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

[PNjunction]

It isn't an argument, it's real-world ownership experience. The consumer grade junk you speak about is what the average DIY'er is going to use in the first place, like a Pb based mppt controller on his new LFP, without knowing that you need to disable temp-comp if you are going to shoehorn the engineering.

This is the argument. Let's use NiFe as an analogy:

1) Op buys NiFe batteries and wants to know how to charge and maintain them.
2) Based upon specs alone, and being a well-intentioned non-owner, I just parrot back what I read on the net.
3) Consult an actual owner, like Mike, for proper guidance.

I'd choose option #3.

This is why you don't see me making any recommendations about NiFe that I can't back up. I don't own any, so you shouldn't trust me until I do!

Sorry man, can't resist this one about seatbelts - if they are made of straw, then it is a feel-good strategy.

Here's the deal - put some money on the line, and get an actual LFP prismatic bank. A 4S GBS, CALB, etc bank will do. Becoming an owner kind of changes things. You'll like it, and the eyeballs will glaze over as you investigate top-balance with no boards, top-balance with junk boards, bottom balance and the all fun stuff most other non-owners speculate about. Kinda' changes things when your wallet is on the line.

[jflorey2]

Sorry man, can't resist this one about seatbelts - if they are made of straw, then it is a feel-good strategy.

Yep. But they're not.

Here's the deal - put some money on the line, and get an actual LFP prismatic bank. A 4S GBS, CALB, etc bank will do. Becoming an owner kind of changes things. You'll like it, and the eyeballs will glaze over as you investigate top-balance with no boards, top-balance with junk boards, bottom balance and the all fun stuff most other non-owners speculate about. Kinda' changes things when your wallet is on the line.

Indeed it does. And yet EV manufacturers, renewable energy manufacturers and battery manufacturers use balancing circuits - and they have much more to lose than your typical hobbyist. (And have the years of experience to make those good decisions.) Personally I will go with them, rather than hobbyists.

[inetdog]

Indeed it does. And yet EV manufacturers, renewable energy manufacturers and battery manufacturers use balancing circuits - and they have much more to lose than your typical hobbyist. (And have the years of experience to make those good decisions.) Personally I will go with them, rather than hobbyists.

You are observing high quality gear sold into a specific market, with generally knowledgable DIY hobbyists or specifying engineers. Or gear designed for the average consumer for a very specific use pattern.

What the PV energy storage experimenter will be exposed to will be a wide range from component parts which must be put together intelligently to cheap "systems" that in fact are not well engineered for his particular use and may be in a very price competitive market.

If the Tesla Powerwall includes balancing and not just monitoring circuitry, as it probably does, I would expect it to be engineered for the discharge regime(s) the unit is expected to be used in, including essentially unlimited access charging power for grid time shifting and limited access time and power charging from a PV source.
Believe me, that is not what you get with a typical "hobbyist" Li pack with built-in BMS. The BMS is there to allow it to be advertised that way, not to do a particularly useful job.
Putting together raw cells and component balancers without understanding how they should interact is a disaster waiting to happen.
JMO

[jflorey2]

Putting together raw cells and component balancers without understanding how they should interact is a disaster waiting to happen.
JMO

Indeed it is - as is true with any battery (or solar) technology. Hopefully forums like this one help people make better decisions on such issues.

[PNjunction]

I agree - but everyone needs to keep their eye on the ball on the application at hand - and this is where it gets so contentious by forgetting that application matters.

Here, the application is a solar housebank, which differs in usage/design than those for an EV, or an RC model environment - yet many from the latter categories have NO CLUE as to what it takes to successfully run the former!

Additionally, many come to just get a shopping list of online junk to slap onto their cells, and get generic advice, such as a 14.6v charge for LFP, which when given without taking the ops skill level or application into account leads to financial bluners, safety, or performance problems.

If you want info on solar housebank use of LFP, talk to actual owners - even if they disagree amongst themselves - their ownership and experience are immensely better than those of non-owner speculators.

[drpatso]

Appreciate all the input guys. Manual balance is not in the question for me, and I'd like to get better density than LiFePO4. I have been amazed at the lack of options for batteries other than lead and gel.

I have a budget of about 600$ for the battery and charger.

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.

[inetdog]

...I have been amazed at the lack of options for batteries other than lead and gel.
...
...
Of course 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.

1. Just to keep the language correct to avoid problems later: GEL is a particular form of Lead Acid battery, along with the open system Flooded Lead Acid (FLA) and the sealed, pressure regulated, Absorbed Glass Mat (AGM) form. AGM, being sealed, has advantages for a boat and can also deliver higher power over a short time than FLA. GEL is also sealed but has serious problems accepting charge quickly and is, with a few possible special construction exceptions, considered unsuitable for PV or engine alternator charging.
2. You are using "Lithium-ion" and "Lithium Polymer" (LiPo) as if they described chemistry and associated voltage and energy density. They do not!!!!
Lithium-ion can refer to the use of a soluble lithium compound for an electrode instead of lithium metal. Lithium polymer refers to a particular kind of construction with a soft case and soft separators. They do not tell you what the electrolyte or electrode chemistry are. You need to look at the actual chemistry, such as Lithium Cobalt (LiCo) or Lithium Iron Phosphate (LiFePO4) when making your evaluations. The physical construction as well as the chemistry affect the charge and discharge rate, resistance to thermal runaway, and intrinsic safety of the batteries.
3. OK, you say a failure would only kill the ship. Actually a failing lithium chemistry battery can also produce highly toxic fumes that can kill you before you are able to jump off the ship. Some of these batteries are 100% safe as long as you do not store them at high temperatures or charge or discharge them at any temperature.

For a good discussion of LiPo and Li-ion, check out this thread on CandlepowerForums: http://www.candlepowerforums.com/vb/...=1#post4471076



While we are on the subject, I should also mention some other manufacturer recommended terminology:

Lithium batteries do not catch fire, they vent with flame.
Lithium batteries do not explode, they undergo spontaneous rapid disassembly.

[Mike90250]

The biggest problem with any of the Li chemistries, is the breakdown that happens at low cell voltages and high voltages. Ask Boeing and Samsung about Li battery fires.
Out of all the different cell types, the LFP / LiFePO4 is the most robust and forgiving. But it's not the highest power density,
If you are charging with a 10A charger, you need balance boards that can handle 10A, not 500mA or 2A.
You need to make sure the spaghetti wiring mess for the BMS does not cause a fire if a wire gets nicked.
The automotive systems have thermal controls and voltage controls to watch over the batteries, are sized just right for the battery pack and the charge and discharge patterns are well known. Taking BMS #S and attaching it to battery #G - may or may not be technically acceptable, but Marketing will sell it, they both worked last week

[drpatso]

I don't know if I was extremely clear, this is going to be for an unattended drone boat designed around 400W of panels, using compass control and gps waypoint navigation. The system will power motor, rudder servo and electronics.

I am reluctant to choose 4s LiFePO4 as I will be effectively lowering the capacity charging so far below fully charged voltage before dark as well as increasing volume and weight dramatically compared to other technolgoies. It seems charge controllers capable of running a 24V lead acid / gel bank match up quite well with 7s "Lico"? packs (lithium cells that are 4.2V fully charged,NCR18650B or similar). I think Lico or similar is only risking the boat as it will not have any occupants.

That said, with the available charge controllers it looks like these are my options. I think most likely I will be running a 12V motor, not terribly afraid of running a step down or slightly above 12V to the motor controller. A lot of motor controllers accept a wide voltage range. We already have a nice waterproof buck converter for 5v electronics.

4S LiFePO4 with MPPT set to 14.2-14.4V
5S LiFePO4 (no charge controller? I don't much care for this idea)
8S LiFePO4 with MPPT

7S LiCO (4.2V fully charged) It seems like the problems most people have with this setup is ****ty bms. If a great quality BMS is sourced I think this could be a feasible option)

[Mike90250]

I understand it's a small drone boat in the middle of nowhere. if you can come up with a robust BMS to keep the cells in healthy condition, great. I don't know much about Li other than to beware.
As to the motor, have you considered AC motor with controller. Small electronics to drive it, but better efficiency, Will prop be vari-pitch or is this single speed ?

Any thought of ballast compartment like a sailboat keel ?

Anyway, our job is to give you all the choices for the battery, pros, cons and it's your job to sort it out and chose what you want. And please keep us posted.
(electrics and salt water - yum)

[drpatso]

I think motor will be the last thing we decide on when we have a better idea of the weight and hull. Definitely won't have variable pitch, likely a brushless for efficiency and they typically have a very wide throttle range, we'll control it with PWM or a DAC if it's a simpler motor controller. We will be monitoring the pack voltage and GPS clock for the throttle setting. Battery must be topped off before sundown and we'll try and design it to run on 3-4amps all night and of course shutting the motor off if the voltage gets too low.

I will hopefully be getting one of the 100W panels the boat will have and a charge controller shortly after christmas and try and do some prototyping on the battery.

[Sunking]

[QUOTE=drpatso;n336341]Appreciate all the input guys. Manual balance is not in the question for me, and I'd like to get better density than LiFePO4. I have been amazed at the lack of options for batteries other than lead and gel./QUOTE]

Purely market driven and simple economics. A FLA battery is 1/4 the cost and last twice as long than any lithium battery. Why would any fool buy lithium for a solar application when there are better and less expensive options.

An EV can justify the expense, but not solar. That is why you are not finding a lot out there, There is no MARKET for it.

Which gas station would you use and which one stays in biz. The station on the Corner that sells gas for $2/gal, or the one across the street that sells gas for $10/gal. It is that simple. Only a fool would pay $10/gal.

[Sunking]

Indeed it is - as is true with any battery (or solar) technology. Hopefully forums like this one help people make better decisions on such issues.

How is that working? Everyday fools come here that have already bought equipment and want to know why it is not working.

[Sunking]

Bzzt. Most balancing circuits are the CAUSE for killing packs. The "balancers" are what kills them..

Well budder my butt and call it a biscuit. Now tell that idiot Karrak.

[Sunking]

Indeed it does. And yet EV manufacturers, renewable energy manufacturers and battery manufacturers use balancing circuits -

True but rarely if ever used. No EV manufacture allows their customers to fully charge the EV battery. they only allow you to use 60 to 80% of the capacity.

Tesla uses the the same TI chip most BMS manfacture uses. All work on the exact same principle. Fact is once a Lithium battery pack is balanced rarely ever needs to be rebalanced. Additionally the last thing any user wants to do is fully charge their battery packs as that is extremely FOOLISH, thus why EV manufactures do not allow it to happen. In order to Top Balance you must fully charge the battery. Do that and you cut cycle life in half.

Lastly BMS are usefull in say a 32S and up packs where 3 volt swing is normal. However on a 4S, battery even 1 volt off is going to get your attention real fast Set the LVD to 12 volts, an initial Balance, and charge to 13.6 volts. No BMS is required or ever needed.