Battery capacity testing (for 48v)

[jamdaaman]

Hi I am trying to figure out if the capacity of my battery (48v 20AH) is true.

I have looked at discharge capacity testers on you tube but am struggling to find any that would suppport a 48v battery. Could someone direct me to a device/method that would support this high voltage and also not be so expensive.

P.s. I have bought a battery tester from ebay however it doesn't actually provide me with the battery charge - the bars are full everytime i connect it up to a battery (does a battery need to have current drawn from it to show the capacity?)

Perhaps there may be an error on my part when Im connecting this tester up - here is the tester I purchased:

https://www.ebay.co.uk/itm/12V-6-63...var=512031424538&_trksid=p2060353.m2749.l2649

 

[VEBill]

I'm assuming that you mean that you're attempting to confirm the "20AH" claim.

"Does a battery need to have current drawn from it to show the capacity?" Yes.

I'm not aware of any quick and small method to confirm that. There are cheap, easy and off-the-shelf testers for small Li-ion cells. They might take an hour or two to test a typical 18650 Li-ion cells. A larger battery would not be so simple. These Li-ion cell capacity checkers devices are effectively a "demonstration" test. They actually exercise the cell to see how it does.

If it's a one-time test, then it might be simplest to conduct the test manually over a (long) day. Even a 2A current draw at 48 volts is basically 100 watts, which is why such a test may be easiest when taken slowly. If you try to do it more quickly, then you'll have to find a way to dissipate a significant power. Manual test means monitoring the voltage and current regularly, on the assumption that it's not changing quickly. You'll need to find a suitable load, and a couple of DVOMs.

Because it'll be non-trivial, you might also wish to reconsider bothering.

The eBay gadget is a battery 'fuel gauge'. I don't have one, but I understand that they rely on measuring the voltage to indicate (approximately, relatively and probably non-linearly) how much charge is left in the battery. One would have to refer to the manual to know how to set it up. With eBay, obtaining the correct manual or instructions, and in English, is sometimes an issue.

 

[IRstuff]

"If you try to do it more quickly, then you'll have to find a way to dissipate a significant power."

There's that, but the other issue with rapid discharge is that the rated ampacity cannot be achieved.

http://learningrc.com/lipo-battery/

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

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[jamdaaman]

Thanks .

I am considering another method but I am uncertain.

The battery is for an ebike with a 1000W motor. The controller that I have also connected states that it draws out 26+-1A of current (the controller is rated to 30A i believe.). Is this figure indicative of maximum current drawn or average current drawn?

If I were to charge the battery, connect it up to the motor and turn the throttle to max and time it, would it be an accurate method?

I have estimated that it will last (if the 20AH figure is correct) 20AH/26A = 0.76...... * 60 mijnutes = 46mins - if it lasts this long/close to it the battery figure will be accurate.

 

[IRstuff]

The battery is for an ebike with a 1000W motor. The controller that I have also connected states that it draws out 26+-1A of current (the controller is rated to 30A i believe.). Is this figure indicative of maximum current drawn or average current drawn?

> average, but it might not include the controller consumption

If I were to charge the battery, connect it up to the motor and turn the throttle to max and time it, would it be an accurate method?

> no, that's a variable load

I have estimated that it will last (if the 20AH figure is correct) 20AH/26A = 0.76...... * 60 mijnutes = 46mins - if it lasts this long/close to it the battery figure will be accurate.

> possibly


TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

faq731-376 forum1529 Entire Forum list

http://www.eng-tips.com/forumlist.cfm

 

[VEBill]

It seems like you may have a case of Early-Onset Range Anxiety. ;-) !!!

Hopefully your e-bike, in normal operation, would use much less than maximum power. Otherwise it would continuously accelerate, leading to a very high speed crash. Cruising on level ground might be just a few hundred watts.

Simplest approach would be to skip the battery test and just get it running.

YouTube videos indicate that some are modifying their e-bikes from lead acid to Li-ion, either for crazy speed or long range.

 

[jamdaaman]

I have used the bicycle for several weeks.

I just dont have any experience of what 20AH is in terms of range. I use it hills a fair amount but I am just uncertain whether this truly is the correct value - it is a Chinese import after all/

 

[VEBill]

Is the battery lead acid, or Li-ion?
If it's lead acid, then the route to improvements is well mapped (Li-ion).
If it's already Li-ion, then about the only thing to do is add more cells.

--

Thinking out loud here about your 'excessive' 48 volts:

I wonder if the little eBay battery testers could have their voltage sensing separated from the current measuring path (perhaps a Hall Effect sensor). Many of those eBay battery testers allow you to use your own load (external) resistor, within the current limits of the device. So with a bit of Ohm's law and soldering, they could be adapted to semi-automatically run down your fully-charged battery and display the Ahr findings on their display. You'd need to run them with an external power supply (that's normal). They'd have no inkling of your actual battery voltage, so any watt-hour info would be meaningless. Or perhaps you could apply some fraction of the battery voltage, to keep the gadget happy. But the basic Ahr measurement might be extracted semi-automatically. It'd be a little project in itself to modify the gadget and make sure it works.

Perhaps there's a way forward using this sort of approach. Maybe.

 

[itsmoked]

If it's lead acid you can get pretty close to the remaining energy just by measuring the 'discharged' voltage.
Got battery specs for us?

There is only one way to estimate how far your fully charged e-bike will go. You put an electrical energy consumption meter on it. Then setup the meter by telling it how many amp-hrs the batteries are. It will add up your trip consumption and subtract it from the rated amp-hrs of your battery and tell you what percentage of energy remains. Conversely it will watch as you recharge the batteries and recompute the immediate energy storage.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[ScottyUK]

To give some idea of real power output on a road environment, the image below was taken from a Strava recording of my first ride out of the year. Not really pushing it effort-wise, just a run out to shake out any problems with the bike, but I got nowhere near 1kW output. I could probably achieve half that output for a short period, but it wouldn't be sustainable for more than a few minutes.