PINNED - Lithium battery conversion/info

[Burgerman]

Turn balance entire charge OFF!
Set balance current limit to MAX!

Unlike most LiFe cells, the headways are pretty much constant voltage from about 60 percent to about 97 percent charged. But there is SOME variation between cell voltages on different cells AT THE SAME STATE OF CHARGE. So you don't want it to try to balance anywhere but where the voltage suddenly rises at the end of charge. The Hyperion balances right at the top (3.600v) only.

So the voltage may be 3 to 8mv different across cells, but they are absolutely equally balanced for capacity. If you attempt to balance them there based on volts, they you are actually wasting power and time UNBALANCING them to try to make the voltages equal. Only to have to fix it again at the real end of charge where the voltages go high and split apart.

So if it lets you, set up a profile that only balances from 3.450v upwards. And then charge to 3.600v. And if it allows you to tell it when to end charge, do so when charge current drops to less than 100mA.

Now you know why I decided to help hyperion to get things right. That charger can also do this stuff though I think. IF you set it correctly.

[steves1977uk]

Thanks for the info BM.

I had to modify a LiPo preset to set a higher balancing voltage which is 3.50v since it only allows .1v adjustments. I've also set it to terminate the charge when it reaches 85ma, as this can be set in 5ma stages. Charge voltage is 3.600v.

Also I have a digital volt meter that shows me the average volts over the pack per each parallel rows of cells. The cells voltages are within 0.04v of each other in the 3.30-3.34v range. Overall voltage after 4 days without charging is 26.5v and the chair still feels like it has plenty of charge in it using it indoors only. The low voltage alarm is set to 2.7v.

Steve

[Burgerman]

At the end of charge the best solution is to not terminate at 85ma, but hold cells at exactly 3.600v for an hour after this point. If it allows for this. Then everything including balance off.
Then it will ensure that the last cells to arrive at 3.600v get enough "soak" time to stabilise at this voltage.

[Burgerman]

See how many days you can get - down to about 3v. (24v)

The controller will say your battery is dead...
Your alarm may beep under load.
Your battery is safe. Then you will know how far you can really go. Range should be pretty good.

[steves1977uk]

Some of the cells do dip down to 3.22v under load on the slowest speed. Think I have the min amps set to 60 in the PM and the max 100. Should I up the min to 100 as well?

I now have set the charger to terminate when all the cells reach 3.6v and hold them there for 1hr.

Thanks for your help BM,

Steve

[Burgerman]

Yes min Amps to 100 too. You will get full torque at slow speed settings or small stick movements. Makes it move over obstacles slowly without needing more "throttle"...

>>>I now have set the charger to terminate when all the cells reach 3.6v and hold them there for 1hr.

AFTER it reaches 80mA. Or better still hold it at 3.600v for 90 mins after it reaches 200mA because it may never reach 80mA as it gets older.

[FJC10]

I tested my wheelchair TDX SP with 2x yuasa NP7-12 12v 7Ah and the wheelchair apparently is OK, no show error code 1 or 2, now show error code 7 (battery low) but this error code I think is OK due this little batteries.

Well, now I want make lithium conversion:

How many cells I need to test if the electronic of my wheelchair accept this type of batteries? Min number of cells, because first is for test purposes, if test is OK I'll add more cells. Maybe 8 cells? 8 x 3.2v = 25,6v? cells of 12Ah or 15Ah?

The space available in my wheelchair for this batteries:

depth: 41 cm
width: 28 cm
height: 25 cm

In this space, how many cells can I fit of 12Ah or 15Ah?

What charger I need, cell connectors, holders, BMS, etc?

Thanks in advance

[Burgerman]

http://www.wheelchairdriver.com/convert ... ithium.htm

http://www.wheelchairdriver.com/BMS.htm

And read all of this thread.

You need 8 cells in parallel. You need as MANY CELLS as you can fit. Do not test with just 8.

You need a good hobby charger that can balance cells as it charges. You do NOT want a BMS...

[terry2]

Great info. I will be trying this out once the warranty runs out on my chair.
But it does give me time to save for all the updates I will need.

[maker102]

Just a few questions: Is this the best battery monitor to use to avoid over discharging the batteries?
[urlhttps://www.wirelessmadness.com/index.php?_route_=fusion-smart-alarm-lipo-battery-checker-and-alarm-fs-bc06][/url]

I understand that LiFePO4 equipped wheelchairs are not allowed on airlines, is this still correct?

When building the battery pack will I need any 4 hole connecting plates?

Are these one massive cell or a pack, and would you recommend them?
www.batteryspace.com/lifepo4-prismatic- ... dgr.aspxrl

[woodygb]

http://www.batteryspace.com/lifepo4-pri ... d-dgr.aspx

One cell.

[Burgerman]

http://www.batteryspace.com/prod-specs/ ... 0100V2.pdf

And quite low C rate (3C max at best) and as shown here, they don't much like 3C...

http://www.batteryspace.com/prod-specs/ ... 0100V2.pdf

At the rated 10C pulse they would be down to about 1.8 volts...

[terry2]

I take it there is no good lithium battery pack that I could swop out?
I would buy them now if there was.

I don't want it for speed(yet) but for distance and hopefully my chair won't slow down to 2mph on a very slight slope.

[Burgerman]

There are good cells, and there are good chargers. And there are good ways to convert a chair. But there is no good simple way that's any good. No plug and play fit and forget solution for the average couldn't care less user. That said its all pretty easy ONCE YOU UNDERSTAND!

[terry2]

There are good cells, and there are good chargers. And there are good ways to convert a chair. But there is no good simple way that's any good. No plug and play fit and forget solution for the average couldn't care less user. That said its all pretty easy ONCE YOU UNDERSTAND!

I'm still trying to understand but I know your right BM.
I just can't take it all in at the moment, especially the part about sorting out the bad ones(my meds don't help). I'm going to get that charger you talked about BM while it's cheap.
I wonder if that bike shop you posted that sells the battery's would make me one up if I gave them the measurements and how many?
I'm really fed up with the fusion, 3 months old and it can't go up a very small in climb faster then 1-2mph. On the flat it's great.

[Burgerman]

If you get a bike shop to sort out a pack they will try and sell you a BMS and a dumb charger.

It will cause problems...

And they will not understand how to wire it or what connectors to use, or what size to make the pack (it will end up too small) etc.

Its something you really need to get your head around. You don't "have" to measure the cells. Just build it. It may take a long while to balance up sometimes if you don't charge regularly. That's the only real difference.

[Burgerman]

On the other hand measuring self discharge is EASY!
Slow way but easy...

1. Charge each cell full. One at a time. Label each one 1 2 3 4 etc.

2. Discharge each with the same charger by say 3Ah exactly. (Watch the figures and stop at 3000mAh with the button).

3. Store untouched for 2 weeks to a month.

4. Recharge each one slowly (say 1A charge rate) to 3.600v and read exact mAh from the charger on completion. Write the figure on the cell. It may be say 2870 or 3080mAh for eg. Most will be very close.

This tells you the amount they lost in 2 weeks plus the 3Ah you replaced back. The figure may be a bit less than you expected for tech reasons. Don't worry about that. (If any cell is vastly different to the rest, replace it)

5. Now divide your cells into 8 groups, to give you the 24V battery you desire. But make sure that those numbers you wrote down add up to approx. the same for each group of 8 cells. This is your battery.

At this point the groups of cells will all have the same AVERAGE self discharge rate. So if stored for a few weeks they will not go out of balance much. So subsequent recharges will be faster.

[FJC10]

http://www.wheelchairdriver.com/converting-to-lithium.htm

http://www.wheelchairdriver.com/BMS.htm

And read all of this thread.

You need 8 cells in parallel. You need as MANY CELLS as you can fit. Do not test with just 8.

You need a good hobby charger that can balance cells as it charges. You do NOT want a BMS...

Thanks. You're right. I think begin buying the Hyperion charger. What power supply I need (or recommended) for Hyperion charger?

Thanks. You're right. I think to begin I go buying the Hyperion charger. What power supply I need (or recommended) for Hyperion charger? Where can I buy it? Ebay?

[Burgerman]

Wherever you can find it. Its discontinued. Or use a iCharger.

Get a big enough supply to use full power on whatever charger you buy.

You need about 700 watts for the Hyperion. Maybe double that for the bigger iChargers. I use some Digimess 40A 30V adjustable one. And some smaller cheap industrial 600 and 700 watt ones from ebay. And my car.

[mous3]

Well after over 6 months of not caring about batterys going flat sometimes going 2 weeks on one charge the finale did go flat on me but even then by stopping switching of and waiting they did get me on the bus and I did make it home 2.7v per cell this bounced back to 3v after buy the time I hooked up the charger that's a 60ha 32cells sorry grammar is poo today. I will put this same pack under the spectra XTR when i get it as 1/4 the weight of the 60ha led that it is designed to carry and less than half the size allowing me to customize my C.O.G and carry bits and peaces under their or improve the not so hot ground clearance.

[Burgerman]

Lithium is quite amazing compared to lead isn't it. You wont have hurt the lithium much running it "dead". LiFePO4 is quite tolerant.

What matters is how many Ah the pack is, and how many you got back in - read from the charger. If its a 70Ah pack and recharge got 60 back in then it wasn't fully discharged. If it got 70 back, then no worries. If it got say 65 back and there were balance issues (long time) then you may have hurt some cells. Unlikely doing it once.

[mous3]

I have a 60ha pack and returned 56ha i have one weak cell in group 4 as I did some Alankey welding when i had finger trouble during construction.
They are 15ah cells, what i like best is they don't fall over under load and that little extra free speed off a fresh charge then of course their is the huge gain in range my pack maybe small but It's twice what my chair lumped about of lead and i can pick it up at 16kg rather than over 20k per 12v.
And i can rebuild the pack easily at any time to fit another chair

[Burgerman]

You shorted a cell? Just swap one cell. Pleased its working for you. They perform much better than lead under load don't they? Non of that nasty sag...

[mous3]

The cell is not totally dead but when i rebuild it I will hunt it out and replace it

[wilsonintexas]

I am the guy building an off-road cart that my daughter can but her existing wheel chair onto. It has a lot of reclining features to it and I did not want to try and duplicate that. There is NO WAY this is anything but out-door. I have all of space I want for things like batteries. SO......

I would like decent range, but do not need it to run for a week at a time. It will usually be for weekend outings. It will be of-road, so I expect more power than top end speed. (thinking quickie 6.5 motors with bigger ATV type wheels).
Cost for me will be a driver.

It looks like (5) 12 ah in parallel gives 60 ah. John uses 6 for 72ah. But he gets a week out of them.

I am thinking that for a weekend I might be able to get by with 40ah. I am leaning toward the CALB 40 ah or 60 ah cells. I can get the CALB 40ah for around $58 and the 60ah for around $81

So, it looks like, I trade range (ah) for top speed (volts). I am not sure how much the difference from 40, to 45/8 and 60 ah is in range for me. ( I know he obvious, 60ah is 50% more range..... I have no way of knowing what that might be.... )

The cost for 40ah pack of 13 is $754 (calb)
The cost of 45 ah pack of 11 is $765 (3-15 ah cells)
the cost of 48ah pack of 11 is $792 (4-12ah cells)
The cost for 60ah pack of 11 is $891 (calb 60ah)
The cost for 60ah pack of 13 $1066 (calb 60ah)

So, the question, putting a thumb in the air, making a WAG (Wild Ass Guess) for a weekend in the woods, how many AHs do you think I will need? I will then let price decide on how many volts I can afford.

I am split between the first three right now.

I know that my mileage will vary.
Recommendations / coments welcome.

[Burgerman]

>>>I am thinking that for a weekend I might be able to get by with 40ah. I am leaning toward the CALB 40 ah or 60 ah cells. I can get the CALB 40ah for around $58 and the 60ah for around $81

Ah is only a part of the picture.
How long do you want these cells to last?
The reason I use 78 cells and 3.2kwk pack is many...

First I have to try to explain that motor Amps and battery amps are NOT the same! Drastically different in most cases. And that when you double the battery VOLTAGE you half the battery AMPS at the same motor speed/load. So that: A 70Ah 48V battery will give the same range as a 140Ah 24v battery if used on the same motor with the same gearing. What matters is total WATTS. (Volts x Amps = Watts)

So if the motor cables measured, takes say 100A at 18V at stall, and max out the controller (100 limit), that is then at a 75% pulse width. Or 100A X 18V = 1800 Watts. That means that the battery Amps will be less! Because the volts are higher at 24. Or if you prefer, 1800W div by 24V = 75Amps. And if you DOUBLE the battery volts, this battery Amp level is then halved to 37.5Amps.

Do you understand this? So you cannot only look at Ah. You must multiply the Battery Ah by the Voltage to convert to Kw/Hour. My battery is 3.23kW/hours. Or if you half the voltage you need to double the Ah...

[Burgerman]

>>> >>>I am thinking that for a weekend I might be able to get by with 40ah. I am leaning toward the CALB 40 ah or 60 ah cells. I can get the CALB 40ah for around $58 and the 60ah for around $81

Continued...
Calb cells are 3C So the MAX amps you can take from a Calb cell without extremely rapid demise, would be 3x 40A, or 120 Amps. You have 2x 150A capability with the Roboteq. Or 300A is a possibility. Now that will actually "work" although you would get a short service life and quite heavy volt sag. And absolutely non of the advantages of using lithium batteries at all.

The advantages, and reason to prefer them is that they have a higher energy density allowing you to get MORE RANGE than before. So in a powerchair we can get 3.2kwh in the same volume as the 1000kwh lead batteries came out. And by doing so we get 3x the range.

Also because we are fitting 3.2x as much storage we are working the batteries 3x less hard. Lithiums live a very long time if treated well. In this case with 40Ah you will be discharging them at a high C rate. And that shortens service life quite severely. And you will be discharging them deeper as they are small. Ditto. So negates advantage 2...

If you discharge a 3C cell at .3C as recommended for all the large prismatic, don't go over 3.6V and don't go below 2.7V they will last 10+ years, and 2000 cycles or better. That means a discharge rate of 0.3 of 40Ah cells, or about 13.3 Amps...

There is a reason I use 10C rated Headway cells, an a relatively huge 3.2kwh pack.

[wilsonintexas]

Avoid brain surgery if you can. one of my degrees is a ee..... I was not thinking. I understand watts. The C rating of batteries is new to me, so I need to read up some more. IT looks like I am better off with the 12ah cells as you suggested in the first place..... and probably explained xx times someplace in this post. Thanks for your patience.

[Burgerman]

>>> viewtopic.php?f=2&t=4660#p62594

Read link above - absorb!

C rate is easy. A 10Ah battery that is 3C continuous can be discharged at 30A continuous. Without failing instantly. However this doesn't mean its a good idea. Discharging a 3C battery at 3C means a few hundred cycles if you are lucky.

A typical prismatic cell like CALB say 3C max but 2000 cycles at a ten times lower 0.3C DISCHARGE...

Headways are 10C rated. So much more headroom. And at 1C will give 2000 cycles. That's 3x better than the prismatics at the same currents. http://www.evassemble.com/index.php?mai ... oiipkkul10 See chart.

[Williamclark77]

C simply means capacity. A cell that can be discharged at 3C means it can be discharged at 3 x it's capacity. A 10ah cell at 3C COULD be discharged at 30 amps. A 15ah cell at 3C is 45 amps. That's all it is. And exactly why in a powerchair you need a high C rating and use as many cells in parallel as possible to spread the load over each cell as well as add more capacity to your pack.

Pulling 30 amps from one 10ah cell that is rated for 3C hits its maximum. However, running 3 in parallel while pulling the same 30 amps draws only 10 amps from each one and will drastically increase their lifespan (not to mention that you now have 3x the range by adding capacity). Hence why we used Headway cells rated at 10C and run as many in parallel as space permits because powerchairs can routinely draw 150+ amps depending on the controller and electronics.