270ah DIY LiFePO4 build

[mitiempo]

I have never been a fan of drop-in batteries, even though I sell Victron which are good quality. Of course the Victron solution to drop-in batteries is quite expensive.

A DIY system doesn't have to be expensive - in fact it can be a lot less expensive than drop-in batteries if you search out the correct sources.

For example I have purchased and received 8 Calb CA180 cells @ $80 US each - landed cost in Canada $1179 (902 US) for a total of 400 AH @ 12 volts. BMS is a Electrodacus @ $159 Cdn. Grade A cells for less than any drop-in I know of and I get Victron at cost as I work for a major distributor. At retail the saving would be much greater.

I will be using a Victron DC-DC charger between the engine battery (Fla) and the LiFePo4 bank. My primary charge source will be solar.

With the ABYC regs for LiFePo4 coming soon I believe, at least for marine use, drop-in batteries will be very rare as with the exception of Lithionics they will not pass a survey.

 

[Poey50]

You seem to be advocating using the lead acid start battery to protect the system by absorbing spikes.
The page you link to really doesn't say that, there is a Sterling alternator protector in the diagram to do that.

Anyone who's looked at desulfator circuits with an oscilloscope will know that lead acid batteries are not really that great for absorbing spikes.

What keeps the vessel alive if the 'drop ins' disconnect when the engine isn't running?

There is a lot of half baked stuff in this.

Collins entirely makes clear that protection comes from a combination of keeping the start battery in the system together with a Sterling Alternator Protect. As you say it doesn't offer any additional protection against disconnect when the engine isn't running but it doesn't claim to do so.

 

[Zing]

I'm in two minds whether to resurrect this thread. On the one hand it is very long, on the other it holds a lot of information in one place.

Anyway I think this LFP topic is relevant to this thread as I seem to have spent quite a lot of time issuing dire warnings about drop-in LFP batteries. I won't repeat myself (much) but these are, at the same time, the most tempting solutions for boaters and the most problematic. As said several times, the safety of a system can be tested with a thought experiment - if you are crossing a busy shipping lane at night, how will you know your LFP pack is about to disconnect and isolate itself and what will happen to your system when it does?

A step towards making drop-in LFP safer on boats has been taken by Rod Collins of Marine HowTo. One big problem with drop-ins is that during alternator charging a BMS disconnect dumps the alternator load and can take out the alternator diodes and, because the load and charge buses are not separated as recommended, the huge voltage spike can also take out marine electronics. Until now the main recommended solution was for LFP drop-ins to be charged via the engine battery with a battery to battery charger. But Collins has a simpler and cheaper solution to the B2B, one that allows drop-ins to be charged direct by an alternator with external regulator. It uses a solenoid connecting house LFP to lead acid starter. It switches on with the ignition circuit and always retains a lead acid starter battery in the system to absorb spikes, keeps the start battery in good health, and keeps essential loads running from the start battery in the event of a disconnect. This setup still doesn't of course provide warnings of disconnect (although that could be built into the system) but it does open up further options for drop-ins to be charged more safely at higher rates. The advert is below and it come with interesting blurb and a downloadable manual. Click on the downward pointed arrow at the end of the blurb.

CMI LiFePO4 150A Load-Dump & Stay-Aive Protection Solenoid

I’m a bit confused as to the need for this. I don’t think it is properly explained and I’m not sure it is a great idea.

The manual says:
It simply parallels the LiFePO4 bank with the lead acid bank anytime the engine or a genset is set to ON/RUN. So long as the engine switch remains ON the LFP bank can safely disconnect from the bus and the vessel remains powered via the cranking or reserve Lead Acid battery bank.

I can see a problem where the little engine battery gets drained after a few hours following a main battery shut off event. You then turn the engine off and can’t start again without resorting to your hopefully functioning house battery to sort you out. Not to be taken for granted, as if there was a battery disconnect event, there could also be a fatal fault there. Now you are really in a mess and worse than having left the engine battery unparalleled.

He also says:
Imagine docking and all of a sudden, the vessel loses all DC power. Imaging passing through a bridge with downbound and upbound traffic when you lose all DC power? Imaging transiting a difficult inlet when you lose all DC power.

I don’t think any of these scenarios are a major problem. Most engines will continue to run with no electric connection. Surely even the common rail units have a protected supply? The worst thing would be to lose your chart plotter, but you will have your Iphone backup surely. Why does he think it a problem for docking? Ditto when passing a bridge channel? It doesn’t make sense to me and don’t understand what he is getting at.

 

[Kelpie]

Re the ABYC regs, do we know what systems are passing that standard? Is it even possible for a system built from bare cells to pass, e.g. if signed off by a marine electrician?

 

[Poey50]

I can see a problem where the little engine battery gets drained after a few hours following a main battery shut off event. You then turn the engine off and can’t start again without resorting to your hopefully functioning house battery to sort you out. Not to be taken for granted, as if there was a battery disconnect event, there could also be a fatal fault there. Now you are really in a mess and worse than having left the engine battery unparalleled.

Yes, of course. Falling back on the engine battery buys a little time, that's all. Edit: the engine battery is only used for as long as the engine is running since the solenoid isolates the house LFP from the start battery once the ignition circuit is de-energised. So it works as long as you have fuel to run the engine.

He also says:
Imagine docking and all of a sudden, the vessel loses all DC power. Imaging passing through a bridge with downbound and upbound traffic when you lose all DC power? Imaging transiting a difficult inlet when you lose all DC power.

I don’t think any of these scenarios are a major problem. Most engines will continue to run with no electric connection. Surely even the common rail units have a protected supply? The worst thing would be to lose your chart plotter, but you will have your Iphone backup surely. Why does he think it a problem for docking? Ditto when passing a bridge channel? It doesn’t make sense to me and don’t understand what he is getting at.

It's the difference between losing essential systems - lights, plotter, VHF, AIS and Radar and not losing them. If there are other means to compensate or prevent that then fine. He is giving one method.

 

[TernVI]

I’m a bit confused as to the need for this. I don’t think it is properly explained and I’m not sure it is a great idea.

The manual says:
It simply parallels the LiFePO4 bank with the lead acid bank anytime the engine or a genset is set to ON/RUN. So long as the engine switch remains ON the LFP bank can safely disconnect from the bus and the vessel remains powered via the cranking or reserve Lead Acid battery bank.

I can see a problem where the little engine battery gets drained after a few hours following a main battery shut off event. You then turn the engine off and can’t start again without resorting to your hopefully functioning house battery to sort you out. Not to be taken for granted, as if there was a battery disconnect event, there could also be a fatal fault there. Now you are really in a mess and worse than having left the engine battery unparalleled.

He also says:
Imagine docking and all of a sudden, the vessel loses all DC power. Imaging passing through a bridge with downbound and upbound traffic when you lose all DC power? Imaging transiting a difficult inlet when you lose all DC power.

I don’t think any of these scenarios are a major problem. Most engines will continue to run with no electric connection. Surely even the common rail units have a protected supply? The worst thing would be to lose your chart plotter, but you will have your Iphone backup surely. Why does he think it a problem for docking? Ditto when passing a bridge channel? It doesn’t make sense to me and don’t understand what he is getting at.

Do you have an iphone backup for your echo sounder?
Bow thruster app?

I agree with your point about engine start batteries. If you are thinking it's there as a no-nonsense means of starting the engine, it should not be doing anything else. If it's not solely reserved for starting the engine, don't call it the engine battery.

If your boat has solar power, presumably one needs to consider the possibility of a disconnect when the engine isn't running.

Personally, if I wanted a system where the chartplotter and echo sounder might drop out at an interesting moment, I would have kept the MAB I had last century.

Much of this stuff is just for people who are excited by battery tech and gimmickry they've seen on youtube.
If you look at the actual cost/benefit of enjoying time on your boat it doesn't seem to stack up.

 

[Zing]

Re the ABYC regs, do we know what systems are passing that standard? Is it even possible for a system built from bare cells to pass, e.g. if signed off by a marine electrician?

From my cursory look at it, the prior warning of cut off is more of a problem for drop ins to pass. A decent BMS will give you that in bare cell systems.

 

[Poey50]

Re the ABYC regs, do we know what systems are passing that standard? Is it even possible for a system built from bare cells to pass, e.g. if signed off by a marine electrician?

The regs haven't come in yet, only the technical guidance and of course these only apply to the US. No drop-in battery currently meets the proposed standard for a warning signal to be given. My DIY system does have two levels of warning but based on the Victron BMV712 rather than the BMS. DIY systems using higher end BMSs like the Orion Jnr or REC Active should be able to give warnings.

Any system can add a Class T fuse which will be another requirement.

 

[Zing]

Yes, of course. Falling back on the engine battery buys a little time, that's all.

It's the difference between losing essential systems - lights, plotter, VHF, AIS and Radar and not losing them. If there are other means to compensate or prevent that then fine. He is giving one method.

None of those are essential systems in the scenarios he describes. They might be in fog or night (just for lights), but he didn’t say that.

It may be a help also be a help to have everything on-line, but without a simultaneous warning that you are on limited power you are potentially creating a bigger problem, so as things look, it’s not for me.

Do you have an iphone backup for your echo sounder?
Bow thruster app?

I thought about those as a possible reason for Collins explanation, but it can’t be. A bow thruster cannot work off engine batteries anyway. An echo sounder is not a problem to lose in the scenarios he describes.

 

[Kelpie]

It's funny, you'd think lithium batteries were the only type which ever runs out of juice.
I've had both my chart plotter and autopilot shut down when my lead acid batteries got too low. My own fault, great sailing for a couple of days so I hardly ran the engine and didn't keep a close enough eye on the batteries.

Re the cost: benefit, so far I've spent £407 on my 4x270Ah cells and 120A BMS. I added a B2B charger (thanks David) which you could argue was optional. There are other costs like fuses, isolator, cabling, but these would be about the same for any new battery system.

I had previously budgeted for a set of four T105 Trojans, which would have given me about the same usable Ah, but would have cost me £690.

Lithium probably still doesn't make sense for weekend cruisers who get ten years out of a cheap leisure battery. And it rapidly becomes more expensive and and complex once you start adding shore power and high levels of automatic battery management.

 

[Poey50]

It's funny, you'd think lithium batteries were the only type which ever runs out of juice.

I'll just respond to this point. When lead acid runs out of juice, you generally have plenty of warning because of voltage sag, not so with LFP. But more significantly an internal BMS may suddenly take your house power away for a whole variety of reasons - none of which may be obvious. Collins lists them in the manual.

• Amperage Overload
• High or Low Cell Temp
• Delta Voltage Between Cells (can’t keep up with balancing)
• Cell High Voltage (Not to be confused with “pack voltage”)
• Mosfet Temp
• Circuit Board Temp
• Error in the Chip/BMS Computer
[Also cell low voltage]

 

[TernVI]

I'll just respond to this point. When lead acid runs out of juice, you generally have plenty of warning because of voltage sag, not so with LFP. But more significantly an internal BMS may suddenly take your house power away for a whole variety of reasons - none of which may be obvious. Collins lists them in the manual.

• Amperage Overload
• High or Low Cell Temp
• Delta Voltage Between Cells (can’t keep up with balancing)
• Cell High Voltage (Not to be confused with “pack voltage”)
• Mosfet Temp
• Circuit Board Temp
• Error in the Chip/BMS Computer

Indeed.

People are also prone to comparing Lithium against only ever using 50% discharge on lead acid, whereas in reality, the other 50% is there as a reserve and it doesn't hurt much to use it now and again. (feel free to change 50% to some other arbitrary % of your choice!) Some people might run their house batteries through the exact same cycle hundreds of times a year, many people do not.

 

[TernVI]

None of those are essential systems in the scenarios he describes. ...... An echo sounder is not a problem to lose in the scenarios he describes.

An echo sounder is a potential problem to lose in any scenario where you are avoiding other vessels and the seabed.
You don't spend hundreds of pounds 'upgrading' your electrics to increase the risk of that if you have any sense.

 

[Kelpie]

I'll just respond to this point. When lead acid runs out of juice, you generally have plenty of warning because of voltage sag, not so with LFP. But more significantly an internal BMS may suddenly take your house power away for a whole variety of reasons - none of which may be obvious. Collins lists them in the manual.

• Amperage Overload
• High or Low Cell Temp
• Delta Voltage Between Cells (can’t keep up with balancing)
• Cell High Voltage (Not to be confused with “pack voltage”)
• Mosfet Temp
• Circuit Board Temp
• Error in the Chip/BMS Computer

Fair points and well made. I suppose I just get a bit tired of people comparing Li to Pb and thinking that nothing ever goes wrong with Pb. This is especially true when taking about things like fire risk.

Btw I am fully persuaded on the merits of using lead acid only for non critical loads. My plotter, sounder, autopilot, and nav lights will remain on the lead acid system. I haven't decided about radar yet, it's a big consumer but then again often used whilst motoring, much the same as the autopilot.

 

[TernVI]

Fair points and well made. I suppose I just get a bit tired of people comparing Li to Pb and thinking that nothing ever goes wrong with Pb. This is especially true when taking about things like fire risk.

Btw I am fully persuaded on the merits of using lead acid only for non critical loads. My plotter, sounder, autopilot, and nav lights will remain on the lead acid system. I haven't decided about radar yet, it's a big consumer but then again often used whilst motoring, much the same as the autopilot.

Nothing much does go wrong with lead acid, unless people seriously abuse it or have unrealistic expectations.
Those problems are likely to be worse with any other technology.

 

[Poey50]

Fair points and well made. I suppose I just get a bit tired of people comparing Li to Pb and thinking that nothing ever goes wrong with Pb. This is especially true when taking about things like fire risk.

Btw I am fully persuaded on the merits of using lead acid only for non critical loads. My plotter, sounder, autopilot, and nav lights will remain on the lead acid system. I haven't decided about radar yet, it's a big consumer but then again often used whilst motoring, much the same as the autopilot.

The point is that you have thought about the 'sudden disconnect problem'. I frequently read stuff that fails to even mention it. I come across people who have 'upgraded' to drop-ins who haven't thought about it. I think you can boil it down to three little questions:

1. How will you know if your LFP is about to disconnect?
2. What will be the effects?
3. How are you going to prevent or mitigate these?

 

[Poey50]

Just in case anyone thinks I'm going soft on drop-ins this is now my ideal DIY model for a safe and, as far as I can tell, ABYC compliant system.

1. Plastic-cased new Grade A cells matched for capacity and internal resistance. E.g. Winston.
2. 4S configuration (or 8S for 24 volt)
3. Compression with aluminium end-plates
4. A full-featured BMS that, as well as the usual cell monitoring and balancing functions, is configurable by Bluetooth, controls charging sources, and facilitates disconnect warnings.
5. Separate charge and load buses
6. External fail-safe latching relays not internal mosfets
7. LFP charged direct with suitable alternator and external regulator
8. All other charging sources fully user-configurable by Bluetooth.
9. Alternator protect device
10. AGM start battery charged from LFP by B2B
11. Class T fuse

My system doesn't measure up to my ideal on points 1, 3, 4, and 11. Of these I can fix 3 and 11. I might eventually fix 4 if costs come down, and I've already decided to live with 1.

 

[TernVI]

Just in case anyone thinks I'm going soft on drop-ins this is now my ideal DIY model for a safe and, as far as I can tell, ABYC compliant system.

• Plastic-cased new Grade A cells matched for capacity and internal resistance. E.g. Winston.
• 4S configuration (or 8S for 24 volt)
• Compression with aluminium end-plates
• A full-featured BMS that, as well as the usual cell monitoring and balancing functions, controls charging sources, and facilitates disconnect warnings
• Separate charge and load busses using external bistable relays not internal mosfets
• LFP charged direct with suitable alternator and external regulator
• Alternator protect device
• AGM start battery charged from LFP by B2B
• Class T fuse

I suspect the aluminium endplates will have to be quite massive, or much more subtle than mere 'plates' to give uniform compression across the cells?
Bistable relays seem like a retrograde move with no defined failure state.

 

[Poey50]

I suspect the aluminium endplates will have to be quite massive, or much more subtle than mere 'plates' to give uniform compression across the cells?
Bistable relays seem like a retrograde move with no defined failure state.

6mm for the plates is adequate. Compression does not need to be high. Good point about bi-stable. I should have written fail-safe external latching relays which is what I use. I've re-edited.

 

[Poey50]

Class T fuse