Akku power battery tester

[Khreat]

Is anyone familiar with the Akku power ad60 battery tester or have any opinions on it?

[Burgerman]

Depends. What do you want to use it for?

It cant test say an 8S pack for capacity and balance etc and show individual cells like the PL8 and other hobby chargers can. So its really only any use for capacity testing lead acid or complete lithium packs with no cell detail. It also requires that you know the exact battery specs before its results mean anything.

Lets say I want to test a gel battery from MK.
On the PL8 I would first correctly charge the thing. Then I would set it to discharge at the 20 hour rate and discharge at this rate until it saw 10.8V AND THEN STOP. (all as recommended by MK). Then read capacity.

It can do the same I presume.

But it cant do this to a lithium battery as it doesent look at the individual cell voltages. So it will not tell you WHY or if a cell is bad or if the pack is out of balance etc. So here its use is a bit dubious.

So why and what do you want to test?

[Khreat]

It is to test complete lithium packs for customers and give a health status of the pack as a whole, dismantling the pack to test individual cells isn't feasible.

We have an mk tester for lead but with increasing lithium use I'm looking for a good solution which is cost effective.

I haven't been in to double check, but I'm pretty sure that cell spec isn't mentioned anywhere on the most common packs ( as you pointed to and I'm concerned about).
I have dismantled one pack in my own time out of personal curiosity and hobby interest but I can't necessarily do that with every variation that needs testing.

BTW, I was looking at investing in a pl8 for myself and further learning with lithium but they seam difficult to find now. Have you found a suitable currently available alternative?

[Burgerman]

ShirleyHK keeps suplying new and used pl8s. Get a couple they are well worth it! But they are no longer made. Theres nothing else that comes close. At least with sensible PC software. The MK tester is almost a waste of time. At least as far as I can tell without buying one. Far too basic.

Testing a lithium pack as a whole doesent really help much as you cant see a cell group that is perfectly fine just out of balance due to dismal BMS and self discharge differences between cell groups over time.

[Khreat]

Thanks burgerman, I'll send Shirley a message about the pl8s.

The mk tester is basic but gives us a health status report and printout to either claim against warranty or advise a customer to keep or replace their batteries and not have to send anything away for a 3rd party to test, reducing turnaround and getting people back in their own chair or scooter sooner. From what I've researched it's a far more accurate test than the simulated digital testers.

We need a similar tester for lithium (dumb bms packs, i think you call them), to test the whole pack for the same reasons I mentioned.

I want people to be back on the road ASAP and not have the service cost more than it has to.

[Khreat]

Even if we could test individual cells, do you think would it be worth replacing defective individuals? These are lithium ion, not lifepo4. With the much lesser lifespan of li-ion I believed it wouldn't be worth doing this, not to mention the cases being sealed and my inadequate lnowledge currently.

[Burgerman]

Well it all depends.

For e.g your MK tester. At what point is a battery "bad"? They start deteriorating after around the first dozen charges. And continue to do that until it becomes a problem to the user.

But it all depends on the user, the chair the use to which its put. I used to get around 9 to 10 months from a set of MKs. At which point it either became "gutless" and had no torque for wheelies etc or good steering etc. Or range became an issue. So to me these were now end of life.

I gave a couple of sets to the old folks home behind my house. That was a decade ago. They are still using them. The sort of use they get, in the weedy cheairs they are in, never go far enough or need enough amps to notice!

So the question is at what point is a battery bad? Answer is when it becomes problematic for the user, chair and expectations. You cant put a number on it.

And I had several laptop lithium packs, for a dell rugged laptop. These were barely used. But they were stored for a year. When tested in the laptop which measures ah used, etc they were both around 1/3rd the rated capacity. Were they bad? No. It just took a few days use in the laptop for a few out of balance cells to finally become balanced. They were previously at around 30% when the battery charge ended. And it was so far out of balance that the laptops BMS wasnt getting close to balancing on a single charge. My multimeter told me this was the problem. So I just charged them many times. And now they have the exact rated capacity that is written on the case. If I tested them with a simple tester after 1 charge then it would have said they were bad. (very bad). And that wouldnt have been correct. So its not so simple.

But if all you want is a quick dirty test, then many things will do that. But it may miss a lot of important stuff.

[Khreat]

Totally agree that "bad" is subjective but we have to have some sort of bench mark to use, in this case 60% of stated capacity. A lot of the issues the chairs/scoots come in with report lack of power and loss of range but I'll look for any other issues which could contribute to this asside from aged batteries.
It's always the customers call and we just have to try and give the best advice to people who mostly, aren't very interested in the technicalities and a lot of the time can't make sure the batteries are put on charge when necessary.

I think there are a lot of bad chargers about (having read at least one of your threads regarding this) and I'm looking at making an adapter to try and read charger values and amps. I'll be seeking advice from others when I'm further along.

Regarding lithium examples you mentioned, it is an interesting point. A laptop battery would have a similar bms to that found in a scooter lithium pack, wouldn't it? So without knowing what the charger is putting out for now, it may be a case of leaving a suspect pack to charge for an extended amount of time?

Thanks for your time burgerman

[Burgerman]

60% or rated capacity to my mind is absolutely knackered.
When using lead batteries on say a smaller chair with smaller batteries even a 100% capacity battery is inadequate. So drop that to 90% and its a joke.
On a group 24 chair that same level of usability may be 80% of original capacity.
On a 230Ah lithium battery, with 6x the range of a set of group 24 batteries in a modern full sized chair then even 20% of remaining capacity would be ok for daily use and still match a set of brand new lead bricks!

So even here it depends on what battery, what useage, and so on. I throw away lead bricks when capacity in my own chairs drops by 10% so that I only have 90% range remaining because I notice it a lot!

The other issue is that impedance counts more that Ah does. A battery like a MK gel that has been charged at too high voltage (thats most of them) will have voids and cracks in the gel that forms a part of the current path. Severely increasing the internal resistance (measured as AC Impedance) and also its peukert levels. Even if capacity remains at say 95%. But its RANGE may only be half of what it was when new.

Because the increased impedance/Peukert means much higher voltage drop under load. Your chair starts flashing red, way way sooner. And it has less torque for curbs, ramps and if programmed properly also control. No wheelies, no hard acceleration, no steep ramps etc. Even with great Ah remaining.

So again any capacity tester, is only a tool to help you decide what to do. And only part of the story. And many cheap batteries START OUT with 8 to 12mOhm impedance. MK gel starts at 4.5mOhm. My Odyssey battery is smaller and lighter and has 65Ah compared to MK74Ah. But it takes me just as far. If I drove a slower 2 pole chair, and drove it like my granny then the MK would take me further.

To understand this the cheap AGMs are typically 6 to 10mOhm. Thats TWICE AS BAD as an MK is at 4.5mOhm. Which is again twice as bad as the smaller group 34 Odyssey at 2.5mOhm. Which will start a truck in a siberian winter when half dead.

And as you discharge a lead battery its impedance increases. As the acid is used up and turned to lead sulfate and lead dioxide. This means the voltage drop under load is much greater as the battery is discharged. This is why you will typically only get 40Ah out of a grp24 74Ah battery in a wheelchair and why impedance matters more than capacity.

So again you must measure internal resistance. When fully cycled and recharger PROPERLY to also help make an assessement of suitability. And that depends n use and user too. As well as the chairs demands.

[Burgerman]

Regarding lithium examples you mentioned, it is an interesting point. A laptop battery would have a similar bms to that found in a scooter lithium pack, wouldn't it? So without knowing what the charger is putting out for now, it may be a case of leaving a suspect pack to charge for an extended amount of time?

Thanks for your time burgerman

Most BMS are only balancing at the top voltages. And they do so with a tiny current. So balancing only really begins when the top cell starts to reach full voltage of 4.2V. At this point the charge current drops to a low level (or in fact because of the way a BMS works switches on and mostly off completely) for a certain time. Depending on the actual BMS and the actual device used to charge it may stop charging and balancing soon after when the charger turns off. So leaving on charge for long periods may not do it. Multiple charges may be needed. And without tapping in to measure cell volts you will not know what is happening.
On some "chargers" they are just a supply. So the thing will eventually balance but it then leaves all cell cooking at 4.2V indefinitely and thats really bad for them. So again it all depends what you have.

In an ideal world you stop the cell charging as soon as all cells are balanced, and when current falls to a low level as determined by the cell maker. In the case of the 5000mAh ones (tesla 21700) in my RC transmitter this is at 1/200th C.

So you cant easily tell without a voltmeter on each cell, to see when they are all balanced or to see it in fact they are still actually balancing. Some BMS balance at a lower voltage even if you dont charge. This is a terrible idea with LiFePO4 for a bunch of reasons, but OK on Lithium ion. Only careful examination will tell you what they actually do. Or measure capacity on each subsequent discharge /charge cycle.

[Burgerman]

PL8s https://www.wheelchairdriver.com/board/ ... 65#p198557

[Khreat]

Thanks for the link bm. That's great.
You mentioned that I should get 2 pl8s but this is a personal funded side project and that's not really small change for me. With a single unit and board, I will be able to work with packs up to 8s, won't I?

Regarding your other 2 posts, I'm grateful for your input and looking into how I can put them to use and improve areas in my work.

[Burgerman]

Yes. 2 was in case one dies. Or in the event you want to test 16S packs as they link together. I have 3 on my bench so an do 24S lithium packs if needed. And a spare one in my van for charging hobby stuff.

But you cant officially charge or discharge lithium ion without cell tap connections (nodes) as it deems this unsafe. Same with LiPo.
You can however lie to it and choose lead, 2.1V per cell with double the cell count though, and then it doesent care. So you can then choose 2S lead for every one lithium ion cell. Up to 6S lithium. Thats because 2.1V is 4.2V for every lithium cell. But to know whats really happening you do need a cell tap. So it shows 8 seperate discharge curves.

[Khreat]

It would seam a waste to go for this charger and not exploit the ability to monitor individual cells.

[Burgerman]

If you dont trick it then you must use a balance connector. But at least this way you can see clearly what is really going on.

Heres a single graph for a 75Ah AGM lead battery.
This was set as per manufacturers settings to discharge over 20 hours to 1.8V per cell. (10.8V) and so far its doing exactly as per spec. But its only 5 cycles old.

[Burgerman]

Heres what a BMS does on charge, nasty isnt it... this is set to monitor only.

[Burgerman]

This is a PL8 charging a lifepo4 pack.