Hi all

My lead acid cells seem to be coming to EOL.  I'm thinking of going with a DIY LFP solution.

I've noticed these cells for sale:

100AH 3.2v 2nd Life LiFePO4 (lithiumbatteriessa.co.za)

Anyone had experience with this seller?  Anyone else attempted to do this yourself?

I built an eBike and used a smaller version of this JBD 200a SMART BMS.  They are fully customisable in terms of cut-off voltages, balancing, etc. and on my eBike, that BMS has been incredible rock-solid. (not to mention that online they refer to these BMS as "overkill" solar BMS)

I'm trying to wrap my head around the high cost of pre-built units for LFP.  Is it because of the protocol they have to communicate with the inverter?

Also why do they even need that protocol/communication between inverter and battery?  If you have a BMS that balances and top out at your charge voltage of 3.5v per cell I don't really get what the protocol is adding there.  Perhaps someone can elaborate that part for me.

Edited October 28, 20214 yr by Gnome

What inverter are you going to use? Does it support charging LFP batteries?

The owner of that company is on the forum @Bain Viljoen

4 minutes ago, PowerUser said:

What inverter are you going to use? Does it support charging LFP batteries?

I'm using an Axpert King, but IMO any inverter that support constant current constant voltage can support any lithium chemistry assuming a BMS is present to balance the cells and cut off in case of overcharge.  It should simply be a matter of setting the maximum charge voltage to 3.5v per cell and minimum cut-off at 2.5v (probably 2.6 to be safe).

Hence asking for those that have perhaps attempted not buying the really expensive Pylon and such batteries and instead just buy cells + BMS.

Basically, why do batteries like Pylon need to communicate with Axpert inverter?  What are they sending to or getting from the inverter?

Edited October 28, 20214 yr by Gnome

Lots of people buy cells and BMS. Search around the forum. There are many threads with self build batteries from cells.

I was also researching that option but at the end of the, because of availability issues, I decided to go for a commercial battery. 

You can't go wrong on the DIY route. Once you have successfully built the first one, you can't wait to start the next and ....

I have 4 banks running harmoniously with the Ant and JBD bms.

 

10 minutes ago, GVC said:

You can't go wrong on the DIY route. Once you have successfully built the first one, you can't wait to start the next and ....

I have 4 banks running harmoniously with the Ant and JBD bms.

 

Nice.  And in terms of the Inverter settings what did you do there?

Running it on a Victron system using a BMV 702 to bring it all together. The Ant and JBD can both talk directly to the inverter, but at this stage it is not necessary as the 2 different bms are controlling themselves rather well. (Besides, I don't want to confuse the poor inverter handling different types)

Gotcha, yeah I mean I could probably code something that would allow JBD BMS to work with my Axpert, but not really sure what I would gain from that...  Maybe better running time predictions.  Since I already have a JBD BMS for my ebike, I'll play around with the protocol a bit and see what I can get done with my inverter.

But yeah LFP home made battery definitely seems to be the way to go.

Pylontech is really expensive for what you get.  You essentially need three of them for a 5kW inverter whereas these cells can discharge up to 100amps with no problem whatsoever.  Thus 16s is sufficient.  That said, I'm thinking I'll go for 17s

I see the guys already making 18s 280Ah banks on the inverters that can handle that voltage.

1 minute ago, GVC said:

I see the guys already making 18s 280Ah banks on the inverters that can handle that voltage.

18s is near the maximum you can go with the Axpert King inverter.  But cost/benefit, my opinion was that 17s hits the sweet spot.  One both sides of the voltage slope it still has breathing room. ie. 42v -> 60v (17s) vs 45v -> 63v (18s).  Axpert claimed voltage range is 40v -> 66v but if their MPPT is anything to go by, you want to stay away from the top range, voltage wise.

And I'll almost certainly set my cut-off voltage at no lower than 2.6v anyway (or even higher depending on the battery slope).  I really don't need that last 10% so badly.

1 hour ago, 87 Dream said:

This is responsible use of LFP. Mine go from 3.48v to 3.1V & have discharged 100ah by then & they are 120ah. The last 15% is the stress on the cell & reduced cell life. Stay away from the steep parts, keep them on the straight slope & they will last the said 6000s of cycles.

87

Yeah looks like a good value is no lower than 3v per-cell generally speaking.  I think your range is pretty much spot on.

Have you guys used these 2nd life cells.  What are the opinions on them?

I didn't realise but they are essentially recycled EV cells.  Given that I would have actually expected the price to be a bit lower.

Any other sellers you guys could recommend?

Edited October 28, 20214 yr by Gnome

Hi All

I'm leaning towards the same path just needs some advise I have purchased a bms , but after reading I'm not sure to cancel my project or go ahead so I want to use a Daly 16s 100amp charge and 200amp discharge current and looking towards 310 LFP cells. Main thing is to keep the cells safe do I get a 5amp active cell balancer or a better bms or cancel my project all together your advice will be appreciated.

Hi All

I'm leaning towards the same path just needs some advise I have purchased a bms , but after reading I'm not sure to cancel my project or go ahead so I want to use a Daly 16s 100amp charge and 200amp discharge current and looking towards 310 LFP cells. Main thing is to keep the cells safe do I get a 5amp active cell balancer or a better bms or cancel my project all together your advice will be appreciated.

2 hours ago, Raj35 said:

Hi All

I'm leaning towards the same path just needs some advise I have purchased a bms , but after reading I'm not sure to cancel my project or go ahead so I want to use a Daly 16s 100amp charge and 200amp discharge current and looking towards 310 LFP cells. Main thing is to keep the cells safe do I get a 5amp active cell balancer or a better bms or cancel my project all together your advice will be appreciated.

Hi Raj , your BMS may or may not be suited. It depends on your particular power demands. Question , do you have 310ah cells for greater immediate power demand ,or are they there to give you longer backup periods at lower power. If the first one, you need a larger rated BMS, if second you can throttle charge current at the inverter, and also set appropriate charge and discharge limits on the BMS. 

People like @87 Dreammay be able to drill down further per your requirements .

2 hours ago, dropkick said:

Hi Raj , your BMS may or may not be suited. It depends on your particular power demands. Question , do you have 310ah cells for greater immediate power demand ,or are they there to give you longer backup periods at lower power. If the first one, you need a larger rated BMS, if second you can throttle charge current at the inverter, and also set appropriate charge and discharge limits on the BMS. 

People like @87 Dreammay be able to drill down further per your requirements .

@dropkick my power requirement are around 100amps and less,  the 310amp are for longer backup periods. I do have 1 x hubble AM2  so would it be better to add another AM2 which gives me 10kwh 8kwh usable or build a 15Kwh system and usable 13Kwh.

Edited October 29, 20214 yr by Raj35

@87 Dream your response to the above would be greatly appreciated.

On the subject of BMS.  I did a lot of research before buying one.  Generally JBD is as good as it gets for the cheap BMS.  Plenty of people have used Daly and then moved over to JBD.  The general feedback is that JBD is more reliable.  There are plenty of people happy with their Daly BMS.  So don't just write it off.

As to 100A BMS, it should be ok for 3kW but at 5kW you are not looking at making full power with just a 100a BMS.  Even if you 5kW inverter was 100% efficient, at 100 @ 48v = 4800w.  And that is assuming your battery is still above 48v, at 42v you are looking at 4200w.  Taking inefficiency of inverter any everything into account you should assume that BMS will allow you to provide 3.3kW output from the inverter (Worst case).

FYI: JBD also makes a 300a version of their BMS.  The BMS is programmable so even if you get a Li-ion JDB BMS 20s you can use it in LiFePO with fewer cells in series.

23 minutes ago, 87 Dream said:

4) Only down side is that the provided BMS cable is underspeced. After replacement with suitable 50mm cable very capable of this 200A. It's peak is 600A. I have seen for a few seconds up to 275A with zero issues or heating.

This is a general problem with inverters.  Yahoos in SA are installing inverters with 8mm or 10mm wire to the batteries.  The Axpert inverter recommends 50mm (since the King model).  And that is roughly what the specs of the wire say also if you want to provide max power continuously without losing a lot of power to heat.

Just keep in mind they are using silicone wire, so it WILL do 200a but it will get really hot.  Silicone wire is specced up to 200 degrees.  But it is just sad to have such losses on an inverter.  For an ebike it makes more sense.

JBD started by targeting ebikes where weight and size matter and there I think silicone wire that is thinner makes sense.

Either way as you say.  Slap some 50mm or 70mm on there and you are good to go

@87 Dreamcan you advise on which one is best   https://a.aliexpress.com/_mqFwX4q is this a good on or this one https://a.aliexpress.com/_mN3PRIa as I think I'm going to go with making my own bank. Is there any other source that keeps these bms in SA thanks.

4 hours ago, Raj35 said:

@87 Dreamcan you advise on which one is best   https://a.aliexpress.com/_mqFwX4q is this a good on or this one https://a.aliexpress.com/_mN3PRIa as I think I'm going to go with making my own bank. Is there any other source that keeps these bms in SA thanks.

 https://a.aliexpress.com/_mqFwX4q

 

https://a.aliexpress.com/_mN3PRIa

 

Definitely take the first!  Else you are spending $82 JUST on shipping

Edited October 30, 20214 yr by Gnome

@Gnome thanks 

On 2021/10/28 at 5:05 PM, GVC said:

You can't go wrong on the DIY route. Once you have successfully built the first one, you can't wait to start the next and ....

I have 4 banks running harmoniously with the Ant and JBD bms.

 

I agree , with the help of people on this forum like @87 DreamI am also the proud owner of my first 6kw pack. It also made me learn a bit more about the underlying technologies including the BMS and that can only be a good thing . Not unlike the fact when you know a bit more about your car , you tend to understand better how to drive and treat it it in its safe working parameters.

I am curious as to what you guys think of listings like these ?

 https://www.aliexpress.com/item/1005003337628969.html

It seems so cheap surely these cant be new or not crazy bloated?  If its not a scam lol

 

18 minutes ago, Nexuss said:

I am curious as to what you guys think of listings like these ?

 https://www.aliexpress.com/item/1005003337628969.html

It seems so cheap surely these cant be new or not crazy bloated?  If its not a scam lol

 

Free shipping to South Africa...  They need to put it on a boat, feels like that should be more expensive.

I haven't bought cells from AliExpress, @87 Dreamcan probably comment, he imports cells.

13 hours ago, Nexuss said:

I am curious as to what you guys think of listings like these ?

 https://www.aliexpress.com/item/1005003337628969.html

It seems so cheap surely these cant be new or not crazy bloated?  If its not a scam lol

 

@Nexuss that's definitely a scam delivery alone will cost around 25k.