Replacing house batteries project
- Thread starter SimonNZ
- Start date
Tranona
Well-known member
"normal folk" is the key. Advocates of lithium in particular, but of batteries in general almost always concentrate on the properties of the type they are promoting rather than starting the other end and asking what the requirements are - that is how much of your storage capacity do you use in a daily cycle and how many discharge cycles do you expect to use. Second question is what mechanisms do you have for replacing the energy you use in a cycle.
A 24/7 liveaboard will have very different needs from a "weekend" sailor, or an owner of a 26' basic boat very different from a state of the art 40 footer. The vast majority of boaters are in the "weekend" category so maybe 50 cycles a year (based on a day being a cycle) - in other words about 1/7th of a full time liveaboard. So clearly large numbers of cycles are less important. Broadly speaking FLA (Leisure) type batteries are good for between 5-700 cycles, AGMs 1000-1500 and lithium 2-3000. Reported life of leisure batteries is in the 5-10 years, AGMs 10-15 years for "normal" users.
To achieve this sort of life you need to have a charging regime that keeps the batteries within the "safe" range - 40-90% SOC (it is difficult to fully charge with onboard means when cruising). The use of mains charger is valuable or alternatively if on a swinging mooring for example, a solar panel is key to be able to start a "cycle" - weekend away with maybe 2 overnight stops at anchor as motoring and basic solar is unlikely to replace more than half of what you use.
Based on my own experience over 6 seasons with my Bavaria 33 I found my typical daily consumption was 80amps including fridge but no night sailing. Motoring put in about 20-30A a day so a deficit over a 2 night weekend of between 100-120 amps. The house bank was 3*95Ah AGMs so at the end of that cycle the SOC would be 60%+. Plug into shorepower and next day comfortably on float. Over the 6 seasons there was no measurable deterioration in performance of the batteries (nor of the other 2 of the same type for engine start and bow thruster/windlass). So every expectation that they would last 15 years.
Personally I think that leisure batteries or AGMs still offer the best solution for "normal" usage, but the falling cost of AGMs means that the price premium is now significantly less than the greater number of cycles - something like 50% potential longer life for a 30% premium.
With my latest boat daily consumption will be lower - no fancy integrated electronics, no pressure water, no fridge (at the moment) so I have cut back to 2*95Ah but still a dedicated start and bow battery.
PaulRainbow
Well-known member
For your usage pattern Lithium would be a waste of money.
Cutting back to 2x95ah wouldn't be a good idea.
Separating them into two banks would be an even worse idea. The first battery would cycle a ridiculous amount, you'd always need to switch to the second battery and they would take longer to charge if you did that individually.
Without making calculations or closely watching a battery monitor (the Smartshunt would be a good idea though) just ask yourself, how often do you need to switch to the second battery bank ?
I suspect that 3x100ah AGMs would be fine for your usage, particularly as you have 310w of solar.
If you can fit batteries with a slightly higher Ah rating in the same place i would do so, the added cost would be small.
Skimping with battery capacity is a false economy, you cycle the batteries harder, so they die sooner.
ckris
Member
I am one of the numpties who bought a drop in replacement LiFePO4, all be after 5 years of on and off research and agonising. Early on I almost bought cells to build my own but never quite was confident enough to go through with it. Then I nearly went for Leoch lead carbon as it seemed like a good compromise, but decided there was still too many downsides (mainly on charging efficiency). Then the price of drop in replacements became so much cheaper but I worried about alternator protection, B2B chargers, the problem of suddenly "going dark" (the BMS switching off the battery at a bad time) and all the extra add-ons that made it a costly and complicated exercise. Finally I read about hybrid (pairing lithium with FLA), it made sense to me so I tried it. For me it has been a revelation, it just works and life on board has become so much simpler (and quieter with significantly less engine running to charge batteries). Of course, everyone's set up and usage is different but I would find it hard to think of a situation where I would not prefer LiFeP04.
A few points by way of contrast :
There are decent UK suppliers who offer good quality drop in LiFePO4 for much less than than the premium brands (eg Life Batteries, Fogstar). £3.50 - £4 per usable AH is quite doable, cheaper than premium AGMs and similar to cost of mid range AGMs. It is quite possible to use 100% of the rated capacity of LiFeP04 though my BMS is set a little more conservatively but still can use 90%+ if needed.
Once you take into account LiFePO4 lifecycles, the cost is considerably less. Of course, if you properly look after good quality FLA this may be irrelevant but I replaced my FLA house batteries 4 times in 15 years so will be significantly cheaper for me. My experience of FLAs, particularly cheap ones, is they never get any where near the rated cycles, particularly when it was a constant battle to bring up to full charge (mid-river mooring no shorepower). I would bet the Eurobatt 120 would not last much more than 100, maybe 200 cycles in my situation, after 50 cycles I would would expect to start noticing capacity reducing. I will be surprised if Lithium does not last 20 times longer.
I mainly charge using a standard Volvo 115A alternator, the AGMs used to start charging at 70A but charge acceptance would rapidly reduce, after 30 mins it might be 35A, after an hour it would be 20A at which point I would switch off the engine with the batteries at 80-90% SOC. Now the LiFeP04 charge at a fairly constant 60A with only a small drop off in charge acceptance until they are almost fully charged. Overall I think it has more than halved the time I need to run the engine probably saving £175 pa on diesel cost alone.
Even better, when returning to the mooring on a Sunday I used to leave the engine running until the last possible moment until I left the boat in an attempt to get the batteries as fully charged as possible, then the 100w solar panel in the summer would get the batteries to full charge by Tuesday or Wednesday before sitting at float until I get back to the boat the following weekend. Now I switch off the engine as soon as I return to the mooring, enjoy the peace and quiet happy in the knowledge that I can leave the LiFeP04 at partial soc with no worries Then during the week I get ALL the benefit of solar using every amp to bring the LiFeP04 up to maybe 80% charge by the time I get back to the boat, just motoring off the berth is enough then to fully charge for the weekend ahead. I rarely need to run the engine just to charge the batteries now, it used to be a daily routine that is a beautiful thing not to have to do.
Another thing that mattered to me, as well as 100AH LiFeP04 being approx the equivalent usable capacity of 2 x 100AH FLA, they are lighter and easier to move around, but also the form factor (box size) is often smaller. Depending on the size of your battery box you may be able to get 150AH or 200AH in the same space as a you kept a single 100AH FLA - that could be 3x or 4x usable capacity in the same space.
Final unexpected benefit for me was the higher voltage, having your system sit at 13+v most of the time rather than 12.5 or less (under load) means all those pesky voltage drop problems you may have at the end of long cable runs (the fridge dropping out etc) magically go away!
I always felt like FLA was a battle: keeping an eye on the battery monitor to to make sure we charged before they got below 50% SOC, trying to work out how much the capacity was degrading, worrying about not getting to 100% SOC often enough and the hours of running the engine on low load. The LiFePO4 was about the same price as the AGMs we would have bought anyway, they have saved us diesel cost + less wear on the engine, should last for as long as we own the boat and have made life on board much more relaxed and quieter!
A few points by way of contrast :
There are decent UK suppliers who offer good quality drop in LiFePO4 for much less than than the premium brands (eg Life Batteries, Fogstar). £3.50 - £4 per usable AH is quite doable, cheaper than premium AGMs and similar to cost of mid range AGMs. It is quite possible to use 100% of the rated capacity of LiFeP04 though my BMS is set a little more conservatively but still can use 90%+ if needed.
Once you take into account LiFePO4 lifecycles, the cost is considerably less. Of course, if you properly look after good quality FLA this may be irrelevant but I replaced my FLA house batteries 4 times in 15 years so will be significantly cheaper for me. My experience of FLAs, particularly cheap ones, is they never get any where near the rated cycles, particularly when it was a constant battle to bring up to full charge (mid-river mooring no shorepower). I would bet the Eurobatt 120 would not last much more than 100, maybe 200 cycles in my situation, after 50 cycles I would would expect to start noticing capacity reducing. I will be surprised if Lithium does not last 20 times longer.
I mainly charge using a standard Volvo 115A alternator, the AGMs used to start charging at 70A but charge acceptance would rapidly reduce, after 30 mins it might be 35A, after an hour it would be 20A at which point I would switch off the engine with the batteries at 80-90% SOC. Now the LiFeP04 charge at a fairly constant 60A with only a small drop off in charge acceptance until they are almost fully charged. Overall I think it has more than halved the time I need to run the engine probably saving £175 pa on diesel cost alone.
Even better, when returning to the mooring on a Sunday I used to leave the engine running until the last possible moment until I left the boat in an attempt to get the batteries as fully charged as possible, then the 100w solar panel in the summer would get the batteries to full charge by Tuesday or Wednesday before sitting at float until I get back to the boat the following weekend. Now I switch off the engine as soon as I return to the mooring, enjoy the peace and quiet happy in the knowledge that I can leave the LiFeP04 at partial soc with no worries Then during the week I get ALL the benefit of solar using every amp to bring the LiFeP04 up to maybe 80% charge by the time I get back to the boat, just motoring off the berth is enough then to fully charge for the weekend ahead. I rarely need to run the engine just to charge the batteries now, it used to be a daily routine that is a beautiful thing not to have to do.
Another thing that mattered to me, as well as 100AH LiFeP04 being approx the equivalent usable capacity of 2 x 100AH FLA, they are lighter and easier to move around, but also the form factor (box size) is often smaller. Depending on the size of your battery box you may be able to get 150AH or 200AH in the same space as a you kept a single 100AH FLA - that could be 3x or 4x usable capacity in the same space.
Final unexpected benefit for me was the higher voltage, having your system sit at 13+v most of the time rather than 12.5 or less (under load) means all those pesky voltage drop problems you may have at the end of long cable runs (the fridge dropping out etc) magically go away!
I always felt like FLA was a battle: keeping an eye on the battery monitor to to make sure we charged before they got below 50% SOC, trying to work out how much the capacity was degrading, worrying about not getting to 100% SOC often enough and the hours of running the engine on low load. The LiFePO4 was about the same price as the AGMs we would have bought anyway, they have saved us diesel cost + less wear on the engine, should last for as long as we own the boat and have made life on board much more relaxed and quieter!
Poey50
Well-known member
Just a couple of points as I'm in a rush.
The lifetime cost of LFP compared to AGM (and probably other lead acid depending on how both are used) is in favour of LFP. I think that argument is over. Of course, not everyone wants to, or can, make the upfront investment. For example, anyone planning to only keep the boat for a couple of years will not get their money back in the resale price.
For me the main questions are whether anyone considering LFP can make a safe and seaworthy system - and one that they actually need for their type of sailing.
ABYC explicitly rule out hybrid systems and it is likely that ISO have or will go the same way. This matters since eventually insurers - via surveyors - will demand compliance with emerging regulations. Their argument, as I understand it, is that two such different chemistries should not be connected in parallel. I know there are counter-arguments but that is what the emerging standards are likely to specify.
Buying drop-in batteries on cost per watt-hour is a bad idea. Paying for reliability is much more important and because the cells, welding, wiring, and BMS are hidden away in the case then lower costs can be gained by sub-standard construction and components. See the various break-down videos on Will Prowse YouTube channel, for example.
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Pete7
Well-known member
Ckris, you're not alone, we also paralleled our LFP with a flooded lead acid battery. Two years on, couldn't be happier
This in conjunction with lots of solar has enabled lots of electric cooking on sunshine. Problem with ABYC is when pressed to explain why not and produce the evidence to show why not, there is silence. Thankfully they are only an advisory group.
Pete
goeasy123
Active member
Why is hybrid a bad idea?
Poey50
Well-known member
I'm not confident that it is. Zwerfcat makes a convincing argument in favour, for example, - Lithium-Hybrid -
Rod Collins, a powerful voice on the ABYC regulatory side, is adamantly against. My point is that anyone buying and installing LFP needs to look to the long term (otherwise what is the point?) which, for insurance purposes, will probably mean compliance with regulations. At the moment these are at advisory level (TE13 for ABYC) but are likely to be adopted as regulation this year. Europe will likely follow the US. It may be that things will be much looser that this and insurance companies will be more relaxed. But insurers are twitchy and I've heard of people being refused insurance after installing LFP. Time will tell. My conservative approach is to be as compliant as possible to the regulations as they emerge, although if insurers end up insisting on professional installations only, then I am also stuffed.
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geem
Well-known member
Add Trojan T105s and Numax leisure batteries. My Numax were 8 years old when I sold the boat. They were used for for weekend sailing/summer hols and only charged via solar. My T105s are 4 years old and used as full liveaboard batteries so are discharged to 80% SOC each night. Tested recently and still perfect. They are subject to high heat in the Caribbean and super high heat in the Caribbean summer
GHA
Well-known member
Chatting with another boat today, another option could be have a smallish drop in LiFePo just to power maybe the fridge & laptops or whatever so the precious lead acid doesn´t get cycled anywhere near as much overnight. DC/DC buck boost to stick some charge back in during the day when the sun is up.Ckris, you're not alone, we also paralleled our LFP with a flooded lead acid battery. Two years on, couldn't be happier
The Catl LeFePo4 I bought recently says on the datasheet 4,000 cycles from full to 2.5v @ 0.5C discharge. That´s basically running completely flat every single night for nearly 11 years after which the capacity will be 50% of what they are new. Under constant temperature laboratory conditions but even so , a drop in could run for years and years taking lots of cycling away from the lead acid.
goeasy123
Active member
The options we've gone for is swapping ye olde LA with lead carbon (LC). These charge faster and are therefore experiencing better SOC characteristics over time. To get the benefits of LiFePo4 we have an Echoflow Delta. The LC is normally charged by mid afternoon on summer Med days. On the odd occasion we need more juice we can put the Echoflow onto the bus. There are various ways to do this,... in theory. But since getting the LC's we've never had to do it. Nevertheless, the Echoflow is very useful as you can take it off the boat, it can run powertools and electric cooking gadgets.
In our case, not in a million years would I trust a LiFePo4 only setup. We make log passages and spend time in remote locations. The binary failure mode of LiFePo4 is not tolerable. I'd like to solve this dilema with a hybrid system, but for some reason that's a problem with ABYC. Why?
nova_castria
Member
Alternator output needs to go direct to engine battery then get a b to b charger to charge lithium . The charge rates on lithium are very high .
Poey50
Well-known member
There are two meanings of hybrid when it comes to LFP design. The type that the ABYC people are against is the paralleling of LFP with lead acid. The other meaning is the use of lead acid for essential safety loads leaving LFP to run everything else. There would be no objection to that and it would be the system I would install if forced to use drop-ins.
Morgan's Cloud - until recently, opposed to LFP - now show a safe and elegant design. All charging sources go direct to the LFP bank (so external regulation of the alternator is necessary). The LFP bank is made up of modestly-sized drop-ins connected in parallel. The idea here is that high current demands are then shared across several BMSs which makes the failure of the MOSFETs less likely (since they are each contributing lower current) and non-catastrophic since one drop-in taken out by its BMS leaves others to manage. The lithium pack maintains the lead acid battery powering essential services via a B2B but there is no paralleling of LFP or lead acid at any point. In the event of a complete failure of the LFP bank the lead acid would begin to lose power so the charging bus can be then switched over to charge the lead acid battery directly. There is a 1+2 BlueSea switch which allows this (not a 1+2+both switch). The voltage sense lead from the external regulator has to be connected to the charge side of the 1+2 switch in order to sense the specific battery being charged.
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GHA
Well-known member
Just had a play combining Trojans with LiFePo4 then running a compressor through an invertor.
LiFePo4 voltage & current gauges top right on the tablet.
Drawing about 40A from LiFePo4 & nest to nothing from Trojans, maybe just bleeding off a bit of surface charge.
Trojans had a charge yesterday & voltage still above 13v.
Start of the video is switching the 1/2/both switch to combine them. (Should get a few on here frothing at the mouth
)
And again with hoover added. This time LiFePo4 voltage sags enough for the trojans to actually do something, first time voltage wasn´t low enough, trojans were still accepting a little charge.
LiFePo4 voltage & current gauges top right on the tablet.
Drawing about 40A from LiFePo4 & nest to nothing from Trojans, maybe just bleeding off a bit of surface charge.
Trojans had a charge yesterday & voltage still above 13v.
Start of the video is switching the 1/2/both switch to combine them. (Should get a few on here frothing at the mouth
)And again with hoover added. This time LiFePo4 voltage sags enough for the trojans to actually do something, first time voltage wasn´t low enough, trojans were still accepting a little charge.
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PaulRainbow
Well-known member
Just had a play combining Trojans with LiFePo4 then running a compressor through an invertor.
LiFePo4 voltage & current gauges top right on the tablet.
Drawing about 40A from LiFePo4 & nest to nothing from Trojans, maybe just bleeding off a bit of surface charge.
Trojans had a charge yesterday & voltage still above 13v.
Start of the video is switching the 1/2/both switch to combine them. (Should get a few on here frothing at the mouth
If the Trojans and LiFePo4s are in parallel that's to be expected. Because the LiFePo4s have a much lower internal resistance most of the current will naturally be supplied by them. Basically, all the Trojans will be doing is trying to charge the LiFePo4s back up.
That's one of the "benefits" of some of the hybrid (parallel) systems. You connect the loads to the LiFePo4s and the charging to the lead acids. (simplified explanation)
GHA
Well-known member
Nope, check the voltage. Trojans still burning off a little surface charge, trojan/LiFePo4 voltage never dips low enough for the trojans to do anything significant. Trojans have no idea what is connected, voltage drops below cells voltage, current will flow out, in this case to the inverter.
Impossible for the trojans to charge LiFePo4´s unless there are way down to like below 20% SOC
Edit - Current flowing in/out of LiFePo4 below, never gets above zero. Zoomed in there's actually a tiny blip from the LiFePo4 into the trojans when they get combined. More accurate on the 2nd video would be to say the trojans help a little by lessening the current flowing out of the LiFePo4. But they never try to charge, physically impossible.
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Slahm
New member
Question, as I am also buying batteries right now... Do the lithium batteries not have twice the usable capacity as the lead acid, and therefore the price being 3x is more like 1.5x? Buying 500 AH batteries that you can only use 250 AH or less seems to me like a bit of a fib by the dealers.
geem
Well-known member
You can't discharge lifepo4 for to 0% and expect a good life out of them. 20% SOC is considered normal. Some only drop them to 30%. Charging to 100%SOC will also shorten the life if you leave them at 100% with no load connected. In addition, if you are using any battery technology in high ambient conditions >30degC you are not going to see anywhere near the predicted life from the batteries.
Poey50
Well-known member
Just had a play combining Trojans with LiFePo4 then running a compressor through an invertor.
LiFePo4 voltage & current gauges top right on the tablet.
Drawing about 40A from LiFePo4 & nest to nothing from Trojans, maybe just bleeding off a bit of surface charge.
Trojans had a charge yesterday & voltage still above 13v.
Start of the video is switching the 1/2/both switch to combine them. (Should get a few on here frothing at the mouth
Sorry to report very little frothing!
It's a while since I read the Zwerfcat stuff but from memory they custom built their own BMS and it wasn't as straightforward as it appeared at first glance. The only big argument I can see in favour of paralleling LFP and lead acid is that in the event of an BMS shut-down you keep a battery in the system so there is no damaging voltage spike or sudden loss of power. However, because LFP sits at a higher voltage than even a full lead acid (once the surface charged has been wiped off) then the LFP will be doing all the work until its voltage drops level to the lead acid. You might only have 20% left in the LFP at that point. I think Zwerfcat arrange for the low voltage cut off on the BMS to be high enough not to damage the LFP but basically then the lead acid carries on alone with the LFP shut down. I suspect one concern from regulators is that the BMS is being used in the day to day management of charge and not reserved solely for catastrophic protection - a last line of defence, which many - including me - prefer.
Problems would also come with charging the combination back up. The LFP can be fully charged at anything above 13.6 pack voltage. And that assumes you want to charge to full. That is not going to be sufficient to bring the lead acid up to full so sulfation and a short life for the lead acid are risks. One option is to have some additional charging (a dedicated solar panel, for example) to help the lead acid, but already this simple hybrid solution is looking more complex. As said above, using the lead acid to separately power essential / safety-critical systems looks to me the better use of the characteristics of both LFP and lead acid.
Edit: just an after-thought. If an LFP, connected in parallel to a small lead acid battery, is discharged only to 20% and then recharged, the lead acid barely gets used. Paradoxically this is an advantage since the lead acid is then kept on a near permanent trickle charge from the LFP and is not then in danger of sulfation. That could be a long-lasting solution. The only function of the lead acid is then purely to provide a buffer against load dump / voltage spikes, not to add capacity to the LFP.
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GHA
Well-known member
Doubt the trojans will ever be really used again, that test was just to get some data & see what happens. The amount of data logging I know exactly how the liFePo are doing, no point using the trojans for anything. Welding big rods I might parallel just to get a bit lower draw from the LiFePo4 but that will be pushing the inverter as well so will likely not actually happen. . With ig loads any BMS current overload feature can be turned off, I´ll know exactly what's going on. Actually, 2mm welding rods are fine , tried that already. Not even down to 3v per cell. Might have Bart Simpson screaming "run for your lives" as a low voltage alarmSorry to report very little frothing!
It's a while since I read the Zwerfcat stuff but from memory they custom built their own BMS and it wasn't as straightforward as it appeared at first glance. The only big argument I can see in favour of paralleling LFP and lead acid is that in the event of an BMS shut-down you keep a battery in the system so there is no damaging voltage spike or sudden loss of power. However, because LFP sits at a higher voltage than even a full lead acid (once the surface charged has been wiped off) then the LFP will be doing all the work until its voltage drops level to the lead acid. You might only have 20% left in the LFP at that point. I think Zwerfcat arrange for the low voltage cut off on the BMS to be high enough not to damage the LFP but basically then the lead acid carries on alone with the LFP shut down. I suspect one concern from regulators is that the BMS is being used in the day to day management of charge and not reserved solely for catastrophic protection - a last line of defence, which many - including me - prefer.
Problems would also come with charging the combination back up. The LFP can be fully charged at anything above 13.6 pack voltage. And that assumes you want to charge to full. That is not going to be sufficient to bring the lead acid up to full so sulfation and a short life for the lead acid are risks. One option is to have some additional charging (a dedicated solar panel, for example) to help the lead acid, but already this simple hybrid solution is looking more complex. As said about, using the lead acid to separately power essential / safety-critical systems looks to me the better use of the characteristics of both LFP and lead acid.
Really not in the least bit interested in what any regulatory body says, they need to cater for the masses.
Spending too much time in here again, log off & delete password - see ya'll in a while
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