PINNED - 230Ah (245Ah certified) A grade cells Amy, Docan

[Burgerman]

I've always found that difficult to understand. I assumed that he aluminium casing were either electrically isolated from the positive and negative, or at the same potential as the negative aka 0V.

Take the plastic cover from an AA cell. Or any cell... What do you see?

They ARE at 0V on individual cells. But then you connect each negative to a positive in series... So now the 0V on that cell is 3.x volts higher than the previous cell.

You see a metal case, a tube, where te bottom end is the negative. Its all one bit like a coke can. On the inside the roll of neg/positive plate material has the negative touching the case all around the inside.

And that is the same metal can and so the bottom/negative too.
Only the top terminal is different.

YOUR square cells are the same way. Inside the negative plates are in contact with the casing. At least on the cells I looked at so far.

So when not connected, loose cells, thats all safe.
Once you connect in series, all the cells negatives, and case, are 3.x volts higher than the one before...

[Burgerman]

Also. To fill space around the battery in the chair you can use that polyurthane spray foam. Used for sealing gaps in building etc. Spray a small amount in a bag, shove it down the sides of the batt. It expands and sets in the bags and fits the gaps perfectly. Sometimes used for packing parcels in boxes or holding PC parts inside a PC for shipping. Just lift out when needed.

Like this... https://www.amazon.co.uk/s?k=expanding+ ... _sb_noss_1

I used to use the stuff to mould plane wings...


youtu.be/2KA08uWOOiI

https://www.amazon.co.uk/s?k=expanding+ ... _sb_noss_1

[Scooterman]

I did think of lining the battery compartment with vinyl wrap or sticky back plastic and using expanding down the sides. But I never thought of spraying it into a stuffed down the side plastic bag, it's a good idea.

What I ended up doing was slicing up one of the boxes the cells came in and jamming several layers down each side. The cell pack is clamped in placed lengthways and it sits on three long strips of Velcro. I can't physically move it so pretty confident it should stay put.

Re the cells, they've been for a few test runs.

I have two almost identical chairs. Same r-net, same programming, same motors, same wheels and tyres same seating position.

But docan chair is slighty heavier due to docan 230Ah.

The other chair has 5 year old aliexpress 150Ah so it a bit lighter but has done a lot of outdoors miles, mainly tarmac.

But the docan cell'd chair is a noticeably faster and more responsive than the aliexpress cell'd chair.

I guess the volts don't drop as much under load and the docan cells probably have a better C rate if that is applicable, I understand volt drop under load but not C rate as much apart from higher C rate is better.

[Burgerman]

C rate is the supposed max you should take from a cell.

So a 1c 100Ah cell should never exceed 100A.
A 1c 200Ah sholdnt ever exceed 200A...
A 5c cell thats 100Ah can do 500A max current.

But its not so simple. Theres is no cut off point. Lithium hates to be discharged fast. The faster you draw power, especially the peaks, the shorter the lifespan.

In model use we take 100A from a tiny 4Ah cell (though it is 25C rated pack). So that should be OK right? And I get 20 flights and the battery is toast...
That SAME pack used in my auto mower worked great for 18 months charged daily and some days twice all automatically. So maybe 500 cycles.

The cells you got from docan are EV rated, and so can do 1C continuous. If you tried that of course you will severely shorten their lifespan compared to doing the RECOMMENDED 0.2C discharge. So 20% of the 230Ah. or 46A... At that level they last maybe 10x as long!

The reason the chair feels faster is really the cell resistance. At a super low 0.2 to 0.3 of a milliamp per cell thats almost non existent! Same as 12 inches of heavy duty jumper cable... So very little voltage drop.

I suspect your cheap aliexpress cells are at least 10x that.

[Burgerman]

Its why I have one of these:

So I can measure this! Under a quarter of a milliohm! About the same as the metal frame on your chair!

[Scooterman]

Understood, thanks

How does your meter and the PL8 measure cell resistance? And can you measure cell resistance with ordinary multimeter?

[Burgerman]

A battery cant be measured with any DC current or device because its a big low impedance capacitor when you think about it. Worse, some have a surface charge affect meaning that chemically all the ions next to the plates get moved and depleted as soon as you draw any current and the opposite as its charged. This continues over time. So initially you would read a really low resistance. And a fraction of a second later its dropped by half. And again a second after that...

So a DC resistance can only give an interesting number that doesent really relate to anything! So to measure the resistance of a battery or cell, you need AC. That way the battery is charged and discharged at 1000 times per second. Its capacitance, resistance, etc will read a constant fixed rate over time. That impedance thing really just means AC resistance instead of DC. Its the only way to get an accurate measurement from a cell.

As such, and because its such a low measurement you need either enormous cables, or the battery resistance (impedance) would include the cable, or 4 connection. One set adds an AC current. The other set measures the voltage change at the TERMINAL only. All at 1000hz. So look carefully at that meter. Its got two pins on each probe. Thats why!

So no the PL8 cant measure it, and the multimeter cant inject an AC signal. Either... So no.
Its SO low that if you try and measure impedance on the threaded part that is SCREWED in you get a higher impedance as it now includes the connection... So you cant do that!

[Scooterman]

Oh, well I never! Yes I can now see the two pins on the probes. If someone had given me a set of probes with double pins it would have truly baffled me.

I just googled impedance and unlike resistance which is a fixed value, impedance varies with frequency, etc.

So as you say one set injects AC and other set measures the voltage change.

So re the PL8 internal resistance measurement. How do they calculate that value? I'm guessing it's not that accurate otherwise you wouldn't have bought a specific lithium battery tester. And why does the PL8 internal resistance values changed for charge to charge? Sometimes one cell might be higher than the rest, but on the next charge it's the same as the rest, and maybe a different cell is higher.

[Burgerman]

So re the PL8 internal resistance measurement. How do they calculate that value? I'm guessing it's not that accurate otherwise you wouldn't have bought a specific lithium battery tester.

They look at voltage change across a cell. And the current through the string. And include all the various connections and cables... So even if you could measure a battery that way with DC, and you cant, then the connections and cables will have much more resistance than the cells do. So they make the effort, but its a waste of time.

And why does the PL8 internal resistance values changed for charge to charge? Sometimes one cell might be higher than the rest, but on the next charge it's the same as the rest, and maybe a different cell is higher.

Because they are not measuring cell resistance but all the cables and connectors. Give them a wiggle and everything will change. You cant measure cell resistance that way.

[Scooterman]

Yes! I’ve noticed that when I’ve wiggled the d-sub connector and the balance connector where it plugs into the pl8

[Burgerman]

Think about this.

A 2 meter long cable 3.5mm diameter which is 10sqmm or 7awg that you connected your battery with, has a resistance of 3.55mOhm without connectors added... The cell resistance you are trying to measure isnt 3.55mOhm, but 0.22 of a single milliohm! One fifth of 1 milliohm.

So its 5x 3.55 = 18 -- So its over 18x lower resistance than the heavy CHAIRs cable...

Its much lower than the charger cable. Or the balance cable. And its also lower than a terminal connection... Or plug. So even if it was possible to measure resistance as DC you cant do this down wires carrying a current. Or across any connectors.

[White Lightnin']

How do I connect the 8 gauge wire from the batteries to the four mm banana plugs in the Pl8. Shirley is referring me to a D-sub connector. Can someone refer me to the directions where the D-sub connector is to be connected to the Pl8? I'm very obviously lost and MS is making it worse. My batteries haven't been charged in so long I think they are gone and I will have to rebuy them anyway. I'm waiting to get the rest of the answers I can on this before I order new ones. Chaulk it up to experience.

[Burgerman]

Well is this a temporary thing or is it in a chair?

I use a cable on the cair with 9 small wires for balance and a couple of 12awg wires in silicone to a special sub D connector.

What were you using last?


Below is the half that connects to the charger. And is left in it.

The opposite half stays on the chairs and battery.

I connect 1 plug, then press GO!

https://www.wheelchairdriver.com/BM3-co ... DCABLE.jpg

https://www.wheelchairdriver.com/BM3-co ... -pl8v2.jpg

https://www.wheelchairdriver.com/BM3-co ... -pl8v2.jpg

https://www.wheelchairdriver.com/BM3-co ... nector.gif

[shirley_hkg]

9 pins Dsub will also do.

[shirley_hkg]

. Shirley is referring me to a D-sub connector. Can someone refer me to the directions where the D-sub connector is to be connected to the Pl8? .

Solder the balance wires to a Dsub, and the small white JST connector goes to PL8.

[Scooterman]

I use D-Sub but balance wires can be tricky to solder if you've not got good eyes and a steady hand. I didn't realise my eyes had got so bad until I tried soldering a D-Sub! But then went and bought some reading glasses which made things easier.

Initially for my first lithium pack I mounted pre-wired female revolectrix connector and anderson side by side under chair seat. And used anderson and pre-wired male to male revolectrix for charge lead.

But D-Sub is more convenient

[Burgerman]

Dont use the conectors in that vid above.
Use the intrinsically safe ones.

Because the ones shown will melt and damage the PL8 at high currents. You need the 32A capable ones in the link. Tested at 40A without issues by Revolectrix And me! The others will pull out, and will melt!
And...
The metal parts can touch while a battery is on the opposite end with thousands of amps. Which will make a great firework display or burn your house down.

So... Use THESE

https://www.ebay.com/itm/196730422263 usa

https://www.ebay.co.uk/itm/396948022339 rest UK

https://www.ebay.co.uk/itm/305884035908

https://www.ebay.co.uk/itm/306440252832

ONLY!

[emilevirus]

Sooo... I just ordered 8x cells for my new Bounder. My last build I used plastic holders from Docan but it adds a few mm so it won't fit in a grp 24 box. What do y'all use to secure the cells in the box?

[Burgerman]

Duct tape.

[emilevirus]

Amy offers me 314ah cells cheaper than LF230. Would that fit in a bounder grp 24 battery box? Cells are 72 x 175 x 208mm

[Burgerman]

No. Well it might, but MEASURE VERY CAREFULLY.

[Burgerman]

. Shirley is referring me to a D-sub connector. Can someone refer me to the directions where the D-sub connector is to be connected to the Pl8? .

Solder the balance wires to a Dsub, and the small white JST connector goes to PL8.

Not with those 4mm connectors! They will melt or short out the battery if touched.

Use only these:

https://www.ebay.co.uk/itm/305884035908
https://www.ebay.co.uk/itm/357596009159
https://www.ebay.co.uk/itm/396948022339

https://www.wheelchairdriver.com/BM3-co ... DCABLE.jpg
https://www.wheelchairdriver.com/BM3-co ... -pl8v2.jpg
https://www.wheelchairdriver.com/BM3-co ... le-40A.jpg

[Scooterman]

No. Well it might, but MEASURE VERY CAREFULLY.

Is the bounder gap 24 box oversize cos 72mm seem too thick to fit, that rhymes!

[Scooterman]

On second thoughts they would fit in if additional length on battery box could be gained.

[Burgerman]

Some bounders can fit grp 27 batts.

[Scooterman]

Some bounders can fit grp 27 batts.

Ah!

[emilevirus]

According to Bounder themselves, box is 290 x 375 x 304. It'd be snug but it'd fit. Not sure if I trust them tho. It seems oversized for grp 24. I don't want to pay $500 for it to not fit.

[Scooterman]

4 x 71.5 = 286

2 x 173.6 = 347.2

+ insulation

As you say it seems as if they should fit.

[emilevirus]

I mean.. It's $50 cheaper than 230Ah. I'd be dumb not to get that if it fits. One charge will get me to the moon!

[Scooterman]

I would go for it if I was you. There’s a LOT of upside. Not only cheaper but many more Ah’s. I wish they’d fit in my spare chair cos I’d whip out the 5 year old 150Ah lithium and pack in 314Ah!