Check the battery initial capacity?

[cwah]

Hello there,

I'm now discussing with Conhismotor about my 36V10AH Limn2O4 battery that only has 250W remaining on the battery pack. So 2/3 of its capacity.

The seller told me the pack was at 36V7AH so it's normal to only have 250wh of capacity.

But I believe my pack is a 10AH rather than a 7AH. It weight exactly 3kg and they are not selling any 36V7AH pack on their site.


To be sure, I need to check what's the battery initial AH.

Is there a way to check that?

 

[Scottyf]

You need a Watt metter and some light bulbs.
Enough light bulbs and wattage to create a 36v series string and enough wattage to create a 1c draw. From that you can see how many watt's you have in the battery.

Failing that a lipo smart charger will usually have a discharge option that will test the amount of capacity a pack has.

 

[cwah]

I know how much capacity is remaining (around 250wh).

But I'd like to know what's the initial capacity of the batteries.

They said it's a 7AH battery but I believe it was a 10AH battery.

 

[rog_london]

There is no way to check what the initial capacity of your battery might have been unless that information is printed on the case - other than either opening it up and looking to see if there's any information printed on the cells, or obtaining some documentation elsewhere. The weight of the pack isn't very helpful.

Electrically, you can only check what is there now - and you already know that.

Rog.

 

[flecc]

There are two variants. Firstly the capacity of any battery depends on the current usage rate, the higher the rate, the lower the capacity. A to B magazine carried out a series of test on one e-bike battery that was nominally a 36 volt 10 Ah one. At the lowest rate of throttle usage it delivered the full 10 Ah, but at the other extreme of full throttle usage it dropped to just below 7 Ah. Clearly the motor/controller power rating determines the usable capacity.

The other variant is the low voltage cutoff point of an e-bike which prevents usage of the entire content in the interests of long cell life.

 

[cwah]

yeah, but as rog said there is no way to check the initial capacity.

I even opened the open to look at the cell individually and there was nothing written!!! I'm sure conhismotor is trying to con me lol

 

[JuicyBike]

We have a tester that can draw 10 amps, at steady temperature, linked to a timer, which measures the time taken to the bms cut off.
This gives a very accurate measure.
The problem with lamps in series, whilst an excellent, inexpensive solution, is accuracy, due to resistance changing with temperature.
We are happy to measure battery capacity for others, in exchange for a stimulating chat... Tests can take more than an hour, so bring some decent anecdotes

 

[flecc]

yeah, but as rog said there is no way to check the initial capacity.

He means statically. The capacity is easily measured by using the content as Juicybike indicate or as A to B did it, by using the content on the road. In both cases it's measuring what passes out and this is accurate.

 

[rog_london]

Sorry guys, correct me if I'm wrong, but nobody seems to be reading what he's after....

He has asked what the ORIGINAL capacity of his battery would have been. He's not interested in what's there NOW. He's happy that he knows that.

I suppose the only way he might be helped would be if someone (other than Conhismotor, presumably) could identify his battery and tell him what its original design capacity should be. Conhismotor tell him it's a 7 amp hour battery 'as supplied' but he thinks it should be a 10 amp hour job that's getting tired.

Obviously unless you have a crystal ball with a reverse gear fitted you can't answer that question unless you can positively identify his battery and have the necessary information to hand.

I suspect, from what he says, there's nothing printed anywhere so he might well be unlucky.

Rog.

 

[NRG]

cwah, how old is the battery?

If the capacity today is 7Ah and you can prove that 7Ah is really the available capacity then if the battery is say a year old there is no way it would have not suffered some sort of capacity reduction in that time. Meaning if they say it was 7Ah from new, I would have expected you to loose some capacity IE 10% in which case your battery should be 6.3Ah now...

 

[cwah]

The battery is about 6-7 months old.

Just had an answer from Conhismotor:
"I think you have some misunderstand in battery capacity, battery capacity only decide the lasting distance for one full charge, but not as your calculation 360-250=110W missing.
For example 36V 7AH battery use for 36V 250W Motor can ride about one hour, and then 36V 10Ah can ride about 1.44 hours but not miss 110W.
You can even use 36V 20AH to get much longer distance for one charge than other small capacity battery, hope you can understand this. "

I think he completely misunderstood how batteries work or am I wrong?

 

[flecc]

I think it's as much language difference as anything else leading to misunderstanding.

I refer you back to what I've said about discharge rates. Reading what you've posted elsewhere about high powers, if the rate of discharge is high the useful capacity measured will normally be below the specified capacity. 10 Ah batteries only deliver that if used at low discharge rates, as the discharge rate increases, the capacity available decreases.

Peukerts Law

Strictly speaking Peukerts Law applies to lead acid batteries, but all types exhibit the same phenomena.
.

 

[rog_london]

The battery is about 6-7 months old.

Just had an answer from Conhismotor:
"I think you have some misunderstand in battery capacity, battery capacity only decide the lasting distance for one full charge, but not as your calculation 360-250=110W missing.
For example 36V 7AH battery use for 36V 250W Motor can ride about one hour, and then 36V 10Ah can ride about 1.44 hours but not miss 110W.
You can even use 36V 20AH to get much longer distance for one charge than other small capacity battery, hope you can understand this. "

I think he completely misunderstood how batteries work or am I wrong?

I'm having trouble in making sense of what he's saying, but I suspect he's not understood your question either. Crikey! I'm getting that pain between the eyes again - Nurse, the screens....

He's just done a straight conversion between ampere hours and watts at 36 volts. It's a very simplistic thing to do, though if the battery were rated at a 1C discharge rate then his calculation would be valid.

I think I'd have to give up if I were you! You're going to get the runaround and Chenglish doesn't help.

Rog.

 

[cwah]

Thanks guys for the advice.

I decided to test my battery today:
- At home at 22 degree celcius
- At full throttle no load which is equivalent to 2amps
- Had a break after 2 hours to allow the battery and motor to rest.
- Did 2 amps continuous until low voltage cutoff

So it was the perfect condition. 2 amps for a 10AH battery means 0.2C. So even if the battery suffer from Peukerts Law, I should have full capacity.

RESULT=> I ONLY HAVE 275wh remaining on a 360wh battery.

Morality: Do not purchase LiMn2O4 battery they don't worth it.

 

[cwah]

They do not want to recognise anything:
Me:
"Ok, I can understand that I'm wrong.

But can you explain me why I had a maximum distance of 27 km when I had my battery for the first month, and now I only have a maximum distance of 21 km?"

Conhismotor:
"Maybe you do not charge full electricity. And or because of abrading, it will become short. Thanks for your understand. If you have any need and help, you can contact us freely."

 

[flecc]

Only just over 7.6 Ah then. Obviously they are just ducking away from the issue with excuses.

Manganese cathode batteries haven't performed well ever since they replaced cobalt cathodes on safety grounds, and at first they were terrible. Back in 2006 my first one was finished and useless at 3 months old on a fairly high powered motor, the second one lasted just 10 months with care. It wasn't until better compound cathodes were introduced from early 2008 that I could even use that e-bike properly.

 

[cwah]

Thanks for the summary Flecc.

These damn Conhismotor are really not reliable