MPPT solar controller and LiFePO4 battery for backpacking

[Dave C]

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.

But it won't be an open circuit until the battery has reached 14.6V. If the controller keeps it at 14.2V, it will never be an open circuit unless the battery is physically disconnected. Also, Genasun says that the load terminals on the GV-5 are supplied from the battery only.

[Sunking]

But it won't be an open circuit until the battery has reached 14.6V. If the controller keeps it at 14.2V, it will never be an open circuit unless the battery is physically disconnected.

You already confirmed the battery disconnects when charged up. .

[Dave C]

You already confirmed the battery disconnects when charged up. .

Yes. The disconnect occurs at 14.6V.

[Sunking]

Yes. The disconnect occurs at 14.6V.

It is real dang simple to tell what is going on. Put the battery on th echargger and wait for it to disconnect. Measure the voltage on the Charge Port from the GV5, and the Load Port on the Battery. Bet you $100 you see Voc from the GV5 and 14.2 volts on the battery load port.

There is only one possible way for that to happen. The GV5 output is open circuit. Why? Because your battery HVC disconnected. If the GV5 did charge the battery up to 18 volts (impossible), the battery would explode before it reached 18 volts.

Try this. Connect the GV5 to the battery load port. Don't use the battery charge port, leave it disconnected.

[Dave C]

It is real dang simple to tell what is going on. Put the battery on th echargger and wait for it to disconnect. Measure the voltage on the Charge Port from the GV5, and the Load Port on the Battery. Bet you $100 you see Voc from the GV5 and 14.2 volts on the battery load port.

There is only one possible way for that to happen. The GV5 output is open circuit. Why? Because your battery HVC disconnected. If the GV5 did charge the battery up to 18 volts (impossible), the battery would explode before it reached 18 volts.

Try this. Connect the GV5 to the battery load port. Don't use the battery charge port, leave it disconnected.

Yes, of course. Measuring the voltages is what finally just occurred to me. Unfortunately, I don't have a GV-5 on hand. But I could charge up the battery with the 14.6V AC charger and see what the voltage is when it switches to CV.

I think we've both been looking at this too narrowly. I think this could have happened for any of the following reasons:

1) The controller simply failed to prevent the voltage from rising to the battery's HVD.

2) The controller's actual CV voltage was higher than specified, and must have been at or above 14.6V.

3) The battery's actual HVD is lower than specified, and must be at or below 14.2V.

4) Both controller CV and battery HVD were different than specified and overlapping

5) Some other charging parameter mismatch. I would have no idea what this could be. Is this even possible?

Actually, the thought occurs to me that Genasun might have sent me a custom programmed unit by mistake. That's one possibility that might correspond to number 2 above.

As an aside, again, the manufacturer assured me that the two ports on the battery don't perform different functions, and my experience confirms this. They are both soldered to the same points on the battery pack. They just provide two different connector types, one for the AC charger, and one for a power pole connection for both charging and load. The barrel connector would also supply a load.

[karrak]

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).

Absolute rubbish, all MPPT controllers do have a load connected to them internally, it is their own control electronics. It doesn't take any extra circuitry to modulate to 0%, it is just software.

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.

Why can't a controller go to 0% modulation?

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.

Absolute rubbish

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.

It is Dave C's PCM that protected his battery from damage.

I may not have time to answer any further posts for a few days. I will be back

Simon

[karrak]

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?

You are nearly right, the GV-5 should never let the voltage get above 14.2 volts, it should have back down the current to match what the battery wanted. When the charge voltage rises to 14.2V and changes to CV the battery hasn't finished charging. The 200mA that you are seeing is the battery still charging. This current will slowly taper off to zero as the battery reaches full charge. It is because your GV-5 is "leaking current" that the voltage went up to 18 volts. Rather like you putting your finger in a leaky tap and feeling the water pressure go higher and higher.

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?

I would call it a design flaw or it could be a defective unit. I think it stems from the fact that the GC-5 was originally designed for Lead Acid batteries which do have high leakage so the current being supplied by the GV-5 to a lead acid battery would never get down to zero.

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.

Very good questions.

Simon

[Dave C]

You are nearly right, the GV-5 should never let the voltage get above 14.2 volts, it should have back down the current to match what the battery wanted. When the charge voltage rises to 14.2V and changes to CV the battery hasn't finished charging. The 200mA that you are seeing is the battery still charging. This current will slowly taper off to zero as the battery reaches full charge.

When you say "slowly," what kind of time frame would be typical? I observed the GV-5 first indicating full charge for at most a couple of seconds, and then showing high battery voltage.

It is because your GV-5 is "leaking current" that the voltage went up to 18 volts. Rather like you putting your finger in a leaky tap and feeling the water pressure go higher and higher.

I would call it a design flaw or it could be a defective unit. I think it stems from the fact that the GC-5 was originally designed for Lead Acid batteries which do have high leakage so the current being supplied by the GV-5 to a lead acid battery would never get down to zero.

I forget, do you speak from experience with the GV-5?

Do you think any of the 5 scenarios in my last post could be valid?

[Sunking]

Simon you are full of crap. You can look the info up and see it for yourself. A varible Power Supply can go to 0% if designed to go mili-volts, But for a solar controller on a battery has no need to go to zero and will always bbe in a state of On to some degree. You can read it right out of Fairchild and TI application notes. Geez you dunno chit about electronics or batteries. Why the hell do you think controllers cannot operate without a battery. If they could you could bypass the battery and operate directly from the controller if it worked the way you you imagined. .

[Sunking]

I observed the GV-5 first indicating full charge for at most a couple of seconds, and then showing high battery voltage.

That is when the battery disconnected, and the controller voltage pumped up to 18 volts with no place for the charge to go.

It is impossible for your controller to go from 14 volts to 18 volts in a hew seconds if a battery is connected. To do that the current would have to be a few hundred amps, and the battery would explode. Only way for that to happen is the BATTERY DISCONNECTS. You can prove it with a volt meter.

[Dave C]

That is when the battery disconnected, and the controller voltage pumped up to 18 volts with no place for the charge to go.

It is impossible for your controller to go from 14 volts to 18 volts in a hew seconds if a battery is connected. To do that the current would have to be a few hundred amps, and the battery would explode. Only way for that to happen is the BATTERY DISCONNECTS. You can prove it with a volt meter.

Yes, I understand this. There was a disconnect involved. I was responding to Simon's statement that at CV the current goes slowly from 200mA to 0A, and I was asking him if he considers a couple of seconds slow in the realm of electronics.

Edit: Actually, I meant to say that I was asking him if he considers a couple of seconds to be slow in the realm of an LFP battery at CV going from 200mA to 0A. I'll have to wait until he gets back.

[Sunking]

Yes, I understand this. There was a disconnect involved. I was responding to Simon's statement that at CV the current goes slowly from 200mA to 0A, and I was asking him if he considers a couple of seconds slow in the realm of electronics.

An eternity, but it depends on the size of filter caps. Your observations is telling you Simmon does not have a clue.

[karrak]

When you say "slowly," what kind of time frame would be typical? I observed the GV-5 first indicating full charge for at most a couple of seconds, and then showing high battery voltage.

If the battery was charging normally I would expect the reduction in current to occur over minutes or tens of minutes. If the drop in current from 200mA to 0mA occurred in a few seconds I would think it was caused by the battery being internally out of balance and the BMS disconnecting the battery from the outside world because one of the cells voltage went to high.

I forget, do you speak from experience with the GV-5?

No, I have never had anything to do with a GV-5. My comments were are my educated guess as to why the GV-5 would work with Lead Acid batteries if it will not maintain a regulated 14.2V with little or no load current.

Do you think any of the 5 scenarios in my last post could be valid?

From the information I have I think:-
1. Is correct, but given the time frame of the drop in current is not the reason for the battery BMS disconnecting the battery
2. Is not correct, the controllers voltage is 14.2V but it can't maintain regulation with little or no load current
3.Is not correct, the battery's BMS HVD is around 14.6V
4. Is not correct, if the controller is regulating its output, the output will be 14.2V, The battery's HVD is around 14.6V
5. This is unlikely.
Simon

[karrak]

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?

I don't think you are misinterpreting him. I think either he is wrong or the unit you had is faulty or maybe it is a Pb unit for use with Lead Acid batteries which may operate differently to the Li unit.

From the information I have I would think the PCM will come into operation if the voltage on any of the four cells that make up the battery go outside the range 2.5V to 3.65V. This would occur under the following conditions.

• The battery charger supplying more than 14.6V
• The output voltage being under 10.0V under load i.e. flat battery
• The battery being out of balance and one of the individual cells going outside the range 2.5V to 3.65V before the others.

Simon

[karrak]

Simon you are full of crap. You can look the info up and see it for yourself. A varible Power Supply can go to 0% if designed to go mili-volts, But for a solar controller on a battery has no need to go to zero and will always bbe in a state of On to some degree. You can read it right out of Fairchild and TI application notes.

Wrong yet again, if the output voltage from the solar controller is greater than it should be the solar controller should disconnect the solar panels from the output (0% modulation) until the voltage drops down to what it should be. If the solar controller control electronics is being powered from the output they will supply the necessary load to reduce the voltage. No external load or battery is required. When the voltage drops to the correct voltage the controller should start switching through just enough current from the solar panels to supply the control electronics and the battery/load to maintain the correct voltage. It there is no battery/load, the current will be the amount that the control electronics needs.

Geez you dunno chit about electronics or batteries. Why the hell do you think controllers cannot operate without a battery.

You obviously don't take any notice of what other people say do you?

On MPPT controllers, the housekeeping supply (the power supply that provides power to run the oscillator, gate drive, feedback amp, processor etc) is powered from the SECONDARY or load side. This is because the power from the PRIMARY or line side goes away sometimes (i.e. at night) whereas the power on the secondary side (the battery) never goes away while the system is commissioned.

That is why MPPT controllers can't work without a battery.

If they could [operate without a battery] you could bypass the battery and operate directly from the controller if it worked the way you you imagined. .

If you run the control electronics from the solar panel as the GV-5 does, you could do just that. Only problem is that solar power is an unreliable supply. Lets say you have a 200W panel connected via a solar controller to a 100W 12V light globe. In full sunlight the panel supplies 200W and the solar controller only lets 100W through to the light to maintain the voltage at 12 volts. If a big cloud comes between the sun and the solar panel the power delivered from the panel to the solar controller could easily drop to say 50W. The controller now cannot supply the 100W required by the light and you get a brownout. It is not the controller that needs the battery to work, the battery is there to make sure that the load has a reliable power supply.

Simon