PINNED - Lithium battery conversion/info

[Burgerman]

>>> low voltage cut off 28v, although this shouldn't of caused the PSU to blow

That could be the problem.
You want that set to a figure way below where the voltage may fall to under load. Like 10V. Or it may cut in and out fast, the power supply may not like it.

http://www.rcgroups.com/forums/showthre ... &t=1837319

[steves1977uk]

I see my error now Lesson learned.... Now set the low supply limit to 10v.

Steve

[Burgerman]

Have asked digimess if they could upgrade my PSU to 50a if it would be possible for them to do so.

It can do 50 now. Unofficially. There are a few pots inside for adjusting the limits and setting meter accuracy. But its rated at 40 so that it doesn't fail used all day every day in industry. They get used for metal plating and 1001 other things. I would leave it at 40A. That still allows a 1200 watt charge rate.

That's already some 4.5 times more power than a 225 watt mobility 8Amp charger.

And I have 2! And now I have 2 PL8 chargers. So can charge at 2400 watts or so,,, There are some settings that piss me off though. Its like having big brother on your back telling you what to do. Incorrectly! It will not allow a long enough CV stage to charge my camera battery without cell balance connections for eg. I need some modifications to the lead acid charge algo too. And a few fine tuning ones to the LiFePO4 options. I don't believe that half the planet use these things but they don't know any better...

[steves1977uk]

There are some settings that piss me off though. Its like having big brother on your back telling you what to do. Incorrectly! It will not allow a long enough CV stage to charge my camera battery without cell balance connections for eg. I need some modifications to the lead acid charge algo too. And a few fine tuning ones to the LiFePO4 options. I don't believe that half the planet use these things but they don't know any better...

Agree! Even some of the users over at rcgroups says it's ok to balance from 3.3v upwards for Headway cells! Maybe I should see if they will let me unlock the OEM firmware if I email Revolectrix? Although I suspect this will be the same hassle as getting an OEM programmer!

Steve

[Burgerman]

It wont actually do much harm balancing from 3.3v if you charge at a high rate. Its just that it would be better from above the normal 3.3xx volts because the discharge curve is all but totally flat.

If it sees an tiny voltage difference here (and it will since all cells are marginally different even at the SAME state of charge when top balanced) it will try to level them. This might be 30Ah of difference due to the flat discharge curve. When they were already in perfect top balance. But as long as it rebalances again later on it won't matter much. Just wastes time and power... Balancing for the full charge makes sense for other lithium chemistries. It also keeps trying to tell me how long I am allowed to stay at CV for. And often its far from long enough. And it wants to cut off charge early on many situations. It wont let me choose!

Its all dumbed down for safety of fools. At the expense of anyone that has a clue. And they don't get lead at all. But then neither do any of the others. Its why I ended up getting involved in hyperion firmware development.

I will see if I can get a few fixes organised here! But I doubt it, they think they know better.

[steves1977uk]

Here's my charge graph from yesterday.......

8s5p.jpg (30.83 KiB) Viewed 10822 times

Notice how it starts to balance and then go out of whack.... Would this be because of using thin wires on the balancing connector?

I use a metre cable from the charger to the OBDII male plug, then about 75cm from the female side to the battery pack.

Steve

[Burgerman]

You are using a LiPo preset? Use a high power A123 one. For now.

Well thin wires doesn't help, I use the same connector but heavier cables. but if this is less than a week from the last charge you have other problems.

Maybe a bad cell, or more likely a loose connection ot bolt or 3...
They shouldn't take more than a few mins to balance. It goes out of wack because it has to throttle back charge to stop the full ones going too high. Something a BMS just mostly ignores! Its supposed to do that.

Do a full balance but set it to do this:

Balance for full charge: Choose NO. It will then only balance right at the end and you will see balance at CV in grey.

Choose 100mA (NOT C5, C10, C20 ETC) for termination current. It will take longer, at least the first time or two. But allow it to end if possible. This will properly balance the cells and complete the charge probably for the first time...

Choose CV to continue indefinitely. No time limit.

Then send me your pre-set. Save it on your desktop and email it to Burgerman@ntlworld.com. So I can see what you have set up.

Then do a full charge. Drive it a few miles, then try charging it again... Lets see what it does. Should be fast. At least closely in balance. I haven't tried this charger on lithium ion phosphates yet. But that should work and properly charge them.

[Burgerman]

http://www.wheelchairdriver.com/BM3-con ... %20end.gif



This took 10 mins to balance 13 cells on my BM3. And the balance circuits are 300ma compared to the PL8 1000mA... This charger pulses on and off. But the result should be similar. Or you have a loose screw or 3.

[steves1977uk]

Hi BM,

I charge my lithium chair every 7 days at least, and it's always done the charge like this. I don't go out much in winter due to it causing pain in my left leg (ugh!)

My local engineer was going to re-do the wiring on the pack with 12-core trailer cable which will have heavier wires. Will have him check the bolts too.

Thanks for your help and time BM,

Steve

[Burgerman]

It shouldn't always do that. Maybe after a month left uncharged it will.

You have a bad cell or two, unlikely.
You have a bolt or half a dozen loose. Use CAP SCREWS and test every one twice. A lot of bolts, easy to miss a couple.
You have never had a full proper balanced charge? Cant know without seeing your settings file.

Wires being thin might not help.

[terry2]

Morning all.
I've tried reading this thread many times but it goes way over my head
All my friends are network techs(same as me) and this is like a foreign language to us.

What's the best way of doing this.
I want to keep my VR2 controller which is 70 amp but replace my batteries with lithium ones. Is this possible?

Thanks

[woodygb]

Yes.

B.M. will point out that your losing out on the benefits of a higher voltage ..but you can replace your current batteries with 24v of lithium ( LifePo4 ).

[shirley_hkg]

Provided you are fitting more AH than what you had; say double it.

[terry2]

Yes.

B.M. will point out that your losing out on the benefits of a higher voltage ..but you can replace your current batteries with 24v of lithium ( LifePo4 ).

I thought as much. But money is very tight and will be for the next 2 years. I've had to pay for my physiotherapy and that's not cheap.

Could I use the full 70 amp of the VR2? or doesn't it work like that. I just can't work out how many lithium batteries I would need.

[woodygb]

Peak voltage is your only concern .... and 8 off lithium cells has much the same peak voltage as a pair of charged 12v batteries.

[terry2]

Peak voltage is your only concern .... and 8 off lithium cells has much the same peak voltage as a pair of charged 12v batteries.

What about this http://www.eclipsebikes.com/eclipse-com ... -1059.html
or is the volts to high?

If anyone knows what battery pack and where I can buy it please say.

[steves1977uk]

I'm using a 24v 75Ah Lithium pack with a Pilot+ 100 amp power module with no problems.

You can't buy ready made packs, you have to measure the battery case(s) size and work out how many cells you are able to fit in the space including the cell holders.

Steve

[terry2]

I'm using a 24v 75Ah Lithium pack with a Pilot+ 100 amp power module with no problems.

You can't buy ready made packs, you have to measure the battery case(s) size and work out how many cells you are able to fit in the space including the cell holders.

Steve

How many batteries in your pack? I can fit 60 LifePO4 38140S 12Ah in mine. But that's way to much money for me.
If someone were to make a pack for a straight 12v swop they would make a bomb.

[steves1977uk]

Hi Terry,

I have 40 15Ah cells in my pack, 8s 5p (8 in series times 5 in parallel). I use the 40152S cells in the pack I'm using in my chair.

There are 12v lithium 50Ah battery that Nandol is using in his chair (2 in series to make 24v), but these come with a BMS (Battery Murdering System as BM calls it) which you don't want or need.

Steve

[Burgerman]

>>> There are 12v lithium 50Ah battery that Nandol is using in his chair (2 in series to make 24v), but these come with a BMS (Battery Murdering System as BM calls it) which you don't want or need.

By doing this he gains ZERO range. And his battery life will be much shorter. And that BMS caused him to break down and be rescued at least 3 times so far. So what's the point? No advantage over lead.


There ARE no packs that are a straight swap. Or rather there are, but they fail to fit enough Ah of battery pack, Or an adequate C rate for good cycle life, and so completely miss out on almost all the advantages. Money wasted.

ALL the ready to fit "packs" also involve a battery destroying BMS that doesn't allow adequate current, and do evil things to cells during charge. And the same BMS causes problem used in a powerchair.
ALL ready to fit 12v lead brick replacements are also too small capacity. Meaning the cells are worked harder and discharged deeper. So range isn't improved, cells die early and cycle life is both used up and reduced in number.

The whole point of fitting lithium is to get the range, longevity and performance advantages. If you fail to do that then its just an expensive marketing exercise.

Ideally then you need to fit as many hi rate lithium A/hours of storage as poss in the space available.
That means 72x 12Ah cells, two 12V packs. 6x6 cells in each.

That gives you a USABLE capacity of 2.7 times that of the lead battery you throw away. Obviously you are buying 2.7x MORE capability. So obviously its more expensive. But in the long term its actually much cheaper because its last many times longer too. But only if you fit ENOUGH Ah to start with.

>>>What about this http://www.eclipsebikes.com/eclipse-com ... -1059.html
or is the volts to high?

You would get about 4 or 5 miles range. And throw it away as ruined inside 6 months.
Of course if you fitted FIVE of those, throw away the now unneeded BMS system, you will get 60 miles of range, and the cells will likely live 10 to 20 years.

[terry2]

So it's all or nothing. Dame and blast.
I was hoping it could have it's own charger but use the VR2 for controlling.
Thanks all. Will revisit in 3 years time.

[Burgerman]

The VR2 doesent enter into this in any way???

[terry2]

The VR2 doesent enter into this in any way???

Thanks for putting me right I will look in to getting two Odyssey batteries.

[terry2]

BM if I change my VR2 for another system would that help? And what is this BMS system? confused.

Do you know what the full price would be to replace the VR2 with tilt for another system?

[Burgerman]

The controller has nothing to do with charging or looking after your batteries. It doesn't matter what controller you use. Apart from the fuel gauge will no longer be reliable.

[terry2]

The controller has nothing to do with charging or looking after your batteries. It doesn't matter what controller you use. Apart from the fuel gauge will no longer be reliable.

You said
"Of course if you fitted FIVE of those, throw away the now unneeded BMS system, you will get 60 miles of range, and the cells will likely live 10 to 20 years"

What is this BMS system I need to get shot of and what do I replace it with?
I thought only us network people that had special\shortened names for things

Sorry to ask so much BM. But I'm wake for the next hour or so.....soooooo

[Burgerman]

BMS is BATTERY MANAGEMENT SYSTEM. It does a lot of things. Things you may not understand. Designed to allow a dummy with no idea what they are doing, to fit a lithium battery in a place it shouldn't be, that wasn't designed for lithium with inadequate understanding. Almost every battery pack sold has one inside and they cause all the problems. In a properly integrated system, with correct cells and in the correct quantity, with a cell balancing charger you don't need one.

[terry2]

BMS is BATTERY MANAGEMENT SYSTEM. It does a lot of things. Things you may not understand. Designed to allow a dummy with no idea what they are doing, to fit a lithium battery in a place it shouldn't be, that wasn't designed for lithium with inadequate understanding. Almost every battery pack sold has one inside and they cause all the problems. In a properly integrated system, with correct cells and in the correct quantity, with a cell balancing charger you don't need one.

Now I understand And that's why you make your own battery packs up.
With your knowledge I don't understand why you don't make battery packs for power chairs.
I think everyone here would buy from you, if it was a straight swop.

[Burgerman]

That's because you still think wrong. You think lithium is a battery. Rather than a part of a system.

[terry2]

That's because you still think wrong. You think lithium is a battery. Rather than a part of a system.

Well sell the whole system then(what ever that is). I'm sure it would be a hit world wide and it would push the chair makers to changing.