PINNED - Lithium battery conversion/info

[woodygb]

Here's a pic using your notations.

I've shown just ONE horizontal bus bar joining each 6 cell battery ..... you could add more ... as many as an additional 5 .... shown as purple bus bars @ the far right of the pic.

BUT only add them .... in a ladder .... to the ones I have drawn in the left of the pic.

PACK8.png (149.94 KiB) Viewed 13794 times

[cdb0ewm]

Thank you for the feedback. Is there a clearer picture available that is less confusing

[woodygb]

Does this single row make sense?

single row.png (39.85 KiB) Viewed 13792 times

[cdb0ewm]

Absolutely...thank you for sharing

[woodygb]

Then you need to think of each vertical stack of 6 cells as ONE SINGLE CELL.

single row column.png (73.04 KiB) Viewed 13791 times

[cdb0ewm]

One last question
What is the purpose of the additional purple busbars and why only on the 'B' side

[woodygb]

One last question
What is the purpose of the additional purple busbars and why only on the 'B' side

The additional bus bars are optional ... depending on current draw from your pack ... I'd probably add at least one more.

I could only bothered to draw one set of bus bars....I've added them in this pic of " 3" super cells ... remember ... ONE column of six cells = A Super cell .

busbars.png (26.69 KiB) Viewed 13786 times

[Burgerman]

http://scriptasylum.com/rc_speed/lipo.html

Theres a site here that tries to prevent blown chargers and burned down houses!

[woodygb]

Whoops! ... missed drawing in one of the optional bus bar ...but you should get the idea.

I'd probably go for two connecting bus bars per paired column.

[Burgerman]

http://www.wheelchairdriver.com/BM-MK3- ... rchair.htm

Scroll...

[BounderGimp]

I find the wiring diagrams for the battery pack confusing. Would it be possible instead to just draw a circuit digram for the pack using the schematic symbol for a battery cell, showing all individual cells wired correctly for parrell/series connections? It would be a very basic two dimensional schematic which would eliminate all questions as just what is connected to what.

[woodygb]

Is this drawing of a 7 cell pack ... 6 cells per column = ONE CELL .... less confusing ?

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[Burgerman]

http://scriptasylum.com/rc_speed/lipo.html

On here you can choose cell count, and parallel count, show balance wires or not etc in super simple graphics.

[Burgerman]

It just occurred that because of the exchange rate at 1.70 dollars to the pound, approx. that it will be costing those in the US about 70 percent more to buy lithium cells. Since they all originate in china.

[cdb0ewm]

Ok ... thanks to input from you and Woody, along with his review, here's my battery pack wiring with the balancing connectors.

[Burgerman]

Yes.



Its easier to do it than draw it because you can physically see what is connected to what.

[shirley_hkg]

Found 2 cells and they are really a bargain.

42110 --- 11Ah --- IR 4-6 mohm --- @ $4.5 US
38106 --- -8Ah --- IR 9-11 mohm -- @ $3.2 US

[Burgerman]

That would be true, if they are what they claim. Cheap cells from china tend to be anything but!

[ex-Gooserider]

The other problem with those cells (possibly solvable, but not easily) is that they have plain terminals - not the threaded ends like the Headways. This will make getting a secure and reliable connection to them much more of a challenge. The two approaches that seem most likely would both be difficult - either some sort of mechanical clamping, which is going to need hardware on the ends and be a challenge to keep tight under bouncy conditions, or to tack weld connecting strips between the cells - this is what the commercial pack makers usually do, but requires some fancy and expensive gear to do....

ex-Gooserider

[Burgerman]

http://www.ebay.co.uk/itm/110V-Hobby-Mi ... 233b2875e5

I used to make hobby batt packs without one of these, with an old 2v battery cell although you are supposed to use AC. Some use a rewound microwave oven transformer. Google. Easy project. But they are a bit big. An old instant 100 watt soldering iron, with the "loop" replaced with two electrode points works as well. You need some thin stainless steel sheet for connecting straps. I also used to build pulse jet engines with spot welds the same way.

[robnnorthaustin]

Shirley can you post a link to the batteries you found?

[Burgerman]

I would order 3 or 4.

Then test them on my hyperion, for capacity, internal resistance, and then try overcharging them to see if the catch fire or explode. Outside!

Then I would cycle them for a couple of weeks solid about 10 a day to see if they keep their rated capacity.

Only then would I consider them for a powerchair.


Watch this to the end...
There are a LOT of dodgy cells about.

http://www.youtube.com/watch?v=eOshOXcSkDA

[shirley_hkg]

Shirley can you post a link to the batteries you found?

http://item.taobao.com/item.htm?spm=201 ... 551c3cbea8

This is an honours seller whom I bought all my cells from . You have no less than 90% of his claimed capacity.

Nevertheless, I'd still suggest to have the biggest amp hour you can afford to reduce the discharge C rate.

If any forum member want me to help as a go-between , I'm at your service, no charge.

I'd ask him to weld the cells in parallel, at your selected pattern and leave tabs for your own connection in series.

Below is just a pickup image, and it is NOT done by him. He does it much better.

[shirley_hkg]

Carrying it this way was just meant for temprarily measure for trial run. However, that last for 5 years untill it retired 24 months ago, because its hard to find other place on chair with power seat.

This is my first LiFePO4 pack at 24V - 40Ah. It still holds 35Ah upon retirement when I swap to full lithium.

[shirley_hkg]

Latest piece, added power pack to extend range of a pair of 3 years old gel batteries which are ageing but too wasteful to be disposed of. Now the range is good . Charged every weekend.

Need 2 rows of these. Chair has no power seat so they hide beneath the seat neatly. Post pics ASAP.

[shirley_hkg]

I use a different approach. With a decent 2.50 / 3.65 cut-off BMS, lithium add-on ( < 50Ah ) becomes hassle-free.

I don't need to disconnect it from time to time , once connected. Charging both batteries simultaneously with the orginal lead charger.

Seperation for balancing the lithium pack is only necessary when I notice not all the 8 LEDs light up but that doesn't happen often.

[Burgerman]

3.65 is too high. The manufactures only choose that because almost all bms balance boards have useless 100ma balance capability. So natural balancing occurs through overcharging. They get less packs returned due to balance problems that way.

I charge mine to 3.55v. Only use 3.60v if they are very unbalanced after storage. Never 3.65.

Heres a chart from BatteryUniversity showing the reason...
This chart if for lithium polymer, designed to charge at 4.2v max. I charge mine to 4.15v for the same reason.

But the same applies to LiFe type lithium cells.

[shirley_hkg]

I agreed but this is the lowest I found.

It takes a minute or 2 to jump up to 3.65 from 3.55 and charging stopped. 100 mA discharging current will then drain a 40Ah pack down to 3.55 in half an hour.

It won't stay overcharged very long and significant harm done to battery may take years. We shall have many options by then.

[Burgerman]

Fortunately you are charging slow, with a lead acid 28.8v charger (which is 3.60v per cell) so things sort of work out...

As long as balance isn't too bad. But lithium chargers charge at more... Which sends high cells very high!

[shirley_hkg]

This BMS starts balancing at 3.50 V . No wonder all LEDs light up , even with my charger set at 28.2V