PINNED - Lithium battery conversion/info

[Burgerman]

Whatever looks mechanically right. I wouldnt get it wet. Corrosion = all sorts of balance problems.

[shirley_hkg]

Add hot glue to base of each peg to reinforce it.

No problem for 5 years since installed.

[ex-Gooserider]

Whatever looks mechanically right. I wouldnt get it wet. Corrosion = all sorts of balance problems.

Hard not to get it wet to some degree... There isn't a closed battery box on the Jazzy, the batteries just sit in the open sided frame, and get splashed by the motors / wheels, and so on, quite aside from going through the occasional deep puddle... With the usual lead bricks, this isn't a big deal since all the electrical connections are on the top of them which minimizes the amount of exposure... Depending on how they were laid out, the newer prismatic cells would be similar as all the terminals are on one end...

But Headways have terminals on both ends so one set HAS to end up on the bottom of the pack... It might be possible to find / make some sort of container for the pack, but then that becomes a trap for any water that does get in....

My pack layout has four strips of 4x4 plates on the bottom of the pack (total 6s8p) making four of the serial connections, and the only other wiring will be the 4 balance wires for those connections.

Right now I'm thinking in terms of making strips of the plastic sheet I have to go over the stripes of connector plates, and then use the yoga mat pad to cushion them... I think that will minimize the path for any corrosion current and limit how much water can get to the connections...

ex-Gooserider

[Burgerman]

A tough heavy polythene/ plastic bag.

[ex-Gooserider]

Dont crimp...
Or if you do solder it as well.

Yes your cables are overkill. I just use a ring terminal and solder it same as balance wires and add a 150A MIDI fuse.

If my cables are overkill, what would you suggest for power between the pack and the chair power module? (and between the two 4-cell sub-packs?) I know you were using 10mm^2 for the BM 2/3, but that translates to AWG 7, and while there are specs for the odd # AWG sizes, only the even sizes actually seem to exist... So I was going big on the choice between AWG 6 and 8, particularly for charging off the car...

Charging the pack off the PL8 doesn't need as much obviously, I think the spec for the DB connectors Shirley and others have used was AWG12 for power and 22 for balance....

ex-Gooserider

[Burgerman]

7awg is already bigger than needed. I used 10mm2 but that too is bigger than needed. Take a look at stock wiring. It works, but could do with being a little heavier.

Most of the time a chair takes quite low battery current.

Even if both motors are stalled on a typical 4 pole chair thats quite a low battery current. At least 4x LESS current than the motors themselves.
Thats because the motors pull 120A at about 1/4 battery voltage (a 25% pulsewidth). Typically. And while 6V x 120A = 720watts. But 720 watts at the 24v battery is only 30A.

As you accelerate at full power towards flat out from zero, maybe up a slope or hill, then things change. Now the pulsewidth gets wider, (motor voltage eventually reaches battery voltage) as you speed up. At around half speed this reaches a peak and needs full100% pulsewidth in order to maintain the same acceleration rate. (amps=torque). To maintain this same accelertion level requires the same 120A. But because of the motor generator effect the voltage this occurs at increases with speed. At this point and only for an instant, as you pass the peak current/speed under load, the current can reach 120A at the motor while now at full battery voltage/100% pulsewidth. So thats a peak value. Most users will NEVER see this because their programming is too mild to ever make it happen. I do see it... So now battery voltage = motor voltage and so current = same at motor and battery. So you CAN if aggressive pull 240A for an instant.

As you speed up further the 100% pulsewidth so 24V motor feed is no longer enough to maintain 120A and acceleration falls away. This is what limits the max speed ultimately. The motor when turning a its 6 or 8mph is PRODUCING 24V. So a 100% pulsewidth is required just to maintain full rpm. current is zero. If you go downhill at full speed and 100% pulsewidth then current actually reverses. Now it flows into the battery. Even at max pulsewidth.

So how big battery wiring? If it can do 15A thats fine for rolling at constant speed. If accelerating at 100% pulsewidth (if your programming even allows this) up a steep slope or ramp then it can touch 240A for an instant. And everything in between. But we have thermal mass. Take a fuse. I can blow a 120A fuse. I cant blow a 150A one. Even though I have seen peaks of 200A plus when measured. But not for long enough to heat up a fuse until it blows. Most people will never blow the stock 120 or 125A fuse. Many chairs even use a 100A fuse!

So can your wiring survive more than a 120A fuse? If so then thats only going to happen in extreme situations. So even 6mm2 cable is probably fine.

[shirley_hkg]

Making a 2 metres charge cable right now, 10awg seems more comfortable at 20 amp plus.

8awg inter connects between cells is enough.

[Burgerman]

For charge cables I use 12swg silicone, at 40A no problem. They get just detectably warm at 40A continuous after about 5 to 10 minites at this level.

[ex-Gooserider]

Thanks.... Of course it turns out that 6mm^2 ~ AWG 9 so the effective choice is between AWG 8 and AWG 10 - at least I have plenty of both...

For the charging connection I'm using the same D-shape connectors that BM is showing in his photos, with three large and ten small pins (I like the one's Shirley showed w/ 4 large and ? small pins better, but I already have the others so am somewhat stuck with them...) and I am planning to use AWG 12 on those, as I think it's the largest size they are supposed to fit, and should be plenty, especially since I probably won't be maxing out the charge rate on the PL-8 due to the limits of how big a supply I can connect to a US 110V / 15A AC outlet...

I was more thinking about the interconnect wiring between the two packs, and to the chair power module. For the interconnect I'll probably use AWG 8, and just reuse whatever I've already got for the power module connection....

ex-Gooserider

[Burgerman]

Why dont you just use metric cable?

The internet, ebay, amazon etc all have both the incomprehensible AWG sizes and metric stuff.

Theres another advantage with the mm2 sizing. And that the rule of thumb.

With PVC cables you just use the size as a current guide. Because it is cross sectional area.
So for e.g you can use a:
2mm2 at 20A continuous.
4mm2 at 40A continuous.
6mm2 cable at 60A continuous.
8mm2 at 80A.
10mm2 at 100A etc.

If its silicone insulation, you can double that.
If you dont care it gets hot you can triple it.
Makes it easy to grab the right sized cable..

Also you would then be using Si units...
Like the rest of planet earth.

My nephew asked me the other day how much the water in his 440ml can (like a coke can but bigger) weighed. Hes not too bright.
Do you know the answer?
Well its easy. I litre by definition is 1000 grammes. So 1cc or 1ml (1/1000th of a litre) and so is 1gram. So 440 of them is 440 grams. Or 44% of a litre, 44% of a KG.
Try that with the old imperial system. I just makes everything in engineering so much easier.

[Superchunk]

Has anyone ever tried to put 16 cells in an 8s2p/2p8s configuration?

Was looking at the Eve-105 cells. I believe 16 could fit in my battery box, which would give me 210 Ah.

Is this a bad idea? If not, would 8s2p be better or 2p8s?

[Burgerman]

Whatever gets the most Ah in the space you have works best.
What space do you have? 2P 8S is the only one that makes sense from a simple charging perspective.

Generally a 230ah x 8 set will fit if correctly laid out. If you have grp 24 or 70 to 85Ah lead batts normally. Not in a permobil though - height issues.

This keeps changing over time as new cells are introduced and old ones end.
Whats the chair?

[Superchunk]

yeah it's a permobil so height issues are the problem more than anything.

16xeve-105 should fit though. Does the continuous discharge rating increase with capacity when wired in parallel?

[ex-Gooserider]

yeah it's a permobil so height issues are the problem more than anything.

16xeve-105 should fit though. Does the continuous discharge rating increase with capacity when wired in parallel?

Yes and no.... The cells have the same per cell discharge rating no matter how they are wired up, i.e. a cell rated for 1C continuous and 2C peak will ALWAYS have that rating, but since you are spreading the discharge across all the cells, the more cells in parallel the higher the 'effective' rating for the entire pack...

i.e. a 1p8s pack of 210Ah cells would have a PACK rating of 210A continuous and 240A peak (which would make it unhappy quite fast) but a 2p8s pack would have an effective rating of 240A continuous and 480A peak... So given a stock controller, with a 2p8s pack you would never be able to pull more than a bit under 1C and most of the time a lot less than that, so your pack would stay happy and last a long time....

ex-Gooserider

[ex-Gooserider]

Why dont you just use metric cable?

The internet, ebay, amazon etc all have both the incomprehensible AWG sizes and metric stuff.

<SNIP>

Try that with the old imperial system. I just makes everything in engineering so much easier.

No argument about the advantages of metric, but money matters, whether it's dollars or those heavy (Imperial Measure ) things you use...

While you CAN get metric size wire on ePay or Amazon in the US, every time I've looked you have a lot more choices and MUCH, MUCH lower prices for AWG sizes... Ditto Metric vs. US hardware, etc...

ex-Gooserider

[shirley_hkg]

Has anyone ever tried to put 16 cells in an 8s2p/2p8s configuration?

Was looking at the Eve-105 cells. I believe 16 could fit in my battery box, which would give me 210 Ah.

Is this a bad idea? If not, would 8s2p be better or 2p8s?

https://www.wheelchairdriver.com/board/ ... start=4770

[shirley_hkg]

yeah it's a permobil so height issues are the problem more than anything.

16xeve-105 should fit though. ?

Too optimistic I guess.
Unless they were welded to connect with each others, they'll be 220 high, if you were using studs and lock nuts.

EVE-105 comes with shallow M4 thread hole, which is weedy. You will be extremely careful with it.

I did have poor experience with these.(2P8S)

I'd suggest to configure them in 2 X 24V packs.(1P8S) * 2

[Superchunk]

yeah it's a permobil so height issues are the problem more than anything.

16xeve-105 should fit though. ?

Too optimistic I guess.
Unless they were welded to connect with each others, they'll be 220 high, if you were using studs and lock nuts.

EVE-105 comes with shallow M4 thread hole, which is weedy. You will be extremely careful with it.

I did have poor experience with these.(2P8S)

I'd suggest to configure them in 2 X 24V packs.(1P8S) * 2

Damn, thanks for this info, appreciate it.

Looks like 8s eve-160 is really the only option for Permobil then?

[Burgerman]

Well I havent looked to see what will fit one. Because its better for any number of reasons to not go with permobil. In my case for sure. But only a thorough search and size examination will tell you this.

[shirley_hkg]

160 is a lots in wheelchair sense.
You can use 140 out of it safely.

[Superchunk]

160 is a lots in wheelchair sense.
You can use 140 out of it safely.

I'm currently on the standard permobil 85Ah GEL/AGM hybrid, it doesn't last me the whole day. Was hoping for a bigger jump than 2x for all the effort but I guess it's better than nothing.

[Burgerman]

Same here.
But you can only get around 45 to 50Ah from that gel battery at best. At that point your chair literally stops. This is because a lead battery sufferes from something called the Peukert effect.

The faster it is discharged then the less capacity it provides. The only way to get 85Ah is to discharge at a constant slow 4.25A over a 20 hour long period. And if your chair is 7mph, fully charged, then you set off on the street it runs out of steam at around 15 miles. In IDEAL circumstances. The real world isnt ideal so you actually get less. And you take current in huge pulses and spikes not smoothly and not over 20 hours. So you STOP at around 45Ah.

But with a REAL 140Ah from lithium you will get almost 3x the range that you get from 85Ah lead with a little reserve.. Why?

You get say 2 hours at full speed. At 7mph. So thats 45Ah used. 14 miles approx.
140 real Ah (lithium) all is usable. So 140 div by the 45Ah of lead is 3.1x as far. So now you COULD drive for 6 hours. Or 45 miles. But you need to leave 20Ah in reserver. So lets say 2.6x as far as lead.

Now its true that doing this deep discharge daily will shorten its lifespan. And that it can take it above 1C discharge rate periodically, which again they dont like, but it should still last longer than lead. Just dont expect the 2 to 3 decades of life you would get from that 230Ah pack.

[robint]

OK BM got down to my shirt sleeves now and ready for a beating
Im on page 229 here and it start in 2012 - things have changed 1000% since then, though I daresay much of your early wisdom (howling at the moon) hasnt changed

So I can get up to speed on here pls advise maybe some earlier stuff I must look at - given that we are in Lifepo Prismatic country now. I fully accept the the criticisms levelled bms but they were designed for unattended solar panel use. We are a kind of quasi EV use - different app.

Correct me on my design bullets
. cells can be strapped together with fibreglass separators/inc bottom layer using gf packing tape (no clamping rods)
. cells must be in a convenient case with lid but line with dense foam against vibration shock.
. cells must be Z linked with flexible busbars (relieve any stress on terminals)
. a commercial charge controller may be used for monitoring cell volts and maybe blue tooth but simple metering may
also be used if the volt are kept to 3.55V/cell. OVP/cell may be done by individual audible modules
. charge supplied by a PSU with CC/CV setting
. charging not to take place unattended or overnight
. OCP by 15A Ato fuse
. OVP by PSU settings

Running use
. SCP done by 80A Maxi fuse for each battery 12V bank
. OCP done by resettable PB thermal for each battery bank
. Motor connected to controller then battery via isolation switch
. Means of motor plugged (resistive sc across terms) in event that battery becomes disconnected - prevent runaway no
braking tba?

What have I forgotten? Please dont sh*t on me from a dizzy height

Robin

[robint]

BTW I forgot to post my creds
here with a Lifepo 24 50Ah battery bank I built cw JK bms and Victron smart shunt

image_2024-08-09_193413158.png (176.46 KiB) Viewed 1405 times

[Burgerman]

One of the unmentioned issues wuth all that BMS etc is that it wastes a ton of space that would allow a much bigger lithium pack instead.

Correct me on my design bullets
. cells can be strapped together with fibreglass separators/inc bottom layer using gf packing tape (no clamping rods)
. cells must be in a convenient case with lid but line with dense foam against vibration shock.
. cells must be Z linked with flexible busbars (relieve any stress on terminals)
. a commercial charge controller may be used for monitoring cell volts and maybe blue tooth but simple metering may
also be used if the volt are kept to 3.55V/cell. OVP/cell may be done by individual audible modules
. charge supplied by a PSU with CC/CV setting
. charging not to take place unattended or overnight
. OCP by 15A Ato fuse
. OVP by PSU settings

I dont understand what all this stuff is for?
Why charge with a power supply? Hobby charger.
Why use any OVP at all the hobby charger does all that externally.
whats the 15A thing for?

All you need is 8 cells, taped together with a bit of insulation between, and under them. And linked with ring terminals and cable.
Dont know what you want all the rest of this for?
I just add a 150A main fuse to the chair controller for power.

Running use
. SCP done by 80A Maxi fuse for each battery 12V bank
. OCP done by resettable PB thermal for each battery bank
. Motor connected to controller then battery via isolation switch
. Means of motor plugged (resistive sc across terms) in event that battery becomes disconnected - prevent runaway no
braking tba?

I just use that 150A fuse... Whats all the rest for?

[Burgerman]

Everything else is just plugged into the charger, set to 40A and press go.
It has 9 balance wires, 2 heavy wires, all in one charge cable. You dont need anything on the chair or scooter at all. Other than a 150A fuse and 8 cells...

You dont need any of that stuff. Just a connector. SET to charge to 3.550V safely. And to end after 30 mins post alance at 350thC.
So PROPERLY charged.

The only time you need the protections of a BMS is if the pack is too small for its purpose so that you dont kill it and the reason manufacturers want you to use one is because they would get all the cells they sell back under warranty because of ignorant users. So the BMS nonsense became the"law". Its a nonsense.

The only other thing they do is allow a dumb charger to be used without destroying the cells straight away... But again thats not the best way by far as you can see below. And they are a space wasting thing and a fire hazard to boot. Those that use them have usually been on too many you tube "experts" or dummy forums. The ONLY time they make sense is for solar use. Whare you cant use a proper programmable cell balancing charger. And you may run the TOO SMALL pack/solar system too low...

[Burgerman]

THIS however is what happens if you charge with a BMS and a power supply.

And MONITOR IT with the PL8 only... Not charge it. Just watch what the BMS is actually doing.
And the charger or power supply doesent know when it ends, when it SHOULD end, when its balanced, while the BMS keeps cycling the charge vcurrent on and off... Marvelous! Does it work? Sort of. Does it like it? No!

[Burgerman]

I use these PL8s, theres 3 on my bench, 1 in my van, one next to my bed, to charge my chairs, my hobby stuff, my tools, my nikon camea batteries, my transmitters, my quodcopters and helis, my van, my AA and AAA cells, and 101 other things like my mower, etc.

NON of these packs have anything at all other than the cells. And a balance connector added.
Allowing the PL8 to do a better job that all the BMS nonsense in the world. And you dont need to count Ah out on a chair or scooter uf the pack is big enough in the first place. Likewise you dont need any BMS protection either if its big enough for the job.

And so no BMS, no current measuring, devices = more space for cells... KISS.

[robint]

OK blown away

I am negotiating with Shirley for a zxd2400 - maybe I should ask him for a PL8 btw these arent made anymore

Are there any specs on what the PL8 does?

Is there an alternative to the PL8 on the market?

What kind of sc fuse protection are you using? Maxi?
Robin

[Burgerman]

MIDI

No PL8 was the best. Only place to still get them is shirley. Get a few...
You NEED the balance connector cables, and the FUIM3 PC connections at the same time to make use of them.

Theres non other that comes close. Some are using the iChargerss, not sure which ones. These work, are less electrically robust, you cant set the terination current in the same way as it is a percentage of charge current, and no useful PC software.

But these are current.

With the PL8 I spent 2 years with dozens of experimental firmwares and beta tesing to make the things work properly for large packs, lifepo4, and led. Hundreds of changes... I did the same with the unreliable hyperion chargers and they then vanished for years... And so PL8.

I didnt do that with the ichargers so it is what it is.

PL8s can fail too. I never had one that did yet but they are hobby quality. Super cheap compared to the capability. Which is quite remarkable when you try to find anything else that is this capable.

You dont need one for lead.
But they can do that and measure capacity too. But they take 20 hours to discharge a big lead battery. As tha is 100 watts or 10A max whichever is sooner. But then to measure one accurately you need to do it at the 20h rate anyway. Faster doesent work with lead.

They require a 24V power supply ideally a good one. Like the ZXD. From 10V (so it runs from a chair or a car at 12V or 24V too) up to (max 30v) as well.

They are plastic, lightweight and once you learn how/what it can do and how to properly configure it charges everything properly.



What does it allow?
You can charge anything from a watch battery to a full size EV.
You decide how.
1S up to 8S. Any chemistry.
It charges and discharges.
It has a lot od parameters to choose fro, and charges at 100mA up to 40,000mA (40A). Balances at 1000mA or less and you decide. You decide on balance voltage start, type, termination time and current, accurate to 1mV and 1mA, and all controllable via your laptop. Including setting everything up and graphing it as it happens.