WheelchairDriver

charger > http://www.evassemble.com/index.php?mai ... cts_id=224

the batteries are I am using > http://www.evassemble.com/index.php?mai ... ucts_id=18


It is advertised as a charger specifically designed for lithium batteries. And being a tetraplegic C4/5I have to rely upon PAs to put the wheelchair on charge, often without me being able to supervise. So plug and go is very much desirable. Also, that looks like it has fins for cooling, instead of Fans, and so it would be very quiet.

Any advice welcome, 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.

forget that, somebody else's already told me that's not a balance charger.

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.

Yep, that just pumps in too many volts and hopes the BMS can sort out all the problems!

They still spend ages trying to balance, and repeatedly going to 3.7 or higher while they react. For hours...
And most try to balance all day, and in fact do the opposite.

If you are bypassing the BMS and only using it as a balancer then there are simpler ways.

http://www.bestechpower.com/balanceboard/JH-D131A.html

http://www.bestechpower.com/balanceboard/

Do they cut off when overcharging occur and what's cut off voltages ?

No they don't. Those are cell balance only. Your charger should slow down as it approaches CV stage so they can cope.

BMS cut-offs generally occurs to slowly and too late. And then repeats over and over... Its the wrong way to do it. Although if done well it works.

There are cell and battery charge managers on that site too. But they do the same thing as the BMS you are using. But on an individual cell basis.

If you care about battery life best to use a cell balancing charger that throttles back proportionally while the balance pulls the voltage down. So no cells exceed 3.600v.

As long as it is bypassed for the power take off to the chair (so the BMS has no affect). And as long as you use a charger that lets you choose 3.55v instead of something huge, and only use the BMS for cell balancing at a lower voltage then it will be fine. But the problem is that a novice as you put it will not make all these parameters correct. They will just use a generic BMS and charger and connect the powerchairs electronics to the BMS output...

What you are doing is basically taking control away from the BMS manually. Which also works of course. Provided 3.55v per cell, and at a low charge rate.

Shirly_hkg you need to treat yourself to a 40 amp charge 1A balance 1344 watt PL8v2 charger.

Here are 2 FMA PL8v2 chargers.
And 2 Hyperion 1420.
And 2 40A 30V power supplies.

I can charge anything!

Burgerman wrote:As long as it is bypassed for the power take off to the chair (so the BMS has no affect). And as long as you use a charger that lets you choose 3.55v instead of something huge, and only use the BMS for cell balancing at a lower voltage then it will be fine. But the problem is that a novice as you put it will not make all these parameters correct. They will just use a generic BMS and charger and connect the powerchairs electronics to the BMS output...

What you are doing is basically taking control away from the BMS manually. Which also works of course. Provided 3.55v per cell, and at a low charge rate.

for me is fine,also easyer...if instead of 1'0yrs batt lasts 8yrs...ok too.

obg João & SHK

for me is fine,also easyer...if instead of 1'0yrs batt lasts 8yrs...ok too.

What does this mean?
DO you understand what he is doing?
He is using only a PART of the BMS. The part that balances cells. Ancd charging with a power supply set to a low enough voltage that the BMS doesent try to overcharge the cells due to the flawed way they work.

Get any details wrong and it might last a week...

Shirley; for the stupid who are still completely buffaloed by the electronics and workings of these lithiums (LiFePO4) Not any of the other lipo's thrown in at all, guys like me. Could you explain how you do your system, both words and pictures would help.

Sometimes when I get into this I think I get it ! And then something else gets thrown in ! Then I feel like my head wants to explode. I am betting I am not alone on this confusion.

I saw a 12 volt 40AH with a pack relatively inexpensive with an advertized C rate of 3, on some site I have to search to see if I can find it again. Pair something like this up in series and even if you get 32AH after 5 years is 100% better than LA/pb deep cell batteries that must be replaced every 3 years or less.

"OR IF" there is enough physical space, hook 4 packs -- 2 in parallel to the other pair and then in series which seems to be exactly the same as can be done with indivudual cells. It is really the failure factor (BMS) in the middle of a intersection or sitting in the woods, or on the beach ALONE with the tide coming in, those things worry me to death. The very few seconds of maximum draw that obviously confuses the BMS. Circumvent that fear somehow and I am good to go.

My two sets of NF-22 batteries (4 altogether) are getting close to their (in my head) expiration date. I rarely come close to a full deep draw cycle. And charge them nightly leaving them on charge hours after that little green light comes on though I doubt the validity of that light or that the charger is doing anything after it comes on.

To understand me I worry a dollar bill to death before I spend it! And I am perhaps the cheapest bastard on the planet. I also do not suffer failure well !

One of the things I like using single cells in home made packs is the versitility of building packs to varying AH and/or voltage combinations for whatever reasons you choose. However, this is still an expensive proposition (at least for me) and with my still limited real knowlege I try to understand what will work for me, with very little risk of failure.

I will try to clarify what shirly is doing and why for you.

He uses 2 kinds of packs.
1. Was a lot of old A123 soft pouch cells, these were still good.
2. Was a load of smaller cylindrical cells. These were also not new from memory.
Doesn't much matter as long as healthy. In both cases the C rate doesn't much matter because the packs were very large Ah and so the actual amount of draw per cell is proportionally lower.

Maximising Ah means you can use proportionally lower C rate cells, and still have plenty of headroom because the max Amp draw from the controller is a fixed value.

And he uses a BMS for CHARGING and not for driving... So the powerchair runs directly off the battery. It is not using three quarters of the BMS at all, he has bypassed its electronics. So it cant cut off power, or cause all the other driving problems. But it also cannot then protect from:
1. over discharge amps (you do this by using a large enough, high C rate pack)
2. over discharge level, by voltage. (you do this with an external monitor or buzzer, or Ah meter.)

He ONLY uses the BMS as a charge balancer. Its not very good at this. So if left to its own devices, and a typical lithium battery charger it would repeatedly send the highest cells over the safe voltage and keep cutting off power from the charger completely while it drops the high cells voltage lower. To stop this happening he charges at a lower voltage of 3.550V per cell, (total voltage 3.55V x 8) and provided all cells are healthy this allows an even charge, and allows the weak BMS balance circuits to keep the cells low enough to allow a safe charge.

It works but is a bit "messy" and requires that you know what its doing and to monitor it now and again.

http://www.bestechpower.com/balanceboard/JH-D131A.html

I am still confused with the C-rate stuff, How AH fit into the calculation. and do multiples of cell groups increase the AH ? I would however almost always use a less than 100 amp controller, and not over 24VDC. I think i am now too old to try to progress further or need more "speed". I just want to make stuff easier for the home stretch, whatever will accomplish that.

I get the part why shirley circumvents all but the cell balancing, but I seriously doubt I would get how to do that. It would seem you would have to eliminate a part of the circuitry of the BMS. Nope

What about these gadgets and how do they relate to what we are trying to accomplish? http://www.bestechpower.com/balanceboard/JH-D131A.html

Do they have a way of connecting cell groups individually? Or each cell individually ? I seem to remember some dude finding or making BMS like units for individual cell groups. But he invalidated himself due to some of his other ideas, or so it seemed.

I have to find that AD for the cell pack I spoke of. I think I may have answered my own questions while writing this. But if you do have time please reiterate or answer those suppositions I have. Thanks guys

http://www.bestechpower.com/balanceboard/JH-D131A.html

That's a board that you connect to all cells, only to charge and balance. It only has a tiny 70mA balance current, and then only once well over the set voltage. Once the voltage goes too high on the first cell group to reach 100% full it has to keep on disconnecting the charger from the whole pack, waiting till voltage is pulled lower enough, then reconnects and causes overvoltage again. Rinse and repeat indefinitely until all the other cells can catch up and get 1000% full... It does this exactly the same as a normal BMS.

Unlike a full BMS. It has nothing to do with overvoltage (re-charging on overrun as you slow or descend a slope). Or under-voltage as you load the battery, or as you run it down low. Or over current as you pull 200 Amps from the battery with your 100A controller. (that's 100 x 2 motors!)

I am still confused with the C-rate stuff, How AH fit into the calculation. and do multiples of cell groups increase the AH ? I would however almost always use a less than 100 amp controller, and not over 24VDC. I think i am now too old to try to progress further or need more "speed". I just want to make stuff easier for the home stretch, whatever will accomplish that.

OK read this twice!
Take a single cell...
A 10Ah cell, rated at 10C can have 10Amps max taken from it without instant trash can.
A 10Ah cell, rated at 50C can have 50Amps etc.
In both cases they will have an extremely short lifespan.

A 20Ah cell, (or 2x 10Ah in parallel), rated at 10C can then have 20A taken from it and wont die... You just add up the cells in Ah as they are in parallel. So:
A 20Ah cell, (or 2X 10Ah or any bunch adding up to 20Ah in parallel) rated at 50C can have 100Amps taken from it and not die. 50C is common on hobby stuff.
A 100Ah cell (or 10x 10Ah cells or whatever you use in parallel) rated at 10C can have 1000Ah taken from it and not die.

In every case above these batteries will last weeks.
Why? Lithium live longer, the slower you take power out, and the slower you put it back. Measured against each cells C rate.

Your powerchair CAN demand 200A. With a 100A controller. Although typically its much less and usually will not exceed 150A unless you are driving at speed up a hill or across sand.

So...

100Ah 3C battery? CAN do 3C (300A) so you will never exceed its max C rate allowed. And will spend most of the time much, much lower so it will live a long happy life.

50Ah 3C battery? Can do 150 MAX. Or the cells are very rapidly damaged. You may or may not get away with this, and the AVERAGE discharge rate is now twice as high as the previous example, meaning that even if you never reach 150A the battery will still have a shorter life. You are working every cell twice as hard. And also discharging it by double the amount (wearing it out by deeper cycling too!) So the 50Ah battery gets charge twice as often, and/or discharged twice as deeply, as well as being discharged at double the amp load per cell. All these 3 things mean a much shorter life. You THROW AWAY much of the lithium advantage.

So the smaller battery would need to be a higher C rate (double) to attempt to stop this higher Amp discharge per cell. But you still lose out on depth of discharge, and number of charge cycles.

Most prismatic cells are 1C with 3C pulse.
Headways are rated at 10C continuous by the manufacturer, Down-rated by many resellers to 3C and 10C pulse in an attempt to get less cells returned... Usually killed by BMS!

So 3x better than prismatics. Or you need a 3x bigger prismatic pack. No problem in a car...

I get the part why shirley circumvents all but the cell balancing, but I seriously doubt I would get how to do that. It would seem you would have to eliminate a part of the circuitry of the BMS. Nope

You just connect the power to the chair directly to the BATTERY rather than the BMS.
But that's not ALL he is doing. He is charging via a power supply that is set to 3.55V per cell rather than 3.65V per cell. To give the BMS with its feeble balance circuits a chance to get the cells balanced before the charger pushes the highest ones too high, ands to therefore stop it from endlessly overvolting the high cells.

What about these gadgets and how do they relate to what we are trying to accomplish? http://www.bestechpower.com/balanceboard/JH-D131A.html

They do the bit that shirly "keeps" on his BMS. They pull down the highest cell, albeit with a minute inadequate 70mA. My two PL8 hobby chargers also pull down the highest cells. But they do it with 1000mA. And they throttle down the charger progressively from 40A down to under 1 amp if required so NO cell ever exceeds the set voltage.

Do they have a way of connecting cell groups individually? Or each cell individually ? I seem to remember some dude finding or making BMS like units for individual cell groups. But he invalidated himself due to some of his other ideas, or so it seemed.

In a 24V LiFePO4 battery there are 8 Cells. Or 8 GROUPS of cells that are all connected in parallel, then in series. So you always need NINE balance wires. And every cell connected in parallel is at the SAME voltage. They cannot be otherwise.

I have to find that AD for the cell pack I spoke of. I think I may have answered my own questions while writing this. But if you do have time please reiterate or answer those suppositions I have. Thanks guys

I did my best...

https://www.commonsenserc.com/page.php? ... iring.html

Lipo rather than LiFePO4 but same setup...

Read, and try the interactive options.

It only goes to 5S and 3P (5 Series, 3 Parallel) max.

My BM3 battery is 6x 12Ah cells all connected in parallel. And it has 13 of these connected in Series.

That makes it 12Ah x 13 series = 72Ah
And it makes it 3.3V x 13 lots in Series. so 42.9V Nominal. About 45V in practice.

To find stored energy:
Ah x Volts = Watts. (3240 watt hours in BM3 my case)

And 72Ah x 10C = 720Amp cont rated. Half that is realistic! So I am miles away from its limits.

OK read this twice!
Take a single cell...
A 10Ah cell, rated at 10C can have 100Amps max taken from it without instant trash can.
A 10Ah cell, rated at 50C can have 500Amps etc.
In both cases they will have an extremely short lifespan.

A 20Ah cell, (or 2x 10Ah in parallel), rated at 10C can then have 200A taken from it and wont die... You just add up the cells in Ah as they are in parallel. So:
A 20Ah cell, (or 2X 10Ah or any bunch adding up to 200Ah in parallel) rated at 50C can have 10000Amps taken from it and not die. 50C is common on hobby stuff.
A 100Ah cell (or 10x 10Ah cells or whatever you use in parallel) rated at 10C can have 1000Ah taken from it and not die.

Hasn't waken up completely from pub last night.

A 20Ah cell, (or 2X 10Ah or any bunch adding up to 200Ah in parallel)

Should be A 20Ah cell, (or 2X 10Ah or any bunch adding up to 20Ah in parallel)

Someone on this site is going to build a 24V 180AH block

He means nandol. But I wouldn't do it this way. For a number of reasons. Not the cells that are a problem, because even though they are lower C rate there is enough added Ah to cope - at least on a 24 volt pack. Although quality or service life/reliability is unknown. And finding or swapping a bad cell is almost impossible as the hundreds of small cells are all welded up...

But the charge system is messy, offers little information, is slow, and relies on a weedy low power BMS balance circuit...

So I watch with interest!

My 3240wh pack made from headway cells can be bought for around 950 uk pounds for eg. 1300 us dollars. So not sure there's any advantage doing this. Although a larger capacity increase is possible. A 24V 120Ah pack would be under just 1k with headway cells. http://www.evassemble.com/index.php?mai ... ucts_id=21 for a price.

But if I did use those cells as they allow a bigger capacity, I would throw away the bms and use a 40A PL8 HOBBY CHARGER so that they were properly and safely charged and so I could graph and see that this was the case. Because it takes 40A to charge a 180Ah battery in 4.5 hours.

Here's how a lithium-ion battery degrades over time

http://www.engadget.com/2015/03/23/lith ... cale-view/

Those are not Lithium ion Phosphate batteries though.

I can tell you this. These are what they don't like...

1. Over discharge. (Discharge 101% a few times, and throw them away. Discharge to 99 to 100% capacity, and they will last 1500 cycles. 80% 2000 cycles. Discharge to 70% 6000 cycles approx.

2. Over charge... (Never charge a cell above 3.55V and it will last VERY long time. 3.60V last less well but best balance between charge time and service life. 3.70V or above, and don't last long at all! (Like a BMS repeatedly allows...)

3. They don't like heavy discharge rates. Discharge at a slow rate (say 1/10th of the continuous allowable C rate) and get the full rated cycle life. Discharge at the full cont C rate get about 10% of this!

4. Charge at max allowed C rate and get short life. Charge at 1/5th max allowable C get a full life.

5. Heat. So store somewhere cold.

6. Being stored FULL. Discharge to 40 to 70% charge if stored for more than a few days. Its not critical. Or use it but don't yet recharge.

In short they don't like being hot, full, empty, or have large currents put in or taken out.

John,the excellency of the forum you ve made is based ( among other good things ) in the Exchange of ideias between members...and i think,according to my physical limits + CARERS,that SHK solution is more practic-plug-play for me.

i still use dayly a old monobloc 50A with BMS and make 20kms...last time cells were cheked was 2-3 yrs ago

John...how much it cost you 180A at 24V Headways + charger,acessorios,etc....? for sure,not 1000 quid .

120Ah is the most you will fit using headways.
That will cost
http://www.evassemble.com/index.php?mai ... ucts_id=21
$18.99 x 80 cells. $1520
or...
£12.63 x 80 cells. £1010

That is for cells that will give you FULL rated capacity, and are 10C rated. And 2000 cycles tested.
See http://www.evassemble.com/index.php?mai ... ucts_id=21

BMS that you would connect up and use ONLY for charging £12
http://www.evassemble.com/index.php?mai ... cts_id=209
If not that one find a better lower voltage one... BMS are cheap. You would connect the powerchair directly to the battery like lead. So BMS only working for charging.

Charger?
Any 12V charger, designed for say gel. Or AGM.
You have some.

Or, from http://www.evassemble.com/index.php?mai ... cts_id=167 £24

I doubt you will measure the full capacity from the smaller welded cells. Probably nearer 150Ah if you did a full capacity test on a hobby charger. I would need to test a couple of cells to find out for sure. But I have looked at these small cells in the past and they don't often measure full capacity.

£1010
£24
£12
+ carriage. And you MAY have to pay tax but so far no problem here.

Also needed cables and connectors (Andersons?) etc. All these prices are on the evassemble site.

I think that I would throw it away!
And use a 40A PL8 or similar hobby type charger.
Then I can see any cell balance issues, failing cells or connections etc as I charge. Graphically in detail. And I get to see how much in, out, etc. And have accurate adjustable charge control, as well as 1000mA balance capability. And its still simpler to connect everything up than what you have there. And one connector.

Other than charging all the rest of its functions are not needed and may cause issues. To me it makes things more complicated rather than simpler! And adds more complication, failure points, and less capability.

But it will work.

For Nandol who wants to be simple and use a dumb 2 wire charger its really the only alternative. I would still connect the chairs power system directly to the battery, and only use it as a cell balancer. Then its less likely to die, or cut out etc in use.

What are these LiFeSo4 cells? (instead of the LiFePO4 that we know are safe/2000 cycles etc?)