Basic Care and Trouble Shooting of a LiFePO4 E-bike Battery

July 19, 2012

A common choice for powering a hub motor kit is a LiFePO4 battery pack (Lithium-Iron-Phosphate).  Brand names include Pingbattery, and V Power HK, and there are no-name versions known as a duct tape LiFePO4 pack. Many people new to E-bikes make easily avoidable and simple mistakes that lead to problems, and sometimes even battery death.

Battery break-in of new packs

The brand new cells may or may not need a break-in. There is no way to really tell if they do or do not, so follow this simple break-in procedure to be sure. When the battery arrives, plug in the charger to the battery, then plug the charger to the wall, and observe how it reacts. It should display a red light, indicating it’s charging. After awhile, it should change to a green light indicating it’s charged. Leave it plugged in for about an hour or more after the green light turns on. The charger may cycle from red to green periodically, as the battery management system balances the battery.

Pingbatterys battery management system (BMS) will have a row of LED’s visible. The battery is fully charged and balanced when all the LED’s are lit. The BMS will have 12 LED’sfor a 36V battery, and 16 for a 48V battery.  For others, just make sure to charge it long enough to stop cycling from on to off and on again. Here is a Pingbattery battery management while charging, and at 54V. I have the voltage displayed on a cheap voltmeter, it’s not part of the BMS.



Here is the same battery at 58V, with nearly all the BMS lights shining.



Now run some shallow discharges.  If you have the bike ready to roll, ride around the block, then put it back on the charger. If the bike is not ready, the battery can be stored safely for a week or two. The idea is to get the cells used to taking a full charge, and balancing. If your BMS is the type with the LED’s, you can actually see the battery perk up and balance faster. Usually about 5-6 cycles like this does the trick. Your LiFePO4 bike battery is now ready for riding, and should be safe to ride for long distances with no problems from one or two undercharged cells causing a reduced pack capacity.

Charging your battery

Charging is simple, plug in the charger provided with the battery. Unplug later, when the green light has turned on.  There is little reason to use timers, or get up in the night to unplug the charger. When the green light is on, the charger uses very little power, and is not overcharging the battery. The BMS will discharge any high voltage cell groups to the proper voltage. Leaving it charging overnight will just give it more time for the battery management system to balance the battery.

Balanced is when all the cells are charged to their full capacity. The battery management system will start discharging the over-full cells when the charger turns off, showing a green light. Then later, the charger will go red and continue to charge the lower voltage cells in the pack. This repeats till the battery is balanced.

Don’t worry about this process wasting cycles. If you discharge the battery 100%, (meaning, you ride until the BMS shuts off the battery) that is one cycle. If you routinely discharge less than that, you simply get more cycles. Limiting the discharge depth to 80% tends to lead to a better balanced battery that takes less time to recharge, and may lead to even more cycles than the seller promised. So charge whenever you can, and don’t worry about trying to discharge deeper to get 100% of the rated cycle life.

Not all battery chargers are built to withstand severe vibration. So if you do carry the charger around, carry it in a way that limits the bumps and bounces on the road, such as in a knapsack. Best of all, stash an extra charger at your work if you can.

Turning your E-bike on and off

If your bikes controller has an on off switch, you do not have to unplug the battery every time you park it. But if there is no switch, you should unplug the battery. If the controller is left turned on, it will drain the battery at a rate of about 3-watts. About 7 days in storage with the controller turned on would completely drain the battery, risking severe damage if your BMS does not shut the pack down.

When you plug in the controller, the capacitors inside pull a rush of current, which causes a large spark. This spark is generally harmless with small controllers for 1000W or less. If the spark damages a particularly cheap connector, then replacing the connectors with 45-amp Anderson Powerpole connectors is one way to simply solve that problem.  Power poles are designed to handle the connection spark with no damage.

 Protective Battery Box

Many of the larger LiFePO4 E-bike batteries do not come in a protective box. You should make something to give the battery some extra protection in case you crash, or just knock over the bike. A tight fitting custom plastic battery cover can also prevent chafing when the battery moves slightly inside it’s box or bag that you are carrying it in.  Coroplast is a very easy material to work with. Cut and tape, to make a tight fitting box around the battery that will not allow the pack to chafe. All wear and tear is then transferred to the battery cover, instead of wearing on the battery itself.  Other materials work well too. I have used an aluminum cookie sheet to make a battery cover.  Others have used peel and stick floor tiles to give a battery a bit more durable outer shell.

Here is how I made a battery cover for my 48V / 15-Ah LiFePO4 ping battery.
The material chosen was a lid to a large plastic storage tote.



The battery is placed on the material, and a line traced around it.  The plastic was cut at the corners and folded up into a box with 5 sides.  Extra material is left at the corners, and folded over to strengthen the corners.  Extra material left on the long sides is folded over to protect most of the top.



Then the battery is placed on the cover and the sides folded in and taped as tight as possible. Use plenty of tape to secure the corners. The last step is to put a nylon strap overlapping the bottom, and taping it in place.  This way I have a convenient way to carry the battery when I need to. Notice that the BMS is still able to get some ventilation, and I can see the 16-LED charge indicators on the BMS.


Battery Calamity

One day while riding fast on a very rough dirt road, the metal toolbox I carry the battery in lost its lid. The battery flew over my shoulder, and landed in the dirt 15 feet ahead of me.  The battery cover protected it perfectly, and there was no harm at all to the battery. A naked battery would have been ruined. So cover em up, because stuff happens.

Battery Size

Don’t buy too small a battery for your electric bike. This type of LiFePO4 battery pack generally has a discharge rate of 2C maximum. What does that mean? If you have a battery of 10 amp hour size, a 10-amp discharge would be a 1C discharge rate. So the most you can ask of it is 2C, or 20-amps. But that does not mean your battery is going to like a 20-amp discharge. It should last longer if you back off some. So 10-15 amps is about the limit for a 10-Ah LiFePO4 of this type. 20-25 amps from a 15-Ah size, and about 30 amps from a 20-Ah size. Other types of LiFePO4, such as Headways or A123 have higher C-rates.


Now it’s time to talk about troubleshooting. Some of the procedures will simply give you peace of mind even if the battery is acting fine. It’s nice to know what voltage your battery is charging to for example.  A simple digital volt meter can be very cheap. Harbor Freight voltmeters go on sale all the time, and can even be free with a small purchase. Just having a voltmeter with you as you ride, or attached to the battery as you charge will let you know the battery actually did get charged. Or let you check the voltage if you suspect a problem. Even better, have watt and volt meter, such as a watts up or a cycle analyst installed on the bike.

But suppose you don’t have a voltmeter, and now your battery ran out earlier than usual. What do you do?  Well, go buy a voltmeter for one. You really must have something, however crude, to get started with a trouble shoot.

One thing you can do without using a voltmeter, is to take a good hard look at your charger, connectors, plugs, and fuses.  If possible, inspect the battery management system for obvious damage like something that looks burned or melted,  With some chargers, the plugs and wires are very low quality, and break easily. This pic shows that inside this charger plug, the wires are still well attached.



It should not look frayed, or have solder that doesn’t look like it melted right. Does the charger light up?  When the AC plug is connected, and it’s DC plug is connected to the battery and charging, you should see a red light.  This pic shows a common 5-amp pingbattery charger while it’s charging. LED #2 has turned amber.



The LED’s on chargers vary, some have one LED that changes color, others have two colored LED’s. But by one variation or another, it’s red light is to indicate charging, the green light means fully charged. But, here’s the catch-22, if the battery is charged, or if the battery is disconnected from the charger, the charger light turns green. So sometimes the green light means the battery is charged, and sometimes the green light means the plug is broken on the wire between the charger and the battery. This shows the pingbattery 5-amp charger unplugged, with green light that also is used to show if the battery is charged.



In this case, LED #1 stays red all the time, indicating the charger is plugged into the wall.  LED #2 changes from green to amber. So if you don’t see the green light turn red when trying to charge, look for connector problems. It could be disconnected wires where the wires are soldered to the plug, or even disconnected wires inside the charger where they solder on to the board. If the charger will not go from green to red when you plug in, look for a broken plug or wire first. Next, get your voltmeter. Here is a typical digital voltmeter set up to check pack voltage or charger voltage.



Switch on, red lead plugged into the voltage socket (in this case, that socket is marked “V” for voltage, Omega for measuring resistance, and “mA” for measuring milli-Amps. One of these three test options is selected by the main rotary switch), and the black lead is plugged into COM (meaning “common”, or ground). The main selector switch is set to DCV (meaning DC-volts), and also set it to 200V (meaning 0-200V range). When checking lower voltages (such as individual cells)set the switch to “DCV, 20V” for a more precise reading. Be very careful with the probes, and don’t short one probe to the other while checking the voltage of batteries. At 48V, it will surprise you with a big spark.

See what the voltage of the battery is. Make contacts on the plug on the battery that connects the battery to the controller. Use the red probe on the red wire, and the black wire on the black. If you can’t tell the colors, just probe with any color on each wire. When you get the red probe on the positive and the black on the negative, you will see a positive number on the voltmeter like the picture above. If it’s a negative number, simply switch the probes on the wires or plug parts (the meter will not have been damaged).

If the charger still won’t start charging the battery, check with the voltmeter to see if the charger has voltage.  Most chargers, once you plug them in, will have detectable voltage at the charger plug.



36V chargers should show 44V –46V.  48V chargers should show 58V-60V. If the charger has no voltage output, you may want to unplug it and take it apart, and just check that the wires leading into the charger are connected (from the AC main supply wires). One common failure for chargers is a resistor right where the AC connects. Look for anything that looks melted or stinks, and that would indicate that the charger failed. Cheap solder will melt at a lower temp compared to a quality solder, and sometimes a bad charger can be easily repaired.

Sometimes a battery will get discharged so low that a perfectly working charger will not start up when you plug in the battery. This might be the case if a battery is showing less than 30V for a 36V battery, or less than 40V for a 48V battery, etc. For this to have happened, it’s likely that the battery management system is malfunctioning. When the battery voltage is really low, like 0 to 10V, it often just indicates the BMS switched off. In this case, a charger will start when you plug it in, because the charger is using a different plug that is not switched off (some chargers have more than one charge-plug, so it can charge multiple packs). It can be helpful to check the battery voltage at the charging plug and the controller plug, and compare the two. A normal looking reading should be seen on the plug that the charger wants to use for charging the pack. If the charging plug also shows a much lower than normal reading, you have real trouble.

If your battery is showing that kind of low voltage, or it is simply running empty far sooner than it should, it’s time to start looking at the packs individual cell voltages. Typically, the easiest way to do this is to unplug the BMS, and use the plug (or plugs) on the battery side to read the voltage of each cell. Here is the BMS plugs on the wiring to my 48V Pingbattery BMS. It has 16 cell groups, and the wires to each cell group are in two sets of plugs.



Now, the picture shows the plugs on the battery side, after they are unplugged. You will probe with the voltmeter on these exposed copper strips, two by two.



Probing the first two contacts on the plug will give me the voltage from one cell.



3.4V–3.5V is pretty normal for a charged LiFePO4 cell. It may be higher when fresh off the charger. Now move both probes down one cell. Move both probes, but only to the next contact, not two contacts down the line. In the previous picture, the black probe will move to the contact where the red one is in the picture, and the red one moves down just one space. Repeat this till you have all your cell voltages recorded.

What you are looking for is a pattern. Is one cell way too low?  Like 0V or 1V?  There’s your problem. That’s a cell that is over-discharged and ruined. Or horrors, are all the cells reading about 1V or less?  If so…the whole battery is no good. If all the cell voltages read good, about 3.5 volts or more when fully charged, chances are the trouble is in the BMS.  Look at the BMS, and see if anything looks burnt. In this picture, the BMS has heat damage to the electronic switch on the upper left corner.

Hopefully, you just have a battery that has become unbalanced. That would be indicated by a battery that when fully charged has one or more undercharged cells. If most of the cells are normal at 3.5V, but one or two cells at are at 3.2V, that would indicate some undercharged out-of-balance cells. The undercharged cells are causing the BMS to shut off the power sooner than usual. Plug the BMS back in, and put the battery on the charger. Leave it charging for a long time, overnight for sure, but possibly for a week or more!  If the battery fails to balance, you may have to resort to charging your battery one cell at a time to restore balance.

If your battery is known to be balanced ok, but still has abnormally short range, then you are likely to have a low capacity cell, or group of cells. Batteries are often made by connecting many cells in parallel groups. Just one bad cell in one parallel group will lower the entire packs capacity. Replacing the bad cells can be a pretty advanced task, but identifying the problem may give you a basis for deciding if the battery could be repaired easily or not.

Charge the battery and balance it. Then ride the bike till the battery is nearly discharged. Checking the individual cell voltage again will show which cell groups are discharging the fastest. The lower capacity cells will have the lower voltages. Knowing how far off the voltages are from each other, and how many low capacity cells you have, can help you decide if you wish to attempt a repair. Or you might discard the whole thing if many of the cell groups show low capacity.  If you have lost 25% of your range or more, it’s just like having a battery that is too small. The remaining cells will work harder, and might be getting discharged at a C-rate that is too much for them to last for long.  So it might be best to replace a battery that has lost a lot of it’s capacity. It could still be used for a very low wattage bike perhaps, or to do something useful such as powering an emergency light source at home.

Written by DOGMAN, July 2012

Eric has been involved in the electric bike industry since 2002 when he started a 6000 square foot brick and mortar Electric Bike store in downtown San Francisco. He is a true believer that small electric vehicles can change the way we operate and the way we think.


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