BMSBattery - dead at 6 weeks or am I missing something?

[dabeindan]

On Nov 14 I posted my first Yuba built, basically a BMSBattery kit, 36v 35 watt, 12 ah LifePO4 battery. This afternoon riding home it stopped working. Here is some history and what I observed.

My commute one way to work is 6 miles, since the beginning I can easily ride 2 round trips (24 miles approx) and the battery meter will go down to 65 - 70% mark. I am not sure if that means I have another 30 miles range to go? But I will usually charge it at that level. I ride to work about twice a week, so two round trips = 1 week of riding. I have ridden about 120-150 miles so far and charged it 6 around times total. I always pedal when I ride, so I have been getting good range overall per charge.

Today was the 2nd day of the ride, this morning the battery level was 1 level less than full as shown on the built in battery meter. I don't remember if I checked to see the charge level coming home but given the history of the battery I should have plenty to get home. Riding condition was normal; not raining (I have never ridden this bike in the rain thus far), 34 degrees, I peddled as normal. 2/3 way home I went to twist the throttle and nothing, was working fine till that point.

I checked the following:
- No unusual smell or marking.
- I cycled the power button on/off, pressed on the battery level button and totally blank.
- I took the battery off but made no difference, even totally by itself it had no indication of life whatsoever.
- As far as I can tell there is no fuse to reset on the battery, not on the outside anyways.
- I always store the battery in the house, not cold in the garage, but it hasn't been that cold in Chicago anyways.

Here are my questions:
- Should I try to charge it? I know it sounds like a dumb question but it seem like more than just a drained battery. I don't want to damage it further so I thought I should ask first.
- If something is wrong, where and how do I start to isolate the problem.
- If it's LifePO4, is it safe for me to open the casing and see maybe something was knocked loose? Scorch mark?

Below is an example of pressing the button and nothing happened. This photo shows the main switch being off, and I had flipped it on and same blank display. Any help is much appreciated. Thank you.

 

[dnmun]

do you have a voltmeter and know how to use it?

 

[dabeindan]

I located a voltmeter and measured 15.6v, same with switch on or off. Low for sure, is it just a depleted battery?

 

[dnmun]

if it measured the same with the switch off, your voltmeter is not accurate. where do you measure? can you take the plastic end caps off and expose the BMS and charging fuse? i assume it is not charging now. can you measure the charger output voltage too?

 

[melodious]

Since you say it's LiFEPO4, I'd just charge the sucker and see if it was just a freak incident. That chemistry is rather abuse tolerant and I'd be doubtful you'd see a fireball like the RC LiPo overcharging events . Fear is fear nonetheless, charge the battery away from the bicycle and other stuff you cherish. Maybe put a timer on it. I'm assuming you have a feel for how long it normally takes to charge to full capacity? If not, a voltmeter to gauge the total volts 1/2 to 2/3 of the way to a typical full charge timing cycle.

A real surefire way to find out is to open the case and check each battery individually for a "dud" or low cell with a voltmeter.

You play a conservative game with your LiFEPO4 battery by charging it when it gets close to 80% (which is a full discharge cycle). IMHO, just plug it in and charge it whenever you can. Lithium chemistry suffer no memory effects unlike a lead chemistry.

Temperature has an effect on your working voltage. The colder the environment, the more sag you will feel. Sag = less voltage. Chicago = cold.

Here's some tips I learned the hard way (I ruined my first LiFEPO4 battery this way): If/when you reach a LVC event, DON'T use your battery further. Your more likely to damage the whole pack that way. For instance, don't turn the system off and on and get more juice/distance to get you to your destination. Ride it like a real bike to where you can assess why it cut off in the first place. That is unless you have a true visual indicator of your total pack voltage in a Cycle Analyst/Volt meter.

 

[SamTexas]

I agree with melodious. Just charge it up for now. No need to go through complicated processes until there is a need for it.

 

[Lessss]

Open the case ans investigate, do not just charge it as you will likely end up killing cells.
You might have a lose cell to cell connection or a dead cell.

 

[d8veh]

Your BMS is switched off either because it's detected a problem or faulty switch. The switch on the side switches it on/off. First thing to check is that the charger is actually charging it. Assuming it is and that it doesn't come back to life, remove the end-cap and check that a wire to the switch hasn't come off. It's better to charge your battery after every journey.

 

[dnmun]

he never replied to anything. whatta waste again.

 

[neptronix]

It lasted an entire 6 weeks? they must be doing better quality control these days, that's above average... :lol:

These packs tend to come with cells of varying quality and capacity. There are likely a few funky cells in the mix causing problems. The worst cell is probably the one which powers the BMS, which may be why you are getting a 0 reading. Just a guess.

Have you contacted them for support?

 

[dogman dan]

I would just charge it. If it works again, charge daily. Your battery meter lies. Didja perhaps leave the bike turned on at work that day?

Likely he just charged it, and it works now. If you expect a thankyou stop expecting one, but appreciate the few you get.

 

[melodious]

He may not be responding as of yet if his battery is still charging... (over 48hours of continuous charge). If your charger is taking this long to charge your pack, you have 1 or more bad cells within. If this is the case, the internal resistance of your bad cells is interfering with the normal charging cycle. Simply, you've lost some of your voltage (speed), and capacity (range) as well.

 

[lbz5mc12]

Maybe you blew a fuse. That happened to me on a similar battery. If you did blow a fuse you may have a crossed wire in the case. It could just be that one of the wires on the on/off switch came loose. It could also be a loose wire on the charge port; I've had that happen on another battery pack.

 

[dabeindan]

Hey everyone, have been dealng with family issues in LA, should be able to get back to regular life soon but havn't had anytime to deal with the battery. I appreciates all the help thus far, I think I will attpenpt to open the case and do a visual this weekend and proceed. Will update either way. Happy new year.

 

[dnmun]

go to harbor freight and buy a couple of their cheap voltmeters. they have them on sale all the time. item #69096, sometimes $3.99 or $4.99 on sale. buy two. then try again to measure the voltage of the charger. we can start there.

 

[USAEBIKECO]

Have you tried contacting BMS Battery and asking for their help/ or replacement??

Is there a warranty?

 

[dabeindan]

Hi everyone, finally have a few hours to look at this. here are some observations. I will try to respond to each post.

I found a there is a 20a fuse on the bottom after all, but tested OK as far as I can tell.

Opened both ends the case, the wiring on both sides appears to be ok, but this is a visual check only. As you can see the connections are either glued in place or crimped; and was difficult to insert probes. It appears to be relatively solid; not wanting to make things worse I did not take it apart to take readings.

Also it wasn't possible to remove the cells without cutting wires on one end of the end caps, so I wasn't able to check the actual poles or connections. The pack was firmly packed in there, so hopefully it wasn't a vibration / loose cells induced failure.

The charger output is 43.5v.

At this point I have it on the charger, see what happens.

 

[dabeindan]

(I am reviewing all posts and answering questions I missed).

I took the voltage reading at end of the battery, from the outside, inserting the probes in the female plugs. The charger measured 43.5v.

As far as contacting BMSBattery, no I have not, not yet anyways. I want to run by the forum first to see what my options are, as well as learn as much as I can about electric bikes. This is my first electric bike, I have no doubt I will always have an electric bike going forward, so minds as well start learning now. Another reason was the language barrier; on several occasions I communicated with them post sales, it was hard to understand (both ways I am sure). Plan is to charge it all day and see if it comes back to life as suggested. Maybe this is a none-event after all, but if it just needs charging, seems odd that it shows no light at all rather than a red / empty LED or something. I am just speculating at this point so I will wait patiently till the evening before I do anything else, including contacting BMSBattery for resolution. I will update more. Thanks again for all the help.

I also will order the voltage measuring gadgets tomorrow so I have them on hand.

 

[dnmun]

do we know that this is really lifepo4? i do not see a BMS, just the led driver board. is there a BMS connected on the end where the charger plugs in?

 

[dabeindan]

Huh, other than the small circuit board for the battery meter, I did not see any other that could be a BMS. Not that I have ever seen one, but at BMSBattery site they look like circuit boards.

This is what I bought, description from their website, not saying that's what I got however. I can't see the actual cells as they were shrink wrapped in blue, so it could be all within the blue pack?
36V12Ah LiFePO4 aluminium shell ebike battery pack. inlcuded 12s polymer cells, 1pcs 15A continuous discharge current smart BMS, 1Pcs 36V2.5Amps LiFePO4 battery aluminium shell charger EMC-120.

 

[dabeindan]

So I just looked at the battery and the charger shows the battery is fully charged - and then the charger cut itself off. Turned on the battery and it now has indicator lights and appears to be back to normal. Voltage is now registering 41.9v. The whole charge took around 6-7 hours. So far so good I guess.

Assuming the battery was operating as normal, then I must have ran the battery down low enough to have it cut off; hopefully at the designed safety cutoff and not a total drain. I will start riding this week and see if a) it still has good capacity or b) will it just cutoff pre-maturily; at least for now I am cautiousley optimistic.

If everything is (and was) working as within intended operating parameters, then I definately cannot assume 3 out of 5 LED lights (on battery gauge) means I still have 60% capacity. I will start charging it after every ride.

I will update this weekend after I get a few rides in. Thanks again for all the help.

 

[Rassy]

I think you have it figured out. Those LED gauges were designed for SLA and even then are only somewhat helpful. They work for SLA because as the battery is discharged the voltage drops in a fairly linear curve (i.e., no curve, just a straight line). In other chemistries, like LiFePO4, the voltage tends to stay fairly constant during most of the discharge and then falls very fast near the end.

Even with SLA, If the LEDs are part of the throttle, most of us just cut out the wire to the LEDs, because it carries the full battery voltage, which is more apt to short accross to the other wires, sometimes putting you in wide open throttle mode, paticularly if your throttle or connectors get wet.

 

[melodious]

FYI: once you achieve a LVC don't power it further! Instead, pedal the rest of the way. There is very little room to play with until you reach a point where you are going to permanently damage the batteries. Of course, you could make it even easier on yourself by buying a real meter: http://ebikes.ca/drainbrain.shtml or http://www.hobbyking.com/hobbyking/store/__471__157__Tools-Watt_Meter.html

 

[amberwolf]

So I just looked at the battery and the charger shows the battery is fully charged - and then the charger cut itself off. Turned on the battery and it now has indicator lights and appears to be back to normal. Voltage is now registering 41.9v. The whole charge took around 6-7 hours. So far so good I guess.

you may want to leave the battery on charger even after it cuts off and monitor it. after a while i bet it turns bac on as the bms balances the cells. some new packs can take days or weeks to fully balance, and some have such mismatched cells (internal resisntace or capacity or both) that it needs to stay on hte charger overnight even when you only use a little bit of the packs' capactiy.

 

[dnmun]

yes, the charger has a small balancing current it delivers through the shunt resistors to the last cells to finish filling up. this is when the charger has reached final voltage.

you can actually see the current if you send your charger current through a wattmeter or ammeter. for something like the old headway BMS, the shunt resistor is 20 ohms, so the shunt current is about 3.9V/20 or 195mA max. for the other BMS battery BMS we saw it had three 100 ohm resistors in parallel so that was 33ohms, and 118mA balancing current.