DIY battery keeps blowing charger's fuse

[tsourorf]

Hello everyone!

I have built a battery for my brother's bike and I have a problem I cannot figure out how to solve. First of all, I have built 3 identical 13S2P (48V) packs using very cheap Chinese re-wrapped 18650 batteries. They are supposed to hold 6Ah each, but I guess they will be more like between 1Ah and 2Ah. Anyway, the 3 identical packs I am connecting them again in parallel to give power to a 48V 500W controller and motor.

All the individual cells have integrated protection board, so I thought I didn't have to use a BMS. Now, whenever I connect them to the charger (Before even plugging the charger to AC), the charger's fuse gets blown (10A fuse).

Does anyone have any ideas on this? What have I done wrong here? Do I need a diode or something for the connection to the charger so as to only let current in and not out? In each pack, I have one plug connected to the two poles of the 13S2P. I have tried the batteries on the bike motor and they give power just fine! It's only that I cannot get power in them now that bothers me.

I feel I have done something stupid but I don't know what! Please don't judge too harshly!

 

[dogman dan]

Does the fuse blow if you plug in the charger to the wall first?

The charger is not designed to have it's capacitors filled backwards, from the DC side. the inrush limiter is on the AC side.

 

[tsourorf]

The first charger I bought didn't have a fuse and got blown altogether. That one, I connected the AC first and the battery afterwards. Once I connected the battery, a tsaf noise came from the charger along with a burnt smell. I disconnected both as fast as possible. Connecting the charger to AC once again and testing the DC output with my multimeter gave me nothing. So, I have read that the charger should be connected to the battery first and then to the wall (This instruction came with the new charger as well). Now, whenever I connect the battery to the charger, the fuse gets blown without even connecting the charger to the wall.

You say the charger is not designed to have its capacitors filled backwards... does that mean I have to block the current on the battery side so as to allow flow only towards the battery and not the other way around? I assume something like that is done in a BMS... how can I fix the existing packs though without disassembling them and re-assembling them with a BMS?

 

[amberwolf]

What voltage is the battery at?

What voltages are the individual cell groups at?

Are you sure you're connecting positive from charger to positive from battery? And negative from charger to negative from battery?



You might want to post some detailed pictures of what you've built so we can see if perhaps there is a construction error causing a short, or some other problem.



It's also possible you've gotten multiple bad chargers, as quality varies on them--but it is more likley there is something in the pack itself.

 

[dogman dan]

I just meant chargers are supposed to be powered up, then plugged into the battery. Then the caps don't fill from the DC side.

However, you can do it wrong for years with no problems on most chargers. I just thought maybe you had a fuse that could not take that inrush. Or a charger that could not handle it, backwards.

It does sound like something is wrong. Sure you have the polarity correct on the DC plug? Maybe your charge plug has + and - backwards.

My bet is that you got the polarity wrong. I've done it myself, twice in a row! Two fried chargers. Now I'm trained to double check polarity right after I assemble all plugs.

 

[tsourorf]

This is the schematic of the battery I created. 13 pairs of 18650 batteries. Nominal 48V.

The connector is a C14 connector (Male). The C13 (charger side) and C14 (battery side) connectors have the letters 'L' and 'N'. Using my multimeter I can verify that the 'L' of both sides is the one that gives the positive voltage.

Regarding the charger's connection, as I said, the first time I connected the charger, I first plugged it to the wall and then to the battery. However, the second charger came with instructions that specifically say it should be connected to the battery first and then to the wall.

 

[amberwolf]

What voltage is the battery at?

What voltages are the individual cell groups at?

<snip>


You might want to post some detailed pictures of what you've built so we can see if perhaps there is a construction error causing a short, or some other problem.



It's also possible you've gotten multiple bad chargers, as quality varies on them--but it is more likley there is something in the pack itself.

 

[tsourorf]

What voltage is the battery at?

What voltages are the individual cell groups at?

<snip>


You might want to post some detailed pictures of what you've built so we can see if perhaps there is a construction error causing a short, or some other problem.



It's also possible you've gotten multiple bad chargers, as quality varies on them--but it is more likley there is something in the pack itself.

Mate, I just answered those questions!
48V nominal voltage. 13 batteries of type 18650 connected in series. I hope you know 18650 has a nominal voltage of 3.7V, right?
What more detailed would you like as a picture? I sent a complete representation of the battery.

 

[Jon NCal]

Could you show a photo of the charger/s and connections?

 

[tsourorf]

Could you show a photo of the charger/s and connections?

You can see the charger I've got in this link: http://www.aliexpress.com/item/48V-...e-Shiping-Hight-Power-Charger/1352337032.html

 

[kdog]

AW means actual pack voltage measured with your DMM (like 52.34v for example); and actual S group voltages like 3.99, 4.00, 3.98 etc
Jon Ncal means a photo of your set up-not a link to a mfrs photo- that provides no info on your build.
Info=solution

 

[999zip999]

Pic's
Battery voltage
Charger voltage
Cell parallel voltage like.
1. 4.04v
2. 3.99v
3. 4.21v


13. Xxx v
Confused 18650 6ah cell. One 18650 cell. Cell info.

 

[amberwolf]

Mate, I just answered those questions!

Unfortunately, you didn't; you only posted what it is capable of, not what it is actually at.

When there is a problem, to find out what is causing it, measurements of actual voltages/etc must be made, to know whether or not the cells are good or bad, or are in some other way the cause of the problem.

What more detailed would you like as a picture? I sent a complete representation of the battery.

Which is useful only to the point that we can see how you intended the pack to be built. But it does not show us how it was actually built, and does not help diagnose a possible problem with the actual way it is built that might be causing your problem.

Actual pictures (photographs, chemically-processed or digital) might show issues with construction, cell-appearance that matches known issues, etc., that we would recognize and be able to help you fix.


--Something is causing a problem.

--two separate chargers have reportedly failed in the same way.

--it is unlikely both have the same internal problem causing the failure.

--this leaves a problem with the pack itself as most likely.

--could be voltage of a cell or cells

--could be a physical construction error

--could be cell quality problems (internal shorts, etc) or other things.

Without measurements, pictures, etc., we can't help very much in any direct way. We can certainly suggest possible problems, that you can then check, but it is not very efficient, compared to simply providing those measurements and pictures.

Without those, it would be more efficient for you to look around at all the many other battery troubleshooting threads, and see what went wrong with theirs, and then you can check your own pack for those problems. If you don't find it, move on to the next thread, and continue the process. Eventually you will eliminate all the possible problems the pack could have. But it will probably take longer than simply measuring, etc.

 

[dogman dan]

Looks like you'd know it if you had the polarity reversed on the pack. If so, your charge plug would be shorting your discharge plug, the way you wired it. So both plugs on your pack have the polarity the same.

But on the charger? does the polarity of the charger plug match the polarity of the pack you built? You might have the plug one way on the charger and the other way on the pack.

Or maybe not, It's just the more likely scenario for what you are having happen. fuses pop, or chargers fry when the polarity is wrong on plugs.

 

[tsourorf]

My apologies to all. I have built the battery for my brother's bike and my brother lives in another country, so, it was a bit difficult to ask him for photos and measurements.

After a few instructions on how to use the multimeter, he managed to get readings from the charger. I was really surprised to hear that the new charger had the polarity reversed! Why would anyone make a charger with a C14 plug used for DC and put the + on the 'N' and the - on the 'L'??? That was the reason for the blown fuses.

I guess that the first charger I got was so cheaply made that just blew even though it had the correct polarity (I did check that myself back then). I told my brother how to make a cable to reverse the polarity and voilà, the battery is being charged as I'm writing this!!!

Please accept my apologies for wasting your time everyone! Thank you very much for your replies! I really appreciate it!

 

[SlowCo]

Great result and good that you posted the reason.
That shows again it's best to measure to be sure everything is connected correctly.

 

[eyebyesickle]

very funny trick is what I thought. that will teach you to tamper, huh? label it correctly, but wire it backwards. Er wait, other way around... Let me put it this way; I will ALWAYS double check polarity manually, never relying or taking for granted - anything. good thing for xt-90s.

thankfully the lesson only cost me fuses, it could be worse. break out with that meter before final connections... double check that polarity

 

[Hillhater]

......I have built 3 identical 13S2P (48V) packs using very cheap Chinese re-wrapped 18650 batteries. They are supposed to hold 6Ah each, but I guess they will be more like between 1Ah and 2Ah. Anyway, the 3 identical packs I am connecting them again in parallel to give power to a 48V 500W controller and motor.

All the individual cells have integrated protection board, so I thought I didn't have to use a BMS. Now, whenever I connect them to the charger (Before even plugging the charger to AC), the charger's fuse gets blown (10A fuse).

I feel I have done something stupid but I don't know what! Please don't judge too harshly!

Well you did do something stupid...you invested time , effort, and money building packs from cells you knew were fake and falsely described.
You should consider yourself lucky that the packs are of any use at all !
Did you do any testing of capacity or voltage stability on those cells ?
What capacity did the finished packs give ?
I certainly hope the cells were very cheap, because even genuine branded cells are available from reputable suppliers, for not much more than a dolla each !
Let us know how long the (3- 6 Ahr ?) packs /cells last powering that 500W motor !

 

[tsourorf]

Well you did do something stupid...you invested time , effort, and money building packs from cells you knew were fake and falsely described.
You should consider yourself lucky that the packs are of any use at all !
Did you do any testing of capacity or voltage stability on those cells ?
What capacity did the finished packs give ?
I certainly hope the cells were very cheap, because even genuine branded cells are available from reputable suppliers, for not much more than a dolla each !
Let us know how long the (3- 6 Ahr ?) packs /cells last powering that 500W motor !

Hello Hillhater,
That is your opinion. Mine is that when your opinion is purely judgemental, you should keep it to yourself. I only asked for some help on a specific point, not anyone calling me stupid for my battery choices. Just for the sake of the argument though, I will provide you with the info you are asking for:
The batteries were (at best) 1/5 of the price of a good Panasonic set. That's what anyone else would go for, right? My three battery packs (total of 78) cost me about £90-£100 if you consider all the cables, switches and wrapping that I also purchased to make the packs. If I had made the same three packs using Panasonic ones (Not individually protected), I would also need a BMS on top of the cost of the batteries. According to my calculations, the total sum would go somewhere around £500.
Now, I cannot prove the theoretical calculations for the Panasonic batteries, but, having said that, the 3000mAh capacity ones would create a pack of total 18Ah capacity. Theoretically, since the motor would need 10.41Amps per hour, they would last 1 hour and 43 minutes. I highly doubt that would be true and I would compromise to 1.5 hours. My 1/5 cheaper pack lasts for half an hour (Tested to last between 28 and 34 minutes). Now, would you please tell me why I should pay 5 times the price I paid for 3 times better batteries? I wouldn't call that stupid at all.
I give you that there is the argument of weight since I would need more batteries to provide the same Ah capacity. That was not a problem in my case though.
I am available to discuss whatever details you might like.

 

[Punx0r]

The good quality batteries also deliver a quality premium. This can manifest as a longer service-life (actually making the expensive cells cheaper when total life-cost is considered), not letting you down (stranding you at an inconvenient time) or safety (not burning down your house - large li-ion battery fires are more common than many of us would like to think).

Anyway, your cells are protected and this raises a number of potential issues. Firstly, there are a number of different types of protection and only one includes protection from over-charge - are you sure your cells include this?

ebike packs don't generally (ever?) use protected cells. The protection features are limited by the series voltages the can withstand, so in at typical ebike pack voltages they are apparently useless.

Lastly, and perhaps most pertinent to your current difficulties, I'm not sure how these protection circuits behave when charging in a series string. A quick google search suggests that the string must be still be parallel (balanced) charged, because otherwise once the first cell in the string is full, it will go open circuit and break the series string, preventing further charging of any of the cells.

 

[tsourorf]

The good quality batteries also deliver a quality premium. This can manifest as a longer service-life (actually making the expensive cells cheaper when total life-cost is considered), not letting you down (stranding you at an inconvenient time) or safety (not burning down your house - large li-ion battery fires are more common than many of us would like to think).

Anyway, your cells are protected and this raises a number of potential issues. Firstly, there are a number of different types of protection and only one includes protection from over-charge - are you sure your cells include this?

ebike packs don't generally (ever?) use protected cells. The protection features are limited by the series voltages the can withstand, so in at typical ebike pack voltages they are apparently useless.

Lastly, and perhaps most pertinent to your current difficulties, I'm not sure how these protection circuits behave when charging in a series string. A quick google search suggests that the string must be still be parallel (balanced) charged, because otherwise once the first cell in the string is full, it will go open circuit and break the series string, preventing further charging of any of the cells.

Hello Punx0r,

Thank you for all the info. I have to say though, this discussion has gone off topic as people don't give a few seconds' time to read that it has been resolved. Having said that, there has never been a question of the batteries' performance or any quality issues.

E-bikes do have protected cells. They just normally do it using a BMS instead of using individually protected cells. The cells I have used have over-charge, under-charge and short-circuit protection. Everything that a BMS would do, without the hassle of having a million cables going to each individual cell.

I knowingly didn't go for 'quality', I went for a 'cheap' solution to my problem. However, the 'cheap' solution has proven to be of a rather good quality! Has anyone's 'quality' solution proven to be cheap as well???

Regarding the connection of cells in series and some ideas on how to avoid the problem you mention, here is a link that describes a solution much better than I would ever do: http://www.smartgauge.co.uk/batt_con.html (Yes, I did use such a methodology in my connections)