To be complete about the wheels on sand prehistory, there are also the Speedsails who use 12"x2" pneumatics.
And there is also the option to use twin wheels as below…This picture has been taken during a raid across the Sahara in the 70’/80’.
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Well, maybe there’s a reason why people don’t ride electric skateboards on the beach.
First, the good news (in order of priority)
- I’m alive
- my house did not burn down
- The battery pack burst into flames while I was home
- my car did not burn down
- I managed to get it outside and hose it down before it was fully engulfed
Second, the mystery
- why did the battery pack burst into flames 15 hours after I stopped riding the skateboard
So what happened was the machine was working perfectly - It had enough power and speed to bomb down the beach and we spent a good 3 hours playing with it.
At one point the charge port started to smoke, and a small electrical fire started. I managed to get the wires disconnected and the fire went out. The board still worked so we kept riding. Then another small fire on a different part of the charge port. Again, I separated out all the wires so nothing was touching and the fire went out, but we decided to call it a day. I disconnected (hard disconnect) the main power and loaded the thing back in the car, where it sat for another hour or so before we actually started the drive back.
3 hour drive home followed by the board sitting in my dining room overnight. In the morning it was fine.
Miraculously I am working from home. I hear a pop, but I ignore it since all the windows are open I assume it’s something outside, but when I hear that hissing sound I know exactly what that is. I run down and sure enough, flames are just starting to come out from the board.
I grab it and drag it outside onto the grass in the back yard, turn on the water and hose it down. Puts the fire out no problem, but the batteries are still hissing. So I just keep watering it. I also put out two small grass fires.
Finally I get it to the point where it’s no longer combusting. I take it into the shop, remove the orange cover, cut out all the wiring and start to remove each battery bank (each bank has 10 batteries) The first bank starts to hiss again, so I take it outside and hit it with the hose again.
My system of having each battery bank separated by a small distance (about an inch) actually did what I intended for it to do and the fire did not spread to the last 3 banks. It may have not spread to the second bank, but because it was so close it’s completely black so I can’t really tell until I do a full post-mortem.
Analysis:
I do my charging with an external balance charger 6 cells at a time. I do this because (ironically) I live in fear of a battery fire and I want to use a charger I trust.
this picture was taking during development, the wires were routed after this. Notice, though, the orange circle. This is a screw terminal that connects to the volt meter. The pins are 0 and 40V - full voltage, and they are only 0.1" apart. This is where the first fire started.
This charge port has been essentially the same since the very first build. It has survived rain and hail. In this case I even made little caps to put over the white plastic connectors to keep the sand and water out of them.
My best guess is that wet sand got between all the connections and began to conduct. As it conducted it heated up. As it heated up the solder started to melt and at that point the mixture of solder, sand and salt water created a dead short from all battery connections to the ground plane.
What I don’t understand is how a fire starts 15 hours later.
The irony is that I used to have PTC fuses on every balance wire to handle just this sort of thing, but I took them off because they wouldn’t allow me to do high-current charging.
I guess I’ll be putting them back on, and redesigning (and conformal coating, and 3D printing a cover for) the charge port. However, I might not ever bring the Sand Runner back. I might retrofit my other two boards with newer safer charge ports and re-introduce the PTC fuses to make sure the other two boards are safer, but it seems like salt-water and electric skateboards might not be such a good idea.
I got to it before it could seriously damage the floor, but still, that’s going to take a bit of sanding.
And now all the battery banks are entombed in concrete for at least a week before I’ll even look at them. I do think I can recover the last 3 banks. I tested one and there are volts still there.
And here is a (somewhat boring) VIDEO of the last glorious ride of the Sand Runner
I’m not sure I’m ready to go through all of lessons learned, but here are a few
- If anything even vaguely hinkey happens to your board that involves the battery pack, do not store it inside your house or anywhere where a large fire can cause real damage
- fuses or PTC’s on all balance and auxiliary power wires.
- battery fires can happen long after an event. So if something happens quarantine your board for at least a week
- stay away from salt water.
- check your smoke alarm batteries
- if you are running LiPo do not do what I did. I took a huge chance grabbing a burning board and dragging it out the back door. I did this because the batteries are Li Ion and encased in metal. I was fairly certain that they wouldn’t explode. With LiPo that’s not the case - they will explode. Either call the fire department immediately or throwing something really heavy over it and maybe try to drag it out. But a LiPo will destroy your face if it explodes.
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Damn that really blows, I’m so sorry for your loss. Is anything else salvageable from the pile?
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Actually most of it. the motors and gearboxes are fine, the wheels are fine, 3 of the 5 battery banks are fine, the Unity is probably fine.
The wood deck is destroyed, most of the 3D printed plastic parts, the orange cover, all the wiring and 2 of the 5 battery banks. So insignificant as compared with how bad it could have been.
I was telling a friend, there were 10 ways this could have gone really bad and only 1 way it could have gone ok, yet here I am 
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Its good to hear that it didn’t go 100% bad at least
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Glad to hear you are safe, got that outside and it wasn’t worse bro.
A beach environment is a massive challenge for an EV. Give it some time, emotionally recover…but don’t give up!
I know it seems over the top, but maybe saltwater and sand needs potting of elecs and batteries - @b264 seems to be interested in a robust approach to this…
Thiiiiisssss foooo…
My car didn’t burn down, It caught on fire… Still running with a new interior!
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Shiiiiiiiit! I can’t believe you kept riding after your board caught on fire 
Good luck with the salvage bro, this build is too good to let a mere battery fire stop it!
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Ow what a bummer 
But good to see you came out if that more or less without harm to you or any property.
I can say, don’t do that at all.
LiIon can start to vent and throw flames up to 2m from one second to the other. That’s a serious risk if you stay close by.
Throwing a fire blanket does really help.
It might not safe the floor and not put out the flames by it’s own, but it will contain the flames so that they will not harm you or set surroundings on fire. Besides this, they are like 10-15$, so why not.
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I’m definitly buying one ! Any recomandation ?
Gosh for sure wet sand is an hasard, but this build was clean, i thought this happens only to poorly built battery packs, I’m freaking out right now ahahahah
I’m always preventing from driving on puddles or even wet surfaces, but who knows
I’m glad you’re alright and still motivated ! Hope you get it together soon !
Oh god this terrifies me. My board has been running on the same battery I built for over a year now but I still get scared. I keep it on the concrete floor of my garage at lest 3 feet from anything else. I am so sorry about the fire.
The wood deck is destroyed, most of the 3D printed plastic parts, the orange cover, all the wiring and 2 of the 5 battery banks. So insignificant as compared with how bad it could have been.
@DougM, you belong to a selected group of lucky Esk8 survivors from the seven corners of the Earth who managed a swift scape from their burning e-vehicles or blasting basement infernos… @eBoosted, @Touch_V, @KaramQ among some notable riders.
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Oh man sorry for your loss Doug, I’ve run on wet sand quite a bit, My choice was an aviation port with a screw on cap, no ragrets
these dohickeys, 2-pin rated to 10A
Rebuild it with improvements, now I’m off to view your video, g’luck
Actually nope, but I did ask for permission
are you considering a bms now?
+1 for team BMS…makes life simple, try picking up one of the fancy new smart BMSs and you’ll be happy about it
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Seems like more onboard electronics is probably not the solution.
I do like @magharees idea of a waterproof aviation connector. I’ll probably switch to that.
But I also have to beef up the seals around the battery box as well, and I’ll still add a lot of fuses
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A smart bms will give you a real time display of what’s going on with your battery, it’ll also eliminate that changing nightmare that probably caused your fire to begin with. Either way, glad you didn’t lose more in the fire.
Can you send me a link to these smart BMSs?
Thanks,
Ah man,
this is not how i imagined this thread going.
sad for you and the board, at least nothing further got damaged. Salt water is an absolute bitch.
probably was a drop of water drying and forming a salt crystal bridge across contacts that did for it.
really hope you revive this in the future, the beach is a fantastic playground.