Benefits of Closed Loop Comms?

[Will Prowse]

I'm running 170kWh of batteries with voltage cutoffs. Call me old fashioned, but after setting up every communication protocol out there, I don't think it's worth the headache.

Besides code compliance, is there any real benefit to using closed loop comms?

I think rapid shut down of the entire system is cool, but if there is an issue, each pack has its own set of safety features to remove itself from the system. And if that fails, each pack has a breaker that is DC rated. If multiple parallel strings were dumping current into a failed cell AND the BMS also failed, the breaker would catch it.

In that situation above, having rapid shut down and closed loop communication would not help. You would have to have BMS failure where the fet bank is not able to disconnect the pack from the system. So whether you have closed loop communication or not, the breaker will come in to save the day. Again, this whole situation is extremely rare, But I'm trying to think of everything possible here.

One argument I've heard is that the inverter charger will slow down the charging when the batteries are nearing 100% SOC. That benefit is short lived and most of these packs balance just fine regardless. Not worth the trouble at all. Such a weak argument.

I can't think of anything else. Is there any benefit here besides code compliance?

 

[Brett V]

None that I can see. My experience mirrors yours.

I do think closed loop has a place in systems for people with no inclination to understand how it works and want it to just work in the background. Sort of an idiot proofing measure.

 

[timselectric]

The only benefit of closed loop, is that you don't have to know anything about the batteries or charging.
It helps beginners get started, with little knowledge of how everything works.
I used it in the beginning, until I educated myself on LFP.
Then I took off the training wheels.

 

[empowered]

I'm running 170kWh of batteries with voltage cutoffs. Call me old fashioned, but after setting up every communication protocol out there, I don't think it's worth the headache.

Besides code compliance, is there any real benefit to using closed loop comms?

I think rapid shut down of the entire system is cool, but if there is an issue, each pack has its own set of safety features to remove itself from the system. And if that fails, each pack has a breaker that is DC rated. If multiple parallel strings were dumping current into a failed cell AND the BMS also failed, the breaker would catch it.

In that situation above, having rapid shut down and closed loop communication would not help. You would have to have BMS failure where the fet bank is not able to disconnect the pack from the system. So whether you have closed loop communication or not, the breaker will come in to save the day. Again, this whole situation is extremely rare, But I'm trying to think of everything possible here.

One argument I've heard is that the inverter charger will slow down the charging when the batteries are nearing 100% SOC. That benefit is short lived and most of these packs balance just fine regardless. Not worth the trouble at all. Such a weak argument.

I can't think of anything else. Is there any benefit here besides code compliance?

my inverter tails the current down towards 100% without comms...

 

[timselectric]

my inverter tails the current down towards 100% without comms...

The battery is doing that, not the charger.
When the battery gets full, it stops drawing current.

 

[400bird]

The battery is doing that, not the charger.
When the battery gets full, it stops drawing current.

Umm, I can still dump 100a of current into a 3.65 volt cell. If the battery was going to limit current when full, how were there so many reports of bloated cells from overcharging back when more people were assembling packs? Why even run a BMS if the cells limit current when full?

The current tapering on everything I've worked on is managed by the charger

 

[ScrodusGargleRotten]

Umm, I can still dump 100a of current into a 3.65 volt cell. If the battery was going to limit current when full, how were there so many reports of bloated cells from overcharging back when more people were assembling packs? Why even run a BMS if the cells limit current when full?

The current tapering on everything I've worked on is managed by the charger

Not really manged by the charger.

Charger sets voltage. When a battery hits the v limit it will naturally take less and less current.

You can charge batteries with a normal power supply. It doesn't manage anything except the voltage. Wouldn't recommend charging with a power supply to unless it's just one cell

 

[740GLE]

Umm, I can still dump 100a of current into a 3.65 volt cell. If the battery was going to limit current when full, how were there so many reports of bloated cells from overcharging back when more people were assembling packs? Why even run a BMS if the cells limit current when full?

The current tapering on everything I've worked on is managed by the charger

First you’d need widely out of balanced cells to even come close to hitting 3.65v on a single cell.

How would you even get there in the first place?

 

[Osmethne]

For my setup, yes there's a good reason I use it. I use an NHX-10k and I have an EV TOU plan. Peak hours are 3-8pm. Before closed loop coms I would charge it up to 100% before 3. This would waste a lot of solar power. Now it's programmed to keep it to a progressively higher SOC before 3 so I make use of much more solar power.

 

[EZPZ]

None that I can think of other than giving you a general idea of how full the batteries are at a glance. Also the eg4 lifepower v2 batteries bms does current limiting independently of what the inverter is set to and reduces charging current the “fuller” it gets thus negating that closed loop argument of the inverter throttling back.

 

[HighDesertOffgrid]

Not really manged by the charger.

Charger sets voltage. When a battery hits the v limit it will naturally take less and less current.

You can charge batteries with a normal power supply. It doesn't manage anything except the voltage. Wouldn't recommend charging with a power supply to unless it's just one cell

I agree with the majority of this with the exception of having used a power supply to charge dozens of 12.8v lfp batteries.
Even the majority of LFP chargers have no comms with the battery's individual cells. They are simply a constant voltage power source.

 

[timselectric]

Umm, I can still dump 100a of current into a 3.65 volt cell. If the battery was going to limit current when full, how were there so many reports of bloated cells from overcharging back when more people were assembling packs? Why even run a BMS if the cells limit current when full?

The current tapering on everything I've worked on is managed by the charger

The current tapering is the battery reaching the chargers set voltage (AKA full).
You can definitely overcharge the battery if you set the charger voltage too high.
Two power sources (battery and charger) connected in parallel will always equalize to the same voltage.
Once equalized, no current flows.
I've said this over and over, current is drawn, not pushed.

 

[ScrodusGargleRotten]

I agree with the majority of this with the exception of having used a power supply to charge dozens of 12.8v lfp batteries.
Even the majority of LFP chargers have no comms with the battery's individual cells. They are simply a constant voltage power source.

Right, I simply said I wouldn't recommend it.
I would do it in a pinch for sure.

 

[timselectric]

I use power supplies to charge batteries, all of the time.
Both, the EW charger and the chargeverter are power supplies.

 

[Mercracing]

The only benefit of closed loop, is that you don't have to know anything about the batteries or charging.
It helps beginners get started, with little knowledge of how everything works.
I used it in the beginning, until I educated myself on LFP.
Then I took off the training wheels.

This mirrors my experience to date, I agree with this statement completely.

 

[Robbert]

Many BMSses are not configurable to set absorbtion time, float voltage etc.
I set that in my charger manually.

I got my hands on a couple of batteries the other day that where used for a approx 2 years and charged daily with closed loop. These batteries showed a huge imbalance, with one cell over 3.7v

 

[SeaGal]

With 170kWh of batteries and/or lots of panels and living much nearer the equator, I can understand that closed-loop doesn't add much. But for us up here at 52 north and with only 15kWh of batteries it becomes more useful.

For example:-

- in Winter months we can charge up batteries on cheap tariff overnight, but to a specific SOC based on anticipated solar production and house usage the next day.
- we have software that will divert energy to an immersion heater if there is still sufficient SOC to get through to the next morning, or switch back to standard heating if not.
- we can adjust charge rate from solar, based on SOC and time of day, so for example can slow down battery charging on summer day to power other things (like charge the EV) as we don't need to get to high SOC until later in the day - and potentially get paid for more export that way
- we can also adjust charge rate based on both temperature and SOC... as detailed in my posting here
https://diysolarforum.com/threads/science-based-discussion-on-charging-lifepo4-below-32°f.50642/post-646862

 

[SolarUKWM]

The current tapering on everything I've worked on is managed by the charger

If the "compliance voltage" of your charger is set correctly for your cell chemistry and cell count, then the battery will _have_ to start drawing less current as the battery and charger will be at pretty much the same voltage. To drive more current, and keep a "constant current" you'd have to exceed the maximum voltage of the battery. Which is bad...

 

[SparkyJJO]

I like tech but all this fancy comms seems like more stuff to go wrong. Does the comms ever take into account cell imbalance and have the charger cut down current so the BMS can balance it out better?

I'll stick with non comms. Not like my Radian can do anything else anyway but I don't care.

 

[Daag]

First post but been lurking a while. In my case, the "benefit" of closed loop is my inverter randomly goes to standby mode with nary a clue as to why.

 

[frankrudis65]

As @timselectric (hi there) said the batterie draws less and less current while getting towards the 100 SOC,I personally don't find any better performance or what so ever with a closed loop communication.I like to keep things simple,even to avoid hickups.Having more then one security feature isn't that bad after all.If everything is set within good limits and well balanced there shouldn't be a problem.Having seperate parts "looking" after each other,makes it more simple to have for example 1 bank of batteries serviced while the others are going....Best regards Frank

 

[Tulex]

I don't see the down side of closed loop, other than I can't be closed loop and monitor the batteries directly with SA. At least not easily with Seplos batteries.
I would imagine the preference has a lot to do with how and if your batteries communicate with the inverter, if your batteries are all the same, etc.
For me, SOC is so much easier to internalize and control things based on it.

 

[CommandoJoe]

If you ran lead acid and you won't have these problems...

 

[Tulex]

If you ran lead acid and you won't have these problems...

They still make those things?

 

[empowered]

With 170kWh of batteries and/or lots of panels and living much nearer the equator, I can understand that closed-loop doesn't add much. But for us up here at 52 north and with only 15kWh of batteries it becomes more useful.

For example:-

- in Winter months we can charge up batteries on cheap tariff overnight, but to a specific SOC based on anticipated solar production and house usage the next day.
- we have software that will divert energy to an immersion heater if there is still sufficient SOC to get through to the next morning, or switch back to standard heating if not.
- we can adjust charge rate from solar, based on SOC and time of day, so for example can slow down battery charging on summer day to power other things (like charge the EV) as we don't need to get to high SOC until later in the day - and potentially get paid for more export that way
- we can also adjust charge rate based on both temperature and SOC... as detailed in my posting here
https://diysolarforum.com/threads/science-based-discussion-on-charging-lifepo4-below-32°f.50642/post-646862

most AIO inverters will let you charge from the grid as well, without using SOC, but voltage instead.