Testing a Shorai LiFePO4 on solar!

[Sunking]

The Hyperion EOS Pack Sentry unfortunately looks like it needs a Shorai-specific cable, and goes into *automatic* top balancing. Not really liking that.

I use Hyperion batteries in my RC planes and know exactly what you are talking about. Depending on your charger it can be fixed real easy. For example my 3S Hyperion batteries come with a 4S balance plug (5 pins). All I have to do is shift the wires over one pin. That fixes the problem. Take a close look at the balance plug, and I bet you will notice it will have one extra pin and all the wires are shifted by 1-pin.

[Sunny Solar]

PNJUNCTION From all the testing and experimenting we have done at work over the last 6 yrs or so . Generally its a lot harder to balance large cells. Over 200ahr are really a problem..They just seem to drift regardless of who manufactured them..
10ahr is the "perfect" size we found..and easy to replace if one goes faulty..(rare).

Its most likely why car manufacturers use thousands of very small cells. Big cells just are to much trouble??

[PNjunction]

Completely dependent on a manufacture to manufacture, and model to model. Generically you can say do not exceed 1C charge rate. However many recommend much higher rates up to 5C for a maximum 15 minute recharge.

The Shorai's seem to indicate about a 3C max on their label. I have no need for that fast a charge, and will limit myself to probably 2C max just to be conservative. Since they have such low internal resistance, my latitude is probably going to be 0.1C to 2C. This is unlike my fav Odyssey agm's, which need 0.4C minimum to be healthy. I like having that wider range of charge options without any chemical degradation from a low current input.

My other toys came in yesterday. The Optimate TM291 Lithium charger is functioning just fine when monitored with my Fluke, and both Shorai's which were subject to many previous standard terminal charges passed with flying colors. The Hyperion EOS Pack Sentry unfortunately looks like it needs a Shorai-specific cable, and goes into *automatic* top balancing. Not really liking that.

What became immediately apparent when I laid out all these toys is that there is only ONE thing I can count on - my Fluke 87V. Epiphany! Because of this, I'm not going to depend on anything but my own bottom-balancing with a break-out cable as opposed to top-balancing from devices that I have no idea of their accuracy or ability to maintain it over time or differing temperatures. There are a LOT of disputes over this in other forums so I'll just say that I'm not going to have my batteries depending on top balancing from unknown and possibly uncalibrated little devices. Maybe if Fluke got into the bms market, I might reconsider.

In reality, I'm just going to depend on the Optimate TM291 which uses a different method of balancing than top or bottom, and instead relies on pulsing the last 10% of charge compared to internal resistance templates for lifepo4, among a bunch of other useful tests. Seems reasonable enough, especially since the Shorai is only a 4S configuration no matter the capacity model chosen. And this will not be used each and every time, since solar is part of my equation for buying them in the first place.

Well, that's the plan anyway. Might take some time to get back with figures unless I encounter early failure.

The best part from this experiment is that for me, it looks like If I go with larger cells, I'll be doing my own 4S configuration, with no BMS, and instead rely on quality cells that may have simply been bottom-balanced at the start, and from then on just quality monitoring. Looks like I'll need three more Flukes.

[Sunny Solar]

Cant' say I know of any practical application in a solar application that only uses a 12 volt 10 AH battery JohnI cant think of one either that's why I made the systems I built 30ahr.
After looking at the build dates its now over5 yrs since the first solar lighting ones assembled.. Nothing has been replaced or needed and maintenance. Its exactly as how the customers wanted it.

[Sunking]

I've been searching, and see references to charging LiFEpo4's between 0.5-1C for best life, but don't have any hard data on what <0.5C does to them.

Completely dependent on a manufacture to manufacture, and model to model. Generically you can say do not exceed 1C charge rate. However many recommend much higher rates up to 5C for a maximum 15 minute recharge.

The driving force today and for the foreseeable future is the Electric Vehicle market. Tons of money both public and private is being poured into Lithium Battery development. Two of the most critical characteristics of a lithium battery in a EV is very high charge/discharge rates. They will have to have that in order to be able to compete with ICE cars. The market (mass public) demands a 15 minute or less recharge time similar to filling up with your car with gas today. Without that moderate long distance trips are not possible. Right now technology exist to get 5C charge rates and up to 50C discharge rates. However it is very expensive and cycle life is not acceptable at 500 or less cycles to 80% rated capacity.

[PNjunction]

Solar on my two Shorai's is working well.

I have no need to actually charge up to 14.4v, so I put back the jumper in my little Morningstar pwm CC's which set at 14.1v. Batts are still fully charged by the time I get to them. What a joy it is not having to deal with long absorb times and watch the lifepo's just gobble current until the very last minute. Nice since in my location in winter, I don't have much solar insolation due to long shadows from neighborhood trees, etc.

Basically, I love how fast and how hard you can hit them - much like my beloved Odyssey tppl agm's. However, unlike the Odysseys, I have a bit more latitude with low-current charging, although I want to hit them with about 0.5 to 1C. Apparently this is good for the best reformation during charge, although lower currents are not supposed to damage cycle life, unlike an Odyssey which basically demands 0.4C to keep them healthy.

I've been searching, and see references to charging LiFEpo4's between 0.5-1C for best life, but don't have any hard data on what <0.5C does to them. Being an Odyssey agm fan, I'm obsessive over supplying the proper amount of current. If anyone knows if <0.5C is harmful overall to lifepo4's, I'd appreciate an update.

After an initial balancing with the Shorai charger, I have been through about 10 cycles with charging from my carefully selected standard agm charger limited to 14.4v, and subsequent recharges with the balancer don't seem to take any longer than it did the first time out. Still waiting for my more advanced charger and Hyperios EOS voltage / balance checker to arrive...

And yes, my low-current application is at least 3 times the cost of an Odyssey agm. (Based on ACTUAL ah/wh, NOT that funky Pb/Eq value that is marketed towards SLI and CCA's) Knew that going in, BUT if I take care of these Shorais, maybe I can eek out twice or more the cycles out of them in the long run making them a bit less of a hit on the wallet.

[Sunking]

Cant' say I know of any practical application in a solar application that only uses a 12 volt 10 AH battery John. A good 4S 10 AH LiPo pack cost around $300 + a $100 state of the art balance charger. a Good 12 volt 10 AH AGM battery cost $20 and uses a $50 state of the art charger. If I am going to pay for LiPo, you can darn sure bet I am going to pay a small price for a good balance charger. That same Balance Charger I am speaking of can charge any battery chemistry at optimum charge rates and algorithms up to 400 watt input. That means I could charge a 12 volt 30 AH LiPo in 1 hour or a 12 volt 120 AH LiPo in 4 hours. You can darn sure bet I am willing to pay a measly $100 for a good balance charger for a $1000 battery investment. You can use your $50 charger all you want.

It is economics 101.

[Sunny Solar]

After putting into service 4 systems using 12x 10ahr cells per system in constant use over 4 yrs and another now over 3 yrs.As I said in a previous post they don't get very far out of balance and easily kept in check by simple means.. Its not necessary to spend a fortune on doing this. Same goes for charging a PWM charger than can have the charge voltage altered and equalizing turned off works fine.
Having tested hundreds of various sized cells at work have found they are NOT that sensitive to overcharging. We have long term tested many to 14.5v and never had one die from that.. Low voltage is another story. 2.3 v is rock bottom. and its safer have disconnect at 2.5v.. I have destroyed cells from 10ahr to 400 ahr with just one discharge to 2v.and some even at 2.2v

In real life you shouldn't get to that low a figure as 4 cells at 2.5v =10v . Any half reasonable inverter will shut down before 10.5v.. But there is no way I would trust that only, a LV cut off switch is really mandatory.

[Sunking]

IE will 100 mv difference between cells in a lithium phosphate pack cause a life threatening situation.? I doubt it.

John there are two points I think you are over looking.

1. Lithium batteries are extremely expensive. Some 4 to 10 times more expensive per watt hour than their lead acid cousins. That alone justifies a balanced charger.
2. Initially you are right a 100 mv is not a lot to worry about. But liithium batteries are extremely sensitive to over charging. The weakest battery in a series string will have the highest voltage applied during recharge. That results in an over charge condition of that cell and under charge of the normal cells. With each cycle the damage is compounded and accumulative causing premature failure. Now go back and look at reason #1.

[Sunny Solar]

Nobody who is not interested in best battery life cares much about that for two reasons: I dont understand what that means???
1. A specific gravity measurement is more informative than a cell voltage measurement and
2. FLA batteries rarely if ever catch fire unless you short circuit them.

And the points you make were not what I was getting at..
1. how do you measure specific gravity on "no maintainance " batteries.?
2.Lithium phosphate batteries are not the ones that usually catch fire either.

My point was you can be over concerned about small battery differences in ANY type of multi cell battery. And in many cases there is NOTHING you can do about it.
IE will 100 mv difference between cells in a lithium phosphate pack cause a life threatening situation.? I doubt it.

[PNjunction]

You might want to ask that question of Boeing and Yuasa!

Those bad boys were the Lithium-Cobalt chemistry, not LifePO4. Picture of them near bottom of this thread:

http://www.advrider.com/forums/showthread.php?t=757934&page=21

Like most consumers, I didn't know the difference in safety until very recently.

[inetdog]

If you carefully measure the cell voltage in lead acid batteries.there are most times slight differences between cells .

Nobody who is not interested in best battery life cares much about that for two reasons:
1. A specific gravity measurement is more informative than a cell voltage measurement and
2. FLA batteries rarely if ever catch fire unless you short circuit them.

[Sunny Solar]

If you are using cells no larger than 10ahr then they are easy to balance. I think many people are over worried about balancing cells..
I have now built 5 x 240w solar systems using 10ahr cells . 4 of the systems have been in constant use over 4 yrs and have had no problems and nothing has been done to them since installed.. And use nothing more complicated than a simple auto low voltage cut off switch. Cells die easily if taken below 2.2v. and for balancing a simple zenner diode 1w and 1 w resistor across each cell.. In my experience the differences between cells is small and easy to rectify. The solar battery charger in all cases an old Steca design but Chinese copy PWM .. Easily adjusted for Lithium Phosphate cells..And very reliable.
If you do use cells above 10ahr . ie 200hr and above then you need to use a much more ruggard method to balance them..

If you don't want to go to any trouble you can buy "made up" batteries almost any voltage with built in BMS. You then just use them as you would a regular lead acid battery

If you carefully measure the cell voltage in lead acid batteries.there are most times slight differences between cells . And have you ever heard of anyone trying to balance them????.. I know in most cases now you cant measure the individual cells as they are sealed. So no one knows or gives it any thought. And its usually one dead cell that kills a lead acid battery.

[inetdog]

This brought up something I thought about long ago - is the need for constant balancing really covering up poor cell quality issues?

You might want to ask that question of Boeing and Yuasa!

If you assume that any lithium cell has a measurable probability of failing in some way, then the monitoring part of a BMS (rather than a simple balancing network) just might save your equipment.
Note that the cell by cell data from the internal BMS was not preserved through the fire, so data about just how the early stages of the problem presented themselves are not available. <sigh>.

[Sunking]

The Optimate TM-291 Lithium charger intrigues me - knowing that it will be attached to various 4S-XP cells, it seems interesting that they will just pulse the battery between 14.1 and 14.3 volts when it hits the miniscule absorb for their EQ.

Huh? Lithium charging algorithm does not use PWM, Absord, or EQ. Optimum Lithium uses a very simple Float Current Taper algorithm.