diy solar

diy solar

BMS common port vs seperate port

Lol please NEVER charge LiFePO4 to 4.2V. goodness I need to be careful what I say on here. You will have gas creation and swelling before you hit 4.2V. But no thermal runaway yet.

And here is a source: A LiFePO4 battery can be safely overcharged to 4.2 volts per cell, but higher voltages will start to break down the organic electrolytes.


Gas creation can happen at lower voltage but it takes awhile for it to occur. I've also seen it mentioned in papers on LiFePO4.

The iron phosphate crystal is pretty robust though and over charging can technically do very little damage if it is for a short time. Electrolyte instant degradation occurs at 4.2V, and long term degradation happens while holding the voltage above 3.65V. If temperature increases, this effect will worsen.

But yeah, you can overcharge them for a few minutes on accident and pull full capacity. I've done it a bunch. The electrolyte will degrade a tiny bit but that's all.
 
Last edited:
  • Like
Reactions: Dzl
Maybe the Daly , or other BMS , acts like a Bluetooth BMS just without the Bluetooth connection to exchange the data i.e. it uses all the data to effectively control all the operations of the BMS but does not send it anywhere ?
Can some of the electronic design engineers contribute here please ?
They say one is not to trickle charge Lithium stacks. But it is ok to float them. I ask, in lieu of an BMS. Is there a minimum safe charge that can be used ? Like 1/10 C ? Or if 3.65v is the cell full charge voltage, can one float at 3.5 times 16 ?
 
Can one charge lithium cells safely until a rise in cell temperature is detected ?
 
Do any of these BMS throttle the charge current? I don't want an on/off outcome.
None of the popular low to mid range options can do this as far as I am aware, they are all on/off. But I think more sophisticated high end options like the Orion Jr. or others may be able to if paired with the right compatible chargers. I have never seriously looked into the $400+ options so I may be mistaken about that.


In theory one could ramp the charge current down as soon as one cell reaches 4.2v, allowing the others to continue to absorb energy. And as more hit 4.2v the throttle keeps ramping lower in current.
Do not charge to 4.2V. With or without hypothetical throttling, with or without a BMS, regardless of current. Follow manufacturer recommended parameters or established best practices. There is almost nothing to be gained above ~3.65V.
A good primer on voltage setting can be found here

Please NEVER charge LiFePO4 to 4.2V. goodness I need to be careful what I say on here. You will have gas creation and swelling before you hit 4.2V. But no thermal runaway yet.
3.65V is MAX potential per LiFePO4 cell. My absorption recommendations are here
 
Last edited:
They say one is not to trickle charge Lithium stacks. But it is ok to float them.
I think the important takeaway regardless of the language that is used is to not continually hold lifepo4 at a full or near full state of charge.

I ask, in lieu of an BMS. Is there a minimum safe charge that can be used ? Like 1/10 C ?
Not sure I understand your question, but I think any C-rate can overcharge (or overdischarge) a cell if you don't have a BMS. If you look at many of the cases of people overcharging cells it often occurs during top balancing, at a C-rate well below C/10 (0.1C)
Easy answer, just use a BMS.

Or if 3.65v is the cell full charge voltage, can one float at 3.5 times 16
Generally speaking, most sources recommend a float voltage less than or equal to 3.4V per cell. 3.5 is still a little too high. This is in part because while 3.65 is the highest recommended voltage and fastest way to achieve a full charge, any voltage above 3.45ish will lead to a full charge if held there long enough. So holding at or above this level is holding them at an elevated voltage even though it doesn't appear to be at first glance.
 
Last edited:
I'm sorry to use the 4.2v threshold. Guess 3.5v is the high bar. Cells are not delivered yet. Haven't been able to find the bms I want. Would it be a bad idea to leave a lead acid 48v string breakered in the picture when I finish the LI string ?
 
How do I get this site to email as soon as someone posts a reply ? I look at the preferences page and everything seems to be checked. So I know not what to change or do. If a mod can 'fix' this to accomplish my cited goal, please do so.
 
How do I get this site to email as soon as someone posts a reply ? I look at the preferences page and everything seems to be checked. So I know not what to change or do. If a mod can 'fix' this to accomplish my cited goal, please do so.
If you look in account details .... make sure there isn't a typo on your email address .... and there are a couple check boxes for receiving emails.
 
Hi there,

for my boat a bought 4x280a cells with a Daly 150a seperate port bms. Victron mppt with a small pv panel and a 30a AC-DC charger.
Is there a clever way to install the aliexpress budget TR16 battery monitor with shunt? I can't figure out where to place the shunt so he can monitor the load and charge....

edit: found my anwer here:
Thanks for the internet!
 
Last edited:
Hi there,

for my boat a bought 4x280a cells with a Daly 150a seperate port bms. Victron mppt with a small pv panel and a 30a AC-DC charger.
Is there a clever way to install the aliexpress budget TR16 battery monitor with shunt? I can't figure out where to place the shunt so he can monitor the load and charge....
I had not previously imagined/considered this problem before.
I can only see one option. The only point where all current in/out would pass through the shunt is in between the BMS and the battery.
separate-shunt.png

But I don't know if this is advisable. I believe some people (@FilterGuy @smoothJoey ?) have a conceptual problem with anything coming between the BMS and the cells because they consider both to be part of the logical (and physical) 'battery.' I'm not sure what (if any) practical problems this arrangement might introduce.

Alternatively you could try to find a battery monitor that works on the positive side, I don't know if any exist but I do know its possible as the SBMS0 (BMS) works this way.
 
You could alternatively put both charge and discharge leads through a hall sensor.
Regarding anything coming between the bms and the cells, you convinced me otherwise many months ago.
 
  • Like
Reactions: Dzl
You could alternatively put both charge and discharge leads through a hall sensor.
Regarding anything coming between the bms and the cells, you convinced me otherwise many months ago.
Good idea with the hall sensor. Something along these lines?
hall sensor.png
 
From seperate to common again ... when connecting the negative load and charge? If the bms likes that afterall.
 
With a little formatting, I think you just wrote an accidental Hiaku (probably the first Hiaku about a BMS).
From seperate to common again ...
when connecting the negative load and charge?
If the bms likes that afterall.
Beyond the poetry of it though, the question or statement went over my head, can you rephrase?
 
With a little formatting, I think you just wrote an accidental Hiaku (probably the first Hiaku about a BMS).

Beyond the poetry of it though, the question or statement went over my head, can you rephrase?
LOL I had to look that up.
I spent some time in Japan and the only word I knew that resembled that was hiyaku ... we used that word to try to get a taxi to go faster.
 
Back
Top