Why do I need a charge controller when the BMS does the same thing?

[qrper]

Well gang, the subject line says it all.

The wife and I have been snowed in so to kill time, I've been watching a boat load of youtube videos on lithium batteries. Apparently the BMS cuts off the charge when the batteries are full to prevent over chargingâ€"exactly like a charge controller wouldâ€"so why would I need one ( a charge controller) if the lithium battery uses a BMS?

Mike wb8vge

[LilMT]

I may be way off base here, but my understanding is:
The charge controller will tailor the voltage and amperage to provide what is "Best" for the battery.
As the light provided to the panels throughout the day changes, the output from the panels changes as well.  Increasing and decreasing panel voltages.
Not good for charging, and Li batteries are kinda sensitive about the charge voltages and the charge amperage.

Please correct me if I am off base on this.

Thanks,
LilMT

[boB]

Yes, a BMS may help protect the batteries from overvoltage by shutting off.

Unless it has a separate charging input though, you won't be able to use the energy until the sun drops enough that the BMS turns back on again.

If the battery terminals have been disconnected by its internal FETs or relay and has only one pair of plus and minus terminals, as I have seen, then no energy gets in or out of the battery.

Even then, the BMS has a finite voltage limit where its internal FETs will not stop the high voltage and it will still possibly go boom.

As LilMT says, a charge controller will keep that voltage to a maximum and stop at the right time AS WELL AS still be useful as an MPPT charge controller.  If your battery voltage is say, 24V and your PV array is like, 100V,  how is that going to work ?

I don't know of any BMS's that have a built in MPPT charge controller although that may actually be a thing at some point.

boB   (full power and working warmly in AZ this week)

[qrper]

Thanks, Bob,

I understand the concept of the charge controllers... been using them since '78. I'm still very much old school and prefer to use lead acidâ€"and even the simplest lead acid battery sytemâ€"needs some sort of charge controller.

So many of the videos I watched, when the battery (lithium) needs recharged, they simply hook up a power supply and let 'er rip. Other than the BMS, there's no external battery charging controller.

I have a Bioenno 1212 battery I use for portable HF work and it's charger is stupid, there's no charge controller for battery control circuits in it. It's a cheap swps. Apparently Bioenno relies on the BMS on the battery to keep it from going up in smoke.

We got more snow coming, so I'll park my butt in front of the computer for more videos.

mike, wb8vge

[boB]

Speaking about batteries for ham radio...    I wonder if there are issues with EMI from any of the BMS's ?

That is something I haven't looked into or tested.

boB

[qrper]

With the battery inches from my FT897, I can't hear anything from the battery's BMS. That's not to say it's not making noise, I simply can't hear it above the noise floor. Next time I think about, I'll drape a wire around and see what the spectrum analyzer sees.

mike, wb8vge

[ClassicCrazy]

Thanks, Bob,

I understand the concept of the charge controllers... been using them since '78. I'm still very much old school and prefer to use lead acidâ€"and even the simplest lead acid battery sytemâ€"needs some sort of charge controller.

So many of the videos I watched, when the battery (lithium) needs recharged, they simply hook up a power supply and let 'er rip. Other than the BMS, there's no external battery charging controller.

I have a Bioenno 1212 battery I use for portable HF work and it's charger is stupid, there's no charge controller for battery control circuits in it. It's a cheap swps. Apparently Bioenno relies on the BMS on the battery to keep it from going up in smoke.

We got more snow coming, so I'll park my butt in front of the computer for more videos.

mike, wb8vge

The plug in power supplies are voltage and current limited for a lithium battery . Most of the chargers also change from constant current to constant voltage at the end to be able to let the bms balance the cells ( another thing that bms will do ).

Larry

[mike90045]

The BMS is a last ditch device to try to prevent damage to the fragile battery.   Undercharge / overcharge both rapidly damage the battery, and as a basic, the BMS disconnects the battery from the rest of the gear, leaving the solar charge controllers without any load.  The inverter will shutdown

The BMS can manage to regulate a couple of amps, but can't manage a 15A 90V PV array

[Bob D]

Some BMS's are a last line of defence.
There is also some schools of thought about absorb charging, etc.
However, I use an Electrodacus BMS and it handles turning charging on and off.
When any one cell voltage hits the "full" setpoint, the BMS opens teh charge permissive contact.
In my case, that signal turns off the Classic ( which has V absorb set high enough that it is never achieved; the Classic still does the MPPT work) plus it turns off solid state relays that disconnect a separate bank of panels that are directly connected to the battery, in parallel with the Classic.
Works great.
The BMS balances continuously while charging, and I see very little cell to cell delta V.  Because it balances during charging, there is no need for an end of charge time for balancing.
The Electrodacus BMS doesn't directly handle either the charging or inverter current but instead uses external devices ( SSR's, contactors, or the CC or inverter control inputs) to control current flow to/from the battery.

[boB]

Has anyone here seen a Li battery with separate charge terminals and discharge terminals ?

That could be possibly be useful.  Of course the terminals could be tied together as well.

boB

[Steve_S]

Has anyone here seen a Li battery with separate charge terminals and discharge terminals ?

That could be possibly be useful.  Of course the terminals could be tied together as well.

boB

There are Battery Packs with Separate Port BMS'.  These can be either with Relays/Contactors (mostly EV Application) or MOSFET Only usually for lighter duty.   Separate Port BMS has a Charge Input Line and a separate Discharge Line each controllable relative to the BMS setup.   These are not generally sold to Retail Clients as prebuilt battery packs.

[boB]

Has anyone here seen a Li battery with separate charge terminals and discharge terminals ?

That could be possibly be useful.  Of course the terminals could be tied together as well.

boB

There are Battery Packs with Separate Port BMS'.  These can be either with Relays/Contactors (mostly EV Application) or MOSFET Only usually for lighter duty.   Separate Port BMS has a Charge Input Line and a separate Discharge Line each controllable relative to the BMS setup.   These are not generally sold to Retail Clients as prebuilt battery packs.

OK.   Thanks !

boB