Unexpected Shutoff & Battery Failure (IPS I130)

[Andrew Flewellen-Gore]

Hi all,

I bought my first electric unicycle, an IPS I130, from banggood.com earlier this week. Everything was fine and dandy until I ran the battery too low on one ride

 

The unicycle was complaining about low battery. I continued to ride it for about a quarter mile by cycling power repeatedly (you can ride at good speed for about 10 seconds after power up even when battery is low). Afterwords, the unicycle would not keep charge and cannot draw sufficient power from the  batteries, it seems. See video for symptoms.

 

 

Here are the ratings on the charger:

 

Compare this to the voltage across the battery after a full night of charging & after taking the video above:

I think this means the battery is pretty much toast, since the battery is quite depleted. When I hook the charger onto the battery, a LED indicator turns green very quickly, signalling that the battery should be charged up fairly well. The symptoms present in the video above remain the same though.

Here is a picture of the battery:

Right now there is only one battery, but there is room for an identical battery that can be put in parallel with an an unused connector. I'm hoping that I can solve this problem by just getting two new batteries identical to the above one, one with a male connector and one with the female. Problem solved, and I get more range. I really hope that the electronics on the board are not the cause of this problem, as it is possible that something on the board is broken, and quickly discharging the batteries (though this is unlikely since the charger registers that the battery is full very quickly when it probably does not contain much energy in reality).

 

I am looking for advice on where/how to obtain these battery packs.

 

Also, while I have the euc open, I'd like to mod the buzzer so that It is not as loud & annoying. I don't want to remove it completely though. 

If you can give me useful feedback, or point me to posts that would solve these issues, that would be great. Thanks for the help, if any can be provided! 

[Keith]

@Andrew Flewellen-Gore, whilst it REALLY is not a good idea to keep trying to discharge a battery further as that is only going to damage it, I would expect the IPS low voltage behaviour to be at a voltage well above that which would harm the battery.

My first thought is: if you have only had it one week, how sure are you that it has ever taken a full charge? 53 volts equates to 3.3 volts/cell which is pretty much as low a voltage as you want to be at off of load. So one possibility is that there is something wrong with the charger or charge circuitry which may possibly have been there all the time?

I do not believe that the metal thing in the third picture is the battery, I don't know IPS very well, but I would have thought that was the main control board and didn't need to have been removed. 

Simplest way to quieten that sort of buzzer is to stick a bit of foam tape (draft excluder or double sided tape over the open hole, if that isn't quiet enough a resistor in line with the buzzer or across it might work, not off-hand sure of the best value though.

[Andrew Flewellen-Gore]

@Keith Yeah, that picture is not of the battery. I dug a little deeper and here is the battery.

 

I don't really think it's the charger because it was working well before this incident. I was getting range similar to what I expected on each run (I had about 3 full runs before this issue). The problem might be caused by some electronics on the board that are  between the charger's output and the battery.

Since I know that there are 16 cells now, at about 53 volts that is indeed about 3.3V per cell which is on the low end but okay, I agree. I'll try to figure out more in the meantime.

[Keith]

I'm fairly certain it won't be something on the wheel rapidly discharging the battery as there is enough power in even a small fully charged battery for quite a lot of magic smoke to accompany a fast discharge. Similarly if something was draining the battery as fast as it is charging - 1.7 Amps by the look of it - then the charger would stay permanently on with the red light.

What size is  the battery,  if it is 130Wh battery it will only have 16 off 2200mAh cells? I believe the IPS has a more sophisticated Battery Managment System (BMS) than most with the BMS incorporated into the main control unit - in which case it may be capable of behaviours outside of my personal experience, However my thoughts are that there are probably 3 possibilities:

1) if there are only 16 cells (larger batteries would have 32 or even 64 cells with up to 4 in parallel) then one or more cells may (just possibly) have been out of balance with the others and the deep discharge could have taken their voltage down so low that the cell has failed. That is less likely to happen on bigger packs with parallel cells.

2) The charger has just decided to fail by coincidence at this point.

3) The charge protection circuit in the BMS has failed or is preventing charge because there are some failed cells

The way the charger works is that it will hold a constant current of,by the look of its label, 1.7Amps until the battery reaches 4.2V per cell (67.2V for the 16 cell pack.) during the constant current phase the charger voltage will only be slightly higher than the battery voltage (I.e. Just enough to "push" 1.7Amps) At that point the charger will hold 67.2V and the current will slowly drop as the cells get closer and closer to fully charged. At some fairly low current, typically 100-200mA the red light will go green and indicate charging has stopped, in practice it will probably continue to supply that small current.

So bottom line is if the charger cannot supply more than a few hundred milliamperes (possibly zero) then the green light will come on, so it doesn't have to mean the battery is actually fully charged.

If you are VERY CAREFUL  you can check the voltage and possibly current the charger is supplying, if it is reaching 67.2 V or higher then the problem is in the Unicycle itself, if not it could be the charger. Which pins are positive and negative is shown on your charger label for the different types of plug it can be supplied with.

By VERY CAREFUL I mean that if you accidentally short the positive to negative on the battery, even in its discharged state, very very high currents may flow, enough to possibly arc weld the contacts together and cause a fire.

If you search for Charge Doctor on this site that is a much safer diagnostic tool - I must get around to getting one myself.

[Andrew Flewellen-Gore]

@Keith I found a cable coming from the battery that fed back into the main board with 18 wires. since there are 16 cells in the battery pack I thought that the cell voltages might be coming out on these lines. Sure enough, I was able to get some voltage readings on the individual cells from this connector.

Cell #	Cell voltage
1	3.479
2	3.543
3	3.543
4	3.543
5	3.54
6	3.555
7	0.189
8	3.553
9	3.54
10	3.54
11	3.54
12	3.544
13	3.544
14	3.542
15	3.544
16	3.549
total =	53.288

 

It looks like cell 7 is bad. It has a low voltage and a high internal impedance. The BMS must have noticed this and prevented me from charging the battery! I will look into getting a replacement cell. Hopefully this is the only thing that is wrong.

 

If you have any suggestions about where to get a cell that would work? I believe your calculation above correct, I think 2,200mAh cells are used. I plan to get one, charge it to the right voltage to match the others, and then I'll replace the old one somehow. I don't have a spot welder or anything, so batteries with soldering tabs would be ideal.

[esaj]

At least http://eu.nkon.nl/rechargeable/18650-size.html sells cells with tabs, check the manufacturer / type number from the old cells to get a similar one. I'd prefer spot-welding cell strips to BMS over soldered any day, but it could be ok just with soldering too, don't really know. I didn't build my packs myself, nor have I ever changed the cells in any pack.

[jbwheel]

15 hours ago, Andrew Flewellen-Gore said:

It looks like cell 7 is bad. It has a low voltage and a high internal impedance. The BMS must have noticed this and prevented me from charging the battery! I will look into getting a replacement cell. Hopefully this is the only thing that is wrong.

What about telling the seller about this problem ? Maybe a picture with the voltmeter reading is enough.

[Andrew Flewellen-Gore]

So the replacement cell came in, and while I was soldering it into place I got some sparks/arc for a split second.

I have a big soldering iron that can pump heat extremely quickly, so I decided to solder to the terminal a little bit... this was probably not a good idea on my part. I was soldering around the brown mark on the right of the picture when the arc occurred. I then took off the circular insulator from the cell on the left and got discovered a second scorch mark (the brown spot on the leftmost cell). It looks like some localized shorting occured... I'm wondering If I've damaged both of these cells beyond repair and need to get two more cells and solder much more carefully.

The voltages of the cells looks fine, but this probably isn't a great metric for battery health. 

[Chriull]

I'd order 2 new cells with pre-welded strips on them and just solder the strips neatly together. Be sure to not offend in any way the plastics of the cells - they are the important insulation. Also be sure to find and remove all of these small solder balls that are just "glued" to the caps

ps.: i assume you have a pack with always 2 cells in parallel and the new cell had a different voltage then the "old" parellel one in the pack. So the spark was the "balancing"

[Andrew Flewellen-Gore]

@Chriull All the cells are in series 16s (8s when I did this soldering as I tried to make the process more safe) so there was not any balancing going on. It was very strange since the sparking only occurred when I applied the solder in a particular instance. Thanks for the advice though.

[Keith]

46 minutes ago, Andrew Flewellen-Gore said:

@Chriull All the cells are in series 16s (8s when I did this soldering as I tried to make the process more safe) so there was not any balancing going on. It was very strange since the sparking only occurred when I applied the solder in a particular instance. Thanks for the advice though.

Assuming the arc you saw was the damage on the left (I.e. If wasn't there already) then I can only think of two things that could cause it:

The first is unlikely, but we cannot see what you have done at the other end of the grey cell. If you have accidentally connected it to the same green cell the two would be shorted together and will now be ruined - as I said, unlikely!

The way more likely is that as the negative side of the green cell goes all the way to the top of the cell, and is protected by that green heat shrink then If that spot welded tag extended over the green heat shrink insulation when you soldered it the heat would melt the heat shrink connecting the positive voltage tab to the negative of the same cell, high current would then arc and burn away the short. It is very unlikely the current or heating were enough to damage the green cell and no harm would have happened to the grey cell. If it's voltage is not significantly less than it was before you soldered it, it is probably OK

However, I assume you are fitting a cell that has tags spot welded on it already, if so you really should not have soldered anything other than the tag, even a high wattage soldering iron has a high risk of damaging the cell if it is soldered to directly, as here.  Also as @Chriull has said damage to the heat shrink plastic may cause shorts as will blobs of hot solder.

Finally you did make sure the new cell was at the same voltage as the others before connecting it didn't you? There won't be a balance current surge with only single cells, but it is asking an awful lot of the charge balancing if that cell is at a storage charge of 3.7-3.8V and all the others are still at 3.5V

[Andrew Flewellen-Gore]

@Keith Yeah, I got the new cell's voltage close to the others' first.

I was pretty careful to connect the batteries the right way, anyways, the voltages of the two cells were about the same after this incident.

As for the the even here is some more detail: The arc occurred on the right, on the (-) terminal of the grey battery and seemed to happen right around my soldering iron while i was applying some solder. I'm pretty sure that the damage on the left was also caused by the arc, but there was some insulation covering that spot when the arc occurred so I could not see it there. Your explanation seems good, I did not realize that the neg. side of the cell would encompass so much of the exterior underneath the green shrink-wrap, getting so close to the pos. terminal! But that theory does not explain why the arc terminated around the (-) of the battery on the right. I wonder if the current made it to the (+) of the right-most battery somehow, in addition to your theory.

As for my soldering, job: lesson learned resist the urge to solder directly to the battery terminal

[Hunka Hunka Burning Love]

Yeeks soldering to battery ends scares me.  I know some people do it, but maybe it is best just to check with a local battery shop to see if they can spotweld it instead for you.  I replaced the battery in my Sonicare toothbrush by bringing the battery pack and old connectors in.  They were able to remove the connectors and transfer them over to a new battery for like $10.  Nice and electro-spotwelded with minimal heat increase.  With soldering I've seen some cold solder joints where it looks bonded, but in actuality it's not connected well.  Are you using flux?  I find battery metal ends aren't the best metal to solder to or maybe what is underneath heatsinks the heat too much for a proper solder weld.  Or maybe just buy one of the $60 spot welders on AliExpress or eBay to make life easier if you plan on doing this a lot and sell the welder off later to the next guy.

For something you rely on while traveling at high speed you really don't want a homebrew connection that detaches or something.

[Andrew Flewellen-Gore]

@HunkaHunkaBurningLove Thanks for the advice. As you can see in the picture above, there is also a solder tab that I used, so so the connection to the terminal itself was just icing on the cake. I didn't use flux because the contacts seemed easy enough to solder to without it.

I've cleaned up the connection, and got the battery pack charging successfully. After a quick test run, the wheel appears to run as good as it did out of the box. I will add shrink wrap to the mod-ed battery pack later. Then I will post about what kind of range I'm getting. It will be interesting to see what happens to the range of my unicycle after having this mod done to it.

 

[Hunka Hunka Burning Love]

Ah I see what you did.  You soldered the existing tabs to one another the quick and dirty way. I wonder if maybe instead of trying to get the solder to bridge the tabs whether soldering a short thick gauged jumper wire might have reduced the need for such a large glob of solder.  You can solder with the tabs bent up a bit to avoid heating any sensitive areas up and then bend everything down.  In any case, whatever works I guess.  There's more than one way to skin a cat as they say. 

Regarding the speaker, if you can tear a piece off a cotton ball you can push some into the speaker hole and add some tape on top to muffle the volume.

[esaj]

10 hours ago, Andrew Flewellen-Gore said:

Your explanation seems good, I did not realize that the neg. side of the cell would encompass so much of the exterior underneath the green shrink-wrap, getting so close to the pos. terminal!

AFAIK, the entire outer metal shell under the wrap of the cell is the negative terminal, ie. the whole length of the cell, not just the other end.

 

 

 

[Hunka Hunka Burning Love]

I've always found it weird how they have only a few millimetres distance between the positive and negative surfaces.  Check out this video:

 

[tjcooper]

Andrew,

I am being pushed into an IPS i130 from Banggood as a replacement of a MoHoo that does "unexpected stops" after 20 minutes of operation.  So I want your take on how well the unit worked before the problems set in.  Have you been successful of replacing the injured cell?   Have you put in the second battery to double your watt-hour rating?   I will do this almost immediately when my unit comes.

I have built NiMd and LiPo battery packs for rc planes and drones for many years.  It is a "piece of cake" if you follow the right rules.  See www.rcgroups.com and look under BatteriesAndChargers and DYI battery packs.  They have lots of good video showing you how to follow the rules.

Big Rule of Thumb:  on an 18650 cell, put some solder on the positive cell before doing anything else.  I use the "big black beauty" Weller soldering gun from the old days.  it is like 80 Watts of power in about 6 seconds of trigger pull.  I always put blue tape on the positive end and just cut a hole in the tape where the positive nib sticks up.  Get the solder on it.  Apply no more than 6 seconds of heat with solder tip already hot.  More time than that and you can hurt the circuit under the tip.  Then use silver solder stranded wire to make the connection (keep the insulation right down to the tip).  Again pre-solder the stranded wire.  Then put wire on positive tip and apply no more than 8 seconds of heat to get solder to flow and make a good bond.  Test you solder by pulling on it.  30lbs of force means you have done a good job of joining the wire to the tip.   Then repeat the process of the stranded wire to the next battery tab.  Use liquid friction tape to cover the area you have soldered to be sure nothing is exposed to get short started.

Power Monitor:  see my thread on "unexpected stop" for the MoHoo where I show you how to get off-the-shelf parts that show you the milliamps, volts, and total power you put into the battery.  This costs about $15 and takes 20 minutes to make.  Hope this helps.  Please tell me about how your IPS i130 is working.

   tjcooper

[Jason McNeil]

The standard battery cells IPS uses in the a130/i130 are Chinese branded cells. While they may be not complete rubbish (data I've seen is supporting about 7A sustained), they're nowhere in the same class of the LG HG2s that we had custom built for our a130s.

https://www.ewheels.com/product/ips-a130-turbo-edition/

[Andrew Flewellen-Gore]

@tjcooper

Before the problem, I got about 2-4 miles of range depending on how efficient my riding style was. I now get about 3-5 miles of range since the fix. Overall, I really like the ride quality. The motor seems quite powerful.