Best way to securely mount a LiPo battery?

I'm making the switch from standard 9v batteries to these LiPo variety (400mAh, 3.7v, https://www.sparkfun.com/products/10718). They test fine with my Stratologger - tested each of main and drogue outputs twice to convince myself that the current limiter would hold up and e-match would fire.

How do folks normally securely mount these on an av bay sled? I'm thinking Velcro dots and cable ties would be quick but dirty, so looking for more elegant ideas.

I wrap the cell in foam (thin packing), tape with electrical tape and secure to board with 2 wire ties. One bottom to top and one around the width.

That would do it for sure, rms. Here's the layout that I'm going with if anyone is interested:



Altimeters and their batteries fit nicely on the bottom of the sled; the XBee and its battery will go on the other side.

When I've flown my TeleMetrum, I've just used electrical tape wrapped around the board.

-Kevin

I'd say same as a 9v battery; with zip-ties.

matthewdlaudato said:

That would do it for sure, rms. Here's the layout that I'm going with if anyone is interested:

View attachment 183654

Altimeters and their batteries fit nicely on the bottom of the sled; the XBee and its battery will go on the other side.

Click to expand...

Looks fine to me.
To be honest the foam I use was only for the concern of rough handling and the discharge potential of lithium ion batteries.
Better safe than sorry, so to speak!

Looks like cable ties are the winner. I might use a dab of neutral cure silicone rubber under each as well, since these will essentially be permanently installed. Thanks.

If you're pulling a bunch of G's on launch, I'd go for something a bit more substantial than zip ties.

This may sound strange at first, but I'm using Velcro strips with long overlapping ends. I cut 1/4" Velcro into 3-5" strips and epoxy or screw them to the sled so that they overlap all the way across the battery or whatever piece us being mounted. Easy to attach, easy to remove, and it grabs really well. For square battery i'd use two ties, one horizontal and one vertical.

I got Velcro with some IBM servers, they included 10' roll for cable management


-Alex

Velcro dot plus ties was my initial thought - I like the strip idea better Alex. I think I have some Velcro here that I can adapt.

I would skip velcro and go with zip ties. Reusable is nice, but i replace them on each flight.

jmattingly13 said:

If you're pulling a bunch of G's on launch, I'd go for something a bit more substantial than zip ties.

Click to expand...

Ok, let's do the math on that... the really skinny zip-ties that come with Archetype Cable Cutters are spec'd to 50lb breaking strength, and I'm finding 160mAh LiPo cells for the vicinity of five grams. That's a factor of about 4,500. So, in the absolute worst case where the loading was entirely along the zip tie, you'd need a 4,500 G load to break it -- and that much force would almost certainly crush the battery first.

Even if that is off by an order of magnitude, I don't think their strength is a limiting factor.

matthewdlaudato said:

Velcro dot plus ties was my initial thought - I like the strip idea better Alex. I think I have some Velcro here that I can adapt.

Click to expand...

I guess these ones from homedepot will work. Or a roll like this. Or PM me you address, I'll mail you a few feet of what I'm using.


-Alex

Zeroignite said:

Ok, let's do the math on that... the really skinny zip-ties that come with Archetype Cable Cutters are spec'd to 50lb breaking strength, and I'm finding 160mAh LiPo cells for the vicinity of five grams. That's a factor of about 4,500. So, in the absolute worst case where the loading was entirely along the zip tie, you'd need a 4,500 G load to break it -- and that much force would almost certainly crush the battery first.

Even if that is off by an order of magnitude, I don't think their strength is a limiting factor.

Click to expand...

I was actually thinking more along the lines of constraining motion in all directions (ie axial). I've just had issues with zip ties in high-G flights before.

jmattingly13 said:

I was actually thinking more along the lines of constraining motion in all directions (ie axial). I've just had issues with zip ties in high-G flights before.

Click to expand...

Ahh, that's a different problem... more of a design issue than anything. Yep, you want to make sure there's positive retention in all directions, especially axial... flying batteries could do a lot of damage.

Zeroignite said:

flying batteries could do a lot of damage.

Click to expand...

Not sure the flying batteries are doing as much damage as the parachutes that are no longer deploying...

jmattingly13 said:

Not sure the flying batteries are doing as much damage as the parachutes that are no longer deploying...

Click to expand...

Heh, definitely true. I was picturing a failure mode where the battery slips out of a restraint but the plug stays connected, so it bounces around the inside of the av-bay like a fail

Zeroignite said:

Heh, definitely true. I was picturing a failure mode where the battery slips out of a restraint but the plug stays connected, so it bounces around the inside of the av-bay like a fail

Click to expand...

Either way, a great way to nom up perfectly good electronics.

I use two zip ties, one widthwise and one lengthwise. Then I charge the batteries on the sled.

I ultimately went with two ties in an X pattern, a dab of adhesive caulk under each battery, and likely will add a wrap of electrical tape for good measure. Batteries will also be charged on the sled in this semi-permanent installation. Thanks for the tips everyone.

Oh, regarding charging on the sled (my plan as well) how important do folks think LiPo charge bags are in the real world?

+1 on the replies that refer to failures with zip ties. Things can get weird with high-g events (big deployment bangs, in addition the launches). Saw it a couple of times just last weekend at XPRS.

I also would question the "one tie lengthwise/two around the middle" method, even though I have seen a lot of that and it usually works. If the battery is going to break free in the vertical axis (as might be the case in a violent deployment event), there is only one tie holding it down. And on a fiberglass sled, maybe a sharp edge of fiberglass bearing against the tie can cause the failure by becoming a cutting edge.

I still use ties, but if I have room on the sled I will restrain the fore-aft motion of the battery with little blocks of wood securely attached to the sled (adhesive and small pins) The battery can't move fore or aft, and the cable main job is to keep it from bouncing off of the sled.

I like the idea of screws or wood strips as stops - may just incorporate that.

For those with 3D printers, a LiPo battery mount that screws into the sled and that one can 'snap' the battery into is something I'd like to see...

jderimig said:

I use two zip ties, one widthwise and one lengthwise.

Click to expand...

+1 on zip ties and using them in both directions to make sure there's nowhere for the battery to go during the flight. I drill small holes in the sled at the top, bottom and each side of the batteries for the zip ties.

Sled with batteries secured (adhesive caulk under each; cable ties) and ferrules installed.



Appears very secure mechanically and electrically.



NAR #91867, L2
Member CMASS, MMMSC, RIMRA, CATO

Missile works has a 3d printed 38mm sled that is designed for Li-po, but is sized for their altimeters. It's a nice setup and I've flown it a few times. The pattry mounts on the back, and is held in place with a cover and a screw.

RecoRocket said:

View attachment 184949
Missile works has a 3d printed 38mm sled that is designed for Li-po, but is sized for their altimeters. It's a nice setup and I've flown it a few times. The pattry mounts on the back, and is held in place with a cover and a screw.

Click to expand...

That's a nice sled.

Double sided tape almost always enough. In high G motor environments I add zip ties.

If things go bad, it really doesn't matter.

Ken

Update: the configuration I used (dab of adhesive caulk plus zip ties) held up fine with a J760 in a 14 lb rocket. Was a smooth flight, so perhaps not much of a test.