Electric Bikes - Help! I got a SERIOUS problem with my new LiFePO4 battery!!!

OK, here is the problem. i got my battery connected to the bike correctly (E-zip) to replace my old Lead acid battery that it came with. It starts up just fine, light on the battery meter and all, but if i use the throttle it moves and inch and then it shuts off. however, if i twist the throttle a very short distance i can move from a slow start slowly to top speed, but if i give it too much power at once, it shuts off mid flight. i have a 20aH LiFePO4 battery from ping ping, and i dont think the battery is gone bad, its brand new, but i can only get about 2-3 miles before the bike shuts off no matter how careful i am when twisting the throttle, but the battery is not dead, far from it, the battery reads full charges. if i charge it, it only takes a few min before it goes from red to green on the charger, so its not even close to being dead. what could be going on here? the stock battery runs just fine. here is the bike i have

http://www.walmart.com/catalog/product.do?product_id=8467094

here is the process i have taken to mount my new battery

http://www.youtube.com/watch?v=655TOZdHUhE

The method i have used worked fine for others using even a 36v battery apposed to 24v, so why is my 24v not working right? please help!!!

all Lithium ion batteries should have a curcuit board that protects against excessive charge and excessive discharge.

Remember a stalled motor is a DC short, and a motor under heavy load draws excessive current.

Do you think it is possible that you are drawing too much current from your battery?

lead acid can haz big amps for the startup torque

lithium cannot do that without catching fire

are lithium Iron Phosphate not different from Lithium Iron? and if other people could use a 36V battery opposed to the normal 24v just fine, how am i not able to use a 24v battery, just different battery type? and it doesn't explain how i can still get to top speed, and that i can only ride 2-3 miles but have full charge yet the bike cuts power. something just aint right here...

I've been trying to think of a way for you to test and troubleshoot. Do you have a volt meter?

If you said it trips with a heavy throttle, can you get it to trip long enough to prove that its the battery that is tripping? or when it's tripped do you still have an output voltage on your battery.

My line of thinking on this is, we don't really know what is tripping until you do some testing. Once we know what is tripping, we might have an explanation of what is causing it,

Do you have a voltage cutoff on your controller or BMS? Possibly under heavy load, the lithium battery cannot supply the voltage due to internal resistance and trips the low voltage cutoff on the controller.

That's one of the things I am worried about LiFePO4 batteries - they're usually rated at only 1 or 2C which is pretty low amperage rating - especially when accelerating. You might want to stick a voltmeter between the battery and controller. This way, you can determine if the BMS is kicking in a low voltage safety or not. If it isn't the BMS, then it might be the controller. Try sticking the voltmeter inline with the motor then and pull the throttle and see if you get the controller to shut down the power.

That behavior sounds like a cell by cell low voltage cutoff. In order to prevent overdischarge, the low voltage cutoff for your battery cuts power if any single cell drops below some number, like 2.8 volts or something.

If that's what's going on, one cell is at low charge even though the whole battery is close to full charge. If so, the solution is to discharge all but the lowest cell(s) and recharge... or to buy a single cell charger and charge up the low cell(s).

Your battery management system (BMS) is supposed to keep the battery balanced, but they are not perfect.

if i remember correctly, a BMS will balance the cells after the charger has stopped charging the battery. it only takes an extra 20-30 minutes. however, I'm not confident that I know the limitations of such a balancing, perhaps its pretty hokey at best.

lithium Iron Phosphate not different from Lithium Iron

"Lithium Iron" just looks like a typo of "lithium ion".

As far as I know, Lithium Iron Phosphate is a type of "lithium ion" battery, but not the only type. However, people who say "lithium ion" or "lithium polymer" or "li-ion / LiPo" in the e-bike context are typically referring to lithium manganese or lithium cobalt batteries.

I've been trying to think of a way for you to test and troubleshoot. Do you have a volt meter?

If you said it trips with a heavy throttle, can you get it to trip long enough to prove that its the battery that is tripping? or when it's tripped do you still have an output voltage on your battery.

My line of thinking on this is, we don't really know what is tripping until you do some testing. Once we know what is tripping, we might have an explanation of what is causing it,

I have a voltage meter, but i assume its not the battery tripping, seeing as just flipping a switch off and back on again brings the bike brings it back to life, then i can continue accelerating. I hold the throttle at about 1/10 the way, then after i hit 15MPH or so, i can hold it fully twisted with no problem. Can someone explain in more detail on how i can use the voltage meter to test further?

"Lithium Iron" just looks like a typo of "lithium ion".

As far as I know, Lithium Iron Phosphate is a type of "lithium ion" battery, but not the only type. However, people who say "lithium ion" or "lithium polymer" or "li-ion / LiPo" in the e-bike context are typically referring to lithium manganese or lithium cobalt batteries.

I was judging the name according to the periodic table of elements

Li- lithium
Fe- Iron
PO4- phosphate (4 oxygen for every 1 phosphor)

I have a voltage meter, but i assume its not the battery tripping, seeing as just flipping a switch off and back on again brings the bike brings it back to life, then i can continue accelerating. I hold the throttle at about 1/10 the way, then after i hit 15MPH or so, i can hold it fully twisted with no problem. Can someone explain in more detail on how i can use the voltage meter to test further?

If you know how to trip the bike, then don't hit the switch. Instead, leave the fault in a steady failed state.

Then, you can either follow the battery voltage at the battery to the motor, or you can follow the absense of voltage at the motor back towards the battery.

there is a good chance, you find something that has power going into it, and no power coming out.

Keep in mind that even a working controller will have 0V at the output, unless you twist the throttle a little bit.

btw, when you think you've found the problem. Check it for repeatability. Ask yourself if what you are seeing makes sense. If it doesn't make sense, you might not be looking at the faulty part.

Also. don't forget to check any grounds for a loose conection. Remember, a loose connection can have a resistance to it that won't effect your bike much until you start to draw current.

Have you ever seen the tail lights on a car stop working only when you press the brakes? thats ussually a bad ground

guess what. i tested the stock battery and it read at 25v, the new battery was at 30-31v. i feel this may be part of the problem. where exactly am i supposed to connect the meter to on the bike without cutting open a wire?

thats always a tough one,I'd test at whereever the connections are.

I don't recommend that you poke into the wires, although some people might be comfortable with that.

Beyond that, you might want to invest some time into some jumpers or harnessses that you can use to troubleshoot with, but then you'll have them for future experiments,too.

jumper wires with aligator clips are a good way to jumper together connections while leaving access for you voltmeter probes.

there is the possibility of shorts or clips falling off and shorting to the frame. etc. So, try to really be careful, and spend the time to get everythin well supported and held into place.

Don't be afraid to use up electrical tape or ty wraps. That is always cheaper than replacing melted wires or blown fuses.

guess what. i tested the stock battery and it read at 25v, the new battery was at 30-31v. i feel this may be part of the problem. where exactly am i supposed to connect the meter to on the bike without cutting open a wire?


Well, you are correct. Increasing the voltage on a fixed load( motor) will definitely increase the current flow from the battery, and through the controller.

But I'd still focus on what it is that is cutting out on you. Then we can look at its current rating.

Personally, when I get into this with my own bike, I am going to make my own test harnesses that will allow me to take measurements on connectors that are otherwise sealed and inaccessable.

jumper wires with aligator clips are a good way to jumper together connections while leaving access for you voltmeter probes.

Alligator clips? They might work in a pinch, but that doesn't mean using them is a good idea. Kids, don't try that at home.

A good solution is to wire up a test harness that plugs in between the battery and controller with insulated terminals to connect to your meter. Even better is to use an inline power meter, like one of these (http://www.westmountainradio.com/Whattmeter.htm).

You should be able to find a reasonably priced DC clamp meter on eBay. The advantage to the clamp meter is it measures current without needing to be in the circuit electrically. They typically interface to any DVM and convert current in amps to a voltage, so 1V for example equals 1A.

Combine that with a DVM which has Peak Hold and you'll see the maximum instantaneous current draw.

At least this way you'll know for sure if you're drawing enough current to trip the BMS.

Well, you are correct. Increasing the voltage on a fixed load( motor) will definitely increase the current flow from the battery, and through the controller.

Yes and no.

e-bike controllers normally have an amp limit, such as 20 amps, and regardless of voltage the controller is designed to avoid going above 20 amps. And when the throttle is not at 100%, the maximum amperage (and therefore the power) is lower.

You should be able to find a reasonably priced DC clamp meter on eBay. The advantage to the clamp meter is it measures current without needing to be in the circuit electrically. They typically interface to any DVM and convert current in amps to a voltage, so 1V for example equals 1A.

Combine that with a DVM which has Peak Hold and you'll see the maximum instantaneous current draw.

At least this way you'll know for sure if you're drawing enough current to trip the BMS.

how far away from the motor do you need to be to get a good reading on the cable?

To clarify what cerewa wrote: A current limit creates a critical speed, below which increasing battery voltage has no effect on full throttle power consumption (or output). At higher RPMs, increasing the voltage allows the motor to draw more current than before, so full throttle power consumption will definitely increase with increased voltage above the critical speed.

how far away from the motor do you need to be to get a good reading on the cable?

The ammeter clamp has to go around a single wire, not the whole cable. From the wording of your question, it wasn't clear you understood that.

i have a feeling its guna be a long time before i can get this thing running, seeing as i am going to have to do all this stuff. but, it will be worth it. I'm having a bit of a hard time understanding what i need to do here and with what device. if it wouldn't be too much trouble, would someone be so kind as to post a video or pictures on the steps i need to be doing? Oh, and a bit more info, when i took the bike out for a little 4 mile spin, i came back and remeasured the voltage on the battery. it was 26v. so im guessing the voltage will go down over the time i use the battery per ride.

more info: Good news

i just Google earth'd my bike ride i took yesterday with the LiFePO4, and it looks like i went over 8 miles on a single charge. Even more good news: I KNOW the battery was not even close to no charge left, and i was right. let me explain,

Normally when i use this battery, I have to be very carful with how much i pull the thottle or else the bike will shut off. after about 5 miles or so, no matter how carful i am, the bike will shut off. In this case one would think that the battery is dead, but the meter would still say full. so what i did was not charge the battery at all over the night. instead, just let it sit there. today, i pluged it up to the bike and wa la. it didnt shut off on me like it did at the end of the ride. It does, however,it still shuts off on me when i go full trottle too quickly. So i think it is the controller, not the battery or BMS. what is your thoughts on this?

how far away from the motor do you need to be to get a good reading on the cable?

Shouldn't have to be too far, any EFI/RFI from the motor should be dwarfed by the electrical field created from 60+ amps within the focused confines of a clamp meter's sensor. If in doubt, sample near the battery.

more info: Good news

i just Google earth'd my bike ride i took yesterday with the LiFePO4, and it looks like i went over 8 miles on a single charge. Even more good news: I KNOW the battery was not even close to no charge left, and i was right. let me explain,

Normally when i use this battery, I have to be very careful with how much i pull the throttle or else the bike will shut off. after about 5 miles or so, no matter how careful i am, the bike will shut off. In this case one would think that the battery is dead, but the meter would still say full. so what i did was not charge the battery at all over the night. instead, just let it sit there. today, i plugged it up to the bike and wa la. it didn't shut off on me like it did at the end of the ride. It does, however,it still shuts off on me when i go full throttle too quickly. So i think it is the controller, not the battery or BMS. what is your thoughts on this?

If you can use your SLA without any problems at all, then I'd say,at least to a certain degree, that its definitely your LiFePO4 battery .but your battery isn't necessarily faulty, it may be as simple as it is a poor fit for your controller.

It was helpful that you wrote that the 'LED gauge showed a full charge' while the bike was tripped. To me, that is a strong indicator that the battery is NOT tripping.

furthermore, If the battery is not tripping, then its probably the controller sensing too much current. And, when the bike will not longer reset, its probably the controller refusing to reset because it is too hot. If you want to test this theory, while the bike refuses to reset, can you hotwire power to the motor and verify that the motor will still run? I'd hot wire it with a weak power source like a 12V battery. anything stronger could cause the back wheel to spin dangerously.

If the motor will still run, that rules out any possibility that it is a thermo switch in the motor that is tripping.

is this safe? is there something i can get to restrict the power to prevent it from giving too much power before it gets to the controller?

well, I think unless your budget is really tight. you should consider a better solution then trying to reduce the battery power before the controller. Why don't you consider buying a bigger controller.

Here;s a controller that can handle 48Volts / 50 AMps, and its only $35 plus shipping. If I'm wrong, you've bought yourself a controller. If I'm right, you have a working system that can handle your battery, plus any overvoltage experiements that you might want to try.

http://www.tncscooters.com/LB37.php

A more direct answer to your question: RV supply stores sell a auto-resetting breaker rated for a specific current. of 15, 20, 30 amps. It is commonly used to prevent high charge currents going through to your RV battery, especially if your RV battery is only connected to tiny wires.

These breakers are only $5, easy to find, but there's one thing I'm not sure of: the time that it takes to reset. It may take too long to reset, hence it would be very annoying and not suitable for what you are looking for.

If you want to troubleshoot this problem to a definite answer. then get out your digital camera, and start a journal with lots of pictures. I think there a many people on this thread that would be happy to help you out.

i see. will i have to cut wires from my original controller to put this new one on, or will i simply just need to disconnect and reconnect to the new controller?

No offense, but if you are worried about cutting a few wires, or finding the correct harness connectors, then I'm not sure if fixing this bike should be a do it yourself project for you. You might just consider hiring the work out to a bike shop.

its not that im afraid, i just find it a bit of a hassle...

I'm sorry, I re-read my post, and it probably came off as a bit harsh. I didn't intend it that way. its just that to me, it's the ultimate hobby. If it was a hassle, I could always afford to take it to a bike shop. I general look forward to my equipment breaking down because it gives me an opportunity to work on it. Last year, I blew a transmission on my ATV. Sure, it sucked that I wasn't able to use it for awhile. but I found it very fun and interesting to pull the transmission apart, figure out what was wrong with it, then put it back together. While I was doing the work, I was also cleaning, lubing, and painting various parts on the ATV, by the time it was back into use, it was looking pretty good, and I was feeling pretty good about it too.

im the same way, but im actually a PC builder. I make them from scratch and code my own games and software. its fun to learn, but it just that its a rather big switch going from knowing about about computers to knowing all about E bikes. it just may take a little time for me to learn, thats all.