation from the DIY solar power forum:
Looking from manufacturer specified graphs it looks like one cell would have:
http://www.dcmax.com.tw/LF105(3.2V105Ah).pdf
3.30v @0.33C discharge (0.33*105=35A
3.07v @ 3C discharge (3*105=315A)
extrapolating to dead short and 0 volts (dI/dU) we get 280A/0,23V = 1217A short circuit current per cell. 2 cells in parallel would be ~2400A.
LiFepo4 seem to have rather small short circuit current compared to something like power-optimized Li-Po.
But that is what makes it safer...
(5Ah Li-Po is capable of 2000A short circuit current i.e. 400C)
extrapolating to larger systems 6000A breaking capacity ANL fuse would be ok up to 600Ah LiFePo4.
A separate point to take into account is the resistance of all the various terminal / busbar / cable contacts, plus the cable between battery and fuse; this is most likely going to be in the milliohm range and 3000A across 4 milliohms is 12V
So, I guess the whole subject is still in a state of flux…
Does anyone have insight into changes coming in the ABYC (American Boat and Yacht Council) wiring standard?
I was recently told by a Victron Ambassador that the ABYC is going to change their spec to allow MRBF fuses on single LiFePO4 batteries but still require Class T for multiple batteries in parallel. The implication is that 10KVA AIC is sufficient for single batteries but when LiFePO4 batteries are in parallel, a higher AIC is needed.
Can anyone confirm this? If so, can you provide any studies or background that this decision is based on?
Then there is this research: http://pe.org.pl/articles/2017/5/13.pdf which concludes that the prospective short circuit current (PSSC) for an LFP battery is around 6C. i.e. 600A for a 100Ah cell and so well within the 6kA rating of an ANL fuse.
Also, this calculation from the DIY solar power forum:
Looking from manufacturer specified graphs it looks like one cell would have:
http://www.dcmax.com.tw/LF105(3.2V105Ah).pdf
3.30v @0.33C discharge (0.33*105=35A
3.07v @ 3C discharge (3*105=315A)
extrapolating to dead short and 0 volts (dI/dU) we get 280A/0,23V = 1217A short circuit current per cell. 2 cells in parallel would be ~2400A.
LiFepo4 seem to have rather small short circuit current compared to something like power-optimized Li-Po.
But that is what makes it safer...
(5Ah Li-Po is capable of 2000A short circuit current i.e. 400C)
extrapolating to larger systems 6000A breaking capacity ANL fuse would be ok up to 600Ah LiFePo4.
A separate point to take into account is the resistance of all the various terminal / busbar / cable contacts, plus the cable between battery and fuse; this is most likely going to be in the milliohm range and 3000A across 4 milliohms is 12V
So, I guess the whole subject is still in a state of flux…
Poey50
Well-Known Member
It sounds like the ABYC will follow the ISO on fusing.
Yes ... all figures look a bit provisional at the moment.
ckris
Well-Known Member
Thank you for the comments on fusing. I found the specs for my AGM batteries which quote internal resistance 4.80 and short circuit current 2,555a.
I also did not find anything definitive for the drop in Lifepo4. Life batteries website mentions resistance 20 milliohms which imply a short circuit current around 675A IF the internal short circuit protection fails. Which is pretty close to the 6C mentioned in the research migs found above. However, the Life batteries website quotes the same resistance for any size Lifepo4 battery which I am suspicious of.
My conclusion is that swapping out an AGM for drop in lifepo4 is not inherently more risky, higher IR plus the built in short circuit protection means it is safer than before.
I also am still not persuaded that class t fuse is necessary for small Lifepo4 bank - and appreciate Poey50 pointing out some alternatives. Having said that it is also clear that the Mega fuse installed a while ago was not adequate for the AGM only bank. Ironically you could argue it would be adequate for an equivalent lifepo4 bank : ) but regardless will upgrade that soon, maybe even to class t! So thank you for the folk who started that line of questioning even though it has been a bit of a rabbit hole for the LifePo4 addition.
Finally, apologies to Nina for hijacking her thread and turning it into an anchor type debate. I only commented because I was in a very similar position in discounting lithium because of the complex system upgrades and have been pleasantly surprised how a simple hybrid alternative can work. I am puzzled at the negative reaction this provokes and not seen any persuasive reasons yet why it is a bad idea. However, do not want to extend this further so maybe will start another thread sometime if anyone is interested in continuing that part of the conversation.
I also did not find anything definitive for the drop in Lifepo4. Life batteries website mentions resistance 20 milliohms which imply a short circuit current around 675A IF the internal short circuit protection fails. Which is pretty close to the 6C mentioned in the research migs found above. However, the Life batteries website quotes the same resistance for any size Lifepo4 battery which I am suspicious of.
My conclusion is that swapping out an AGM for drop in lifepo4 is not inherently more risky, higher IR plus the built in short circuit protection means it is safer than before.
I also am still not persuaded that class t fuse is necessary for small Lifepo4 bank - and appreciate Poey50 pointing out some alternatives. Having said that it is also clear that the Mega fuse installed a while ago was not adequate for the AGM only bank. Ironically you could argue it would be adequate for an equivalent lifepo4 bank : ) but regardless will upgrade that soon, maybe even to class t! So thank you for the folk who started that line of questioning even though it has been a bit of a rabbit hole for the LifePo4 addition.
Finally, apologies to Nina for hijacking her thread and turning it into an anchor type debate. I only commented because I was in a very similar position in discounting lithium because of the complex system upgrades and have been pleasantly surprised how a simple hybrid alternative can work. I am puzzled at the negative reaction this provokes and not seen any persuasive reasons yet why it is a bad idea. However, do not want to extend this further so maybe will start another thread sometime if anyone is interested in continuing that part of the conversation.
Poey50
Well-Known Member
The debate seems to lack unambiguous data on the AIC requirement of particular batteries. It does though seem clearer on fuses. Given the lower resistance and higher standing voltage of LFP than AGM it must, however, be the case that the AIC requirements for LFP will exceed AGM. Bluesea MRBF are rated for 10,000 amps; Bluesea Class-T at 20,000. ANL are lower than either of these and Mega-fuses lower still.
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ckris
Well-Known Member
? But the above suggests pssc for lifepo4 battery is 6C = 600A for a 100ah lifepo4.
My 100AH AGM specs say short circuit current = 2550.....equivalent to 25C.
Why must it be AIC requirements for LFP will exceed AGM - what am I missing?