Urgent advice needed

[alanb]

Need advice / please,
Just bought 4 BLUE CARBON LifePo4 12v 200ah batteries....intending to connect to my Hybrid 48v inverter , joining the batteries in series.

Open the box and big shock.....manual states do not connect in series, why ?
Help please before i send them back..regards

 

[Joe BoyKey]

1st of all they should be 12.8v Lifepo4 - 4s = 51.2v, You have to top balance them in parallel, then use a 200a BMS to series them, Joe.

 

[upnorthandpersonal]

1st of all they should be 12.8v Lifepo4 - 4s = 51.2v, You have to top balance them in parallel, then use a 200a BMS to series them, Joe.

Blue Carbon batteries have a BMS. That's also the reason they can't be put in series - the BMS is not designed for that, and that's why the manual states not to put them in series. If one BMS disconnects, it is possible that the voltage over this becomes too high due to the other batteries and damages the FET in the BMS.

 

[Joe BoyKey]

I have 16 E-on Lifepo4 12.8v 50ah Smart batteries w/bluetooth 4s4p = 51.2v @ 200ah, E-on told me not to series, they have been running since 9-2020 without any issues, they cut themselves off when charged and are alway within 4% soc, just fyi. I check each batteries soc via Bluetooth once a week, Joe.

 

[JoeHam]

Definitely a “proceed at your own risk” situation for @alanb

Series use would very likely void any warranty.

 

[time2roll]

I believe it is best to have a 48v battery or multiple 48v batteries in parallel.

 

[HRTKD]

If you need a 48v battery, build a 48v battery, not four 12v batteries.

 

[Forbisher]

If you need a 48v battery, build a 48v battery, not four 12v batteries.

People buy 4 12V 100Ah Battle Borns or other brands then series connect them all the time.
There are advantages and disadvantages to doing it this way.
The OP is in Thailand.
Some drop in batteries can be seried and others can not due to their BMS design.

 

[HRTKD]

As you said, not all batteries are created equal. I stand by what I said. A 48v battery has fewer components than four 12v batteries put in series.

 

[Hedges]

It seems to me if four batteries in series are charged to 56V, 14V each, and the BMS of one opens it's disconnect, voltage across the disconnect switch is approximately zero. So no damage.

If something like an inverter or other load tries to draw power, it tugs the positive terminal of the 48V (nominal) battery to the negative terminal. Maybe an inverter would disconnect for low voltage. A simple resistive load like a lightbulb, or closing the switch to an inverter attempting to charge its input capacitors, and the positive terminal would be pulled all the way to the negative terminal.
Voltage across the disconnect switch is now -56V. For a set of four 12V batteries to support series connection to make 48V, the switch/FETs would have to be rated > 60V.

Some may be, others probably not.

 

[ttbloker]

The primary reason manufacturers make this restriction is because the MOSFETs they use have a low reverse-blocking voltage rating (because they are cheaper, and have slightly less on-resistance compared to higher voltage spec’d MOSFETs). When you have say 4 units in series, one of the four BMS will shut off first. When this happens, that particular BMS would begin not just its own 12volts, but also the 36v of the other three units that have not yet shut down on low voltage limit (total 48v or so). So the MOSFETs need to be rated 50v or higher and they may well be rated less than that.

When connected to equipment that shuts down automatically (and instantaneously) this likely doesn’t present a problem because the inverter breaks the connection. This is probably one reason many folks have no issues despite the warnings. But there is a simple and foolproof trick you can employ which is passive and has no impact on efficiency, and that is to install pass thru diodes in parallel with each battery. For each 12v batt unit, it will do nothing in normal operation, but will pass-thru any current coming from the other units after it’s unit’s BMS shuts-off—thus basically prevent a single BMS from blocking any more than the voltage of its own 4 LiFePO4 cells (i.e. ~12v).

I like to use these Motorola units pictured. Each one is two diodes; I use a hacksaw and cut them down the middle to get two 150A shottky diodes. But be careful there are many chinese fakes of these diodes. I only buy listings from US or european domiciled sellers with good histories/feedback, and almost only buy used units as this greatly increases chances of not getting fakes. Here is a listing live now, looks legit to me, has 45v rating which is the lowest you should go (at full discharge your bank will be around this voltage).

1 PCS Motorola MBR30045CT POWER MOSFET Rectifier Module | eBay

Find many great new & used options and get the best deals for 1 PCS Motorola MBR30045CT POWER MOSFET Rectifier Module at the best online prices at eBay! Free shipping for many products!

www.ebay.com

The solution is best used when, under normal operation, your own equipment is cutting out , before any of the individual battery BMS do. Once an individual battery unit BMS cuts out, your equipment may reject your series connected bank as being a 48v pack, since it will only see 36v (or lower, in the case multiple BMS hit he cut). Finally, there could be more complex features like networking and communication between battery packs that this solution may not address; I don’t have experience with any of those, so I should just put it in there is a potentially important caveat...


—Tim

 

[NwCali]

I'd contact the people who made them....

I do feel that if it falls below the required voltage what they are feeding should disconnect/turn off instead of trying to run below specs voltage and this might keep things from going thermal. But I have no back ground to support that and would rely on manufacturers specs.

This is why I bought a power wall already at 48volts. But by the time I am ready for more (meaning I have the money) I'll build my own packs. Its just far cheaper and in the long run once you know it far easier to repair/replace.

 

[Hedges]

Interesting suggestion on the diode, like what is done for shaded PV panels.

The eBay listing is $15 each for used.

Here's same part number from DigiKey, different manufacturer. $81 each (pair) and rated 300A. So $162 for a 48V battery.

MBR30045CT GeneSiC Semiconductor | Discrete Semiconductor Products | DigiKey

Order today, ships today. MBR30045CT – Diode Array 1 Pair Common Cathode Schottky 45 V 150A Chassis Mount Twin Tower from GeneSiC Semiconductor. Pricing and Availability on millions of electronic components from Digi-Key Electronics.

www.digikey.com

When one BMS disconnects, load will see 36V so hopefully doesn't draw current for long. Actually, if 3.6V per cell, 14.4V per battery, 43.2V from three batteries. That is above the 42V low voltage disconnect of my inverter set for lead-acid. Better have your low-voltage disconnect higher than that.

"

Voltage - DC Reverse (Vr) (Max)

45 V

"
If all four BMS disconnect, you have four, 45V diodes in series with 56V being applied by SCC. In doing design, I avoid that because can't be certain how voltage will be distributed. If a diode breaks down due to over-voltage, it could present a short circuit when battery reconnects.


"

Voltage - Forward (Vf) (Max) @ If

650 mV @ 150 A

"
That's 100W dissipation. Which is why I say you don't want load to continue drawing current after one battery disconnects; would need a good heatsink.


If you've used this diode scheme, have you put it through its paces, induced all the possible disconnect, charge, load configurations it has to handle?

 

[alanb]

Wow blown away with the replys, thank you individually.

This is the link to the actual product https://bluecarbon2019.en.made-in-c...-Long-Life-Lithium-Battery-Solar-Battery.html
The cost of each 12v 200ah that i paid was 307usd, x4 1225usd all in and the cost of a 48v 200ah is double that.
Bearing in mind Warranty is only one year from the vendor , and would be near impossible to utillise the so called warranty from china.

Would it be worth tearing out their bms system and fitting my own one that is more suitable for the job ( with your collective advice) , i dont think the bms system cost would be that high....
I eventually need to go off grid completly with another 10kw battery in parallel added to this one giving 20kwh ish..
If we can make this work they still have 4 more in stock, so if adding the 2 series in parallel i would have 48v 400ah +/- for 2450usd.

kind regards
p.s. i havent sent them back yet....nearly, refund clock is ticking, also just wondering if the no series connection is to make you buy the bigger 48 v single..

 

[Hedges]

Pretty low price, 50% the cost per Wh of my AGM. I think DIY lithium is slightly cheaper, 40% of my AGM.
I assume return shipping isn't economical.
Could be that using a 16s BMS would be a good solution.
The one you linked says 80A continuous output, which you probably want to derate.
Depending on your inverter's draw, you might be able to put in a BMS supporting higher current.

 

[Forbisher]

Looks like you can easily remove the cover to see what Ah cells and BMS.

If you decide to rework them with a new BMS you could try a 48V series connection just for the hell of it.

 

[alanb]

Pretty low price, 50% the cost per Wh of my AGM. I think DIY lithium is slightly cheaper, 40% of my AGM.
I assume return shipping isn't economical.
Could be that using a 16s BMS would be a good solution.
The one you linked says 80A continuous output, which you probably want to derate.
Depending on your inverter's draw, you might be able to put in a BMS supporting higher current.

The return cost is free, to the thai vendor...so i get all my money back, but if the consensus is to keep them, might be better to go for 8 sets 20kwh

 

[alanb]

Looks like you can easily remove the cover to see what Ah cells and BMS.

If you decide to rework them with a new BMS you could try a 48V series connection just for the hell of it.

is there a 48v 200ah bms?

 

[upnorthandpersonal]

is there a 48v 200ah bms?

The Ah (capacity) of your battery doesn't really matter - what current you draw or put in matters. Do you draw 200A (which would be 9.6kW @48V)?

 

[alanb]

The Ah (capacity) of your battery doesn't really matter - what current you draw or put in matters. Do you draw 200A (which would be 9.6kW @48V)?

The Ah (capacity) of your battery doesn't really matter - what current you draw or put in matters. Do you draw 200A (which would be 9.6kW @48V)?

Well, eventually i want 2 x 200ah .48v
my daily use will be 20 ..to 25kwh a day pv and back up.