Batteries and New Battery Technologies

What I mean is, is there a vast difference in making the batteries imballanced by charging batteries in series or parallel.i.e.

I could charge 8 or 40 batteries in series at 1C. If any of the batteries have reached 3.60 Volt, I could switch off. Assuming that LiFePO4 batteries will not be affected by charging 98% each time. Anybody else who has read something about this??

OR

I could charge all 40 batteries parallel with 40 diodes and ensure that the total current is approx. 40 x 1C. Will have a relay contact in each line and as soon any of the battery's temperature is risen to a particular level, I switch that particular battery off, by cutting the supply voltage to that particular battery.

I am a slow grasper. What does it actual do, in having sometimes small voltage differences. Reduce lifetime by 20%, 5% ??? after charging and discharging 1000 times. I could not care if that is the case. I will be 100 years by that time. Or does it mean, after 10 x charging / discharging one of the batteries will pack up, yes in that case I have to be very carefull.

Thanks Porta for the inputs, but come on guys I spent all that money, give me some input. Even if you guess.
Bert

 

I don't know why, but everyone seems to suggest that batteries charged in parallel is a no-no, and in rural power systems - the trend seems to be in large single cell, (2V), units of the desired "Amp Hour rating" and set these in series to attain the operating voltage of your base system, thereby the Watt hours (or Kilawatt hours?) desired / available - - usually sufficient for 3 to 4 days if limited by PV charging only... The remote domestic power systems I have seen are either 24 or the bigger being of 48 volt battery banks systems driving a large inverter to deliver 220~240V AC domestic power services...

I even saw one of 20 large wet cell lead acid 12V truck batteries wired in series for 240V DC then directly inverted to AC without using a transformer - Disconnecting the batteries whilst still live-wired could have been dam dangerous... but it worked.....

This is of course a different ball game but all the professionally installed and reliable systems that I have seen (not very many - about a dozen), seem to use quite large single cells in series and never in parallel.... I can only guess that this relates to a variability in current through individual cells of the batteries, and perhaps to avoid "fatal" consequences of overload in unexpected paths, whereas in series a dud or shorted cell can be detected without critical overload? - - - - I am no expert, just throwing ideas around...

I am only talking of lead acid wet type cells... All this new stuff is in the realms of "black magic" for me...

In summary, I guess the thing I am suggesting is that, in parallel, a shorting battery can be catastrophic in consequences, in series, problems can be identified and failures may not be quite so devastating???

How about a little circuit self powered by each cell that sends into a "canbus" a signal identifying the battery and its voltage drop across the + & - terminal, would that data be sufficient to assess the condition of that cell knowing the total voltage across the total bank at either end and the total current input or drain... a simple control system could alert of status via the "canbus" lighting either a red or green led of the status of the individual cell... When the system is open circuit (not being used), these little monitors would be switched off...

Then it would be a matter of 'open-circuit the system', replace the 'bad' battery and back to business... The "monitor circuit could be permanently located attached to the cell container

 

I loved your thread. I am also not an expert on LiFEPO4 batteries and need to find my way by falling and standing up again. One thing is for sure. They are flipping expensive and it seem very "femenine" i.e. you need to be carefull.

But, the 40 Lithium batteries I have here, seems to be well made . If you do want to charge your batteries in parallel, one could do that, provided you use either big 20 - 100 Amp diodes with a small resistor in series to allow each battery to charge in its own rithme.

But for me, the new technology is also a large grey issue. But together we will come right.

 

Porta

 

LiFePO4

Thank you Porta,

Much obliged for the clear explanations. many other readers will benifit from the answers you have given. It will make my life much more difficult to come up with a simple algorithm and BMS system. But that makes life more interesting.
Thanks
bert

 

Yes, indeed if you have batteries parallel and one battery has gone bad, it will be fed by all the others and will destroy the bad one even faster. Therefore, whenever you can, use shotky diodes to seperate bateries from each other when connected parallel.

let me think about it, how it can be made simple. Cost will rocket !! and that with the already expensive Lithium batteries on its own, becomes no longer a proposition.

Your 4 inexpensive wet Lead Acid Batteries in a good casing which has low maintenance facility, are only costing about 120 - 140 USA dollar here for 80 Amperehour / 12 Volt. (deepcharging) For you, still the best solution for the time being.
Refer: http://www.battery.co.za go to leisure section

 

200 Amp / 72 Volt Lithium battery

Hi Rick, check this one out. They do supply the BMS also

http://www.alibaba.com/product-gs/239967283/72v_200ah_LiFePo_battery.html

 

Bert
That is more capacity than I want but looks good. I would like to know what A 48V battery of similar capacity costs.

Also they do not give a weight - or I could not find it.

Rick W

 

Rick , I assume quite some dollars. But that English Gentleman who flew to China refer Thread 675 , PBW was going to give some feed back. Maybe he is prepared to highlight cost for the bigger power packs. He, himself need 20 - 30 Kwh packs for his production. (I quite liked his twin motor setup on his website, go to FE 23 Elektra and go to photo 117) He was also investigating this balacing trick, what was proposed by the manufacturer. If it does not harm his competitiveness, maybe he could tell us where to buy single large powerpacks . Most of the suppliers wants 50 to 100 off. This is not in our league.
Bert

p.s. Rick I will ask that question to the company who sold me those 40 LiFePO4.

 

I went to the manufacturers site. It is 168Kg (they state 168000 gram) If we take 40 x 168gram = USA$ 240.00 If 500 was bought. (I paid USA$ 7.50 each for 40) we can then conclude about USA $ 6000.00 + transport cost. Seafreight is the cheapest, Postal service is a no go (dangerous goods) and Airfreight only via DHL, FEDEX, TNT etc at a premium price. (I paid 245 USA$ )

Rick if we calculate the same for 48 Volt 48/72 x 6000 = USA$ 4000 weight then 112Kg
Bert

 

Nice picture in post 768 Bert.
They look like 10.000uF/63V caps.

 

Yes, but 10.000 uF are a lot cheaper and has slugs on them. I felt sorry for the girl who processed my order, maybe her translation program did not worked that well, but she supplied them flat at the top and now I am battling to make them contact between 2 batteries. The sleeving prevent to make contact and I don't want to remove the sleeving. CDK, now I am able to utilize my conductive glue. I will use a Rand 0.10 coin for that.

 

Thanks Bert. I will take a look when I have more time to see if they are offering a 48V battery. This is a common voltage for EV so you would think so.

Rick

 

Lithium Fe

Hi Porta,

I was in the dolldrums and felt low like hell. Here I spent all that lovely money and I understood the BMS will be so tricky, that one should not attempt to use it on a boat.

Untill suddenly, I come accross an article, whereby it is stated:

Commentary: It looks like the magic number is around 3.8 volts. Below that you don't have significant charging, above that you do. A lithium ion battery doesn't care if it is never fully charged, so if all you have available is 3.8 volts and you don't mind the loss in capacity you could use the 3.8 volts. Unfortunately, the supply voltage is probably 3.3 volts in this modern digital age, which won't work at all.

And that was excactly what I was intended to do. charging to 95 -98% and forget the tricky part. Make it simple and it works. I personnaly think that the chemical engineers like to get 100% by balancing , while I am satisfied with 90% and out of balance. Again time will learn

http://www.powerstream.com/li.htm


Click on the purple part and get the curves up on your screen, refer to commentary.

 

Thin Ceramic Membrane Sodium/Sulphur Battery Tech

I was just trying to reference this article to a gentleman and found it had been taken down...so here is a copy of that article in case some missed it:

Thin Ceramic Membrane Sodium/Sulphur Battery Tech

...While this type battery may not be applicable to boats, it is an interesting new technology that demonstrates the diversity of projects being worked on in this country at the time. And it represents the idea of storing electrical energy for later use, be it gotten from several different sources.

Power Shift: New battery could change world, one house at a time
http://www.yachtforums.com/forums/technical-discussion/8826-batteries-new-battery-technologies-5.html