New from San Antonio Lithium Ion battery issues.

[Jicafold]

Hello. I am interested getting started in solar power to run small items such as my laptop computer. I have made one 18650 lithium ion battery based powerpack with a 3S21P setup and BMS…so far. I have a 200 watt Renogy Suitcase panel, Renogy Rover 20A MPPT charge controller, and a Renogy 700 watt inverter. Two main problems:

• There seems to be a discrepancy in the voltage readings. When I first attach the battery to the controller without the solar panel, it reads a voltage of 11.6v, the current state of charge. However, when you attach the solar panel it jumps to 14.3v....boost mode. That readout is supposed to be battery voltage....which isn't true. Unless I'm just not understanding what the screen is telling me. Yes, I have since changed the settings in the “user” mode to not exceed 12.6 volts but still….why does it do that?
• When connecting the above battery at 11.6 volts to the power inverter it does a constant beep. The voltage is not too low or too high, and I hooked it to a ground on my car to rule that out. No change. It still keeps beeping.

 

[MisterSandals]

Sounds like you need to verify voltages with a volt meter.
With solar charging, you often get a voltage bump from increased charge voltage and conversely you'd get a voltage slump from running an inverter. All this read from a single spot on your Renody inverter?

 

[Jicafold]

Thank you. Currently, this battery with the multimeter reads 12.3 V on the discharge side of the battery BMS. The charge side reads 11.93 V. The Renogy charge controller also reads 11.9 volts. So that matches. I do not know what you mean single spot on the inverter. It’s still beeping at me.

 

[MisterSandals]

Can you post a pic or 2 of your setup and wiring? Lots of eyes here to help spot anything unusual.

 

[Jicafold]

Here are photos of the battery I made before I put the paper and shrink wrap on, the solar panel in a temporary position in beautiful sun, and my charge controller currently showing 11.9 volts, a photo I just took, and BMS I used. I am unsure what value these photos are however. Are there other photos you feel are important? Thank you.

 

[MisterSandals]

Tidy battery build!
The little shading on the panels might affect the output. What are the panels specs and what voltage are they producing not connected to anything (Voc)?

3S supposed to be (4.2V x 3 max = 12.6V) so that seems right.
11.9V / 3 = 3.96V which should be close to full.

What BMS do you have? Is it for 3S 18650 cells?

Sorry, just grasping for ideas...

 

[Jicafold]

Here are the detailed specifications for the Renogy 200 watt suitcase solar panel:

Electrical Specs

• Maximum Power (Pmax): 200W (2 × 100W panels)

• Open Circuit Voltage (Voc): 24.3V

• Short Circuit Current (Isc): 10.37A

• Maximum Operating Voltage (Vmp): 20.4V

• Maximum Operating Current (Imp): 9.80A

• Cell Efficiency: Up to 22.5%

• Charge Controller: 20A PWM Voyager (waterproof) (I'm not using this controller).

Compatibility

• System Voltage: 12V DC

• Battery Types Supported: Gel, Sealed, Flooded, and Lithium



Currently, in bright sunlight over 100% of the panel at correct angle and elevation, it reads 19.3 volts of output. With the battery plugged it read 11.9 volts of battery charge. When connecting the solar panel it went to boost mode right away from 11.9 volts to 12.5 volts. How can that be? Battery charge was rated at 71% at 12.5 volts which seems an awfully low estimation for something with a max charge of 12.6 volts. Please see photos.

 

[MisterSandals]

Battery charge was rated at 71% at 12.5 volts which seems a awfully low estimation for something with a max charge of 12.6 volts.

The Soc may be related to the battery type selected or possibly the charge settings.

 

[ConnerLabs]

What are the individual voltages of your 3 series packs? Is it balanced? Could the BMS be cutting it off?

Does the BMS have overcurrent protection? What’s the threshold?

3S of lithium ion is 10.8V nominal. Some laptop batteries are badged as 11.1. Once you add in the voltage drop under load, a 12V inverter will hit its undervoltage cutoff before it can use much of the capacity.

 

[Jicafold]

Well, a 3S lithium power bank with 18650 batteries would have a nominal voltage of 11.1, not 10.8v. They are 3.7 volts each. As noted above by Mister Sandals, they have a max charge of 4.2v. So that's 12.6v. I did not plug anything into the inverter so it has no load other than itself.

The BMS has:

• Multiple Protections: During charging and discharging, it has overcharge protection, overdischarge protection, and overcurrent Protection, short circuit protection; Low Standby current: MOS transistor can control the battery charge and discharge, low standby current consumption.
• Charging voltage:12.6v ~ 13.6v Over Charge voltage:4.25±0.05v Over Discharge voltage: 2.5v±0.05v

Batteries were individually checked for both voltage and capacity by me. They are all healthy and roughly around 2000 mAh.

Is it possible to check individual voltages of each cell once they are all connected?

 

[Jicafold]

The Soc may be related to the battery type selected or possibly the charge settings.

I reset the charge setting to 12.6 volts. I have to recheck other settings of boost, etc in the user menu. So , yes, that may be a cause.

 

[ConnerLabs]

Well, a 3S lithium power bank with 18650 batteries would have a nominal voltage of 11.1, not 10.8v. They are 3.7 volts each. As noted above by Mister Sandals, they have a max charge of 4.2v. So that's 12.6v. I did not plug anything into the inverter so it has no load other than itself.

The BMS has:

• Multiple Protections: During charging and discharging, it has overcharge protection, overdischarge protection, and overcurrent Protection, short circuit protection; Low Standby current: MOS transistor can control the battery charge and discharge, low standby current consumption.
• Charging voltage:12.6v ~ 13.6v Over Charge voltage:4.25±0.05v Over Discharge voltage: 2.5v±0.05v

Batteries were individually checked for both voltage and capacity by me. They are all healthy and roughly around 2000 mAh.

Is it possible to check individual voltages of each cell once they are all connected?

You can check each group of parallel cells within the series string. They should have similar voltages. So if fully charged they should all read 4.2. Within a parallel group, the voltages are all the same by definition (you welded the terminals together)

Voltage check is important because these small BMS for Li-ion don’t do any cell balancing. You had to balance them yourself. The BMS will cut off when the voltage of any group goes above 4.25 or under 2.5.

I guess what is happening here is that the BMS is disconnecting on cell overvoltage when you hook up the panels. Then the DC voltage spikes enough that your inverter beeps to complain about overvoltage.

PWM charge controllers are prone to this issue. MPPT have better control of their output voltage and are a safer choice for all lithium ion chemistries.

 

[Jicafold]

I guess what is happening here is that the BMS is disconnecting on cell overvoltage when you hook up the panels. Then the DC voltage spikes enough that your inverter beeps to complain about overvoltage.

ok. I'll check the cell voltages a bit later today. However, can you explain the 2 sentences above? I am not following you.

 

[ConnerLabs]

ok. I'll check the cell voltages a bit later today. However, can you explain the 2 sentences above? I am not following you.

Battery is already full

As soon as you connect the PWM charge controller, one cell goes above 4.2V

BMS says nope and disconnects

Now the PWM charge controller is connected directly to the inverter with no battery. And it's a PWM unit, so it has no voltage regulation. The panels are connected directly to the inverter with no battery.

Inverter sees Voc of the panels, almost 24V, and starts to complain and beep

All of this could happen within one cycle of the PWM before the charge controller can do anything about it. And being PWM, all it can do about it is disconnect the panels completely.

I didn't make this scenario up. It's described in great detail by Nordkyn Design. He warns against using PWM charge controllers with lithium ion batteries.

Charging Marine Lithium Battery Banks | Nordkyn Design

nordkyndesign.com

The worst ripple voltage is produced by solar PWM charge controllers, followed by old-style transformer/rectifier battery chargers, which should not be associated with lithium batteries. In the case of a solar PWM charge controller, the solar array is connected and disconnected from the battery at a fixed frequency. The open-circuit voltage of a solar array charging a battery in a 12VDC installation typically reaches up to about 22V (36-cell panel). Once the battery can no longer accept enough current to keep the voltage down, every time the controller sends a pulse to the battery, the cell voltages are gradually driven towards 22 / 4 = 5.5V. If the pulse voltage reaches 4.2V, there is sufficient energy for the electrolyte decomposition reaction to take place and the cells get rapidly destroyed, even if the average battery voltage as measured by a multimeter appears acceptable.

 

[Jicafold]

Battery is already full

As soon as you connect the PWM charge controller, one cell goes above 4.2V

BMS says nope and disconnects

Now the PWM charge controller is connected directly to the inverter with no battery. And it's a PWM unit, so it has no voltage regulation. The panels are connected directly to the inverter with no battery.

Inverter sees Voc of the panels, almost 24V, and starts to complain and beep

All of this could happen within one cycle of the PWM before the charge controller can do anything about it. And being PWM, all it can do about it is disconnect the panels completely.

I didn't make this scenario up. It's described in great detail by Nordkyn Design. He warns against using PWM charge controllers with lithium ion batteries.

Charging Marine Lithium Battery Banks | Nordkyn Design

nordkyndesign.com

However, I'm not using a PWM controller. I am using a Renogy Rover 20A MPPT controller as stated in the first post.

I never connected the controller directly to power inverter. I only connected the battery by itself with no load which resulted in continuous beeping.

Currently the 3 cells are reading 4.05, 4.09, and 4.17. There is a total of 12.32 at the battery itself.

 

[ConnerLabs]

However, I'm not using a PWM controller. I am using a Renogy Rover 20A MPPT controller as stated in the first post.

I never connected the controller directly to power inverter. I only connected the battery by itself with no load which resulted in continuous beeping.

Currently the 3 cells are reading 4.05, 4.09, and 4.17. There is a total of 12.32 at the battery itself.

I see, I saw this upthread:

• Charge Controller: 20A PWM Voyager (waterproof)

and thought it was referring to the controller you were using. I have no idea what the problem is then.

 

[Jicafold]

My mistake for including that. The panel came with the Voyager PWM. I'm not using it.

 

[ConnerLabs]

My mistake for including that. The panel came with the Voyager PWM. I'm not using it.

I see I re-read the thread more carefully...
Can you verify with a multimeter the voltages on the BMS board:

At the BMS Charge terminals when the MPPT is connected and the panels are getting sun
At the BMS Discharge terminals when the inverter is connected and turned on/beeping/complaining
At the BMS battery terminals (0V and 12.6V)

Hopefully this will show up some unexpected voltage drop or some quirk of the BMS.

 

[Jicafold]

I see I re-read the thread more carefully...
Can you verify with a multimeter the voltages on the BMS board:

At the BMS Charge terminals when the MPPT is connected and the panels are getting sun
At the BMS Discharge terminals when the inverter is connected and turned on/beeping/complaining
At the BMS battery terminals (0V and 12.6V)

Hopefully this will show up some unexpected voltage drop or some quirk of the BMS.

At the BMS Charge terminals when the MPPT is connected and the panels are getting sun: 12.6 volts. The controller says the battery voltage is 12.5 volts. Interestingly the controller says the battery is at 77%.


At the BMS Discharge terminals when the inverter is connected and turned on/beeping/complaining: 11.69 volts.


At the BMS battery terminals (0V and 12.6V): 12.38 volts. The discharge terminals without it connected is also 12.38 volts.

 

[MisterSandals]

The controller says the battery voltage is 12.5 volts. Interestingly the controller says the battery is at 77%.

I suspect this is because the controller is setup by you or at factory based on lead acid voltages.

 

[SLTech23]

However, I'm not using a PWM controller. I am using a Renogy Rover 20A MPPT controller as stated in the first post.

I never connected the controller directly to power inverter. I only connected the battery by itself with no load which resulted in continuous beeping.

Currently the 3 cells are reading 4.05, 4.09, and 4.17. There is a total of 12.32 at the battery itself.

4.17 with a little tick it will give signal to BMS to cut the supply,

 

[Jicafold]

4.17 with a little tick it will give signal to BMS to cut the supply,

So I am wondering where to go from here before I make a bigger battery. It seems I cannot fully charge this one and I have a power inverter that doesn't like it either. I imagine I would have the same problem with a different BMS.

 

[ConnerLabs]

So I am wondering where to go from here before I make a bigger battery. It seems I cannot fully charge this one and I have a power inverter that doesn't like it either.

Can you try a different inverter? Or some other load that draws a lot of current at 12V like the proverbial car headlamp bulb. Just to validate that the voltage at the Discharge terminals holds up under load and there isn't some weird issue with the BMS causing it to shut off prematurely. I don't think the inverter should complain at 11.7V, most 12V units are good down to 10V input.

As another poster mentioned, one of your cell groups is pretty close to the 4.2V cutoff voltage too, so it might be a good idea to discharge the battery some before trying the solar charger again.

You'll also need to set the solar charge controller for a max voltage less than 12.6. Settings for lead acid or 4S LFP will be excessive and will cause the BMS to trip off on overvoltage.

 

[Jicafold]

Can you try a different inverter? Or some other load that draws a lot of current at 12V like the proverbial car headlamp bulb. Just to validate that the voltage at the Discharge terminals holds up under load and there isn't some weird issue with the BMS causing it to shut off prematurely. I don't think the inverter should complain at 11.7V, most 12V units are good down to 10V input.

As another poster mentioned, one of your cell groups is pretty close to the 4.2V cutoff voltage too, so it might be a good idea to discharge the battery some before trying the solar charger again.

You'll also need to set the solar charge controller for a max voltage less than 12.6. Settings for lead acid or 4S LFP will be excessive and will cause the BMS to trip off on overvoltage.

Yes. I was going to discharge the battery and then try charging again with the depleted. Of course I cannot use the power inverter for that. I may have to try that headlight. I have the controller set for maximum voltage of 12 .6 already. I wish I had a different inverter. I guess I could buy one, try it, and return it.

 

[ConnerLabs]

Yes. I was going to discharge the battery and then try charging again with the depleted. Of course I cannot use the power inverter for that. I may have to try that headlight. I have the controller set for maximum voltage of 12 .6 already. I wish I had a different inverter. I guess I could buy one, try it, and return it.

I think in this case, it is OK to (temporarily, for test purposes only) bypass the BMS and connect the inverter directly to the battery terminals.

You know the battery is almost full, so if you only run it for a few minutes, there's no chance of overdischarging any of the cells.
And since the inverter can only consume DC power, there's no risk of overcharging them either.

If it runs and powers a load without beeping, that would tend to point a finger at the BMS.