270ah DIY LiFePO4 build

[Zing]

I really struggle to understand the Dacus website. Ie what features it has / what parts you need, etc... Or is that just me?


@Mikedefieslife Would be interested in your design/Parts/features.

Me too. I gave up.

 

[Poey50]

I really struggle to understand the Dacus website. Ie what features it has / what parts you need, etc... Or is that just me?

@Mikedefieslife Would be interested in your design/Parts/features.

Some members of the Lithium Batteries on a Boat Facebook Group use the Electrodacus. Might be worth a question there. They are usually very helpful.

 

[JohnGC]

Poey,

Now that you've had some experience using your battery, I wonder if there is anything you'd do differently?

I'm also particularly interested to know if you have monitored cell temperature during heavy charge or discharge?

 

[Poey50]

Temperature first. I've charged and discharged at 90 amps. That's the biggest rate I will ever use. The temperature rose only 2-3 degrees above ambient. That is a 0.3C charging rate which is likely always going to be fine.

There's a couple of issues that have struck me with more emphasis now I've moved from theory to practice. I hadn't fully anticipated the need to have all charging sources with a manual override so I can leave the pack around 40-60% SOC. It is very wierd to turn down energy and to be able to give up the endless lead acid quest to get back to float.

Also how important it is to plan for a secure installation of the pack in order that the cells can't move. I had to finalise that at installation but should have had it completely nailed at the planning. For the same reason it is good to have busbars between the cells that have some flexibilty in order not to strain the tapped aluminium holes of the terminals. The R J Energy ones are flexible if pressure is placed on them as I discovered by accident with one.

For all charging (other than alternator) I would stick only to Victron bluetooth units. User controllability, updatable firmware, cross-communication and compact size are all superb.

The decision to go for a Balmar alternator, external regulator, and serpentine belt upgrade and charging the LFP directly from the alternator has proved an excellent choice for fast charging.

Overall I'm delighted with it. All cells remain within 0.01 volts as they were when first balanced.

Finally I still recommend using new plastic cased Winston cells for a DIY project if you have the space and the money rather than this grey import method but so far, so good.

 

[JohnGC]

Thanks Poey,

At 90A with a internal impedance of 5mR you'd get a dissipation of 4W per cell. Presumably that is reasonably well distributed throughout the cell volume. So a temperature rise of just a few degrees seems to fit. It's also a rough indication of how much energy is need to raise the temperature of the cells in the event you need to charge when they are below 0C. Much will depend on individual construction.

Our new to us boat has MasterVolt 2kVA / 100A invertor/charger and MasterVolt's high current at low speed alternator/regulator combination. Whilst not ideal, because I can't separate the charge and load circuits, it is expensive kit which I don't want to replace.

Those are very encouraging balance figures.

 

[nfluester]

Courier just delivered my 8 270AH Cells from China along with a metal case they sourced for me. Took just over 1 month to arrive in the UK.



Unboxing coming soon.... ?

 

[Poey50]

Courier just delivered my 8 270AH Cells from China along with a metal case they sourced for me. Took just over 1 month to arrive in the UK.

View attachment 102063

Unboxing coming soon.... ?

Exciting...

 

[nfluester]

here we are my evenings work:

amazingly well packaged, make sure you subscribe to the channel as i will be documenting the whole project in the coming weeks ?

 

[vas]

interesting, isn't this metal box for all 8 of them a bit too much? will you be able to handle it (how heavy is it going to be?)
would there be an issue if you did two smaller boxes 280Ah each and then parallel them?

looking fwd to the next installments!

V.

 

[sailaboutvic]

here we are my evenings work:

amazingly well packaged, make sure you subscribe to the channel as i will be documenting the whole project in the coming weeks ?

I'm not a follow or you tube channel but interested in this by subscribe , what happen ,?
Do I get the next video link ?

 

[Poey50]

interesting, isn't this metal box for all 8 of them a bit too much? will you be able to handle it (how heavy is it going to be?)
would there be an issue if you did two smaller boxes 280Ah each and then parallel them?

looking fwd to the next installments!

V.

That would make two separate 12 volt packs and each would require a BMS. I believe he intends to put the 8 cells first in parallel pairs and then put the 4 pairs in series. That's usually designated as a 2P4S configuration.

 

[nfluester]

yep it is a heavy single box but compared to the lead it's replacing its as light as a feather ? i will probably end up mocking up and stress testing here at home over the winter (nothing better to do whilst locked down ?) and then break down and re assemble on the boat. regarding configuration as @Poey50 mentions above the current plan is a single big 560AH 2p4s pack as i don't really want to have to buy 2 BMS's and it keeps it simpler.

i may change my mind and go with 2 separate packs and use one for the inverter and the other for onboard 12v sources. I haven't bought the new inverter yet so potentially could go 24v 8s1p pack but then i would need to step up charging sources and step down to 12v for on board devices so unlikely.

 

[nfluester]

I'm not a follow or you tube channel but interested in this by subscribe , what happen ,?
Do I get the next video link ?

? it's a youtube thing to grow the following on my channel, i will be creating a lot more videos around putting this together but i'll post them here to so if you are not into the whole subscribing to youtube channels don't panic ?

 

[vas]

thanks Poey50 and nfluester, makes sense.
I'll hopefully go the same route (only my system is 24V) once prices drop and my Trojans are caput...
BTW, what's the estimated weight of this box+8batteries+ electronics? less than 50kg that you get on a typical 200Ah 12V LA truck battery?

Keen to see your overcharge protection measures (and subsequent developments on this front) and evaluation of how good they may be as this seems to be the main issue...

V.

 

[Poey50]

thanks Poey50 and nfluester, makes sense.
I'll hopefully go the same route (only my system is 24V) once prices drop and my Trojans are caput...
BTW, what's the estimated weight of this box+8batteries+ electronics? less than 50kg that you get on a typical 200Ah 12V LA truck battery?

Keen to see your overcharge protection measures (and subsequent developments on this front) and evaluation of how good they may be as this seems to be the main issue...

V.

Overcharging is certainly something to be avoided. But perhaps less well known are the dangers that can accrue from over-discharge. This (below) is quote from the excellent ZwerfCat site which I would add to the list of essential reading as it is full of accessible information together with the simplest recommendation for a hybrid LFP / Lead acid system which seems well thought through.

Lithium management


What happens when lithium batteries are being overdischarged?

Allowing a Lithium cell to drop below 2.5V will not only damage the cell but it converts the cell into a timebomb. Due to unavoidable variations in capacity of the individual cells, not all cells are empty at the same moment. Keep in mind that in a series circuit, the current through the whole circuit is everywhere the same: If one cell is no longer able to produce the required current but the other cells are still feeding current through the circuit, the empty cell now sees a reverse polarity and copper from the anode starts dissolving into the electrolyte. When recharging this copper gets deposited onto the cathode where it forms very sharp dendrites which slowly grow and start piercing the insulation between anode and cathode. The subtle signs that this has happened is that the cell becomes warmer than normal when charging and that the cell displays a much higher self-discharge rate: Cells that discharge by themselves within a month or so are not healthy! A consequence is that such a damaged, self-discharging cell is now guaranteed to drop below 2.5V prematurely during the next discharge and the dendrites will consequentially grow some more. The cell is now on a pathway to catastrophic self-destruction: When the dendrites have grown large enough they will at some point completely short-circuit the cell and you just have to hope the cell will fail "nicely". Unfortunately, it appears that a cell which is damaged by overdischarging tends to self-destruct much more violently than a cell which is "normally" short circuited.

 

[vas]

Overcharging is certainly something to be avoided. But perhaps less well known are the dangers that can accrue from over-discharge. This (below) is quote from the excellent ZwerfCat site which I would add to the list of essential reading as it is full of accessible information together with the simplest recommendation for a hybrid LFP / Lead acid system which seems well thought through.

Lithium management


What happens when lithium batteries are being overdischarged?

Allowing a Lithium cell to drop below 2.5V will not only damage the cell but it converts the cell into a timebomb. Due to unavoidable variations in capacity of the individual cells, not all cells are empty at the same moment. Keep in mind that in a series circuit, the current through the whole circuit is everywhere the same: If one cell is no longer able to produce the required current but the other cells are still feeding current through the circuit, the empty cell now sees a reverse polarity and copper from the anode starts dissolving into the electrolyte. When recharging this copper gets deposited onto the cathode where it forms very sharp dendrites which slowly grow and start piercing the insulation between anode and cathode. The subtle signs that this has happened is that the cell becomes warmer than normal when charging and that the cell displays a much higher self-discharge rate: Cells that discharge by themselves within a month or so are not healthy! A consequence is that such a damaged, self-discharging cell is now guaranteed to drop below 2.5V prematurely during the next discharge and the dendrites will consequentially grow some more. The cell is now on a pathway to catastrophic self-destruction: When the dendrites have grown large enough they will at some point completely short-circuit the cell and you just have to hope the cell will fail "nicely". Unfortunately, it appears that a cell which is damaged by overdischarging tends to self-destruct much more violently than a cell which is "normally" short circuited.

blimey scary stuff!
maybe I should stick to Trojans and remember to water them regularly

 

[vas]

BTW, don't know if it's been discussed before (and sorry for the slight offtopic) would it be possible to keep and decent LA bank AND add LIPO4 bank as well and charge the LIPO4 from the LA? Not sure how discharging would work and how you'd change over from LIPO4 to the LA when LIPO4 go low (or pump some amps from the LA again... too complicated as a concept but maybe create a buffer that would save the LIPO4 when worse comes

 

[Poey50]

blimey scary stuff!
maybe I should stick to Trojans and remember to water them regularly

LFP is fine with a BMS. The main difference to lead acid is that you can moderately abuse lead acid and get away with it. With LFP you have to colour inside the lines.

 

[Poey50]

BTW, don't know if it's been discussed before (and sorry for the slight offtopic) would it be possible to keep and decent LA bank AND add LIPO4 bank as well and charge the LIPO4 from the LA? Not sure how discharging would work and how you'd change over from LIPO4 to the LA when LIPO4 go low (or pump some amps from the LA again... too complicated as a concept but maybe create a buffer that would save the LIPO4 when worse comes

Not off-topic at all. Further back I mentioned some hybrid systems - detailed by Nordkyn. But an intriguingly simple method is carefully explained by ZwerkfCat. I've not heard of anyone using this method even though, as they explain it, it seems safe and obvious.

Lithium-Hybrid

 

[vas]

brilliant, so not a stupid idea after all!
will read through that and think again. So when do we expect a 24V circa200Ah LiPO4 system to cost circa 600euro then?


cheers

V.