2014 Electrical Systems-Close Call & Lessons Learned Thread

bigmoose

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Amberwolf was talking to me (in 2013) about having a central thread where good electrical system design could be discussed. Items that were outside the scope of our 20XX Li Battery Catastrophic Events - Summary of Current Year Thread that is located here: http://endless-sphere.com/forums/viewtopic.php?f=14&t=56305

I fully supported Amberwolf's idea. By pooling our field experience the shortcomings of products and design approaches can be shared when used in our application environment. This knowledge would clearly benefit more than a few of us.

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 and discussion in this thread. Pictures of the problem always help.

The 2013 Electrical Systems-Close Call & Lessons Learned Thread is available here: http://endless-sphere.com/forums/viewtopic.php?f=2&p=693880#p693880
 
Don't use a battery if it does not have a BMS to protect it. Your asking for trouble if you don't use a BMS. Don't accidentally burn down your house.
 
When using bullet connectors dont talk to other people or plug then in outside in the dark. Iv found if I use a black marker pen and draw a line down both connectors on one side, it makes them fairly idiot proof then as you just have to line up the black lines. Iv also done away with all the parallel / serial connectors and soldered them all instead and only left the battery connectors on, this way its less likely il plug it in backwards when not concentrating.
 
My experiences:

1: Don't use the same coloured wires just because it's all you have lying around. Go out and buy/find some. I once used 2 red wires for my main discharge leads on a battery pack. I marked one with some black tape so I knew it was the negative terminal, but working in the dark, I plugged the battery into the controller reverse polarity and boom! Controller was fine, however I had 2 melted wires where my Anderson plug used to be!

2: Leave only one, or better yet no exposed leads when assembling a pack. If you need to move wires through a hole through which the plug cannot fit, unplug ONE wire from the plug, thread it through, then reinsert it into the plug. THEN follow with the remaining wire. This will keep only one exposed wire at a time. No matter how careful you are and no matter the odds, exposed power wires have a habit of finding each other and making contact. Thoroughly insulate all exposed leads that may stray to areas you don't want them touching.

3: Never use a power driver on Headway cells. You may think you're saving time by not using a manual screwdriver, but you risk 2 things. You may over tighten the screw terminal and damage the cell, and the nickel tab may rotate with the screw and contact the nearest cell/tab, creating a short.

4: If you plan on attaching a BMS to your battery pack, attach all the balance leads to each cell bank AND check for single cell voltage between the leads at the other end of the cable (just watch you don't contact the voltmeter probes together while doing this!). If all that is good THEN you may plug the balance lead(s) into the BMS. If the BMS gets more than single cell voltage on a line it will most likely burn. Also, by leaving the balance leads unplugged until last, any stray balance wires shouldn't short out any cells they may come into contact with.

5: A screwdriver wrapped up in insulating tape is NOT sufficient for levering open a hot-glued battery pack. That tape will wear through, the driver will conduct, and you'll have a hole In your cell followed by the smell of burning electrolyte.

6: Remove anything metallic when working on packs, especially jewellery. Metal wrist watches and rings make great conductors. You want to keep that finger right? Once the dangling zipper from my jacket shorted some cells I was working on as I was leaning over them!

7: The adhesive used on duct tape + sweaty palms = more conductance. After unwrapping a duct-tape battery pack from China I picked up the pack, flat-palmed on the exposed cells. My hands tasted 60V DC. Not fun.

8: If you need to drill/cut on your e-Bike frame near the battery, remove the battery first. I know it's extra work, and I know you think you'll be careful, but a friend of mine, whilst drilling a small hole in the frame near the battery, found out the hard way that once the drill bit breaks through it will pull itself through the hole and into the battery. All he could do was back away and watch it smoke and burn.
If you really don't want to remove the pack, or can't, put something solid like a piece of metal flat bar between the battery and the surface you're drilling/cutting.

9: Angle grinders kick back. When modifying the axle on the exposed stator of a hub motor, the grinder kicked back and I nicked one of the winding coils. Luckily I didn't cut all the way through, but it was very close indeed, and left part of that winding uninsulated.

10: Use a BMS. I've now had 3 packs where the BMS has cut off power to the controller, and upon inspection, I've found the cause to be a faulty cell(s). Replacing the cells rectified those problems and those 3 packs have been going strong ever since. Replacing a single cell or a few is cheaper than replacing the entire pack.

I look forward to everyone else's experiences!
 
TheThirdWheel said:
2: Leave only one, or better yet no exposed leads when assembling a pack. If you need to move wires through a hole through which the plug cannot fit, unplug ONE wire from the plug, thread it through, then reinsert it into the plug. THEN follow with the remaining wire. This will keep only one exposed wire at a time. No matter how careful you are and no matter the odds, exposed power wires have a habit of finding each other and making contact. Thoroughly insulate all exposed leads that may stray to areas you don't want them touching.

Staggering the lead lengths can also help, if you are using connectors like Powerpoles or bullets whose housings are on individual wires, instead of in a cluster. Then it is not easily possible to short connections, or to plug the wrong connectors into each other, even in the dark.
 
4mm Dual Banana Plugs (some Turnigy Batteries, etc)

Color codes are your friend - design your harness so wire colors match across connectors. Use a color band when the wire color must change from end to end of one wire. Make a diagram showing your setup and wire color arrangement and follow it when reconnecting.

When connecting the pack to the harness always check the wire colors across the connector before plugging in. Plugging a battery into a battery (causing plasma event) requires crossing the colors, always a bad idea. Design your harness so this doesn't happen normally so it can be recognized as an error.

Plug in slowly (check those colors), if you do make a mistake the tips will vaporize and open the circuit, destroying the connector but the plasma will mostly remain inside the connector tubes, avoiding injury. Wear glasses when plugging in, and leather gloves are a good plan also.

Consider making a last post to the 2013 thread on Electrical Systems Close Calls thread linking to this one for forward reading continuity.
 
Make sure your multimeter is set how you want it before measuring anything. I tried to check a lipo pack voltage with my meter leads in the unfused 10amp max ports. I mostly use it on the fused ports to check voltage and just didn't think about it. Vaporized the leads and sent sparks everywhere which could have been a fire or eye hazard.
 
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