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Difference between a 'CCCV' supply and just a 'CC' supply.
#11
(06-21-2020, 12:46 PM)daromer Wrote: The bms does not cut on low current. If you plan that as a Charger you need to build that Logic your self. The bms only protects.


Note that you can have that running  24/7 IF you want towards lithium as Long as top voltage per cell is below max. The lithium battery Will raise in voltage so in end the current is 0. As Long as you dont have self dischargers that is.
The BMS I am using - the Tiny BMS - states in it's manual that it monitors charging both by voltage, current and balance. The BMS manual says that it disconnects the charge circuit when the voltage or current conditions are met, and is capable of issuing a variety of error codes should one be met without the other.

So unless I am misunderstanding something, I believe this BMS does indeed disconnect the charger on low current.
(06-21-2020, 12:49 PM)daromer Wrote: Note that you only can vary voltage a tiny bit.
Als note that they have No current controll
They Will supply all they can and then go into over current protection.
Without extra electronics they Arent made to work as battery Charger.....

The PSU I posted above has a voltage adjustable by internal pot to 100-110% of its nominal range of 43-55v. It also has "constant current level programming" of 0-15.7A.

The only difference I can discern from this PSU and a dedicated 'charger' is that a charger would have its own circuits to disconnect the charger on one of the conditions the BMS seems capable of taking care of?

This was the point of this thread though - if I have misunderstood this then I would like to understand how.
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#12
No the bms does not disconnect on low current. Only on critical values. A bms is not a Charge controller. That PSU is also not a Charge controller.

Its better to get a Charge controller IF you ask IF its doable to be honest.
It can be used but... And thats a but Smile
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#13
So what is the difference between a "critical value" and "low current"?

What is the charger or "charge controller" doing that is different to the BMS?
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#14
A bms monitors and disconnects if something goes wrong on a cell level.

A battery charger follows a charge profile and changes voltage and current levels.

A bms disconnect based on theses settings (can vary)
* High total total voltage
* High cell level voltage
* Low total voltage
* Log cell level voltage
* Over current
* Over temperature
* Under temperature

A bms does not regulate. But what most bms do is balance to maintain the battery. This also does not a normal battery charger do unless its an rc charger with balance function.

So as you see there is no such thing as disconnect the charger if the current is low. How would that work ? It would disconnect it even before it started to charge....
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#15
Then why in the TinyBMS manual does it say:


Thebattery is fully charged, the Charging Done (0x63) event is generated, BMS goes to the Fully Charged state and the SOC value is set to the 100 % value only if all three conditions are met:
•The voltage of the all cells is at the Fully Charged voltage limit;
•The cells imbalance is less than the Allowed Disbalance setting;
•The charging current becomes lower than Charge Finished Current setting value.


I still am not understanding what a charger is doing differently that a CC managed PSU. Here is my understanding of what a CC PSU does:

Current is set to a max value of "x"
Voltage is set to a Max value of "y"

1. Battery is plugged in
2. Battery draws circa 'x' amps until internal voltage reaches 'y'
3. Battery no longer draws as much current due to reaching higher SoC and limited by 'y'.
4. PSU limits 'y' to prevent over voltage
5. Battery current draw reaches near zero.
6. Battery is disconnected by external circuit.

Is this incorrect? If so why?

I'm not trying to be obtuse here, but you are saying something which seems contrary to other advice I have read and received so I really want to understand what I'm not getting.
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#16
The BMS can controll some chargers yes. It does NOT change the input.
A charge controller follow several aspects like
* Min current to start charge before voltage reach
*Min voltage before error at min voltage
*max voltage to show error
* Time to charge at CC
* Time to charge at CV
* Min current before shut off

The PSU dont know anything about the battery nor the SOC. it only checks voltage and current. For instance that psu does not disconnect and it does not detect low current. Its a PSU and a PSU will deliver power untill switched off!

None of those is done by a PSU. None of those are done by a BMS.

The BMS states that it sets SOC to 100% when those conditions are true. It does not controll the input nor the PSU based on them....

Once again it can be used as a charger but it is NOT a charger. Not even with that BMS in between does it become a charger. Its still a PSU
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#17
Quote:For instance that psu does not disconnect and it does not detect low current....
None of those is done by a PSU. None of those are done by a BMS.

What you are saying here does not gel with what I am reading in the manual, within the TinyBMS manual is says that:
Quote:Charger is detected, when charger is connected and the charging current starts to flow...
Quote:Tiny BMS controls the charging process only by turning on or off charging port (internal CFET or external relay / contactor)...
Quote:When the BMS is in the Fully Charged state, the battery charging process is restarted only by physically disconnecting the charger from the BMS and reconnecting it again, or at least one of the cells voltages reaches Fully Discharged Voltage level.
Quote:Charger disconnection is detected by the current. When charging current drops below 80 mA, the Tiny BMS finds that the charger has been disconnected, turns off charger port and generates event Charger Disconnected (0x65)...

This, to me, reads that there is an internal relay that is able to disconnect the BMS from the charger once the internal conditions are met and only reconnects once the battery is removed and plugged back in. I cannot see how what the manual says is not flying in the face of what you are saying it is not capable of?
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#18
If so that specific BMS have incorporated that function to help people not wanting to utilize a proper charger.

Did not read that BMS manual so did not know it mention that part or i missed that you written that before Smile So i have to stand to be corrected and im happy you proved me wrong Tongue
With that said its not common that they work that way but what they do is talking to the charger to limit things.

So yes with that combo you will get it to shut off when current is low and i guess it open that port when the voltage is below a specific set value or SOC.

But if you read back i also stated that the turn off part is not really the critical part. On Lithium you can have it running 24/7 if you want. Its only on some older chems you had to cycle to keep a battery running in good shape.
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#19
Haha, thanks - I was hoping it was just that the vast majority of people here use the generic BMS that don't have these functions, but I was convinced I must have some serious misunderstanding somewhere Tongue

As it happens one of the main Mean Well suppliers in the UK have just got back to me and said the adjustment range which says 


"Adjustment of output voltage is allowable to 40 ~ 110% of nominal output voltage."

is within the 43 ~ 55V range, and not on top of.

This doesn't really make sense to me, as if you take its 'nominal' output of 48v then +10% would be 52.8v, not 55v... But they cited their testing of the RSP-1000-48 which they said achieved 57.11v - maybe good enough for an almost 4.1v charge, but I don't want to be taking anything to the edge of it's voltage limits.


All this to say, this is pushing me back in the direction of the RPB-1600-48 which is a full blown charger  Angel
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#20
Yeah i dont get their numbers together between voltages and the %... But with that said they most likely have a formula.

Note that many cheap systems use a very very simple psu as charger and rely on the BMS to cut out on voltage being to high as example. Low current shut off is most of the cases ignored...
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