Using 4 cell 18650 li-ion with 4 100W solar panel

[Sunking]

I'll let the cat out of the bag here. We have a hull design in progress and a pid controller on the rudder servo with input from tilt compensated compass, iridium satellite link, GPS, and voltage monitoring. This power system will hopefully be floating around the ocean next summer..

Now I'm at a complete loss.. I just want a light, cheap efficient method of storing the energy from 4 x 100W panels. The guy who made the sea charger has a 5 cell lifepo4 connected to solar panels directly to the 5 cell pack with a balancing circuit, maybe that's not a great method but the thing has been out at sea and running for months and months. Ofcourse fire is a concern but it'll only kill the ship, I have considered lithium polymer as you can get 14.8V 16Ah for 50$ now.

Look forget LiPo an extremely unstable battery with a very short cycle life of 200 to 300 cycles.

You can certainly use lithium battery for your project. It does not require any BMS, just a good strategy like NASA uses. NASA uses Lithium Batteries in all satelites and NO BMS. They cannot afford the the weight or space. Use 4S LFP cells, perform an initial Bottom Balance, and set the charger voltage to 13.6 to 14.0 volts and you are good to go.

If you insist on a BMS, then buy a 12 volt LFP battery with built-in BMS. All they require is a 14.4 volt source which means set your charge controller to 14.4 volts and call it done. Personally I would set the voltage to 14 volts so the BMS is never used which gives you twice the cycle life.

[SunEagle]

Look forget LiPo an extremely unstable battery with a very short cycle life of 200 to 300 cycles.

You can certainly use lithium battery for your project. It does not require any BMS, just a good strategy like NASA uses. NASA uses Lithium Batteries in all satelites and NO BMS. They cannot afford the the weight or space. Use 4S LFP cells, perform an initial Bottom Balance, and set the charger voltage to 13.6 to 14.0 volts and you are good to go.

If you insist on a BMS, then buy a 12 volt LFP battery with built-in BMS. All they require is a 14.4 volt source which means set your charge controller to 14.4 volts and call it done. Personally I would set the voltage to 14 volts so the BMS is never used which gives you twice the cycle life.

But if his project is a surface RC then LiPo would be my first choice depending on the distance and course being traveled. There are a lot of 4S flying RC that can go multiple km and get back using the RTH technology as well as a programmed flight pattern. Why not one using a nautical GPS program. It would be interesting to hear about the outcome of his experiment.

[Sunking]

But if his project is a surface RC then LiPo would be my first choice depending on the distance and course being traveled. There are a lot of 4S flying RC that can go multiple km and get back using the RTH technology as well as a programmed flight pattern. Why not one using a nautical GPS program. It would be interesting to hear about the outcome of his experiment.

OK I must be missing something. As you know I am a RC pilot with around 100 LiPo packs lying around in a fridge. LiPo's are used for 1 primary reason, they can deliver extremely high Continious Discharge Rates up to 50C or 1 minute. That is one reason they are so popular with E-Bikers and EV Drag Racers. LiPo' have 3 significant disadvantages: Very high $/Wh, Very Unstable requiring Fire Proof Charge Bags to contain them, and short cycle life. If his project demands such high performance and has the budget OK.

If not then LiFeP04 would be a batter choice, perform better for his application, and a whole lot less expensive. As an RC Pilot I am sure you are aware the larger E-Planes use a separate battery from the LiPo Traction Battery. They use a small 2S LFP like 1500 mah for the RX and Servos. They do that because LFP is more reliable and gives them the ability to do a Dead Stick Landing if they do not get the plane down before exhausting the Traction Battery.

Or he could use the LiPo now that he knows why you would chose one over the other. Bottom line is chose the best technology for the specific application. No such thing as Best Battery Type for any application. Sounds to me like that is the trap the OP fell into with Lithium.

Anyway to OP we as consumers in reality only have access to 3 basic types of Lithium Batteries and a rare forth kind. The really good ones we cannot buy. Your choices are LFP, LCO, and LiPo. Ironically LiPo is not a Polymer Battery, it is a LCO hybrid on steroids using an organic Gel Electrolyte which makes them unstable and HOT. Each has a different application and operating voltage. LFP = 3.2 volts, LCO = 3.6 volts, and LiPo = 3.7 volts. LFP is the safest and longest lasting of the 3 that works up to at least 1C charge discharge rates.

There is a 4th and you can buy them in 18650 form factor called Lithium Titinate (LTO). They are used in 1 EV. On paper the longest lasting battery of 10,000 cycles but never has been documented or tested. There claim to fame is like LiPo with extremely high charge and discharge rates coupled with the safety of LFP. They have two huge disadvantages Extremely expensive ($4/wh), and a Energy Density that of a Lead Acid with a LTO voltage of 2.4 volts meaning WH to WH weigh about the same 50Wh/Kg. LTO = 2.4 volts

Lastly go read this quick White Paper on Lithium Batteries. There is more than one type. Hopefully you will pick up that the higher the cell voltage, the greater the energy density. So from the 4 I spoke of highest to lowest energy density is LiPo, LCO, LFP, LTO a range from 250Wh/Kg to 50Wh/Kg. Lastly the most important thing if you intend to use Solar as the charge source means you need to use a Lithium cell compatible with Lead Acid battery voltages. That leaves you one choice, LFP

[PNjunction]

Ok, now that we know what the application really is :

Headway LiFeP04 cells. Provides the cycle life and energy density which is appropriate for a boat already having 400w worth of panels and all that other gear.

Unlike large prismatics that top out at about 3C, the Headways are 10C (burst) capable. As individual cells, you'll need to make your own pack conveniently with the holders. Fortunately large enough to handle without doing something stupid like trying to diy solder tabs onto 18650's. Choose your voltage and capacity and make your own xSxP pack.

For additional assistance see the message forum on the Wheelchairdriver "Everything Wheelchair > Step by Step Lithium Conversion" thread. There is a reason they choose these high-rate LFP's, one of which is that they are inches below their butt, but they have the performance necessary for motor propulsion that typical large prismatics come up short with. And since they sit on top of these things, the packs are built RIGHT, with safety in mind.

Since those guys rely on hobby chargers (like the very nice PL8) to do all the balancing during charge, and not vampire boards, you'll probably want something like this instead:

CleanPowerAuto LLC's own bms, which incorporates HVD, LVD, relay contact points, etc - all the stuff your tech will want when putting together the Headway pack for the target voltage and capacity.

But before you buy, be sure to calculate your power draw over time, and if your 400w panels will be able to recharge between the typical 80% and 10% DOD during your use timeframe and solar insolation hours of the geographical area, which should be done with the WINTER data.

[SunEagle]

Ok, now that we know what the application really is :

Headway LiFeP04 cells. Provides the cycle life and energy density which is appropriate for a boat already having 400w worth of panels and all that other gear.

Unlike large prismatics that top out at about 3C, the Headways are 10C (burst) capable. As individual cells, you'll need to make your own pack conveniently with the holders. Fortunately large enough to handle without doing something stupid like trying to diy solder tabs onto 18650's. Choose your voltage and capacity and make your own xSxP pack.

For additional assistance see the message forum on the Wheelchairdriver "Everything Wheelchair > Step by Step Lithium Conversion" thread. There is a reason they choose these high-rate LFP's, one of which is that they are inches below their butt, but they have the performance necessary for motor propulsion that typical large prismatics come up short with. And since they sit on top of these things, the packs are built RIGHT, with safety in mind.

Since those guys rely on hobby chargers (like the very nice PL8) to do all the balancing during charge, and not vampire boards, you'll probably want something like this instead:

CleanPowerAuto LLC's own bms, which incorporates HVD, LVD, relay contact points, etc - all the stuff your tech will want when putting together the Headway pack for the target voltage and capacity.

But before you buy, be sure to calculate your power draw over time, and if your 400w panels will be able to recharge between the typical 80% and 10% DOD during your use timeframe and solar insolation hours of the geographical area, which should be done with the WINTER data.

If you are charging the batteries at home then I would use a hobby BMS charging system. If the plan is to use solar cells on the craft to keep the batteries charged to extend the "voyage" then it may be harder to find a BMS system that works with solar but it may not matter if all you want to do is just perform some type of trickle charge to get a few more hours of use out of the LiPo or LFP.

[inetdog]

If you are charging the batteries at home then I would use a hobby BMS charging system. If the plan is to use solar cells on the craft to keep the batteries charged to extend the "voyage" then it may be harder to find a BMS system that works with solar but it may not matter if all you want to do is just perform some type of trickle charge to get a few more hours of use out of the LiPo or LFP.

I may be wrong, but I get the impression that the OP is looking at long distance unattended travel or station keeping, in which case the system would be sized for multi-day unattended operation, with PV supplying the entire power budget of the craft.
That sort of use actually, IMHO, puts a lot more emphasis on increasing the performance and reliability of the array than increasing the energy density of the battery.
Energy density would be a major factor if the voyage would start with charged batteries and lose net energy with every hour or day of operation.

[mike3367]

i am testing a 18650 16 cell battery i made. so far for such a little battery it doing pretty well. i have it set up as a 16 volt battery, and run it thru a dc to dc converter that does constant voltage. the balance charger im using, just hooks up to my battery bank. it takes 11 to 18 volts in to make it work

[inetdog]

i am testing a 18650 16 cell battery i made. so far for such a little battery it doing pretty well. i have it set up as a 16 volt battery, and run it thru a dc to dc converter that does constant voltage. the balance charger im using, just hooks up to my battery bank. it takes 11 to 18 volts in to make it work

Interesting mechanical arrangement. 4S4P?
What are those black and red blocks?

[mike3367]

am i aloud to give you the url to the place where i bought them?

[inetdog]

am i aloud to give you the url to the place where i bought them?

I think so, but recognize that your post may not be visible immediately if the software decides that it needs approval by a moderator first.

If you were the person selling them at that URL the answer might be different.

[mike3367]

www.batteryblocs.com this is where i got them he also has a you tube page showing how to use them

[karrak]

I'll let the cat out of the bag here. We have a hull design in progress and a pid controller on the rudder servo with input from tilt compensated compass, iridium satellite link, GPS, and voltage monitoring. This power system will hopefully be floating around the ocean next summer..

Now I'm at a complete loss.. I just want a light, cheap efficient method of storing the energy from 4 x 100W panels. The guy who made the sea charger has a 5 cell lifepo4 connected to solar panels directly to the 5 cell pack with a balancing circuit, maybe that's not a great method but the thing has been out at sea and running for months and months. Ofcourse fire is a concern but it'll only kill the ship, I have considered lithium polymer as you can get 14.8V 16Ah for 50$ now.

I have had more of a look at the HQST/etracer MPPT controller and you can set up any voltage between 9-17 for 12 volt operation and 18-34 volt for 24 volt operation using the "User" battery type option. This gives you allot of flexibility of what battery you can use.

I agree that getting a decent commercial programmable BMS preferably with remote access is a pain! That is why I designed and built my own. There are a few other open source BMS systems around, not sure if you want to go down that route.

What exactly do you mean you have voltage monitoring, could you use this to monitor the individual cell voltages?

On first glance using the 5 cell LiFePO4 option on a 12 V panel doesn't seem like a particularly good option as the maximum panel voltage Voc could be around 22 volts which equates to 4.4 volts across each cell. Now if you could get a panel with a Voc of around 18 volts that arrangement could work quite well. How about making your own solar panels?

Simon

Off grid 24V system, 6x190W Solar Panels, 32x90ah Winston LiFeYPO4 batteries installed April 2013
BMS - Homemade Battery logger https://github.com/simat/BatteryMonitor
Latronics 4kW Inverter, homemade MPPT controller

[Mike90250]

..... How about making your own solar panels?......

Yeah, that's going to work like a champ for a ocean going test craft. The odds of being able to mfg and seal a DIY panel in ocean spray for a couple months voyage is ZERO

[PNjunction]

i am testing a 18650 16 cell battery i made. so far for such a little battery it doing pretty well. i have it set up as a 16 volt battery, and run it thru a dc to dc converter that does constant voltage. the balance charger im using, just hooks up to my battery bank. it takes 11 to 18 volts in to make it work

STOP RIGHT NOW!

Look at your cells. There is NO SUCH THING as a 9800mah 18650. What you have are dangerous fakes. At the very least, purposely mislabeled to fool the unknowing. Do not trust those cells in the first place.

Do not rely on any passive-resistive balancing features inside that dinky little voltage monitor! They are TOO SMALL in the first place, and if any cell gets out of balance, will subject the other healthy cells to too much TIME waiting for the laggards to catch up. Instead, use your charger's balance leads. The lack of balance leads from the charger caught my eye right off the bat. And truth be known, most of their resistive balancers are too small for a battery of what you *think* you are using.

Balance - Now that you have paralleled 4 cells for a larger-capacity cell, how well are you going to balance if just ONE of them is sitting at 50% DOD perhaps? I'm sure you charged each one before assembly, but with those 9800mah fakes, this could easily happen and how do you suppose those cells will react? Since you are not putting any sort of balancing on EACH cell, if something like this happens with those fakes, you, anyone near you, or your property is in danger.

[PNjunction]

Mike3367 - here's what you do in the interest of safety.

First, visit this forum to get schooled on how to identify fakes. Also see the excellent reviews by op HKJ of what REAL 18650's do:

http://www.candlepowerforums.com/vb/...eries-Included

Safely discharge your fakes, and MARK them as bad and recycle. This way, dumpster divers may have second thoughts about recharging them.

It appears like you are just trying to make a nominal 12v battery setup. But by using the wrong lithium chemistry with higher nominal voltages you have to resort to dc-dc converters.

Instead, use LiFeP04, with it's nominal 3.2v rating (3.6v max charge), and make a simple 4S battery. You can ignore the dc-dc converter now.

Your charger should have setting for LiFe, LiFeP04, or in some cases is labeled as "A123", which is lifepo4. Do NOT use "lipo" or the like, which is the wrong voltage.

Choose your desired capacity, and strive to reduce cell count to minimize the rat's nest. Ideally, get cells that meet your capacity needs in the first place. You may want to look into Headway LFP cells.

What I suspect is that you got suckered into thinking you can make a lithium ion battery on the cheap, and the vultures saw you coming. Hit up Candlepower to get some background and do your project right. Change your chemistry to LFP and simplify, simplify, simplify.