2013 Electrical Systems-Close Call & Lessons Learned Thread

[kfong]

I use them, but feel a lot of users just don't take the precautions needed. Until you have experienced a lipo fire, you really don't know how agressive these packs can burn. I still don't recommend them to my friends, never will. Plenty of other choices for the casual user.

 

[-dg]

So, do you think the secondary spark vaporized enough metal to create a sustaining plasma? Was the connector shell on the bike female contacts? 14S only about 60 volts... unexpected failure mode for sure.

I'm considering using db-25 connectors for charging and thinking I should order the pins/wires to limit the potential between nearby pins, ie all the grounds at one end, ascending in balance tap order to hots at the other end so that each successive pin is only 3.7 V from it's neighbor. It would still be possible to have a short, but hopefully it would not self-sustain or jump. This seems more difficult with a circular connector. wannesd, what was the voltage difference between adjacent pins on your connector?

 

[wannesd]

kept all the balance taps together, so around 4V.
Main plus and minus were both 5 pins, but they were together. Although I was nowhere near those pins when the arcing started, it is a good idea of having them as far apart as possible. But hard on a circular connector.
What stopped me from going DB25 or similar, is the lack of weatherproofing.

The connector I selected has a screw on cap, for weatherproofing. Also, the male part has a screw-on ring, ensuring a good connection.

 

[boo]

Sorry for your hand wannesd....

For me, I cover the exposed test lead of my multimeter with a shrinkable tube. Only the pointed portion left open.

After I melted some connectors during charging, I decided to build a single plug-in charge cable and used a DB37 connector. Cut a small PCB, mount zero ohm chip resistor to bridge the batt pack and the charger. Zero ohm resistor hopefully will act as fuse and will open when there's a short.
Due to close proximity of the wirings, I sprayed conformal coating to prevent the solder from corroding and protect from moisture.

 

[jonescg]

The point about fuses is a good one - how many folks here on ES don't have fuses ANYWHERE in their system? Totally worth it aye.

 

[megacycle]

Zero ohm resistor hopefully will act as fuse and will open when there's a short.

Just need to ensure they have the correct current rating for the application.
Insertion loss could be 25-50mohms too.

 

[boo]

Just need to ensure they have the correct current rating for the application.
Insertion loss could be 25-50mohms too.

Yeah. Thanks.
It should be fine, I used bigger package for the main charge wires and smaller for the balance wires.
I charge at 4.3A only.

 

[megacycle]

It's a really 8) idea for safety boo.
Just a few design concerns.
1. With the links not strictly being a fuse, as such, we don't know how they are going to behave at all and so it's guess work and becomes a worry. The fusing current, I2t, resistance value tolerance- could put out your balance currents, kA value eg will it arc, carbonise, throw bits around, under short circuit, in that tight spacing.
Could go here and go through these and then that issue is sorted.
http://www.tme.eu/en/katalog/1206-smd-fuses-ultra-fast_113002/
2. If the bms has no individual cell indication, if a balancing fuse goes, there's no indication of this.

 

[boo]

It's a really 8) idea for safety boo.

Thanks... Initially planned to use SMD fuses but i just used what i have on hand

we don't know how they are going to behave at all and so it's guess work and becomes a worry.

In my experience it will carbonize pretty fast when there is a short. Underside PCB of the carbonized chip will burn a bit but should not spread on the whole connector. By the way the PCB is UL94 V-0 cert and should not burn that long .

2. If the bms has no individual cell indication, if a balancing fuse goes, there's no indication of this.

I'm using turnigy charger. Charge and balance 3 6S lipo pack at the same time. If any wires were open it should have a warning right? :?

 

[megacycle]

If any wires were open it should have a warning right? :?

I'm not conversant with that charger, maybe just opening a balance lead connection and check it out.
LED indication across each balance lead, for those without alarm or means of stopping charging would work, might be a bit full on though :? .

 

[boo]

maybe just opening a balance lead connection and check it out.

I don't want to try that as yet. I opt to leave it alone Have checked the charger's manual and it should prompt error and terminate the charge cycle. http://www.hobbyking.com/hobbyking/store/uploads/84734390X447211X18.pdf
Thanks for highlighthing

 

[megacycle]

8) wish you all the best with it, another creative idea in action.

 

[winkinatcha]

For What It's Worth

Boo I have the same 4 port Turnigy charger and yes it will stop charging and warn if a balance lead becomes disconnected, or refuse to charge if the balance lead is already disconnected.

Joe

 

[rafeh1]

Amberwolf was talking to me this morning about having a central thread where good electrical system design could be discussed. Items that were outside the scope of our 2013 Li Battery Catastrophic Events - Summary Thread that is located here: http://endless-sphere.com/forums/viewtopic.php?f=14&t=47012

I fully supported Amberwolf's idea as I also thought the gent who just had a "lessons learned" while using an automotive fuse in the system that "got crispy" would be beneficial to us all. To me his experience is the kind of thing that can happen to any of us. However by pooling our field experience the shortcomings of products and design approaches can be shared when used in our application environment. His knowledge would sure benefit more than a few. Thread here: http://endless-sphere.com/forums/viewtopic.php?f=3&t=47192 Also Amberwolf's recent AC connector failure, documented here: http://www.endless-sphere.com/forums/viewtopic.php?p=693832#p693832

Right now these nuggets are scattered throughout the forum. Perhaps this thread will help, and we can fine tune the format as we go... For now lets just post the issue here and discuss it here. Pictures of the problem always help.

After getting sparked a few times simply while plugging in charger I learned my lesson. I worked with my battery supplier to put a switch right on the BMS. When the switch is off both the power cable and charging cable go dead and can be easily worked on.

 

[kfong]

http://endless-sphere.com/forums/viewtopic.php?f=28&t=52029

One of the reasons I've never liked canvas bags. No support or protection from external elements. I crash all the time on my setup and have been happy with my choices. Four hard trail crashes last weekend at Highlands State park due to leaves covering the forest floor. One even left me a bit shaken up and I actually sat for a moment. Something I rarely do. Bike was fine, only had to adjust the steering for one of the falls.

 

[rich43]

Don't connect one battery to another! *BANG!* (I use HXT 4mm). The Lipo usually survives when that happens though due to the 4mm connectors acting as a fuse and melting, gives you a hell of a fright though! Burnt my finger once.

I used a black permanent marker pen to mark which connector is wiring harness and which is the battery, hopefully it will do the trick until I can afford more fancy expensive connectors. I also put heat-shrink tubing around the connectors that I rarely ever need to take apart, because if they do come apart that's just another plug for me to short out