MPPT solar controller and LiFePO4 battery for backpacking

[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.

[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.

[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]

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

[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]

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]

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.

[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.

[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 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?

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.

[Dave C]

Simon you have really proven beyond a shadow of a doubt you really do not know much about controllers or batteries. You really need to quit embarassing yourself.

So far almost everything he has said has lined up exactly with what I've learned from the manufacturers and what I've observed, and he has adjusted his approach as necessary as new information has come out. You have also added some valuable information. The only embarrassing content in this thread has been the pejoratives.

[Sunking]

Simon you have really proven beyond a shadow of a doubt you really do not know much about controllers or batteries. You really need to quit embarassing yourself. 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. It cost manufactures real money to make a Buck/Boost, and PWM voltage regulators variable all the way down to ZERO volts. In fact you would have an extremely hard time to even find a high quality Bench Power Supply capable of doing that if not impossible to find one. WHY??? There is no reason too you fool. Who the Hell needs a ZERO VOLT POWER SUPPLY except you? If I need one to go to ZERO VOLTS, I would just turn it off. Built to many of them from the age of 12 years old when I started ham radio. I have forgotten more than you will ever know. Never built one that goes to Zero. Nor does anyone else.

[Dave C]

You are doing very well at learning about all this, before you know it you will be an electronic engineer.

Did Boz confirm the GV-5 OCV problem? His comment regarding TVS makes me think that the overvoltage will only be a transitory event.

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?

A better device than a zener is a https://en.wikipedia.org/wiki/Transient-voltage-suppression_diode&quot;]Transient voltage suppression diode[/URL].

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.

When you say default you do mean the 14.2 volt Li version not the Pb version?

Simon

I meant the Li version and "default" as opposed to custom programmed.

[karrak]

No offense, but my paranoid red-flags are going off - I see buzzwords being thrown out again which tend to excite the engineering crowd to tear each other apart - mostly from speculating on gear we don't own, and interpreting it all from the distance of a forum.

While I'm not making any accusations, I do see the buzzwords and indications bordering on FUD about Genasun. The questions are interesting, but seem obsessive.

Just calling it like I see (read) it.

The original post detailed the problem that Dave C was having with the GV5 when used with his Bioenno battery. It is a serious problem if the GV5 or for that matter any MPPT controller looses regulation and lets its output rise to the solar panel voltage. This could easily damage any LFP battery connected to it.

As with most engineering projects "The devil is in the detail". If the detail in this case involves what you call buzzwords and FUD, so be it. These details need to be sifted through to try and work out what exactly the problem is and if it can be solved. Unfortunately this can be a messy process on forums like this but in this case is I hope leading to a simple solution that means that Dave C should be able to use the Genasun GV5 with the Bioenno battery. It has also highlighted some issues to be aware of when charging LFP batteries from solar panels.

Simon

[PNjunction]

Oh man. Let's take a break and look at the application for a second from the very first post:

4.5ah LFP battery. (four and a half amp hour)
28 watt panel.

WORST case, it will take about 2.5 hours to fully charge under best conditions with your current gear. That's do-able unless you are using the system in Norway in the winter.

I can understand wanting to shave weight to the bare minimum, but really - how much trouble is it to carry your existing stuff? Would it all be much easier / cheaper to just replace the R28 Powerfilm with the next size up if you wanted more efficiency / faster than 2.5 hours for nearly a FULL discharge?

No offense, but my paranoid red-flags are going off - I see buzzwords being thrown out again which tend to excite the engineering crowd to tear each other apart - mostly from speculating on gear we don't own, and interpreting it all from the distance of a forum.

While I'm not making any accusations, I do see the buzzwords and indications bordering on FUD about Genasun. The questions are interesting, but seem obsessive.

Just calling it like I see (read) it.