PINNED - Lithium battery conversion/info

[Burgerman]

Yes but then I would need to keep taking it off and finding it again later... Would be lost in a week!

And theres no need.

[Burgerman]

Quick test of a 2 year old 12Ah Headway. After around 100 cycles.

Its still got the same 12.3Ah (123xx mAh) it had when new. This is part of my lawnmower!

And this shows why hobby chargers are so useful. I test batteries regularly. This shows you EXACTLY what the battery capacity now is. Its still at 100% capacity.
This was at the 10A rate (a fraction less than 1C or 1 hour discharge.) From 100% charged to 2.5V CV and to 250mA termination.
If you discharge a lead battery in 1 hour down to 10V you get under half of its capacity when new so it would read under 6Ah... And after 2 years about 3...

[Burgerman]

And here is my 1 year old quadcopter battery. Its 4S and supposed to be 5.5Ah.

As you can see Cel 3 (of 4) -- the yellow one -- isnt well! This is already empty at under 4Ah..

I have cut off the graphsomehow but you can still see the value of testing. My Quadcopter would fall from the sky if I was expecting 15 mins of flight time...

[Scollard]

BM, so is that a LiPo discharge curve. Not as flat as a LiFePO4?

[Burgerman]

No. Starts at 4.2V and drops as you see here. When flying my quadcopter I make sure its down by 3.7V per cell. After that it drops off a cliff. And there's almost zero drop under load. They don't last either. Used hard in planes etc 60 to 90 cycles and they go in the bin. But cheap and exciting! Boom...

[Scollard]

All my R/C stuff is gas. Plane, buggy, airboat. Although I've been too busy in the last 20 years to do any playing. I'm going to get back into it now that I've retired. And maybe some model rail.

[ex-Gooserider]

What a shame, wasting perfectly good explosions on a bin... I'd think it would be more fun to 'minimize the disposal hazard' by seeing how big a boom one could make... I'm visualizing a guillotine type gizmo that drops the pieces in a bucket of water....

ex-Gooserider

No. Starts at 4.2V and drops as you see here. When flying my quadcopter I make sure its down by 3.7V per cell. After that it drops off a cliff. And there's almost zero drop under load. They don't last either. Used hard in planes etc 60 to 90 cycles and they go in the bin. But cheap and exciting! Boom...

[Burgerman]

I used to blow them up by overcharging, or just fully charge and drop onto the concrete but that didn't always work. A nail, and a bit of bluetack, and a long broom handle to tap it always works well!

After many batteries and explosion you get a bit bored of it and it smells horrible.

[Scollard]

I have the two batteries all hooked together with the balance wires all attached.

I got the charger-side cable done today. Charge mains are not hooked up yet, I will do that when I actually install the batteries. In the meantime I'm using the Anderson to charge and the balance wires are all running through the Combo Sub-D. Just taking a look at the cells now on the Hyperion.

[Burgerman]

The cells always look pretty much the same at anything under 97 poercent charged. So you cant tell much. Once you charge, then the cells will go all over the place and will look horrendously unbalanced over the last tiny bit. It can take a long time (potentially days) to balance at the top. So to speed up the first charge you really need to charge the lowest groups, individually or drag the high ones down with a resistance like a car headlamp bulb or something. Or you may be some t i m e ...

And you need self amalgamating tape for the end of that sleeve mesh.

[expresso]

Looking good Scollard - your just about done -

everytime i see these packs build - connected etc, - all the wiring etc, - i feel i never can do it - seems so complicated and serious i still excited over the ADD ON - Cant wait to get started with mines soon -

[flagman1776]

I have the two batteries all hooked together with the balance wires all attached.

Buttoned up.jpg

I got the charger-side cable done today. Charge mains are not hooked up yet, I will do that when I actually install the batteries. In the meantime I'm using the Anderson to charge and the balance wires are all running through the Combo Sub-D. Just taking a look at the cells now on the Hyperion.

First Look.jpg

Well done, Scollard. Clicking on the images, I see you have everything clearly marked, not just for assembly but also future maintance. It is always step by step, one wire connection at a time.

Expresso, it is about as complicated as a BMS system which you have successfully done. One way of looking at it is that the Smart charger does the same job (off-board) as on-board BMS.

[expresso]

Yes - at first you see all these wires - big and small etc, never seen anything this way - but it works with the right guidance and one step at a time - and comes all together in the end before you know it - its done and looks complicated till you do it a few times - most important is getting the correct layout of the Cells and correct connections of the buss bars - label and take pictures -

i have a utility cart full of stuff ready to start next week

[Scollard]

BM, when you tested the capacity of your BM3 battery, what voltage/cell did you discharge to?

Or, in other words, what should I set on the Hyperion for the Discharge Volts.

[Burgerman]

The problem with discharging a huge pack is that its limited to a low watts.

So I only ever removed 25 or 30Ah from the whole thing normally with the Hyperion as it takes days. 1.8 Amps or something at 45V (80 watts). But I discharged it fully a couple of times, to 2.6V. The problem is that there's a bug introduced sometime in the PC software and it stops graphing after 15 hours (I think?). And they never fixed it as it was discontinued. So you need to restart it... The charger carries on. Better way is to add a old style car headlamp bulb or two. Say 2x for 24V = 200 watts. Because the discharge is over 3x as fast. Measure the Amps and watch the time and add it to the charger Ah. Otherwise it can take half a week.

But I don't advise doing this anyway. Discharge by 10 or 20Ah to store. And top up to see if it all ends at the same time. It should if you have all healthy cells and no loose bolts! No need to discharge fully. If you test a single headway it will have a fraction more than it says on the tin.

But that doesn't fully discharge it anyway.
The PL8 gets a more accurate measurements, since it also has CV discharge. And at up to 40A if you dump it to a couple of old lead batteries with a load!

Rather than cutting off at a specific voltage it holds that voltage and reduces amps. The reverse of charging.

If they are this close together after a few cycles, then you have no problems!

[Scollard]

Right. So at 24V the most I can dissipate is about 3A which would be about 36hrs on a 105Ah pack.

I have the time, no problem discharging to 2.6 V/cell then?

I'll do the partial discharge 1st a couple of times to see that everything is coming back to the starting point. Then I will setup a longer deep discharge to see the capacity.

[Burgerman]

Yes.

I do wish you luck though... It going to take forever with a large pack! This was meant for hobby use. You may need to keep track and restart. The software will definitely give up at about 15 hours from memory. There was an earlier version that didnt but it had other problems.

If you move to the PL8 it can do 100 watts internal (still useless, what does it do with the power?) or up to 40A into a load. But that means you need to provide a load.
So for eg, a set of old powerchair batteries, and depending on how fast you want to discharge will if flat allow about 1.5kwh (haalf what you need. Or use a suitable load. Can be maybe a 24v inverter with something like a 1kw heater connected. Or, a bunch of truck 100 watt 24v headlamp bulbs... 10 = 1000 watts. Or whatver you want!

But thats a lot faster. Can be 2 or 3 hours. At the super slow discharge rate you will get using internal heat loss, you will not see full capacity. Because the cells work better when loaded (warmth) and because they need a CV discharge. The low rate approximates that however.

[Burgerman]

I have the time, no problem discharging to 2.6 V/cell then?

You will see more Ah by going lower. But I wouldnt want to hurt a new battery!

So yes 2.6?

[Scollard]

I'm kind of interested in how many Amp-Hours gets me down to 2.6V. I was thinking of using that as a setting for a warning buzzer.

[shirley_hkg]

There are not much left @3.0V , in real practice .

No need to go further. Hurting a cell on testing seems worthless.

[Burgerman]

Going to 2.6v doesn't actually get the cell to 2.6v. It bounces back when you take away the load. So you don't measure max capacity. But I wouldn't bother testing new cells for capacity. I have tested a few. They are as claimed. You need to discharge to a CV low current and below 2.5v to do that.

Like this: download/file.php?id=4477&mode=view

12.3Ah... One spare cell. And it still bounced back to 2.9v.

[Scollard]

I am interested on where the cliff is located and at what Ah consumed. So at 3.0V/cell we are over the cliff.

I let it discharge overnight. It took out around 45Ah, just putting it all back now.

[Burgerman]

Depends on load... As you know from the hyperion graph, at a low rate its almost a straight line. At a higher rate (1C as on my curve above it isnt...) You will know, it goes slower, and you start losing lights. Then stop. 3V off load and theres not a lot left.

[Scollard]

Right. So 3V on load would be a good starting point for a Safety Beep. I can't see myself ever getting there. I'm going to have about a 50 mile range and I'm never going to get beyond half of that.

[Burgerman]

Best way is to monitor Ah out, with a Turnigy meter. Very cheap, pretty accurate. But they only read up to 65Ah. Still if you know that, you can reset it at 50 or 60Ah and carry on. But that's a lot more than you would ever get from a set of lead bricks. There are plenty of meters that can read more than 65Ah but they cost more.

[steves1977uk]

Here's the top side of my lithium pack, can't get the bottom easily as all the wiring is fixed and my Brother don't want to touch it.



Steve

[expresso]

Steve - thats a very nice looking clean pack - your tech did a great job - very neat - i like that

i just checked my order - i got everything except 12 15ah cells - will arrive on Wed. i can start charging tomorrow

[expresso]

Steve - you had a fuse on both pos and neg wire ? what amp fuse did you use - why both wires ? why add a fuse if the chair has a fuse also - ?

besides the fuse on the charge cables -

[Burgerman]

steves1977uk, you are supposed to have all the parallel ones linked with a bar. And only need each series sets linked with one bar. As it is, any difference in cell resistance will mean a different voltage per cell under load, and those thin balance wires will be trying to balance a x amp load... That's probably why it never looks very balanced as you charge.

[expresso]

@ BM - Ok i charged up one Cell to test it - i see how to discharge it now - but i find it very hard to get the same amount each time - i tried it 3 times and each time was a different amount -

it may not be in my best interest to try to discharge each Cell - i may be making it worse in the end - i think i will just charge them all up and sit for 4 to 6 weeks

I saved the Graphs etc, - but i dont have a program to open them - - Can you tell me what program i can use to open the graphs ? any free program i can download and use ?

i am going to start charging them up tomorrow - - So Far so Good - charger working great -

thanks -