Fuses and circuit breakers for LiFePO4

[hjohnson]

Originally Posted by Sailing Paul

Thanks, I was thinking about how to charge my small batteries away from shore power.

Regarding 100% charge, our usage pattern of the boat would typically mean no more than 100 days sailing between May and October, with frequent marina stops and probably no more than 50 cycles per year. Would it really be a problem charging to 100% for each cycle? The battery would be left for no more than 2 weeks at 100% SOC.

So we make pretty heavy use of our sailboat, though not as heavy as that. We’ve also had a lithium system for 2.5 years now.

Back in January, I went aboard to do some checking on the battery system (We were in a -12C cold snap, and my battery had alarmed out) and while there I plugged into my BMS to modify the settings a hair. As it turns out, over the 2 years of service at that point, I had done 15 total cycles, at least based on the counter in the BMS. That’s it. Despite having been out for several 2 week trips, multiple overnight trips, and so forth.

Once you get up to a certain size (we’re 460Ahr at 12v nominal), your biggest effect is calendar aging, rather than cycle aging. A cycle is defined as basically taking the battery from fully charged to fully empty, so if you’re just boucning between, say, 85% and 65%, it takes 5 of those to equal a cycle. Even longer if you’re hovering fairly high due to engine use or solar input.

[CaptainRivet]

Originally Posted by more

ussualy all european boat producer use nh 50ka fuse., you dont need nothing also betwen battery you dont need fuse by law.i dont reed certification books,becouse this is not my job .but if boat producer dont use fuse betven batery i also dont use. iaam not sure for big disconector but for off grid use i like use MCCB Moulded Case Circuit Breaker Battery with termal protection.also this is ussualy 25ka

Well i wish you luck if you have a battery related insurance claim...insurance will bail out easly.

[CaptainRivet]

Originally Posted by Sailing Paul

I want to know the impact on the battery given our proposed usage pattern. I would like the battery to be useful for 10 years (no more than 500 cycles). After that I suspect I would be able to replace with twice the capacity at half the price. The cost is about £400, for DIY build, with components and case from a reliable UK supplier.

Our daily usage is about 40Ah, maybe 50Ah in hot weather for the fridge, less if just sitting at anchor as no autopilot or nav instruments in use. So a 280Ah battery should go 5 days and we have 2X90Ah lead to push another day should we need it. This summer it is unlikely we would be away from shore power for more than 3 days, so initially we plan just to charge on shore power. Depending on how things go, I may buy some solar, although if prices keep falling adding another 280Ah LFP might be more cost effective and less hassle. I really cannot forsee us ever being away from shore power for 10 days. Alternator charging would be the last thing we added after more battery capacity and/or solar.

I currently have a couple of 3A LFP chargers and a 10A charger. I will look for a 20-30A charger for faster charging, but my question was really about whether it would be better for the battery to charge at 3A when we are in no hurry, as indicated by the manufacturer of my 60Ah battery, or does it really not matter?

If we are away from the boat for a couple of days, a 50Ah top-up to 80% SOC might also be preferable to using a 30A charger that takes it to 100% in a few hours.

Edit: what would the impact on the battery be if I did leave it at 100% SOC for 2 weeks?

Forget that small charger....with 280AH a 50A will be more appropriate.
Forget that 3 A chargers, they are hardly appropriate for your 18AH battery...the 10A you can put in parallel to the 30 or 50A charger or use the 10A for your main propulsion battery.

And yes its an issue to keep it at 100% SoC for 2 weeks...keep it at 60-70% SOC, you have enough capacity anyhow and the 10AH missing at your propulsion to full is quickly recharged, its lifepo4 and not lead.Like this with your small usage they will last far more then 10years.

[CaptainRivet]

What i would do is get a raspberry pi and put venus OS on it and install in your boat. But you need a victron smartshunt for that so VRM gets the battery data. Like this you have via victron VRM remote monitoring. Put the shorepower charger with its remote onto raspi with relay output. Then you can switch on at home via VRM app/internet interface your shorepower charger the night before and its charging your 280AH plus 50 and 60AH battery full and you can leave with full batteries.
Don't assume 280AH will go lower then 90Euro for garde A...thats already very low. But yes your concept makes sense to add another 280AH if thats not enough and charge via shorepower. Installing solar will be more expensive.
Done a big version of yours on a 44ft Beneteau with 3040AH LFP bank who goes out for a week till 10 days and then come back to his berth or into habour for a day to refill water, go shopping, clean the boat and recharge bank overnight...just needed 2xMulti 12/3000 with 120A so 240A charge+50A seperate charger so 290A charge so over night he got his bank recharged over night and can leave in the morning with a full bank.

[Pete7]

Originally Posted by Sailing Paul

Our daily usage is about 40Ah, maybe 50Ah in hot weather for the fridge, less if just sitting at anchor as no autopilot or nav instruments in use. So a 280Ah battery should go 5 days and we have 2X90Ah lead to push another day should we need it. This summer it is unlikely we would be away from shore power for more than 3 days, so initially we plan just to charge on shore power. Depending on how things go, I may buy some solar, although if prices keep falling adding another 280Ah LFP might be more cost effective and less hassle. I really cannot forsee us ever being away from shore power for 10 days. Alternator charging would be the last thing we added after more battery capacity and/or solar.

CaptRivet has recommended NH fuses. We bought ours from Bimble Solar for half the price of Class T which are really expensive in the UK. Replacement fuses are £5 each, not £45.

We also aren't normally away from a harbour or marina for more than 3 or 4 days, but that's because we want to us them. However, in 3 weeks last summer the only time we plugged in was Portland and only then to run the vacuum cleaner because its rated above the inverter capacity.

This brings me on to inverters. 1000w is an odd size neither fish nor fowl. Right on the limit for a small electric kettle or toaster from Argos, so pushing it. 1600w better but since you only want to do this once, I would suggest a 2000w pure sine wave from Photonic Universe for £300. Get the one with the remote display and switch so you can mount the inverter out of easy reach.

We have chosen to wire the two batteries together with a battery master switch then the NH fuse and on to a Victron Lynx Power In Not cheap but the cost of separate fuses and all those connections isn't either. What it does is provide a brilliant single location to connect charging sources and loads together in one place. There is a feed wire off to the original yachts domestics panel, all nicely fused in the Power In.

Attached is our latest wiring diagram. That's not to say what you should do, just what we have done and updated since we discussed electrics back in October. The extra 110w solar panel again will help in inclement weather and we plan to connect the 75Ah dinghy LFP battery into the domestic bank so it can be charged and do something useful if we aren't using the dinghy.

With 700w of solar we don't need to use expensive marinas and prefer old fashioned harbours, boat yards or anchoring for going ashore.

Pete

[justinfinity]

I read most of this thread; fascinating discussion about fuses.

One basic thing that didn't exactly get covered is that you have to size your wiring for the total current, not just the loads, but the charge current as well.

So, even if you think you won't have more than a few amps from your solid state electronics, you have to take into consideration all your charge sources and how much current they can supply both individually and combined.

For example, one might have multiple charge sources: shore power, solar, alternator, and generator. These can all easily provide continuous charge current in excess of whatever nominal current your loads might require. On my boat, I have 200A shore, 170A alternator; 120A generator, and 85A of solar. On average, I'm regularly seeing over 100A continuous charge current to my lithium batteries.

So, size your wire for the maximum current (load or charge), and make sure you size according to the full circuit run from the battery and back to the battery. Check out the Blue Sea wire size chart.

[CaptainRivet]

Originally Posted by justinfinity

I read most of this thread; fascinating discussion about fuses.

One basic thing that didn't exactly get covered is that you have to size your wiring for the total current, not just the loads, but the charge current as well.

So, even if you think you won't have more than a few amps from your solid state electronics, you have to take into consideration all your charge sources and how much current they can supply both individually and combined.

For example, one might have multiple charge sources: shore power, solar, alternator, and generator. These can all easily provide continuous charge current in excess of whatever nominal current your loads might require. On my boat, I have 200A shore, 170A alternator; 120A generator, and 85A of solar. On average, I'm regularly seeing over 100A continuous charge current to my lithium batteries.

So, size your wire for the maximum current (load or charge), and make sure you size according to the full circuit run from the battery and back to the battery. Check out the Blue Sea wire size chart.

That’s why a good and clean install have separated load and charge bus so you can size all accordingly. Exception are the big inverter/charger combo like Victron multi which are both. That goes onto a combo bus and I personally connect that combo bus to the main bus fuse in parallel where it’s used most, so on my cat onto load bus main fuse as the inverter is running 24/7 and I hardly ever use shorepower and if then via the Honda gen on anchor after a week of bad weather. The combo bus is not cut off via a relay/SSR but via remote of the 2 inverter/charger. The load and chargebus have a SSR so BMS and BMV can cut if necessary.

With your charge sources it makes sense to spec it to 200A shore+85A=300A, so 120sqmm or 2x70sqmm which can do 400A so you have reserves and less voltage drop. You will always run solar plus one other charge source. But You won’t have engine and generator running in parallel plus solar or shore power plus generator and solar. But if you do accidentally or need then 2x70sqmm can handle that with a bit higher voltage drop.

[Sailing Paul]

Thank you to everyone who has contributed to this topic, the discussion has been very informative.

@hjohnson, thanks for pointing out how partial cycles accumulate to full cycles. I had not appreciated that and agree with you that the number of cycles we get through will not be the limiting factor in LFP lifetime. Calendar aging does seem to be the limiting factor.

@CaptainRivet, A 50A charger does seem to be the way to go. To keep below 80% SOC when leaving the boat wouldn’t be too big a problem. On arriving we would charge up and set a phone alarm to turn off the charger before the SOC reached 80%, or turn off just before leaving the boat. Then on coming back to the boat, turn the charger back on to take the SOC up to 100%. Turning the charger on remotely is a possibility, but as the battery has Bluetooth it should not be necessary to use a shunt or specialist OS on a Raspberry Pi. Alternatively a simple Bluetooth enabled microcontroller, such as a Pico W or Arduino nano 33 BLE could read the SOC and turn off the charger once the SOC got to 80%. We would then turn on again once we arrived at the boat.

@Pete7, I came across Bimble Solar in searching for NH fuses, so thanks for the endorsement. I like the idea of having a fuse holder that completely encloses the terminals. Do you know whether this one is like that? It looks like it is from the picture.

https://www.bimblesolar.com/extras/d...sconnect-1pole

An inverter is a project for next year, if at all. I take your point about the power output. At present I only envisage using an inverter to boil a low power 700W kettle, the toaster and maybe my wife’s hair dryer, so I thought 1000W might be sufficient. I guess a larger one would open up other possibilities, such as an induction hob. Are there any particular issues involved with using an inverter with an LFP battery, such as the high inrush current?

700W of solar on a Moody 31 sounds impressive and if it means you can avoid expensive marinas your payback time will be much reduced. Another project for next year or the year after I think, but I might get a portable 100W panel to experiment with. I want to upgrade our AIS from receiver to transceiver and that is a higher priority. Next year or maybe the following we are planning some longer trips, up the Irish Sea and to Scotland where there may be far fewer opportunities for shore charging.

[Sailing Paul]

I have been trying to find some definitive information on how best to manage LiFePO4 batteries so I can understand the long term impact of occasional ‘bad behaviour’ such as discharging down near BMS cutoff or leaving charged at 100% for a few weeks. The curious thing is the literature I have seen does not indicate a problem leaving a battery at 100% SOC provided the temperature stays below 30C. This paper for example notes no discernible drop in capacity after leaving a cell at 100% SOC for 240 days.

https://hal.science/hal-00876555

There are measureable loss of capacities at higher temperatures of 45C and 60C.

This paper confirms this finding. Keep the batteries cool (below 35C) and leaving at a 100% SOC for a few weeks should not cause significant lasting damage.

https://www.sciencedirect.com/scienc...52152X21011889

Does anyone else have any links to testing like this?

[CaptainRivet]

Originally Posted by Pete7

CaptRivet has recommended NH fuses. We bought ours from Bimble Solar for half the price of Class T which are really expensive in the UK. Replacement fuses are £5 each, not £45.

We also aren't normally away from a harbour or marina for more than 3 or 4 days, but that's because we want to us them. However, in 3 weeks last summer the only time we plugged in was Portland and only then to run the vacuum cleaner because its rated above the inverter capacity.

This brings me on to inverters. 1000w is an odd size neither fish nor fowl. Right on the limit for a small electric kettle or toaster from Argos, so pushing it. 1600w better but since you only want to do this once, I would suggest a 2000w pure sine wave from Photonic Universe for £300. Get the one with the remote display and switch so you can mount the inverter out of easy reach.

We have chosen to wire the two batteries together with a battery master switch then the NH fuse and on to a Victron Lynx Power In Not cheap but the cost of separate fuses and all those connections isn't either. What it does is provide a brilliant single location to connect charging sources and loads together in one place. There is a feed wire off to the original yachts domestics panel, all nicely fused in the Power In.

Attached is our latest wiring diagram. That's not to say what you should do, just what we have done and updated since we discussed electrics back in October. The extra 110w solar panel again will help in inclement weather and we plan to connect the 75Ah dinghy LFP battery into the domestic bank so it can be charged and do something useful if we aren't using the dinghy.

With 700w of solar we don't need to use expensive marinas and prefer old fashioned harbours, boat yards or anchoring for going ashore.

Pete

Pete is right, good setup with NH plus lynx
And especially about inverter. My recommendation here is to look for a used Victron multi 1200 or 1600 or 2000, you can often get them for a good price because they got often upgraded to the 3000 multi and sold in good state around the 300-400 you mentioned. That gives you a shorepower charger as well as a good inverter in a small form factor (and only one pair of cable to connect) which again you can operate remotely via Venus OS and raspi. He needs a shorepower charged too so to add that to your 300 too.
Wife’s fan with 700W, connect and measure…hard to believe…more likely 1200W+

[CaptainRivet]

Originally Posted by Sailing Paul

I have been trying to find some definitive information on how best to manage LiFePO4 batteries so I can understand the long term impact of occasional ‘bad behaviour’ such as discharging down near BMS cutoff or leaving charged at 100% for a few weeks. The curious thing is the literature I have seen does not indicate a problem leaving a battery at 100% SOC provided the temperature stays below 30C. This paper for example notes no discernible drop in capacity after leaving a cell at 100% SOC for 240 days.

https://hal.science/hal-00876555

There are measureable loss of capacities at higher temperatures of 45C and 60C.

This paper confirms this finding. Keep the batteries cool (below 35C) and leaving at a 100% SOC for a few weeks should not cause significant lasting damage.

https://www.sciencedirect.com/scienc...52152X21011889

Does anyone else have any links to testing like this?

That study didn’t look at the cells after 2 years…the capacity loss and more the different internal resistance acour over time and not directly while keep them at 100% SOC. Avoid keeping them long at 100% SOC….other then that use as you want, they are speced for being used like that and not sensitive leads. You can make more harm try to optimize then just simply use them.
I deal with lithium since 20 years and my buddy is CEO of an NPO producing powerwalls and commercial EVs and I have access to his R&D. Just don‘t overthink, best forget all you know about lead and use them.
More important as your boat is often in storage unattended is that a leaking seal and Bilge pump is not draining your lithium house to death or alike.
That’s how most banks get killed…shorepower outage, cable broke or a continuous running bilgepump due to blocked float switch…
Well a remote monitoring even you don#t live far away is the simplest and solve a lot of other issues too…a raspi is not that expensive.

[Sailing Paul]

Originally Posted by CaptainRivet

That study didn’t look at the cells after 2 years…the capacity loss and more the different internal resistance acour over time and not directly while keep them at 100% SOC. Avoid keeping them long at 100% SOC….other then that use as you want, they are speced for being used like that and not sensitive leads. You can make more harm try to optimize then just simply use them.
I deal with lithium since 20 years and my buddy is CEO of an NPO producing powerwalls and commercial EVs and I have access to his R&D. Just don‘t overthink, best forget all you know about lead and use them.
More important as your boat is often in storage unattended is that a leaking seal and Bilge pump is not draining your lithium house to death or alike.
That’s how most banks get killed…shorepower outage, cable broke or a continuous running bilgepump due to blocked float switch…
Well a remote monitoring even you don#t live far away is the simplest and solve a lot of other issues too…a raspi is not that expensive.

My plan is to disconnect the LFP when we are away from the boat. The bilgepump will be handled by the lead/shore power. Ideally I would not charge the LFP when away either, but that may not always be practical.

I would like remote monitoring. I was planning to do this over the winter with a Raspberry Pi to monitor temperature and humidity, but did not get round to it. Monitoring bilge pump current sounds like a good idea as well.

[s/v Jedi]

Originally Posted by Sailing Paul

My plan is to disconnect the LFP when we are away from the boat. The bilgepump will be handled by the lead/shore power. Ideally I would not charge the LFP when away either, but that may not always be practical.

I would like remote monitoring. I was planning to do this over the winter with a Raspberry Pi to monitor temperature and humidity, but did not get round to it. Monitoring bilge pump current sounds like a good idea as well.

You can partially charge LFP by changing the settings in the charger, or by switching the charger on/off based on SOC% of the battery. A Victron battery monitor can do that automatically for you.

[hjohnson]

Originally Posted by Sailing Paul

My plan is to disconnect the LFP when we are away from the boat. The bilgepump will be handled by the lead/shore power. Ideally I would not charge the LFP when away either, but that may not always be practical.

I would like remote monitoring. I was planning to do this over the winter with a Raspberry Pi to monitor temperature and humidity, but did not get round to it. Monitoring bilge pump current sounds like a good idea as well.

I’m a huge fan of the Victron ecosystem myself. Been deep into it for two and a half years now, and it’s been working fantastically.

When I’m away from the boat for an extended period, I use the Cerbo to override the BMS’s voltage target and let my system bus drift down to 13.3V, which is about 60% charge. Then, the day before I head out I remote in again and turn the override off, letting the BMS bring itself back up to 100%. Even if my shore power gets disconnected, I have about a week to get to the boat before I hit LVD.

And the remote monitoring that you get through VRM is hard to beat. Not only do I know my system voltage from an app and widget on my iPhone, I know the current SoC, how much liquid is in my tanks (fuel, potable water, blackwater) and bilge, as well as the temperature/humidity in the cabin. I’ve also got it rigged to tell me if and how often my bilge pump has operated.

Lastly, because it’s connected to my N2K bus and In leave my sensors on, I can remote in and check on current wind at my marina, depth under the keel, and everything else.

I absolutely love the setup.

The next I want to add is good quality high powered relays so I can remotely turn my hot water tank on/off, and maybe an electric heater in the cabin to help dry it out in the winter and/or keep the battery from freezing.

[more]

Originally Posted by CaptainRivet

Well i wish you luck if you have a battery related insurance claim...insurance will bail out easly.

insurance is for pussy and amater. i have insurance for passenger accident, if i hit somebody. for my boat i dot need insurance because i don't planning sink,hit or burn boat.my insurance is my bank account. different country different rules. if in storm my boat be destroyed this is good will , dont cheat good.also your system don't pass inspection becouse is different from original ce certification.som state alowed marine designer must make plan and you must past certification.Electrical installations in ships -- Part 507 -- Small vessels (IEC 60092-507:2014; EN 60092-507:2015)