Looking for an MPPT solar charge controller without BMS

[Dave C]

For my portable solar setup, I use a PowerFilm R28 rollable 28W panel and a Bioenno Power 4.5 Ah LiFePO4 battery with internal balancing and BMS. It’s a great battery–its internal balancing circuit makes long-term, off-grid use of a multi-cell LiFePO4 battery possible. I currently have a compatible controller, which I bought from Bioenno Power. However, the controller isn’t MPPT, and it requires a button press to show status. Bioenno Power recently added an MPPT controller with LED indicators to their catalog, but its size and weight make it impractical for inclusion in my pack. I tried the Genasun GV5, which was perfect for my needs in every way, except that it passed panel open circuit voltage to the battery terminals when the battery was fully charged. Can anyone recommend a small, lightweight MPPT controller that doesn’t have BMS?

[Dave C]

Just wanted to clarify some of my misconceptions and share additional info.

BMS stands for “battery management system”.  It’s a feature of many Lithium Iron Phosphate (LiFePO4) batteries that provides protection for the battery from things like too much charging voltage and current, too much current drawn by the load (the equipment that draws power from the battery), etc.  BMS is not a feature of solar controllers, so asking for a controller that has no BMS is meaningless.

I’ve consulted with experienced solar users online, and I’ve reached out to the manufacturers of the battery and MPPT controller for more information.  I’m getting closer to understanding whether or not the two components are compatible with one another.  I’ll post what I find in case anyone is considering going the solar power route for backpacking and/or disaster preparedness.

[Richard Nisley]

David,

Your Bioenno Power battery has an integral pulse code modulation (PCM) charge controller; the addition of a maximum power point tracking controller (MPPT) is superfluous.  An MPPT can be more efficient than a PCM but, it requires more electronics and weight which largely negates the advantage with portable panels like you are using. Without the integral PCM controller, your solar panel voltage would vary significantly depending on the sun’s w/m2 and the amperage being drawn (worst case is strong sun and your battery already charged). Each type of battery chemistry needs a different controller profile regardless of the type (On-Off, PCM, or MPPT). The integral  controller uses PCM in combination with a charge profile optimal for LiFePO4 cells (3.6v each) which is near optimal for your portable system.

[Dave C]

Richard,

Thanks for your reply.  I’d be very interested to learn more about your setup.

In my research, neither the battery mfr. nor any of the other experienced solar people I’ve consulted with have suggested that I not use a controller.  The way I understand it from Bioenno Power, their BMS serves to protect the battery against overcurrent, overdischarge, overvoltage, and undervoltage. It can’t change the voltage it receives; rather, it functions to disconnect the battery for protection under certain conditions. And the way I understand it, it’s the role of a controller to manage panel voltage in order to supply a safe charging voltage to the battery, and in the case of an MPPT controller, to track a panel’s changing voltage to maximize charging efficiency.

Which Bioenno battery do you have? Ah–I wonder if you have one of their power packs, which DOES have an integrated controller! If that’s the case then I’d be even more interested to learn about your experience with it. I think it has a 10 Ah battery, right?

Regarding MPPT controllers weighing more, I agree, most of the ones that I found were too heavy–upwards of a pound–whereas the Genasun GV-5 weighs only a couple of ounces! Plus it’s marine grade.

So, I’m actually saving considerable weight and space by using a Bioenno 4.5 Ah battery and the GV-5 controller, as opposed to the Bioenno power pack. (I’m also giving up 5.5 Ah, but for me, the weight advantage outweighs the additional hours between charges.  Also, I don’t really need that many hours of battery life.) I can easily fit the battery, controller and wires inside my rolled up PowerFilm panel. I put that all in a bag I made from silver-plated nylon fabric for EMP protection (yes, I guess you could call me a prepper), and that goes inside a dry bag. It all fits in one of the external compartments of my Osprey Xenith 105 bag (which is not exactly for backpacking light…).

After much discussion, I’ve learned that the Bioenno Power 4.5 Ah LiFePO4 battery and the Genasun GV-5 are compatible. Those, combined with a PowerFilm R28 panel, make for a good, portable power setup, able to be used for even long-term off-grid use. Those who choose this battery/controller combo should be aware ahead of time that when the battery reaches full charge, it disconnects from the controller, and this causes the GV-5 to show an error condition. This error can be ignored, though, as it results in no damage to any of the components. I’m still trying to piece together exactly what happens to the load when the battery disconnects from charging, so before anyone lays out cash as a result of reading this, you might want to wait until I’ve finished researching, or until you’ve consulted with someone more experienced and knowledgeable than me.  Also note that a battery that doesn’t have an internal balancing circuit needs to be balanced periodically with a non-portable AC balancing charger.  Bioenno Power is the only company I found who offers internal balancing in a battery that’s small and light enough to take on the trail.

[Richard Nisley]

David,

I made a mistake when I read the specs for the battery you are using. The specs said, in part, Protection: PCM. I knew there are generally three technology options for 12V class portable solar panels (On-Off, PCM, or MPPT). From that, I erroneously concluded it had an integral pulse code modulation (PCM) controller. I used your input and another source to now ascertain that the battery specs meant protection circuit module (PCM). I will make another post relative to this topic later when I have time.

[Richard Nisley]

David,

A LiFePO4 battery that is commonly run without a charge controller is the K2 Energy K2B12V10EB 12V 10Ah.

“Another perk of the LiFePO4 battery, at least the K2B12V10EB, is that you can charge it with folding solar panels and not worry about using a solar charge controller.  For example, the Powerfilm F15-1800 30 Watt panel is almost a perfect match for a 10 AH LiFePO4 battery.  It provides about 1.8 amps at 15.4 volts when operating under peak conditions.  The battery will essentially clamp the panel voltage, and it will slowly rise until the battery is fully charged at 14.6 volts.  Battery voltage will continue to rise slowly after that point.  If left on the charger for days it is possible that the battery overcharge circuit might kick in, allowing the panel voltage to rise to its maximum open circuit voltage of 21 volts.  But according to the application engineer that should not be an issue for the battery.  Just be aware that you can’t use a LiFePO4 battery as a “load” to regulate the solar panel voltage.  In other words,  you don’t want to charge your battery with your radio hooked up at the same time.”

Source:

 

[Dave C]

Thanks a lot for that information.  Very interesting.  I’ve actually been looking at the K2B12V7EB, which is 6.4Ah.  At 2 lbs, the 7EB is pushing it for me in terms of weight, so at 3 lbs, the 10EB is definitely too heavy.  I also see in the 7EB specs that its charging voltage cutoff is 14.6V, which is the same as my Bioenno Power battery.  So, the K2 batteries might not offer an advantage over the Bioenno battery in terms of compatibility with the Genasun controller.  I’m also investigating this battery on batteryspace.com..

[Richard Nisley]

David,

Which components of your proposed power system do you already have?

What devices do you need 12 volts to charge?

I am trying to understand your thinking regarding why you chose your sophisticated, but heavy and expensive, 3 component system versus a more backpacking-common 2 component alternative? For example, an Anker 21W SunPower solar array with integral controller and near equivalent capacity battery at 14.6V * 4.5Ah = 65.7Wh versus 3.6V * 20000mAH = 72Wh at $98 and 27.2 oz.

[Dave C]

I already have the panel, battery, and a PWM controller.  I want to replace the controller with the GV-5 becuase it’s MPPT , it has better status indicators and it’s waterproof.

I need 12V because I’m powering a ham radio (Elecraft KX3).  If not for that, then I’m sure there are a number of good 5V solutions that would be smaller and lighter and cheaper.  The one you recommend looks great.

[Larry De La Briandais]

“5V * 20000mAH = 100Wh at $98 and 27.2 oz.?”

Are you sure that the 20,000mAH is at 5V and not at the batteries voltage of 3.6 (or so)?  Most (all?) of the USB battery packs are rated at the batteries nominal voltage.  Not that it wouldn’t still be a better choice if 12V wasn’t required.

 

 

[Richard Nisley]

Larry,

Thanks… you are correct… I fixed my post.

[Nick Gatel]

Generally, MPPT controllers are for large systems where the array voltage output is much higher than the battery bank voltage, and the battery bank can accept wide variations in charging amps (e.g., flooded deep cycle batteries).

I have had solar systems on 3 campers, which are larger and different than what you are trying to accomplish, but one thing I have found is that most charge controllers and onboard converters do not charge batteries per the battery manufacturers’ specifications. The point being, you need to take a deep dive into what the battery manufacturer says and then try to match a controller. The other problem is that many battery manufacturers do not provide enough information about their batteries so the owner can make educated choices in charging systems, the specs are often “smoke and mirrors.” Here is an article I wrote about how I went about figuring our how to match up a system, to the point of adding a temperature probe to ensure the controller would adjust to ambient temperature. Although not specific to you application, the thought process might help.

Here is another article I wrote a few years ago discussing solar for backpacking, which I am not interested in doing. If I were to take a lot of electric devices backpacking, I would, as Richard suggested, probably bring a battery pack as it is more weight efficient for the average backpacker.

[Richard Nisley]

David,

Your required support for a 12V ham radio makes your solar system component decisions very clear. Also your Genasun LiFePO4 MPPT controller looks like the optimal solution for not only your requirements but, also many other portable 12V solar applications. Thank you for sharing your project with us.

[Richard Nisley]

Nick,

That was a valuable post which I totally agree with. David seems to have found a charge controller manufacturer who provides a good match for his battery.

His Bioenno Power BLF-12045W 12V, 4.5Ah Lithium Iron Phosphate (LiFePO4) Battery) has a nominal voltage of 12.8 volts (at 3.2 volts per cell it has 4 cells).

The GV-5-Li-14.2V: 12.8/13.2V (4s) Lithium Iron Phosphate controller at 2.8 oz. matches his battery.

[Nick Gatel]

Thanks, Richard.

At the end of the day, what matters to me is how many amp hours I am going to use versus how much I can put back in, and how much reserve do I have if there is no sun for a period of days. Typically we use about 10% of our usable capacity each day, meaning we can go for 10 days without a charge. The other thing that is important to me is how many discharge cycles the battery can take — for us it is over 3,000 cycles if we never discharge under 80% versus 1,250 cycles at 50%. My batteries are different than what David is using, but I think the same approach is good; that is understanding all the variables, especially since he is going to pay $79 for a 5ah battery versus around $100 for a 100ah 12v lead acid deep cycle battery, which probably weighs 55lbs.

That’s a lot of consumption for a controller. Our PWM controller can handle a 45 amp current and self consumption is less than 20ma with the optional meter consuming 7.5ma.

 

[Dave C]

Great articles, Nick.  Thanks for the info.  I must admit that my motivation for having any electronics in my pack stems from my wanting to be able to communicate with family and friends in the event of a disaster that knocks out conventional communications.  For sake of weight, I’d much prefer to have no electronics.  Before I leave this thread, I’ll weigh my power and communications gear and post the total here.

Richard, so far, everything is sounding fairly promising with my current choice of gear, but I’m not yet ready to recommend it to anyone.  Once my questions are all answered, and I’m sure this is a reliable system for long-term, off-grid, personal power, I’ll recommend it wherever I can.  I haven’t seen any other portable power system for ham radio that’s as light as mine.  There are probably others out there using this or a similar setup, but I haven’t seen anyone post anything about this combination of components.  In fact, this thread is the only result in Google in which my panel, controller and battery are mentioned on the same page.

I can’t take credit for this, though.  Without some expert advice early on, I doubt that I would have found these components on my own.  I got started in solar by reading an article that a ham operator had published online about his test results with different solar panels.  He was kind enough to respond to my introduction email, and he ended up providing shortcuts to volumes of information on solar panels, charge controllers, batteries, radios and antennas.  Thanks Charles!!!  In that spirit, I’d be happy to pass on the info that he shared with me with anyone who’s interested

[Nick Gatel]

David,

For systems where the panel output is close to the battery voltage there isn’t a lot advantage to MPPT, but I am a huge advocate of accurate battery monitors, and it sounds like that controller has some of that built in.

I know a little bit about Li batteries as I researched them for my current camper, mostly due to the significantly lighter weight, but for my use a 300aH Li battery is $3,500. I did buy a controller that can be programmed to handle Li batteries, just in case the prices go way down :)

The only electronics I use for backpacking are a camera and a headlamp, but I can’t be critical of those who want more, seeing our camper has everything our house does to include a 35″ LED TV and a microwave, both of which can be operated off the battery bank.

 

 

[Dave C]

Cool.  Do you have room for one more next time you go into the wilderness with your microwave and TV?  ;^)  Seriously, having a solid structure around you with a self-sufficient power supply and some home-like comforts would be very welcome in an extended emergency situation.  I know this website isn’t geared towards disaster preparedness, but along those lines, it seems that you guys are all set in terms of shelter.

When you say “close to the battery voltage,” what do you consider close?  My panel’s operating voltage is 15.4V, whereas the max battery charge voltage is 14.6V.  My understanding is that MPPT will aid in charging during times of less direct sunlight, like in the morning.  Also, I just learned that charging at the higher voltage would shorten the life of the battery.  I think it’s better to charge at under the battery’s max charge voltage than over it.

Edit:  Strike those last two sentences.  You’re recommending that PWM is fine in my situation, not that I should go without a controller.  It’s late…

[Nick Gatel]

When you say “close to the battery voltage,” what do you consider close?  My panel’s operating voltage is 15.4V, whereas the max battery charge voltage is 14.6V.  My understanding is that MPPT will aid in charging during times of less direct sunlight, like in the morning.  Also, I just learned that charging at the higher voltage would shorten the life of the battery.  I think it’s better to charge at under the battery’s max charge voltage than over it.

With any battery it is crucial to charge at the manufacturer’s specifications. This is especially true with LiFePO4 batteries, which need very precise charge points and require a two-stage charging strategy; whereas a lead acid battery needs a three-stage strategy, plus an occasionally equalization charging phase, similar to what your BMS does to balance the cells.

Solar panels are rated much higher than what is needed to charge, because the rating is at full sunlight at a standard temperature (usually not real world conditions). So lets look at my two 140W Kyocera panels. Each is rated at max power of 17.7 volts and max amps at full power of 7.91 amps. So…

V x A = W

17.7 volts x 7.91 amps = 140 watts

However, the battery state of charge will determine how many volts and amps can be delivered (pushed into the battery), plus temperature and sun position will determine the max voltage and max amps. Lets say my battery bank is at 12 volts when I start charging, I am going to lose my potential wattage.

12 volts x 7.91 amps = 95 watts (actually 94.92 watts)

Where did the 45 missing watts go? With a PWM controller the panels are directly connected to battery and will cause the panels to operate at battery voltage. So the panel and the battery are not well matched because there are many variables. For us the system works because even in winter our battery bank is fully charged by noon as long as it is sunny.

A PWM controller simply steps down the voltage (DC to DC) to the battery’s state of charge voltage. A MPPT controller converts DC to AC to DC voltage, which better matches the panel to the battery and controls the panel to produce its rated wattage by increasing the amps delivered to the battery.

Because of the sophistication of a MPPT vs. PWM controller, the MPPT’s are much more expensive. They don’t provide much advantage in summer. Plus, nothing is 100% efficient, so results are not as dynamic in winter as the theory would indicate. My explanation MPPT is very simplistic and not very scientific but explains the high level view, plus my PWM controller has a temperature sensor, so it will kick up the voltage charge points when it gets cold. You do not want temperature correction like this with LIFEP04 batteries. My panels are rated 2.3 volts higher than your’s and we both have 12 volt batteries, so you can see how MPPT would better suit my set up.

—————–

Re: extended emergency situations…

We are good with our power situation, plus we have two 30# propane tanks, so the limiting factor is water. Most travel trailers have 30 to 50 gallons of fresh water storage. We have 100 gallons of fresh water storage, plus two 50 gallon tanks for holding grey and black water waste. I also have a 45 gallon bladder that can be put into our SUV. On extended trips of a couple weeks, water is always our limiting factor when camping in places that don’t have water available. We can conserve our electrical power requirements and make our battery bank last a couple weeks if needed.

Our two previous campers were tent trailers, which suited me just fine. My wife wanted our current trailer and that was okay by me, since most years we camp around 100 nights together. The trailers had nothing to do with emergency preparedness or SHTF situations, but it is ready if we get another big earthquake. I prefer backpacking, but she won’t sleep on the ground so backpacking is a solo endeavor for me.

 

 

[Dave C]

PLEASE READ BEFORE PURCHASING ANY EQUIPMENT I HAVE MENTIONED IN MY PREVIOUS POSTS.

While the components I mentioned do work for me, I need to share some additional information about the Genasun GV-5 controller and its compatibility with the Bioenno Power 4.5 Ah 12V battery.

First, while these two components are compatible in most ways, and while they are my chosen portable solar power components, there are significant issues to consider.   First, with no battery connected, the Genasun GV-5 passes panel open circuit voltage to the battery and load terminals. I’ll explain the significance below.  Second, the Bioenno battery’s BMS (battery management system) has a “low current threshold”.  The combination of these two factors results in the following:  During charging, as the battery voltage nears the controller’s CV voltage (the pre-programmed, maximum voltage to which the controller will allow the battery’s voltage to rise), and the controller backs down current towards zero (in order to keep the battery at the CV voltage), the BMS’s low current threshold causes it to disconnect the battery at 90mA.  When the battery disconnects, the controller’s battery and load terminals go to the panel’s open circuit voltage (Voc), which is around 20V.  This then creates an over voltage condition that causes the battery to remain disconnected until the panel is disconnected from the controller.

The good news is that the BMS board in the battery pack can handle more voltage than the panel can produce.  The bad news is that when the GV-5’s load terminals go to panel Voc, any equipment rated for less than 20+V that’s connected to those terminals could be damaged.  I’m told by a couple of electrical engineers that with a load (in my case a radio) connected to the controller, the Voc problem won’t happen.  However, because the radio mfr., Elecraft, tells me that my radio would be damaged, even when powered off, with an input voltage of > 15V, I’m not going to risk it.

Instead, I’m going to work around this problem by using a DPDT switch to connect either the panel or the load to the controller, but never both at the same time.  A switch isn’t necessary–you could manually reconnect and disconnect components, but a switch is a cleaner, more reliable, more fail-proof, long-term solution.

The other major correction that I need to make is that the Genasun GV-5 IS NOT WATERPROOF!!!!  To work around this issue, I will house the controller, battery and other electronics in waterproof enclosures (probably jars made of PET).

In conclusion, I plan to continue to use my Bioenno Power battery, and I have purchased a Genasun GV-5 controller.  The benefits of this combination are super light weight (the lightest combination of 12V components with enough power for my needs that I’ve found after much research), MPPT charging and internal cell balancing.  However, due to some quirks of both components, I would recommend never connecting both panel and load to the controller simultaneously.  I would also recommend housing the controller and other electrical components in waterproof enclosures.

[Larry De La Briandais]

Not sure why you want to use a DPDT switch, all you need to a simple SPDT.

 

https://www.google.com/search?q=spdt+switch+wiring&espv=2&biw=1358&bih=842&tbm=isch&imgil=nOvAO9CPLn6jIM%253A%253B7KG-BYQhwxEUlM%253Bhttp%25253A%25252F%25252Fwww.learningaboutelectronics.com%25252FArticles%25252FToggle-switch-wiring.php&source=iu&pf=m&fir=nOvAO9CPLn6jIM%253A%252C7KG-BYQhwxEUlM%252C_&usg=__1egLFEy7cLWZR8v79vA3zFvke0s%3D&ved=0ahUKEwjb1Y-k4L7MAhUFOiYKHcQ2AXgQyjcIOQ&ei=BwspV5u2AYX0mAHE7YTABw#imgrc=nOvAO9CPLn6jIM%3A

 

[Dave C]

Thanks, Larry.  The reason why I chose a DPDT over SPDT is that there’s no common connection between the panel and load circuits external to the controller–they’re two independent circuits.  Let me know if you see a different way to do this.  I’m also using a second DPDT to reverse polarity on the power meter, so that I can measure either charging or discharging power with a single Watt’s Up meter.  The Watt’s Up isn’t damaged by reverse current flow (some meters are), and I won’t be floating the battery (instead, I will be manually setting the direction of current flow into or out of the battery with the first switch), so I can get away with just one meter.  I think bi-directional meters are more expensive.

[Larry De La Briandais]

If there is nothing common, then the DPDT is a simple way to wire it.  There are more complicated ways of handling the meter.  You could use diodes to control what polarity the meter sees, and LEDs to indicate if it is charge or discharge current, but a switch is the simplest.

I’m not sure what you are using for a meter, but I found some really small digital volt meters in banggood.  They might have amp meters also.  Here is a link to the volt meters:

 

http://www.banggood.com/0_28-Inch-2_5V-30V-Mini-Digital-Voltmeter-p-974258.html?utm_source=review_email_1.1&utm_medium=rem_1.1_eur_product&utm_term=rem_1.1_eur_product&utm_content=rem_1.1_eur_product&utm_campaign=rem_1.1_eur_product

 

[Dave C]

Thanks for the diode suggestion.  Working that out would be a good learning experience for me.  The meter that I’m using is the Watt’s Up meter, which is used by a lot of RC hobbyists.  I saw a number of cheap meters on Amazon and elsewhere, but most ammeters required an external shunt, and many would have been damaged by reverse current.  I’m a novice at wiring circuits, and because I saw the Watt’s Up meter used in a few small 12V solar applications, I saw it as a time saver.

[Larry De La Briandais]

That looks like a very good electric monitoring system. It’s much more than just a meter.  Only draw back is that it’s a bit big and heavy.  And yes, most amp meters will require a shunt.  That meter just has it built in.

 

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