Help and suggestions for lithium or lead

[nealnlx]

I think my box case has like i said around 40cm long by around 30cm width and around 16-17cm height
If i use headways 10ah they are around 12cm long. Those orange fixing things are 4cm x 4cm . So i could maybe fit in like two packs of 10cells long by 4cells height
in a total of 80cells
Would be a 100ah of my sholders when im always thinking how far more can i go

That is withou the exact dimensions because i dont have access to it now, and with no modification, but if i need to i can change a bit the battery box support frame which is removable from the chair.

[Burgerman]

80 USABLE Ah compared to 40 usable from your existing batteries means double the range.

It also means half the average DoD level so the battery will live a long time either through half the charges, or half the daily discharge.

It also means peace of mind, - you know you can get back reliably, meaning you will likely venture further afield. And if charged with a decent hobby charger to a sensible voltage you should get about 10 years life.

[nealnlx]

How can i have 40ah on my actual chair now if i have 2x 12v 26ah?


Yes,peace of mind says it all

[shirley_hkg]

My maths tells me that your box may house 56 cells of 38140.

That will be a 8S7P set up.

This is 7X12 =84Ah @24V.

[Burgerman]

But he must measure carefully.

Each cell is 40 x 40 x 174mm long with the screw, and plastic building block.

[shirley_hkg]

I know. He may need 22cm in height.

[nealnlx]

After a week of waiting just to know some dimension i finally have half of what i asked for, but thats tytical...if you want it properly done do it your self, right?...

So the news are...
The box is: 20cm width x 36cm long x 20cm height
That is a bummer to start with, but lets see...
The good part is its height that i thought would be just around 16cm and its 20 with the possibility to go up maybe a finger or two
The worst part is its width. I thought it would be around 30cm and its much less...
The guy said that maybe i can have some room left, like 10cm from side to side untill it reaches the motors. From what i can see in the pics, i think maybe 5 or 6cm is more realistic.
In the and and with it all touching all sides i will try to see if i can gain enough to squeez in a two rows of cells instead of just one in the midle to make it better.

How much space do you guys think two cells of headways 10ah need to fit side by side?
I refer the 10ah ones just because they are the smaller ones and that would be more menagable to put more inside.

Here is a pic of it back view

[Burgerman]

Well a 12A one is 174 x 40 x 40.

A 10Ah one will therefore be the same but 20mm shorter.
So 154 x 40 x 40.
So 2 will be 80 x 40 x 154...

[nealnlx]

When i said two rows i meant like two packs, one on the side of the other.
Like the pic bellow show, buts instead of the led would be another pack/row of cells

In terms of each pack it self and to menage to fill all the space, i was thinkin...since i have 20cm of height it could get 5 cells upwards making to the top of the 20cm. And with 36cm length can get 9 cells.
So 4x5=20cm and 4x9=36cm

If the 10ah ones have 15cm long i would need a box with 30cm width to fill in those to packs/rows of 5x9cells.
One on the right and the other on the left.

Do you think tha this way it might short due to its proximity?
Even if i put like an acrylic sheet in betwin them kind of to avoiding the screws to make contact?

[Burgerman]

If the 10ah ones have 15cm long i would need a box with 30cm width to fill in those to packs/rows of 5x9cells.
One on the right and the other on the left.

154 mm inc the orange blocks. And yes, they must be separated.

The block of batteries shown here are in my BM3 chair. That's 78x 12Ah cells.
So 174 wide, 240 tall, 520 long. That's a 13S or 45V battery. If it was 24V and had 2 cells more it would be a 120Ah battery. That is what is going into my BM2 chair currently being rebuilt. See here: viewtopic.php?f=2&t=5380&start=60

[nealnlx]

would it safe? or maybe risky?

[Burgerman]

Well terminals touching means a huge short circuit and thousands of Amps flowing. So not unless you want to get a very hot backside.

[nealnlx]

That means a two pack/rows side by side even with acrylic sheet like 3or5mm is a no no?

[Burgerman]

No that would be fine. But you don't want a short.

[nealnlx]

No way, my ass worth ten times its weight in diamonds. I got a promisse to keep so i cant burt it.

Thats a releive to know that it can be side by side.
I was all most watchin my self going backwards with half of space capacity.
With acrylic in the midle of it it will be much better
Now all i have to do is to bring back my chair and find a way to gain those 32cm width.


Btw, shouldnt it be the way we all should monitor our power?

http://zeva.com.au/index.php?product=119

Take a look a tell me if you know it and if it works and how good is it.
Looks simple and straight foward to me.

[Burgerman]

For LiFePO4, we recommend an undervoltage threshold of 2.8V (which results in 2.6V cutout and 3.0V re-enabling for any loads on the battery), and an overvoltage threshold of 3.6V (for 3.8V charger cutout and 3.4V re-enabling). These thresholds give about 1% hysteresis on the battery state of charge to avoid rapid cycling of the charger or outputs.

A proper charger like the hyperion (out of production) or the PL8 I am using now, charges and cell balances to much better accuracy. To 0.003mV per cell in fact. It doesent keep bouncing them to 3.8/3.4V all day while it tries to balance them.

As BMS systems go this is better than most but still intended to allow diy conversions by those that don't realise you don't need one! It only does 12S anyway I think. Most real EVs are using high voltages and probably 5x this. My battery is already too many at 13S.

Seriously most of this things job is already taken care of by you. By using adequate C rated batteries and enough capacity that the battery is barely loaded whatever you do. You can then go nowhere near its current or discharge limits where the BMS needs to "cut the power". And a controller with current limiting already prevents overcurrent, and a charger that balances cells and charges better than that BMS can, and that displays the same data and cell voltages plus graphs and history, internal resistances, of every charge on a cell by cell basis, does the rest. Its for DIYers that "know" lithium must have a BMS! Trouble is they are wrong. You only need one if you fit the wrong battery into the wrong place, or if its too small for the job.

It does lead too. You could fit one to your lead chairs. But I also don't see the point. It really is the same thing. And it STILL cant tell you the state of charge!

The only advantage that would have is that you can use a simple 2 wire charger.

[nealnlx]

I just said that because like me many of wheelers dont know a thing about this thecnical stuff, so it would be nice to have a litle screen on board to show us what we are spending and how much we have left and so on, but in that more accurate fashion way and not only by those dot light we all have that dont mean a thing.

Now that im more clarified about the quantity of cells i need, more or lees, depening still the exact dimension that i need to nkow.
You said :
"If you want ultimate range, battery service life etc then forget add ons, and forget BMS systems. And simply fit as many Ah as possible into the space you have, charge with a quality cell balancing hobby charger."

What do you really mean by this?
Is it like just connecting all the cell toguether with the plates without any wiring system and then just use it like we do with regular small batteries we use on our tv remote control?
Clear me on this one so i can understand better what you are saying when you start to speak your hi-tek chineses.
Remember, be patient im still learning for my diploma.

[Burgerman]

With lithium you have to watch several things.

Thing 1 Cell Balance.
Max voltage that each cell reaches when charged in a string of 8 cells for your nominal 24V in this case is very important. You want all the cells to reach an identical full voltage. Accurately.

Charge each to 3.55V and they live almost forever. 3.60V and live a long time. 3.65V and you start to hurt them relatively fast. 3.70 volts and your are damaging them very fast. More still and its not very clever at all.

When charging a string of cells, by applying power to each end as all chargers do, one or two will always get full first. These full ones then, shoot up dramatically from the 3.30 to 3.35V. And climb up to 3.60V or above super FAST! The voltage just goes mad on LiFePO4 cells when full, it shoots up high quickly. The BMS if you have one tries to stop this, it drags the high cells down - usually with a feeble 100mA current balance circuit. 10X too small. It fails dismally of course, since that cell is already full and you are charging at say, 20Amps! Wiring... Take a look here. http://scriptasylum.com/rc_speed/lipo.html

So the highest cell goes up to about 3.8V before the BMS does the only thing it can. It cuts the power off from the dumb 2 wire charger. Then it waits till the weak 100mA dump balance circuit, lowers the cell down to 3.4V and then reconnects the charger again. So the whole battery gets connected and disconnected to the charger repeatedly, and the high cells get sent up to a high voltage and then drained slightly again and again often for many hours. The net result is that your battery cells have a short life.

My Hobby charger never exceeds the voltage I set. It throttles back, reduces power proportionally and has 1A balance circuits that pull the voltage down on any high cells proportionally, and so is in proper control. So I can choose say 3.550V volts per cell, and it makes absolutely sure that this voltage isnt exceeded. It brings all cells to this exact same voltage smoothly and without exceeding what I choose. No pulsing, no high voltages etc.
(+/- 0.003V accuracy claimed, actually better in reality, acording to my rather expensive calibrated test meter). So all cells are treated well.

[Burgerman]

Thing 2 Discharge Amps

If you discharge a lithium cell at a high rate (called C rate) they die much faster. If you exceed the cells C rate, they die very fast. If you only take current out slowly, they live a long time. So in an ideal world, you need a high C rate battery, and a low current draw.

What is C rate?
C stands for capacity. So if you buy a 5C cell, and it is say 10Ah capacity then it can safely give you a MAX Amp output of 5C x 10Ah or 50A.
Packs are rated in continuous C and in "Pulse" C.
Ignore pulse ratings... Its meaningless, unless you want to murder your cells. Its a max they can do. For a very short period like a second.

A 1C 10Ah cell can give only 10A.
A 2C 10Ah cell can give 20A

A correctly sized BMS is usually fitted to a pack to stop some idiot exceeding the C rating. That means they fit say a 3C 20Ah pack on an e-bike. Meaning 60Amps max before damage. The BMS will trip, and cut power if you exceed 60Amps.
And the e-Bike motor and controller can draw 70+Amps peak, because it has no current limiting. So the BMS is needed here because the dummy on the bike will kill the pack without it. He would suck too many amps and kill the cells. So the BMS cuts off power like a fuse.

In a CORRECTLY implemented system, we choose adequate capacity, and adequate C rate, and a CURRENT LIMITED controller (that you already have) so that you cannot EVER approach HALF the max allowable Amps the cells can produce continuously. So the BMS isnt needed to do this job (badly) either!

The other benefit is that if you do this correctly your cells have an easy life and last a very long time. Because you dont ask them to work hard.

Theres a few other things a BMS does too. Non of which we need or want in a thought out system.

[Burgerman]

Thing 3...

Lithium cells die a very rapid death if you discharge them too low. A BMS attemps to determine this based on voltage. When it does so, it usually gets it wrong. And cuts power off as you try to climb a ramp or something. It just looks at voltage. When it sees voltage drop to X point it literally switches off...

As you are trying to cross a road or climb that ramp onto a train... Why? Voltage drops under load (resistance) and the BMS sees that!

So again. We dont want a damned BMS interfering, we need to decide ourselves when we have gone far enough.

My approach? Fit a battery that is bigger than I can ever use up in a day!
And...
Watch the voltage with a tiny alarm. Or a volt meter.
And...
My controller (roboteq) is programmed to flash an LED / sound a buzzer on my pod when the battery gets to a voltage I choose. (2.7v per cell in my case) It can also be programmed to use that signal to stop the chair.

I actually do all 3 of these.

So again a BMS is redundant if you use any alternative. In your case you will see a light or two dissapear on your pod. Thats it, end of play.

[Burgerman]

Has that made it clearer or worse?
Read several times, then ask questions.

[nandol]

i already spoke on phone with Nuno (we live 10km distance ) and gave him my contacts and some tips...i expect next 1st december to fly and stay for quite a long time to northeast brasil

[nealnlx]

With lithium you have to watch several things.

Thing 1 Cell Balance.
Max voltage that each cell reaches when charged in a string of 8 cells for your nominal 24V in this case is very important. You want all the cells to reach an identical full voltage. Accurately.

Charge each to 3.55V and they live almost forever. 3.60V and live a long time. 3.65V and you start to hurt them relatively fast. 3.70 volts and your are damaging them very fast. More still and its not very clever at all.

When charging a string of cells, by applying power to each end as all chargers do, one or two will always get full first. These full ones then, shoot up dramatically from the 3.30 to 3.35V. And climb up to 3.60V or above super FAST! The voltage just goes mad on LiFePO4 cells when full, it shoots up high quickly. The BMS if you have one tries to stop this, it drags the high cells down - usually with a feeble 100mA current balance circuit. 10X too small. It fails dismally of course, since that cell is already full and you are charging at say, 20Amps! Wiring... Take a look here. http://scriptasylum.com/rc_speed/lipo.html

So the highest cell goes up to about 3.8V before the BMS does the only thing it can. It cuts the power off from the dumb 2 wire charger. Then it waits till the weak 100mA dump balance circuit, lowers the cell down to 3.4V and then reconnects the charger again. So the whole battery gets connected and disconnected to the charger repeatedly, and the high cells get sent up to a high voltage and then drained slightly again and again often for many hours. The net result is that your battery cells have a short life.

My Hobby charger never exceeds the voltage I set. It throttles back, reduces power proportionally and has 1A balance circuits that pull the voltage down on any high cells proportionally, and so is in proper control. So I can choose say 3.550V volts per cell, and it makes absolutely sure that this voltage isnt exceeded. It brings all cells to this exact same voltage smoothly and without exceeding what I choose. No pulsing, no high voltages etc.
(+/- 0.003V accuracy claimed, actually better in reality, acording to my rather expensive calibrated test meter). So all cells are treated well.

Lets see..
What a charger does is to apply power to each end of a cell or a battery untill it overlows. They go to the fullest and dont stop making the cell voltage goes mad like you said.
Its like filling a bucket with sand untill it passes the top.
And what a BMS does is analyzing it ONLY AFTER it already passed the top and then when sees the overflow the BMS unplugges the thick charger cables and connect his litle board ones and kind of slowly sweeps the exccess of sand out untill its all leveled with the bucket.
It does this to all the buckets/cells several times until they are all at the same lever/voltage.
The result is that with this the cell are not only going through the roof getting damaged in the first tick cables charge because they pass the expectable safe voltage and also get into a kind of cycling methog that the BMS does when discharging and recharging again taking of life cycles that should be used by us.
Am i right untill now or all wrong?

What you hobby charger does is, because it is pre-programmed to charge a cell only untill certain limits, it does not exceed it.
Instead of fiiling the bucket with all the sand as it can at once, it goes hard at the beggining (like charging at 30A) and when close to the top reduces to that only 1A charging state to in proper control reach that top slowly never letting it overflow.
So your hobby charger can be kind of set/programmed like an alarm clock that when reaches that exact time/volts it rings,in this case stops charging.

Did my thoughts made sence or only said crap?

[nealnlx]

Thing 2 Discharge Amps

If you discharge a lithium cell at a high rate (called C rate) they die much faster. If you exceed the cells C rate, they die very fast. If you only take current out slowly, they live a long time. So in an ideal world, you need a high C rate battery, and a low current draw.

What is C rate?
C stands for capacity. So if you buy a 5C cell, and it is say 10Ah capacity then it can safely give you a MAX Amp output of 5C x 10Ah or 50A.
Packs are rated in continuous C and in "Pulse" C.
Ignore pulse ratings... Its meaningless, unless you want to murder your cells. Its a max they can do. For a very short period like a second.

A 1C 10Ah cell can give only 10A.
A 2C 10Ah cell can give 20A

A correctly sized BMS is usually fitted to a pack to stop some idiot exceeding the C rating. That means they fit say a 3C 20Ah pack on an e-bike. Meaning 60Amps max before damage. The BMS will trip, and cut power if you exceed 60Amps.
And the e-Bike motor and controller can draw 70+Amps peak, because it has no current limiting. So the BMS is needed here because the dummy on the bike will kill the pack without it. He would suck too many amps and kill the cells. So the BMS cuts off power like a fuse.

In a CORRECTLY implemented system, we choose adequate capacity, and adequate C rate, and a CURRENT LIMITED controller (that you already have) so that you cannot EVER approach HALF the max allowable Amps the cells can produce continuously. So the BMS isnt needed to do this job (badly) either!

The other benefit is that if you do this correctly your cells have an easy life and last a very long time. Because you dont ask them to work hard.

Theres a few other things a BMS does too. Non of which we need or want in a thought out system.

Thing 2

First thing...
C rate in a cell/battery means that it can be draing "x" times that capacity withou damaging the cell/baterry.
Like a 5C 10ah that usualy would last thos 10amps for one hour can receive/get a peak of 50amps that it doesnt blow up. Only means that instead of one hour it will last/be drained in minutes. Am i right?

I understand that the BMS here goes to menage control over the amps that the baterry ca sucked of to prevent damage.
How can he or we suck that amout of amps at once from a cell?

"In a CORRECTLY implemented system, we choose adequate capacity, and adequate C rate, and a CURRENT LIMITED controller"
Here you mean, for example, if we have a capacity of 100ah pack, a C rate of 3 (3C) and a corrent controller we never have damage right?
So from what i think it would be like having the 100ah that can get a draining peak of 300amps, right?
But since we have that current limited controller which is our chairs power controller which in most cases dont even are 100A, it mean that not only we have the three time the capacity to kind of play safe but also our power controller and since it only goes to 100amps, never let that happend.
Do i make any sence again?
Our controller can ask for 100amps max at a certing time and that is exacly the amout of Ah we have in our pack. So even if it could have that peak for one hour it would be ok. But onve we have a 3C 100ah we are only a third of our pack limit.
Getting dummer or smarter?

"... if you do this correctly your cells have an easy life and last a very long time. Because you dont ask them to work hard."
This i need to be taught how to do it.

[nealnlx]

Thing 3...

Lithium cells die a very rapid death if you discharge them too low. A BMS attemps to determine this based on voltage. When it does so, it usually gets it wrong. And cuts power off as you try to climb a ramp or something. It just looks at voltage. When it sees voltage drop to X point it literally switches off...

As you are trying to cross a road or climb that ramp onto a train... Why? Voltage drops under load (resistance) and the BMS sees that!

So again. We dont want a damned BMS interfering, we need to decide ourselves when we have gone far enough.

My approach? Fit a battery that is bigger than I can ever use up in a day!
And...
Watch the voltage with a tiny alarm. Or a volt meter.
And...
My controller (roboteq) is programmed to flash an LED / sound a buzzer on my pod when the battery gets to a voltage I choose. (2.7v per cell in my case) It can also be programmed to use that signal to stop the chair.

I actually do all 3 of these.

So again a BMS is redundant if you use any alternative. In your case you will see a light or two dissapear on your pod. Thats it, end of play.

3 thing

"Lithium cells die a very rapid death if you discharge them too low. A BMS attemps to determine this based on voltage."
First thing wrong. I can have a almost fully charged cell and a low voltage...

If voltage drop under load it meand that when our chair is in a bigger effort it requires more power.
Its like a car going uphill. If its loaded with weight at certain point it will need a lower gear to have more torque/power.
In our chairs we need this to so we can overcame many obstacles. But that doesnt mean that the battery is discharged.
I can get out we my chair fully charged now (well actualy i cant because mine is damage and its not even here) and if i go uphill or climb some sidewalk i will need power to get it done.
Who made BMS that way?

"So again. We dont want a damned BMS interfering, we need to decide ourselves when we have gone far enough.
My approach? Fit a battery that is bigger than I can ever use up in a day!
And...
Watch the voltage with a tiny alarm. Or a volt meter.
And...
My controller (roboteq) is programmed to flash an LED / sound a buzzer on my pod when the battery gets to a voltage I choose. (2.7v per cell in my case) It can also be programmed to use that signal to stop the chair. "

How do i know when i have gone far enough?
How do i know how to watch the voltage and know what means what?
How do i know when the chair is in too much effort and will e game over?
And when it happends, what can and shoul i do to make it ok and carry on my path again?

My chair have one box on the left side that has a on/off switch. When i try to climg on to hard curbs and it is in a bigger effort it just shuts down.
Thats when some good samaritan have to reach the on/off button and turn the power on again.
Then the joystick can be turned on and is like reseted to minimum speed. I have put it fast and furious again. Not that fast and neither furious but thats what we have...
What is that box cut off thing by the way?

[shirley_hkg]

You represent the BMS things very well.

Why we always advocate putting some unreasonable large ampere ?

The advantage is we never have to worry the battery is abused again, no matter how far we travel, going up hill, get over curbs.

[Burgerman]

He means that if we fit a large Ah and C rate bbattery then we never need worry about any of that stuff again.

[Burgerman]

How do i know when i have gone far enough?

Fit a big battery and you will tire, or the day is over long before it matters. And also a low voltage alarm.

How do i know how to watch the voltage and know what means what?

Read the lithium thread pinned at the top of the forum. And read above.

How do i know when the chair is in too much effort and will e game over?

If you fit a large enough Ah, and high C rate cells, its impossible.

And when it happends, what can and shoul i do to make it ok and carry on my path again?

If you fit enough Ah, and large enough C rate cells it wont happen.

[LROBBINS]

My chair have one box on the left side that has a on/off switch. When i try to climg on to hard curbs and it is in a bigger effort it just shuts down.
Thats when some good samaritan have to reach the on/off button and turn the power on again.
Then the joystick can be turned on and is like reseted to minimum speed. I have put it fast and furious again. Not that fast and neither furious but thats what we have...
What is that box cut off thing by the way?

Hard to know for sure without seeing it, but from the description this sounds like a circuit breaker that is cutting off all power when it senses that too much current is being drawn. It could be undersized, or it could be old and tired - especially if it's been tripped many times. If it is a circuit breaker, somewhere on it it will say how many amps it should continuously carry. It will trip after a significant delay at twice that current, and much faster the more the current exceeds its rating. If it has gotten weak, it may trip at a much lower than rated current.

If you suspect that it is tripping too easily, it is probably easier to just replace it rather than try to test it - for that you'd need a peak-hold ammeter to see what current was actually flowing just when it trips. If it is a standard type, you should be able to find a replacement at an electronics supply for a price much better than what a wheelchair dealer would charge. Even if you can't find it there, you may be able to find it online from a wheelchair parts supplier (such as Monster Scooter); they are not the cheapest source, but still better than the dealers.

Ciao,
Lenny

[nealnlx]

[b][size=150][color=#400000]
You represent the BMS things very well.

Thanks Shirley, if you say that it means i been learning a bit around here. Nice.

He means that if we fit a large Ah and C rate bbattery then we never need worry about any of that stuff again.

Do we still need to worry about it ?

How do i know when i have gone far enough?

Fit a big battery and you will tire, or the day is over long before it matters. And also a low voltage alarm.

What do you mean by you will tire, or the ay is over lobg defore it matters?

How do i know how to watch the voltage and know what means what?

Read the lithium thread pinned at the top of the forum. And read above.[/quote]

I will read the thread and red the above. I understand that when it reaches such a low voltage the alarm buzzes, but being to noob i am at this, how do i know what it really representes and what steps to do to take care of this properly. (funny to talk about steps around here isnt it?)

How do i know when the chair is in too much effort and will e game over?

If you fit a large enough Ah, and high C rate cells, its impossible.

And when it happends, what can and shoul i do to make it ok and carry on my path again?

If you fit enough Ah, and large enough C rate cells it wont happen.[/quote]
Does this two answers respond as well to the abover question? If i fit enough Ah and large C rate cells, will it prevente the chair to go on lower voltage?
Its a bit of a paradox in my head about this now because; if its a large Ah and large C rate it means it can deliver a big juice when needed on thoses peak momentes right?
But its also right that if voltage drops under load, it means that when in those needy efforts moments, although we have power on batteries te voltage still goes down anyway.
Am i having wrong thinking through this one?

And what it is for you a large anough Ah and C rate cell for these things to turn impossible to happend?