MPPT solar controller and LiFePO4 battery for backpacking

[karrak]

The king of battery IC's is Texas Instruments, If you look back I gave you a link to the most popular TI IC used in MPPT controllers, and there are dozens of designs out there on the internet with the chips. However here it is againa 24/12 volt, 20 Amp MPPT controller using a TI MSP430F5132 controller IC.

You just make all this stuff up, exactly the same as you made up what you thought was inside a Bioenno battery. The link you gave to the "TI LM5019MR 100V, 100mA Constant On-Time Synchronous Buck Regulator" in post #132 has nothing to do with MPPT controllers, it is a low current buck mode power supply which only supplies 100mA, hardly suitable for an MPPT controller. It has nothing to do with the TIDA-00120 that you mention in the above paragraph. The TIDA-00120 is not a full MPPT controller, it is what is known in the industry as a "reference design" provided by TI to try and sell their products. Sunking you have no idea how many MPPT controllers out in the market use the TI chips.

Take note of what the description is telling you in the TEST REPORT. What Simon does not understand the output never goes to 0% because the circuitry uses 10 ma from the output. Anyone who has electronic design experience knows you cannot power anything with ZERO VOLTS, AMPS & WATTS. Thus the output never goes to ZERO. That tells you Simon Mathews is a pretender.

In the TIDA-00120 documentation one of the entries in a table shows the output to the battery at zero current which is what you were saying was impossible in previous posts. If the output voltage rises above the programmed output you don't know if the MSP430F5132 controller IC in the TIDA-00120 turns the switching FETs between the solar panel and the battery completely off. In this case the controller electronics would draw the 10mA from the battery and the capacitors in the output circuit of the TIDA-00120. I have never said that the voltage goes to zero. I have said that the current goes to zero. FWIW the MSP430F5132 is not a specialised chip but a general purpose microcontroller not unlike the Frescale 68HC12 that I use in my MPPT controller. The control of how much of the time (%modulation) the switching FETs that connect the solar panels to the battery are on if totally controlled by software running on the microcontroller.

I use to work in Telecom for 30 years for a major telco and have installed thousands of DC battery plants. After being laid off in 2003 I started my own engineering company doing the same work for more money, an dhave built over 200 Off-Grid Battery systems at remote cell sites, and some large grid tied systems for Walmart and DOD.

Sound like you are a Systems Integration Engineer. From what you have written in the past it looks to me like you might know how to connect solar panels to a solar controller to Lead Acid batteries but don't understand how the electronics work.

Back to Current Sources. Makes no difference is the Current Source is from a Voltage Source or Solar Panel, if you open the load, the voltage goes to the source voltage. A Solar Panel is a Current Source and the controller has a huge capacitor at its output. Your own eyes have seen what happens when the battery is disconnected. Your eyes are not lying to you.

If the controller reacts quickly enough and disconnects the output from the source the output voltage will not go to the source voltage. The huge capacitor will actually try to stop the output voltage changing, that is what capacitors do. I would say that to save space and weight that the GV5 doesn't have a very large output capacitor.

[karrak]

Sunking, if I understand you correctly, you're saying that at CV, current comes to a stop, and voltage simply remains at that voltage ("set point" is s new term which I think equates to CV voltage). My question is what keeps it there? I think you must mean that either: 1) the set point is equal to the "full" point of the battery, so that the system comes to some sort of equilibrium with no current flow; 2) the controller actively sets current to 0A; or 3) self discharge makes it so that current flow never stops. If the CV voltage of a controller is 14.2V, and the saturation point of a 4-cell LFP is 14.6V, then if there was such a thing as "equilibrium" in an electrical circuit, then the system couldn't be at equilibrium at 14.2V, right? If the controller actively stops the flow, then by Simon's illustration, the "pressure" on the controller would be panel Voc, right?

The current doesn't come to a complete stop, it reduces to the leakage current of the battery plus any current drawn by the BMS circuitry. For LFP batteries without any BMS this is virtually zero.

The solar controller will actively adjust the current output to keep the voltage at the set point.

The equilibrium you are talking about here is the equilibrium between the SOC of the battery and the voltage. At a voltage of 14.2V when the charge current has tapered to zero the battery might be at an SOC of 99.5% whereas at a voltage of 14.6V the SOC will be 100%.

When the current being supplied to the battery is virtually zero the voltage from the solar panel at the input of the solar controller will be close to the Voc of the panel. It will not be Voc because of the current being used to run the controller electronics.

Simon

[Dave C]

The current doesn't come to a complete stop, it reduces to the leakage current of the battery plus any current drawn by the BMS circuitry. For LFP batteries without any BMS this is virtually zero.

The solar controller will actively adjust the current output to keep the voltage at the set point.

The equilibrium you are talking about here is the equilibrium between the SOC of the battery and the voltage. At a voltage of 14.2V when the charge current has tapered to zero the battery might be at an SOC of 99.5% whereas at a voltage of 14.6V the SOC will be 100%.

When the current being supplied to the battery is virtually zero the voltage from the solar panel at the input of the solar controller will be close to the Voc of the panel. It will not be Voc because of the current being used to run the controller electronics.

Simon

Okay, thanks. This answers my final questions. Thanks again for all of your help.

[Sunking]

Simmon Mathews is a salesman of cheap Chi-Com consumer electronic junk, and sales to suckers in Australia.

[Sunking]

You just make all this stuff up, exactly the same as you made up what you thought was inside a Bioenno battery. The link you gave to the "TI LM5019MR 100V, 100mA Constant On-Time Synchronous Buck Regulator" in post #132 has nothing to do with MPPT controllers, it is a low current buck mode power supply which only supplies 100mA, hardly suitable for an MPPT controller.

You are a pretender. Any damn fool who knows anything about micro controllers and linear circuits knows they are low current and you use a MOSFET or Transistior to control the high current. You have been exposed as a FRAUD.

[jflorey2]

The battery just needs to stay connected PERIOD. . . . It requires the battery to turn it into a VOLTAGE SOURCE so the Controller can regulate the voltage.

Back to Current Sources. Makes no difference is the Current Source is from a Voltage Source or Solar Panel, if you open the load, the voltage goes to the source voltage. A Solar Panel is a Current Source and the controller has a huge capacitor at its output. Your own eyes have seen what happens when the battery is disconnected. Your eyes are not lying to you.

Sorry SK you are just plain wrong here.

Any MPPT controller out there is nothing more than a smart buck converter. And buck converters can go to zero output, and they do not need a battery (or a load) to regulate voltage. Any basic book on SMPS design will tell you this.

Just to provide an illustration, I connected an off the shelf 60 cell panel to a Midnite Kid and connected the output to an 8 amp hour gel cell. Turned it on and the battery quickly went into absorb at 13.96 volts, drawing about 2 amps. Input was 34.8 volts. Noise was 112 millivolts peak to peak. Then I disconnected the battery. Output voltage went up a few millivolts to 13.99 volts and the noise went up to 216mW (after losing that great battery "filter.") Input voltage rose to 36 volts as the panel unloaded. Output voltage stayed rock steady at 13.99 for an hour as the meter was reporting 0.0 amps out.

So no, you don't need a battery to "turn it into a voltage source." And no, if you open the load, the voltage is not required to go to the source voltage. When a current limited voltage feedback SMPS is in current limit, it is a current source. When it is regulating voltage, it is a voltage source. When it is open circuit (i.e. no load, no current) then it is by definition not in current limit so it is a voltage source.

[Sparkletron]

At the risk of raising ire over reopening this old contentious thread, I also had difficulty getting Genasun and Bioenno to work well together. In my case, a series of cloudy days would run my system down to the point where the battery's LVD would kick in. Once this happened, the Genasun no longer saw the battery and would therefore not charge it even after the sun returned. So basically my system couldn't automatically recover, and I had to manually jump start it to get the battery charging again.

My solution was to use a separate LVD to keep Bionenno's LVD from ever kicking in. As I write this, there are few LVD's designed for LiFePO4. The disconnect/reconnect settings are just too low. Fortunately, WMR's PWRguard PLUS allows you to set these values to whatever you want. So if you never want your Bionenno discharged more than 50% (perhaps around 12.85V), you can do that.

The PWRguard is small and light and compatible with the OP's backpacking scenario. It might help. While it duplicates what both the Bioenno and Genasun do, it does so in a way where you have complete control. For example, the GV5-Li-14.2V's LVD disconnects at 11.0V and reconnects at 12.0V. Those values are far too low to be useful! A Bionenno is essentially spent at 12.2V.

Now I understand that the OP's issue is not LVD, but the battery's BMS disconnecting itself (or not accepting any current whatsoever) from the Genasun when it's full, causing the Genasun's load output to rise to Voc. My point is simply that just because these products come with certain features, doesn't mean you can't reimplement them on your own terms. I don't agree with some who say you shouldn't buy a battery with a BMS-of-last-resort. Sh*t happens, and I can't tell you how many times the Bioenno's BMS saved itself.

I agree with those who say that if the Genasun always requires a battery sink, then just give it one. It could be a voltmeter, ampmeter, multimeter, LED, whatever. Check this out. Or you can use a DC-DC buck converter on the Genasun load terminals to ensure that the voltage doesn't exceed 14.8. Something like this. All of these solutions introduce inefficiencies and are not ideal, but it's what we have until more flexible solar controllers are available.

[Dave C]

At the risk of raising ire over reopening this old contentious thread, I also had difficulty getting Genasun and Bioenno to work well together. In my case, a series of cloudy days would run my system down to the point where the battery's LVD would kick in. Once this happened, the Genasun no longer saw the battery and would therefore not charge it even after the sun returned. So basically my system couldn't automatically recover, and I had to manually jump start it to get the battery charging again.

My solution was to use a separate LVD to keep Bionenno's LVD from ever kicking in. As I write this, there are few LVD's designed for LiFePO4. The disconnect/reconnect settings are just too low. Fortunately, WMR's PWRguard PLUS allows you to set these values to whatever you want. So if you never want your Bionenno discharged more than 50% (perhaps around 12.85V), you can do that.

The PWRguard is small and light and compatible with the OP's backpacking scenario. It might help. While it duplicates what both the Bioenno and Genasun do, it does so in a way where you have complete control. For example, the GV5-Li-14.2V's LVD disconnects at 11.0V and reconnects at 12.0V. Those values are far too low to be useful! A Bionenno is essentially spent at 12.2V.

Now I understand that the OP's issue is not LVD, but the battery's BMS disconnecting itself (or not accepting any current whatsoever) from the Genasun when it's full, causing the Genasun's load output to rise to Voc. My point is simply that just because these products come with certain features, doesn't mean you can't reimplement them on your own terms. I don't agree with some who say you shouldn't buy a battery with a BMS-of-last-resort. Sh*t happens, and I can't tell you how many times the Bioenno's BMS saved itself.

I agree with those who say that if the Genasun always requires a battery sink, then just give it one. It could be a voltmeter, ampmeter, multimeter, LED, whatever. Check this out. Or you can use a DC-DC buck converter on the Genasun load terminals to ensure that the voltage doesn't exceed 14.8. Something like this. All of these solutions introduce inefficiencies and are not ideal, but it's what we have until more flexible solar controllers are available.

Sparkletron, I'm the OP, and I'm also revisiting this old thread. I use the GV-5, which has a default LVD voltage of 11V and reconnect voltage of 12V.

Regarding a battery sink, I found that a DC-DC buck-boost converter prevented the Bioenno low C disconnect, but I could not find one that was suitable for my application. One was quiet enough, but did not produce enough current. Another produced enough current buy was too noisy. It became clear to me that finding a regulator was going to take a long time. I considered trying to develop one based on a TI reference design, but decided instead to build my own LFP battery. That battery works great with the Genasun controller. And as I learned recently, so do Bioenno batteries.

Bioenno changed their BMS some time after 2015, the year I bought my first LFP battery from them. They no longer disconnect near end of charge when paired with a controller sold by another manufacturer. So, although I learned a lot about solar charging in this thread, it contains a lot of outdated information. If you are considering pairing a Bioenno Power battery with a Genasun charge controller, know that they are now compatible and no battery sink or any other workaround is required.

This thread has gotten a fair number of views over the years, so I wanted to set the record straight.