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Author Topic: Battery as a dump load  (Read 6953 times)
billi
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« Reply #15 on: January 16, 2011, 07:39:35 PM »

Quote
Depends on the capacity of both your battery banks and the difference in the level of charge, also the type of battery.  But its more than likely to do damage, either damage the wiring due to over current or your batteries due to over charging/discharging.  A high charge or discharge will damage plates in wet batteries

sorry just went for a pint and remembered my intention  Grin

So if we compare two batteries   with two ponds ( had only 2.5 pints  Wink )  the main pond fed with max  2000 watt  the second  pond/battery  connected to the main  one ,

 the main pond starts to be full at 29 volt  but flow rate is  still  1800  watt to grant the 29 volt for full charge , so 200 watt has to go  , in a PV setup  its just wasted before the pond overflows to the second pond

If we allow a relay to open a valve to let the water /watt flow to the second pond , that then would mean the second battery would get a decent (perhaps too much ) of a charge for a very short while  simultaneously  the water-level (volt) of the first pond  will/would drop , but the chargcontrollers destination is to keep 29 volt for say 4 hours , so himself as the gate master  Grin  will open the gate as often as needed to let the first pond overflow , but take care that the upper battery/pond stays charged  and he (a Solid State Relay) can  do that as often as needed  10 times per hour (depending how much flow into the first battery ) 50 times per hour or each second  if needed , just to keep the voltage level in the first battery at 29 V  , so ingeneral i guess its just the surplus watts  of the 2000 watt inflow that is passed through to the second battery
So there will not be an enormous dam  brake between the two ponds to overcharge

Sure the second pond needs a dump , but  there are so many things one can do  cheaply with AC voltage  combined with a cheap inverter that can start dumping via a relay at a certain voltage  , instead of looking around for expensive DC gear   .... and the main Battery/pond  stays in good performance

Where is the Whisky now   and the hat

Billi
« Last Edit: January 16, 2011, 07:41:52 PM by billi » Logged

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
EccentricAnomaly
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« Reply #16 on: January 16, 2011, 08:06:49 PM »

Billi would need a fair few of them to use as a dump load for his 1600watt turbine.

Like 750 worth for the second hand laptop packs for just one hours worth of dumping or 1.6kWh.

Billi's a bright chap, though.  He's not likely to let his main bank fill completely then try to divert everything to the second bank (at least if he hasn't had too many pints).

OK, I know the following numbers are highly biased but they do show that the costs of alternatives to lead-acid aren't completely out of the ball-park.

Outasight's NiCd packs: 12 V 4.5 Ah = 54 Wh.  25 so about 0.47/Wh.

Rolls Solar 4000 12 V 106 Ah = 1272 Wh.  But you only want to discharge them to, say, 20% DOD so 255 Wh usable capacity.  133.05 from Wind and Sun so 0.52/Wh.
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Justme
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« Reply #17 on: January 16, 2011, 09:10:50 PM »

But you are comparing new prices with second hand prices, not exactly cricket.
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biff
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« Reply #18 on: January 16, 2011, 09:47:48 PM »

hi billi,
      have you a little still going down there ?. i hear they brew exellent moonshine down there in kerry,problem is,,,it can overexcite the dump load after a hefty charge and leave you shouting for your brown trousers,,, sh*tfan hysteria hysteria
                              biff
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billi
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« Reply #19 on: January 16, 2011, 10:02:41 PM »

 Grin   problem is all the gear is AC and the moonshine is not enough for the pv  to produce   some  high percentage  juice
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EccentricAnomaly
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« Reply #20 on: January 16, 2011, 11:26:19 PM »

...not exactly cricket.

Indeed, hence "highly biased".

New LiFePO3.  $1.35/Ah.  Probably 1.35/Ah after shipping, import duties, VAT, etc.  At 3.2 V that's 0.42/Wh.

Lead-acid only looks so cheap because the actual usable capacity is usually grossly overstated.  Perhaps somebody ought to call trading standards.
« Last Edit: January 16, 2011, 11:28:15 PM by EccentricAnomaly » Logged
Outtasight
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« Reply #21 on: January 16, 2011, 11:43:03 PM »

But you are comparing new prices with second hand prices, not exactly cricket.

Believe it or not, the 25 NiMH packs are new.  I bought a new one for the old laptop.  It was actually way better than the original Toshiba spec. pack which was only 2.6Ah.  I remembered the capacity a bit wrongly; just checked and it's only 4.0Ah.  

They've gone up a bit in price since last year but you can still get them for 30.85.

http://www.laptopbatterypack.co.uk/cheap.php/Laptop-Battery/TOSHIBA/PA2429U.html

Just checked Rapid Electronics and they're doing Ansmann 10Ah NiMH D cells for 20.34 for twin packs (101.70 for a 10Ah 12V pack), but the laptop pack is cheaper per 12V Ah (7.71 against 10.17).  And the laptop packs come in handy rectangular bricks that are pre-wired with thermistors and exposed gold pads on the edge.  You could easily solder wires on to the pads directly to make up series / parallel packs.  You don't need any clever cell balancing gubbins either because NiMH is intrinsically safer than Lithium.

I'm digressing a bit from the original question here though.  I'm not suggesting that such small packs would be useful as a dump load but just that you could use them as a secondary low power store of solar power that you can run small inverter loads from to spare cranking up the big beastie.  

A certain oil company owns the patent on NiMH cells, which is why there are no large format NiMH cells produced (Toyota and Panasonic were forced to close down the production line they'd built) but the patent expires in 2015, so we'll be free to have them again.  There's a good video on YouTube about a guy with one of the few full EV Toyota RAV4 cars that were sold before Toyota were ordered to shut down their battery factory for infringing the patent.  Laptop makers and AA cell makers were exempted from the patent and Toyota had to resort to building a hybrid (the Prius) because the patent only allowed them to make small NiMH cells that couldn't be used for an EV.  

This car was on sale (well, leased) in 1997.  They had a mini SUV with a 95Ah 288V (24x 12V) pack that could do 80-120 miles per charge... It didn't need a cray supercomputer to keep the cells in balance (it had passive balancing for goodness sake!).  The oil companies didn't like it, so they bought the patent on the NiMH technology and killed it.  Practically criminal.

If you extrapolated that the Toshiba laptop pack has increased in capacity for the same size by 1.538x in the same time frame, then the Toyota EV today would have a 146Ah pack in the same size and be able to drive at least 123-184 miles today.
« Last Edit: January 16, 2011, 11:55:48 PM by Outtasight » Logged

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« Reply #22 on: January 20, 2011, 01:07:39 PM »

A general word to battery selection in my opinion is  , while battery technology improves perhaps  but in parallel prices for PV drop a lot

So why should one buy a much more expensive battery  and dump his money there , instead of saving part of that cash to buy more PV ?

If whe look again at the prices of the LiFePO3   and  take
Quote
$1.35/Ah
as a price guide  for a 3.2 volt battery  = 1080 Dollar for a 200 ah 12 volt pack  say   or  5000 dollar  for a 1000 ah  (import delivery and Vat  i guess 5000 Euro  then )

That is then about 3300 Euro more compared  to an of the shelf  new forklift battery  in that size

3300 euro buy me a 2000 watt PV then for free  Grin 
With PV prices down  so much i would rather oversize the spendings on PV than on battery

Billi

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EccentricAnomaly
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« Reply #23 on: January 20, 2011, 01:39:40 PM »

That is then about 3300 Euro more compared  to an of the shelf  new forklift battery  in that size

Yes, but you can only actually use about 200 Ah of your 1000 Ah forklift battery.  You need to compare the price of 200 Ah of LiFePO4 vs the price of 1000 Ah of forklift batteries.

Also, when you have a run of dark days you don't have to sit and fret about your LiFePO4 batteries sulphating or worry, until the run gets very long, about starting up your nice reliable (?) generator.
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Justme
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« Reply #24 on: January 20, 2011, 01:56:34 PM »



Yes, but you can only actually use about 200 Ah of your 1000 Ah forklift battery. 

Rubbish.

Even going on the more normal 50% rule for normal sized deep cycle bats you are way out & for forklift cells you can use 80% without too much loss of life. We keep to 50% SOC/DOD on ours. Most forklift drivers will drive them till they stop  due to system shut down on low volts.

You do have a point about the sulphating. But the 3K saving buys a lot of fuel for the genny at 50p per litre.
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billi
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« Reply #25 on: January 20, 2011, 02:02:15 PM »

LiFePO4 batteries are then charged by the mighty hand of god i suppose  overnight
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clivejo
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« Reply #26 on: January 20, 2011, 04:29:07 PM »

LiFePO4 batteries are then charged by the mighty hand of god i suppose  overnight


I want some of these batteries!
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DaveSnafu
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« Reply #27 on: January 20, 2011, 07:47:12 PM »

Theres another factor that needs to be considered, 1200 will buy you a new 1100ah forklift battery, it,ll weigh somewhere near 500kg, it,ll last for many years, and batterys are 400 a ton at the minute, so in 5-6 years you will get 200 back in scrap, lead is not gonna go down in price.
Our batterys were second hand forklift batteries 375, we bought them 5 years ago, yes they are bumblebeed now but whatever you put in they give you back, we have run them down to 22v many times, these days in frost they are usually flat in a couple of days.
Time for another set, trouble is we can,t afford new ones, and all the ones on ebay that I have seen have all been through the same hard winter as us.
Its a toughie, but the batteries are working for us not the other way round, they won,t last for ever no matter what you do, if they last 5-6 years from new its just 200-250 a year.
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