270ah DIY LiFePO4 build

[vas]

Sorry, don't understand that.
Do you mean that current in and out of each cell needs to be measured down to mA resolution? Not come across that before.
A smartshunt is measuring amps in/out, 100% was set charging at 3.6v per cell when the current going in had tailed off to about 3A.

DiyBMS looks like it has microcontroller on each cell, can´t see the point of that with no active balancing. I´m going for op amps as differential amplifiers with unity gain, then an ADS1115 to do the measuring. Should be sub mV accuracy.

Something like ......
But will need to drop the + voltage a bit as op amps aren´t rail to rail. Maybe a low pass filter in case the inverter puts some noise in. Learning as we go along here
An ESP32 to do the thinking, it can get current data from the smartshunt, control the latching relays & send voltage data o a raspberry pi.

Voltage followers soldered on a test PCB already, need to ad the differential op amps & test. JLCPCB will make the boards (plenty spares ) once it works.

sorry, not meant measure each cell mA in out, whole bank via decent current monitor.
OK, reset mA in/out at 3.6 (too high for my liking) maybe 3.55, or less as unless you setup the system to reach that voltage per cell, in/out tally will keep on growing without resetting. OK, in theory no problems, just would be nice to say once every couple of weeks you get the battery to the top to reset counters.

 

[GHA]

sorry, not meant measure each cell mA in out, whole bank via decent current monitor.
OK, reset mA in/out at 3.6 (too high for my liking) maybe 3.55, or less as unless you setup the system to reach that voltage per cell, in/out tally will keep on growing without resetting. OK, in theory no problems, just would be nice to say once every couple of weeks you get the battery to the top to reset counters.

Ta. Smartshunt must be as accurate as there is so happy with that, and agree, won't go as high as 3.6v next time even though within datasheet. No need just to get a tiny bit more capacity. Just metered each cell with a fluke, every cell resting at 3338mV

 

[vas]

true, if you see the graphs going from 3.55 to 3.6 you probably gain a few Ah, not worth it imho. I love LifePO4 mainly for the fact I can have them idle or taxing them with 90A running my 1.8kW watermaker and they'll be at the same voltage! The anxiety of getting enough sun and throttling use so that at the end of the afternoon trojans were back to 100% and floating is not here anymore and that's great!
It's also imho important to keep the trojans onboard and charging at the same profile so if something happens and you have to disconnect the lifepo4, you still have proper voltage to run everything. I need to do that as I've not sorted (and most likely wont!) alternator charging, so if I motor for hours eventually lifepo4 bank is full so needs to disconnect and I don't want to burn the regulator so current from the alternator has to go somewhere ==trojans

 

[GHA]

true, if you see the graphs going from 3.55 to 3.6 you probably gain a few Ah, not worth it imho. I love LifePO4 mainly for the fact I can have them idle or taxing them with 90A running my 1.8kW watermaker and they'll be at the same voltage! The anxiety of getting enough sun and throttling use so that at the end of the afternoon trojans were back to 100% and floating is not here anymore and that's great!
It's also imho important to keep the trojans onboard and charging at the same profile so if something happens and you have to disconnect the lifepo4, you still have proper voltage to run everything. I need to do that as I've not sorted (and most likely wont!) alternator charging, so if I motor for hours eventually lifepo4 bank is full so needs to disconnect and I don't want to burn the regulator so current from the alternator has to go somewhere ==trojans

Cruising I don't think people really pay enough attention to the psychological side of things, not constantly having the background niggle of getting the trojans back to 100% the relief was instant! No more running the genny for hours and hours about once a week to get all the way back up if spending a winter up a river or whatever. Just doesn't matter. And was half thinking of a bit more solar to get more power in during bulk. Not thinking that any more
And the trojans stay, though doubt if they will get used at all, just give them a little top up once in a while. Going to hard wire the alternator to them, there's a 25a dc/dc coming from aliexpress to get some charge into the lifepo4 when the engine is running. And can combine the banks to make full use of the 120a alternator but that would be bit dodgy, might get a chunk of power before it overheated (of course there's a thermometer on it going in to signalk)
And just had another thought, made up a switch panel so the mains charger and solar can go to either or both banks, might be able to plug the mains charger into the inverter running off trojans/alternator and get some more safe charge to the lifepo4 when the engine is running......... Hmmm...... Knew going for the big alternator option would pay off one day

 

[GHA]

sorry to revive the thread,

Quick Q, what rules have you set in your LifePO4 banks? do you let them charge at say 0.1C or 0.2C at 2 or 3Centigrade? or do you disable charging at these temps altogether and only use them for certain small loads until the weather improves?
Have 3-4C on board atm and expected to stay like that for the rest of the week, stock rules means that it's disconnected atm, wouldn't mind turn it on for some 1-2Ah loads (304Ah bank) and possible 2-3A charge via solar.

cheers

V.

Came across this over morning coffee. You first

 

[vas]

Came across this over morning coffee. You first

nah, my victron mmpt is controlled from the diyBMS via canbus. Same goes to the Multi II. so just set a couple of values in the BMS and all is sorted, tail current and all, v.happy with that.

 

[GHA]

nah, my victron mmpt is controlled from the diyBMS via canbus. Same goes to the Multi II. so just set a couple of values in the BMS and all is sorted, tail current and all, v.happy with that.

It was the charging under zero bit that thought might have been of interest.

 

[vas]

It was the charging under zero bit that thought might have been of interest.

ah, OK. this guy annoys me I must admit, so couldn't watch the lot will have a coffee and try again harder later!

 

[GHA]

ah, OK. this guy annoys me I must admit, so couldn't watch the lot will have a coffee and try again harder later!

it´s only a few seconds so maybe not worth the bother. Loads interesting testing on that channel though.

 

[GHA]

gonna start selling power soon at this rate

 

[Poey50]

gonna start selling power soon at this rate

Very nice! What happened yesterday - did you have a dull day or a big blast on the inverter?

 

[GHA]

Very nice! What happened yesterday - did you have a dull day or a big blast on the inverter?

Never considered for a moment getting a compressor onboard til someone showed a hookah setup for diving on coppercoat, now compressor turns on flick of a switch gets used lots! Yesterday was sanding, air gun handy to blow away the worst of the dust
LiFePo4 - what a huge gamechanger for liveaboarding!!!

 

[vas]

LiFePo4 - what a huge gamechanger for liveaboarding!!!

I'd add old boat maintenance as well there!
I believe all boats in swing moorings (or without shore power) should have 300Ah lifepo and 300W of solar

 

[GHA]

I believe all boats in swing moorings (or without shore power) should have 300Ah lifepo and 300W of solar

Don´t need so much solar with Lifepo4 as lead acid though, no more watching the little electrons drip drip into a lead acid desperate to get back up to 100% again!.
All cells within 1mV of each other, feels kinda good....

 

[vas]

Don´t need so much solar with Lifepo4 as lead acid though, no more watching the little electrons drip drip into a lead acid desperate to get back up to 100% again!.
All cells within 1mV of each other, feels kinda good....

actually you do need lots of solar! you have a bank which has much higher capacity (and usable one!) than the previous LA (more often at least) and you end up being less careful on el.usage so you end up with lifepo4 bank hovering between 20 and 50 that's my personal experience from last summer season onboard. OK, generator clocked 3h only compared to the 30odd of previous year

 

[geem]

actually you do need lots of solar! you have a bank which has much higher capacity (and usable one!) than the previous LA (more often at least) and you end up being less careful on el.usage so you end up with lifepo4 bank hovering between 20 and 50 that's my personal experience from last summer season onboard. OK, generator clocked 3h only compared to the 30odd of previous year

I plan to build a lifePO4 domestic bank in the summer. We plan to stay during hurricane season. I am doing it for the fun if it. I will, at a later date, convert it to liquid cooled.
However, we have 720w of solar charging the domestic bank. The domestic bank is 4x225Ah 6v Trojan wet cell batteries. They are coming up to 4 years old. They typically get down to 80% charged over night. The night time load is pretty normal but we have two relatively small fridges with a freezer inside one of them. The fridges are energy efficient.
The batteries get to float every day with only solar and we switch on the immersion heater for a couple of hours each afternoon to heat a tank of hot water.
The engine and domestic bank have battery balancers and desulphaters installed from new.
Everything works very well and efficiently and we have no battery charge anxiety.
The lifePO4 build will be for fun not out of a need to improve the system. I may well run three banks of batteries until the Trojans die of old age. I suspect that may take a while. Friends with a similar set up, full time in the heat of the Caribbean got 8 years from their Trojans.

 

[GHA]

Does anyone else log the voltage of each cell to influxdb? Can the various BMS's even output cell voltage to a Rasp Pi?

 

[Kelpie]

Being able to run power tools and a 1kw wet and dry vac was a game changer for me when working aboard. We have 1.2kw of PV and look a bit like a small floating power station

@geem if you build an experimental LFP pack you'd be in a good position to try out a little idea I had: charge the LFP rapidly during the day, then use it to trickle charge your lead acid batteries overnight to get them up to 100%, prolonging their lives.

I investigated this plan but when I came to decide how to split the Ah between LFP and lead acid, I found I could get LFP cheaper anyway so just kept it simple. I think prices have risen in the two years since then, though.

 

[vas]

testing generator, started it for 10mins this morning. Cells fairly unballanced after 4 months doing bugger all (mostly), monitoring cell temps and passive ballancer temps as well

 

[vas]

Kelpie, doesn't work, or rather you need a B2B to do that.
what I've done is I still have the halfdead Trojans online and in parallel to the lifepo. So if something goes wrong and lifepo disconnect, I still have batteries online to take the load (say alternator) and everything's fine.
I wouldn't dare have service bank lifepo only tbh.