270ah DIY LiFePO4 build

[vas]

I’ve just ordered the CPM BMS from GWL. It looks like it will do all I need. High and low cell monitoring and a pulse to a latching relay to a cut off. No balancing, which I see as an advantage. Not too expensive either at EUR 138 plus vat. 16 cell monitoring.

morning,

trying to follow various threads here and elsewhere re LiFePO4 and getting a bit confused on what I've read where. I surely remember someone somewhere mentioning that after 2+ yrs of operation his batteries haven't lost their balance. Cannot be OP in here as iirc he's only got them in last season.
So, is that the reason you see lack of balancing as an advantage?
should be monitoring the cell prices closely and see when I can get from Prague (EU much better than all the agro of non-EU and not knowing what the local taxman will stick on top of the price!) 8Xcirca200Ah cells for under 1 grand...

cheers

V.

 

[sailaboutvic]

morning,

trying to follow various threads here and elsewhere re LiFePO4 and getting a bit confused on what I've read where. I surely remember someone somewhere mentioning that after 2+ yrs of operation his batteries haven't lost their balance. Cannot be OP in here as iirc he's only got them in last season.
So, is that the reason you see lack of balancing as an advantage?
should be monitoring the cell prices closely and see when I can get from Prague (EU much better than all the agro of non-EU and not knowing what the local taxman will stick on top of the price!) 8Xcirca200Ah cells for under 1 grand...

cheers

V.

Just to say when RJ Energy quote me they included everything , shipping, taxes,,custom dues

 

[Poey50]

I’ve just ordered the CPM BMS from GWL. It looks like it will do all I need. High and low cell monitoring and a pulse to a latching relay to a cut off. No balancing, which I see as an advantage. Not too expensive either at EUR 138 plus vat. 16 cell monitoring.

That's an interesting option. It does allow separating charging from load (dual bus system) and also offers more cell-level controls of individual chsrgers than the 123SmartBMS does (unless you buy the extended module). But you do lose the (passive) balancing, temperature sensing, state of charge measurement and cell level display with historical information so I guess you either have workarounds for those or they aren't significant for you (such as temperature which matters less on a boat). Are you planning to simply manually balance occasionally? I wasn't sure how you adjust the settings (something very simple to do with the 123Smart app).

 

[Poey50]

morning,

trying to follow various threads here and elsewhere re LiFePO4 and getting a bit confused on what I've read where. I surely remember someone somewhere mentioning that after 2+ yrs of operation his batteries haven't lost their balance. Cannot be OP in here as iirc he's only got them in last season.

No it wasn't me. There are different views on balancing. One is that you need a balancing system and that you should fairly regularly charge up high enough so that balancing has a chance to do its job. My 123SmartBMS starts balancing at 3.4 volts and monthly balancing is recommended. Battleborn recommend always charging their batteries to full in order to hold balance. Another school of thought is that charging to full is the very thing that causes imbalance and that more conservative charging practice (say up to 90%) avoids the need for balancing other than very occasional manual balancing. From memory this is the Nordkyn view.

 

[Zing]

I surely remember someone somewhere mentioning that after 2+ yrs of operation his batteries haven't lost their balance. Cannot be OP in here as iirc he's only got them in last season.
So, is that the reason you see lack of balancing as an advantage?


cheers

V.

Yes, if you keep out of the top and bottom area of capacity there is no risk of problems from an out of balance situation and you should do that as doing so is very worthwhile for battery life. They also don’t go out of balance if kept in that area, so you are very unlikely to need a balance system. The balancing systems have failed, draining the battery and destroying it. Also it is not practical to balance anyway because with the tiny current rating of balance resistors it means you have to hold volts at an unhealthy high level and worse, for an unhealthily long period. All in all, not attractive.

That's an interesting option. It does allow separating charging from load (dual bus system) and also offers more cell-level controls of individual chsrgers than the 123SmartBMS does (unless you buy the extended module). But you do lose the (passive) balancing, temperature sensing, state of charge measurement and cell level display with historical information so I guess you either have workarounds for those or they aren't significant for you (such as temperature which matters less on a boat). Are you planning to simply manually balance occasionally? I wasn't sure how you adjust the settings (something very simple to do with the 123Smart app).

Indeed. I don’t need any of that except battery capacity and I use my old lead acid amp counter for that, with volts and a look up table as a cross check. Plus I have a couple of cheapo displays I plan to plug in for an occasional monitor. One from Junsi and another colour one, I can’t remember the name of.

Another feature this control card has is a signal 0.3v above the low cut off and below the top too. I am thinking of using them as a genset start/stop trigger.

 

[Poey50]

For those reading over our shoulders, we aren't talking about the initial top balancing - pretty much everyone now agrees that an initial good balance is needed - this is about balancing for ongoing maintenance of the pack.

I'm a bit more of an agnostic on this than Zing. It think it is true that for a conservative range (say 15-90% state of charge) you are unlikely to see any imbalance and it MAY be the case that not charging frequently to full charge avoids imbalance.

Zing writes "Also it is not practical to balance anyway because with the tiny current rating of balance resistors it means you have to hold volts at an unhealthy high level and worse, for an unhealthily long period."

It depends on the BMS and on the magnitude of the imbalance. I can alter the threshold at which balancing starts - the recommended figure is 3.4 volts per cell and this gives plenty of opportunity for balance before state of charge gets too high. Some people have the threshold higher than this and drop-in batteries seem to require always taking the battery to full charge and that might be more of a problem.

 

[kitling89]

I have been running my ~500ah LiFePO4 battery bank on the boat (with typical boat loads) continuously for the last 6 months with zero need for balancing.
On the other hand my 40 ah, 96v pack in the eBike typically needs some balancing every few charges. Particularly if discharged below 40%. Some of this may also be down to high loads and homebuilt battery quirks.
Depending on what I have my BMS set for, balancing across 22S8P can take over 2 hours at 150ma.

 

[Poey50]

I have been running my ~500ah LiFePO4 battery bank on the boat (with typical boat loads) continuously for the last 6 months with zero need for balancing.

Good to know. What range of SOC are you using?

Depending on what I have my BMS set for, balancing across 22S8P can take over 2 hours at 150ma.

22S8P!

 

[kitling89]

Good to know. What range of SOC are you using?

I am using 4x Valence u27-12xp 130 ah lifepo4 which regrettably are designed for an external BMS controller. The onboard chips do some BMS functionality independently but they are a black box so I don't know what exactly. They definitely don't have a way to isolate the battery so I have had to control under/over voltage, current, temp protection, etc externally. Also I have an older Victron Multiplus that lacks any sort of lithium functionality.

That being said I have the charger set at max bulk voltage of 14.6 as per the battery manufactures spec. Which I hold there for 30 min because I assume that is what voltage the balance circuitry requires and I want to give it a chance.

Then it floats at 13.4. External cutoff at 10.5 but we never go below 11.5 before I start the motor.

22S8P! - Only way to get 3.7v nominal cells to 94+v.

 

[Poey50]

I am using 4x Valence u27-12xp 130 ah lifepo4 which regrettably are designed for an external BMS controller. The onboard chips do some BMS functionality independently but they are a black box so I don't know what exactly. They definitely don't have a way to isolate the battery so I have had to control under/over voltage, current, temp protection, etc externally. Also I have an older Victron Multiplus that lacks any sort of lithium functionality.

That being said I have the charger set at max bulk voltage of 14.6 as per the battery manufactures spec. Which I hold there for 30 min because I assume that is what voltage the balance circuitry requires and I want to give it a chance.

Then it floats at 13.4. External cutoff at 10.5 but we never go below 11.5 before I start the motor.

22S8P! - Only way to get 3.7v nominal cells to 94+v.

Crikey another set-up without a BMS. May you be ever vigilant (and lucky)! I'm lazy and forgetful so ... not for me.

 

[Kelpie]

Two things in reply. First I think your questions are too high level. You need first to more basically work out what kind of lithium system to have on your boat - how all the parts of that work together safely and, as far as possible, automatically. I spent about 18 months researching before spending anything and the most useful series of articles were the 6 by Nordkyn Design which I reference near the beginning. My system has four levels from oversight to catastrophic level protection. For me that was the minimum and that has weaknesses as I have shown in different posts. It is not in the same league as Chris's system which requires little human intervention. It is said that the best systems are where people forget where they installed their LFP. Anything that needs human intervention is a weakness. If you are going to spend a lot of money on cells then you need to keep yourself safe and have a long life from your investment.

So second, I don't believe it is possible to drop safely below £1500 spend, and in the end with fully upgraded alternator charging I spent twice that. I'm happy to be proved wrong (a Zwerfcat hybrid system shows promise here) but for a permanent installation it has to have an upfront investment.

Yes I suppose I am quite out of my depth. It's a very steep learning curve, and it seems that there is never one 'right' answer to designing or specifying a system- it depends on the user's requirements. So I'm at the stage where I trying to learn what the different options entail, and what you lose when you move away from the best practice approach- basically, trading lower costs for higher risks etc. Also for me it doesn't help that I have two quite different applications in mind- a small pack to power my trolling motor, and a permanently installed house bank in the yacht (and yes it's crossed my mind to try and combine these functions, e.g. have two or three portable packs which I can tap in to for extra power on the yacht...I do love to overthink things sometimes).

My budget was originally just for four Trojan T-105s (current best price £690 delivered, so just over £3 per useable amp-hour). We're setting up the boat for bluewater cruising and there are a lot of things needing money spent on them, so I can't push the budget all that much higher.

At the moment I am intrigued by the idea that not pushing charging/discharging to the limit means that you can get away with much simpler protection systems. E.g. if I just set my (4S 12v) battery to stop charging at 14.2v, and to disconnect at 12.6v, that should be enough to keep the cells very happy indeed. I won't get 100% of the potential Ah out of them, but in the scheme of things upgrading to slightly bigger cells might be cheaper than an all singing, all dancing BMS with cell-level protection.

I'm working through the six Nordkyn articles just now and won't actually make any decisions or spend any money until I feel a lot more clued up.

 

[crisjones]

Another feature this control card has is a signal 0.3v above the low cut off and below the top too. I am thinking of using them as a genset start/stop trigger.

Unless you can program this 0.3V difference to a lower value it is not very much use for LiFePo4 cells because of the very flat voltage profile.
Our high voltage cut-out (disconnect) is set at 3.700V per cell, so the 0.3V difference is 3.400V, this equates to about 80% SOC so a good way from normal full charge. At low voltage our cut-off is set at 2.900V, 3.200V is then about 30% SOC.

It might be just about OK for a genset start stop but it is not good enough for controlling other parts of an integrated system. For instance you could not use it to sound an alarm as the cells approach high voltage - it is too far away.

 

[vas]

the more I read about them the more I realise this v.flat voltage profile is annoying in setting up triggering points for charging/disconnecting...
v.good in discharging them though

V.

 

[GHA]

Another cruising boat installation>>

Nice to see she's carrying on after the the sad loss of Patrick.

 

[Poey50]

At the moment I am intrigued by the idea that not pushing charging/discharging to the limit means that you can get away with much simpler protection systems. E.g. if I just set my (4S 12v) battery to stop charging at 14.2v, and to disconnect at 12.6v, that should be enough to keep the cells very happy indeed. I won't get 100% of the potential Ah out of them, but in the scheme of things upgrading to slightly bigger cells might be cheaper than an all singing, all dancing BMS with cell-level protection.

As you read more deeply you will find why cell-level protection is required rather than pack-level protection. An unbalanced pack may stay under your apparently "safe" high voltage disconnect while one cell is exceeding this and becoming damaged. Imbalance at the lower end may mean one cell becomes overly discharged before disconnect creating what Zwerfcat describe as a time-bomb. So cell-level protection is most certainly "not all singing, all dancing" it is really quite basic.

 

[crisjones]

I have been running my ~500ah LiFePO4 battery bank on the boat (with typical boat loads) continuously for the last 6 months with zero need for balancing.
On the other hand my 40 ah, 96v pack in the eBike typically needs some balancing every few charges. Particularly if discharged below 40%. Some of this may also be down to high loads and homebuilt battery quirks.
Depending on what I have my BMS set for, balancing across 22S8P can take over 2 hours at 150ma.

I top balanced our Winston Cells when they arrived to 3.65V per cell using a bench power supply and the instructions from MarinHowTo. I do not have the balancing function activated on our Orion Jr BMS so they have never been balanced since installation.

They have been in daily use on board Nimrod for almost 2 years of full time liveaboard usage completly off-grid without a mains generator or any shore power. Charging by solar and engine alternators if required. The batteries have been cycled down as far as 10% SOC and are frequently charged to 3.5 VPC (14.0V) and I consider this to be 100% SOC.

Whenever I check the cell voltages on the BMS they are always within 0.005V or less of each other at any state of charge, so my view is that so far my Winston cells have remained in near perfect balance without any auto balancing or manual balancing.

 

[gregcope]

@Poey50 Do you not have a little mini-ballancer as well?

 

[vas]

so, is there a cheapish BMS that will do the connect/disconnect on overall SOC, and monitor per cell and disconnect if one goes off, BUT NOT do the (passive?) balance thing?
I mean if crisjones setup works fulltime on lifeaboard for 2yrs, that's probably 15+ yrs of my 2-3m seasonal use in the Med, I can live with that!
I could every winter do a top balance by disconnecting the poles and doing one by one manually balancing, no big deal, a couple of evenings with the right drink at hand

V.

 

[vas]

I agree I wouldn't accept to live in the dark, I'd definitely need a way of monitoring V per cell, but that should be dead easy with any pcl/arduino whatever

 

[Poey50]

I top balanced our Winston Cells when they arrived to 3.65V per cell using a bench power supply and the instructions from MarinHowTo. I do not have the balancing function activated on our Orion Jr BMS so they have never been balanced since installation.

They have been in daily use on board Nimrod for almost 2 years of full time liveaboard usage completly off-grid without a mains generator or any shore power. Charging by solar and engine alternators if required. The batteries have been cycled down as far as 10% SOC and are frequently charged to 3.5 VPC (14.0V) and I consider this to be 100% SOC.

Whenever I check the cell voltages on the BMS they are always within 0.005V or less of each other at any state of charge, so my view is that so far my Winston cells have remained in near perfect balance without any auto balancing or manual balancing.

From my understanding, Winston cells come more reliably matched for capacity and resistance so I wonder if that too is a factor in holding balance and may be something to keep in mind when weighing up whether to go quality plastic-cased or grey market aluminium-cased. That said, I haven't balanced my cells over the last three months and they are still within 0.01 volts.