How to tell what Ah your battery pack is other than what they say it is?
- Thread starter Gr3
- Start date
harryS
Well-Known Member
Buy a wattmeter. You can either hook it up in between the controller or battery, or between the charger and the battery. The last part might be easier on a commercial ebike where the preious wires are hidden. It involves cutting/splicing. so maybe it's best done on the charger cable which is expendable and doesn't need to carry heavy current.
Then you charge the battery to max, and run it down til the bike stops, measuring the AH used if you have the meter on the bike. If not, you charge it back up and measure the AH going back into the pack. They will be the same, no matter how you do it. The measured AH is never is good as advertised because an ebike controller is designed to only use about 10% of the available AH to provide more safety margin,
Here's a picture of a cheap $15 wattmeter. It can display amps, peak amps seen. amp-hr, volts, watts, watt-hr. I've found that only the amp related values are accurate.
Does running the battery flat shorten life? Yes, you won't get much more than whatever minimal cycles wee advertised.
Then you charge the battery to max, and run it down til the bike stops, measuring the AH used if you have the meter on the bike. If not, you charge it back up and measure the AH going back into the pack. They will be the same, no matter how you do it. The measured AH is never is good as advertised because an ebike controller is designed to only use about 10% of the available AH to provide more safety margin,
Here's a picture of a cheap $15 wattmeter. It can display amps, peak amps seen. amp-hr, volts, watts, watt-hr. I've found that only the amp related values are accurate.
Does running the battery flat shorten life? Yes, you won't get much more than whatever minimal cycles wee advertised.
6zfshdb
Well-Known Member
- Region
- USA
- City
- Northeast Pennsylvania
If your battery is indeed Chinese, you may have reason to suspect it's rated capacity. Check out this you tube video. It's a bit technical but the end results are interesting
Accurately measuring a batteries capacity is a complicated process. This very technical video explains the procedure. It's geared for cell phone batteries but the same process applies to those used in ebike battery cells as well.
For us mere mortals who want to take simple, albeit less accurate measurements, there are less complicated ways. Keep in mind that completely discharging a lithium battery can cause internal cell damage. Most ebikes have a battery maintenance system or BMS. It can be located in the battery case, the motor controller or elsewhere on the bike. The BMS shuts down the system when the battery reaches it's terminal or minimum safe voltage. However you measure your battery, make sure you do so with the BMS in the circuit to avoid damage. The method posted by harryS above is a safe and effective way to do it since it incorporates the bikes BMS.
I made a rig for bench testing my ebike batteries using four 25 watt automotive brake light bulbs and a DC hour meter. Placed in series with the hour meter, the bulbs draw 100 watts (2 amps) at 48 volts. I connect the rig to a fully charged battery with alligator clip leads (my batteries have an internal BMS) and let it run until the lights go out. I multiply the hours displayed on the meter by 2 to get the AH rating of the battery.
Note that this is a simplified static test which is similar to that used by battery manufacturers to determine published ratings. Dynamic readings, taken under varying discharge rates and temperatures, will produce different results.
Accurately measuring a batteries capacity is a complicated process. This very technical video explains the procedure. It's geared for cell phone batteries but the same process applies to those used in ebike battery cells as well.
For us mere mortals who want to take simple, albeit less accurate measurements, there are less complicated ways. Keep in mind that completely discharging a lithium battery can cause internal cell damage. Most ebikes have a battery maintenance system or BMS. It can be located in the battery case, the motor controller or elsewhere on the bike. The BMS shuts down the system when the battery reaches it's terminal or minimum safe voltage. However you measure your battery, make sure you do so with the BMS in the circuit to avoid damage. The method posted by harryS above is a safe and effective way to do it since it incorporates the bikes BMS.
I made a rig for bench testing my ebike batteries using four 25 watt automotive brake light bulbs and a DC hour meter. Placed in series with the hour meter, the bulbs draw 100 watts (2 amps) at 48 volts. I connect the rig to a fully charged battery with alligator clip leads (my batteries have an internal BMS) and let it run until the lights go out. I multiply the hours displayed on the meter by 2 to get the AH rating of the battery.
Note that this is a simplified static test which is similar to that used by battery manufacturers to determine published ratings. Dynamic readings, taken under varying discharge rates and temperatures, will produce different results.
erider_61
Well-Known Member
WOW...that first video with results of 900 mA on a 4,800 mA rated battery was quite shocking. Now I realize a static test like this does not represent a real world discharge rate but at 1/5 the capacity claimed this shows an alarming discrepancy of the counterfeit battery. Would like to have seen the results for genuine brand name batteries to make an actual comparison..
harryS
Well-Known Member
Well, there are no real 4.8AH 18650 batteries either, so is Ultrafire guilty of counterfeiting if the prototype doesn't exist? Guilty of crazy claims anyway.
I believe the most recent high AH batteries are pushing 3.3-3.5AH.
A genuine name brand battery advertised at 3.2AH will deliver 3.2AH, if tested per the manufacturer standard.
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