PINNED - Lithium battery conversion/info

[Burgerman]

This is a "system" http://www.wheelchairdriver.com/BM-MK3- ... rchair.htm

As is this http://www.nissanusa.com/electric-cars/ ... .vlp.image

And http://www.brammo.com/home/

As is your laptop and its battery and management system. The lithium pack forms a part of an integrated system that was designed to work together. Like the 72V Segway.

The motors, and controller and its programming and voltage, current demands and battery monitoring as well as cell count, C rate internal resistance etc are all tailored to work correctly together at best efficiency with longest service life. A complex careful balance. Its not a drop in replacement "battery". For e.g. the lower internal resistance and lack of peukert affect means it makes sense to roughly double the battery voltage for a 100 percent gain in either range or speed FREE of any downsides. Or it allows a smaller battery to do the same job without exceeding cell capability for a sensible service life.

Cloning a lead brick in lithium demands a BMS and loses at least half the benefits, and it wont live long.

And there's a reason your laptop runs on 19 volts rather than 6 or even 12v. And a reasons that e-bikes, cars, segways, and motorcycles are running on 48 to hundreds of volts. And reasons they use brushless motors, specific software on controllers and battery monitors etc. All designed to work together as a system.

[funkykeyboard]

sorry, is there a web page created now, that runs through the whole process from beginning to end? Tried looking through the thread, but couldn't find it. Sorry.

Had several teething problems with the battery pack I built (or my electrician did) and it has gone and died on me. want to make sure I do it properly this time.

Thanks in anticipation,
Funky keyboard. C4/5 tetraplegic. Currently using a modified life stand wheelchair, with lithium batteries, USB charger, modified lighting system. Trying to build a copy of the BM 3.

[Burgerman]

How do you mean it died on you?

Details, cells? Number, type, charging details, etc.

[funkykeyboard]

I'm sorry, I am, Funky keyboard. C4/5 tetraplegic. Currently using a modified life stand wheelchair, with lithium batteries, USB charger, modified lighting system. Trying to build a copy of the BM 3. which means, I don't really have the knowledge of physical capability to do all this, and soI have to rely upon other people to do all this for me.
so how do I mean it has broke?

Well, it's complicated.
Because I have only just devised a method of my supervising my PAs plugging the wheelchair in, for the vast majority of time I have just had to rely upon them to do it properly, when they haven't been doing. I thought the chair was balancing properly at one point, but it wasn't. added to that, I put a USB charger for my phone, but when the electrician fitted it, he only fitted it to one battery pack. (With the design of the life stand wheelchair, there was to 18ah batteries on each side of the wheelchair, now there is 32 cells of lithium batteries, 16 cells on each side.) So one battery pack became very unbalanced, and one night the chair had run down so far one side, I couldn't drive it there was no power. anyway, we managed to get it all going again, but more recent problems I've had mean that instead of doing 8 miles, it will only do about 2 miles before the chair starts to judder with lack of power. When I check what is left in the batteries using the Hyperion charger by going to balance mode, and then pressing down 3 times, it tells me the cells are down to2.6 and less sometimes, which my electrician has told me means they are on the way out.

I hope my Lehmann's speak, is adequately informative for you to understand what I am saying, or at least trying to.

[Burgerman]

The cell voltage measured as your engineer has, cannot tell you they are on the way out.

The problem from the start here is that your engineer is an idiot. I see this over and over. These are the experts...

If the cells are correctly assembled, pre charged to 100 percent individually to rebalance, and charged and balanced correctly afterwards as a pack and then re-installed it will likely be fine. And if only ever charged and monitored correctly or on a PC, to check, then non of this can happen. Quite likely all of your cells are still fine, and just need correctly balancing and setting up. The Hyperion can do this just via the balance ports but that can take literally a week or two if they are miles out. They will only be damaged if run below 2 volts. Even then the Hyperion can tell you this and measure their ability in exact detail.

Lithium isn't as simple as lead. It requires a little user knowledge and ability to understand what's happening. If you do, then its super reliable. If you don't then this is the result. Everything has to be right and monitored to be sure it stays that way.

This is the reason that getting someone to build you a chair will never work, and the reason I would never sell my chairs to anyone. Not just lithium batteries but everything.

[shirley_hkg]

What on earth could a qualified electrician make such terrible mistake.

That 4 SLA are a 2P2S setup.

[Burgerman]

It doesn't much matter how its set up as long as you end up and are using a 8S 24v pack.

And because the world is full of them.

This is why battery sellers push BMS setups to try and cover user ignorance.

[shirley_hkg]

2.6V is completely empty. Can you just charge the under-voltage pack only , with the Hyperion ?

[Burgerman]

I would fully charge each parallel group full. And soak at 3.600v for a few hours. Then charge normally.

Have a read http://www.wheelchairdriver.com/BM-MK3- ... rchair.htm

[flagman1776]

It hardly seems possible that a correctly wired pack would give this result. My suspicion is either the load wiring is incorrect or the charging wiring is incorrect. This should not be difficult to figure out. Then, as BM suggests, the cells should be charged completely including balancing. There could be a mistake or a bad connector somewhere. (I had to resolder some most of the original balance leads when I converted my generic china pack. I'd have been better off to have built my own from Headway cells.)

With correct wiring, charging should be simple. Charging my LiFePO4 pack requires 2 plugs, they're different & keyed so they can't be assembled wrong. Start the smart charger & push enter until the charging cycle begins.

[funkykeyboard]

Well you already know lots, so its easy for you.

Go to http://www.evassemble.com or wherever you choose and for group 24 replacement order 72x 12Ah headway cells. And 72 orange blocks (included), and enough bus bars. (13 x 6 x 2 + 26 on my 78 cell pack). You will need to work out how many...

Then charge every single cell to 3.600 volts, and leave on charge afterwards for 2 hours minimum to soak. You can do this in parallel in big groups of say 10 at a time. Will take about 2 days. Then put them all in a box, disconnected and loose and forget them for 2 weeks or preferably more. Now charge each one individually (will take just a few mins) and write capacity added in Ma at the charged point in software on each cell in pen or on a sticker. This is a measure of self discharge. How much it lost over time in storage.

When you have done this you need to put them in groups of 9 (each parallel group) that add up to the same Ah lost when averaged. So all the parallel groups are as similar as possible when added up. You will have 8 bags/ boxes with 9 cells in each with similar average self discharge levels.

When you get this far email me or post here! I may have a page up by then.

This is for group 24.

For group 34 it doesent work out well, and is an awkward configuration. With 56x 12 Ah cells. Thats 28 per block but it can still be done.

For 22nf it can also still be done with less 10 Ah cells but ends up with each pack about 12mm wider. This may or may not matter. A tape measure will tell you.

I'm just wondering;
"When you get this far email me or post here! I may have a page up by then."
do you have a page up by now?

[Burgerman]

Yes but not finished and you probably saw it already.

But I suspect your case is a number of different issues.

You need to get everything right and understand what you are doing.

1. I will put money on 1 screw (battery end terminal) being loose. Or more. That causes mayhem with cell balancing. THROW AWAY all screws and fit cap screws, and Loctite every one as you go.
2. connecting ANYTHING to part of a pack. Massive balance problems.
3. Not fully charging each cell individually, as you build the pack.
4. Not fully charging and balancing the battery before use first time. Significant out of balance may take days...
5. Taking it off charge before it has ended. Or not setting the charger correctly...

You MUST understand what is going on. Then its easy. If not then you are in a world of trouble.

ALL the above must be true. And your engineers are idiots! They almost always are though.

[Burgerman]

Remove pack.
Replace every bolt tightly with cap (allen) bolt.
Charge each PARALLEL group separately as a 1S pack and fully to 3.600v until it has been sat on charge at CV 3.600v for at least 2 hours. Do all 8 groups.

Connect charger and balance leads and charge and balance until all cell groups are at 3.600v.

Use a PC for all the above so you can SEE what is happening.

Replace battery.

Use chair for a day.

Put on charge and watch on PC. All graph lines should charge up as a close group. And balance will end inside 5 to 20 mins. If you did the rest of this message correctly and no cells have been ruined this will be the case.

[flagman1776]

I can't find where we discussed my Pride Wrangler LiFePO4 conversion project before. I will find it eventually. To refresh everyone it has 2 "Group 27" SLA batteries ("90" Amp) under the cover. The question is... to use big cells like Winston or CALIB OR to use many Headways cells. In either case, some rework of the molded battery mounting recess taper will likely be required... cutting, grinding, fiberglassing of the plastic body panel... so I consider that to be equal.
Planning to stay with approx "24" volts. The original charger would be deleted in favor of charging via a smart charger with balance connector.

[Burgerman]

Since you have room for a lot of Ah, and scooters are easier on batteries than powerchairs it would probably be better to use large prismatic. At least as far as cost and number of connections.

[flagman1776]

Large cells would be easier to connect if a good fit match could be achieved. Might save a bunch in hardware over Headway. I've been reading up on CALIB & the idea of squeezing them in a mass is scarey. Why? A lot of fuss about shipping them in US.

[MViper]

I have a question, if I missed the answer somehow please point the link to me.

I'm looking to go with Sunrise Jive R2 wheelchair with R-net controller. I will also equip it with lithium batteries. All fine and dandy.

The thing is, stock battery indicator is useless now, it always shows full juice. Are there any ways to install any kind of indicator (even external will do) to see the levels of remaining battery power?


Thank you so much!

[Burgerman]

Yes. But not voltage based.

You need something that measures Ah to do this accurately. Unlike Lead, Lithium Ion Phosphate cells don't suffer from the Peukert affect that makes it impossible to predict remaining range.

But they have another issue. They drop very fast - in the first 20 yards - from the freshly charged voltage to around 3.3X volts per cell. And then for the next 1/3rd the capacity voltage does not drop at all and can actually rise slightly. At about 40 percent it drops in a small "step" then tails off extremely gradually. Not fast enough to determine accurate state of charge from the slope without 3 decimal places and some careful calibration. Then at about 90 percent they start to fall fast.

So the only good way to really know, is to use a meter that can measure Amps used over time and give you the Ah count up. Then if you have fitted say a 108Ah battery and have used up 50Ah, you know to go home and have 8Ah spare.

But if you do the job correctly and fit a 108Ah of lithium (72X Headway 12Ah cells) you will have 2808 watt hours. Compared to around 760 x 2 less about 30 percent not accessible. From fully discharged set of 73Ah MK gels...
In other words 3x the range. So I don't think you need worry much!

[MViper]

Thanks Burgerman!

What you're talking is giberish to me, because I know bollox about electricity

The thing is, I do a lot of office work at home and was recharging existing chair (truetrack) once per week (now after 5 years on second or third day). I do rarely 20-30 miles drives and than recharge it every night.

So basic metering would be great. At least some annoying beep at 50% or 30% or something like that would be grand.

[Burgerman]

I will also equip it with lithium batteries

What you're talking is giberish to me, because I know bollox about electricity

recharging existing chair (truetrack) once per week (now after 5 years on second or third day

Well then...

Why would you want lithium?

And how are you going to equip it, figure out charging balance cables, charge profiles, or an Ah measuring device?

And had you charged that lead chair every day it would still be good now.

[MViper]

I want lithium coz I do 30 miles or so distances about 2 months per year. And would absolutely hate stock 15 miles radius.

The official reseller is doing me a favor of giving me option of lithiums. So he will be fitting it. Except he can't fit indicator yet, that's why I'm asking.

You sure? Afaik those batteries have lifetime of 4-5 years anyway.


So what you're recommending me is: charge lithiums everyday and you won't need any indicator. ?

Makes sense.

[shirley_hkg]

Gauge does not help, especially when you're using BMS, because poor balanced cells would cut output without notice.

Watch the voltage when It's less than 26.00, and go no further. @24.00.

You will learn fast, just a few trials.

Price of lithium battery is only 1/3 of that of GEL. So, put some more than you need and less abuse of battery.

[MViper]

Cheers

I never had any experiences with lithiums. As you can see, I did not even know that you need to recharge chair everyday. So I look like a real tit now.

Now that I have a bit more of a time, let me explain to Burgerman:

In wintertime I don't go outside a lot, but in warm months along with my usual indoor use I do. When I am outside I do sometimes around 30 miles per day, sometimes 5, sometimes something in between.
So stock radius of 15 miles would be a bit of a shock comparing to current chair when I can do a lot more than that. So to be honest I'm still in a dilemma of sticking to stock gels or fitting lithiums.

And since lithiums are supposed to be lacking indicator of usage, and to my poor knowledge of not knowing that you absolutely need to charge chair everyday day, I asked if there's a way to install it.


So to ask another question (I apologize if I'm asking dumb things) to the users of lithiums: You just recharge it every day and simply driving it with no worries, no need for any kind of indicators to see remaining power?

[Burgerman]

The official reseller is doing me a favor of giving me option of lithiums. So he will be fitting it. Except he can't fit indicator yet, that's why I'm asking.

Official reseller? What does this mean...

At a guess, battery too small, with a BMS built in and endless problems with a service life about half of what it could have been. Be sure he is fitting AT LEAST 100Ah. Its not only for range.

The whole point of lithium is that its more energy dense. So its possible to fit much more Ah than you can with lead. This also gives the battery an easy life so it will last 10 to 15 years. But not with a BMS... And dumb charger.

[MViper]

I don't know exact terminology in English. But when I was ordering the chair the bloke gave me an option of lithiums. I'm not the first, couple of other users are using them for 2-3 years now and all of them are very very satisfied.

So I have 3 options. 60Ah (10-12 miles range), 72Ah (15-17 miles range)(extra payment) or lithiums (around 30-32 miles)(extra payment)

OK, so you need to remove stock BMS and put other version? to make best use of lithiums?

Stock charger is okay? Or which one would you recommend?

[terry2]

So I have 3 options. 60Ah (10-12 miles range), 72Ah (15-17 miles range)(extra payment) or lithiums (around 30-32 miles)(extra payment)

Are they doing a battery pack like BM has designed? if not what make model battery are they supplying.

[MViper]

All I know is LiFePo4.

I've sent some emails.. waiting for feedback. I'm afraid they use stock charger. No idea about BMS.

[Burgerman]

It will have one. Or you couldn't use a simple dumb charger.

It will likely be considerably less than the 108 Ah possible... Because of the way its packaged and to make room for BMS.

They don't know any different. Because that's how lithium's are sold to people.

Exactly what cells/battery?


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

[terry2]

I know BM may or may not tell me off again. But I'd rather be stupid for 30 seconds then be a fool for the rest of my life.

Can I do this. Replace my gel with 2 packs of 16 Headway LifePO4 38140S 12Ah batteries.
Till I save up enough to buy the other parts. I know I will have to buy a Hyperion EOS1420i-NET3+power supply.
I just haven't got a lot of cash at the moment so I thought I maybe able to do it this way?

OK BM you can slant me now

[Burgerman]

You need two packs of 6x6 or 36 cells. That's 72 cells total. That's 108Ah and high rate. No more Hyperions so now PL8v2 chargers and I am helping with some firmware, presets changes as we type...