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Author Topic: Blasphemy..... Solar power.  (Read 148476 times)

AdeV

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Re: Blasphemy..... Solar power.
« Reply #195 on: November 19, 2017, 07:16:00 PM »
Quote
They certainly aren't ideal for off grid power use.

Certainly not as-is, if they're not doing per-cell management... but if you've got the electronical wizardry necessary (I haven't... but I do have a very clever friend I can ask who would be able to work it out), and you can modify the pack to do per-cell management, then you'd be able to rescue a cheap "dead" pack, quite possibly to near-original efficiency.

This used to be what killed laptop batteries off: The individual cells would drift out of sync, so when you charged them, the charger stopped when the most-charged cell reached capacity; but your battery would be "flat" when the least-charged cell discharged. Meanwhile, if the "most charged" cell still had 90% of its charge - tough! The battery was apparently flat. And charging the battery would only put (in this case) around 10% charge into the discharged cell before it stopped. Hence the "5 minute runtime" and the bad rep Lithium batteries got early in their lives. These days, all cells are individually monitored and charged, so laptop batteries don't degrade anything like how they used to. I do wonder, how many perfectly good LiIon or NiMH batteries got thrown away, just because they weren't being charged correctly?
Cheers!
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BruceM

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Re: Blasphemy..... Solar power.
« Reply #196 on: November 19, 2017, 08:22:26 PM »
I concur, AdeV.   Same thing happens with lead acid batteries, but there regular equalization charging (adding water and sacrificing positive plate life for the best cells) is typically used to compensate for the drift in charge rate of individual cells and groups of cells (batteries).

The AGMs in the early EV days were dying very quickly until battery management was developed to reduce it. They could not be equalized for long periods or the electrolyte got dried up.  The simple individual 12v battery shunt regulator (limiting individual battery voltage) as used by Manzanita Power saved the day and is the approach I used for my 120V bank. It works surprisingly well; the batteries become more and more matched over time instead of less, kicking to absorption and float stages within half a minute of each other and a bad battery can be replaced without concern for matching.  Watering just a bit over a gallon every 2nd year doesn't break my heart either.  On my neighbor's upgraded version, we found equalization charging to match individual cells within a battery (checked via hygrometer) can be virtually eliminated by a slight increase in float voltage, since the batteries are typically in float all afternoon.  His system bulk charges at a higher current than mine so we watched things closely the first year.

I think even in 48V wet lead banks battery life could be improved by individual battery management. Yes, it adds cost and complexity, but over time, the ongoing replacement cost of batteries is the biggest component of your power bill. I haven't seen it offered in any 48V system yet.




starfire

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Re: Blasphemy..... Solar power.
« Reply #197 on: November 20, 2017, 10:12:14 AM »
Interesting. I dont know for sure but this is what Im thinking.
Prius packs are packs of 7 volts that are seriesed to 210 volts or so.
The packs as received  are monitored at 1/3rd  sections, or at the 70 volt taps.
If they were  seriesed to two  x 15 paralleled, ie 14 volts x 15, to get a nominal 14 volts at  6.5ah X 15 = close to 100ah.
Monitoring parallel packs is easier than many  series cells, so runaway cells "should" be held down by the other paralleled cells.
By making two independent packs of 50ah, each can be alternatively 100 percent discharged so every charge cycle starts from a known start point.
As I understand it, they dont mind a hefty discharge cycle, but are fussy about charging.
If charging from a known low state of charge, then a simple watt hour meter will control /indicate a reasonable charge time.
If a fixed charge rate can be given, then a simple timer may be sufficient.
The charging can easily be kept below the 100 percent full without damaging the pack, or needing fancy charge controllers.
The encouraging thing with these, to get the equivqlent AH from lead acid requires  around 800ah to prevent excessively hard discharge cycling.
The size reduction and maintenance issues are also bloody enticing as well.
A low voltage detect will allow each bank to switch itself in and out when it needs to be charged.
Problems with inverters are likely as the bank voltage rises, if we have a "48 volt" system, the nearest pack voltage will be 7 volts X 8 cells = 56 volts, probably too high, or 7 volts X 6 cells = 42 volts, probably too low.
14 volts for a nominal 12 volt system is good, and the higher current drain suits these cells.
Thats my thinking anyway.
By using light intercell interconnections, a shorted cell will fuse itself automatically isolating itself from the bank.

BruceM

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Re: Blasphemy..... Solar power.
« Reply #198 on: November 20, 2017, 04:32:48 PM »
I did some reading on manzanitamicro.com about their lithium battery regulators. I was dead wrong about paralleling of lithium cells being a problem; since voltage and state of charge are directly linked for lithium cells (unlike lead acid) parallel cells can be managed together.  Alas, series lithium cells MUST be managed separately according to literature at manzanitamicro.com and other sources.  So it would seem there there is no way to avoid series cell management if long battery life is desired.  Prius switched to the battery they used late in the game and it pretty well proves that short cuts don't work; their early failure rate is commonly acknowledged.  They are only monitoring current and temperature in pairs of 7v modules and are not doing cell voltage limiting.

Manzanita's scheme for lithium batteries is similar to their lead-acid; shunt regulators with thermal feedback to the charger to have it cut back on charge current as shunting current (heat sink temp) gets higher.  So rate of charge is limited by amount of current handling of the shunt regulators, keeping the best cells from overcharging. They use on/off switching of a shunting mosfet and power resistor to limit the cell voltage.

Other regulator schemes use more elaborate means- using the shunted power through a switching power converter to help feed the other cells rather than dissipate it all as heat.  The trade off being much higher complexity, and a lot of EMI generated.

All together, the individual cell regulators, monitoring equipment and variable rate charger that manzanitamicro sells is a fairly complex system-  but with our present battery tech, it's the best approach to get good battery life.  Tesla does something similar, but I have not studied their design. I don't believe they would add the extra complexity and cost unless it was absolutely needed. 







« Last Edit: November 20, 2017, 04:37:43 PM by BruceM »

BruceM

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Re: Blasphemy..... Solar power.
« Reply #199 on: November 21, 2017, 12:42:49 AM »
I couldn't resist checking for information on Tesla's battery management scheme.  They don't provide any technical details but others have torn apart batteries to have a look and have reported their findings.  I had a couple hours entertainment searching for useful engineering info.

Their modules of cells use a TI battery management chip (bq76PL536A) which I could read the datasheet for.  It is stackable to 191 levels on the SPI bus and handles 6 series cells per chip. It has 6 dedicated outputs to drive N-ch mosfets with power resistors for cell balancing. It monitors voltages and temperatures so the main charge controller can adjust charge current, etc. 

A nice bunch of electronics to manage the Tesla batteries with their racks of small lithium cells, but they did it right.




starfire

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Re: Blasphemy..... Solar power.
« Reply #200 on: November 21, 2017, 03:36:32 AM »
I think the longer a series string becomes, the likelyhood of mismatched cells/charging increases.
With low voltage  parallel strings, the problem diminishes.... I think.
However, 1000 AH of lead acid runs to $3000 here in NZ to give the 20 percent depth of discharge of 200ah and maybe 5 years of useful life.
For the same price we can have the equivalent in Lithium cells that will do the same job, smaller with no maintenance, and even if the lifespan is similar, they still have these advantages anyway.
One faulty cell in a series string limits the whole battery to that what the faulty cell can provide, one faulty cell in a parallel config will reduce the AH by a paultry 6/7 ah, everything else remains the same., both current and voltage.
This allows the battery to be micromanaged, replacing faulty cells only, not the whole thing.
It would be uneconomic to have a hugely fancy and complex charge controller, but if one was not required, the economics are there and make more sense.
The likes of Prius/Tesla, they have to consider fast charging, regenerative braking power inputs, output currents, temperature etc, this may explain the complexity,  but with off grid stuff, its a simple known current in, known current out thing.
Thats why I thought to divide the bank into two, and charge one while using the other, overcharging seems to be the bain of these type of battery, and unlike lead acid, will not be damaged by full discharging, and partialy full charging... maybe to 75 percent only.
The electronics to detect low voltage and when to switch out a bank is trivial, as is a timer to control charging time. Both sytems can simply control an old fashioned low tech change over relay even via the ubiquitous 555 timer..

The internet seems confusing at times just what these batteries need, but for off grid use, I think it can be kept quite simple. Even if each paralleled pairs were seperately and manually monitored with a voltmeter once a month by having shorting links, battery health could be monitored initially to see how its working out.
If there were a constant degradation then it would need looking into, but chances are they would perform reasonably well.
Even a real time battery capacity test could be automagically computed by monitoring output watthours, then charging the same bank with an added 20 percent or so, whatever the charge/chemical efficiency is.
The best scenario is just to connect and forget.
My lead acids have a few years left yet, but I do think these Prius packs are worth a try.

starfire

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Re: Blasphemy..... Solar power.
« Reply #201 on: November 21, 2017, 04:13:29 AM »
And Bruce, thats a great bit of info you linked to, thanking you.
They appear to ground the center tap, and differentially compare the end voltages to detect battery malfunction.... the absolute voltages are ignored, only the difference will flag a battery error, this is a good way to do this. The charging/discharge current of 63 amps ( 63 x 210 = 13 kW) does give a very large total voltage change, but remember, this is  with all in  series .
The equivalent charge rate at the nominal 14 volts will be  well over  900 amps.... hardly likely in real life.
A 14 volt paralleled pack would change from approx 6.2 x 2 = 12.4 volts discharged to 8.2 X 2 = 16.4 volts during charging.... a tad high, but this would reduce at a lowered charging current.... most connected inverters would overvolt and shut down at this point.
By bank switching, this is not a problem however.
Its unclear if each module can be further disassembled to replace individual cells, but everything is possible.
The main cell failure mode seems to be shorted cells, or chemical degradation over time.
Looking at the figures, an off grid situation will baby these cells compared to what EVs demand from them.
Thats if I have interpreted the figures rightly.
As mentioned, shorted cells become increasingly manageable at low voltages and paralleled modules.

starfire

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Re: Blasphemy..... Solar power.
« Reply #202 on: November 21, 2017, 04:30:02 AM »
Another thing of interest is the cell leakage problem, where moisture can cause power leakage to ground or adjacent cells. This will not be an issue at lower voltages either.  As we go higher in a series chain, the voltage to ground increases, and smaller amounts of leakage will have a larger effect.
The mention that cells degrade faster as we get to the center of the pack, suggesting temperature damage, will also not be an issue with much less charging current.  However a high discharge current could still cause temperature differential.
My answer to this would be simply to immerse the whole thing in a container  of oil.
Again, Prius takes 63 amps from each cell. Off grid at say a 100 amp draw would take 100/15, or only 6 amps per cell, thats a huge difference, a factor of 10.

BruceM

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Re: Blasphemy..... Solar power.
« Reply #203 on: November 21, 2017, 04:38:06 AM »
I don't think lithium cell charge/discharge rate is the only issue, as most laptops charge at moderate currents and discharge slowly yet most have gone to per cell management.  It's the varying charge resistance and efficiency over time between cells.  Each cell must be kept within a range of voltages (high and low) for good lifespan, somehow. Since you are contemplating a very low voltage battery, with massively parallel 6 ah cells, it seems some cell balancing via simple fixed voltage shunt regulators would be a reasonable effort and expense.

Prius got mostly away with more limited cell management, so with some clever design you could too. I will eagerly await your report, Starfire. 





starfire

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Re: Blasphemy..... Solar power.
« Reply #204 on: November 21, 2017, 05:24:03 AM »
Tesla I think is largely a collection of existing technology with  some clever marketing. It uses nothing more than a large bank of laptop batteries, a powerful electric motor, and clever and visible  electronics, all packaged to appeal to the American love of horsepower and bling.
Even the exclusive price tag creates an elite ownership, and is not seen  as a disadvantage.
Prius on the other hand appeals to the commuter, the greenie, the average bloke wanting reliability and cost effective motoring at a good price. This meant a smaller electric motor and battery, and the petrol engine to compliment it.
More complex by far, and having far more innovation.
Not to belittle any of this, but at the end of the day we are really looking at nothing more than a laptop battery pack, an electric drill power pack, or anything similar, running an electric motor, just on a much bigger scale.
Economies of scale suggest that a Prius battery pack containing 38 modules of 6 X 1.2 volt 6.5 ah Lithium cells will be the cheapest and most convenient way to buy them in this quantity.
Looking on Allibaba,  I see these......

https://www.aliexpress.com/item/Big-promotion-100-PCS-many-of-the-original-18650-2600-mah-lithium-ion-rechargeable/32319166341.html?ws_ab_test=searchweb0_0,searchweb201602_5_10152_10065_10151_10344_10068_10345_10342_10547_10343_10340_10341_10548_10541_10562_10084_10083_10307_10175_10060_10155_10154_10539_10312_10059_10313_10314_10534_10533_100031_10103_10073_10594_10557_10596_10595_10142_10107,searchweb201603_1,ppcSwitch_5&btsid=d8063deb-3f6e-4745-9c80-e68c47d48db3&algo_expid=9f772f63-0e80-4d46-bbb8-59c3d938dbcf-23&algo_pvid=9f772f63-0e80-4d46-bbb8-59c3d938dbcf&rmStoreLevelAB=0

at 2600mAh, so we need to parallel 3 to get our 6.5 ah at 1.2 volts.
We then need  12 in series to get our 14 volts.
We then repeat this 15 times, to get our equivalent 100ah.
Thats 3 X 12 X 15 =  540 cells.
$400 for 100 cells, special promotion price, we are  gunna spend around $2400
Then we need to package them.
I dont know about you, but to connect 540 batteries together would drive me nuts, and take me hours to do.
Toyota have already done this for us......
Looking at it this way, they seem pretty good value.

Has Glort surfaced..... im getting a little concerned about him......???

BruceM

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Re: Blasphemy..... Solar power.
« Reply #205 on: November 21, 2017, 05:36:07 AM »
Prius gets mileage similar to many small economical diesel cars sold in Europe (but no offered in the US), but at many times the price. Hurray for greenwashing. Americans...well, what more can you say, we're notorious and infamous.

I'm standing in for Glort. I hope he's just on vacation.


starfire

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Re: Blasphemy..... Solar power.
« Reply #206 on: November 21, 2017, 05:53:08 AM »
Your messages are far too short to be a good Glort, but I appreciate you trying though.....

LowGear

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Re: Blasphemy..... Solar power.
« Reply #207 on: November 22, 2017, 05:36:59 PM »
I was diesel crazy a couple of years ago until I got used to the truck smelling - - - kinda sweet from fry oil.  Then I realized how much of the fuel was being ingested by my lungs.  Next thing I thought of was the day I washed the cream head liner in my Karmen Ghia.  It was actually white and the yellow crap streaming down the windows - YIKES!.  I was tobacco clean a month later but not free at least six months.  I had a chest X-ray 40 years later and the evaluation included some discussion about my smoking.  Flabbergasted; I was.  You might conclude Never Free From the Man.

I've never slowed down or changed routes for a Prius.  Buses and large trucks - Absolutely.

Amen starfire.  Nice introductory glort styled paragraph but your 5000 words short on the conclusion.  I hope my Greenie reply is with merit.  (Not a hidden ad for menthol cigarettes.)
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mikenash

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Re: Blasphemy..... Solar power.
« Reply #208 on: November 22, 2017, 11:11:31 PM »
FWIW if you go to Wellington (capital city of our small country) the CBD roads are clogged with Prius taxis.  You'll never see a "Kiwi" face driving them, they are all folks from the Indian subcontinent & neighbours like Afghanistan - Hard-working folks whose English and qualifications aren't good enough to get them a regular job and who are self-employed as a result.  I figure they kinda stick together, cos someone has been importing Priuses (is that the plural?) from Japan by the container-load.

BUT, here's the thing - they say they are all Gen11 models.  Not the Gen 1 and not the later ones.  Allegedly the battery packs on these models are the "goodies". 

Might just be gossip, or might be the Good Oil

Speaking of oil, is Glort dead?  I figure he'd have to be fairly seriously injuired to be silent?  Hope he's OK?

starfire

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Re: Blasphemy..... Solar power.
« Reply #209 on: November 22, 2017, 11:13:29 PM »
Well Lowgear, I gave up smoking as a teenager, started again a few years back. I was becoming concerned I may live too long and end up with Alzheimers, dementia, arthritis, or 100 other horrible age related diseases. The tobacco companies promise a timely and quick  death, heart attack or anurism....  I hope they are correct and I wont have to sue them for false and misleading advertising.