Cobbled together PV in W.Sussex

[biff]

hi outta,
        your little geni is a beezer,the faulty fuel tap lever was a problem from the moment they came out of the box but once that is sorted you will find that this geni is capable of powering grinders and drills to 1kw without a bother even though it says only 650 watts.
     the throttle govner is cute,very quick to respond to a sudden load.the filter going up into the tank is a better idea than the origional.the geni came origionally with a set of leads to charge 12v batteries.there is a little connection there somewhere.
     getting a proper seal on the tap is tricky,it might take 2 or three efforts with the no14 and it needs to be pulled tight.sometimes the rubber seal supplied does not work. if you are closing it down for a period of time,turn of the tap and let it conk out rather than leave the fuel in the carb,
                    good luck,          biff

[Outtasight]

That's a bit startling, not to say disappointing; won't the MPPT60 limit the current without letting the smoke out even just as far as the glass?

The fuse is an in-line one (not inside the charge controller).

The Tristar does limit the current (to any value you program or a default of 60A).  The recorded surge was 1960W, which was about 74A.  The Tristar was bouncing off the 60A limiter when the fuse went.  The other controller was doing just over 14A (just shy of its 15A limiter) with only a pair of Sharp 170W panels (340Wp). It recorded delivering 376W (110% of PV nominal rating) at the moment the fuse went pop.

The problem is one of the fuse I used being a bit undersized at 60A.  If you run a fuse at its rated current, it will eventually blow (especially if it is subjected to surges which cause thermal shocks to the metal in the link).  I should have used a 70A fuse but they don't make one in this type (60A is the biggest).  I suppose I could reduce the current limit on the controller to 55A, but if the fuse blows once in every two years, then it's not such a big deal.  Nothing else on the circuit gets even remotely warm, as I used 20mm² cable or fatter throughout and 100A switch gear.

It's pretty rare that the array hits 60A for more than a few seconds, so I'd figured that it wouldn't spend enough time at the limit for it to be an issue.

Fuses get "old" as well...  Putting the new one in, I noticed that it didn't get warm today, with the power of the sun.  Also the Tristar got to the absorption Voltage before the other controller and started blinking sooner.  I put this down to the old fuse slowly degrading with heat, causing its resistance to increase, so it drops more Voltage and heats up more and so on until it finally blows.  The flexing of the link with heat will also cause the resistance of the metal to change over time, as micro fractures in the metal cause it to conduct less well, reducing the fuse effective rating.

In the other controller which limits at 15A, I used a 20A fuse and haven't had a problem.  The 20A fuse also has a link that is apparently gold plated... maybe to prevent surface oxidation from heating.  The 60A one had a plain grey looking link.

[EccentricAnomaly]

Thanks for the clarification, Outta. I guess if a fuse runs warm then it's time to replace it and if the replacement runs warm it's time for a bit of investigation.

[Outtasight]

getting a proper seal on the tap is tricky,it might take 2 or three efforts with the no14 and it needs to be pulled tight.sometimes the rubber seal supplied does not work. if you are closing it down for a period of time,turn of the tap and let it conk out rather than leave the fuel in the carb,

I got lucky and the seal worked.  Good tip on letting the engine conk out from fuel cut-off rather than using the switch.  I'll remember that.

I'd noticed it was pretty quick to respond to changes in load.  I was playing about with a 100W bulb attached to it and the throttle reacts very quickly to the light being turned on and off.  The guy who sold it didn't have the 12V cable set or the plug spanner.  I'm not too fussed about the 12V feed though, as I'll use my spare 24V mains charger anyway.

[Outtasight]

Whoa!  It's been a long time since I posted here.

Quite a lot of changes since July.  Got most of my array up on the roof of the house (where it belongs, rather than on the lawn and patio).

Got some more PV on the cheap from eBay - four cheapie Chinese 100W 72 cell modules.  Interesting because I don't have to use them in pairs like the others.  I put a couple up on the garden wall and have kept one as a mobile one that I use at eco-fairs for demo purposes.  We did an outdoor demo in Horsham town centre to promote an eco-fair at the town hall.  100W of PV can easily run a battery and an inverter to make mains for my friends LED lighting display.

Then things just went along "business as usual" except that I made a lot more power with the PV on the roof.  Much lower shading issues.

December brought the usual "oh no, the batteries are getting old and wonky" blues again and I bought a pair of cheap Chinese 180Ah AGMs that haven't exactly worked out...

All of which brings me to the latest (and certainly most expensive) part of my off grid experiment to date...

I'm converting the battery system to use some new Winston LiFePO4 batteries!

It's a totally new learning curve and I'm approaching the problem with the ususal "pair of pliars will do in the absence of a socket wrench" approach.

BEHOLD!!!  A 400Ah "24V" lithium iron yttrium phosphate battery.  It's only nominally 24V as the 8 cells are about 3.00V when discharged (so 24V) and about 3.35V when fully charged, so 26.8V.  When charging they can go up to 4.00V or 32.0V but I'm advised that it's best to keep them under charged at all times (totally the opposite of lead acid batteries).  The safe top Voltage is about 3.60V or 28.8V - which cunningly matches up nicely to what solar chargers are capable of and inverters can handle.

If you take a middle resting Voltage figure of about 25.0V for calculations then this thing holds about 10kWh of energy, if you push it.  Realistically, you can cycle it to about 80% DoD without harm and it will be good for 5000 cycles of 8kWh. 

Each cell is just under 14kg (including the massive M14 terminal bolts!) and pretty small at just 46 x 6.5 x 28.5 cm in dimensions.

The University of Prague has tested them on the bench in an automated charge / discharge loop for 13,000 10% DoD cycles with no loss of performance, even when charged and discharged at 1.5C rate.

[stannn]

Outtasight
You didn't mention the price. Is 10kWh for the one battery or for 7 of them?
Stan

[fred bloggs]

Nice to see you back Ottasight!!

Thought you given up, although I have looked at your Blog a couple of times.

Interesting stuff with the LiFePO4 batteries! Unfortunately management (Supreme allied command) limits the budget to anything second hand (or free) therefore Lead acid batteries only!!

Very interesting to see someone actually trying this much applaud

Please keep all of us updated regularly.

Best Regards

Fred

[StBarnabas]

Outta
welcome back from Japan. I never did thank you for your Christmas card, Very much appreciated thank you. Your new battery technology is something I know nothing about so it will be great to see how you get on. Give my regards to Mrs Outta, Mrs B thought she was great company when you visited.
Sean

[Outtasight]

Hi all.  Sean, it was a pleasure visiting and I'm also glad your friend won the compo for the Hexam hydro project.

@Stan - They are all individual 3.2V nominal cells at 400Ah.  I'm using 8 of them to make a 400Ah 24V pack (more of a hang-over from lead acid and the fact that I'm using a 24V inverter).  At the mid-range pack Voltage of 25V, that makes the whole pack capacity about 10kWh.

Cost... An eye-watering 4096 Euros which translated into £3540 including 20% VAT 2% credit card payment surcharge, 2.5% currency exchange charge (from VISA as it was in Euros to Pounds) and TNT overland shipping (quite quick at 3 days from Prague).  At least when I put the payment in it was the week when all the Euro countries got their credit ratings downgraded and the Euro slumped against Sterling.  Pretty steep but maybe not so far off what a new set of good OPz cells would cost.  

You can't compare Ah like for like with lead acid.  I reckon a 400Ah LiFe pack is equivalent to a 1600Ah lead pack in cost, life cycles and usability.  I'm assuming that you'd have to limit the lead DoD to 20% and the LiFe DoD to 80% to get 5000 cycles.  All the lead batteries I've had haven't made it past 2.5 years in service (850 cycles at best).  I've also got no desire to keep 1600Ah of flooded lead acid behind the sofa in my living room - for starters, the fork lift truck to deliver them won't fit through the patio doors and wearing a gas mask while watching TV might wrankle with the missus.

The final straw was discovering that AGM lead batteries are literally time bombs.  They have a (now becoming recognised) fatal failure mode in that as they get old, they dry out (no big deal other than they die).  Not so...  As they get to being dried out, the gas recombination efficiency increases dramatically and this causes a near death supernova of a positive feedback loop in the float current which heats the cell which causes more current to flow which heats the cell (from recombination heat) and at float while doing nothing in particular... BOOM!

That's why UPS batteries are swapped out way before "end of life".  It's because of the number of them that have melted / caught fire in service.

You can monitor the temperature of the pack and adjust the float voltage down to compensate for the increasing current BUT absolutely nobody has a charger that has a temperature sensor on each and every cell in the pack to spot the one that it going to go boom first...

It's battery russian roulette.  Flooded cells don't do this as when they get old they gas more but the gas escapes from the cell, taking the thermal and chemical energy away with it (to explode in the confined space outside the cell )

[Eleanor]

Look forward to seeing how you get on with them. It's a good thing they're going behind the sofa - that yellow colour really doesn't go with the carpet 
What are you planning for your furry friend and do we need to call the RSPCA 
Our new bank hasn't arrived yet - you'll laugh, it's FAAM this time. Maybe if we haven't gassed ourselves, blown ourselves up or set ourselves on fire we could compare them in a year or two

[Outtasight]

Hi Eleanor,

Nice to hear you finally beat the supplier into submission on those pick'n'mix cells your were sold

Just a shame it took a materials scientist and an electron micrograph to get them to 'fess up.

Actually, I was thinking of just putting some glass over the new cells and making them into a coffee table talking piece

Let's just hope I don't literally turn them into bricks...  The worlds most expensive Lego set

The Chinese operator's manual is a bit of a giggle.  Lithium ion cells have had such a bad rep since the manganese cobalt days that Winston include all sorts of additional tests to prove the safety of these yttrium ones.  Including:

Putting them in a fire (to show that while the plastic will burn, they don't explode because of the lithium or the oxide releasing its oxygen - the main cause of manganese cobalt cells going off like bombs),
Soaking a broken one in water (to show that they don't explode because of free lithium coming into contact with water),
Short circuiting to 5000 Amps (to show that although they'll get hot and blow their vents, they  won't explode or catch fire),
Shooting them with a gun (For those in seedier parts of New Mexico who are off grid.  The cell will fizz and pop and vent but not explode or catch fire).

They even made a promo video where you can see the boys at the lab doing all of these things to a bunch of cells for a larf... Including the shooting a cell "gangsta" test.  Quite how a battery technician came to have a gun in the lab is a more interesting question.  

[Outtasight]

Oh, yeah... The dog...

It's my fail-safe backup for stopping the charging cycle... A watchdog timer 

[billi]

exciting  Outta ......  but surely a big pile   of $$ 

Anyhow  can you hook  them direct to a solar  charge-controller ? I read  somewhere   one needs an additional BMS (Battery Management System) ..... 

How does this work ?

[Outtasight]

Yup, it's certainly a hill of beans.  Maybe someone will give me a job as a lithium power systems consultant after I've figured out how not to do it (inventing the Edison way).

Mind you, the house is conspiring against me on this project.  Today the washing machine blew up.  Literally.  It was doing it's spin cycle and a bearing or something let go in the motor and it made a grinding noise and then the whole house RCD popped.  Luckily it had finished pumping out the water and was almost finished.  We managed to get the clothes out but the machine is toast.

I'm reliably informed by one Jack Rickard (of EVTV fame) that I don't need a BMS to run a lithium pack.  If you talk to him and even mention BMSs he gets worked up into a lather.  It's all just a ploy from the battery suppliers to make extra money (and lots of it - a typical BMS can be another £600).  He should know because he's been running several cars powered by these Winston (and other similar prismatic) cells and doesn't use any form of active cell management during charge or discharge.  If you bottom balance the pack and then always undercharge it, you don't get the kind of fires that have burned down the Chevvy Volt.

In most cases it's the BMS that starts the fire.

In my experience it's very easy to arrange for a solar charging system to chronically under charge batteries   But seriously, I do have some ideas on safety controls for this thing.

Stay tuned...

[stannn]

Can't wait! You make me chuckle. I see that if we all get together and order 25000 of these cells, then we can get the price down by a quarter!     
Stan