PL 8 - Q and A section - How to Set up - Use etc,

[Burgerman]

LEAD
I have a pair of 28mAh sonnenshein gels that I want to connect in series on the bench and cycle to test their usable capacity down to about 50% DOD?
I will be using 4mm pvc flex as the charging cable.

BM - I am going to use on of your lead gel series presets. And I was going to set CC to C/3, and DC also to C/3 which will make both about 9amps is that okay?

To charge, you can save time if set to about 50% or more of the 20 hour rate. So say 14A. It shortens the CC stage.
To discharge a lead battery and get any meaningful measurement is complicated by peukert, voltage depresion etc. They are the exact opposite to the LiPo. So you MUST use the 10 hour rate discharge, or the 20 hour rate which will be more accurate. So that means discharging for 20 hours. Or if you KNOW the 10 hour rate Ah, which will be about 10% less, you can do it over 10 Hours.

On a 28Ah battery that means dischargeing at either 2.80A (10 hour rate) or half that so 1.40A for 20 hours.
For the 10 hour discharge use 10.5V. (21.00V in series or 1.750c per cell)
For the more accurate 20 hour rate, use 10.8V (21.6V series or 1.80v per cell) and ignore it for 20 hours.

These will give you the same measurements that the manufacturer specifies (I think, not looked at the spec sheet for Sonnenschein for years). You can go lower, and will see about .5Ah extra, but the batteries dont like it. Its beyond 100% DOD.

If you discharge lead at 1/3rd C then you will see a much lower capacity. Once you learn a bit about batteries the PL8 is a very useful tool. As you are discovering.

*** Unlike MK sonnenschein say that you can charge at 14.4V max. But since they are gel, its better for longevity to charge the same as MK. At 14.1V. They also say that a long 16 hour CV is beneficial for a battery thats been stored a long time, or discharged very deeply. So you may want to set that 8 hour limit to none or off. Set Termination to 28mA for daily charge. Or a little less to get a longer CV if needed.

[Scooterman]

My MK Gel charger


My Scooter AGM sunrise OEM batteries


My Sonnenshein Dryfit 28Ah and 60Ah Gels


My Sonnenshein Dryfit 28Ah and 60Ah Gels


Hi BM, thank you for your reply, sorry I'm a bit late replying.

Of course! I'd forgotten that increasing c-rate discharge reduces the capacity you get out of the battery, especially lead! That's one of the big advantages of lifepo4. It's capacity isn't affected so much by higher discharge rates.

Before reading your post I thought of using these figures for C.V. they're middle of the manufacturers spec. If I've posted the right charts?

Sonnenschein Gel. Charge @ 2.32v /cell
Sunrise OEM AGM Charge @ 2.43v / cell

Whether I do the discharge test I'm not sure yet. I will do it but perhaps in a little while, maybe next week I'll have a go. But thank you for the values, I've screened grabbed your reply and have saved it for future reference. It's actually the 60Ah sonnenshein gels that I'd like to test as they're the ones that came with the salsa, and even a short 1 mile round trip to the co-op and I"m halfway in the orange joystick leds. Drive much further and you suddenly feel the chair's performance drop off. When I've put the lithium in the scooter, I will put the scooter's 75Ah AGMs in the Salsa.

At the moment I'm making some leads so that I can monitor with the PL8 what my OEM mobility chargers are doing while plugged in and charging my scooter and the salsa.

As you say the PL8 is a really great device, it's so programmable and also shows you what's happening. But dangerous in experienced hands! That's why I trying to feel my way gradually. I initially bought it for charging lithium but it's such a great tool for diagnosing the health of batteries, both lead and lithium.

[Burgerman]

Sonnenschein Gel. Charge @ 2.32v /cell

2.35v per cell, 14.1 MAXIMUM at room temp. And you need to use this as it speeds up the very slow absorption of gels. Up to 16 hours for a charge.

Sunrise OEM AGM Charge @ 2.43v / cell

Correct. Or 14.4V and 2.400V per cell. As they generally charge faster anyway. 2.45V per cell on Optima/Odyssey.

At the moment I'm making some leads so that I can monitor with the PL8 what my OEM mobility chargers are doing while plugged in and charging my scooter and the salsa.

Every one is different. And non of them do as it says on the tin.

[Scooterman]

Thank you BM. I've got a XLR to banana plug charge cable I need to make up. And I will input the values you recommend into the relevant presets.

[Scooterman]

The first graph, which is the latest cycle is good

600mA Charge, 600mA Discharge, 3.13V DV

Although the CV stage only last about 5 mins, is this okay?

NB: 600mA lifepo4 connected in 2P4S

[Burgerman]

On discharge those cells are not going out of balance as such, they are becoming empty at different times because their capacity varies. Also you are charging them way too fast, and discharging them way too fast, due to their internal resistance. Horrible cells...

[Scooterman]

On discharge those cells are not going out of balance as such, they are becoming empty at different times because their capacity varies. .

Ah thanks! I guess the same is happening during the 5 min cool down period prior to discharge (first graph)

Also you are charging them way too fast, and discharging them way too fast, due to their internal resistance. Horrible cells...

Understood


Also, generally for lithium is there a ratio between CC and CV you like to see?

E.G.

2/3rds of charge CC 1/3rd CV ?????

[Burgerman]

Long enough for all cells to be balanced and long enough so that the last cell to reach CV has enough time to fully charge. Or that cell will drop lower after charge. But they dont like being full at max voltage so the sooner that all happens the better. So as usual it all depends.

On cell quality and how equal they all are. Internal resistance. C rate. Cell chemistry. Charge voltage. For e.g. its OK to hold a LiFePO4 cell at 3.550V for a good while. But at 3.650V then it hurts them more so not for as long. And a high impedance cell like your little LiFePO4 cells, they need longer. The LiPo needs about 3 mins...

[Scooterman]

Got it!

I will try reducing the TC and see if that extends CV phase

[Burgerman]

It will. But at very low currents, its less accurate and a little unpredictable. Remember its a 40A charger. So expecting it to be accurate at current measurement, or to be able to maintain the correct really small current accurately. As the current wavers about it goes high low and triggers too soon. Worse if the power supply isnt that stable.

[Scooterman]

Understood

I’ll try powering the PL8 from a couple of series LA batteries

[Burgerman]

If you do that, you can also do regenerative discharging... Read the manual. So that you can discharge your LiPo at up to 40A...

[Scooterman]

Ooh good thinking, I'll do that

[shirley_hkg]

Long enough for all cells to be balanced and long enough so that the last cell to reach CV has enough time to fully charge.

OK to hold a LiFePO4 cell at 3.550V for a good while. But at 3.650V then it hurts them more so not for as long. And a high impedance cell like your little LiFePO4 cells, they need longer. ...

Too low termination current is not a wise pick then . Right ?

[Burgerman]

Well you dont want them sitting balanced, at 3.6V for 4 hours. If not nessassary.

[Scooterman]

When they test the LF90s they terminate at 50mA or C/1800. I guess that's to squeeze as many Ahs into cell as possible?

[Burgerman]

Yep, and at 3.650V.

The difference between 3.650V and 3.550V (or even 3.500V) is well under 1% of capacity. Like maybe .3Ah. But the battery doesent like it...

They discharge to 2.5V as well, or lower. like 2V. To read the last 2 or 3% capacity. And they dont like that either!

Tesla for e.g. uses the lithium ion cells like in a laptop. Those have a cycle service life of 500 to 700 cycles if you use the full rated capacity. That means if you charge to 4.200V per cell, and discharge down to under 3 volts. But the tesla company is cleverer than this. It fits a battery rated by THEM at say 100kwh. But its really 140kwh. So they never fully charge, or fully discharge. They only use the middle bit. So they effectively ignore the full Ah.

So charge to 80% and never go below say 20%. The BMS isnt dumb. It cools or heats the pack with water as required for best longevity, or performance depending on what it needs. A cool pack last much longer, but performs crap. It also allows you to charge more full from say 70 to 85% if you choose to do that. But in times of peril like tornados, the company allow the full capacity all 100% to be utilised for a few days via a network link. Its BMS is no rude dumb cut off power, and ruin cells on charge thing like the chinese sell to everyone. The chargers are built in, fully computerised, like a clever PL8 controlled by an inteligent computer, and its fed simple AC power.

This way you can expect 10,000 cycles, the 500 cycle battery will still be good after decades and many thousands of cycles. Unlile many lesser eletric cars with too small packs and dumber simple BMS.

With lithium, once you learn that theres no "correct" charge voltage (just a never exceed without ), then things become clearer. Likewise theres no fixed low voltage. The correct one depends of what you are trying to achieve. Only one thats too low and

So its all a compromise.
1. Its about less current per Ah on discharge and charge. (C rate is simply a guide) and again less Amps per Ah is better -- So fit a BIG pack.
2. Its about charge voltage. Too high, or held or left full for a long time, HURTS! So dont charge as high. Dont store full!!!
3. Its about discharge level. 100% used and get many less cycles. 80 discharged and get nearly double. 70% discharged and get 5x more cycles. So again fit a BIG pack.

[shirley_hkg]

I built this guy a 140Ah pack with 40152 cells ,
together with a 60Ah add-on.
He recorded the recharge history . 27 charges throughout last year , with average 150Ah DOD .

He is thirty-ish . I told him his battery will live longer than him, but regret that he has no pleasure of lithium building … AGAIN

[expresso]

I built this guy a 140Ah pack with 40152 cells ,
together with a 60Ah add-on.
He recorded the recharge history . 27 charges throughout last year , with average 150Ah DOD .

He is thirty-ish . I told him his battery will live longer than him, but regret that he has no pleasure of lithium building … AGAIN

nice - my goal on my next full chair is to try to fit 200ah in the chair - -

[shirley_hkg]

nice - my goal on my next full chair is to try to fit 200ah in the chair - -

My G24 compartment still has some space left , after 16 cells @EVE-LF90 . I am filling another 75Ah into gaps there . Forming a single G24 battery of 255Ah 24V , the biggest pack ever possible.

BTW , I'm not quite comfortable with the 176Ah cells . They are designed for energy storage , so low C rate .
They should be 200Ah ones , if in good health .

[Burgerman]

Sounds good. I may order some of the 90Ah cells soon.

[expresso]

i cant picture fitting more in the G24 space - you must have a very large G24 battery compartment -

can you post some pictures of it - - how can you fit 75ah more in there - ?

16 90ah Cells plus 8 75ah Cells ?

[Scooterman]

BM - I haven't read your detailed reply above yet but am looking forward to it.

In the meantime your opinion on this?

Prior to arranging 16 cells as 2P8S.

Would there be and benefit in cycling two 8S packs in the bench. Noting weakest through to strongest cells based on which cells spike earliest and trough first.

Then pairing weakest from pack A with strongest from pack B, and so on balancing 2P8S pack. I know it's not perfect as you'd be grouping random cells in the two 8S packs.

It was just a thought, I was curious...

[Burgerman]

You could. But unless theres an obviously bad cell then its not worth it. Not enough to worry about. Just build!

[Scooterman]

Okey dokey

[Gnomatic]

nice - my goal on my next full chair is to try to fit 200ah in the chair - -

My G24 compartment still has some space left , after 16 cells @EVE-LF90 . I am filling another 75Ah into gaps there . Forming a single G24 battery of 255Ah 24V , the biggest pack ever possible.

i cant picture fitting more in the G24 space - you must have a very large G24 battery compartment -

can you post some pictures of it - - how can you fit 75ah more in there - ?

16 90ah Cells plus 8 75ah Cells ?

I have no idea how 255Ah can fit in a G24 space, but I would like to see what that looks like. Hopefully shirley will post some pics of his mega-pack.

[Scooterman]

I have no idea how 255Ah can fit in a G24 space,

[Burgerman]

Because 16x 90Ah cells leaves a gap... And room for 8 smaller cells as well.

[expresso]

Because 16x 90Ah cells leaves a gap... And room for 8 smaller cells as well.

i have a hard time figuring how 16 90ah cells fit - i love to see some pictures when done - i have an empty battery tray that 2 MK 24 sit in perfect - from the 646 chair - but i dont think i can even fit 90ah cells in there at 36mm x 173mm size - i look forward to seeing how it fits - maybe i am missing something here -

[Gnomatic]

The LF90's aren't a good fit for my chairs's battery area either, two cells side by side are 260mm which is about 10 1/4" and about the exact room I have in my battery area. Not enough clearance for my liking as I'd need to mod my chair to accommodate insulation and cell protection etc. In the other direction, I would have a couple inch gap of free space, but not nearly enough to fit eight of any 75Ah cells I'm aware of.

Regardless, its great if others can. And I hope shirley posts a couple pics of his 255Ah mega-pack, would be cool to see fitted.