thousandsuns.com LiFePO4 12v 30Ah Battery again

[DamonHD]

Hi,

I'm having another serious think about boosting my off-grid storage from ~0.25kWh (with a ~0.1kWh/d steady load) and experimenting with LiFePO4 for better round-trip efficiency too.  (A whole-house load-shifting experiment that I'm plotting as a follow-on isn't much worth doing with a whole-cycle efficiency of much less than 90% for example.)

The thousandsuns (I hope this doesn't indicate what happens if they go wrong!) pack here:

http://www.thousandsuns.com/LiFePO4_-_12v_30A_Battery/p432875_1537130.aspx

claims to have an integrated BMS, and from its 10V--14.6V range looks as if I may simply be able to drop it in instead of my 40Ah SLA gen with one of my Morningstar PWM solar controllers.

Has anyone done this?  Am I (or the battery) going to die horribly if I do this?

Also, for Li packs with integrated BMS is it likely to be safe to parallel them up to increase the storage at a given voltage, eg I'd like to get 3x30A 12V to give me ~1kWh of usable storage.

I'm itching to do it, but if it goes wrong it may (a) fry my server and (b) my family since these things would be in the kitchen by the exit door unless I take steps to relocate them...

Rgds

Damon

[fabricator]

Everything I read about the LiFeP04 batteries seems good, as far as I can find they simply don't burn up, the early lithium polymer batteries did burn up regularly in spectacular fashion, I fly electric RC planes and had a 2100ah lipo pack burn up, that was very early in the lipo craze though, now days most have multiple taps and on board regulation systems and the chargers are smart balancing chargers.
As far as I know the LiFePO4 batteries will not crash and burn even if the cells become unbalanced and one get horribly over charged, one or the other of these types of batteries IS the future of RE storage, I say go for it, drop em an email and explain your plans and see what you get.

[dnix71]

"The thousandsuns (I hope this doesn't indicate what happens if they go wrong!) pack here:"

That sounds like something Iran or North Korea would be interested in.  

Fortunately the lithium iron phosphate batteries won't burn. Those are the safe one. Still too costly for me. My ebike has an optional LiFePO4 battery that costs about what you are quoted there. If you doubled the voltage to 24 that would make a 15ah pack that cost almost as much as the bicycle itself. The SLA 24v pack is rated at 12AH.

Since you can't take an SLA all the way down without ruining it, you could probably get by with 1/2 the same size in lithium. That would still be over $200US just so I didn't have to pedal. If the price came down a little more that might be worth doing just to save the weight and space.

You do NOT want to short out that pack, though, even though it won't burst into flames. One major advantage of lithium is you can fast charge to 90% in 15 minutes. If you get variable sun all it would take is a little bit of full sun to get them almost to the top.

http://www.batteryspace.com/lifepo4battery128v20ah256wh60aratewopcm-replaceslawith10timeslongerlife.aspx  These are a drop in replacement for 12v 10AH sla's, but it doesn't come with PCM protection unless you pay extra. http://www.batteryspace.com/pcmprotectioncircuitmodulefor1cells32vlifepo4batterypackat20alimited.aspx
The PCM's are finally for sale by themselves. People used to buy tool battery packs and disassemble them to get the circuit. The PCM monitors each cell during charge/discharge to keep each cell voltage within specs. Without this you can easily ruin a VERY expensive battery by simply overcharging.

[DamonHD]

Thanks for that.

I'm hoping to go and actually look at a sample pack (or even buy one) at their London office tomorrow morning!

Rgds

Damon

[DamonHD]

OK... Went and visited thousandsuns' office.  1.5hrs walking round London because of the Tube strike...

Anyhow, I bought one of their prototype LiFePO4 primsatic 20Ah packs (that sure looks like a bomb all bound with tape and with wires hanging out), and I've worked out a way to hooking it into my system to sorta kinda double up storage capacity.

It's about 1/3rd the size and weight of my 12V gel SLA 40Ah (ie same usable capacity), so I was able to plonk this in my backpack with my laptop.

But it's an odd one, with a common +ve rail for its separate charge and discharge connections...

I think I'll need to break out the drawing package tonight and do a schematic to how to wedge it in.

Basically I'm going to detach a small portion of my off-grid PV and use it to directly charge this pack via its BMS, then preferentially power my server from this falling back to the SLA c/o a couple of Schottky diodes.

I shall be keeping it at a very low SoC in this config, and primarily relying on the SLA for system stability for now.

Rgds

Damon

[dnix71]

How much did you pay retail for that pack you bought? Did you get the correct charger with it?

[DamonHD]

About £200 (excluding VAT).  The same usable capacity in SLA would cost about half that here.  It includes the complete BMS.  I shall wire its charge inputs directly to an isolated (small) set of panels and then diode-OR its output (currently 13.4V at about 50% charge) with the LVD output of the solar controller for the input to my server's power-supply.

The new battery should thus take all the load from the SLA until the LiFePO4 is virtually exhausted or the SLA is floating nicely.

It should test how well the Li battery copes with being completely drained, and should keep the Li battery in a low-ish SoC and the SLA in a high-ish SoC, which should suit both of them.

Not perfect, but I should be able to do it tomorrow am before going to see a client.

Expect to see a full write-up soon!

Rgds

Damon

[DamonHD]

OK, it's integrated and indeed powering my SheevaPlug server.

I've created a place-holder page here for now that I'll update with my results:

http://www.earth.org.uk/LiFePO4-battery-testing-with-solar-PV-off-grid-system.html

There is a crude sketch of my crude integration to hold the fort.

The LVD was about to operate on the SLA anyway (flashing red this morning), so this is a 'just-in-time' lash-up.

I will need to get more panels in due course to make it through the winter...

Rgds

Damon

[Bruce S]

Damon;
Are you using the capacity of the 40Ah SLA at 50% DoD or 20%?
During the past winter, what was the average charge amount?
Curious
Bruce S

[DamonHD]

I aim never to go more than 50% DoD, so I assume a usable capacity of about 0.25kWh for a 12V 40Ah SLA.

I do have the numbers to compute an approximate average charge amount but it would make me cry as I have too many other things to do.  I can tell you that I spent maybe 2.5 months back on-grid when I would otherwise have gone over 50% DoD, ie below 50% remaining charge.  So really most of *winter* I didn't have adequate insolation (or charge).  I'm hoping an extra 100W of panel south-facing will sort that, and a little extra storage.  But itself 100Wp should generate on average 100Wh mid-winter which ignoring all losses should be enough to cover the server's consumption.  But I already had over 100Wp, so "ignoring all losses" clearly doesn't work in practice.

Rgds

Damon

[Bruce S]

I aim never to go more than 50% DoD, so I assume a usable capacity of about 0.25kWh for a 12V 40Ah SLA.

I do have the numbers to compute an approximate average charge amount but it would make me cry as I have too many other things to do.  I can tell you that I spent maybe 2.5 months back on-grid when I would otherwise have gone over 50% DoD, ie below 50% remaining charge.  So really most of *winter* I didn't have adequate insolation (or charge).  I'm hoping an extra 100W of panel south-facing will sort that, and a little extra storage.  But itself 100Wp should generate on average 100Wh mid-winter which ignoring all losses should be enough to cover the server's consumption.  But I already had over 100Wp, so "ignoring all losses" clearly doesn't work in practice.

Rgds

Damon

Damon;
 Thanks for the info.
My reasoning is such that if you were able to move away with the SLA's limitations by making use of recycled "other" chemistry based batteries that can take being drained much further than 50% and still survive.
Would you have enough solar source(s) to effectively recharge the "other" types of batteries if they were drained during one exceptionally long overcast week.

Thoughts?
Bruce S

   

[DamonHD]

I believe that I neither have enough panels nor storage at the moment.  But now have up to twice the storage I did 48 hours ago (up to maybe 4 or 5 days' worth), and I have ordered a 100W panel which should nearly double daily energy capture: heavy overkill in summer but then I may be able to divert some of that 'extra' energy sensibly as well as taking down a few of the panels...

Am I answering your question?

Rgds

Damon

PS. To be clear: I don't much care about battery chemistry (though anything other than just LA makes life more complicated), only about 'usable capacity' which I take to be about 50% of nominal for LA and nearly 100% for Li.

[Bruce S]

I believe that I neither have enough panels nor storage at the moment.  But now have up to twice the storage I did 48 hours ago (up to maybe 4 or 5 days' worth), and I have ordered a 100W panel which should nearly double daily energy capture: heavy overkill in summer but then I may be able to divert some of that 'extra' energy sensibly as well as taking down a few of the panels...
Am I answering your question?
Rgds
Damon
PS. To be clear: I don't much care about battery chemistry (though anything other than just LA makes life more complicated), only about 'usable capacity' which I take to be about 50% of nominal for LA and nearly 100% for Li.

Damon;
Kinda.
Here's where I was going with this. There seems to be a fine line of balance on needed versus available to use and replace, with respect to most RE systems.

My Solar system is no where near as large as yours, but I get great SUN during the winter months due to trees losing their leaves. Even now after having moved my panels up a full 11/2 stories higher than they were, I still have shade problems in the latter part of the day.
In the winter time with my small (90watt) system I can fill my NiCd battery packs (currently 64Ah at 14.4Vdc) if drained completely in about two days of winter sun, as of last years testing, and they bounce right back. If I were to try that what the backup pack of SLAs which are 12Vdc at 72Ah, they would not last much more than a season or two.
Since you have long term data of your system, I was trying to see if there's a more defined correlation.
I of course am not taking into account losses either since we use the packs every morning (coffee pot being the heavy hitter at 600watts).

Plus, if you were up for the challenge, I would offer some of the NiCd packs for you to try and re-purpose into packs similar to what Norm has done
These and a Ghurd controller would be all you would need for all the extra power you have in the summer.

CO has a BD person in London now and can ship to him, then to you.
I know and understand the environmental impact of Cadmium but my stance is to completely use them up before recycling.
Cheers;
Bruce S


 

 

[DamonHD]

Hopefully my LiFePO4 stuff should be almost fully cycleable and not die in the process, and still last 10x more cycles than a (gently cycled) SLA.  But I may have lost significant capacity already; I don't know.

Thanks for the offer on the NiCds but the disposal would be a problem here and I don't want to make too many changes and add too much complexity all at once!  B^>

I do have a Ghurd controller waiting in the shadows (thanks again G), primarily in case I improve the wind input which is currently to0 tiny to be a problem, so that does make your offer even more tempting.

What's the round-trip cycle efficiency of those beasts?

Rgds

Damon

[Bruce S]

What's the round-trip cycle efficiency of those beasts?

Not sure what you mean by this? 

I can pull numbers from my "watts up" meter and let you know those number if you wish.

The beasts are 14.4V at 16Ahr x 4 banks, were originally built for our e-bike which is 48Vdc 550watt. Now this set is running as the main power packs.
One of Ghurd's dump controllers is set to send dumping to the 12V 18Ah x 4 packs.
I see the unit dumping on the Sunny weekends when we don't normally have more than a single pot of coffee.
Our DSL router, and laptop, & inkjet printer are power via the SLAs just to keep them cycled.

Bruce S

[DamonHD]

Hi,

Sorry, let me rephrase...  %-P

If I put 10Wh in while charging, how many Wh do I get out?

For SLA it is around 8Wh, for Li it is around 9Wh or better.

Rgds

Damon

[Bruce S]

Hi,

Sorry, let me rephrase...  %-P

If I put 10Wh in while charging, how many Wh do I get out?

For SLA it is around 8Wh, for Li it is around 9Wh or better.

Rgds

Damon

Yeah on the drive home my brain had time to understand what you meant  .
The NiCds are on par with the Li's if a little better,  but I don't have enough of the LiOn batteries from laptops to do any real testing.
The biggest difference I can tell so far, is long term storage. Li's probably have 10x the long term storage capability, NiCds love to be used, NOT be used for storage.
 
NOT always trusting the internet for information .

I did my own testing and found battery-college for NiCds to be right on target. Except once they get down to about 1V/cell they seem to take a very long time to drop past that.
I do have to say that for larger inverters ( above 400 watts) I build the packs to be 14.4Vdc to help negate the voltage sag that I've seen when starting up the inverters. I would build them up as 13Vdc but the packs would be lopsided.

I disconnected the dump controller so I can do a real world test using our 1000 watt inverter and 700 watt microwave. I'll let you know the outcome if you would like.
A single 1.3Ah 12Vdc pack weighs in at 256 grams. I just weighed one on a postage scale .
Cheers
Bruce S

[DamonHD]

Yes, I would be interested in a real-world round-trip efficiency test!  Wikipedia seems to be suggesting 70%--90%, ie between LA and Li.

Rgds

Damon

[DamonHD]

Update on the new new battery...

Other than about 8 hours total with good sun where the SLA voltage has been lifted well above 13V, the LiFePO4 battery, nominally half-charged of its ~300Wh max capacity, has been shouldering the load of my server for more than three days now.  Terminal voltage still above 13V, indeed more-or-less unchanged since the first few hours.

An unexpected oddity is that there seems to be nothing preventing power loss back through the charging leads, eg I can run a 3W 12V LED off them quite happily even at night.  All my panels in that set happen to have blocking diodes, so it's not actually a problem, but it's not the expected behaviour...

Rgds

Damon

[Bruce S]

An unexpected oddity is that there seems to be nothing preventing power loss back through the charging leads, eg I can run a 3W 12V LED off them quite happily even at night.  All my panels in that set happen to have blocking diodes, so it's not actually a problem, but it's not the expected behaviour...
Rgds
Damon

Damon, Could be the common rail ve+ going on keeping the BMS updated. At 0.25A that's a lot to us, but not when it comes to watchdog circuitry.
Bruce S

[DamonHD]

I hear you, indeed, but it could also be quite enough to damage a panel I imagine, if you were unlucky.

Anyhow, the battery voltage has finally dropped below 13.1V after nearly 4 days of supporting the load.

I hope to set up voltage monitoring/graphing of it this weekend and I will re-arrange panels a little to give it a bit more input charge.

Rgds

Damon

[DamonHD]

Updated the graph to show the Li battery voltage too, and removed a false offset of about 0.3V from the LA voltage before.

http://www.earth.org.uk/off-grid-stats.html

The voltage shown for the Li battery before about mid-day today is spurious: just where the unused input was set to.

Rgds

Damon

[DamonHD]

My new 100Wp mono panel arrived today, and I'm doing a major re-arrangement of my off-grid system to suit my new 'dual battery' arrangement.

Basically my motley collection is split into two entirely isolated sets, one of which charges the SLA via the Morningstar MPPT and includes the new panel, another 20Wp mono panel, and about 60Wp of my 'winter-only' TopRay amorphous.

The lower-voltage 60Wp Uni-Solar triple-junction (and some TopRay amorphous) are now directly driving the BMS charging input for the LiFePO4.

The main (server) load is driven from the diode-or of these two.

Rgds

Damon

[DamonHD]

OK, now the output of my tiny turbine (with its crowbar over-voltage circuit) is plumbed into the input of my LiFePO4 battery.  Several things would have to go wrong at once for anything to get fried, I think.

I note that the blocking diodes I have in several places were warm with full sunshine pushing lots of juice into the batteries.  I'm well within their ratings though, in each case.

Rgds

Damon

[ghurd]

Off topic.
Can you measure the temps of the diodes wires near the body?
And what style are they?

Curious if the cathode is hotter.
G-

[DamonHD]

Maybe I *might* be able to do it if I stood out there with the junction box open to the elements but carefully shaded from direct sunshine.  But I'm not around for the next few days anyway...

I do have a simple probe thermometer.

The devices are axial, some P600A Si 6A but mainly Schottky 8A.

Maybe if you send me an email Thu night and I'll get my rear in gear on Friday if it's a sunny day?

Rgds

Damon

[DamonHD]

Sorry, G, forgot: might try again tomorrow or on Monday when I may need to open things up anyway...

BTW, the new battery is still playing nice.  The Schottky diode-or arrangement seems to be working fine, with the batteries sharing the load much of the time.

The Li battery's built-in BMS is doing the job of solar (and wind!) controller and I'm guessing that the lost efficiency from doing without MPPT is more than made up for by the better round-trip efficiency of Li chemistry...

Rgds

Damon

[DamonHD]

Another few days and another surprise: in good sunshine today
the voltage leapt from about 14.4V to 15.5V
when I'd expect the BMS to disconnect from its input (charge source) when full,
capping the output voltage at somewhere around 14V.
The battery was warm (not hot) to the touch as it was climbing past 15V.



I had to adjust the upper bound on the graph to 16V from 15V,
and I'll have to check that everything upstream of the DC-to-DC converter
whose maximum input voltage is 28V is good to something similar,
certainly over 16V which was nearly reached today
and also over the 21Voc of the UniSolar panel.
I may also have to move the small amorphous panel with a potentially higher Voc
back to the SLA string.

The cap on the input of the DC-to-DC converter is rated 25V.

[DamonHD]

So far it looks as if the output does not go above 15.5V, presumably while the battery is topping off, so that should be safe for most purposes, though the only item downstream of it at the moment is my 25V+ max DC-DC converter for my server.

I'll keep watching!

Rgds

Damon

[Bruce S]

Yes, I would be interested in a real-world round-trip efficiency test!  Wikipedia seems to be suggesting 70%--90%, ie between LA and Li.

Rgds

Damon

Damon;
While trying to play catch up on postings. I do not see the small post here for my findings of my NiCd bank.
I wonder if I ever hit the post button 

I took the numbers of input versus output and my math tells me I'm at about 82% eff.
This is coming from a setup that I'm sure less than desirable, as I don't have a fancy NiCd battery cutoff regime. I use HF panels and a ghurd dump-load controller to keep things on the up n up.
My big 12V bank is 10s12p setup the controller is set to begin dumping at 13.5V This gives me about 95% of a fully charged bank each 16Ahr bank has a dump controller on it. I did it this way as these originally were on the e-bike, before we went with the 14.4V setup for it.

Plus a watt's up meter for a "fuel" gauge.
Sorry for the wait.

Cheers
Bruce S
 

[DamonHD]

Hey, thanks for that!

80%+ is pretty respectable, eg I'm sure matches SLA in the real-world.

Rgds

Damon

[DamonHD]

After our very snowy weather of the last week or so my off-grid storage is nearly exhausted, even though I did [edited] clear most of its PV panels of snow, unlike my grid-tie stuff on the roof which has generated zero today and yesterday!

I'm deliberately going to let it run into the ground.  First the SLA should drop out c/o the LVD in the solar controller, then the LiFePO4 battery which is very very nearly empty should drop off rapidly.  I expect it to be disconnected by its BMS and my server to go off-line overnight.  (If not, a little sunshine is forecast for tomorrow.)  I am logging the voltage...

Rgds

Damon

PS. Even before I'd successfully posted that the SLA cut out and the LiFePO4 battery instantly gave up too and hasn't rebounded now that I've temporarily shifted the SheevaPlug to mains...

[TomW]

After our very snowy weather of the last week or so my off-grid storage is nearly exhausted, even though I could clear most of its PV of snow, unlike my grid-tie stuff on the roof which has generated zero today and yesterday!

Might be worthwhile to rig a couple windshield wipers from an auto to swipe the lower end of the higher ones.

Then just swipe them occasionally. Seems once a spot is clear the rest clears pretty easy? Here a wiper assembly would be cheap at the auto junkyard. One for a rear window be easiest to rig to a panel I think.

Just an idea

Tom