270ah DIY LiFePO4 build

[geem]

Do we really need to fuse the battery?

I don’t have one. All consumers downstream are fused. All cables from the battery are very big and routed separately to the main bus with no feasible possibility of a short as the neg wires are remotely located. In effect the battery can be thought of as directly connected to the bus bars.

I have some ridiculous peak currents in my setup. A big electric bow thruster, electric furlers, winches and windlass. Unlikely to be on at once, but if they were to be, no fuse could cope, so another reason to not do it.

I understand this is a common practice, as it is to not fuse the wires to the starter.

A bigger risk is an battery internal short. Maybe that should be addressed first.

My boat was built 42 years ago. The starter battery domestic battery and windlass all have fuses. All original

 

[Zing]

My boat was built 42 years ago. The starter battery domestic battery and windlass all have fuses. All original

I'm sure it reflects the details of the installation. If the battery fuse is big enough to not fail in normal use it will give protection from a catastrophic short and that is a good thing. Of course all consumers need fusing.

 

[mitiempo]

Of course all consumers need fusing.

Including engine start batteries in my opinion. Any engine of a smaller size - under 150 hp or so - can be easily fused.

 

[Poey50]

Given the flurry of Lithium posts on the forum at the moment, I thought I'd resuscitate this thread and do a brief update on my system built in August 2020.

My pack is now two and half years old and has performed very well. The 123 Smart BMS has many excellent features but because it uses individual cell boards, cells 1 and 4 (which power respectively BlueTooth and the latching relays) tend to drop below the middle two cells in voltage. No problem if you charge to full once per month to engage the passive balancing.

I have two measures of capacity - a Victron BMV 712 and the inbuilt capacity measure using information from the Hall effect sensors. Both are fine when the system is being regularly used but both drift during winter lay-up or other periods of non-use. I find that reading the cell voltages gives a better measure of capacity during low-use periods.

When leaving the boat whether for short or long periods I leave one 80 watt panel connected powering the pack by way of a Victron Smart MPPT. I have storage settings of absorption and float at 13.2 volts. This holds everything steady maintaining a state of charge around 60%. I usually have my DIY 'Remot-a-Boat' connected to monitor voltage of LFP and my Red Flash start battery. I can also switch on remotely a second panel if I want to up the charge in the days before going to the boat (this has a separate MPPT with absorption at 13.8 volts). Another remote relay switches on the Victron B2B if I want to give the start battery a boost.

When I imported the cells from China through RJ Energy I went into this with my eyes open with full knowledge that I was not buying grade A new cells (despite the advertising) but most likely ex-military cells being sold off relatively cheaply. I did however have knowledge that RJ Energy would honour their warranty if there was a problem since I had read some accounts of this, in one case when there had been clear operator error. Three of my cells were very good but one seems to have always lagged in terms of capacity and was not well matched to the others. RJ Energy (by way of Carl Wu) have now agreed to replace that cell and have just sent me the tracking number. This was done without having to return the bad cell. So that seems fair.

When it arrives I will do a rebuild of the pack using the better flexible busbars mentioned a couple of pages ago. I will also be adding an active balancer and the Class-T fuse and holder. Finally I will test for capacity to see how close the pack still is to 270 ah.

That's enough technical stuff. The user experience has been excellent. I have little space for solar on our Sadler 32 and LFP absolutely maximises my small solar capacity. Given Brexit and some health issues we are no longer heading to the Med post-retirement but instead going north where the sun don't shine so well, so I am very glad to have bitten the bullet and added the Balmar alternator, external regulator and serpentine belt upgrade to add 80 ah per hour under engine.

 

[Poey50]

I'd be interested to hear progress on the other builds that have popped up on this thread, especially any lessons learned.

 

[LoneHort]

Thanks Poey. So I took a different route when redesigning mine and went with the relay driven X2 BMS from Batterybalance. An excellent bit of kit and I have it deployed with 3 relays , 1 for all my chargers, 1 for my consumers and the 3rd allows me to connect back my chargers to my consumers and in turn drive the boat off my LA starter battery should anything happen the lithium bank. I love the way this BMS connects up teh Lithiums and LA banks which allows my alternator and any other charge device to always see a battery (i.e.) the LA one. The BMS may close the charge relay and indeed it notifies my mastervolt external regulator 3 seconds in advance to shut down the alternator but even if that failed it should not damage the alternator as it will still "see" the LA. My cells 8 x 280A from Shenzen Basen make up my 24v bank and those flexible busbars are great. 1 cell is reading like yours lower my about 26mv but the builtin balancer on the bms usually corrects it.

 

[Draystone]

I've followed this thread from the beginning and will embark on my own project in the new Year. Thanks for posting it has been very interesting.

Regarding the 123 Smart BMS module current imbalance. Assuming the worst module current drain is acceptable; you could increase the other module loads so that they are much better matched. IE, add a resistor to each of the other modules. A resistor around 420R will take 9mA from a 3.7V cell, dissipating <35mW.

That's based on 2mA and 11mA given for the boards in the datasheet.

Just a thought.

 

[Poey50]

I've followed this thread from the beginning and will embark on my own project in the new Year. Thanks for posting it has been very interesting.

Regarding the 123 Smart BMS module current imbalance. Assuming the worst module current drain is acceptable; you could increase the other module loads so that they are much better matched. IE, add a resistor to each of the other modules. A resistor around 420R will take 9mA from a 3.7V cell, dissipating <35mW.

That's based on 2mA and 11mA given for the boards in the datasheet.

Just a thought.

Thanks for the suggestion. I think it's likely that one of the inexpensive active balancers should fix this. Unlike passive balancers that burn-off power from my cells when charged above 3.4 volts, active balancers operate to transfer power from higher to lower cells.

 

[Poey50]

Thanks Poey. So I took a different route when redesigning mine and went with the relay driven X2 BMS from Batterybalance. An excellent bit of kit and I have it deployed with 3 relays , 1 for all my chargers, 1 for my consumers and the 3rd allows me to connect back my chargers to my consumers and in turn drive the boat off my LA starter battery should anything happen the lithium bank. I love the way this BMS connects up teh Lithiums and LA banks which allows my alternator and any other charge device to always see a battery (i.e.) the LA one. The BMS may close the charge relay and indeed it notifies my mastervolt external regulator 3 seconds in advance to shut down the alternator but even if that failed it should not damage the alternator as it will still "see" the LA. My cells 8 x 280A from Shenzen Basen make up my 24v bank and those flexible busbars are great. 1 cell is reading like yours lower my about 26mv but the builtin balancer on the bms usually corrects it.

I've heard good things about the X2 BMS. May I ask how much that cost, if that isn't too bold? One of the other advantages of keeping a lead acid start battery available is the ability to soak up the voltage spike from a BMS-inspired shut-down. It sounds like your system takes full advantage of that. Do you have a schematic?

 

[nfluester]

i have some cells in the for sale forum if someone wants some smaller sized ones to dip your toe into lithiums

 

[Kelpie]

We're a little over a year in to our budget lithium project. Overall I'm very pleased with it. It's in daily use, driving quite heavy loads for cooking. Compared to a lot of other systems it's all very basic- nothing is automated, no heat mats, no engine charging, and the only shore power charging is via a simple 30A charger.

The only major failure so far was that my original Epever inverter failed after a BMS shut off. If I had still been in the UK I would have had various options for refund, repair, or replacement, but instead I bought a Victron which cost almost as much as the rest of the system combined!

I have also had to top balance the cells once, which I put down to not being careful enough first time round. It's been fine now since January.

My JBD BMS and Alibaba cells have been perfect. Still find it hard to believe that I was able to build a 271Ah battery for £407 including delivery.

I originally bought a 3kw inverter and planned to run it via a relay. But I never got around to wiring that up, and have just run it through the BMS which is rated up to 120A. When the inverter died I replaced it with a smaller one (2400w). I have also now bought a new JBD BMS, rated at 200A, which I hope will run cooler and have a longer life, whilst allowing me to draw more current. The 120A unit will go in to the spares locker.

I know it's possible to build a much more complex system but I'm perfectly happy with my cheap and cheerful setup.

 

[sailaboutvic]

@ Poey 50 can I ask was it cell 1 or cell 4 that was drifting?
I sold my boat so I can't say how my set are still performing but the other boat I set up at tge same time is still going strong but like mine if I tried to charge to over 14.1v cell 4 in my case would run off the same would happen with the other boat , even tho they where top bal and A grade Calbs cells .
As you know I wasn't impressed with the 123 smart bms mostly because of it passive balancers you might fine if you add a active balancer it may help to keep them more in line with each other.

I'm planning to build a new bank over winter for the new to us boat , but I won't be using 123 smart this time .

 

[Poey50]

@ Poey 50 can I ask was it cell 1 or cell 4 that was drifting?
I sold my boat so I can't say how my set are still performing but the other boat I set up at tge same time is still going strong but like mine if I tried to charge to over 14.1v cell 4 in my case would run off the same would happen with the other boat , even tho they where top bal and A grade Calbs cells .
As you know I wasn't impressed with the 123 smart bms mostly because of it passive balancers you might fine if you add a active balancer it may help to keep them more in line with each other.

I'm planning to build a new bank over winter for the new to us boat , but I won't be using 123 smart this time .

It was cell 1 that was out of step with the others Vic. Do you have a new BMS in mind?

 

[Poey50]

We're a little over a year in to our budget lithium project. Overall I'm very pleased with it. It's in daily use, driving quite heavy loads for cooking. Compared to a lot of other systems it's all very basic- nothing is automated, no heat mats, no engine charging, and the only shore power charging is via a simple 30A charger.

The only major failure so far was that my original Epever inverter failed after a BMS shut off. If I had still been in the UK I would have had various options for refund, repair, or replacement, but instead I bought a Victron which cost almost as much as the rest of the system combined!

I have also had to top balance the cells once, which I put down to not being careful enough first time round. It's been fine now since January.

My JBD BMS and Alibaba cells have been perfect. Still find it hard to believe that I was able to build a 271Ah battery for £407 including delivery.

I originally bought a 3kw inverter and planned to run it via a relay. But I never got around to wiring that up, and have just run it through the BMS which is rated up to 120A. When the inverter died I replaced it with a smaller one (2400w). I have also now bought a new JBD BMS, rated at 200A, which I hope will run cooler and have a longer life, whilst allowing me to draw more current. The 120A unit will go in to the spares locker.

I know it's possible to build a much more complex system but I'm perfectly happy with my cheap and cheerful setup.

That is an incredibly low price.

 

[sailaboutvic]

It was cell 1 that was out of step with the others Vic. Do you have a new BMS in mind?

Not yet need to do more research,
Much have changed since I build mine.
Personally for the price of the 123 smart I felt it was very poor , plus all tho bits or wire to connect.
Plus it was open to get damage .

 

[Kelpie]

Not yet need to do more research,
Much have changed since I build mine.
Personally for the price of the 123 smart I felt it was very poor , plus all tho bits or wire to connect.
Plus it was open to get damage .

My JBD cost about £65. The newer 200A one was £100. The only thing I can really say against it is that the balance current is pretty small (60mA on the 120A, not sure on the larger one) and it's a bit of a blunt instrument which does not do any clever interfacing with other equipment. It just protects the cells.

In my experience, which is not extensive, the balance current is perfectly good. If you need active balancing or much higher balance current then there is something wrong.

 

[Poey50]

One of the 4 cells on my 271 ah pack has been lagging behind the others so I thought I would put the 5 year warranty claim to the test. With barely any hassle a replacement cell arrived from RJ Energy in China last week. I top-balanced the pack with the replacement cell and did a fresh capacity test. The test was ended when any cell reached the low voltage cut-off figure of 2.9 volts. This came to a very satisfying 266.5 ah. So 4.5 ah has been lost from pack capacity in 29 months, equivalent to a respectable 0.7% loss of capacity per annum. Not bad for second-hand* cells bought on the grey market.



* These aluminium prismatic cells are invariably marketed as new and Grade A. That always needs to be taken with a large pinch of salt. The most likely account I have read is that these companies like RJ Energy are traders passing on ex-military cells, despite the websites showing factories and certificates. The cells do usually deliver the stated capacity but it is as well to check this with an inexpensive capacity tester - the green object on the right. Many of these 'firms' nevertheless have good reputations. The DIY Solar forum is a good source of information on respectable traders / 'companies'.

 

[Trident]

Very good indeed . Just to show that "good" drop in batteries also last well IF properly installed with regard to charge etc, my Renogy 700ah bank has been used full time as a live aboard for almost 4 years now, with heavy draws for electric cooking etc and has lost 0.53% of its capacity in that time.

 

[Poey50]

The rebuild was a good chance to try out my Yaorea YR1035+ resistance tester to check the internal resistance of the cells. Measured through the busbars the resistances varied between 0.75 milli-ohms and 0.22 milli-ohms, but with the bus bars removed and measured direct on the terminals the resistances varied only between 0.17 and 0.16. That seems impressive to me to get such a well-matched set of cells as a grey import. The other lesson is that the busbar to terminal connection is clearly vulnerable to mismatch and, for anyone building a pack, that alone might justify the purchase of a resistance tester (which is ridiculously easy to use) to check that all connections are good. Cost of the unit from Ali Express is currently £42. It looks very well made. Real Four Wire Lithium Battery Internal Resistance Tester YR1035+ Nickel Hydrogen Lead Button Polymer Alkalinity|Battery Testers| - AliExpress

Off-Grid Garage has a video on it.

 

[gregcope]

The only thing I can really say against it is that the balance current is pretty small (60mA on the 120A, not sure on the larger one) and it's a bit of a blunt instrument which does not do any clever interfacing with other equipment. It just protects the cells.

In my experience, which is not extensive, the balance current is perfectly good. If you need active balancing or much higher balance current then there is something wrong.

I see JK now do a 4S 200A BMS that is quite small that has a 2A active balancer current if that is required. Take your point about not being neccessary.