MPPT solar controller and LiFePO4 battery for backpacking

[Sunking]

Would the BMS be sophisticated enough to test if a load has been connected?

Very doubtful. LVD's just monitors cell or pack voltages, not current.

Would the presence of a load affect whether or not the battery disconnects?

It should. The controller needs a load, some current flowing to maintain controlled voltage regulation

What kind of load would you recommend connecting to the battery terminals? What kinds of complications would that introduce?

Any load. It does come with a catch. It drains the battery. All your issues revolve around a battery with a HVC circuit disconnecting the charger. How do I know you have HVC and LVD? Because your battery says it does. In your case the term PCM = Protection Circuit Module. . Here is another battery similar to yours, a 4S 6.6 AH with two ports, a charge port and discharge port with PCM. Sound familiar?

What battery would you recommend?

One without a HVC circuit. Your battery module has a HVC as part of the PCM. It is unnecessary automation which causes more problems than it is worth in my opinion. It makes it incompatible with Solar. I assume you want something modular in a box right? Something on the lines of a Power Stream 12 volt 7 AH LiFe battery. They are drop in replacements for AGM batteries in Alarm Systems. It has a crude BMS with balance boards and LVD. However no HVC and will work just like a regular battery. It can be charged as high as 1C and discharged at 2C continuous. It will work with any solar charge controller or battery charger made for lead acid. Ideally you want a CC/CV charger set to 13.8 to
14.6 volts. Just what the Doctor ordered.

[Sunking]

How the hell do you know this is the case, have you disassembled the Bioenno battery in question or have access to the circuit diagram of the battery?

What the hell do you think PCM means. Let me educate you

PCM = Protection Circuit Module

Here is a supplier with a lot of 12 volt lithium batteries. Most of them have PCM.

[Dave C]

If you can't find an MPPT controller to match the GV-5 specs without the annoying problem that the GV-5 has there are ways of getting round the problem.

I'm fairly settled on the idea of ordering another GV-5, but what would you recommend as an alternative?

With your weight requirements, am I right in thinking you are a long distance bushwalker? Have you heard of the Bibbulmun track?
Simon

In the U.S. we're just called "hikers" or "backpackers", but I do like the sound of "bushwalker". I've never been to Australia, but will check into the Bibbulmun track if I go there. Are others besides you in this forum also based in Australia? Are you a bushwalker?

Besides my interest in backpacking, there's also a fair amonunt of disaster preparedness involve I this for me. The world is becoming more and more "interesting" every day.

[karrak]

I'm fairly settled on the idea of ordering another GV-5, but what would you recommend as an alternative?

Sorry I can't help you there. The GV-5 should be OK if you place another load on it while you are charging the LFP battery. When I get some time in the next few days I will send an email to Genasun and Bioenno to see if I can get their thoughts on this problem. Hopefully I will get an answer from someone who has some technical knowledge.

In the U.S. we're just called "hikers" or "backpackers", but I do like the sound of "bushwalker". I've never been to Australia, but will check into the Bibbulmun track if I go there. Are others besides you in this forum also based in Australia? Are you a bushwalker?

I am sure there are others from Australia, I think solar pete hails from here.

Yes, I am a bushwalker, my walking is usually limited to less than two weeks at a time. I have walked the whole Bibbulmun track in stages. It is a great walk! Very well resourced with huts and water every 20km. Other great walks are the Overland Track in Tasmania and the Larapinta Trail in Central Australia.

Besides my interest in backpacking, there's also a fair amonunt of disaster preparedness involve I this for me. The world is becoming more and more "interesting" every day.

Yes, with all the human stupidity evident at the moment I find it hard to be optimistic about the future.

Simon

[solar pete]

I am sure there are others from Australia, I think solar pete hails from here.

I resemble that remark

[Mike90250]

What the hell do you think PCM means..........

I answered Pulse Code Modulation. But I worked with it in radios for years....

[Sunking]

I answered Pulse Code Modulation. But I worked with it in radios for years....

Understood. But when it comes to Lithium Battery Modules it means Protection Circuit Module. If you see a Lithium Modular Battery with Charge and Discharge leads, it has a PCM and will say it in the description. Here is an example of one. If you were to back up a page on the website, you can see quite a few of them. With a Charge and Discharge port, you can bet the battery has a HVC and LVD. No other reason to have separate charge and discharge ports. Not something you want to use with a solar charge controller because no controller is made to operate at Zero volts.

[Dave C]

You all have been very generous with your time in providing a lot of great information. Now let's see if I've learned anything here... I've been looking at this battery made by K2 and this one, sold at batteryspace.com. Of these two, i think the batteryspace battery would be a better fit because of its higher charge voltage cutoff of 15.6V. My reasoning is that at 14.2V, the GV-5 won't charge that battery to capacity, so the battery won't disconnect. Am I close? Can anyone comment on the quality of the batteryspace battery?

[karrak]

i think the batteryspace battery would be a better fit because of its higher charge voltage cutoff of 15.6V. My reasoning is that at 14.2V, the GV-5 won't charge that battery to capacity, so the battery won't disconnect. Am I close? Can anyone comment on the quality of the batteryspace battery?

The SOC(State of Charge, i.e. how full the battery is, where an SOC of 100% is full) versus the voltage that you charge an LFP battery to is a function of the battery chemistry and is pretty much the same regardless of the battery manufacturer. If you charge an LFP battery to 13.8 volts and wait for the charge current going into the battery to go to zero the battery will be 100% charged regardless of the manufacturer. If you charge the battery at a higher voltage it will get to 100% full quicker, but charging at the higher voltage will decrease the lifespan of the battery. You really do not want to leave a 12 volt LFP charging at more than 14.6 volts. 14.2 volts is OK.

As long as the charge controller keeps the charge voltage at 14.2 volts you will be OK, even with your current battery.

Even if your battery disconnects because it is badly out of balance, as long as you have another load on the GV5 the output voltage from the GV5 will stay at 14.2 volts.

I have contacted Genasun's distributor in Australia. The first response didn't answer my question so I have sent another email asking for clarification of their answer.

Simon

[Dave C]

The SOC(State of Charge, i.e. how full the battery is, where an SOC of 100% is full) versus the voltage that you charge an LFP battery to is a function of the battery chemistry and is pretty much the same regardless of the battery manufacturer. If you charge an LFP battery to 13.8 volts and wait for the charge current going into the battery to go to zero the battery will be 100% charged regardless of the manufacturer. If you charge the battery at a higher voltage it will get to 100% full quicker, but charging at the higher voltage will decrease the lifespan of the battery. You really do not want to leave a 12 volt LFP charging at more than 14.6 volts. 14.2 volts is OK.

As long as the charge controller keeps the charge voltage at 14.2 volts you will be OK, even with your current battery.

Even if your battery disconnects because it is badly out of balance, as long as you have another load on the GV5 the output voltage from the GV5 will stay at 14.2 volts.

I have contacted Genasun's distributor in Australia. The first response didn't answer my question so I have sent another email asking for clarification of their answer.

Simon

Simon,

Thank you for that info. I look forward to hearing about what Genasun has to say.

Let me see if I understand this correctly: It seems to me that the only alternative to passing panel OCV to the open battery terminals would be for an MPPT controller to divert all of the power from the panel to a resistive load. (I gathered this from the Wikipedia article on MPPT.) If this is true, wouldn't such a load add considerable weight to a controller? If so, it might explain why other MPPT controllers I've seen are so much heavier than the GV-5. Most are upwards of a pound, where as the GV-5 is only a couple of ounces.

If the above is true, then in my case, the lightness of the GV-5 is a plus that far outweighs the annoyance of seeing an error condition, because I'm assured by Bioenno that their BMS is not affected by the 18-20V that the GV-5 will pass to it.

[karrak]

I look forward to hearing about what Genasun has to say.

Ha Ha Ha, here is the response

Sorry I didn’t respond to this yesterday. Yes the Genasun will hold the battery down at 14.2V. All regulators will have this function to prevent over charge of the battery.

This was my question,

If one connects the GV5 to an LFP battery and starts charging the voltage will rise to 14.2 volts and then the current will drop to virtually zero as the "leakage" current for an LFP is very small. Under these circumstances what will happen to the output of the GV5, will it stay at 14.2 volts or will it drift up towards the solar panel voltage?

Let me see if I understand this correctly: It seems to me that the only alternative to passing panel OCV to the open battery terminals would be for an MPPT controller to divert all of the power from the panel to a resistive load. (I gathered this from the Wikipedia article on MPPT.) If this is true, wouldn't such a load add considerable weight to a controller? If so, it might explain why other MPPT controllers I've seen are so much heavier than the GV-5. Most are upwards of a pound, where as the GV-5 is only a couple of ounces.

Diverting the power is only one alternative, the other is to cut back on the the amount of power taken from the panel, rather like turning off a tap. The problem with the GV5 is that it is a leaky tap and can't be turned completely off. If you want to keep the voltage down at 14.2 volts you only have to use the leakage, not the full current.

If the above is true, then in my case, the lightness of the GV-5 is a plus that far outweighs the annoyance of seeing an error condition, because I'm assured by Bioenno that their BMS is not affected by the 18-20V that the GV-5 will pass to it.

If Bioenno said that 20 volts is not a problem them you are OK. Did they give you a absolute maximum voltage that you mustn't go above?

Simon

[Dave C]

This was my question,

"If one connects the GV5 to an LFP battery and starts charging the voltage will rise to 14.2 volts and then the current will drop to virtually zero as the "leakage" current for an LFP is very small. Under these circumstances what will happen to the output of the GV5, will it stay at 14.2 volts or will it drift up towards the solar panel voltage?"

here is the response

"Yes the Genasun will hold the battery down at 14.2V. All regulators will have this function to prevent over charge of the battery."

The problem with the GV5 is that it is a leaky tap and can't be turned completely off. If you want to keep the voltage down at 14.2 volts you only have to use the leakage, not the full current.

Okay, let me see if I understand what you're saying. The GV-5 should never have allowed the battery to reach 14.6V. It should have backed down current to the battery's leakage current (200mA, I thnk) once it reached 14.2V, thus preventing the voltage from drifting upwards any further. But because it's a "leaky tap" it allowed higher current to pass, thus causing the battery voltage to reach the high charging voltage disconnect point. Is that what you're saying?

If so, then it seem's you're implying that this is a design flaw. I guess it could also have been a defective unit. But could it be something else? Perhaps it's an issue of timing? Maybe the GV-5 backed the current down too slowly? Could mismatches in some other charging parameters have resulted in the GV-5's failure to keep the voltage down?

If Bioenno said that 20 volts is not a problem them you are OK. Did they give you a absolute maximum voltage that you mustn't go above?

I'm waiting for Bioenno's answers to 2 questions: 1) under what conditions will the battery reconnect after it has disconnected due to high charging voltage; and 2) what's the max voltage the BMS can handle.

[Sunking]

Okay, let me see if I understand what you're saying. The GV-5 should never have allowed the battery to reach 14.6V. It should have backed down current to the battery's leakage current (200mA, I thnk) once it reached 14.2V, thus preventing the voltage from drifting upwards any further. But because it's a "leaky tap" it allowed higher current to pass, thus causing the battery voltage to reach the high charging voltage disconnect point. Is that what you're saying?.

No that is not how it works. Understand the difference between an Open Circuit, and a Load. No MPPT Controller can modulate 0%. To do that takes more circuitry and expense. A Controller is designed to have a battery connected at all times (load) and not be disconnected (open circuit).

MPPT controllers have large filter capacitors on the output. That capacitor is to hold a charge in between on/off times of the controller. During the off time, the capacitor discharges into the load or battery. If you open the circuit, there is no place for the capacitor to discharge. The fact that no controller can completely shut off or go to 0% modulation it keeps pumping some energy into the capacitor keeping it fully charged up because it has no place to go.

The issue is your battery has a PCM aka Protection Circuit Module as you noted. The two ports, one for charge, and the other for discharge tells you the battery has a HVC circuit to disconnect from the charger when fully charged up. Your battery is simply not compatible with solar charge controllers.

As for the GV5 it will work, but you have to put up with nuisance High Voltage alarm. The GV5 gets its power from the solar panel where others get their power from the battery. A possible work around is to keep a gizmo connected to the battery load port. So when the battery reaches full charge, the gizmo load shunts enough power to keep the battery connected to the GV5 which will maintain 14.2 volts and FLOAT the battery.

The issue again is your battery and its PCM, not the controller. Best solution is to get a standard 12 volt Lithium battery as I linked too earlier. Something like this one. Stay away from batteries with a PCM and two ports. Click this link to see what is available. Take note some are PCM, stay away from them.

[Dave C]

No that is not how it works. Understand the difference between an Open Circuit, and a Load. No MPPT Controller can modulate 0%. To do that takes more circuitry and expense. A Controller is designed to have a battery connected at all times (load) and not be disconnected (open circuit).

MPPT controllers have large filter capacitors on the output. That capacitor is to hold a charge in between on/off times of the controller. During the off time, the capacitor discharges into the load or battery. If you open the circuit, there is no place for the capacitor to discharge. The fact that no controller can completely shut off or go to 0% modulation it keeps pumping some energy into the capacitor keeping it fully charged up because it has no place to go.

The issue is your battery has a PCM aka Protection Circuit Module as you noted. The two ports, one for charge, and the other for discharge tells you the battery has a HVC circuit to disconnect from the charger when fully charged up. Your battery is simply not compatible with solar charge controllers.

As for the GV5 it will work, but you have to put up with nuisance High Voltage alarm. The GV5 gets its power from the solar panel where others get their power from the battery. A possible work around is to keep a gizmo connected to the battery load port. So when the battery reaches full charge, the gizmo load shunts enough power to keep the battery connected to the GV5 which will maintain 14.2 volts and FLOAT the battery.

The issue again is your battery and its PCM, not the controller. Best solution is to get a standard 12 volt Lithium battery as I linked too earlier. Something like this one. Stay away from batteries with a PCM and two ports. Click this link to see what is available. Take note some are PCM, stay away from them.

Then what did the Genasun rep mean when he said "Yes the Genasun will hold the battery down at 14.2V. All regulators will have this function to prevent over charge of the battery"? To me, that sounds like the controller is designed to prevent the voltage from rising above 14.2V. Are you saying that he was mistaken, or that I'm misinterpreting him? The PCM doesn't come into play until the battery's voltage has risen to the cutoff, right?

[Sunking]

Then what did the Genasun rep mean when he said "Yes the Genasun will hold the battery down at 14.2V. All regulators will have this function to prevent over charge of the battery"? To me, that sounds like the controller is designed to prevent the voltage from rising above 14.2V. Are you saying that he was mistaken, or that I'm misinterpreting him? The PCM doesn't come into play until the battery's voltage has risen to the cutoff, right?

No he is absolutely correct. But he assumes you have a battery connected or a load connected. Now ask what happens if you open the circuit (disconnect the battery)? His answer will be do not do that because the regulator is not designed to regulate an OPEN CIRCUIT. It has to have a battery connected like any controller. You gotta get your head wrapped around that.

You have already proven that to yourself in you initial statement. You connected the panel first, the GV5 went into HV alarm. You connected the battery and it charged up. While charging the GV5 dis what it is suppose to do. When the battery charged up, the HVC disconnected the GV5 and it went into HV alarm as it is designed to do.