PINNED - Lithium battery conversion/info

[hotwheels_75]

Can someone tell me if I did this right? I’m trying to build an 8p 8s 24v pack. Having a hard time wrapping my head around this and the more I read the more confused I get.

If I link these together like this will it be correct or am I going to fry something?

Blue being negative and red positive. Black is connector bars.

Do the plates on the back go to same place as what I’ve shown here?

[Burgerman]

The way you have assembled/drawn it gives me a headache. You need to connect half of those series connections at the rear.

download/file.php?id=4301&mode=view the other side is the opposite.

[snaker]

@hotwheels_75: You have 8 groups and 9 connections that join those 8 groups in serial. Firstable, you must specify the start point (the 24V negative = connection #0), the end point (the 24V positive = connection #8) and the other connections (1-7). Use pieces of paper tape, stick them on those 9 connections and note their numbers from 0 to 8. Everything would become clear and easy.

[Burgerman]

Or visualise doing it with just 8 cells.

Power goes from +- +- + - + - + - + - + - + - and on...

[shirley_hkg]

Can someone tell me if I did this right? I’m trying to build an 8p 8s 24v pack. Having a hard time wrapping my head around this and the more I read the more confused I get.
?

The GREEN connections go to the opposite side .
The RED connections , as well as the [+] & [--] terminals are on this side ( now we see )

[Burgerman]

1 year 4 months old and only a few cycles maybe 12? 120Ah headway pack.

Stored 6 last months.

Capacity tested down to 3.000V per cell, (or 1V above safe limit), and/or 24V total.
Still discharging here at 119.6Ah out. Ended at just over 120Ah. So as new.

Computer went to sleep so missed the start of the graph

[Burgerman]

When using the PL8v2 with longcables (as we are) and on packs bigger than about 30Ah, the balance works better and faster if you set MODE to on/off rather than Proportional. And if you do this you can sert the balance deadband to 2.

[shirley_hkg]

Let's see how much will PL8 return it full .

[Burgerman]

That figure is never correct. Why? It only measures what goes out. It ignores the power taken by the balancer. And the return efficiency is usually about 5% worse, as the waste goes in heat in cables, waarmiung up the pack, etc. Resistance. And at the top at CV the lower the termination the more waste there is. So if you have a long CV then the cell balancing thaat happens a little all the tims adds up. So uit can be 10 percent. In this case the returned figure was 131.x Ah.

[steves1977uk]

Just updated my presets to have the balance mode set to digital on/off and set deadband to 2mv. My charge cables are about 3 foot.

Steve

[expresso]

what section on the presets would that be ? i will check mines - but i dont have a problem so far - my new cable is 3 feet long - on the PL 8 end and i am sure another 3 feet on the chair end -

[Burgerman]

It will give faster and more accurate balance at the top during CV. Long balance wires reduce the current. So the proportional balance trying to work at say 12 or 35 percent when it sees a voltage difference isnt very effective. It takes it longer. Esp if a pack is big. This was really intended for hobby packs and short wires. So proportional works well. 1A balance on a 2Ah battery is a lot! In our case its not.

Wont make a vast difference. But closes up small 3,5 or 8 mV differences a lot faster.

So look under the BALANCE tab. Then:
MODE and choose ON/OFF
And then 2mV in the deadband field.

[expresso]

ok i see that - should i do that to all My presets ?

[Burgerman]

Wont hurt. Will make less difference on your smaller addons. And esp if they use shorter cables. Try it. I was testing on a 120Ah pack. Definitely better there.

[expresso]

Wont hurt. Will make less difference on your smaller addons. And esp if they use shorter cables. Try it. I was testing on a 120Ah pack. Definitely better there.

[Burgerman]

The only place it seems worse is on the small hobby packs of 1 to 10Ah. The application of 1A balancing on/off makes the voltage overshoot and bounce about when its almost perfectly balanced on these. Makes no difference when miles out as the charger would have used max 100% balance regardless. So it keeps trying over and over for nothing to get it to get all within 2mA. And so we set that to 4 since its easier and so faster. Like its trying to crack a nut with a sledgehammer. So proportional is best on small packs. And short balance leads.

Its faster on bigger packs. It takes a while to change the voltage of say 30 to 150Ah of cells! So 100% on/off is faster as it doesent go: "Oh look its only 4 or 5mV out of balance, so we will use only 10% of balance power". It uses 100% now, or nothing and so the last bit of balancing can be more accurately arrived at in a sensible time frame (to a better 2mV) and faster to get there. You will get a thinner CV line quicker!

[expresso]

sounds nice - will be updating them all - and leave just the small pack preset alone -

but the chair with lead and 36ah ADD ON - i should change that also ? Combined preset

[steves1977uk]

These changes make the charge take longer for me...

Steve

[Burgerman]

It might, as you are actually now balancing faster, but to a tighter tolerance. 4mV high or low was considered done previously. Now its 2mV so more accuracy. Keep the ON/OFF and set the deadband back at 4mV and it will be faster. Or 3 if you want.

In other words the ON/OFF is faster. But the tighter2mV deadband takes longer. Swings and roundabouts.

If you want to watch this in action, and remove the on screen averaging, and have scruffier looking graphs, set the program at the top bar to:

View/preferences/cell display/4digits and then watch the graphs, and esp while monitoring after charge. After you are done, put it back to 3 digits as it will drive you nuts. Then you will see the affect 2 versus 4mV deadband actually has! Normally the pl8 hides thissmall difference from the user.

[steves1977uk]

Makes sense! Thanks BM

Steve

[Burgerman]

Edited and added to, as you were replying, reread.

[Gnomatic]

I updated one of my presets so Balance Mode was set to Digital ON/OFF and turned the Deadband down to 2mv as suggested.

Not much changed for me as far as I can see. About the same amount of time at CV as what I got before.

[Burgerman]

You will only actually SEE the difference on a graph when you set the no of decimal places to 4. That also removes the cell grouping averaging. So you see reality rather than everything within +/- 4mV or so, displayed using the same pixels on screen. Very informative. But makes people worry more with a less tidy "appearing" graph!

Go to: view>preferences>cell display>4 digits... Dont leave it set this way as it will drive you to distraction. Doesent bother me, but it lets you see which cell groups are hard to balance etc.

[frogsuk]

Can anyone please help me with this battery set up?
I would like to know how to wire the balance wires up please?
Also, is someone able to do a charging profile for PowerLab 8v2?

The cell set up is 8s2p
16 x 15Ah 40166 LifePO4 CELLS
Specification:
Nominal Capacity: 15000mAh
Charging Voltage: 3.65V
Typical Voltage: 3.3V ≤10mΩ
Cut Off Discharge Voltage: 2.0V
Charging Mode: CC/CV (Constant Current/ Constant Voltage)
Maximum Discharge Constant: 10C (150A)
Maximum Charge Current: 3C (45A)
Cycle Life: (Minimum) 2000 Cycles, Capacity >12Ah
Operating Temperature:
Charge Temperature Range: 0~45 C
Discharge Temperature Range: -20~60 C
Diameter: 40±1mm
Height: 166 ±1mm
Weight: 465g
Energy Density
Gravimetric: >105Wh/Kgs
Volumetric: >220Wh/L
Power Density:
Gravimetric: >850W/Kg
Volumetric: >1,750W/L
Initial Internal Impedance: <3 mΩ

[frogsuk]

Can anyone please help me with this battery set up?
I would like to know how to wire the balance wires up please?
Also, is someone able to do a charging profile for PowerLab 8v2?

The cell set up is 8s2p
16 x 15Ah 40166 LifePO4 CELLS
Specification:
Nominal Capacity: 15000mAh
Charging Voltage: 3.65V
Typical Voltage: 3.3V ≤10mΩ
Cut Off Discharge Voltage: 2.0V
Charging Mode: CC/CV (Constant Current/ Constant Voltage)
Maximum Discharge Constant: 10C (150A)
Maximum Charge Current: 3C (45A)
Cycle Life: (Minimum) 2000 Cycles, Capacity >12Ah
Operating Temperature:
Charge Temperature Range: 0~45 C
Discharge Temperature Range: -20~60 C
Diameter: 40±1mm
Height: 166 ±1mm
Weight: 465g
Energy Density
Gravimetric: >105Wh/Kgs
Volumetric: >220Wh/L
Power Density:
Gravimetric: >850W/Kg
Volumetric: >1,750W/L
Initial Internal Impedance: <3 mΩ

Or should the battery layout be like this? I would still like to know where the balance leads should go and the charging profile for PowerLab 8v2

[Burgerman]

The parallel cells should already be connected to each other. Your drawing only makes sense if you have 2x 24v packs.

So its harder to explain.

http://scriptasylum.com/rc_speed/lipo.html go here, and try a lot of options till you understand how cells are wired. The parallel cells should be connected together. Then in series. Then you need NINE balance wires for 8S.

[frogsuk]

The parallel cells should already be connected to each other. Your drawing only makes sense if you have 2x 24v packs.

So its harder to explain.

Yes, I have 16 cells making 2x 24v (29.2v) packs (8s), doubling them up to 2p to give higher amperage 24volt

Not sure how to fit the balance leads though, or do I have to charge both packs separately? In which case the 1st picture layout would seem the best layout I think? I was hoping to charge as one unit

[Burgerman]

No, I mean every cell should already be connected to its parallel partner. Not just the 8 cells/24v.

Then its easy. Connect 2x 15Ah cells in parallel. Then the next 2. Then the next 2. Until all 8 parallel pairs are connected in parallel. THEN connect in series.

As you have it drawn, you will need 18 balance wires. Because the parallel cells are not connected. And under heavy load or charge, if any cells are higher or lower impedance the current will melt the balance wires joining the cells.

[Burgerman]

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

Choose 5S (they dont allow 8) and 2P.

NOTE that each cell is joined, not only the 0 and 24v ends.

Then tick the balance wire box and it shows you where they go.

[frogsuk]

Thank you so much BM. I'll let you know how I get on