A common limitation with all charge controller and AIO systems

coolbz

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They are all based on battery voltage, for start/stop charging, and for switch between grid and battery. This is a problem because battery voltage fluctuate too much under normal load/charge due to internal resistance.

I reported in other thread, that my battery system seems to have around 50 mohms internal resistance, which is big enough to cause several volts of fluctuation under normal amps draw. And this can screw any charger or AIO systems and fool them to think battery is too low or too high, even though that's not true.

So my question is, are there any shunt based charge controller or AIO system on the market?
 

Bud Martin

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What kind of system are you running? Makes? model? battery type?
How much of the Voltage swing are you seeing at the battery terminals with load and with heavy load?
What is the Voltage settings on you SCC for it to switch to grid when the Battery Voltage is below set point and what Voltage is it set to go back to inverter mode? What are the Vdrops on your wiring, on the circuit breakers/fuses?
My 12V AIO MPP Solar system with 280Ah LiFePo4 has Vdrops at the battery terminals of about 0.20VDC at 60A Load. It sounds like you have problem in your system.
 
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Ampster

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So my question is, are there any shunt based charge controller or AIO system on the market?
They are all based on voltage because that is the most reliable way to know when the battery is near full. On my AIO the load is served by the inverter so when charging the battery the voltage is a non loaded voltage.

It is not a common problem as the title suggests. The problem may be in the system configuration or wiring. Tell us more about you system, and maybe we can help. For starters the questions posed by @Bud Martin would be good question to answer.
 
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coolbz

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They are all based on voltage because that is the most reliable way to know when the battery is near full. On my AIO the load is served by the inverter so when charging the battery the voltage is a non loaded voltage.

It is not a common problem as the title suggests. The problem may be in the system configuration or wiring. Tell us more about you system, and maybe we can help. For starters the questions posed by @Bud Martin would be good question to answer.
Unless voltage is measured when amps is zero or the battery system has zero ohms, otherwise there will be voltage drop/raise due to amps out/in, and it is not accurate indicator of battery capacity.
 

coolbz

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What kind of system are you running? Makes? model? battery type?
How much of the Voltage swing are you seeing at the battery terminals with load and with heavy load?
What is the Voltage settings on you SCC for it to switch to grid when the Battery Voltage is below set point and what Voltage is it set to go back to inverter mode? What are the Vdrops on your wiring, on the circuit breakers/fuses?
My 12V AIO MPP Solar system with 280Ah LiFePo4 has Vdrops at the battery terminals of about 0.20VDC at 60A Load. It sounds like you have problem in your system.
Mine is Growatt 3kw 48v 120v system with 5kwh battery.
Under 1kw load, battery voltage drop 1 volt.

You can read details in my following post:
 

coolbz

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By the way, I have been running/tuning my system at home for half year. So all observations and conclusions are based on something.

I said "Common" because I have checked many products manual and settings on the market, so far I have not seen any system that is based on an shunt/battery capacity device. Unless there is ohms-less battery, otherwise this is a common issue.
 

Ampster

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it is not accurate indicator of battery capacity.
I think everyone agrees voltage is not an accurate indicator of battery capacity. Capacity is not the goal of setting charge parameter. The purpose of a constant voltage setting is to not overcharge a battery.
 

coolbz

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I think everyone agrees voltage is not an accurate indicator of battery capacity. Capacity is not the goal of setting charge parameter. The purpose of a constant voltage setting is to not overcharge a battery.

I guess maybe my goal is somehow different than many here. I just want to charge battery either from free solar or cheap night-hour grid power, and hope the system can be automated based on accurate battery capacity. By using shunt capacity, it would be more accurate to not overcharge/undercharge battery.
 

Bud Martin

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Mine is Growatt 3kw 48v 120v system with 5kwh battery.
Under 1kw load, battery voltage drop 1 volt.

You can read details in my following post:
From the thread you link to:
"Even 1 volt drop has been causing Growatt to switch power mode unnecessarily since most settings are based on voltage. "
"If I try full load of 100amps, the voltage drop will be 5 volt, that is tooooo much."

What is the Voltage setpoint you set the GroWatt to go to utility mode when the Voltage on battery is low?
If 1V is the setting window for your 48V system, that is way too narrow.
5V drops means you have problem in your system.
 
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400bird

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I'd agree you might need to look at something deeper in your set up.

My 48v system was loaded to 2.2kw this evening and the voltage sagged 0.3 volts.

FYI, Schneider advertises using SOC to control battery charge/discharge. I haven't tried it, but that fits your request to use a shunt as best I can tell.
 

Ampster

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I have been running/tuning my system at home for half year. So all observations and conclusions are based on something.
Something?
I have been messing with Lithium batteries for ten years and I like to use physics as a basis for my understanding. I also look at best practices of OEM EV manufacturers, battery manufacturers spec sheets that state a maximum charge current and voltage. All the charge controllers and AIO inverters use two fundamental settings, Constant Current and Constant Voltage.
There is always room for innovation but I am more moved by objective facts if we are going to talk about things in the physical realm or the chemistry of ions and electrolytes.
 

Bud Martin

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I guess maybe my goal is somehow different than many here. I just want to charge battery either from free solar or cheap night-hour grid power, and hope the system can be automated based on accurate battery capacity. By using shunt capacity, it would be more accurate to not overcharge/undercharge battery.
I am curious as to how the AIO or any SCC will know what the real battery capacity is to start with?
 

Ampster

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By using shunt capacity, it would be more accurate to not overcharge/undercharge battery.
Using a shunt as a Coulomb counter to set a low SOC disconnect can be useful especially when under load. My AIO allows me to set that at a percentage of SOC based on the Coulomb counting of the Ahrs discharged. That can be useful since in that situation the battery is often under load. I also set a specific low voltage cutoff on the inverter and a fail safe one in my BMS.
 

Bud Martin

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Using a shunt as a Coulomb counter to set a low SOC disconnect can be useful especially when under load. My AIO allows me to set that at a percentage of SOC based on the Coulomb counting of the Ahrs discharged. That can be useful since in that situation the battery is often under load. I also set a specific low voltage cutoff on the inverter and a fail safe one in my BMS.
But does that mean you need to know what the battery capacity is to start with and it means you have to input new value as battery ages? I.E. 100Ah may become 80Ah so if you put in 50A you would think that you are putting 50% of 100Ah but the battery is now only 80Ah, I hope I am making sense.
 

Ampster

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But does that mean you need to know what the battery capacity is to start with and it means you have to input new value as battery ages? I.E. 100Ah may become 80Ah so if you put in 50A you would think that you are putting 50% of 100Ah but the battery is now only 80Ah, I hope I am making sense.
Yes you need to estimate battery capacity from a known test or specs. I use a conservative number for my battery capacity anyway so I have built in cushion at the bottom. The Coulomb counters I like are ones that use Watthours or kWhs since voltage changes during discharge and that needs to be accounted for.

Yes your post makes sense.

.
 

Bud Martin

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Yes you need to estimate battery capacity from a known test or specs. I use a conservative number for my battery capacity anyway so I have built in cushion at the bottom. The Coulomb counters I like are ones that use Watthours or kWhs since voltage changes during discharge and that needs to be accounted for.

Yes your post makes sense.

.
I am glad you understand my English writing and not coming off as argument with you. I saw one thread a while back that the person puts two 12V 100Ah batteries is series, so he input 200Ah (nstead of 100Ah since he did not know how the Ah is supposed to be when it is in series circuit) info into VICTRON, but when he uses the system, the run time is less than what Victron is showing.
 
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Ampster

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Bogart Engineering is the only solar controller that charges according to the battery monitor.
It is fairly common in EVs to have communication between the battery monitor and the charger. Temperature voltage and current are monitored and current is adjusted if the temperature increases during high speed DC fast charging.
I appreciate that level of sophistication when traveling in my vehicles but for my stationary pack I am fine with the settings for voltage and current.
 
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Ampster

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By using shunt capacity, it would be more accurate to not overcharge/undercharge battery.
Unfortunately Coulomb counters have drift. I have one in my inverter and another in my BMS and sometimes they disagree. The only time I know they are correct is when they both read 100% and that is because they are programmed to reset when my battery finishes the Constant Voltage stage of charging. However I do pay attention to what my Coulombs counters tell me I have used since a full charge.
I am not trying to argue with you but I just want other readers to see another opinion. I also think charging is a separate issue from discharging. Our batteries are sensitive to over charging and the measure of that is voltage and current. Certainly there are also minimum voltages that the batteries should not exceed. However between the top and the bottom a shunt or Coulomb counter is a very useful tool to see how much energy you have used and how much might be left in you pack.
That is why I do not see the problem stated in the title of this thread as a problem that needs a solution.
 
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