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Discussion Starter · #1 ·
hello,

I am new on this forum and I live in Belgium (europe). I bike since 15 years (mountain bike first, than I switched to road)

I started to build a triple SSC P4 light according achesalot's web site (http://bikeled.org/).
I already ordered everything except the battery. I was thinking to buy a lipo (14.8V 4000mAh) battery because you can find it easily on e-bay for not too much money.

my question is : is it safe to use this battery type ....because you can read a lot of things on internet saying that those batteries can explode...and because I will probably place this battery in a water bottle (between my knees and under my..you know what :D ) , I wanted to be sure to make the good(safe) choice. Are lipo batteries safe???

regards

arnold444
 

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Randomhead
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you need a balancing charger that keeps the individual cells from going over 4.2v That's not a cheap charger for a battery that size depending on how fast you want to charge it.
You don't really hear of too many lipo fires any more,

it used to be much more common a couple of years ago.
 

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if it's in a water bottle, you shouldn't have a problem with punctures, so while riding you will be fine unless some freakishly sharp jagged stick flies into it and punctures everything. they don't really explode, so it's not like it'll blow a leg (or other appendage) off. they just burn rather vigorously. also, if they get going, you gotta wait it out, since it's a metal fire (water makes it WORSE)

really, the biggest danger comes during charging. you need to balance the cells to keep them in any decent shape, and you have to be careful about over-discharging them (never below 3.0V/cell). good cells can be saved below that, but it's not a for-sure thing, and it's a little sketchy. if you're using a bflex, nflex, or maxflex, you can set the low voltage cutoff, so over-discharge won't be a problem.

I recommend a good balance charger though. it'll make your life much easier. I personally have a pair of cellpro4s chargers from www.fmadirect.com and love them. very simple, very controlled, and very safe. the latest versions will charge a 4s 4Ah pack at 1C (4A), giving you an hour of charge time. just need to use a 12VDC power supply. plus you can adapt them for any lithium batteries (including cylindrical cells etc)

Basically, if you're going to be able to take the time to be careful with the batteries, and treat them with respect for what they can do, you will very likely be fine. look on RC sites for lots of instructional threads on safety and care.

finally, for a bike light application (my packs will see 2Amps MAX), I don't see a reason to use lipo vs li-ion cells. lipos are intended for high current applications (in the 30+ amp continuous range, with spikes in the 50+ range). lithiums will weigh roughly the same and be a bit more durable/stable than lipos will, as well as being just as easy to find cheaply. plus, build quality and cell matching is pretty important in lipo packs, and will definitely not be the best in low-end lipo packs. this means a good chance of killing off cells, lighting off a pack, etc.

lots of affordably priced lithium packs here with no-nonsense chargers. this is what I'd do for a DIY project if I didn't want to get into building my own packs.
http://www.batteryspace.com/index.asp?PageAction=VIEWCATS&Category=898

hope that helps...
 

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Discussion Starter · #4 ·
unterhausen said:
you need a balancing charger that keeps the individual cells from going over 4.2v That's not a cheap charger for a battery that size depending on how fast you want to charge it.
You don't really hear of too many lipo fires any more,

it used to be much more common a couple of years ago.
hello unterhausen,

if I understand well, accidents can occur only during charging with an incorrect charger??? but never during use (on my bike :thumbsup: ) ???

My futur battery would be a 14.8V 4000mAH with 4 cells and I was thinking to buy a Esky EK2-0852 charger (http://www.buzzflyer.co.uk/RC-Helic...Li-Poly-battery-charger---EK2-0852-/p-73-191/)

are lipo battery and this charger compatible according you???

regards

arnold444
 

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EDIT: I removed this post, basically covered the same info as Bryguy17 (I should have refreshed before posting) :D

I do want to add however that if safety is the prime consideration, there are Lithium cells out there that are considered safer than the traditional L-ion cells (A123 and LiFePO4), as well as NiMH which can explode too (never seen one go off, but I hear that they are not as bad as L-ion). Also, if you get cells from the Internet, it is wise to make sure they at least have a vent in case they do start to go, the gasses will have an outlet and not build up, causing the cell to burst. If you are unsure about building a pack, it is probably worth buying one pre-made professionally, with a charger, or using some AA NiMh in a holder so they can be charged individually.
 

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I would say the biggest risk when riding is mechanical damage. The lipo catches fire if crushed or punctured.
As Bryguy17 write, the main advantage of the lipo is its ability to deliver extremely high output. Many 4000mAh packs can deliver 40A. This is very good when powering RC models as many motors have very high draw initially. It's also lightweight.
As your light will draw less than 1A, you would do just fine with Li-ion cells. Also have the charger in mind when looking at the price. Lipo balancer for 14,8V is from $40 (chinese copy) and up. A quality charger is around $100.
Also remember you may want to add a protection circuit to prevent over discharge. Those are about $15 for a 14.8V pack.

I have one 4000mAh lipo bought cheap on ebay from hong-kong. Real capacity is about 3000mAh and the pack is more than 50% larger than a quality battery of the same capacity.
I find the 18650 li-ion cells more convenient and a pack of 4 is close to half the size of my Lipo pack. They also have protection circuits inside.
 
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