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brucedownunder2 Guru Joined: 14/09/2005 Location: AustraliaPosts: 1548
Posted: 01:25pm 27 Jul 2017
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There seems to be gathering interest in all things electric these days.
I have been here for a long time ,fiddling around with various electro/mechanical projects ,and have enjoyed this .
My recent thoughts now a centered on the batteries that EV,s have installed and are frequently showing up in vehicles smashed up in wrecking yards.
Can we discuss the merits of these batteries for home solar /wind battery installations-providing they are worth it?.
My system is 48volts and I,m wondering if these EV batteries are similar .
Are they large enough for the average house.?
What would the average pack require in watts solar per day to charge?
I f I see a pack or two at the wreckers , would you recommend I buy a couple _--- or are they completly unsuitable for household application.?
Safety,, given most of us are fairly experienced in safety practices ,are their any important safety issues to flag for home (experienced) diy,ers _ you don,t have to go into details pn this question if you feel uncomfortable ,I,ll understand.
So, thats about it for my most recent hair brain idea -what do you think ? A big "Hello" to Trev,by the way.
BruceBushboy
yahoo2 Guru Joined: 05/04/2011 Location: AustraliaPosts: 1166
Posted: 04:38pm 28 Jul 2017
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There is just not enough EV's in OZ to find a wreck locally.
There have been a couple of guys importing Nissan leaf packs from the US into QLD for exactly this application.
Break em down to module level and wire to 52 volts and do your own balancing and they work fine. I think it is cost effective. About 65% of the cost of new LFP and 30% of the cost of a fancy shiny Li-ion pack, but the lifetime is an unknown with a used battery pack, particularly those without liquid cooling (leaf packs) that have been run in hot climates.
Tesla battery packs are impossible to find and even if you do, the demand in the states is high enough that a seller will not bother with an overseas buyer.
A 100kw tesla pack will probably set you back $25K. with the old batteries that's 16 modules at roughly 26 volts and 6kwh per module. I cant say I haven't been tempted. It would probably last for 25+ years. I'm confused, no wait... maybe I'm not...
brucedownunder2 Guru Joined: 14/09/2005 Location: AustraliaPosts: 1548
Posted: 05:10pm 28 Jul 2017
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Thanks Yahoo.
I have a wrecking yard 20 k from here and he,s fairly good at letting guys with boots walk around and grab things.
Next door is a car wrecking yard also , so maybe I go have a look .
(I wonder if this post should be here or would it be better on another topic site) Glenn ,you can move it if you feel more will participate on a different site.
I still feel the EV car batteries will have a place in our backshed DIY area.
Thanks BruceBushboy
oztules Guru Joined: 26/07/2007 Location: AustraliaPosts: 1686
Posted: 05:17pm 28 Jul 2017
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I doubt if we will find too many running around the place, but they are batteries, and can be used. Some are pretty puny ( prius), and some very big like tesla, and chevy bolt......The leaf is in the <30kwh range... very useful size.
The BMS problem is easily done on stationery packs, and a variety of solutions are available for not much money.. it is easy now to control in the hundredths of volts range now.
Any can be used if you apply some imagination..... and now we can make our own high power inverters... any voltage will do.
........oztulesEdited by oztules 2017-07-30Village idiot...or... just another hack out of his depth
brucedownunder2 Guru Joined: 14/09/2005 Location: AustraliaPosts: 1548
Posted: 05:31pm 28 Jul 2017
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Yes, Oz,I was thinking along the lines of size actually . When I look at my battery bank and realize the space -and,, around the corner ,the power,s that be will require us to house these house batteries in a shed out the back away from the house,,,Betcha???.
watching a doco the other night ,the main battery bank was,I think, like hundreds of doubleA(AA) cells. So thats very compact and light to handle,another thing.
availability ,, not many around now , but a few years ,they could be everywhere.
BMS,, you smart guys on here seem to have a handle on that allready,from what I read .
Lets not forget Trev,up there in Mackay, he,s been fiddling around with these batteries for yonks now , and a smart guy .
Cheers
BruceBushboy
oztules Guru Joined: 26/07/2007 Location: AustraliaPosts: 1686
Posted: 06:31pm 28 Jul 2017
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Yes the tesla packs are over 7000 little 18650 cells the same as in your hand drill I think.
Mobile BMS is a little different to stationery... in as much as we have no limit on space and complexity or wiring problems.
This means the sky is the limit on how you may wind up using solar panels and transmission and charging units.
I can see in my mind how I would do it, and solve all the problems associated with cell balance and balanced string charging, but only on stationary packs, It would add too much stuff and complexity to mobile situations.
So I envisage $400- $500 for a 4-5kw charging system that would charge a nominal 48v bank. Input volts could be anywhere from 150-300vdc... and it is off the shelf parts.
I reread that and it looks like a tease... so I will flesh it out a bit if I may.
Currently there are oodles of very cheap pwm led drivers. Typically 30 dollars with free shipping for 60amps@5v or any other voltage and current combination that adds to 300 or whatever one your looking at.
They typically ( always ) use ka7500 pwm chips, which can be easily made to be any voltage you want and any current you need to be limited to.
They dont always do this off the shelf, as they are cheaply built, and sometimes they get the current limiting resistors wrong. I bought three that blew up in less then 30 seconds, as their upper current limit was set over 20 amps for a 7amp unit... an hour later they were all fixed and new resistors installed of the best value, and now they are bullet proof.
They can be set to very tight tolerance for voltage, and 4.2v will be in their preset range.... and you can limit the current with the resistor you choose internally, or a trim pot if you want.
The other thing that must be mentioned, is that you MUST open them up, and release the screw that makes the 5vneg grounded... most important, or they will all short each other out. Once they are floating above ground on their output only, they are safe to use.
This seems like the best way to assure perfect cell voltage control.. they each have their own voltage and current controlled charger... does not get better than that.
Now the input can be anything over 150v ( and less) directly on the input, as the AC was only going to be rectified anyway. The fluctuation voltages from the panels will cause some mayhem. but should mostly be controllable, with opto's into the 7500 op amps... this will solve the problem of load manipulation, where we can throttle all units at the same time to whatever the power coming in from the panels may be... a poor mans mppt in other words.
Anyway, if you can get some, we can make them work.
.......oztulesVillage idiot...or... just another hack out of his depth
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 03:06am 31 Jul 2017
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I looked at this a while back, and although EVs are still fairly few and far between in oZ, the auto wreckers, panel beaters and mechanics now have an on line system for locating second hand spare parts Australia wide.
If you wanted a left hand rear door from a very specific make model and year, there is an on line search system to tell you who in Australia might be stripping that exact vehicle. That should in theory also be able to find you an EV battery if you know exactly what you want.
The problem then arises of what to do with a 360 volt battery that might contain over a hundred rather small cells.
I am putting together a 100 volt system right now that uses thirty Winston 60Ah cells. The biggest hurdle has been building a really good battery management system for thirty cells. It all starts to become very large and complicated requiring thirty of everything, but its not impossible.
The other alternative is to break the battery up, and start connecting a bunch of these small cells in parallel to build a conventional 24v or 48v battery. That may work, but connecting what might be fairly old cells of unknown history in parallel might create some problems if the cells are not fairly well matched and even in capacity.
Its probably better to keep them in series and monitor every cell individually. That should give a much better idea of what is going on, and if any particular cell needs attention. Cheers, Tony.
Trev Guru Joined: 15/07/2006 Location: AustraliaPosts: 640
Posted: 12:29am 01 Aug 2017
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G'Day Bruce! Hope you are still having fun........yeh I know, its been a while.
I can't imagine there would be too many EV batteries around yet. I don't come across second hand Thundersky Winston's much. If I do they are snapped up very quickly.
Plenty of new Thundersky Winston batteries. The factory tell me I am Australia's number one importer / seller now, have been for many years.
The commercial car manufacturers use the small cylindrical cells, thousands of them. Some have the connectors spot welded on. Years ago some home EV converters got some and built there own spot welder to join these cells up. They blew up a lot of cells with the high local temperature setting them off. I think a lot of the newer cells have bolt on ends.
My view is that any pack should be parallel cells first (self - balance) then series connected. I see no sense in monitoring and balancing thousands of tiny cells all separately.
There is a big difference in the cell chemistries too. LFP or Lithium Iron Phosphate 4 (LiFePO4) and LYP or Lithium Iron Yttrium Phosphate 4 (LiFeYPO4) are the only safe chemistries. All other chemistries can burst into fire.
Cycle life of LFP is said to be 2000 - 3000 cycles and LYP is said to be 5000 - 7000 cycles. My first EV Hilux pack was LFP, 5 years in the EV and now 4 years on the house solar. They have done their time, but still have 50% capacity. Similar now to when I first put them on the house solar. The new LYP in the EV Hilux have done 4 years and still performing well. The LYP chemistry is much better than the LFP. I don't know of any commercial car manufacturer that use the LYP chemistry
I would think that if you could get a second hand lithium pack that is still ok, they should give reasonable service on a solar set up. The solar is very soft on them. In the EV Hilux, I can pull 1000A (thats not a typo, it is 1000A) on acceleration. Real funny listening to the V8's behind me.
So long story short....... a second hand pack may be worth considering for solar, but do look at what the chemistry is and how they connect together
Trev @ drivebynature.com
Revlac Guru Joined: 31/12/2016 Location: AustraliaPosts: 1020
Posted: 02:44am 01 Aug 2017
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Hi Bruce If you manage to find a set of those batteries (must be dirt cheap) they are worth the effort hooking them all up, having wired up some of those 18650 lithium batteries myself (all of them different ages 5-7 years old, used and abused) have about 260Ah all up, they have being running the house off grid for a year now no problems just check them once a week and do a balance up every 3 weeks as i have no BMS yet.
I see Trev Knows his stuff, the cells really stay cool when connected to solar
Cheers Aaron Cheers Aaron Off The Grid
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 12:10pm 01 Aug 2017
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Have to agree... The question then is what sort of final dc voltage might we be aiming for with our multi small cell composite battery ?
Higher voltages are definitely more efficient. From what I gather most off grid batteries around here on the Forum are probably most commonly 48v. But I see a future trend towards higher voltages.
That is not without its problems (and its dangers) but if the BMS problem can be overcome, I think it would be a definite step forward.
Trev seemed mystified when I ordered thirty 60Ah Winstons, but they pack very nicely 6x5 into a standard filing cabinet steel drawer. The nominal operating voltage is convenient too, always just a very few volts either side of 100v. Cheers, Tony.
Revlac Guru Joined: 31/12/2016 Location: AustraliaPosts: 1020
Posted: 03:30am 03 Aug 2017
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I think 100vdc is the next step up for +/-8kw or more and 3phase systems just makes sense, less need for heavy copper cable. Those winstons are in my opinion the best choice for high voltage, good insulation all round when compared to FLA batteries, they leak around the filler cap and the lugs (the old Telecom batteries did) I don't trust my 18650 type cells to run at a higher voltage than a 48volt system, the insulation is so thin at B+ end. I have my cells in a vented steel cabinet outside and out of the weather,need to build a new cabinet soon.
I don't earth my battery bank, no problems balancing and can touch any part of it without getting bitten. good idea or not?
Cheers AaronCheers Aaron Off The Grid
yahoo2 Guru Joined: 05/04/2011 Location: AustraliaPosts: 1166
Posted: 08:40pm 10 Aug 2017
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I totally agree, if someone is thinking about using EV modules the battery charge and temperature management needs to be foolproof it doesn't need to be fancy or complicated it just needs to cut the power when there is a problem so we can step in and fix it but it needs to do it reliably for 10-20 years, no mistakes.
It is actually the aluminium foil that burns, above a certain temperature it can scavenge oxygen from molecules close by and thermally runaway. There are a couple of versions of cells that have electrolytes that dont release oxygen, like the LFP chemistry.
In my opinion a used EV battery has to be a total bargain to be able to justify spending the time and effort installing it. The lithium iron phosphate cells are just such good financial value. I'm confused, no wait... maybe I'm not...
galderdi Regular Member Joined: 12/08/2016 Location: AustraliaPosts: 99
Posted: 08:38pm 04 Sep 2017
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As someone who has purchased an EV battery I can say that for the moment it's not the best direction for you. As previously mentioned there are not enough EVs in Aus. Whenever they are crashed the batteries are snapped up really quick. I have been keeping an eye out for over 12 months. I am even on a waiting list for a wrecker that seems to get more than anyone else.
EV batteries are highly regarded for converting a petrol car into an EV. The EV batteries provide higher discharge rates. This would not be necessary for your home storage project.
You might be better considering hybid batteries. There are many more of these on Aus roads thus increasing your chances of picking up a wrecked one. Their batteries are a different chemistry to the batteries in an EV. They don't handle the same discharge rates and therefore are not snapped up by EV guys like me. But they generally are lower capacity so you might need multiple of them depending on our target capacity.
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 09:14pm 04 Sep 2017
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I suppose it depends if you are building a real mobile EV, or just using salvaged EV cells for a home brew domestic off grid power system.
For off grid, both charge and discharge rates will be quite gentle, and I do not see battery temperature being a serious issue. In most parts of oZ our climate is fairly benign, especially for an indoor battery.
But still, where there are a very large number of smaller sized cells in series, the BMS needs to be the very best you can possibly do.
I am finding out the hard way that a BMS for thirty cells requires thirty (or sixty) of most things, and the cost of that certainly adds up. But I still think its worthwhile running at a higher dc voltage and much lower current.
The BMS in a high voltage system may be fairly large and complex, but the inverter is quite small, and the battery charger microscopic.Edited by Warpspeed 2017-09-06Cheers, Tony.
Notice. New forum software under development. It's going to miss a few functions and look a bit ugly for a while, but I'm working on it full time now as the old forum was too unstable. Couple days, all good. If you notice any issues, please contact me.
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