Planning for DIY LiFePO4

Poey50

Poey50

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For anyone who is a) cycling their batteries off-grid on a daily basis, b) has a minimum of ten years sailing left in them and c) is a bit nerdy, I think there is a good case to be made for a DIY LiFePO4 system. I'd be interested to hear of anyone else working on this as I'm very much at the reading, plotting and waiting-for-prices-to drop-further stage. (I'd prefer not to have to engage in battles over economics as we did that recently. If you get your batteries from a skip, I'm happy for you, but I don't need to discuss it.)

Just to clarify, I'm not talking about so called 'drop in replacement' LFP batteries which I think are not really suitable for marine installations, despite them cropping up on YouTube sailing channels with increasing regularity - although if you feel you have a good system in mind which gets over the problem of a drop-in suddenly disconnecting itself from everything, it would be interesting to hear it. Neither am I tempted by expensive integrated LFP systems such as Victron which look superb but at an incredible price. In fact, cut the top off a Victron Lithium battery (first below) and you will find Winston Thundersky LiFeYPO4 cells which are widely available both by import from China or (without import duty) from GWL in the Czech Republic (second below) at a considerably lower price. Building an LFP battery is not hard, it is keeping it and its owner alive through a sensible marine system that is the challenge.

So .. anyone hatching plans or has an installation?

Inside a Victron LiFePO4 Battery

EV-Power | Winston (40-1000 Ah)
 
I'm waiting for prices to drop.
I think there is a lot of scope for that.
And for the charging/battery management stuff to mature a little.
I sometimes work with someone who has an industrial interest in these things.
Boat wise, I'm taking a long hard look at the demand side of the equation.
For us, storing power is the technically easy bit (if heavy on the credit card!) between not generating enough and using too much...
 
This is a personal viewpoint from using LiFe batterys on a daily basis ... I've posted before about it but here goes ...

In terms of replacing NiCd / NiMh battery packs and systems - LiFe make excellent sense - they are far more tolerant of high discharge rates and can be discharged to low levels and recover.

The expense of using them in higher capacity roles - is amply illustrated by others links / posts ...

But in lower capacities and powering ancillary equipment ... LED lighting ... they are excellent.

Personally I can never see myself paying for large capacity LiFe .. its just way out of economics ... but in smaller - yes no problem.
 
Will be soon be downsizing from over 800 to 300, but also on a plug much more often. Beefing up to an invertor/charger to match the alternator is first priority.
 
ryanroberts said:
Will be soon be downsizing from over 800 to 300, but also on a plug much more often. Beefing up to an invertor/charger to match the alternator is first priority.
Click to expand...

If you'll only have 300Ah of batteries to charge, don't assume you need the same theoretical output current as the alternator. Batteries can only accept a certain charge, regardless of how much theoretical charging current you have. Better to measure the actual charge current the alternator is delivering, then make your decision on a charger.
 
Currently a 15A charger and 110A rated alternator, so some wiggle room. Am reasonably familiar with the joys of batteries living mostly off grid for 8 years.
 
One of the drivers of LFP on boats seems to be the ever-increasing demand for power to drive big inverters, freezers, electric cookers, microwaves and the like. But increasing storage capacity is just one part of the picture, you still need a way of replenishing power used and I've really no desire to become a manager of a small power station. Ours is a 32 foot boat with an L-shaped battery box that can take 2 x 100 SLA batteries or if I pay a lot more 2 x 130amps. (The engine battery is a small sealed AGM which is tucked away elsewhere.) With 8 prismatic cells I can easily fit a battery by joining two sets of four cells (in a 2P2S configuration) in series, each half of the battery occupying the two legs of the 'L'. and then forming a 2P4S single battery of 12 volts and 200 ah. Using a very conservative range for long-life of between 90% and 30% state of charge gives 120 usable amp hours. This compares to something like 70 - 90 usable ah with my SLAs (for brand new 100ah or 130ah with a relatively steep decline assuming difficulty in regularly getting the batteries back to full charge to inhibit sulphating). But the other gains for a small boat is the lower resistance of LFP to receiving charge so charging from alternator and solar is more efficient.

The additional gains are to have the whole system maintenance-free, not to have to intervene at all in normal operation, and never have to buy batteries again. The last of these might sound fanciful but I have about 15 years left in my sailing and reports for those who have well-designed systems is that properly charged LFP batteries are still going strong after 12 years +. There are plenty of examples of LFP batteries with shortened lives through poor charging practices or over-discharge but no-one knows how long good systems will last as they are still going. Lithium battery systems | Nordkyn Design

The ambition is to have 4 escalating levels of protection.

1. Easy monitoring of batteries at cell level - state of charge, cell balance, temperature. (Several BMS's now have Bluetooth.) Only to keep an eye as needed but not required for normal operation.
2. All charging sources automatically controlled and ceasing at 90% charge - no float. No manual intervention required in normal operation. (A B2B charger and solar controllers can be user-defined for LFP.) Passive balancing of cells.
3. Warning alarms prior to low voltage disconnect, high voltage disconnect, high temperature disconnect, low temperature disconnect. (A Victron BMV712 can do this.)
4. Cell level protection to prevent catastrophic damage to the battery. BMS controlling separate bi-stable relays for charge bus and load bus. (Separate in order that a low voltage disconnect of all loads still allows the battery to be charged, and a high voltage disconnect does not cut off the loads.)
 
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Yes watching my current huge mastervolt and engine putting 6A into the batteries is a sad sight in winter. The charge behaviour (and hopefully not having to hoof them out every 3-4 years with heavy use) are a big appeal.
 
I can’t remember details, but my daughter spent lots of time researching before fitting out her van. She has a £700 battery, a 250W panel, split charging, and this is enough for her to work on a laptop all day. There were lots of issues with getting the system right and fire safe.
 
Poey50 said:
For anyone who is a) cycling their batteries off-grid on a daily basis, b) has a minimum of ten years sailing left in them and c) is a bit nerdy, I think there is a good case to be made for a DIY LiFePO4 system. I'd be interested to hear of anyone else working on this as I'm very much at the reading, plotting and waiting-for-prices-to drop-further stage. (I'd prefer not to have to engage in battles over economics as we did that recently. If you get your batteries from a skip, I'm happy for you, but I don't need to discuss it.)

Just to clarify, I'm not talking about so called 'drop in replacement' LFP batteries which I think are not really suitable for marine installations, despite them cropping up on YouTube sailing channels with increasing regularity - although if you feel you have a good system in mind which gets over the problem of a drop-in suddenly disconnecting itself from everything, it would be interesting to hear it. Neither am I tempted by expensive integrated LFP systems such as Victron which look superb but at an incredible price. In fact, cut the top off a Victron Lithium battery (first below) and you will find Winston Thundersky LiFeYPO4 cells which are widely available both by import from China or (without import duty) from GWL in the Czech Republic (second below) at a considerably lower price. Building an LFP battery is not hard, it is keeping it and its owner alive through a sensible marine system that is the challenge.

So .. anyone hatching plans or has an installation?

Inside a Victron LiFePO4 Battery

EV-Power | Winston (40-1000 Ah)
Click to expand...

I installed a 520Ah system with 4 x 130Ah drop in 12V second hand units in December. My control is a Victron Battery Protector which will cut the discharge power if the voltage falls below 12.5V in my case, (I can change that to quite a bit less if I want). I have a Victron BMV 712 monitor which will provide temperature protection and high voltage cut off via its own small relays controlloing a couple of 100A relays in the charging cable, when I fit them.

As to not wanting a system to disconnect itself.... I think in the circumstances that a system would disconnect itself, you would definitely want your system to disconnect itself :)

If you don't build some kind of protection into your multi cell, DIY system, that cuts it off when so instructed, then you might destroy your investment in short order. In fact that is what the BMS you fit will be designed to do.

With LiFePo4 cells/batteries, the chances of killing the owner are fairly slim, but not nil. A bit like the chances of a Lead Acid system exploding and killing or disfiguring.
 
I've found Will Prowse youtube site very useful, and any interviews with the owners of Battleborn batteries are equally informative, even if you dont want a drop in 12V system.
 
Richard10002 said:
I installed a 520Ah system with 4 x 130Ah drop in 12V second hand units in December. My control is a Victron Battery Protector which will cut the discharge power if the voltage falls below 12.5V in my case, (I can change that to quite a bit less if I want). I have a Victron BMV 712 monitor which will provide temperature protection and high voltage cut off via its own small relays controlloing a couple of 100A relays in the charging cable, when I fit them.

As to not wanting a system to disconnect itself.... I think in the circumstances that a system would disconnect itself, you would definitely want your system to disconnect itself :)

If you don't build some kind of protection into your multi cell, DIY system, that cuts it off when so instructed, then you might destroy your investment in short order. In fact that is what the BMS you fit will be designed to do.

With LiFePo4 cells/batteries, the chances of killing the owner are fairly slim, but not nil. A bit like the chances of a Lead Acid system exploding and killing or disfiguring.
Click to expand...

Our posts crossed - I'm not sure how I gave the impression that I don't want the system to disconnect itself - see my other post. What I don't want is for a drop-in LFP with combined charge and load buses to totally isolate itself so that an overly discharged battery can't be charged and and overly charged battery has disconnected itself from all loads.
 
Richard10002 said:
I've found Will Prowse youtube site very useful, and any interviews with the owners of Battleborn batteries are equally informative, even if you dont want a drop in 12V system.
Click to expand...
Yes, I agree that Will Prowse is excellent in his explanations. Battleborn drop-ins look brilliant but not I think suitable for a marine installation for the reasons given. It doesn't really matter if your LFP on the RV goes into a sulk and won't communicate. That's a different matter on a boat.
 
Poey50 said:
Our posts crossed - I'm not sure how I gave the impression that I don't want the system to disconnect itself - see my other post. What I don't want is for a drop-in LFP with combined charge and load buses to totally isolate itself so that an overly discharged battery can't be charged and and overly charged battery has disconnected itself from all loads.
Click to expand...

Sorry... got the wrong end of the stick :(
 
Richard10002 said:
I installed a 520Ah system with 4 x 130Ah drop in 12V second hand units in December. My control is a Victron Battery Protector which will cut the discharge power if the voltage falls below 12.5V in my case, (I can change that to quite a bit less if I want). I have a Victron BMV 712 monitor which will provide temperature protection and high voltage cut off via its own small relays controlloing a couple of 100A relays in the charging cable, when I fit them.
Click to expand...

Is that going OK? The downside I can see is that the protection is at the pack-level (cutting off depending on the whole battery voltage) rather than at the cell level. If one cell goes out of balance then that might not be picked up at pack level creating risk of damage to the cell. Or do you have a BMS that is disconnecting the battery protectors on the basis of cell imbalance?
 
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Poey50 said:
Yes, I agree that Will Prowse is excellent in his explanations. Battleborn drop-ins look brilliant but not I think suitable for a marine installation for the reasons given. It doesn't really matter if your LFP on the RV goes into a sulk and won't communicate. That's a different matter on a boat.
Click to expand...

The interviews with the Battleborn owners give much more information than merely about their own batteries.

For example, I think we all "know" that we shouldnt charge our batteries if the temperature is less than 0C. The CEO of Battleborn explains that we can, if careful. There are other little LiFePo4 nuggets in their chats which I think anyone would find useful.
 
Poey50 said:
Is that going OK? The downside I can see is that the protection is at the pack-level (cutting off depending on the whole battery voltage) rather than at the cell level. If one cell goes out of balance then that might not be picked up at pack level. Or do you have a BMS that is disconnecting the battery protectors on the basis of cell imbalance?
Click to expand...

It's going to be fine.... for me :)

My batteries have a kind of BMS and are connected to a little laptop such that I can see individual cell voltages and differences, along with cell temperatures, (about 8 temperatures in each battery). It doesn't provide any cut off protection in any way... merely information. The BMS does balance the cells given time.

This does mean that, if I plan to charge to a voltage above the upper knee, I need to keep an eye on the laptop to see whats happening. If I charge to above about 14.2V, (roughly 90%), then I need to be careful and keep an eye open. Below that, I can charge and discharge between about 90% and 20% without too much concern.
 
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