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Re: Step by step lithium conversion?

Postby Burgerman » 19 Mar 2013, 20:36

You can only use 24v nominal (equivelent to lead) on a normal powerchair industry standard controller.

So thats 8 cells in series.
Or 8 series 2 parallel (to double the Ah capacity at the same voltage)
Or 8s 3p
Or 8s 4p
Or 5s 5p etc.

So you can use 8, 16, 24, 32, 40, 48, 56, 64, or more etc (Multiples of 8)

This way a 6mph motor is still 6.
An 8.5mph motor such as the groove (AMT) is still 8.5mph.

Range does not change. You can have a 100Ah 24v battery or a 50Ah 48Ah battery. Same total watt hours. Range remains the same.

For what its worth, if you increase voltage you also win a little bit of efficiency too. And you dont HAVE to go 15mph. Set it to 10 in programming. But. You cannot do this with a mobility controller.
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Re: Step by step lithium conversion?

Postby PowerHungry » 19 Mar 2013, 23:52

Thats interesting, so 32 cell pack lithiums would provide same range, and if i wanted to get 10mph speed out of 8.5mph groove motors i need to program it? Is that a complex procedure?
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Re: Step by step lithium conversion?

Postby Burgerman » 20 Mar 2013, 00:02

Same range as what?

To get USABLE watt hours you just multiply.

With lead you multiply Ah x volts. And divide by 2. So 24v x 100Ah div. by 2 = 1200 USABLE Watt/hours
With Lithium you multiply Ah x volts and no need to divide by 2 (no appreciable volt drop under load, no peukert affect, and no need to save the last 20 percent). So my 72Ah x 45v pack gives approx 3000 Watt Hours. Or 2.5x as much stored USABLE power. Thats 78 12Ah cells in 13s 6p configuration.

So any similar amount (Ah) of lithium, will take you between an extra 40 percent and an extra 100 percent further depending on load and C rate.
But 32 cells means just a 48Ah battery. And you are replacing a 70Ah battery. So you will not gain anything if at all. You need to be using 72 cells for 108Ah and around 2800Watt Hours.
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Re: Step by step lithium conversion?

Postby Burgerman » 20 Mar 2013, 00:03

and if i wanted to get 10mph speed out of 8.5mph groove motors i need to program it? Is that a complex procedure?


The ONLY way to exceed 8.5mph is more volts. That means more cells in series, and that means a NON mobility controller.

Double the volts = double the speed.
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Re: Step by step lithium conversion?

Postby PowerHungry » 20 Mar 2013, 00:10

Oh right, what controller would you recommend?
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Re: Step by step lithium conversion?

Postby Burgerman » 20 Mar 2013, 00:28

Well I am using this http://www.wheelchairdriver.com/BM-MK3-roboteq.htm with 13s cells.

That means 47v charged, 42v to 45v running and 15 mph max speed. Its not plug and play. Not designed as a mobility controller. Needs code for turn rates etc, and for motor compensation, and a joystick figuring out.
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Re: Step by step lithium conversion?

Postby maker102 » 05 Apr 2013, 14:41

I know I am beating a dead horse, but I have to ask before I plunk down big money for cells. Are these the ones I want to buy, or does anyone know of something better? With the original post being over a year old now and technology changing daily I just want to be sure. Should I wait for something with a better cost/reward to become mainstream in the next month or two?

http://www.evassemble.com/index.php?main_page=product_info&cPath=2&products_id=21
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Re: Step by step lithium conversion?

Postby Burgerman » 05 Apr 2013, 14:59

They are, for powerchair and high discharge rate about as good as it gets at the moment for safe LiFePO4 cells. Used with a proper balancing charger NOT a BMS.

Care when assembling, and some understanding is required. I am just about to order a set to build 2x 12v packs (72 cell total) for my BM2 chair. If only the damned Odyssey batteries would expire!
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Re: Step by step lithium conversion?

Postby Ramblin Granny » 05 Apr 2013, 17:34

So the Battery management system (BMS) is not the best charger for dummy use? If we are going to get wide spread use of Lixxx in powerchairs, we have to have no engineering knowledge chargers.
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Re: Step by step lithium conversion?

Postby Burgerman » 05 Apr 2013, 18:43

(BMS) is not the best charger for dummy use?


It IS possible to build an integrated charge system, that is vehicle specific, microprocessor controlled etc. One needs to be developed for each specific application. At great time and expense. As used in laptops, full sized cars, etc. But a one size fits all BMS cant work. Too many parameters are just guesswork, cell balance isn't adequate etc. A powerchair manufacturer could easily do this for eg.

BMS systems are not chargers. Cheap, built in BMS, and cheap BMS setups attempt to make an "unfriendly" set of Lithium batteries usable by someone that doesn't understand Lithium batteries. Its a "simple" way of selling Lithium's to the masses without them destroying them straight away through ignorance. Hopefully. They also mean any dumb (or existing) charger can be used. The problem is that if you are very, very lucky, the BMS may help you do this for anything from a day to a year. If at all in some cases...

Their is no cheap, easy, dumb solution that will allow you to use lithium batteries correctly or reliably in a powerchair. All monoblocks (lead replacement bricks) OR packs made from loose cells with BMS are unsuitable for a huge bunch of reasons. Not least is that to CORRECTLY design the BMS you need to know about a dozen different powerchair and cell parameters and then use an integrated BMS controlled charger.

It can however EASILY be done now by anyone very RELIABLY with huge range/capacity/battery service life. It just needs:

a. some USER knowledge and understanding. Don't want to learn? Use lead.
b. a hobby style charger that balances cells properly as you charge and that does not allow them to exceed 3.600 volts each and ensures accurate balance.
c. a high rate cell that can stand up to the amp draw reliably (at least 3x the continuous C rate of your max required Amps)

Do the above and get 10 or 20 years use, extensive range, fast charging, light weight etc. Use a "one size fits all" BMS and you will be lucky to get it to work properly at all. And even if it doesn't cut off power, fry in use, etc, it will definitely allow some individual cells to go over voltage at the end of the charge period and shorten their life drastically or kill them straight away. Or allow you to think its charged when its not so you go too low on some cells subsequently... Monoblock lithium's (with built in BMS are unsuitable, have too low C rate or too low capacity for the volume and have a built in BMS. Battery Massacre System...)
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Re: Step by step lithium conversion?

Postby LROBBINS » 05 Apr 2013, 19:27

Is the following a "doable" proposal:

(1) A battery pack made up as you do with cells mixed and matched to even self-discharge rates.

(2) An on-board, somewhat ruggedized for shock Hyperion with an auto-start program so it runs whenever it gets DC at its input and with charging and balance leads permanently connected.

(3) An off-board mains to DC supply with a zero-insertion-force (or near zero force) equivalent of an Anderson connector. Perhaps one could even make that by adding a lever-turned eccentric to apply the springs to the contacts.

Once the pack is built and the auto-mode Hyperion is programmed, the rest is "plug and play".
Ciao,
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Re: Step by step lithium conversion?

Postby Burgerman » 05 Apr 2013, 20:48

Other than it being a waste of a complex charger, and difficulty in achieving that auto start thing, its workable.

But the BMS doesn't only (try) to balance cells. So while this would allow safe charging, (albeit without you being able to monitor it on a PC to see all is well, and how many Ah was returned etc.) So you would be in the dark as to what was actually happening.

But BMS also does the following:
Over discharge pack protection -- Volts - but ignores volt drop under load - time based - guessed at some random use and causes problems.
Over discharge pack protection -- Volts under load - correct settings depend on cells, cell count (capacity), actual load in use etc.
Over discharge individual cells (as above - both - depends on cells, count, capacity, C rate, load, etc so always wrong...)
Over discharge Amps over a very short indeterminate time (Depends on Cell count, Capacity, and short pulse C rate)
Over discharge Amps continuous (depends on cell count, capacity, and cont. max rating in amps)
Cell balance DURING USE (A really stupid thing to do but many try to do this regardless)
Disconnect charger when balance volts go above typically 3.9v which is way too high...
Disconnect charger when PACK volts go above some way too high figure...

Etc, etc...

Most of the above is totally overcome by using a pack of well matched cells of a high enough C rate that the current never exceeds capability, and by monitoring pack or cell voltage and stopping before the pack is 95 percent empty. Or say 2.7 volts OFF load. And charging with a proper cell balancing charger.
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Re: Step by step lithium conversion?

Postby LROBBINS » 05 Apr 2013, 21:54

But BMS also does the following:
Over discharge pack protection -- Volts - but ignores volt drop under load - time based - guessed at some random use and causes problems.
Over discharge pack protection -- Volts under load - correct settings depend on cells, cell count (capacity), actual load in use etc.
Over discharge individual cells (as above - both - depends on cells, count, capacity, C rate, load, etc so always wrong...)
Over discharge Amps over a very short indeterminate time (Depends on Cell count, Capacity, and short pulse C rate)
Over discharge Amps continuous (depends on cell count, capacity, and cont. max rating in amps)
Cell balance DURING USE (A really stupid thing to do but many try to do this regardless)
Disconnect charger when balance volts go above typically 3.9v which is way too high...
Disconnect charger when PACK volts go above some way too high figure...

Etc, etc...
Yes, that's why I said "after assembling a pack as you did" (or some such). It really does simplify things. BTW, it would not be difficult to have a microcontroller sense voltage at the Hyperion input and electronically push its button once, or even do a sequence of pushes, and it might even be possible for Hyperion to script this into the init's own MCU. Programming the Roboteq to monitor no-load voltage and safety stop the system, or to just give you an audible or visible alarm by hooking a buzzer or light to a Digital Out pin would be a snap. Of course, Dynamic or P&G etc. could easily program their processors to do that too (though we can't). Ciao, Lenny
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Re: Step by step lithium conversion?

Postby stevelawiw » 05 Apr 2013, 22:23

I have been thinking about the feasibility of having a Hyperion permanently attached inside the battery box to simplify the connection process and maybe also shorten the required length for the balance leads, with the bluetooth modification to the Hyperion there is no need to ever use the control buttons on the actual unit, and with the Hyperion suite software running on a computer you can start the charge and also monitor the results without ever touching the Hyperion. The only connector you would need exposed in this situation is the power lead to connect to your psu or battery, probably an anderson. I was thinking that this would make it easier to charge Lithiums while the chair was in a van or of course anywhere with an accessible power supply while the user is still in the chair.
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Re: Step by step lithium conversion?

Postby Burgerman » 05 Apr 2013, 22:53

Well doing that to a Hyperion is beyond me.

But if you can, it will work. But makes it a bit hard to charge 101 other batteries!
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Re: Step by step lithium conversion?

Postby stevelawiw » 05 Apr 2013, 23:38

Yes I wouldn't be able to use it for any other purpose, but then I don't anyway.

What do you see as the difficulties with this? I thought it would be quite straightforward which is now making me think that I'm missing something obvious!
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Re: Step by step lithium conversion?

Postby Burgerman » 05 Apr 2013, 23:43

I think it isn't a problem, but it only addresses a part of the BMS issue.

And monitoring cell voltages as it charges is probably wise so you known what's happening, esp at the end of charge. But this solution requires more complication than just using it as intended.
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Re: Step by step lithium conversion?

Postby ex-Gooserider » 07 Apr 2013, 02:27

I'm not quite seeing the problem -
1. The pack is built along the same lines that yours is - possibly different numbers / arrangements of cells, but same basic design...

2. There would be no BMS - it's functions would be served by the onboard Hyperion and / or your pack design...

3. If I understand the Bluetooth mod properly, it allows the linked PC to do everything you could do from the control panel, or if hooked up via a USB cable, so the charge monitoring and so on would be the same. However I suspect that watching the charge voltages would get old for most of us pretty quickly, so I'd probably want to have some way to monitor the system and do an alarm if something wasn't right....

4. It would mean not being able to use the charger for anything else, but IMHO that isn't a huge deal - I already have adequate chargers for all my other rechargeable stuff, and those would be less hassle than the Hyperion to use...

The only complication I see is in interfacing to the Hyperion with whatever microcontroller one wanted to use - essentially a question of how "open" or easy to reverse engineer the existing interface is... Certainly it is no problem at all to use a microcontroller as a "virtual finger" to push buttons if that's all that's needed....

I still think (and wish you'd suggest it to your contacts there) that they would come up with a "simplified Hyperion" that only had one (or a very small number) of charge profile slots, programmable via computer, but a minimal control panel - presumably a go/no-go LED and a start button...

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Re: Step by step lithium conversion?

Postby Burgerman » 07 Apr 2013, 10:49

What do you see as the difficulties with this? I thought it would be quite straightforward which is now making me think that I'm missing something obvious!


Well I just think that if you are capable of fitting it on board, doing something with the electronics to start it, waterproofing etc., then you should also be more than capable of just pressing the start button? To me that's way easier! I don't see what is being achieved? But as I said it will work. The Hyperion wont much care where it is.
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Re: Step by step lithium conversion?

Postby Burgerman » 07 Apr 2013, 10:53

The only complication I see is in interfacing to the Hyperion with whatever microcontroller one wanted to use - essentially a question of how "open" or easy to reverse engineer the existing interface is... Certainly it is no problem at all to use a microcontroller as a "virtual finger" to push buttons if that's all that's needed....

I still think (and wish you'd suggest it to your contacts there) that they would come up with a "simplified Hyperion" that only had one (or a very small number) of charge profile slots, programmable via computer, but a minimal control panel - presumably a go/no-go LED and a start button...


Who would buy it? Hobbyists want flexibility and info, and speed. And complain about 20 mem slots... Me too. Its not enough.

There are hundreds of simpler hobby chargers on the market already. The 1420 is end of line, the next version will likely be more complex.

I know nothing about microcontrollers so that interfacing bit is beyond me! I honestly don't understand why you cant choose your parameters once, save it, to every memory position if you wish, then just press start at bed time! No need to look at any screen. Then no need to find space on board or do any interface stuff.

I just plug in, press go for 1 second, and go to sleep. Cant see why that's difficult.

Although I usually choose to do it via my laptop. But you don't need to do that. (So I can monitor exactly what happened, see if its fully charged, see Ah returned, cell balance on lipos etc etc.)
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Re: Step by step lithium conversion?

Postby LROBBINS » 07 Apr 2013, 11:37

So, if one wanted to mount it to the chair, once all program slots are set to the chair's program, all that would be needed would be access to the start button or, better yet, have an auto-start electronically sent to the button when the DC is connected. That would be easy to do with a microcontroller and one could, at the same time, have the microcontroller inhibit the chair controller when the DC is plugged in. Even the simplest microcontroller can do this. Total cost, as little as $10 plus a tiny DC-DC converter (about another $10 for an industry quality certified one) and a little box to mount it in.
Ciao,
Lenny
P.S. If you ever want to start learning how to program microcontrollers, I would recommend looking at the Arduino web site. Arduinos are programmed in C++, but the Arduino group has written a user-friendly package that wraps and hides almost all of the nitty-gritty of the microcontroller itself. Moreover, they have lots of learning materials there and links to tutorials and so on.
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Re: Step by step lithium conversion?

Postby Burgerman » 07 Apr 2013, 12:40

Looked at the programming before... Its beyond me!

Yes you could do that. But what am I missing? How is it any easier? Seems to just remove any possibility to charge other stuff without making it any simpler to use to me. And needs added interface/complication.

You could just use its existing Bluetooth connection to start it from a laptop/netbook too. But you can do that now? Or press go.
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Re: Step by step lithium conversion?

Postby LROBBINS » 07 Apr 2013, 13:39

For you no, but for someone like Rachi's aid, or the aids in school when she was in school, having to:
(1) connect balance connector(s)
(2) connect Hyperion charge leads
(3) connect DC box to Hyperion
(4) push a button
(5) remember to not move the chair when plugged in
is a lot worse than
(1) plug in ONE connector and the system does the rest
Ciao,
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Re: Step by step lithium conversion?

Postby LROBBINS » 07 Apr 2013, 13:43

As to programming, you and my son are a good match. He works for Microsoft as a graphics idea generator, but absolutely refuses to learn the first steps of programming. OK, if that's your and his choice, but if one takes it one step at a time entry-level programming really is much less complicated than many of the things that you and he do every day.

On the other hand, though I can make a decent mechanical drawing by using modern tools and sometimes a bit of math, I will never be able to draw a perfect spiral just by moving a mouse as my son can.

Ciao,
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Re: Step by step lithium conversion?

Postby Mark » 07 Apr 2013, 14:18

My take on this is as follows...
The 1420i is a great bit of kit and I would quite like to mount a dedicated one on my F55. It is light, and flexible enough so I Can charge from a variety of DC sources easily. For example charge when in the car via the 12v 12 amp socket (My current car is leased via motability and I am not prepared to wire a high-current Anderson to it). The only drawback is that I haven't found any suitable place to mount it where I can still see the display and reach the buttons.
Hopefully, I've recently bought what will be my last set of MK gels for the F55, and by the time I've worn them out there will loads of lithium experiences posted here to encourage me to open my wallet and spend £1k on headways.
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Re: Step by step lithium conversion?

Postby Burgerman » 07 Apr 2013, 14:26

If you actually take 12Amps from those sockets for more than a couple of minutes they melt! Try it.

But..

If you can, without that, then there are losses so 12v in at 12Amps is about 4 amps out at series charge voltage. So too slow really...

My Hyperion's are all wired and ready to go. One in my van, one by my bed, one on the bench mostly for hobby/cameras etc.

Lead? 1 cable and press go.
Lithium? Two cables (different) and press go...
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Re: Step by step lithium conversion?

Postby Mark » 07 Apr 2013, 15:19

It's not pressing buttons or plugging in cables that I hadn't solved. I was pointing out that I hadn't found anywhere convenient on the F55 to mount the 1420i that allowed easy access to the buttons and display. Good point about the connectors, but they do vary, and 4 or 5 amp charge while driving around is better than nothing. The 1420 can always be dropped into a bag on the back of the F55 when not in use.
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Re: Step by step lithium conversion?

Postby Burgerman » 07 Apr 2013, 15:40

You realise that with BT you can drive it from a laptop/netbook?
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Re: Step by step lithium conversion?

Postby Seajays » 07 Apr 2013, 16:19

This plug and play method would be great for Nandol and other in similar cases.
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Re: Step by step lithium conversion?

Postby Burgerman » 07 Apr 2013, 16:52

But it surely doesn't actually help anything.
He still has to configure the charger correctly first. Ie capacity, cell count, charge amps, charge CV point, TVS, timer off, name the memory, etc, and set charger input amp/volt, weather its on board or on a table...

Then additionally wire the thing up on the chair, modify it to work with some extra logic chip to start it, and then after all of that, he still has to plug in the power supply to the wall/chair then push the go button as before? It saves one simple balance connector, while adding a lot of work/complication. And it means finding space for the charger and another box on board the chair and there's not much space..

What am I not seeing? I just don't see how this is easier. But if you guys do, can figure out how to do it, then it will work - just exactly the same!

If having 2 connectors is confusing (!) just use a single one with 11 wires in it... Like a printer parallel port one.
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