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Re: Step by step lithium conversion?

Postby woodygb » 15 May 2014, 01:00

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.

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Re: Step by step lithium conversion?

Postby cdb0ewm » 15 May 2014, 01:10

Thank you for the feedback. Is there a clearer picture available that is less confusing
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Re: Step by step lithium conversion?

Postby woodygb » 15 May 2014, 01:24

Does this single row make sense?

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Re: Step by step lithium conversion?

Postby cdb0ewm » 15 May 2014, 01:28

Absolutely...thank you for sharing
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Re: Step by step lithium conversion?

Postby woodygb » 15 May 2014, 01:39

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

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Re: Step by step lithium conversion?

Postby cdb0ewm » 15 May 2014, 01:52

One last question
What is the purpose of the additional purple busbars and why only on the 'B' side
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Re: Step by step lithium conversion?

Postby woodygb » 15 May 2014, 08:13

cdb0ewm wrote: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 .

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Re: Step by step lithium conversion?

Postby Burgerman » 15 May 2014, 09:31

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

Theres a site here that tries to prevent blown chargers and burned down houses!
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Re: Step by step lithium conversion?

Postby woodygb » 15 May 2014, 09:33

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.
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Re: Step by step lithium conversion?

Postby Burgerman » 15 May 2014, 20:43

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Re: Step by step lithium conversion?

Postby BounderGimp » 16 May 2014, 16:18

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.
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Re: Step by step lithium conversion?

Postby woodygb » 16 May 2014, 17:15

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

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Re: Step by step lithium conversion?

Postby Burgerman » 16 May 2014, 17:53

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.
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Re: Step by step lithium conversion?

Postby Burgerman » 20 May 2014, 09:31

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.
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Re: Step by step lithium conversion?

Postby cdb0ewm » 28 May 2014, 21:03

Ok ... thanks to input from you and Woody, along with his review, here's my battery pack wiring with the balancing connectors.
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Re: Step by step lithium conversion?

Postby Burgerman » 28 May 2014, 21:39

Yes.



Its easier to do it than draw it because you can physically see what is connected to what.
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Re: Step by step lithium conversion?

Postby shirley_hkg » 04 Jun 2014, 12:00

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
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Re: Step by step lithium conversion?

Postby Burgerman » 04 Jun 2014, 22:02

That would be true, if they are what they claim. Cheap cells from china tend to be anything but!
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Re: Step by step lithium conversion?

Postby ex-Gooserider » 06 Jun 2014, 07:27

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....

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Re: Step by step lithium conversion?

Postby Burgerman » 06 Jun 2014, 09:07

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.
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Re: Step by step lithium conversion?

Postby robnnorthaustin » 06 Jun 2014, 19:58

Shirley can you post a link to the batteries you found?
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Re: Step by step lithium conversion?

Postby Burgerman » 06 Jun 2014, 20:43

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
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Re: Step by step lithium conversion?

Postby shirley_hkg » 07 Jun 2014, 05:15

robnnorthaustin wrote: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. ;)
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Re: Step by step lithium conversion?

Postby shirley_hkg » 13 Jun 2014, 12:52

:D 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. 8-)




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Re: Step by step lithium conversion?

Postby shirley_hkg » 13 Jun 2014, 15:26

:D

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. :mrgreen:



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Re: Step by step lithium conversion?

Postby shirley_hkg » 15 Jun 2014, 04:16

:P 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. 8-)
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Re: Step by step lithium conversion?

Postby Burgerman » 15 Jun 2014, 09:58

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.

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Re: Step by step lithium conversion?

Postby shirley_hkg » 15 Jun 2014, 11:59

:mrgreen: 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. :idea:
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Re: Step by step lithium conversion?

Postby Burgerman » 15 Jun 2014, 12:13

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!
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Re: Step by step lithium conversion?

Postby shirley_hkg » 17 Jun 2014, 11:09

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

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