LiPo Vibration and high G load
- Thread starter Tuntek
- Start date
1500G's is like you want to shoot them out of a cannon or something. I suppose the chemistry would work, so long as the cells stay together.
wesnewell
100 GW
It will survive more than your body will. And you won't survive 100G much less 1500G. Space shuttle launch is 3G.
cal3thousand
10 MW
wesnewell said:
at about 30Gs your organ's have a tough time staying together.
cal3thousand
10 MW
Are you planning on crashing these into a solid object? 1500Gs is a lot
DAND214
10 MW
It's the sudden stop that will kill you, not the acceleration.
What will have 1500G's?
Dan
What will have 1500G's?
Dan
Ypedal
100 TW
it's not the speed that kills.. it's the sudden stop.
itchynackers
100 kW
DAND214 said:
Actually, the acceleration can kill you if it is high enough. Any sudden stop is an acceleration (negative). So the saying is a fallacy. :lol:
dogman dan
1 PW
1500 g's would do the trick I'm sure. I can't imagine the shrink wrap on a lipo brick standing that, nor the pouches themselves. It does sound like he's planning on shooting lipo out of a gun doesn't it. Might make great incindeary ammo.
cal3thousand
10 MW
dogman said:
Well... 1500G's would be like dropping from 1.5m with only 1mm deceleration distance. Probably what you would get from a thin 2-3mm foam. But that would be like dropping something from neck height.
If you are dropping a battery from waist height, you could get away with .5mm of deceleration distance before exerting that much force.
I think you will be waiting a long time for that information. I doubt such research has been done on LC lipo by any organisation, let alone by anyone in this small corner of the internet, who likely has not the time or test equipment required.
It sounds like you want to mount the battery inside a hub motor? The cheapest and easiest solution may just be to try it.
It sounds like you want to mount the battery inside a hub motor? The cheapest and easiest solution may just be to try it.
dogman dan
1 PW
Really? So every time I stepped off an 8' tall wall and landed on my feet on concrete while building a house I got more than 1500 g's ? I always assumed it was less than 10 gs or so, since I could stand it. No doubt, bending my knees greatly reduced the shock on my vulnerable brain cells. But no wonder the feet never liked it.
I do know that a fall that far makes a typical human weigh about a ton when it lands.
With a metal box protecting it, I have watched my pingbattery fly over my head, and land in the dirt about 15' ahead of me. So if that is the kind of shock you are thinking of, yes, pouch cells can stand that if they are well contained in a hard shell box that prevents crushing of cells.
Put a box on em, and yes, they are fairly crashworthy. I do shudder when I see naked cells taped to the frame.
I do know that a fall that far makes a typical human weigh about a ton when it lands.
With a metal box protecting it, I have watched my pingbattery fly over my head, and land in the dirt about 15' ahead of me. So if that is the kind of shock you are thinking of, yes, pouch cells can stand that if they are well contained in a hard shell box that prevents crushing of cells.
Put a box on em, and yes, they are fairly crashworthy. I do shudder when I see naked cells taped to the frame.
jonescg
100 MW
Hehe, on a slight more 'on topic' topic...
I am designing the more intricate details of my LiPo battery pack for the race bike. I was wondering if that 6 mm yoga mat foam would be sufficient for the bottom and sides of the pack. It's going to be carrying 70 kg worth of LiPo, so it will have to be able to withstand a bit of bumping and vibration. But I also don't want to be sacrificing too muck real estate if I can help it.
The non-terminal sides, top and between sub-packs can probably get way with a thin layer of packing foam (about 2 mm) since everything is going to pack in quite snug. Maybe another layer of 6 mm foam in front of the terminations?
I am designing the more intricate details of my LiPo battery pack for the race bike. I was wondering if that 6 mm yoga mat foam would be sufficient for the bottom and sides of the pack. It's going to be carrying 70 kg worth of LiPo, so it will have to be able to withstand a bit of bumping and vibration. But I also don't want to be sacrificing too muck real estate if I can help it.
The non-terminal sides, top and between sub-packs can probably get way with a thin layer of packing foam (about 2 mm) since everything is going to pack in quite snug. Maybe another layer of 6 mm foam in front of the terminations?
Dogman, it's not really the height from which you fall, but the distance over which you stop. Jumping down 8ft and landing well, you're probably only experiencing a couple of G. If you landed on your heels with your upright body as stiff as a board you'd experience more, and probably break something. If your body experienced 1500G it'd be puddle of sticky goo on the floor with small splinters of bone mixed in...
Protecting things from G can be a little counter intuitive IMO. When putting PC's in cars, the hard disk drives are assumed to need protection, and people end up putting them in foam boxes or hanging them from elastic bands. The later tends to result in much greater G loads on the drive, especially if you hit resonance. The true answer is the screw the drive firmly to the chassis. It's so massive that it simply can't (de)accelerate quickly, so the drive experiences only slight G load even in a serious crash which would kill the human occupants.
This leads to me think that the answer on an ebike is to use a little absorbative cushion to insulate the batteries from vibration, but to fix them rigidy to the frame. Give them any room to move and they'll accelerate very quickly compared to the frame when you hit a nasty bump. My own battery boxes weren't originaly held down tight enough and could rattle about. Not good.
I suspect the OP is intended to spin the batteries, though and there's not much you can do to negate the affect apart from mounting them as close to the axle as possibly to reduce the angular velocity (and rate of change of).
Protecting things from G can be a little counter intuitive IMO. When putting PC's in cars, the hard disk drives are assumed to need protection, and people end up putting them in foam boxes or hanging them from elastic bands. The later tends to result in much greater G loads on the drive, especially if you hit resonance. The true answer is the screw the drive firmly to the chassis. It's so massive that it simply can't (de)accelerate quickly, so the drive experiences only slight G load even in a serious crash which would kill the human occupants.
This leads to me think that the answer on an ebike is to use a little absorbative cushion to insulate the batteries from vibration, but to fix them rigidy to the frame. Give them any room to move and they'll accelerate very quickly compared to the frame when you hit a nasty bump. My own battery boxes weren't originaly held down tight enough and could rattle about. Not good.
I suspect the OP is intended to spin the batteries, though and there's not much you can do to negate the affect apart from mounting them as close to the axle as possibly to reduce the angular velocity (and rate of change of).
dogman dan
1 PW
Exactly what I was thinking about a few meters fall not being 1500g's. We've all seen it on the whacky video show or you tube, some dork tricking his skateboard and landing on concrete not well. Always breaks a bone, but doesn't make him into sticky goo like 1500 g's would. We've all seen the chute fail skydiver shots where a guy telescopes his legs and survives. Not sure what g's he pulled, but I seriously doubt it was 1500 g's. The legs going at least absorbs some. 
I'm sure you drop a metal object to metal and the g's are more, as your cell phone knows. But 1500? I need to see that claim proven.
How you land matters, I took a fall from a roof to flat on my back as a kid. That smarted, and I started breathing again about 5 min later. I've landed ski jumps long and ended up on the flat for the landing. Hard snow, 3-4 stories drop I mean. Ouch! Legs can suck up only so much. Gotta do those landings on a steep slope.
I'm sure you drop a metal object to metal and the g's are more, as your cell phone knows. But 1500? I need to see that claim proven. How you land matters, I took a fall from a roof to flat on my back as a kid. That smarted, and I started breathing again about 5 min later. I've landed ski jumps long and ended up on the flat for the landing. Hard snow, 3-4 stories drop I mean. Ouch! Legs can suck up only so much. Gotta do those landings on a steep slope.
dogman dan
1 PW
Back a few posts. Yoga mat is exactly what I put on the bottom of my smaller battery boxes. I don't want lots of cush that allows movement. But I do want zero possibility of a sharp edge under the pouch lipo packs. The sides of the box are lined with coroplast shims. The can compress very slightly, allowing the packs to jam in very tight, yet be removable. If I flip the bike, packs still don't budge in the box even a little bit. completely open top for wire acess. Wood or metal hard sides and bottom to the box, with no sharp edges on the inside.
For a big pack, just create modules of a convenient size to work the same way, holding each paralell group or maybe two groups. Whatever works so it's not so big you can't pack the cells in nice and tight.
No movement is definitely the goal. Any small movement = chafing of the packs or the shrink at least. Any naked pouch on the packs, such as zippys on the bottoms get lots of clear packing tape.
For a big pack, just create modules of a convenient size to work the same way, holding each paralell group or maybe two groups. Whatever works so it's not so big you can't pack the cells in nice and tight.
No movement is definitely the goal. Any small movement = chafing of the packs or the shrink at least. Any naked pouch on the packs, such as zippys on the bottoms get lots of clear packing tape.
cal3thousand
10 MW
The question with the yoga mat is how much compression does it allow? If it is 6mm unloaded and goes down to 1mm at full load, then you have 5mm of deceleration distance.
Now it depends on the distance that the pack is dropping...
Now it depends on the distance that the pack is dropping...
If the pack is held gently, but firmly in place then it won't accelerate much, so won't need much absorption for the deceleration. If you use something softer it will have to be much thicker to be effective. You'd also have to carefully that repeated compression didn't permanently compress it, leaving your pack bouncing off the sides of the battery box (think about the foam in an old sofa).
That's my take on it, anyway
That's my take on it, anyway
cal3thousand
10 MW
Punx0r said:If the pack is held gently, but firmly in place then it won't accelerate much, so won't need much absorption for the deceleration. If you use something softer it will have to be much thicker to be effective. You'd also have to carefully that repeated compression didn't permanently compress it, leaving your pack bouncing off the sides of the battery box (think about the foam in an old sofa).
That's my take on it, anyway
the acceleration may come from a fall though. In which case, you will need all the absorption you can get to minimize the deceleration impulse.
If you used an non- or low- compression material, say wood for an extreme example, it doesn't matter how thick or thin you make it. If it doesn't compress, the deceleration distance is shorted, increasing the G load since this deceleration distance is the denominator in the G load equation.
Hillhater
100 TW
Without even testing, i can guarantee that at 1500g , a lipo pack will totally destruct ! :wink:
dogman dan
1 PW
I coulda been more specific what kind of yoga mat I've been lining battery boxes with. The one I've been using is at most 2-3 mm thick. I don't know how much it compresses under the weight of the packs. It's not there for shock reduction at all. It's main purpose is to allow a small object, such as a stray grain of sand, something soft to dig into. So the mat takes the ding, not the pouches. Before I happend on the mat, I just used cardboard for the same purpose.
In my boxes, it's compression from the sides that holds the packs in place. They don't move any, not even when the bike goes end over end a few times. No top at all on the box. The box compresses the packs endwise on the pouches btw, so zippys fit same as turnigy.
In my boxes, it's compression from the sides that holds the packs in place. They don't move any, not even when the bike goes end over end a few times. No top at all on the box. The box compresses the packs endwise on the pouches btw, so zippys fit same as turnigy.
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