PINNED - Lithium battery conversion/info

[Burgerman]

Theres a bluetooth mod, similar to what I did to my Hyperions.


http://www.wheelchairdriver.com/hyperio ... ersion.htm

Will look for it tomorrow. But it doesn't need any internal changes...

[Gnomatic]

Thanks I'll be interested in seeing what that6 mod looks like

[Burgerman]

And yes, it works with no modification on software or the charger itself. The info is on the cellpro website I think, but I never tested this.
It just plug n play like fuim3 do. Unless you have change HC-06 baudrate into 19200 after that you good to go.

Setup:
1. Prepare a bluetooth module.
2. Change the bluetooth module's baudrate into 19200.
3. Make a circuit like I posted before. ???
4. Hook up power to bluetooth, pair and connect to PC.
5. Make a serial port connection from bluetooth.
6. Connect servo connector from bluetooth to charger.
7. Turn ON charger.
8. Open CCS, select port where the bluetooth is connected.
9. Done, you should have a connection between charger to CCS.

NOTE: From #6 - #8 above it can be inverted. And I have tried to update firmware from bluetooth but no success, better use fuim3 for updating firmware.

http://www.instructables.com/id/AT-comm ... th-module/

[Burgerman]

This is how simple charging a lithium chair is.

One connection. Plug in. Press go.
Or press go on the PC Software on your laptop and monitor it as it charges from 5 to 40 Amps. And balance cells as it goes.

[Gnomatic]

That looks good. About how long is your charging cable in your pic?

As I've mentioned before, from the measurements I've taken, a pack like expresso's will be the best fit for my chair. That's a 7p 8s pack compromised of 56x 15Ah 3.2v Headway cells for a 25.6v 105Ah pack at the end of the day. Just making sure I've got head wrapped around this.

Each 15Ah Headway cell has a 10C rating, so in theory it could supply a current of 150A for six minutes before being completely drained. Do I have that right?

[steves1977uk]

I would buy these if they were available to consumers... http://www.evlithium.com/Headway_Battery/51.html

Steve

[Burgerman]

A metre. Make it longer if you must! But its adequate.

Each 15Ah Headway cell has a 10C rating, so in theory it could supply a current of 150A for six minutes before being completely drained. Do I have that right?

As long as you only want tens of cycles. Its capable. It wont like it!

2000 cycles is at 0.1C

Lithium likes to be charged and discharged at low C rates. Hence large pack, high C cells.
And likes to never be full, never be empty, and use the middle 80 percent.
Charging to end never exceeding 3.550V or 3.600V will see a longer life than charging to 3.65V. And in all 3 cases that's 100% full. BMS typically allow repeated 3.7 or more volts. For hours on end.

[expresso]

I would buy these if they were available to consumers... http://www.evlithium.com/Headway_Battery/51.html

Steve

We cant buy those the same way we order from China EV ?

are those the same size as the 15ah model - or longer - wider etc, -

i wonder if we can get this Cell from the EVASS China - if its the same physical size and not much more in price - would be worth it ?

[steves1977uk]

The 16Ah cells are slightly longer/taller in length. I've never seen them for purchase on evassemble.

Steve

[Gnomatic]

Each 15Ah Headway cell has a 10C rating, so in theory it could supply a current of 150A for six minutes before being completely drained. Do I have that right?

As long as you only want tens of cycles. Its capable. It wont like it!

2000 cycles is at 0.1C

I understand doing that would kill the cells quickly. I'm just wanted to verify I was understanding the specs correctly. Compared to you, I'm a novice at this.

Also, the spec sheet on those rates them at 2000 cycles at 1C to 80% DOD. Where are you getting 0.1C?

[Burgerman]

Does it?

I have read specs on *lots* of LiFePO4 cells. They either don't say, or specify 0.1C for the claimed cycle life.

And this agrees with what we see on hobby stuff too. For EG I use 30C or better cells on model helis. These are usually pulling about 100A peak at full pos or negative pitch, 20A hover from a 4000 to 5000mAh Ah pack. So we are hammering them. After say 5 to 40 flights, the packs swell, or go high resistance and cant give the amps any more. The best packs are 130C! and expensive. And the same size as a pack of cigs, but will start a truck.

We use similar packs in low current transmitters, or FPV screens, and these last approx. 3 to 500 cycles.

[Gnomatic]

http://www.evassemble.com/index.php?mai ... cts_id=175

[Burgerman]

Yes I have seen that. But it seems a little strange and maybe a little less than accurate compared to the spec from most LiFe chemistry cells. Although the headway are 10C cont, compared to the vast majority that claim 3C continuous max. EG Calb, ThundersSky, etc.

So it may be true, or at least more likely to give a good cycle life than the prismatics at high discharge rates.

However there's no fixed figure. They all get worse the faster you discharge them
The lower the discharge or charge rate the longer lithium lasts. This graph is for lithium ion but the same applies. And the difference is not small...



Likewise keep awy from the high volts (and the low ones) and they last well...



Do both, by charging a large Ah battery, to a 90% charge state, and recharging once or twice a week, and discharge at low rate (by using a large enough pack) and you win 3x over. Or do the opposite and the battery will be unreliable and have a short lifespan. Fortunately we can get a 30 to 50% bigger pack i than stock, meaning we win!

Your phone battery charges at 1/2C and discharges at a really low several days 100thC approx. Thats why it lasts many years. Your laptop battery lasts about 12 months if used regularly. Because is charges at 1/2C and discharges in a few hours. (.5 to .2C).

and 0.3 V over-discharge of lithium-ion chemistry can result in 66 percent loss of capacity. Testing has shown that overcharging lithium cells by 0.1 V or 0.25 volts will not result in safety issues but can reduce cycle life by up to 80 percent.

http://www.mpoweruk.com/life.htm#rate

[Gnomatic]

Discharge rate certainly affects longevity, I'm with you.

Using expresso's pack as an example (56x 10C 3.2V 15Ah cells configured in an 7p 8s pack), what would be a typical discharge rate (C rating) per individual cell in such a pack with a 120A controller like R-Net? More importantly, how did you arrive at that figure?

I realize 120A @24v for the pack would not be near continuous real world powerchair discharge rate, but its just a number, I'm more interested in understanding the calculation to get the C discharge at the cell level of a pack such as this.

[Burgerman]

R-net is 120A per channel. So can pull up to 240A as you climb or accelerate up a ramp. And each motor can pull 120A as you zero turn.

So you need a pack that can comfortably do several times this (the more headroom the better) for longevity. It also means yo need a bms if you choose to go that route that can do 240A or so for maybe 4 or 5 secs at a time. That way it wont cut power as you drive up the ramp to a train, or wheelie or turn on long grass etc. And you wont hurt the cells.

Of course you could just use the max cont C rate as a guide although there's no standardized way to measure that, so manufacturers figures can be very misleading. Take 10C from a headway and voltage drops horribly, and it heats up the cell fast. That would be a torture test. It could do it. But not for long.

Many lithium re-sellers take the Chinese C rating and advertise 1/3rd that. So for EG a headway is really good for 3C and sensible performance and acceptable life. http://www.headway-headquarters.com/381 ... ergy-cell/ Pulse means a quick 1 second max. They derate the calb/thundersky cells from 3C to 1C in the same way. Because people take those chinese figures and think it means they can use the cell at 10C for a few days and then wonder why its died...

Notice that these are the newest lower impedance calb cells and so have a higher 0.3C charge/discharge maximum rating if you expect your 2000 cycles. Thats just 30A... from your 100Ah cell. Of course you CAN take much more, they will work. Up to 8C. http://www.headway-headquarters.com/100ah-calb-cell/

[Gnomatic]

R-net is 120A per channel. So can pull up to 240A as you climb or accelerate up a ramp.

120A per motor, I get that. But aren't the motors 12v? So the draw on the battery is still 120A @24v in such a scenario. Is that not correct?

[Burgerman]

At stall, if not moving depending on motor impedance the motor are limited in Amps to 120. That is done by the controller cutting back on the pulsewidth. If you average that stall volts by reading with a multimeter you may see 9V, 12V, or 20V or whatever.

However as you begin to move forwards and the motor turns the current drops. So to give max torque or acceleration the controller now must increase the pulsewidth (volts) to maintain 120A max torque. At anywhere between 1 mph and about 3 or more mph the controller hits 100% pulsewidth, at which point the motors now see full battery voltage in order to maintain max torque. So while accelerating, or climbing a ramp, or wheelies, etc the motors often see max power or 120A and 24V.

If that doesent give you a headache it should. It did me while I was figuring it out...

[Gnomatic]

Uh ..... processing ..... processing ..... processing .....

[Gnomatic]

So lets say the chair is climbing a curb, and for a short bit of time draws 240A from the battery pack - (ignoring other variables for this)

If that particular pack is a 56 cell lithium pack, is calculating the draw per individual cell in that moment as straightforward as dividing the # of amps by the # of cells in the pack? 240A/56 cells = 4.29A per cell discharge rate in that moment as the chair climbs the curb. Is that the way to calculate that?

I realize a chair is only pulling a fraction of that many amps most of the time the above is just an example

[expresso]

i am also thinking now to build another ADD ON - when i do my next pack - or build one for my current chair - with the full pack

then i can just leave it all connected - get a good 55 to 60 miles - never have to worry about carrying a charger etc, - all the cells work less - last even longer and gives me some traction on the rear tires that i lost from removing the Lead

i cant move my seating back so thats not a option and even with the extra ADD ON - it would be less weight than lead alone - not by much - 45ah ADD on i am thinking of doing with the chairs 105ah

[expresso]

getting excited over doing more packs now - that would give me 150ah of lithium - i already seen how i can use up the 105ah pack at 40 miles -

may not happen often but wont hurt to know i have more than enough to make it home

[Burgerman]

So lets say the chair is climbing a curb, and for a short bit of time draws 240A from the battery pack - (ignoring other variables for this)

If that particular pack is a 56 cell lithium pack, is calculating the draw per individual cell in that moment as straightforward as dividing the # of amps by the # of cells in the pack? 240A/56 cells = 4.29A per cell discharge rate in that moment as the chair climbs the curb. Is that the way to calculate that?

I realize a chair is only pulling a fraction of that many amps most of the time the above is just an example

No. You have 8 in series. You have 8x less in parallel.
Or 240A div by pack Ah = C rate max.
cell capacity x C = Amps max drawn per cell.

The figure you arrived at is 8x too low.

[Burgerman]

Expresso is getting carried away...

You will have about 65 to 70 miles range. Can you do that in A day. Dont think I could!

Thats say 7mph without ever slowing for 10 hours straight! In real world conditions you need to slow, turn, eat, drink, stop and look at things, wait to cross roads or slow down on uneven stuff. So maybe 15 hours...

Enter the new york marathon with camera. Battery sponsorship!

[shirley_hkg]

Into S S box .

[expresso]

Expresso is getting carried away...

You will have about 65 to 70 miles range. Can you do that in A day. Dont think I could!

Thats say 7mph without ever slowing for 10 hours straight! In real world conditions you need to slow, turn, eat, drink, stop and look at things, wait to cross roads or slow down on uneven stuff. So maybe 15 hours...

Enter the new york marathon with camera. Battery sponsorship!

Sounds great to me dont think i be doing that much range in a day - but it will put my mind at ease and the pack will never go low enough to worry - i can skip a day charging for sure even in the summer - if i did 30 miles one day - i wont charge and still have another 30 miles to go before charging - i will add some more weight in the rear where its needed more for traction - i can make a charge cable from the ADD on and charge from there - all the time for the whole pack if i just leave it connected all the time - i will have to make a long enough cable so i can use the seat lift all the way up - i will have to see how much longer - and find a good backpack to hold it in nicely -

this way - the chair with the ADD ON now will be my indoor chair next year - that will last for ever that way -

turns out maybe my friend may be interested in a ADD ON now - i emailed him this site link for him to read over some stuff here - now if he starts to save for this - i will - can help him with wiring etc, - i want him to at least get the Cells and charger PL 8 - or else i have the BMS for him - i advised not to but its his choice at the end -

[expresso]

i am planning to travel to where my parents live in the Bronx - i wont have to worry this way - can easily make it back and forth with no charging - i should be able to make it now with the 105ah alone - maybe its a 30 mile run for that

i wonder what the record is for a wheelchair

[expresso]

Expresso is getting carried away...

You will have about 65 to 70 miles range. Can you do that in A day. Dont think I could!

Thats say 7mph without ever slowing for 10 hours straight! In real world conditions you need to slow, turn, eat, drink, stop and look at things, wait to cross roads or slow down on uneven stuff. So maybe 15 hours...

Enter the new york marathon with camera. Battery sponsorship!

wont be a bad idea - or make a record on the Guinness book of records - i wonder if there are any records for a power chair -

[expresso]

Into S S box .

nice box - now you will bolt it to your chair back ? - i have to try and find a plastic container to just sit the ADD ON in and then sit the whole container in a back pack - strap it on the chair - hope to improve on the next one i make - and will shoot for a 45ah ADD ON - instead of 12ah cells i used before - will do 15ah cells - 3 Rows thats more or less what you get from a set of MK 24s Gel - that should give me a good 30 mile range i think ?

[Gnomatic]

No. You have 8 in series. You have 8x less in parallel.
Or 240A div by pack Ah = C rate max.
cell capacity x C = Amps max drawn per cell.

The figure you arrived at is 8x too low.

Okay that makes sense. Thank you.

[Gnomatic]

So, in my example 240A div by 105Ah = 2.29 C rate max

Using 15Ah cells in this scenario 15Ah x 2.29C = 34.29A max instantaneous discharge rate per cell

Compared to say climbing a curb where the controller may call for 240A from the pack very briefly, if just rolling along a flat sidewalk how many amps does a chair usually draw from the battery?