MPPT solar controller and LiFePO4 battery for backpacking

[Sunking]

I meant to say, "the battery is not yet at it's specified CV voltage of 14.6V." In other words, since the battery is not yet fully charged when all is at 14.2V, does the controller have to work harder or faster to bring the current down due to the battery still looking for full charging current?

For Current to Flow, there must be a potential difference of VOLTAGE. In other words the Charge Voltage must be Higher then the Battery Voltage. When you set the voltage to whatever voltage, say 14.2 volts, the battery SATURATES and equals 14.2 volts and all Current FLOW STOPS. You battery BMS has absolutely nothing to do with that.

If you had the Controller go up to 14.6 Volts, your BMS Vampire Boards would Turn On and Bleed Current, and keep BLEEDING Current until the Sun Quits Shinning. You rGV5 only goes to 14.2 and when the batteries SATURATE at 14.2 volts, all current STOPS. Listen to ole SK, he knows WTF he is talking about.

[Sunking]

I am very interested to know how the charging process works.

For the 3rd time READ THIS. As I told you from the start, your BATTERY is the problem, not the GV5. Listen to me. Your battery PCM is what is causing you all the problems, not the GV5. I even showed you a battery same same size as you have now that will work just fine.

[Dave C]

No it doe snot work like that. You can set the Controller to 13 volts. CV is just what it sounds like. Once the Charge Current Tapers to les than Current Limit of the Controller, the Controller holds 13 volts or whatever you set it to. As the battery charges up, it voltage rises to what the supply voltage is. When those two voltages are equal, CURRENT STOPS FLOWING. The cells are SATURATED. Does snot matter if the voltage is 13, 14, or no higher than 14.4. Your battery BMS has nothing to do with the charge current.

Your Battery has what is known as Balance Boards, High Voltage Cut-Off, and Low Voltage Disconnect. The Balance Boards aka Vampire Boards. Just like the name implies Vampire Boards Bleed your batteries. When a cell reaches 3.65 volts the Vampire Board Turns ON. When it turns ON puts a small resistance across the cell to BLEED CURRENT. That clamps or tries to Clamp the VOLTAGE on the cell to 3.65 volts. In other words it bypasses CURRENT around the fully charged up cell to pass it around a lower voltage cell.

Here is the deal. At 14.2 volts from the GV5, the BMS never turns on. It takes 4 c ells x 3.65 volts = 14.6 VOLTS for the BMS to turn ON. at 14.2 volts your cells Saturate, and current stops. Again go read this because you do not understand how batteries charge. Simon if confusing you with fiction.

Sunking, everything I post here is based on a cursory understanding of electronics. I've learned more since my original post than probably my entire knowledge of electronics prior to that. According to both manufacturers, here's what happens: At the CV voltage of 14.2V, the controller starts backing down current. When the current goes below the BMS's low current threshold, the BMS disconnects the battery. That's when the controller goes to panel voltage. Not all controllers react like this. Either you or Simon explained that this is probably because this controller is powered by the panel, which makes sense. Regarding balancing, somehow, Bioenno does it at any voltage during both charging and discharging. Hope this helps. Thanks for the article link. I'll check it out.

My question about the controller "working harder" was an uneducated shot in the dark, trying to understand why the current drops off so quickly.

[karrak]

Boz mentioned that when a BMS has a low current threshold, it's typical to see the GV-5 go to panel voltage for "a few seconds before settling back down to the CV voltage". (I guess this must be with a battery that has no HVD.) Would a few seconds be considered transient?

I think that he is saying that if the BMS disconnects the battery from the GV-5 when there is still current flowing into the battery that the GV-5 voltage will go to the panel voltage.

This could be caused by a HVD or by the low current disconnect. A few seconds is transient, but is enough time to cause damage.

I looked for one, but wasn't sure which specs to look at. I assumed clamping voltage would be the one of interest. I couldn't find one that looked like it would limit the voltage to 15V.

This TVS Diode should do the job. By the way, did you ever get an answer to the question from Bioenno as to what the Absolute Maximum Voltage at the connector should be.

Simon

[Dave C]

I think that he is saying that if the BMS disconnects the battery from the GV-5 when there is still current flowing into the battery that the GV-5 voltage will go to the panel voltage.

This could be caused by a HVD or by the low current disconnect. A few seconds is transient, but is enough time to cause damage.


This TVS Diode should do the job. By the way, did you ever get an answer to the question from Bioenno as to what the Absolute Maximum Voltage at the connector should be.

Simon

Thank you! He never gave me a number, but he assured me that it would take a high voltage to damage the BMS.

I never would have known to choose that TVS diode, because the only voltage mentioned in the specs that's at or below 15V is the Voltage - Reverse Standoff (Typ) of 14V. Which spec would indicate that this diode will keep it <= 15V?

[karrak]

Sunking, everything I post here is based on a cursory understanding of electronics. I've learned more since my original post than probably my entire knowledge of electronics prior to that. According to both manufacturers, here's what happens: At the CV voltage of 14.2V, the controller starts backing down current. When the current goes below the BMS's low current threshold, the BMS disconnects the battery. That's when the controller goes to panel voltage. Not all controllers react like this. Either you or Simon explained that this is probably because this controller is powered by the panel, which makes sense. Regarding balancing, somehow, Bioenno does it at any voltage during both charging and discharging. Hope this helps. Thanks for the article link. I'll check it out.

You are absolutely right and it was me that suggested that it was probably because the controller is powered from the panel.

There is some good information in the sticky that Sunking has written but IMO it is delivered in his usual condescending style with some factual errors.

Simon

[karrak]

Thank you! He never gave me a number, but he assured me that it would take a high voltage to damage the BMS.

That number is important. If it is greater than the OCV of the solar panel you don't have worry about the TVS diode

I never would have known to choose that TVS diode, because the only voltage mentioned in the specs that's at or below 15V is the Voltage - Reverse Standoff (Typ) of 14V. Which spec would indicate that this diode will keep it <= 15V?

It is a bit tricky. The minimum Breakdown Voltage of that diode is 15.6V. This is the voltage at which it will let 1mA of current through, The Reverse Standoff of 14V is when it starts to conduct. At 14.2V I would think it would be letting through maybe up to 0.2mA, which is negligible. I can't see how the Absolute Maximum Voltage of the battery BMS can be 15V when the normal operating voltage is 14.9V. Very frustrating that this information is not on their web page.

Simon

[karrak]

An y damn fool can figure out Solar Controllers have no reason to go to ZERO volts, and charger current never goes to ZERO amps.

Where have I ever said that it goes to zero volts? Voltage stays at the CV voltage, in the case of the GV5, 14.2V. The current can and does go to zero.

[Dave C]

That number is important. If it is greater than the OCV of the solar panel you don't have worry about the TVS diode


It is a bit tricky. The minimum Breakdown Voltage of that diode is 15.6V. This is the voltage at which it will let 1mA of current through, The Reverse Standoff of 14V is when it starts to conduct. At 14.2V I would think it would be letting through maybe up to 0.2mA, which is negligible. I can't see how the Absolute Maximum Voltage of the battery BMS can be 15V when the normal operating voltage is 14.9V. Very frustrating that this information is not on their web page.

Simon

A few things: First, Bioenno said that the BMS, can handle more than panel voltage. Second, I think the HVD is 15V, but I don't think it's critical that we know exactly what it is--we know that it's somewhere between 14.6V and panel voltage--and it's not why I need voltage suppression. Third, unfortunately, the voltage at the GV-5's load terminals equals the voltage at the battery terminals. So, when the battery terminals go to panel voltage ,so do the load terminals. This is why I need voltage suppression, and the 15V value comes from my radio's max voltage rating. I think 15.6V is too high.

[Sunking]

A few things: First, Bioenno said that the BMS, can handle more than panel voltage. Second, I think the HVD is 15V, but I don't think it's critical that we know exactly what it is--we know that it's somewhere between 14.6V and panel voltage--and it's not why I need voltage suppression. Third, unfortunately, the voltage at the GV-5's load terminals equals the voltage at the battery terminals. So, when the battery terminals go to panel voltage ,so do the load terminals. This is why I need voltage suppression, and the 15V value comes from my radio's max voltage rating. I think 15.6V is too high.

You do not need any voltage suppression on a battery circuit. You are chasing ghost. A battery is a surge suppressor. You cannot force a battery to go from 14 to 15 volts without a lot of current which you do not have from a solar panel. It would take a lightning strike to do that, and no TVSS is going to save your controller or battery i lightning strikes.

You have 3 options.

1. Do nothing, let the GV5 disconnect and go into alarm. Nothing is hurt, just a nuisance High Voltage alarm on the GV5 that means nothing. If it bothers you, disconnect the panel or battery, the battery is already charged up an dis done.

2. Replace your battery with one that does not have a PCM board in it that disconnects. Run the voltage on the GV4 anywhere from 13.8 to 14.2 volts and let the battery Float The battery internal BMS will never activate which is what you want. LFP cells DO NOT GO OUT OF BALANCE. Taking them to 100% only shortens battery life.

3. Raise your GV5 voltage to 14.6 volts to give your battery the voltage it wants to keep current flowing. Just understand that is over charging your battery and shortening the life by holding 14.6 volts on them All you are doing is burning power up with the Vampire Boards bypassingg current and stressing the LFP cells floating at 3.65 vpc. No good comes from that.

[Dave C]

You do not need any voltage suppression on a battery circuit. A battery is a surge suppressor. You cannot forse a battery to go from 14 to 15 volts without a lot of current which you do not have.

After the BMS disconnects the battery, it's no longer a battery circuit.

[Sunking]

Where have I ever said that it goes to zero volts? Voltage stays at the CV voltage, in the case of the GV5, 14.2V. The current can and does go to zero.

Repeatably and you do not even know what you are talking about. That is what happens, and the only way it can happen is when you modulate at 0% which you claim any Controller does. So which is it? If they go to 0% modulation, voltage goes to ZERO. Which is it?

[Sunking]

After the BMS disconnects the battery, it's no longer a battery circuit.

So what? A TVSS is a DEAD Short Circuit. Your GV5 does not care if it goes to 15 or 18 volts. It just generates an high voltage alarm you could care less about. A TVSS is not going to stop that.

[Sunking]

Third, unfortunately, the voltage at the GV-5's load terminals equals the voltage at the battery terminals. So, when the battery terminals go to panel voltage ,so do the load terminals. This is why I need voltage suppression, and the 15V value comes from my radio's max voltage rating. I think 15.6V is too high.

DO NOT USE the GV5 Load Port with your battery. Not going to work with your battery. Use the Load Port on the battery.

[Dave C]

So what? A TVSS is a DEAD Short Circuit. Your GV5 does not care if it goes to 15 or 18 volts. It just generates an high voltage alarm you could care less about. A TVSS is not going to stop that.

I don't care about a high voltage alarm if my radio isn't connected to the controller's load terminals, but I sure do care if it is connected.

Maybe I haven't made this point clear. I could just connect the panel after first disconnecting the radio, and connect the radio after first disconnecting the panel. But I'm trying to find out if there's a way to make it safe to leave the radio and the panel connected to the controller at all times in order to maximize both radio availability and battery charging time.

If a TVS diode, which two different engineers have recommended, isn't the right solution, would you please recommend a different solution to keep my radio supplied at <= 15V when the load terminals of the controller are at panel voltage?