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Author Topic: Cobbled together PV in W.Sussex  (Read 142660 times)
Outtasight
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« Reply #180 on: January 08, 2011, 11:43:53 PM »

Well, I found a US supplier of the LiFePO3 Thunder Sky / Winston cells, and they also do the CALB (a Chinese aviation outfit) ones too.  The prices have really come down a lot!  These guys advertise their prices on a plain old web shop at a flat rate of $1.35 per Ah.  So a 200Ah 3.2V cell is $270.  That means a 4 cell, 12V nominal pack is only $1080 (about 696 at $1.55/ + shipping from China, duty & VAT).  

http://lithiumstorage.com/

When you consider that's the price for a battery that does 3000 cycles at 80% DoD, and can sit permanently at 20-80% partial charge level with no ill effect, it's a lot cheaper than the 320Ah gel lead acid cells you'd have to buy that are only good for 1000 cycles at 50% DoD.

Last time I asked, MK (Deka) quoted me 285 for 180Ah gel 6V blocks, so 570 for 12V.
« Last Edit: January 08, 2011, 11:52:28 PM by Outtasight » Logged

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EccentricAnomaly
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« Reply #181 on: January 09, 2011, 11:59:17 AM »

Do we know anybody who might be in to importing renewable energy kit suitable for DIYers from China?
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billi
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« Reply #182 on: January 09, 2011, 06:29:15 PM »

... one can compare it this way and that way ...


and i still have my reservations  about battery hype in the LiFePO3  direction

Might be  that i am conservative   but still i  hold my hand in lead acid  snow

Quote
So a 200Ah 3.2V cell is $270.  That means a 4 cell, 12V nominal pack is only $1080
@200 ah   whistlie

so about 5500 $ for a 1000 ah 12 volt Battery  Roll Eyes

 so still about 2.5 times more than the Rolls with similar  live cycles  ( or close )



  Will see 

Billi


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1.6 kw and 2.4 kw   PV array  , Outback MX 60 and FM80 charge controller  ,24 volt 1600 AH Battery ,6 Kw Victron inverter charger, 1.1 kw high head hydro turbine as a back up generator , 5 kw woodburner, 36 solar tubes with 360 l water tank, 1.6 kw  windturbine
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« Reply #183 on: January 12, 2011, 08:02:26 PM »

I'd like to see what Rolls say the curve looks like if you discharge their battery between 90% and 20% SoC over a week of partial discharge/charge deficit cycles; leave it bumping along at 20-30% with partial charge/discharge cycles for a week; charge it up over another week with partial charge/discharge cycles to an average 90% SoC and then repeat the three week cycle over and over.  That kind of behaviour usually counts as "wilful abuse" for a lead acid battery, that would invalidate the warranty, but constitutes "normal use" for a lithium one.

The optimised cycle life figure the makers quote assumes a single discharge cycle to 20% (or whatever DoD value) and immediate recharge to 100% in one shot.  Not realistic for a solar installation without a grid charger or diesel generator to hand. 

Solar off grid use never leaves the battery at 100% for any appreciable length of time.  Unless you put the battery on charge and then don't use it in the evenings (wackoold), it's going to spend the majority of every day at something less than 100% SoC.  In December it might not see full charge at all.  I had to leave my bank on charge with no load at all for 13 days in a row to get to full charge over Christmas and the New Year.

UPS batteries meet their manufacturers life expectancy because they sit for 24 hours a day at 100% SoC.  Lead acid batteries make perfect sense in this application. 

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« Reply #184 on: January 12, 2011, 08:20:56 PM »

... ok  accepted  , that the possibility to leave them partial discharged  over longer period is a big advantage  genuflect
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« Reply #185 on: January 12, 2011, 08:40:23 PM »

LoL... I'm not having a go at you.  Smiley  Just cheesed off with baby-sitting dodgy batteries.

Speaking of which... Back in dubious second hand battery-land...  We finally had a nice blue-sky day on Sunday and the bank lapped it up... 2.2kWh of DC power absorbed.  The balancing links are helping quite a bit; no suspicious gurgling noises or nasty smells from the end pair of Marathons.  Voltage readings for the whole pack of Marathons still aren't great though.  The lower half reading 14.0V and the top half reading 14.3V at the end of absorption.  I'm still of a mind to try and invent a block balancing circuit, using the same mini dump load technique as for lithium cells.  

I'd need to measure the differential Voltage between the upper and lower half of the bank and then selectively bypass some current through two resistors to nudge the halves to sit at an equal Voltage.  

I've seen a very expensive bank balancing gadget, but that's intended to keep a 24V truck battery pair in balance when you're doing silly things like running a bunch of 12V loads off of one of the batteries.  It uses switch mode tech to redistribute the charge from the high battery to the low one.

http://www.antares.co.uk/prod%20dc%20power%20equaliser.htm

My idea is to just dump charge from the high one so that the total bank Voltage is divided 50:50 between the halves to protect one half from under charge and the other from gassing.
« Last Edit: January 12, 2011, 08:47:14 PM by Outtasight » Logged

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« Reply #186 on: January 12, 2011, 10:15:18 PM »

After trawling around some makers of expensive, high power 12V tap equalisers, I found what looks like I want...  Just a battery balancer for charging control only.  Only 29 (less than 1/10th the price of the big ones but only supports balancing currents of 1A... probably enough for what I need).

http://www.rapidonline.com/netalogue/specs/18-0747.pdf
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« Reply #187 on: January 12, 2011, 10:52:56 PM »

Here's a somewhat droopy circuit of the sort I have in mind for that application.  Basically a MOSFET to control the dump for each battery controlled, via an opt-isolator (not strictly required for the 'bottom' one), from the output of a microprocessor.

Probably about the same price with more hassle but also more flexibility than the controller you reference if you only have two batteries.  Cheaper if you have, say, four 6 V packs.  Very easy to deal with more than an amp if you want.  Can go on the PWM outputs of the Arduino if that's what's used.  The Arduino could also do a certain amount of logging, reporting, over/under-voltage alarming and the like.

Obviously it'd also need sensing of the battery voltages which could be dealt with using some zeners and resistors on the analog inputs.


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« Reply #188 on: January 13, 2011, 08:23:13 PM »

Nice one.  I might look into arduino a bit more.  Looks useful.  The USB prototyping interface I'm using for my load manager thingy is similar in that it's got a couple of A/D inputs, digital inputs, digital outputs, D/A outputs and PWM outputs, but it's actually a dumb device that relies on being plugged into a PC that runs the software.  Ok for my application upstairs, as it's plugged into a machine that is on all the time anyway, but for this sort of low power programmable thingy, arduino would be great.  

As it happens, your post arrived just after I'd placed an order for two of the Rapid Electronics battery balancers, so that's that line of mad inventorism put on the back burner for a while.  Grin

I'll post more when I get the new widgets.  I ordered two, as I've got my battery bank in two halves (the gel one and the AGM one).  That and they had free postage if you bought two Roll Eyes

Quote from the movie, 'Contact' - "First rule of government spending: Why buy one when you can have two at twice the price."   facepalm
« Last Edit: January 13, 2011, 08:25:04 PM by Outtasight » Logged

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« Reply #189 on: January 15, 2011, 06:33:17 PM »

Bit of a retro post this one... 

Back in October, some guys turned up out of the blue, and chopped down the dead fir trees in the garden of one of the houses that back on to the garage courtyard.  Fascinating watching them take the trees down, a chunk at a time, over two days; most of it went into a giant petrol shredder.  Only the biggest sections of log were taken away whole. 

Helped me a bit in the Winter, as the low Sun used to be blocked from shining on the garage by those trees.

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« Reply #190 on: January 28, 2011, 02:11:22 PM »

Well blow me down.  The CamdenBoss battery equaliser turned up today (only one mind... the other is still being made by elves somewhere) and it does exactly what it says on the tin.

I didn't even have to cut off the ring terminals, as the holes where the right size to go on the Marathon battery post bolts.  Just a quick phone call to them to ask if there was any specific order that the thing should be wired up in (some old designs could blow up if you wired them up correctly but in the wrong sequence of terminals).  

And away it went...  Being sunny today, the bank has been charging hard (55 Amps at times).  By the time I'd got the wee beastie on the battery, it was still pulling 11A at the absorption point with a variance of about 0.1V for the upper and lower halves.  This is better than it had been, as I have the inter-string balancing connectors between the mid points of the 3 strings of Marathon batteries, but still not ideal.  With the battery equaliser in the circuit, the bank came into almost perfect balance, just 0.02V between the halves.  The little heat sink on the thingy got slightly warm but not hot.

It doesn't matter now that the equaliser is on just one battery string because they have the commoning links between the mid points, so over time the equaliser will tend to equalise the entire parallel pack.  As it's only shunting a maximum of 1A, there'll be negligable Voltage drop across the 6mm2 equalising bus.

Just need the other one to turn up in the post so I can fit it to the other battery bank.

I was looking at LiFeYPO4 batteries again...  found a european distributor for the Chinese ThunderSky large cells.  

http://www.ev-power.eu/index.php?p=p_33&sName=home

They also do 90Ah 12V lithium monoblocks without a BMS.  Supposedly the internal cells are now so well balanced (through just cell matching quality control) that for lowish power applications you don't need a BMS (provided that you only use one 12V block by itself).  Of course, with my 12V monoblock balancer, I could, in theory, use two such monoblocks in series for 24V without anything bad happening.  They also sell a more sophisticated BMS system to equalise 12V monoblocks, but with over Voltage and under Voltage relay triggers as well, to protect the battery from uncontrolled charge / load.  But I already have solar chargers that can do this and the main load, the inverter, has a LVD trip built into.

I have all the sub-components necessary to start playing with expensive Lithium batteries Roll Eyes.



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« Last Edit: January 28, 2011, 02:15:20 PM by Outtasight » Logged

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« Reply #191 on: January 28, 2011, 06:45:49 PM »

There was something in the specifications of these little balancers that I didn't appreciate.  It's that they only work at 12.8V and above.  So they only become active when you're charging the battery bank.  Below that charge Voltage (or when just discharging the bank) the balancer doesn't do anything.  I connected a 60W bulb to one half of the bank and it caused that half to drop in Voltage. 

The high power balancers actually will shunt power from one half to the other when discharging as well as charging, so you can run 12V kit from one half of a 24V bank.  But then those balancers cost 10x as much...
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« Reply #192 on: February 08, 2011, 01:26:41 AM »

Still playing with my bike generator  Grin

 

Actually this is it running with a car alternator but it was too hard work as you have to waste a huge amount of power to energise the thing and it has a high cut-in speed (not good when the size of the alternator pulley meant the gearing was only 14:1).

I've been running this thing with a 16 pole DC washing machine motor configured with the stator and rotor connected in series.  It's not even a permanent magnet motor but the series winding plus a tiny bit of residual flux in the core is enough for the thing to self-excite and make about 4A at 12V (actually lots more volts as I've blown up a bunch of 21W brake light bulbs that I was using as current limiters in series with the car battery.

 

The bike was a 5 car boot find and was ideal as it had a big fly wheel with a smooth edge for the original friction band.  I just replaced the friction band with a ribbed drive belt and lashed up the motor on some wood.

The washing machine motor cost me 50p at another car boot sale and the power comes from the rotor that is series connected to the stator coil.  As it has 16 poles and DC commutator brushes, I don't need to rectify the output.  When using the battery, it needs a diode to stop it from spinning backwards (motoring) and I had to rig a bulb and a press switch to get the thing to self-excite before it could make 12V and so start charging the battery.  Without a battery in the circuit, it can light any light bulb straight off, without the "starter circuit".  The washing machine motor also had a much smaller pulley on it so the gearing increased to about 30:1 so I can pedal at a comfortable pace.



The beauty of this arrangement is that all generated current is used to both reinforce the field AND charge the battery / power the load.  The washing machine motor makes use of a tiny residual flux in the core that induces a tiny current in the field coils when you first spin the rotor that flows through the load which flows through the field coil and rotor, making a bigger field current that flows through the load and back through the rotor that makes a very big field current... and so on.

I got to thinking that I wanted to use the bike again and make some proper use of the power.  The problem was that the feedback of series wound generators makes it very efficient, but uncontrollable.  It gets suddenly very hard to pedal and can produce enormous Voltage spikes that would kill lots of expensive things.

So I started playing with using a battery to power the field windings, and that way have a fixed strength field that gives a linear output with speed.  At first I tried a spare 12V battery, but the field winding is only 1.8 Ohms, so I had to use 20W bulbs in series to reduce the current.  This wastes a lot of battery power in the bulbs but it did give me the range of current that I needed.  The house battery is 24V, so I needed quite a lot of field current to get the generator to output that Voltage and make some Amps, without having to pedal too fast.  About 3.5 to 4 Amps is ideal.  If I pedal too fast, the open circuit Voltage can shoot up to about 80V.  I almost blew up a 50V 1000uF capacitor that I'd put on the output to smooth any spikes from the commutator Roll Eyes

Then I took a NiCd battery pack from a busted drill and dissected it, stringing out 6 cells on a bit of wood, to give me 7.2V.  That gives me the required 4 Amps without needing any current limiting bulbs or nonsense like that.  The NiCds can charge from a spare solar panel in the day, so the field current is "free".  The cells are a bit manky and old but seem to work, and NiCd cells don't mind being run flat.  I included a 5A breaker as a way to turn the field coil on and off and also for safety.  I got about 8 minutes of pedalling before they died, but I hadn't charged them fully before playing with them so maybe they'll do better after a long slow charge. 

The bike generator is wired into a spur on one of the existing solar panel strings, feeding the Tristar MPPT controller.  This controller is safe up to 150V DC on the input, so it should be ok with the bike. 

I was a bit worried about how the MPPT algorithm would behave with a bike generator, but it actually seems ok.  During the day, the solar panels are making some juice and tend to level out the Voltage, so the MPPT tracks them rather than the much weaker bike source.  I could pedal all I liked, and the DC PV bus just sat at 33V.  Having it use the MPPT control also means that the bike generator can work at the higher Voltage and so line losses are lower but the battery still gets the extra Amps at 24-25V.

I then tried it at night.  To my surprise, it still worked pretty well.  The MPPT sort of settled for 28V to 33V most of the time, although for a while it went up to about 45V.  It didn't hunt too much, and the Tristar has a very fast sweep scan so the motor was only unloaded for a fraction of a second each time.  With the field current set up for a comfortable RPM and load, I wasn't applying so much torque that the motor would over-rev when a scan took place.  It felt like the bike was changing gears on an automatic gearbox Smiley.  Looking at the power trace from the MSView logger, it seemed to make a steady 60W into the house battery.  Result!

Now I just need the NiCd pack to hold out longer and for my legs to hold out too.  Roll Eyes


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« Reply #193 on: February 10, 2011, 03:29:50 PM »

Outta
great work! Have a virtual applaud!
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« Reply #194 on: February 11, 2011, 12:45:11 AM »

Thanks!  

It's working quite well now.  After a few cycles (no pun intended) with slow 8 hour recharges, the NiCd pack is behaving itself better. The cells seem balanced now and none end up being zero Volts at the end of a cycle (pun intended)  Grin

I was doing the weekly shop and noticed this 3m in car power extension.  It has a in-line socket and plug with a switch, LED, and a 10A fuse.  Perfect, I thought... Cut it in half and make it into a battery connector, field coil switch, and battery indicator.

The wire was long enough to just tie the plug to the bike handle bar, and then I can take the battery into the garage, plug it in and turn it on.  No more messing around with chocblocks.

I also bought a 100V 1000uF capacitor to replace the 50V one that almost exploded and improved the smoothing circuit to make an "electronic flywheel".

With the capacitor just connected to the rotor winding, on power dips, the capacitor would actually try to discharge through the rotor winding rather than towards the battery.  With an extra diode before it, the peaks are smoothed and charge is pumped only in the direction of the battery.  I could have just put the capacitor on the left hand side of one diode, but then that would put PV Voltage always across it and risk a serious short circuit hazard if its insulation failed or just might make the MPPT tracking sweep go weird (or something equally unpredictable).


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