How can I check my new battery's true capacity?

Hi EPFMs,

I just received my 30AH battery the other day and just started using it yesterday. It came with a 2A charger and despite charging it overnight before use, it still wasn't full. I think that was a 10-11 hour charge.

I packed the charger with me yesterday and found a chance to charge it for Ann additional 2 hours but I still managed to run it flat on the way home.

The strange thing is that I did about the same millage and the same amount of time charging when I use my 20AH battery.

It's there a way to test the battery for its true capacity

Clinton

You need a watt meter. Plenty of cheap ones on the net. Then make up a load, like a bank of halogen lights or old heater to discharge your batteryin to. Do this through the watt meter into the bank of lights/ heating element. A 2a charger will take 15hrs to charge a 30ah battery from flat, so make sure it's full before you start
Give us more details on your system-Chemistry, voltage, controller, motor, speeds distance etc, and you'll get more specific help.

Yeah a watt meter and a low power ride would show what its mostly capable of... If it claims to be high discharge then a high power ride should hold its ground.
You could open up the pack, unplug the BMS balance tap JST cable and just discharge at 1amp the first 1S set of cells from the 4.20 down to 3.0v or what ever the allowed min discharge is for your pack.. If its Samsung 29E then its as low as 2.5v. Theres little chance your BMS will allow your cells to drop to that low voltage all at the same time.

With BMS's attached theres no way to extract to true capacity of your pack as most BMSs will cut off at around 3v or 2.75 instead of 2.5v etc if your cells are something like Samsung 29E cells.
When pack sellers sell their pack they list it at the max Ah/Wh capable of being discharged as if your discharged each cell by its self without a BMS and at a low C rate draw which can be considerably different then discharging the crap out of it behind a BMS.

Alright. Thanks for that. Is there a way to check the battery's current ammount of ah? Would that still require pluging the watt meter into another apliance or lights?

Ideally, I'd likecto have a precise indicator of how much I have left on the throttle or something. In fact, I have one that burned out when trying to hook it up. Thats a topic for another thread I plan start soon.

Recommend a device called Cycle Analyst from Grin Technologies. It shows you how much Amp Hours you are using while you ride and remembers its data, even when it is off or the power cuts out. Well worth the money to see how much ah you are using and testing maximum capacity and then after that how much ah capacity you have left.

Or for $0, just put a known load on the pack and see how long it operates until it shuts off. Most are calculated with a 0.2C load. A larger load will produce less capacity than a lighter load. If you want to know about how much capacity you get when actually in use, then use the average load you use when actually in use. More options;
https://www.google.com/webhp?sourceid=chrome-instant&ion=1&espv=2&ie=UTF-8#q=how+to+measure+battery+capacity&*

ClintBX said:

Hi EPFMs,
It's there a way to test the battery for its true capacity

Click to expand...

Watthour and/or amphour-meters are your friend.
Il like this one.... (ebay)... though rated for 30 amp max...

[youtube]YGp2wDAfC1k[/youtube]
there is a version with a 100amp shunt though.

fwiw, it's not unlikley that your "new" pack is made from cells that dont' have the same state of charge (and possibly not even the same usable capacity / internal resistance).

you may have to leave it on the charger for days to weeks for it to fully balance any low cell groups. (it wont' matter if the charger is a 2A or a 20A for this purpose; it's up to the BMS to do the balancing, and that's always a very low rate on these packs).


Alternately you can check the voltages for each cell group on the BMS's balance connector. This may require opening up the pack to do this. If the voltages are significantly different then it will take a long time to balance.


But this is generally why packs cut out at a much lower capacity than you expect them to.


BTW, if the cell groups *are* quite different in voltage, then it's also possible the worst ones actually have bad cells in the groups, either with less capacity than the others or actually draining down other cells becuase of internal shorts.

Alright! I'm convinced that I've been sold a lower capacity battery. After only riding 30 kms and that's with charging throughout the day for a total put 3 and a half hours, I was disappointed when it ran flat on my way home.

I tested to see if I could last a day without packing a charger on Tuesday and it went flat at around under 30 kms for fhe whole day. It was a windy day so I thought that maybe that played a role. But after today, I'm convinced that this is not a 30AH battery. My 20AH can do 50 kms in one go.

I bought this on aliexpress. I'm not quite sure how I'm going to dispute this with the vendor. I just ordered a watt meter and have yet to test it.

I guess I'll need evidence to prove that this has Less capacity than promised.

What do I do exactly?

Start a dispute . Tell them your concerns get a wattmeter or C.A. cycle analysis as good money spent. You brought a battery you got a battery. Next time buy a battery that you know what's inside. Buy from a known vendor. No nane vendor and no name cells.

If you don't get anywhere with that dispute then I would recommend opening up your battery and checking cell voltages etc. if you are at all inclined. You'll need a DMM but it could possibly be a rectifiable problem with some investigation. Lots of info/help here for you. Might save you some $$$

I would start by checking the cell group voltages as suggested above, it's very possible that a pack that size could need several days to fully balance if there's a very low cell group. A cheap watt meter is also a great investment, mine cost me like $12 free shipping from eBay. http://www.ebay.com/itm/100A-DC-Dig...le-Voltmeter-Ammeter-with-Shunt-/401163563291

I have one of those mounted in my battery box, it's takes the guess work out of wondering how much range I have left.

If you're going to pursue a dispute with an AliExpress seller, I recommend you arm yourself with as much hard data as possible.

If there is a low voltage cell group, oz that something easy to fix? Will I need more gadgets or is it simply a matter of just leaving plugged in to charge for a few days?

Alright, I've started a dispute and the vendor tells me she'll honor the refund but she wants me to declare only a $60 or less refund for tax purposes.

Is thos fishy?

Fishie a lot of fish in China. Plus they eat fish too ?Hard to say.