MPPT solar controller and LiFePO4 battery for backpacking

karrak · 04-17-2016, 08:46 PM

Originally posted by Sunking

I am typing this very slowly Simon so you can understand and follow along. Yes I clicked the wrong converter.

No you didn't just make a simple mistake and click on the wrong converter, you then went on to describe what the circuit does when you turn the FET off. This means that you did not know by looking at that circuit that it was not a Buck Converter. A first year electronics student would know that. You failed the test.

The Transistor in your circuit is constantly switched on/off to some degree. Pulse width is modulated That means there is always voltage on the output. Without a load (battery) the voltage will go to source voltage because there is NOTHING for the Inductor and Capacitor to discharge the energy into. The CAPACITOR charges to the Input Supply Voltage and holds it. A first year electronics student would know that. You failed the test.

Pulse width modulation goes from 0% to 100%, 0% is turned off, 100% is turned on all the time. A first year electronics student would know that. You failed the test.

Sunking · 04-17-2016, 01:57 PM

Originally posted by karrak

Contrary to what Sunking has been saying you do not need to worry about compatibility between the Bionno battery and an MPPT controller as the BMS can disconnect the battery from the controller if any problem that might damage the battery arises.

It just means the battery is incompatible with any Solar Controller. No controllers out there are made to work without a battery connected. Most controllers would be damaged with the battery disconnected with panels connected in sun light. Just a fact and you can squak all you want about it.

Genasun is the only controller made for a Lithium battery and has a LVD built-in, but is not intended to have the battery disconnected, just the load. Will it hurt a Gnasun Controller having the battery disconnected? Answer is NO. But his battery will never reconnect when the controller output goes to 18 volts with an Open Circuit.

karrak · 04-17-2016, 01:25 PM

Originally posted by Dave C

Bioenno Power confirmed that during CV, when the battery's voltage reaches 14.6V, the BMS disconnects the battery. Not sure why it took so long to get this information. Simon, yes, this should all be clearly documented. To be fair, even if everything was documented, the info would probably have gone over my head--I don't think it would have helped me make a pre-sales decision. So, at very least, when I called with problems, both customer service departments should have had the applicable info at their fingertips and shared it with me.

I think you made the right decision with choosing the Bioenno battery. From what I can see the Bioenno battery just needs a power supply that will provide 14.6 volts (14.2 volts is adequate).

For comparison, can anyone recommend an MPPT controller and self-balancing LFP battery pack that are highly compatible with one another, lightweight, as weather resistant as possible and as hassle free as possible for a non-engineer? Around 5 Ah would be great. The bar is set high in terms of weight and weather resistance--the Bioenno battery weighs about 1 lb., and the GV-5 is marine grade and weighs just 2.8 oz. The system needs to be reliable in a long-term, off-grid application.

Contrary to what Sunking has been saying you do not need to worry about compatibility between the Bionno battery and an MPPT controller as the BMS can disconnect the battery from the controller if any problem that might damage the battery arises. The compatibility issues only occur if the battery does not have the internal circuitry to disconnect itself from the outside world. In this case the BMS has to be able to communicate with the controller to tell it to stop charging or connect to external circuitry that can disconnect the battery if a problem arises.
If you can't find an MPPT controller to match the GV-5 specs without the annoying problem that the GV-5 has there are ways of getting round the problem.

With your weight requirements, am I right in thinking you are a long distance bushwalker? Have you heard of the Bibbulmun track?

Simon

Sunking · 04-17-2016, 01:23 PM

Originally posted by Dave C

Bioenno Power confirmed that during CV, when the battery's voltage reaches 14.6V, the BMS disconnects the battery.

Hate to tell you this; told you so. That is the only way the Genasun controller can go high voltage. Two ways to work around this, well three ways. My way is get a different battery without HVC and LVD. Your Genasun controller has a built in Load Port with LVD of 5 amps, USE IT as it was intended.

Anyway keeping the battery you already have:

1. Lower the Genasun output voltage from 14.2 down to 13.8 to 14.0 volts. That will prevent the battery going to 100% and activation the HVC circuit.
2. Keep a load device connected to the battery load port.

Also do not be fooled by terms. Even the cheapest of cheap chargers are CC/CV. It is not something the BMS does. There is no special circuitry that switches the charger from Constant Current to Constant Voltage. It is just the physical interaction between the battery open circuit voltage, battery internal resistance, the chargers current limit, and the chargers set point voltage. When the battery charges up, it voltage rises to meet the charger set point. When the battery voltage rises to the charger set point voltage current tapers off and voltage stays constant via Ohm' Law of voltage and resistance. Read this it might help.

Dave C · 04-17-2016, 08:24 AM

Bioenno Power confirmed that during CV, when the battery's voltage reaches 14.6V, the BMS disconnects the battery. Not sure why it took so long to get this information. Simon, yes, this should all be clearly documented. To be fair, even if everything was documented, the info would probably have gone over my head--I don't think it would have helped me make a pre-sales decision. So, at very least, when I called with problems, both customer service departments should have had the applicable info at their fingertips and shared it with me.

For comparison, can anyone recommend an MPPT controller and self-balancing LFP battery pack that are highly compatible with one another, lightweight, as weather resistant as possible and as hassle free as possible for a non-engineer? Around 5 Ah would be great. The bar is set high in terms of weight and weather resistance--the Bioenno battery weighs about 1 lb., and the GV-5 is marine grade and weighs just 2.8 oz. The system needs to be reliable in a long-term, off-grid application.

Dave C · 04-17-2016, 01:06 AM

Simon, PNjunction, Sunking and others,

Bioenno confirmed that when the battery voltage gets to 14.6V during CV charging, the BMS disconnects the battery. I sure wish they had told me this in September...

karrak · 04-16-2016, 07:42 PM

Originally posted by Dave C

Guys, any thoughts on my last post?

Sorry, I have have been away.

Here is my take on what is probably happening when you charge your battery using the Genasun taking into account the subsequent commentary.

The Genasun will supply as much power to the battery as the solar panel will supply if the voltage is less than 14.2 volts. When the battery voltage gets to 14.2 volts the Genasun starts to limit the current to keep the voltage at 14.2 volts as it should. Because this is an LFP battery with virtually no leakage the current will drop to virtually zero if the voltage is kept at 14.2 volts. The Genasun is incapable of keeping the voltage regulated at 14.2 volts with no current so the output voltage from the Genasun starts to rise. At some point, probably just above 14.6 volts, we don't know exactly what voltage because of the poor battery documentation the battery BMS disconnects the battery from the battery terminals. The BMS reconnects the battery to the battery terminals when it detects that the input voltage at the terminals has gone down below its safety cutoff voltage.

I am using the word probably because I don't have all the facts needed to make a definite statement.

The documentation that I can find from both Genasun and Bioenno is woefully inadequate.

If the Genasun charger does indeed let the output voltage drift up to the solar panel output voltage if there is no load connected to it there should be a big warning in capital letters in the user manual about if. If i was being polite I would call this a unique design feature. If you tried to connect the Genasun up to an LFP battery without a BMS it could quite easily damage it. This is a good case for buying a battery with a BMS installed.

The Bioenno documentation should tell you what voltage the BMS disconnects the battery from the battery terminals, and should tell you the maximum safe voltage that you can supply to the battery terminals.

While we are on the subject of documentation, Powerfilm should at least tell you what the Vmp (voltage for maximum power) is, and what the power loss temperature coefficient is. Would be nice to have some graphs of power output versus temperature and panel voltage as well.

IMO it is not your fault that has lead to the problems you are experiencing, but problems with the equipment, documentation and customer support. This is familiar story, the manufacturers and others try make it seem like it is your fault when it isn't.

SImon

PNjunction · 04-16-2016, 05:16 PM

Originally posted by Dave C

Originally, they told me that the battery backs down to a few mV when fully charged, so I assumed that it didn't disconnect in the course of normal operation. But in the course of conversing yesterday by email, it came out that after shifting to CV, when the battery voltage hits 14.6V, the charge current goes to 0 A.

The charge current going to zero amps is due to the *battery* doing the current regulating at CV, not the bioenno! This is what is called the CV "absorb" stage. LFP or lead-acid, the basics are the same. What you got over the phone may have been over-simplified so that the guy can get back to work. Both Genasun and Bienno power could easily go bankrupt unless they hired a full time staff to explain the nitty gritty of it all for all the diy callers.

For example, what you described above is what a Battery-Tender designed for lead acid agm absorb (14.6-14.7v) will do! The point here is that it is NOT the battery-tender doing the current regulating once it reaches the absorb 14.6v stage.

The main selling point to me of Bioenno was that their batteries do internal balancing. To me, this made using LFP in my application possible. I had read that LFP batteries degrade quickly if they're not balanced, and the required input current for the balancing chargers I found was too high in a single-panel solar situation. So internal balancing did it for me.

That's fine. It also has under-voltage discharge and over-current protection. Great. Those are things we do ourselves outside our batteries, with no proprietary circuitry. Your choice.

Be on the lookout however, for cheap bms systems that are essentially baby-sitting poor quality cells to begin with! Instead of using quality cells, crap cells are used and a cheap ass bms is there to make sales of these poor quality cells. I'm not saying Bienno is doing that, but there is a lot of disreputable junk out there, so be careful. A deal too good to be true is the big red flag.

Also understand that there are many configurations of batteries - mine for 12v are merely a 4S configuration - 4 cells in series. Pretty easy to keep balanced once the initial balance is done. If a battery consists of a bunch of 18650 LFP batteries, the more they put in to increase the capacity - things can start to go nutty especially if those cells are not reputable without some safeguarding circuitry.

I wouldn't be inclined to take on a diy LFP project with no solar experience and limited electronics experience.

Ok, it's a start and you know your own limitations. Fantastic!

Except I have one more question: When I asked Kevin what is the max voltage his BMS can handle without frying, he answered 15V. Well, the BMS was hit with much more than that every time I connected it to the GV-5. So, I wonder if the BMS might be damaged. It doesn't seem so. The battery still works fine with the Bioenno controller. I wonder if a steady diet of seeing 18 - 20V will damage it over time.

Ah, once the Genasun is connected to an actual battery, it will properly regulate the voltage with it's own circuitry now that it sees a load. When the Bienno says the battery is full, and disconnects, this is now an abnormal setup for a controller to have no battery attached, and we're back to just seeing the ocv of the panel.

If I think about it, without a battery, (either physically missing, or the Bienno cutting it off) the Genasun may be interpreting the open circuit voltage of the panel as the battery voltage itself - and of course at 18v, IS over voltage from a fictional missing battery standpoint!

I think this is the big trip up in understanding. You are questioning a logic-trap kind of situation, so that is very good actually.

Remember that from this distance, there IS the chance that your Genasun unit, may have been defective and returned to sales. Did you get yours directly from an authorized Genasun dealer, or was it some 3rd party online sales deal?

Cabinlakewister · 04-16-2016, 04:19 PM

Interesting topic. My e bike lifepo4 just went 62.6 miles at 5,000k miles 2.5 year old battery. Maybe I shouldn't have just bought a gell cell for my cabin. Anyway I just joined and am trying to post. Where did they hide the post button? How do u post a new topic?

Sunking · 04-16-2016, 02:27 PM

Dave don't feel bad, even lots of engineers do not fully understand Lithium Batteries. They are completly different than any other battery chemistry. One of the huge problems is the technology is still in development and there is no Industry standards. The biggest miss so far is what is a BMS? Ask 100 people and you get 100 different answers. There is NO definition. Every manufactures has a proprietary solution.

A BMS can be as simple as a volt meter reading pack voltage. It can be a cell voltage monitor that read individual cell voltagges. They can read cell temps, , they can discharge cells, they can disconnect chargers, they can disconnect the load, they can balance cells either by bleeding them or taking power from one cell and transfer it to another cell. They can be passive or active. They can be centralized or distributive. They can be analog or digital. They can be anything you want or not want.

There is only one market sector where standards are being pushed, and that market is the Electric Vehicles using CAN BUS, an ASE proprietary communication protocol like Internet Protocol is a standard communications protocol. As of now using lithium batteries in solar systems is not feasible, thus not a lot of things out there. There are a few companies that have integrated lithium products, but each one is proprietary and will not work with other manufactures.

Your own battery is a great example. Most integrated lithium batteries look and behave like any standard Pb battery. They only have one connection point or a positive and negative terminal. Inside they do have a form of a BMS, but very limited using Cell Balance Boards, and some may have a LVD. The only requirement is the charge source has to be a CC/CV at a specific voltage. For 12 volt batteries using LiFeP04 is 14.2 to 14.4 volts. Your battery has more inside the box and keeping is somewhat secretive. It is using two ports, one for charge, and one for load. The charge side has some form of a High Voltage Cut-Off circuit. Perhaps HVC might be the wrong term, but the effect is it disconnects the charger source when the batter is charged up. Solar Charge controllers do not like that as you have discovered. It is incompatible with most charge controllers. Your battery appears to be made to use a DC Power Supply that must supply 14.6 volts and limited to 2 amps maximum output. A Solar Charge Controller is not a DC Power Supply.

What PNJunction and I have been alluding too is if you know how Lithium batteries operate, what the Do’s and Don’t are, a person does not need much in the way of Automated BMS. You can use a Protein based BMS aka common sense and strategy. Joe consumer cannot do that. Lithium batteries are dangerous if abused and capable of self-destruction and worse. However for Joe Consumer and equipment manufactures POV an Automated BMS must be used to make Lithium batteries safe. However to do that you have to give up cash and some battery service life. Unfortunately there is no standards to say how it is to be done and compatible with any manufacture like there is with all other battery types.

Sunking · 04-16-2016, 01:53 PM

Originally posted by jflorey2

So if you apply power to the primary side of an SMPS converter, several things might happen:
1) Smoke (unlikely)
2) Nothing. No power to the gate drive, so no switching, so no output.
3) Ugly startup. If there is enough leakage through the system (due to for example a floating gate) then the output voltage will start creeping up. Once the output voltage is enough to start up the housekeeping supply, the device will go into regulation.

All true Jeff except a Solar MPPT Controller is not SMPS. They are Buck Mode Current Sources. Open th eload on any current source and you know what damn well happens. If you don't, then you are not who you say you are. .Every MPPT controller has large electrolytic capacitors on the output. Those caps must have a place to discharge. True if you disconnect the battery, the gate driver pulse width goes to minimum, (not 0% not thus shutting off the switching transistor completely), The output caps cannot discharge without a load or battery connected. For Petes Sake try it rather than preaching theory on SMPS when a controller is not a SMPS. I have tried it on many on many models, and have schematics of a few MPPT controllers. .

This is all pointless as we already know for fact the Genasun goes to Voc when the battery is removed.

jflorey2 · 04-16-2016, 01:11 PM

Originally posted by Sunking

Semi correct Jeff. If there is No Load (battery), there is no place for the capacitor to discharge.

Nor is there any place for it to charge. Again - you do not need a load to guarantee a buck converter will not go overvoltage.

Read any MPPT controller instructions. Thou shall connect battery first before connecting the panel. Thou shall disconnect panel before connecting battery. There is a damn good reason the instruct you to do that.

There is indeed a damn good reason to do that. 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. On an AC/DC SMPS, the housekeeping supply is powered from the PRIMARY side. That's because on an AC/DC, there is no power on the secondary side.

So if you apply power to the primary side of an SMPS converter, several things might happen:
1) Smoke (unlikely)
2) Nothing. No power to the gate drive, so no switching, so no output.
3) Ugly startup. If there is enough leakage through the system (due to for example a floating gate) then the output voltage will start creeping up. Once the output voltage is enough to start up the housekeeping supply, the device will go into regulation.

Dave C · 04-16-2016, 08:52 AM