MPPT solar controller and LiFePO4 battery for backpacking

[karrak]

Here is what is inside your battery.

You don't know that. Have you taken a Bioenno battery apart?, the circuit you have shown is from a different manufacturer.

[karrak]

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.

You don't know if that is how it works. Bioenno has stated that the balancing works on both charge and discharge so maybe they are using the difference in voltage between the cells as a trigger to do the balancing. If they are using a fixed voltage to trigger cell balancing, you don't know what that is. It might be higher than 3.65V

[karrak]

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?

Wrong, yet again. If there is no load on the output of the power circuit in the MPPT controller the capacitors in the output stage of that circuit will hold the voltage at whatever voltage they have been charged up to. With a load on the output the voltage will slowly go down.

When a MPPT controller switches from an absorb voltage of say 14.2 volts to a float voltage of 13.8 volts it should disconnect the solar panels from the battery i.e.modulate at 0%. It then waits for the voltage to drop down to 13.8 volts and then start switching through power from the solar panel to keep the voltage at 13.8V.

[karrak]

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.

Your radio will be just fine. If it has been built to plug into a 12 volt power source like a battery with an attached charger the radio designers should have take into account issues like voltage transients. The voltage figure in the radio operator's manual will be the maximum operating voltage that the radio should operate at. This is less than the absolute maximum voltage at which damage will occur. Also and here I actually agree with Sunking, having the radio turned on and providing a load for the GV5 when the Bioenno's BMS disconnects the battery will mean the GV5 should be able to maintain the voltage regulation.

Simon

[Sunking]

Here is what is inside your battery. Read the SPECS. If the battery I listed is too heavy/bigg, is because it is a higher capacity battery than yours. Get the right size.

[Dave C]

You need a LFP made as a Drop-In replacement like I already showed you WITHOUT a PCM. BMS is fine, but not PCM. A Drop In LFP Replacement does not disconnect from the charger. A Solar Controller cannot have the battery disconnected.

The battery that you showed me was, unfortunately, too big and heavy. This one is the right size and weight, but it has PCB.

Unfortunately, with all due respect, your abrasive delivery and your unwillingness to adjust your course when new or different information becomes available make me question your advice.

Edit: However, you have provided valuable information. Your explanation of the term "float" is much appreciated.

[Sunking]

This won't work, because, again, the battery's two connectors do not perform separate functions. They're both soldered to the same points.

Same Point electrically but two relays. A HVC relay and a LVD relay in the PCM circuit. They operate independently of each other. That is why the battery has a Charge Port and Discharge Port. Otherwise there would be no ports, just Battery Term Post like any other battery.



Look at the specs

Includes built-in PCM (protection circuit module) which provides balancing of internal cells, and protection from overcurrent, undervoltage (overdischarge), and overvoltage.

I understand what you want to do. You want to FLOAT the battery and leave it connected to the Controller so as to use solar power when available. That is exactly what the GV5 or really any solar controller is made to do. Problem is YOUR BATTERY IS NOT MADE TO DO THAT. You need a LFP made as a Drop-In replacement like I already showed you WITHOUT a PCM. BMS is fine, but not PCM. A Drop In LFP Replacement does not disconnect from the charger. A Solar Controller cannot have the battery disconnected.

[Sunking]

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.

It cannot happen if the radio is connected. The load will keep the controller loaded and regulated.

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?

I have done that many times. You are not getting it. Your battery is not compatible with the Controller. I gave you the three options. I am Ham Radio Operator and have done radio and telecom professionally for 35 years.

1. Get a battery without a PCM board in it.
2. Raise the GV5 voltage to 14.6 volts so the battery current does not go to Zero and keep the radio connected.

FWIW the zener diode is not a TVSS, it presents a load on the controller. If it is a Silicon Avelanche Diode it presents a SHORT CIRCUIT which takes the voltage to 0 volts when it triggers on.

[Dave C]

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

This won't work, because, again, the battery's two connectors do not perform separate functions. They're both soldered to the same points. I've tried to make this clear several times. Email Bioenno if you have any questions about this. With the battery connected to the controller via one of the battery's two connectors, the voltage at the other battery connector is equal to the voltage at the load terminals.

[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?

[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.

[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]

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?

[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]

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.