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Old 03-24-14, 09:57 PM   #1
mrmagoo
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Testing a battery

Got a job with a good bicycle friendly commute. Got the ebike out of the garage and found it isn't taking a charge. Its got a lifepo4 battery. Would sitting for a year kill this battery? How would i figure out if it's the battery or the charger?
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Old 03-25-14, 04:54 AM   #2
FMB42
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Did you maintain the battery by charging it at least once a month?

If not, it could have low voltage in one or more cells.

If you can, provide us with some more info on your system (brand/model, voltage, etc) so that we can help you perform some basic tests (battery voltage, charger output voltage, etc).

Btw, do you have access to a Digital Multi Meter (DMM)?
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Old 03-25-14, 10:10 PM   #3
mrmagoo
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I did not maintain the battery. It is a 24v 30ah duct tape battery- I do not know the manufacturer anymore. I will double check the charger tommorow as it is late, but i think its a 5amp charger. I do have a DMM, but don't know where I would place the probes anymore. Been along time since ive used one. I understand voltage, resistance, amps, etc.
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Old 03-26-14, 05:08 AM   #4
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Ok, if you can, re-read your DMM's user guide. Otherwise, the Internet has basic DMM user guides that can help refresh your memory.

Next, disconnect the battery from the wiring harness/controller and carefully check the batt. output voltage with the meter range set to next highest DC voltage scale above 24v. Be extra careful not to short the meter probes across the battery terminals. If the DMM reads " - 0 " or negative voltage then swap the probes around.

Note: As a safety precaution, the battery charger will not charge the batt. if the voltage reads below a certain level.

Your 24V LiFePO4 batt. has 8 cells.

Each cell has a working (average) voltage of 3.0 -3.3.

Generally speaking, the absolute minimum cell voltage is ~ 2.5V (max is 3.8 - 4.3V).

So, your battery should, at all times, indicate a charge of no less than 20 volts (8 cells x 2.5V = 20 volts).

A battery reading of less than 20V would indicate one, or more, bad cells. Bad cells can sometimes be replaced with new/good cells. However, it's often better to just replace the entire battery.

If the battery checks out, then test the charger output voltage. The DC output for your battery charger should be ~ 30.0 volts.

Note: Ping is a well regarded e-bike battery company that, IIRC, offers well made 24V LiFePO4 batteries at a good price (not sure if they have 30ah capacities tho). Ping is also known for having very good customer service.

Another recommended e-bike battery retailer would be "GoCarLite" (Doug, the owner, is a great guy to deal with).

Last edited by FMB42; 03-26-14 at 05:12 AM.
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