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Re: Rebuild BM2 green...

PostPosted: 01 Jan 2016, 01:31
by Burgerman
My cells have been sat in a box for 6 weeks awaiting recharge.

They were charged individually to 100%, 1000mAh accurately removed (taken out), then stored 1.5 month. 5A charge 25mA termination, @ 3.600CV.

Subsequent re-charge at 5A and 200mA termination current, @ 3.600V Gives me figures like this (this is 8 cells from 80 that I have.)

Code: Select all
Cell  Beep@CVpoint  EndCharge@200mA  Self Discharge mAh (Lost)
1     809      1038             38
2     789      1016             16
3     775      1002             2
4     756      997             -3
5     783      1024             24
6     896      1122             122
7     782      1019             19
8     788      1020             20 


As you can see they all vary, and cell 6 varies more than I like. I ordered 2 extra cells. I may not use the 122mAh lost cell. This way I can assemble GROUP[S of cells that have the same AVERAGE self discharge. So they will stay in balance if unused for a while.

Re: Rebuild BM2 green...

PostPosted: 01 Jan 2016, 20:26
by Burgerman
810_1134.JPG


The long boring process of building a 120Ah battery. Every cell group tested for same self discharge rates, careful planning so we get each cell the correct way around...

One at a time.

Re: Rebuild BM2 green...

PostPosted: 01 Jan 2016, 20:47
by Burgerman
This cell required the 1Ah removed, plus 16 extra mAh to be fully charged. So it had just 16mAh self discharge.

Image1.gif

Re: Rebuild BM2 green...

PostPosted: 01 Jan 2016, 21:26
by Burgerman
The BLACK end is negative obviously. The other end is positive and silver. And vented. Dont use too long bolt here.

810_1136.jpg

Re: Rebuild BM2 green...

PostPosted: 03 Jan 2016, 01:25
by Burgerman
Code: Select all
PL8 charger used.
Charged individually to 100% 15mA termination 3.600v, then 1000mAh

accurately removed, stored 1.5 month in box a cupoboard.

Then, 5A charge 200mA termination, 3.600CV.
Subsequent re-charge gives us the amount lost through self discharge:

Cell  Beep@CV  EndCharge@200mA  Self Discharge mAh (Lost)
1     809      1038             38
2     789      1016             16
3     775      1002             2
4     756      997             -3
5     783      1024             24
6     896      1122             122
7     782      1019             19
8     788      1020             20   
9     690      990             -10
10    712      1104             4

11    725      995             -5
12    756      1011             11
13    813      1019             19
14    781      1016             16
15    815      1020             20
16    813      1023             23
17    819      1034             34         
18    768      1008             8
19    777      1013             13
20    902      1120             120

21    761      1010             10
22    780      1012             12
23    802      1047             47
24    796      1015             15
25    760      1007             7
26    760      1018             18
27      0      44      44? Over full in seconds?  This one wasn't discharged 1Ah...
28    800      1016             16
29    800      1016             16
30    748      1018             18


More done! 30, only 50 to go!

810_1138.JPG

Re: Rebuild BM2 green...

PostPosted: 03 Jan 2016, 20:31
by terry2
Looking great BM(I'm jealous as hell)

Re: Rebuild BM2 green...

PostPosted: 04 Jan 2016, 04:58
by Burgerman
Well its hard work. Esp if you spend most of the time held up waiting for a carer to pick up that screw, tool, bracket, or whatever that you needed and you have been running over all day, or waiting for the post from china for some obscure tiny thing you cant do without...

I have a BM3 with a failed Cush drive rubber I need to fix, so cant use it. But cant fix it because I have a BM2L (lithium) in the way covering every spare bit of space in 200 bits and pieces.

But don't watch. Get the hammer out!

Re: Rebuild BM2 green...

PostPosted: 04 Jan 2016, 05:04
by Burgerman
Anyway, my mates are so used to me turning up with new chairs they no longer go wooo! They don't notice.

That's why I did polished alloys, fat low profile tyres, Kawasaki green ultra bright welding mask paint, orange/blue battery etc. This one was meant to stand out. Might fit a bright coloured car race seat yet!

I am normally of the opinion that chairs should be neat, clean, and go unnoticed. So black and dull and invisible.

Re: Rebuild BM2 green...

PostPosted: 08 Jan 2016, 22:18
by Burgerman
Here's one I made earlier. 80 12Ah cells, split into 2 packs, for easy lifting of uneven size and obscure shape to allow some parts to be 7 cells deep while others are 5...

120Ah and still 50lb lighter than a couple of lead bricks.

Looks odd. Fits great. Will allow HUGE range and uses up space wasted under the seat to the millimetre.

810_1173.JPG

Re: Rebuild BM2 green...

PostPosted: 09 Jan 2016, 22:35
by motoman
Burgerman wrote:[img]

Image


This pic is actually after a mid air collision with a Cessna I believe :) Nomex undies and ear plugs would have been ineffective :(

Re: Rebuild BM2 green...

PostPosted: 09 Jan 2016, 23:06
by Burgerman
Everything would be ineffective!

Re: Rebuild BM2 green...

PostPosted: 15 Jan 2016, 15:36
by Burgerman
Built, cells carefully selected into 8 identical groups, so that they have equal self discharge rates, capacity, etc.

And under test. Wiring will be tidied up and cable tied. This splits into 2 halves.

810_1180.jpg


80 Cells, 120Ah, 3000 plus watt hours, all cell groups selected after 6 weeks for similar self discharge rates, and for Ah capacity. This is under test.

Re: Rebuild BM2 green...

PostPosted: 17 Jan 2016, 21:36
by Burgerman
Tidied up...

Charge cable connected and testing. Just ONE connection. That black connector. One half stays on the chair, bolted under the seat. Other half stays on the charger. That connector has 9 balance wires, and 2 power wires. Safe for 40A charging.

It cant get any easier! The PL8 charger does a much better job of charging, with better control and information than a BMS. And the chairs controller does a better safer current and voltage control limiting than a BMS too. So non is required.

And apart from lasting a great many years, this battery is SAFE! Not all lithium batteries catch fire! These LiFePO4 cells are SAFER than your existing lead batteries.

Re: Rebuild BM2 green...

PostPosted: 18 Jan 2016, 00:23
by Williamclark77
Very nice! I wish I had known of those connectors before I did the Anderson and aviation plug connection to charge my 14s pack. It works fine but is three things to plug in. Simple enough but the aviation plugs are pretty annoying to get connected good.

What's the heavy red cable at the top for? The short one horse-shoe'd over. It looks to be making a parallel connection. I was wondering why it instead of a two hole plate?

Looks good! I'd like to see a real world range test when done.

Re: Rebuild BM2 green...

PostPosted: 18 Jan 2016, 01:21
by Burgerman
viewtopic.php?f=2&t=1813&start=620

Part numbers, pictures of the correct connectors.


The battery is in 2 halves. Hence the link cables. Tried Anderson, has too much resistance and at 40A charge cell 4 shows 10mV too high... So solid cable link. And very tight bus bars. It even matters where you connect the balance wires. Can be 5mv difference from one end of a bus bar to the other...

Get it right and it looks perfect and the exact same voltage to 3 decimal places on every cell.


If you fit the cheap turnigy watt meter, you can find out ultimate range easily. With lithium as you already know, there's no Peukert. They run at full power to 99 percent. So you can measure actual Ah used, over a typical day, use your phone GPS to measure miles, and just do the maths. It will be within 1 percent. Range should be rather good. Lower current 6.2mph motors. Rounded profile 6 ply radial tyres have very low rolling resistance. Battery is lighter, chair is 100lb lighter. The stock chair claims an ISO 24miles from 56Ah Sonnenschein gel batteries. Which is bull but... With better tyres, less weight and a true 120Ah I should go at least 3x to 3.5x further. That's 75 to 85 or more ISO miles. Or real world about about 2/3rds that. We will see -- I am fat!!!

Re: Rebuild BM2 green...

PostPosted: 18 Jan 2016, 01:30
by flagman1776
I actually look at this connector... when I salvaged my generic China pack... was it 2+ years ago? Since I had already made up the Anderson output to the TravelScoot, I just reversed it as the main charge leads...
However, building a pack that doesn't get disconnected with every use, a single connector is so much cleaner.
What is the service life of the connector?
Is there a rule of thumb for getting the best balance reading?

Re: Rebuild BM2 green...

PostPosted: 18 Jan 2016, 01:39
by Burgerman
Service life? Unknown. But I can soon fit another. Looks pretty well made.

Its quite heavy gold plated. But even when that's worn away I don't see much of a problem. If there is it will show on the graph screen as uneven balance? But its proportional, and so will adjust for resistance changes on the fly... Cells all look pretty well matched here to the 0.001V level! (This Shirley, is why we don't use a BMS!)

BM2 one (2 connectors, as a 6S and a 7S pack at once).

charging.gif


And an 8S 120Ah discharge shows why voltage tells us nothing useful... Temperature varies the voltage far more than discharge level:

Image1.jpg


First charge so not completely together:

A123 Graph Volts.GIF


Discharge testing my quadcopter battery, through same connector while testing (only 3 cell, and all 3 well matched, this is LiPo so different voltages:

LiPo Graph Volts.GIF

Re: Rebuild BM2 green...

PostPosted: 20 Jan 2016, 20:51
by Burgerman
More pics while it was in the kitchen... Bit of space.
BIG ONES!
Just ordered anti tip wheels (80mm black hard urethane inline skate wheels) and spacers, and bearings. And a 120mm M16 8.8grade bolt for the tie down. Those have to be fitted, tested for fit and angle befopre battery can be added as I cant get it up on the bed afterwards. Too heavy!

810_1205.JPG


810_1209.JPG


810_1211.JPG


810_1212.JPG

Re: Rebuild BM2 green...

PostPosted: 20 Jan 2016, 21:19
by hank
Should'nt be far away now John. Looking well 8-)

Re: Rebuild BM2 green...

PostPosted: 20 Jan 2016, 21:23
by Burgerman
Once the tie down bolt is in and the correct length, anti tips on, and battery in place then its all over. Just bolt the seat together. And then make a footplate (by a beermat drawing and a online laser cutter!) and drill a few holes etc to fit it. Then we can go for a silly mileage marathon!

At a narrow 24.6 inches wide its the same width as most 55Ah 22nf battery INDOOR/outdoor type chairs that use skinny tubed or rock hard flat free tyres with about 15 miles max battery destroying range like the Smaller TDX chairs, the Pride Quantum 600 and Edge chairs etc. Only with about 60 miles or 4x the range. And the ability to work properly outdoors without filling loss or the casters sinking in or high centering. Its also shorter.