That was a scary story. My rechargeable batteries are all SLA and NIMH, but Andrew's story made me think hard about how I store and charge them.
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That was a scary story. My rechargeable batteries are all SLA and NIMH, but Andrew's story made me think hard about how I store and charge them.
Funny, I just dropped a lipo light pack while walking the battery upstairs to the fireproof safe I store it in. It hit the ground roughly parallel to the side, and on carpet, but it was still enough force to break the shrinkwrap right in the middle, between the two banks of cells.
Looks like I'll be holding her together with duct tape, and probably seeing if Light Monkey can re-shrink wrap it for me while I pay them to replace a cord on another primary that I managed to pull apart after plenty of torture and abuse...
Lipo scare me just a little, hence the fireproof safe. I'm not sure it would contain a large fire, but I think it will help to slow down the speed at which it destroys all of my possessions... and the safe gets left away from walls or other flammable things, too. I also keep a fire extinguisher nearby, I've even left one at my favourite place to stay in cave country just in case! I like runawaylobster's place too much, figured the $20 fire extinguisher and the $20 fireproof safe were well worth it. It's also a convenient way to carry batteries and chargers, though a bit on the heavy side...
Originally Posted by JJ1987
Lipo should scare you.
Lithium batteries increase in volume with respect to state of charge, meaning like a hot dog, they "plump" when you cook 'em.
That however can eventually lead to an internal cell short. No cell protection, PC boards, battery management circuits, fuses etc are of any use if a cell shorts internally.
The swelling of Lipo Cells is exacerbated by over discharge and over charge, and this is usually a direct result of poor cell balancing. Balancing is a complex matter, and the commercial solutions are OK for small capacity cells, and IMO, completely inadequate for larger cells. If cells are not effectively balanced the physical stresses imposed by over discharge and over charge are not trivial.
Cylindrical cells are far more physically robust than a mylar "bag" typical of Li-Po's. Combine good quality graded cells with a topology that provides passive cells balancing and reliability and safety is increased.
In addition 18650 cylindrical cells are produced in the billions annually, compared to relatively few high capacity Li-Po cells. The high production volume lends itself to good SPC QC techniques that simply cannot be realized with low volume, high capacity Li-Po's
The reality is the only benefit for diving applications for using small numbers of High Capacity Li-Po cells is ease of battery pack fabrication. The specific energy and energy density of 18650 cylindrical cells greatly exceeds what is possible with Li-Po's
The 2011 TBM is now available and it makes clear, to those who know how to interpret the results, that good quality 18650's combined with good pack design are very hard to beat.
Tobin
I wanted a charging bench to support up to 4 cavedivers. Hector suggested starting with 3 tier tool cart from Harbor Freight. My total cost was about $150; $70 for the cart and most of the rest for electrical components (15 gfci protected outlets). I'm a packrat and already had the sheet metal and fasteners.
John Ploegert
Don't you just need one GFCI outlet at the start of the chain, or 1 per circuit? And a nice addition would be a timer to stop charging and reduce the risk of fire due to overchargin.
If you are hanging you hat on GFI's and external timers to prevent overcharging you are in deep #@#^#@ already.
Tobin
I believe we have to rely on the manufacturers to begin supplying balance chargers to independately monitor and charge each cell, they way they are being charged now is less expensive to do, but not really optimum. A balance charger is no that expensive really, less than say a mask or a reel for example.
Even if we get decent chargers, I think we need to treat these batteries like they were a can of gas or something similar.
I only know a little about these batteries from model aircraft, if I hadn't played with those things in the past, I wouldn't know anything about them at all, so I think it's perfectly understandable and logical for cave divers on an average to have little understanding about them, we all drive cars, but how many of us actually know exactly what is going on inside of the automatic transmission?
Well don't leave it hanging there, Tobin. What is the average Joe supposed to do to prevent overcharging other than follow manufacturer's recommendations for charging time? Take the pack apart and check each individual cell on a meter every 10 minutes? How do we make it safe and at least somewhat convenient at the same time? Having a timer to control each outlet seemed like a reasonable approach, and was ok when I discussed the idea with Corey at LM.
Ken
The Tech Diver's Prayer: Oh Lord, if I should die, please don't let my wife sell my dive gear for what I told her I paid for it..
1) Good quality packs. Any Lithium-Ion (Li-Po is just a type of Lithium-Ion) pack will have built into the pack cutoff circuits to prevent overcharging. This transparent to the user.
2) Good quality chargers. Good quality chargers will have multiple means of charge termination including voltage and time.
For an external timer to have any effect you'd need multiple failures in both the battery electronics and the charger. In addition a "dumb" timer will either under charge the battery, i.e. too little time, or overcharge the battery, too much time.
GFI? Really? Pretty much any charger will isolate the output from ground. GFI will do nothing to prevent overcharging.
Tobin
I've been using LiPo packs for years now in my R/C airplanes and helicopters.. (from small 2s receiver packs to 16,000 mAh 120A Discharge packs in the helis)
About 8 months ago I purchased a 35w HID that is Lipo powered and I was surprised at the charging setup. No balance connector and simple trickle type charging.
After less than 20 uses I'm not all that surprised that my burn time on the pack has dwindled to about 20 minutes right after being removed from the charger, and not at all after sitting for a while.
The replacement pack I am putting together is balanced and will be charged properly. Not to mention it will only take about an hour to charge using the right charger for this battery chemistry. (Of which I have many)
Hopefully those putting out dive related products using Lipo power lights (etc) will start utilizing the correct charging schema.
Lipo chargers have come down in price in recent years and the safety margins have gone up significantly.
Before we had chargers specifically designed for charging lipo packs, I had one close friend burn his home down and know of at least 4 others who had similar accidents..
In recent years I've heard of none.. That being said, I never charge Lipo's unattended and I always use flame resistant bags.
While I doubt any of these came close to the fireball Andrew got to deal with when his scooter batteries blew, it'll give those not familiar with lipo fires an idea of what these batteries are capable of..
http://www.youtube.com/watch?v=z3o_2mwRPdw
http://www.youtube.com/watch?v=YCWdnjLqVWw
Tobin is right.. LiPo's should scare you, but like many things in this sport, they are as dangerous as you make them..
My next scoot will definitely be LiPo powered.. In a few years I imagine the vast majority of dive products requiring a fair amount of juice will utilize LiPo, Li-Ion or LiFePO4 cells.
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