270ah DIY LiFePO4 build

[Poey50]

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

I did have a cheap active balancer wired in (that redistributes power between cells rather than just burning off the surplus) but I decided to remove it. I didn't want to rely on it as a sticking plaster solution. If there is a problem with the passive balancing on the 123Smart then I'd prefer to find a more lasting solution. As said, so far there hasn't been but it's still early days.

 

[Poey50]

Another cruising boat installation>>

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

How sad that Patrick died. Much more measured and informed view on LFP on boats than most of the vloggers.

 

[Zing]

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.

There is no problem in getting roughly the right area for activation, a bigger problem is getting exactly the right voltage because the switching options are only in 0.1v steps. I can have it trigger a genset on circuit at 3.1v or 3.2v. That corresponds to 90% or 70% capacity about. The 70% would be OK, maybe a little too high. The charge curve is flatter at the top, and my options are to switch off at 3.4v 70%, 3.5v at 90% or 3.6v at 100%, so 3.4v or 3.5Vwould be OK, but ideal would be somewhere in between. There are other options. To feed the highest voltage reading out (which this card can do) to a dedicated voltage sensitive relay and precisely control the switch off voltage at the ideal level or to use a timer - to run the genset for whatever time corresponds to charging it up appropriately. I will still have the HVC for when I cock it up.

 

[Poey50]

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

But people do quite successfully use pack voltage to end charging. My argument to Kelpie was that doing so without a BMS was a risk. (And for me an unacceptable one on a boat pack, although perhaps acceptable for a trolling motor.) I use 13.8v for the alternator charging for example. Using 13.3v or 13.4v as a maintenance voltage on a solar regulator also seems common. Using these lower voltages also makes it less likely that any one cell gets beyond the high voltage disconnect level if imbalance between cells should creep in.

 

[crisjones]

There is another issue with regulation of charging sources that is particularly relevant to Lithium systems, especially solar regulators. My experience is with Victron MPPT units, but they are very common and good quality so are probably the MPPT unit of choice for most people.
Most people are now well aware that it is not a good idea to hold lithium batteries on float at full charge voltage, so if we cannot disable the float phase completely we set the float voltage at a lower level so the battery does not get overcharged. On my MPPT that is set at 13.20V, some use slightly higher levels.
So the sun shines brightly and the MPPT charges the battery in Bulk mode until full charge voltage is reached, then switches to absorption for a short time (15min on mine) and then goes to float mode. Because of the very flat voltage profile this effectively means that the float voltage is lower than the battery voltage and so the MPPT does not produce any charge current at all once it is in float mode. This all sounds perfect for looking after the batteries in the best possible way.

However if you are a liveaboard or have an application where you are regularly drawing power from the batteries this can result in a huge waste of solar energy. The Victron MPPT stays in Float mode until the battery voltage drops below the float setting voltage (0.1V below float for 1 min in mine), this means the battery voltage has to drop to 13.1V before the MPPT switches back to Bulk phase and starts making power again. Since 13.1 volts is around 50% SOC it effectively means that once the MPPT switches to float that is the end of solar charging for the day because we are very unlikely to use enough power to see the battery voltage drop to 13.1V

I do plan to experiment with the settings to see how a slightly higher Float setting would work, maybe 13.4V or even 13.6V would be better to maximise solar power harvest. For a liveaboard application this is probably OK since there is usually enough load on the system from fridge, freezer, computer etc to effectively prevent the battery being held at a high SOC for long periods and hence risk reducing battery capacity over time.

I do have an isolator switch between solar panels and MPPT , turning this off and on again will reset the MPPT to Bulk so that works if I am monitoring the system. Also I tend to run the watermaker once the batteries are full and this is enough to pull the voltage down enough to have the MPPT to return to Bulk.

 

[Poey50]

Great post, Chris. I'm sure you're right that most will be using a Victron MPPT. I can see the problem and will be interested to hear of your experiments. It sounds like there could be a sweet spot for 'float' somewhere within 13.4 - 13.6v depending on residual loads.

 

[Kelpie]

Can loads be put directly on the MPPT?
I read a discussion about doing this with shore power, but that's obviously a much more reliable source.

Or could the MPPT be diverted to a lead acid bank, which then powers the loads, to even out the effects of changing PV output? Maybe the problem here is how to automate the switching, and how to program the MPPT to the new charging profile.

OR... (yes, thinking out loud here) the LFP bank is permanent connected to a lead acid bank via B2B charger, and the loads are taken from the lead acid bank?

 

[vas]

MPPT to FLA and B2B is an option I guess, although it looks like it's getting complicated...
However, the watermaker load would first tax the LiFePO4, when the LFA would be anyway on float (and solar energy lost...)
Unless you have an intelligent CPU which senses loads and inputs and sorts out which bank takes which load and when to switch over, which sounds v.complicated!
Especially for watermaker which is a circa 2KW load, you could start it with FLA, they'll get a decent dip in V which will trigger MPPT to bulk (hence you harvest all energy) and then say 20-30m later, when you've extracted 30odd% off them (with solar pumping in) you switch to LiFePO4 and let the MPPT keeping on charging the LFA.
Then eventually when things settle, the B2B takes over and does it's thing (whatever that is programmed to be)

Of course all the above is pointless on a LiFePO4 only system!

V

 

[crisjones]

MPPT to FLA and B2B is an option I guess, although it looks like it's getting complicated...
However, the watermaker load would first tax the LiFePO4, when the LFA would be anyway on float (and solar energy lost...)
Unless you have an intelligent CPU which senses loads and inputs and sorts out which bank takes which load and when to switch over, which sounds v.complicated!
Especially for watermaker which is a circa 2KW load, you could start it with FLA, they'll get a decent dip in V which will trigger MPPT to bulk (hence you harvest all energy) and then say 20-30m later, when you've extracted 30odd% off them (with solar pumping in) you switch to LiFePO4 and let the MPPT keeping on charging the LFA.
Then eventually when things settle, the B2B takes over and does it's thing (whatever that is programmed to be)

Of course all the above is pointless on a LiFePO4 only system!

V

Maybe easier to manage with a hybrid / combined LiFePo4 and FLA system but the options described above do not really seem that easy a solution!!
We have only LiFePo4 cells in our system hence the problem I described in my previous post.

On our alternators we have programmable external regulators, they are the open source predecessor to the Wakespeed 500 regulators but operate exactly the same. They have a current flow input from the main shunt and when they switch to float mode the regulator senses how much current is required by any loads and it directs the alternators to produce enough power to balance that load - works very well. So the alternators charge the batteries to 100% and then go to float level voltage but still produce some power - end result is the batteries are at 100% and remain at 100% while engine is running but the volatge is not forced too high.

Maybe in the future we will see similar functionality for MPPT regulators, obviously they would need to have a current shunt input to enable it to see the external loads and allow the solar to balance those loads and keep the battey at 100%. That would seem an ideal way to maximise solar power harvest -

No matter what the system you can only harvest the amount of solar power to get the battery to 100% and match any external loads - anything the solar panels can produce above that is always going to be wasted. Unfortunately current solar regulators do not yet allow that level of efficiency.

Just for information for everyone - you do not need a seperate current shunt for each item that needs to see system current flow. One current shunt can be connected to multiple sensors. We have a Victron 500A shunt in our system and it provides current flow info to a Victron battery monitor, Orion Jr BMS and 3 alternator regulators, all works perfectly. Much better than having 5 shunts in a row to provide individual info to each sensor.

 

[vas]

fully agree Chris,
maybe Victron could do what you describe if you have all devices networked (talking about MPPT and BMV with it's shunt) in a later firmware?
wonder if anyone has asked them to do so!
They do seem reasonably flexible (it seems) and the fact that they open sourced their Venus OS is towards this direction I guess.
(fwiw, got it running on a raspberry pi 3B+ well impressed but I'm still on trojans...)

 

[vas]

Maybe easier to manage with a hybrid / combined LiFePo4 and FLA system but the options described above do not really seem that easy a solution!!

pretty sure at least a handful of PBO members could do it, it's not rocket science after all!
monitoring voltages and currents and decision making on 3 or 4 discreet inputs, have done much more complicated things on an arduino...

 

[Poey50]

fully agree Chris,
maybe Victron could do what you describe if you have all devices networked (talking about MPPT and BMV with it's shunt) in a later firmware?

If you have the Victron BMV712 monitor and the Vicron SmartSolar version of the controller then these can make of the VE. Smart networking whereby the BMV sends shunt voltage, current and temperature information to the solar controller.

 

[vas]

well I have the BVM700 & MPPT100/30 (none of them smart) but both are now (as in last few days!) wired to Venus.
The thing is, OK, say they do communicate, does the MPPT get into a different profile and get out of float if there's a big discharge load on the batteries?
Don't think so else Chris would be using it I guess, have to read a bit more about that.
Struggling a bit in getting the MultiPlus 3000/24 to play ball with the rest and then I'll struggle a bit more to get all that lot to talk to N2K

 

[Poey50]

The thing is, OK, say they do communicate, does the MPPT get into a different profile and get out of float if there's a big discharge load on the batteries?

I suppose the networking provides more accurate battery information to the solar controller but that doesn't itself get round the problem of how to nudge the controller out of float assuming that it is the only the battery voltage dropping 0.1v below float for 1 minute which can do this rather than a new load on the battery (but one that doesn't reduce battery voltage by 0.1v for 1 minute) as an alternative independent trigger. I'd be hopeful that tweaking float upwards can improve things.

 

[crisjones]

I suppose the networking provides more accurate battery information to the solar controller but that doesn't itself get round the problem of how to nudge the controller out of float assuming that it is the only the battery voltage dropping 0.1v below float for 1 minute which can do this rather than a new load on the battery (but one that doesn't reduce battery voltage by 0.1v for 1 minute) as an alternative independent trigger. I'd be hopeful that tweaking float upwards can improve things.

The 0.1V below float can be adjusted in .01V steps so that could help a bit also, the 1 min time is fixed.

At the moment we are in the rainy season here in Martinique so we have cloudy skies most of the time, we are lucky to see more than 3hrs sun, usually less!! Also the sun is low in the sky at this time of year, so we are not getting that much solar power.

So our batteries are hardly ever getting to 100% to give me a chance to tweak the float settings, hopefully we will start getting more sunshine hours once we get to December. At least the LiFePo4 cells do not care if they are spending weeks between 30% and 70% SOC

 

[crisjones]

well I have the BVM700 & MPPT100/30 (none of them smart) but both are now (as in last few days!) wired to Venus.
The thing is, OK, say they do communicate, does the MPPT get into a different profile and get out of float if there's a big discharge load on the batteries?
Don't think so else Chris would be using it I guess, have to read a bit more about that.
Struggling a bit in getting the MultiPlus 3000/24 to play ball with the rest and then I'll struggle a bit more to get all that lot to talk to N2K

Our Victron Battery monitor is an older unit so it does not use the same communication protocol as the current range of BMV700 units. We do not have a Venus unit either so no chance of any additional communication with the MPPT.

It would be very interesting to know for sure if the Venus can communicate with the MPPT to force it from float to Bulk if there is load on the system. Even if it can be done, it is no use to me since I am unlikley to go to the expense of a new BMV and the Venus just to get a bit more from the panels. Hopefully tweaking the float setting will provide some useful gains.

 

[vas]

Our Victron Battery monitor is an older unit so it does not use the same communication protocol as the current range of BMV700 units. We do not have a Venus unit either so no chance of any additional communication with the MPPT.

It would be very interesting to know for sure if the Venus can communicate with the MPPT to force it from float to Bulk if there is load on the system. Even if it can be done, it is no use to me since I am unlikley to go to the expense of a new BMV and the Venus just to get a bit more from the panels. Hopefully tweaking the float setting will provide some useful gains.

will report back once I figure out what's going on Chris and will ask at the Venus forum.

just to get it in perspective, a newer BMV (iirc you can keep the old shunt!) will set you back a little (and you can sell back your old one).
further, you don't need to pay 600 or so to get the Venus, I spent 150euro on the raspberry pi 3B+, the 7in touchscreen display and the matching case for the lot. Then 10euro for 2 FTDI usb/serial cables and soldered the 4pin VE.Direct plugs on (which I got from scrap old audio cables off desktop PC CDROMs . I recon it's well affordable, and if you're online most of the time being lifeaboard, you can get all your data on the VRM Portal and be able to plot/check/look back/evaluate visually alterations on the system as well as setup up extra alarms on things going wrong. For the price I think it's brilliant but then again I'm sold on visualising data!

cheers

V.

 

[crisjones]

will report back once I figure out what's going on Chris and will ask at the Venus forum.

just to get it in perspective, a newer BMV (iirc you can keep the old shunt!) will set you back a little (and you can sell back your old one).
further, you don't need to pay 600 or so to get the Venus, I spent 150euro on the raspberry pi 3B+, the 7in touchscreen display and the matching case for the lot. Then 10euro for 2 FTDI usb/serial cables and soldered the 4pin VE.Direct plugs on (which I got from scrap old audio cables off desktop PC CDROMs . I recon it's well affordable, and if you're online most of the time being lifeaboard, you can get all your data on the VRM Portal and be able to plot/check/look back/evaluate visually alterations on the system as well as setup up extra alarms on things going wrong. For the price I think it's brilliant but then again I'm sold on visualising data!

cheers

V.

Very interesting stuff.

Our BMV is one of the original type and the shunt does not even have the little PCB - the shunt connects to a seperate module that then connects to a Blue Power display via RJ45 network cable - pretty sure it will not communicate with a new BMV700 type display. Also the Blue Power display does double duty as an interface with the Multi-plus Inverter so that works very well and it is a very neat small display on the bulkhead.

Good info about using a Pi and display instead of the Venus - I know Victron are very good with making sure their products are generally open source to allow such projects. No doubt you could also communicate with the Multi-Plus without too much effort.

For me if everything is working OK I rarely look at the details of what is going on behind the scenes, I check the battery SOC pretty regularly but that is about it. I might look further into the MPPT info and the BMS info about once or twice a month just to see everything is as expected.

If the boat was fitted exclusively with Victron kit then it might be worthwhile having everything properly networked and connected to the VRM portal, but we also have an Orion BMS and an Outback MPPT that will not interface so I am happy with the way things work and the info I can access when I need to.

 

[Kelpie]

Got my quote back from RJ Energy. I was after a set of smaller cells with a view to building a portable pack for my trolling motor.
Four 84Ah cells would be $172, which is good, but delivery to a non-EU country costs $310. Ouch! Maybe I'll have to have them sent to someone in Ireland and we can pick them up on our way South...

 

[Poey50]

Got my quote back from RJ Energy. I was after a set of smaller cells with a view to building a portable pack for my trolling motor.
Four 84Ah cells would be $172, which is good, but delivery to a non-EU country costs $310. Ouch! Maybe I'll have to have them sent to someone in Ireland and we can pick them up on our way South...

We don't leave the EU until 31st Jan. Or have the costs been bumped up in advance?