MPPT solar controller and LiFePO4 battery for backpacking

[Sunking]

The two ports don't provide two different functions, they just provide two different connectors to the same connection points, one for the wall charger and one for ham radio, etc.

Are you aboslutely certain about that? There is no other reason to have two ports.

[jflorey2]

But the weak link was not necessarily the BMS--based on what you're saying, it was primarily my ignorance of the fact that the controller's output can and must be tuned to the BMS.

It doesn't need to be. One of the primary functions of a charge controller is to prevent the voltage from exceeding a limit. If it does that, it's not working. If it is just that one, then it's defective. If they all do that, then it's a design flaw.

A BMS should NEVER be required to "sink" power to keep voltages under a limit, and does not need to be "tuned" to a given charge controller. BMSes are designed to protect batteries, and in some cases provide other services like balancing. They are not charge controllers. If the BMS is cutting out at the right voltage, it is doing its job. If the charge controller is providing a charge voltage that is safe for the battery, then it is doing its job.

[Dave C]

Hey I just looked at your battery spec and caught something. Your battery has two ports right? One port for the Charger, and another port for the load equipped with an Anderson Power Pole connector right?

Does not change much, just confirms what I said. The Charge Port disconnects the battery from charger when the battery BMS detects it is fully charged. The Genasun does not like that and raises an alarm.

The two ports don't provide two different functions, they just provide two different connectors to the same connection points, one for the wall charger and one for ham radio, etc.

Tell me if this sounds correct when you used the Genasun Controller.. It worked correctly until the battery was charged up, then went into alarm and high voltage. If you had a load connected using power, after some period of time the Genasun alarm would clear and charge the battery again, After the battery charged the Genasun went back into alarm and the cycle repeats itself?

Is that what you are observing? If so you could use the Genasun and just have to put up with nuisance false alarm. Bet a dollar that is what you observed.

That would have been valuable information, but as I believed there were major problems with my setup, I never connected a load for fear of damaging it. As you suggested, a resistor would have been the way to go for testing. Unfortunately, there's a lot of inertia to overcome with my brain--I don't improvise well in areas in which I'm not thinking on a day-to-day basis. Isn't your question answered, though, by the fact that each time I connected the partially discharged battery it was charged by the controller? In other words, I agree that if I had left it connected along with a load, it probably would have resumed charging.

The issue I take with that design approach is it does not allow you to utilize the solar power when the sun is available and the battery is fully charged. I would prefer to use the solar power when available and not use battery power to extend battery life, wear and tear. My design approach is to utilize all the solar power I can possible use, and only use battery power at night or when there is not sufficient solar power available to supply the load. That is a problem with most solar applications using lithium batteries. Pb systems do not work that way as the solar is always connected. That is the philosophy Genasun uses, but your battery BMS is not designed to support that topology.

Of course, this is how I would hope that it works. I don't know enough to assume that the Bioenno Power battery wasn't designed to work this way. You do raise some questions that I will ask, though.

What is giving you trouble is you do not understand how battery chargers work, and how a BMS works.

Obviously. That's why I'm consulting with you guys. I'm very appreciative of the thorough answers you have provided.

The Disconnect is your battery BMS was designed to be charged with a conventional Constant Voltage battery charger operation as a Voltage Source In other words a conventional AC powered charger. It was not designed to be charged from MPPT Solar Controller or a Current Source. That means incompatible. Your other Bioenno PWM controller is made to work with that battery as you stated earlier. Based on that I would say just use the Bioenno controller and forget the Genasun. All you are giving up is some panel power.

The explanation I received from Bioenno back in September is that the AC charger is a CC/CV charger--that it initially provides CC and then switches to CV. Also, Bioenno now offers an MPPT controller that is compatible with their batteries. I'm going to ask them to review this thread if they have time and give me some feedback. It's a lot to ask, and I don't assume anything, but Kevin has provided such great communication and service to date, I wouldn't be surprised if he takes the time to do this.

Thank you so much for sharing your knowledge and years of experience with me.

[Dave C]

Oh, sorry for duplicate info in two posts. I neglected to notice that we had gone into page 2. I thought my prior post was lost.

[Dave C]

Sunking, if an input voltage in the range presented in my scenario were causing the BMS to disconnect due to over voltage, then wouldn't this prevent the battery from ever being charged? I always connected the panel to the controller first in full sunlight, so the BMS always encountered open panel voltage when the partially discharged battery was first connected--granted, at 0A.

Is it possible that the controller misinterpreted the battery's drop in current when it switched from CC to CV as a disconnect? If, on the other hand, the BMS did disconnect the battery when fully charged, shouldn't the controller handle it more gracefully? Or is it possible that this is the only battery that behaves this way?

The battery mfr. states that the BMS expects a CV voltage of around 14V (I've asked for an exact value), and the controller mfr. states that the controller's CV voltage is 14.2V. Would you still suggest changing the controller's voltage?

Not sure if this adds any value, but the generic CC/CV AC charger that came with the battery handles the transition from CC to CV with no problem.

[Sunking]

Hey I just looked at your battery spec and caught something. Your battery has two ports right? One port for the Charger, and another port for the load equipped with an Anderson Power Pole connector right?

Does not change much, just confirms what I said. The Charge Port disconnects the battery from charger when the battery BMS detects it is fully charged. The Genasun does not like that and raises an alarm.

Tell me if this sounds correct when you used the Genasun Controller.. It worked correctly until the battery was charged up, then went into alarm and high voltage. If you had a load connected using power, after some period of time the Genasun alarm would clear and charge the battery again, After the battery charged the Genasun went back into alarm and the cycle repeats itself?

Is that what you are observing? If so you could use the Genasun and just have to put up with nuisance false alarm. Bet a dollar that is what you observed.

The issue I take with that design approach is it does not allow you to utilize the solar power when the sun is available and the battery is fully charged. I would prefer to use the solar power when available and not use battery power to extend battery life, wear and tear. My design approach is to utilize all the solar power I can possible use, and only use battery power at night or when there is not sufficient solar power available to supply the load. That is a problem with most solar applications using lithium batteries. Pb systems do not work that way as the solar is always connected. That is the philosophy Genasun uses, but your battery BMS is not designed to support that topology.

[Sunking]

Maybe the BMS does briefly disconnect as it switches from CC to CV. .

No sir the BMS is not capable of doing that. That is what the Charger does, not BMS. Your Genasun Controller is a CV charger, but also acts like a Constant Current when the battery is low. What is giving you trouble is you do not understand how battery chargers work, and how a BMS works. .

The Disconnect is your battery BMS was designed to be charged with a conventional Constant Voltage battery charger operation as a Voltage Source In other words a conventional AC powered charger. It was not designed to be charged from MPPT Solar Controller or a Current Source. That means incompatible. Your other Bioenno PWM controller is made to work with that battery as you stated earlier. Based on that I would say just use the Bioenno controller and forget the Genasun. All you are giving up is some panel power.

[Sunking]

But the weak link was not necessarily the BMS--based on what you're saying, it was primarily my ignorance of the fact that the controller's output can and must be tuned to the BMS. Too bad Genasun's tech support didn't catch this. If they had, it might have saved us both the hassle of doing a return.

Some truth to that. Genasun assumes incorrectly you matched the battery and controller correctly. What Genasun does not know, and cannot know is how the BMS works. There is no standard definition of what a BMS is or what it does. Every modular battery manufacture uses a different approach and topology.

I still think a controller shouldn't allow open panel voltage to pass to the battery terminals under any circumstance--it should handle a no battery condition more gracefully.

You need to change your way of thinking because it is the nature of the beast. Every MPPT controller I know of does that. This is due to the fact a solar panel is a Current Source and not a Voltage source. With any Current Source when you open the circuit, voltage goes up to supply voltage immediately. That is just the physics and characteristic of a Current Source

My part number was GV5-Li-14.2V.

That is just fine and dandy. Again the issue is your BMS. I believe there are two ways to fix this. 1. is lower the voltage of the controller from 14.2 to 13.8 volts. Ignore Karrak when he said that is not a problem because it is a huge problem. Your battery only has one port, or just a positive and negative terminal. When the BMS disconnects, that also mean your gizmo looses power. If the battery had Two Ports, Charge and Load, you would not have to worry about the error.. 2 Add a shunt load to present a load to the controller.

Try this experiment. Do not use the Load Port on the Controller. Connect a gizmo directly to the battery where you connect the Controller. As for the gizmo, it needs to present a large enough load to keep the charge controller on, and fools the BMS the battery is not fully charged. Bet you a dollar your Controller voltage holds around 14 volts, and the battery BMS does not disconnect. As for the Gizmo it can be as simple as a power resistor, say a 10 watt 15 to 30 Ohm power resistor would be perfect.

[Dave C]

If Dave C didn't specify which Genesun model I would assume he got the Pb unit which will charge to 14.2 volts then float at 13.8 volts which is just fine for the battery.

No, I got the 4-cell Lithium model.

Have you considered that the battery BMS might disconnect the battery from the charge controller when it determines that the battery is full,and not leave the battery on float charge?

I doubt very much that the BMS would try to drag down the input voltage by shunting current. It will just disconnect the battery terminals from the battery.

I don't think the BMS disconnects the battery outright at full charge. It switches from constant current, reducing current to a few mA, and expects constant voltage of 14V (not sure if it's actually 14.2V; I'll find out). In their literature, the default CV voltage of the controller is 14.2V.

Maybe the BMS does briefly disconnect as it switches from CC to CV. I'll see if I can find out.

None of this matters anyway. So what if the BMS disconnects the battery from the charge controller either when the voltage gets too high or if it decides that the charge cycle has finished. Only problem you get is the Genesun giving you a "Battery Overvoltage Fault" and a full battery.

You suggested earlier that the open panel voltage might damage the battery's BMS. But if the BMS can handle 20 or more Volts, then there might not be a problem.

Actually, the BMS must be able to handle open panel voltage in the range presented in my scenario, because otherwise, it would fry when you connect it to the controller after having first connected the panel. (Or, maybe a steady diet of this would damage it over time.) Again, this is a question for Bioenno Power.

I also think that the BMS doesn't disconnect in the presence of any voltage within this range. Otherwise, it would remain open and never accept a charge when you connect it to the controller after having first connected the panel in full sunlight, and this was not the case. The startup sequence with a partially discharged battery was always: 1) connect the panel to the controller; 2) the controller errors and measures panel open voltage at the battery terminals; 3) connect the battery; 4) the controller's status LED immediately goes from error to charging. I never connected a load for fear of damaging my equipment. But it would have been interesting to see if the controller would go back to charging as the load drew power from the battery. I suspect it would have.

If I'm understanding these things correctly, then it seems to me that either the controller misinterpreted the battery's drop in current as a disconnect, or the BMS did disconnect briefly as it switched from CC to CV. I don't think either of these could be overcome by setting the controller to a different output voltage as Sunking sugested. That is, unless in my limited understanding I'm missing something...

[Sunking]

I don't know how you can make these statements without knowing the operating parameters of the battery BMS.

That is because I am a lot smarter than you and have forgotten more than you will ever know about batteries. Been doing it professionally for 35 years.

[Dave C]

Sunking,

Your last post makes sense. I think you might have closed the gaps in my understanding.

But the weak link was not necessarily the BMS--based on what you're saying, it was primarily my ignorance of the fact that the controller's output can and must be tuned to the BMS. Too bad Genasun's tech support didn't catch this. If they had, it might have saved us both the hassle of doing a return.

I still think a controller shouldn't allow open panel voltage to pass to the battery terminals under any circumstance--it should handle a no battery condition more gracefully.

My part number was GV5-Li-14.2V.

--Dave

[karrak]

Well you just might be able to. You have to resolve the incompatibility issue. Since you did not specify what voltage you wanted for the Genasun, you got a default value that is most likely too high for the battery BMS. What you are learning is most Lithium battery problems arise from the BMS. What I think is going on is the Genasun Controller output voltage is too high for the BMS. When the battery reaches full charge, the BMS cannot shunt enough current to pull the Controller voltage down. So your battery Internal BMS sees that as an over voltage, and disconnects from the charge source. When that happens, your controller is seeing an Open Circuit and the voltage shoots up. So now go back to the beginning when you said


That is exactly what is happening, your battery gets disconnected by the BMS when it thinks the input voltage is too high and it is not capable of shunting the current, so it DISCONECTS. Solution, lower the controller voltage.

I don't know how you can make these statements without knowing the operating parameters of the battery BMS.

If Dave C didn't specify which Genesun model I would assume he got the Pb unit which will charge to 14.2 volts then float at 13.8 volts which is just fine for the battery. Have you considered that the battery BMS might disconnect the battery from the charge controller when it determines that the battery is full,and not leave the battery on float charge?

I doubt very much that the BMS would try to drag down the input voltage by shunting current. It will just disconnect the battery terminals from the battery.

None of this matters anyway. So what if the BMS disconnects the battery from the charge controller either when the voltage gets too high or if it decides that the charge cycle has finished. Only problem you get is the Genesun giving you a "Battery Overvoltage Fault" and a full battery.

Simon

[Sunking]

I forgot to mention something about the GV-5. When I received it, I followed the instructions to connect the panel first. I did so in full sunlight. Immediately, the LED flashed red in groupings of 5, indicating that battery voltage was too high. (Looking back, this should have immediately indicated to me that the controller was defective.)

No that meant you had no battery connected and is the crux of your problem. Keep reading.

When I connected the battery, the LED changed to a rapidly blinking green, which indicated charging as expected. When the battery reached full charge, the LED turned solid green as expected, but within a few seconds began to flash red in groups of 5 again. It then alternated a few times between charging and error and finally remained at error. Whenever the controller was flashing red, the battery terminals were showing open panel voltage. This was the case both when the battery was disconnected and when it was connected fully charged.

OK now I know what is going on because that is impossible, even if defective. It means your battery internal BMS is incompatible with the Genasun controller. Only possible way for you to see panel Voc voltage on a battery is if the battery went open circuit which is exactly what happened. Your battery internal BMS disconnected the battery from the charger. So I take back what I said, the controller is fine, your BMS is the problem

It is impossible for a battery to go from say 14 volts at full charge, and go to 18 volts in a short period of time. For that to happen would require a charger capable of producing extremely high amounts of current which your panel is not capable of doing. It would take several hundred amps to do that, and it is not possible for that to happen on solar.

The issue of setting a voltage on the controller probably never came up because the panel voltage and current fell well within the specs of the controller. The specs show that the controller can handle a max panel voltage of 27V and a max input current of 9A. Neither ever got that high.

That has nothing to do with your issue. You are talking maximum Input limits. The problem is the output, not input side. So quit chasing that ghost.
From the GV-5 manual:

Genasun recommends using a lithium battery with a Battery Management System capable of disconnecting the solar charge controller in the event that any cell in the pack is outside of its rated temperature, current or voltage range. Failure to do so may result in property damage, injury or death. Genasun highly recommends the use of a BMS with cell balancing. Cell balancing is mandatory for lithium-iron phosphate systems

There is the crux of your problem. The BMS is incompatible with the controller. It is also some nonsense. There are two unique characteristics of the Genasun Lithium controllers.

1. They only have One-Stage charging known as Float. It is a Constant Voltage algorithm. That is really a good thing as it is a lot less complicated that say a 3-Stage charger for Pb batteries.

2. They are intended for you to use the Controller Load Terminal to protect the battery. The load terminal has a built in Low Voltage Disconnect so if the battery voltage gets too low, it disconnects the battery from the load.

I would like to give the GV-5 another shot. It was great in several ways--small, light, marine-grade, etc. But I'm hesitant, because I don't have a lot of confidence in their customer service

Well you just might be able to. You have to resolve the incompatibility issue. Since you did not specify what voltage you wanted for the Genasun, you got a default value that is most likely too high for the battery BMS. What you are learning is most Lithium battery problems arise from the BMS. What I think is going on is the Genasun Controller output voltage is too high for the BMS. When the battery reaches full charge, the BMS cannot shunt enough current to pull the Controller voltage down. So your battery Internal BMS sees that as an over voltage, and disconnects from the charge source. When that happens, your controller is seeing an Open Circuit and the voltage shoots up. So now go back to the beginning when you said:

I forgot to mention something about the GV-5. When I received it, I followed the instructions to connect the panel first. I did so in full sunlight. Immediately, the LED flashed red in groupings of 5, indicating that battery voltage was too high.

That is exactly what is happening, your battery gets disconnected by the BMS when it thinks the input voltage is too high and it is not capable of shunting the current, so it DISCONECTS. Solution, lower the controller voltage.

I bet you a dollar your Controller voltage is either default 14.2 or 16.7 volts. Determine the maximum voltage your battery BMS can tolerate without disconnecting. Then set your controller to something less like 1 volt less.

What was the Genasun Part Number?

Hint: Either GV5-Li-14.2 or GV5-Li-16.7

[Dave C]

This makes me think that the Genersun is expecting some sort of load. What charge voltage have you got the Genersun set to?

Hi Simon, thanks a lot for your input. I asked Genasun if the GV-5 was expecting a load at the battery terminals, and they never indicated that this was the case. I never set a charge voltage, and I never requested that the manufacturer set it. I didn't know to do that, and support never mentioned this in any of my discussions with them. There were no controls on the unit for me to set it. I returned it for a refund back in October. It seems strange to me that the error LED indicated battery voltage too high when no battery was connected. If this is a design flaw, it seems like a pretty basic, major one that I would expect to be reported often. Again, Genasun said they never heard of this problem, and folks here report they never experienced this.

[karrak]

I forgot to mention something about the GV-5. When I received it, I followed the instructions to connect the panel first. I did so in full sunlight. Immediately, the LED flashed red in groupings of 5, indicating that battery voltage was too high. (Looking back, this should have immediately indicated to me that the controller was defective.) When I connected the battery, the LED changed to a rapidly blinking green, which indicated charging as expected. When the battery reached full charge, the LED turned solid green as expected, but within a few seconds began to flash red in groups of 5 again. It then alternated a few times between charging and error and finally remained at error. Whenever the controller was flashing red, the battery terminals were showing open panel voltage. This was the case both when the battery was disconnected and when it was connected fully charged.

This makes me think that the Genersun is expecting some sort of load. What charge voltage have you got the Genersun set to?

Simon