270ah DIY LiFePO4 build

[gregcope]

Be

Being away from the boat at the moment I been interested in emails I had from several cruisers who are changing to lithium .
All four are cruisers we known for some years and at less 3 out of the 4 are quite knowledgeable when it comes to 12v and batteries.
There are all fitting 12v set up 400ah to 560ah
Here the interesting part ,
They plain not to use a BMS , instead use their victron mppt and b2b to monitor hight and low voltage,
Use cell monitors to keep an eye what each cells doing .
Connect the cells to a active balance board .
Considering the cost of BMS this could be a cheap way forward .

What's the view ?

Sounds like the have high voltage disconnect sorted with MPPT and B2B (if they have a lithium profile) as long as these are the only charge sources.

You could choose to not use a BMS however what happens at low voltage? I recently killed a very old FLA because the Victron battery monitor was happily flashing/buzzing away with no one to hear it for a week or two it killed the battery. You need to be very careful of any small loads.

As @Kelpie points out a BMS need not be expensive and is there to protect some very expensive cells.

 

[vas]

could I please shift the discussion a bit on contactors?
what are you lot using? Obvs not the ones using a BMS that includes one!
looking at various options slightly confused, not quite sure I like the idea of having the contactor coil ON 24/7 and OFF when it needs to disconnect the system, would be much happier the other way round but then would probably not be a very fail safe setup...
Something like that:
https://dc-components.com/wp-content/uploads/2019/03/gv120.pdf
or this:
https://product.tdk.com/system/file..._piezo/hv-contactor/data_sheet/hvc300a_12.pdf
non-latching, first one is available in NO or NC option...
would most likely need two one to connect the FLA which is on standby and one to disconnect the LifePO4
all suggestions that wont cost an arm and a leg, welcomed

 

[sailaboutvic]

Be


Sounds like the have high voltage disconnect sorted with MPPT and B2B (if they have a lithium profile) as long as these are the only charge sources.

You could choose to not use a BMS however what happens at low voltage? I recently killed a very old FLA because the Victron battery monitor was happily flashing/buzzing away with no one to hear it for a week or two it killed the battery. You need to be very careful of any small loads.

As @Kelpie points out a BMS need not be expensive and is there to protect some very expensive cells.

In my case I have a third charging sources , victron shore charger which been used four times over 365 days , it doesn't have a lithium setting but when use it throught the B2B so that sorts out that problem .

As I said this method is probably only suited for people as my self who are full time on board and monitoring their system, not for the fit and leave guy.

Low voltage in my case just don't happen after several days of heavy clouds and no motoring I only every seen a DOD 35% before it's brought back up to a hight state of charge and @35% DOD the cells are all the same .
I not checked how low I can discharged before the cells start to drift .

Only time will it work for them or they end up buying a BMS .
But good to hear your points .
.

 

[sailaboutvic]

This is what I used it's about €60
It's a bistable relay 250A

Bistabiles Relais - Model BSR 750 - 12VDC / 250A

 

[Poey50]

Being away from the boat at the moment I been interested in emails I had from several cruisers who are changing to lithium .
All four are cruisers we known for some years and at less 3 out of the 4 are quite knowledgeable when it comes to 12v and batteries.
There are all fitting 12v set up 400ah to 560ah
Here the interesting part ,
They plain not to use a BMS , instead use their victron mppt and b2b to monitor hight and low voltage,
Use cell monitors to keep an eye what each cells doing .
Connect the cells to a active balance board .
Considering the cost of BMS this could be a cheap way forward .

What's the view ?

People do it .... in the same way that some people don't bother with fuses. Not for me. You have to keep an eye on things every single time. The fact that it was manually managed successfully on 2,000 occasions gives you no credit. On the 2001st it could go horribly wrong if you get distracted. We are 10 years behind the US ... many DIY systems were done without BMS - you don't hear much of this now.

 

[vas]

This is what I used it's about €60
It's a bistable relay 250A

Bistabiles Relais - Model BSR 750 - 12VDC / 250A

thanks Vic,

pity they are all 12V (as far as I can find in this site)
also they seem to change state with a pulse, wonder how the system "knows" contactor is off or on! Some other bistable relays seem to have two pairs of control wires which will be easier to wire to my 4relays BMS. Search is on!

V.

 

[sailaboutvic]

People do it .... in the same way that some people don't bother with fuses. Not for me. You have to keep an eye on things every single time. The fact that it was manually managed successfully on 2,000 occasions gives you no credit. On the 2001st it could go horribly wrong if you get distracted. We are 10 years behind the US ... many DIY systems were done without BMS - you don't hear much of this now.

Your right regarding it could go wrong ,

I understand all four guys are fitting cells monitor to monitor each cell , I guess some kind of alarm could be added .
With the little experience I have after a year use unless a cell just goes pop for some reason and then the BMS wouldn't be much help , difference in cell voltage drift at a slow rate so as long as they are monitored one would hope well before something happen you had plenty of warning .

With an active balancer and keeping charging voltage to no more then 14.0v,
for any cell to top out >3.65v wont happen over night.
At 13.8v which is what I normally charge at the cells are 3.45 v steady across all cells .

As I said for an Weekender and the odd week trip probably best to fit s BMS , but talking for myself and lots of other who live on board we monitoring equipment all the time .

For me it be interesting to see how all four gets on and if any feel at some point they need to add a BMS .

I think we talked about this before but I'm not at all impress with the smart 123 , well over price and hasn't even got a active balance and like you my end cells over over 14v start to drift for that reason .
Add to that I dislike the Micky mouse wires and the module which wouldn't take much to get damage .
So if mine did pack up I be tempted to give it a try if these cruiser get on ok .

 

[sailaboutvic]

thanks Vic,

pity they are all 12V (as far as I can find in this site)
also they seem to change state with a pulse, wonder how the system "knows" contactor is off or on! Some other bistable relays seem to have two pairs of control wires which will be easier to wire to my 4relays BMS. Search is on!

V.

Smart 123 as relay on the last module so mine are connected to them .
The relay control voltage <> of each cell .
Mine is 12v , I remember now your is 24v

 

[Poey50]

Be


Sounds like the have high voltage disconnect sorted with MPPT and B2B (if they have a lithium profile) as long as these are the only charge sources.

You could choose to not use a BMS however what happens at low voltage? I recently killed a very old FLA because the Victron battery monitor was happily flashing/buzzing away with no one to hear it for a week or two it killed the battery. You need to be very careful of any small loads.

As @Kelpie points out a BMS need not be expensive and is there to protect some very expensive cells.

Yes, people need to pay a lot of attention to over-discharge. This is what Zwerfcat refer to as a 'time bomb'. 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.

 

[RogerJolly]

Postings in this thread throw up ‘JBD’ BMS as a possible option.
Searching throws up this Youtube video on the ‘Off Grid Garage’ channel:

More searching (on “Jiabaida SP04S020A"copied from a freeze frame of the video) throws up this site as somewhere to buy it:

39.55￡ 30% OFF|JBD Smart Bms 12V 4S Lifepo4 100A For Rechargable Lithium Batttery 3S 60A 80A 120A With Balance Board Bluetooth|Battery Accessories| - AliExpress

Problem is Aliexpress say their unit is common port, whereas the video talks about being able to independently isolate charging and load, with the control app showing Charge and Discharge on/off switches. Can anyone shed light on this?
The video has a concern that charging is left enabled below the low temperature cutoff, at very low currents, but Will Prowse comments that low temp charging is OK at low currents.

Many thanks

 

[Kelpie]

I'm using a JBD, pretty happy with it but I think it is common port. This doesn't bother me as the couple of times that it has disconnected the battery I have been on the boat anyway and able to get it up and running again.

My MPPT is set up so that it stops charging before the BMS detects a pack over-voltage. Obviously it's possible for the BMS to detect an individual cell out of range etc but that's not an everyday occurrence.

 

[RogerJolly]

I'm using a JBD, pretty happy with it but I think it is common port. This doesn't bother me as the couple of times that it has disconnected the battery I have been on the boat anyway and able to get it up and running again.

My MPPT is set up so that it stops charging before the BMS detects a pack over-voltage. Obviously it's possible for the BMS to detect an individual cell out of range etc but that's not an everyday occurrence.

Thanks Kelpie. Think I will plump for it. Video is generally favourable.

Recognize it's not the full fat affair like, say, the 123, but I'm thinking my demands are fairly moderate.

Take your point about the charge controllers (B2B/Solar) being the main management, with the BMS as a last ditch protection measure.

 

[gregcope]

The video is referring to the ability to switch off the charging or discharge mosfets independently in the app. It is common port as in there is one port for both charge/discharge.

if ordering one ensure you get one with the right number of cables (two to three) for the amps you want to run. Also the overkill solar ones have thicker cable.

 

[gregcope]

I'm using a JBD, pretty happy with it but I think it is common port. This doesn't bother me as the couple of times that it has disconnected the battery I have been on the boat anyway and able to get it up and running again.

My MPPT is set up so that it stops charging before the BMS detects a pack over-voltage. Obviously it's possible for the BMS to detect an individual cell out of range etc but that's not an everyday occurrence.

@Kelpie A few questions if you do not mind?

Why did it disconnect?

Also which MPPT?

Finally would you do the same knowing what you know now?

 

[Kelpie]

@Kelpie A few questions if you do not mind?

Why did it disconnect?

Also which MPPT?

Finally would you do the same knowing what you know now?

It's disconnected a couple of times due to me exceeding the discharge current, when getting a bit carried away with the induction hob. I don't intend to run all that power through the BMS itself, but that's how it's wired for now.

I'm using an Epever MPPT, and inverter.

If I was doing this again... I would have bought more cells. Turns out I got a very good deal- 4*271Ah for £350 inc all fees and shipping.
For drawing big currents it would be much better if I had a larger bank.

 

[gregcope]

Would you get a larger bms or two 120A ones?

 

[Kelpie]

Would you get a larger bms or two 120A ones?

Two JBDs I think... cheap and cheerful!

 

[vas]

I'll write a report on the diyBMS (once I've got everything that is!), it's cheaper and cheerfuller imho.
Not a straight buy 'n fit though but maybe by summertime there's going to be stock to buy the bits you need cheap (in the UK)
Definitely brilliant for the fully Victronised lot!

 

[sailaboutvic]

I'm using a JBD, pretty happy with it but I think it is common port. This doesn't bother me as the couple of times that it has disconnected the battery I have been on the boat anyway and able to get it up and running again.

My MPPT is set up so that it stops charging before the BMS detects a pack over-voltage. Obviously it's possible for the BMS to detect an individual cell out of range etc but that's not an everyday occurrence.

I have a question , how do you know if the bms is malfunctioning?
Do you have Bluetooth and see what the cells are doing ? Or do you plug it i to some sort of PC?
Or is it the case that the first you know it's not working correctly is whe a cell goes pop?

 

[Kelpie]

I have a question , how do you know if the bms is malfunctioning?
Do you have Bluetooth and see what the cells are doing ? Or do you plug it i to some sort of PC?
Or is it the case that the first you know it's not working correctly is whe a cell goes pop?

The BMS has an app, you can watch what's happening in real time. Individual cell voltages, pack net current in/out, temperature.