Only one design of battery onboard and it’s Lifepo4

[wholybee]

Originally Posted by flightlead404

I have to take issue with this theory.

The only reason to have a house bank larger than x is if you think you are going to need more than x+reserves to run the house.

Once you get into x+reserves you've eaten up the reduncancy.

That's a rather opaque way of saying the battery can serve one and only one purpose: contributing to a house bank of suitable size, or providing redundancy. It can't do both.

Fuss is right. Say your daily usage is 300Ah. To have a day of reserve, you build a bank of 600Ah. No one I know would suggest you need 1200Ah total to have an adequate backup. More typical is that a 100Ah start battery would be considered fine as a backup in the event the 600Ah bank failed.

So, if 100Ah is fine for a backup, then why not 300Ah, as half of the house bank, being a backup? 2 300Ah LFP batteries, either capable of being isolated if the other fails. That is perfectly acceptable, even if you regularly use more than 300Ah.

The other consideration is how gosh darn reliable LFP are to being with. With Lead Acid, backup is mandatory. Anyone who has cruised for any length of time has had a problem with a Lead Acid battery, and needed to flip to the backup. Such just isn't the case with LFP. Sure, to be responsible in your planning you will still have something, but in all likelihood, with LFP you will never need it.

[flightlead404]

Originally Posted by wholybee

Fuss is right. Say your daily usage is 300Ah. To have a day of reserve, you build a bank of 600Ah. No one I know would suggest you need 1200Ah total to have an adequate backup. More typical is that a 100Ah start battery would be considered fine as a backup in the event the 600Ah bank failed.

So, if 100Ah is fine for a backup, then why not 300Ah, as half of the house bank, being a backup? 2 300Ah LFP batteries, either capable of being isolated if the other fails. That is perfectly acceptable, even if you regularly use more than 300Ah.

The other consideration is how gosh darn reliable LFP are to being with. With Lead Acid, backup is mandatory. Anyone who has cruised for any length of time has had a problem with a Lead Acid battery, and needed to flip to the backup. Such just isn't the case with LFP. Sure, to be responsible in your planning you will still have something, but in all likelihood, with LFP you will never need it.

You missed the point entirely

Regardless of what you think is an appropriate reserve, a day, 2 days, 6 hours, whatever, once you've eaten into the reserve you've reduced your redundancy. Eat all your reserve and you have zero redundancy. Hence, that battery capacity is either reserve or redundancy, not both.

There's another piece you are missing also. There's a heck of a lot more to a battery system than just the battery. There are cables, lugs, battery terminals, fuses, breakers, and switches. A failure of any one of these might prevent the batteries being able to deliver their power. Redundancy needs to cover all of these as well.

[Kettlewell]

There's a heck of a lot more to a battery system than just the battery. There are cables, lugs, battery terminals, fuses, breakers, and switches. A failure of any one of these might prevent the batteries being able to deliver their power. Redundancy needs to cover all of these as well.

The situation you really want to avoid is not being able to start your engine at 0200 as your anchor drags bag toward the rocks and for some reason your starter battery isn't delivering juice. And, then there is the situation where you lose most of the electrics for some reason and you want to keep the GPS on and be able to start the engine in an emergency. You don't want to be reconfiguring your cables, switches, and battery banks in these situations.

[deltaten]

Yanno...they say "belt and suspenders", not "suspenders and suspenders" for a reason.
just sayin'

[mcarthur]

Originally Posted by Fuss

...Your small diesel would create no problems in comparison, mine is 6l 135 hp so if yours is less than that, you are on the safe side.

I'm interested in your engine start - we have twin 135hp 6c NA Perkins. The manual specs 2 x parallel 12v 600cca (or near) for starting. Actually it's not 600CCA: "each battery must be at least 315amps BS3911 or 535amps SAEJ537"...no CCA so I've interpreted the "535amps" in CCA as 600.

Do you use a FET based BMS? I'm concerned whether it could handle the load, even if it's in the 10's or 100's of milliseconds.

[wholybee]

Originally Posted by flightlead404

You missed the point entirely

Regardless of what you think is an appropriate reserve, a day, 2 days, 6 hours, whatever, once you've eaten into the reserve you've reduced your redundancy. Eat all your reserve and you have zero redundancy. Hence, that battery capacity is either reserve or redundancy, not both.

There's another piece you are missing also. There's a heck of a lot more to a battery system than just the battery. There are cables, lugs, battery terminals, fuses, breakers, and switches. A failure of any one of these might prevent the batteries being able to deliver their power. Redundancy needs to cover all of these as well.

I really don't think I am missing any of that. A 600Ah bank, divided into two 300Ah batteries, each with it's own fuse, wiring and disconnect. Completely redundant.

Eat all your reserve and have zero redundancy? How is that different from switching to your redundant battery and running it down? Whether you have all your Ah in a single battery in one bank, two batteries in one bank, or two batteries split between a primary and redundant bank, 600Ah is 600Ah. If you use it all, it's gone. You don't prevent that with a redundant battery, you prevent that with more total Ah of capacity.

[wholybee]

Originally Posted by Kettlewell

The situation you really want to avoid is not being able to start your engine at 0200 as your anchor drags bag toward the rocks and for some reason your starter battery isn't delivering juice. And, then there is the situation where you lose most of the electrics for some reason and you want to keep the GPS on and be able to start the engine in an emergency. You don't want to be reconfiguring your cables, switches, and battery banks in these situations.

Then switch to LFP. Lead-Acid is far more likely to leave you dead in the water. Either because of PSOC damage you don't catch until your "fully charged" battery doesn't make it through the night, a shorted cell that reduces nominal voltage, or a battery that still runs your electronics but will sag and not start an engine.

Keep an emergency battery if you want, that's never a bad idea. But with LFP you are much less likely to ever need it.

[Fuss]

Originally Posted by mcarthur

I'm interested in your engine start - we have twin 135hp 6c NA Perkins. The manual specs 2 x parallel 12v 600cca (or near) for starting. Actually it's not 600CCA: "each battery must be at least 315amps BS3911 or 535amps SAEJ537"...no CCA so I've interpreted the "535amps" in CCA as 600.

Do you use a FET based BMS? I'm concerned whether it could handle the load, even if it's in the 10's or 100's of milliseconds.

Ok, perhaps first you should look at this thread where I first promoted the idea. https://www.cruisersforum.com/forums...-276834-7.html
There was a lot of push back and even talk of fire, especially from one of the members who says he has 20 years experience with Lifepo4. He says that EVE cells are not made for this task in the slightest. However my opinion is that these are 280ah cells and only are stressed for a second in normal start circumstances. He originally said that they would blow up immediately and later softened his stance.
Its always a problem in a forum, who do you want to believe, someone who talks about it or someone who is actually doing it.



So a couple of points, firstly I like to take things to the edge sometimes. Perhaps you need to be this sort of person too as well as electrically competent to do this.
My Motor Start battery setup also needed 2 12v batteries in parallel to start as per the specs.
I had a 1 2 both switch that performed this task.
Now there is only an Eve lf280 4 cell battery on switch position 1, this has started the motor since the beginning of 2023, the cells do not go out of balance and show no damage. In initial testing I did some extended cranking to resemble a motor problem and since then , it starts the motor instantly.
At this point, I consider that the pushback in the thread above is proved to be not correct and I have now done some testing with connecting a small lead acid to position 2 and this seems to produce a 75 25 ratio of amps pulled when starting. 75% lifepo4 and 25% lead acid... I think it was 40ah lead acid.
Ok, but this does not have easy redundancy in emergencies and also I am using the start battery as part of the house bank (a no no with lead acid but this is 280ah with the ability to use 90% of its capacity and not needing to be kept at full charge so a completely different scenario, but this is another story).
So after the lead acid 40ah battery test in parallel, I am now going to connect a maxwell supercap to position 2 with the aim that the supercap does all the starting work and the Eve Lifepo4 becomes the redundancy backup. Starting will be done with the switch on position BOTH.
Ok, and now onto the question of the BMS. Firstly, my opinion of a BMS is that it is only there to protect the battery with LVC low voltage cutoff and HVC, plus do a little balancing.
With that theory in mind and knowing that Winston , one of the most revered Lifepo4 companies, produces a start battery with no BMS at all, I do the following...
The EVE Lifepo4 start battery has a 100a BMS which is connected as normal with LVC and HVC programmed in to accommodate the charging algorithms of the chargers and alternators. But for starting the engine, this BMS is bypassed.
And lastly to the battery build. The 4 cells have their bus bar connections carefully assembled to ensure they have very good connections. The cells are in a battery box that resembles a lead acid battery. The cables are 50mm2 very flexible silicon and are carefully checked that there is no chance of a short.

[flightlead404]

Originally Posted by Kettlewell

The situation you really want to avoid is not being able to start your engine at 0200 as your anchor drags bag toward the rocks and for some reason your starter battery isn't delivering juice. And, then there is the situation where you lose most of the electrics for some reason and you want to keep the GPS on and be able to start the engine in an emergency. You don't want to be reconfiguring your cables, switches, and battery banks in these situations.

Exactly!

[flightlead404]

Originally Posted by wholybee

Eat all your reserve and have zero redundancy? How is that different from switching to your redundant battery and running it down? Whether you have all your Ah in a single battery in one bank, two batteries in one bank, or two batteries split between a primary and redundant bank, 600Ah is 600Ah. If you use it all, it's gone. You don't prevent that with a redundant battery, you prevent that with more total Ah of capacity.

Because its a separate system that either you have to manually switch to, or which automatically switches AND PROVIDES ANNUNCIATION it has done so.

The entire raison d'etre of redundancy and reserve are different things.

[flightlead404]

Originally Posted by wholybee

Then switch to LFP. Lead-Acid is far more likely to leave you dead in the water. Either because of PSOC damage you don't catch until your "fully charged" battery doesn't make it through the night, a shorted cell that reduces nominal voltage, or a battery that still runs your electronics but will sag and not start an engine.

Keep an emergency battery if you want, that's never a bad idea. But with LFP you are much less likely to ever need it.

FWIW my comments are not related to battery technology, but rather considering reserve and redundancy as the same thing.

[mcarthur]

Originally Posted by Fuss

My Motor Start battery setup also needed 2 12v batteries in parallel to start as per the specs.
I had a 1 2 both switch that performed this task.
Now there is only an Eve lf280 4 cell battery on switch position 1, this has started the motor since the beginning of 2023, the cells do not go out of balance and show no damage. In initial testing I did some extended cranking to resemble a motor problem and since then , it starts the motor instantly.
At this point, I consider that the pushback in the thread above is proved to be not correct and I have now done some testing with connecting a small lead acid to position 2 and this seems to produce a 75 25 ratio of amps pulled when starting. 75% lifepo4 and 25% lead acid... I think it was 40ah lead acid.
Ok, but this does not have easy redundancy in emergencies and also I am using the start battery as part of the house bank (a no no with lead acid but this is 280ah with the ability to use 90% of its capacity and not needing to be kept at full charge so a completely different scenario, but this is another story).
So after the lead acid 40ah battery test in parallel, I am now going to connect a maxwell supercap to position 2 with the aim that the supercap does all the starting work and the Eve Lifepo4 becomes the redundancy backup. Starting will be done with the switch on position BOTH.
Ok, and now onto the question of the BMS. Firstly, my opinion of a BMS is that it is only there to protect the battery with LVC low voltage cutoff and HVC, plus do a little balancing.
With that theory in mind and knowing that Winston , one of the most revered Lifepo4 companies, produces a start battery with no BMS at all, I do the following...
The EVE Lifepo4 start battery has a 100a BMS which is connected as normal with LVC and HVC programmed in to accommodate the charging algorithms of the chargers and alternators. But for starting the engine, this BMS is bypassed.

Thank you. Our lifepo4 will be 48v, so direct connect to engine, bypassing BMS, isn't possible since our starter is 12v (or can be 24v). But it is interesting to hear you're bypassing the BMS to deal with the starting load, and also to hear you got 75-25 on the Both in conjunction with a lead acid. Thanks.

[wholybee]

Originally Posted by flightlead404

Because its a separate system that either you have to manually switch to, or which automatically switches AND PROVIDES ANNUNCIATION it has done so.

The entire raison d'etre of redundancy and reserve are different things.

I understand the difference between redundancy and reserve.
Redundancy doesn't require a switch from one to the other, it is about removing single points of failure. Having two 300Ah batteries in parallel is redundant. Having a single 600Ah is not. Though either could be considered to have 300Ah of reserve. You can improve that redundancy by adding separate wiring and switches, removing more points of failure.

To be redundant does NOT require that you switch to another system. Both can be online and working until one fails. A couple examples out of IT, a load balanced network cluster. Several servers online, sharing the load for better performance, and if any fail, the system keeps working. Or, a level 5 raid, where redundancy is across all drives. Any drive fails, and it keeps working. There is no need to have a completely separate chassis duplicating all the data that you switch to if a drive fails. Or, redundant power supplies, where the load of the server is even between both supplies, and each supply is connected to a separate AC circuit. Either supply fails, or either AC circuit fails, there is no switch, the remaining supply just keeps working.

It is no different with batteries. You can have 100% redundancy with no single point of failure by having 2 batteries in parallel. There is no need to have a "redundant" battery separate from your house bank that you switch to.

There is also nothing stopping you from having annunciation when a bank gets to a certain level. And nothing stopping you from taking action when that alarm goes off. The end-result reliability is the same.

[flightlead404]

Originally Posted by wholybee

I understand the difference between redundancy and reserve.
Redundancy doesn't require a switch from one to the other, it is about removing single points of failure. Having two 300Ah batteries in parallel is redundant. Having a single 600Ah is not. Though either could be considered to have 300Ah of reserve. You can improve that redundancy by adding separate wiring and switches, removing more points of failure.

To be redundant does NOT require that you switch to another system. Both can be online and working until one fails. A couple examples out of IT, a load balanced network cluster. Several servers online, sharing the load for better performance, and if any fail, the system keeps working. Or, a level 5 raid, where redundancy is across all drives. Any drive fails, and it keeps working. There is no need to have a completely separate chassis duplicating all the data that you switch to if a drive fails. Or, redundant power supplies, where the load of the server is even between both supplies, and each supply is connected to a separate AC circuit. Either supply fails, or either AC circuit fails, there is no switch, the remaining supply just keeps working.

It is no different with batteries. You can have 100% redundancy with no single point of failure by having 2 batteries in parallel. There is no need to have a "redundant" battery separate from your house bank that you switch to.

There is also nothing stopping you from having annunciation when a bank gets to a certain level. And nothing stopping you from taking action when that alarm goes off. The end-result reliability is the same.

You are correct, no need to actually have to physically switch something, it could be automatic. But the point is you have changed the source of your power. The intent is to recover from a failure.

Reserve is an "extra amount" in case you use more than you planned for.

[wholybee]

Originally Posted by flightlead404

You are correct, no need to actually have to physically switch something, it could be automatic. But the point is you have changed the source of your power. The intent is to recover from a failure.

Reserve is an "extra amount" in case you use more than you planned for.

My point is that nothing has to switch, even automatically. The redundant battery can be online in parallel and used daily as part of your house bank. As long as you remove single points of failure, you have made the system redundant. It could be considered even more reliable than a completely separate switched battery, because that switch is a single point of failure.

And yes, again, I know what reserve is. Reserve doesn't say anything about points of failure, only about capacity.