Anybody using li-po batteries as a power source in their ships? I am considering them for use in a small boat project but know they are somewhat volitle and prone to combustion due to damage. If used, should a watertight box be utilized to keep them dry? And they need a special charger as well I believe? thanks, Steve
I wouldn't use them. I believe they are the ones that blow up and destroy your ship. A cool trick one...but only once. There are other lith types that are safe for water. Check with strike models. Get the safe ones. No amount of waterproofing will ever ensure your boat is safe. If you're not sure, I would stay away from them and run nimh packs or something.
Lithium Ion's are particularly volatile. Lithium polymer are somewhat, I will not recommend their use, even though I do use them... but I do so knowing that the risk is non zero. my own experience would indicate the risk is small, but it is there. -Greg
Another thought - LiFePO4 aka LiFe or Lithium Iron batteries are reportedly MUCH safer and still save you about 1/2 the weight over a comperable amount of Ah at a given voltage over NiMH. More recharges, too. Strike is starting to carry them, and even Tower Hobbies hase some. You do need a charger that is rated for LiFe, though. Interestingly the cells are 3.2-3.3v each, so an 2 cell pack is 6.4-6.6v. Right in the normal tolerance for most R/C equipment. Many are pretty high C as well (meaning a higher discharge rate does not harm them). Cheers,
I'll have Stephen jump on here soon and make a couple of comments. Strike does carry the batteries, they're just not up on the site yet. The battery charger that will charge the LiFePO4 batteries as well as many others (http://www.strikemodels.com/prod...rgers/). Just catching up on posts, have been at a search engine conference for most of the week and haven't been checking the forums.
Keri, Stephen was going to bring some props to the M&G event next Sunday, maybe he could bring some of the batteries to show me, hey? Just a thought. thanks all, Steve
I know of three different Lithium-based battery chemistries. Lithium-Ion: the first type invented, this is the most dangerous. Lithium ions react in a spectacular manner with water. One person in the WWCC experimented with Li-Ion back when they were first released. Got sunk, recovered the ship, blew the water off. No immediate explosion. Safe, right? Nope, the battery exploded inside the trunk of his car several hours later, totally destroying the experimental ship and severely damaging several others. Lithium-polymer: The second type invented, this is less dangerous. This battery bonds the lithium with a polymer, so it doesn't explode when wet. That's about the only way it's less dangerous, though. pierce it, drop it, charge it wrong, or look at it funny, and it releases its stored energy in a very rapid, hot, and poisonous manner. Its weakness to physical trauma makes this battery unsuitable for combat. Lithium-Iron: I don't know the specifics of this one, but it's a tiny step down from LiPo in energy density, for a huge step up in robustness. I have heard that it is as robust as old SLA batteries. Strike Models chose this chemistry of batteries instead of LiPo because of its robustness and suitability for Model Warship Combat. I have to agree with Strike: these are absolutely amazing batteries. They outperform every other type of battery I have used. Asides from their need for a digital charger designed for LiFe chemistry, and their price, the LiFe chemistry makes for a perfect battery for combat.
So you are saying that LiPO is safe in water, the only drawback is that its package is susceptible to damage? I have read / heard that LiPO reacts to water. If damage is the only concern then how are the new Car packs for LiPO with a hard case any different than an SLA in its plastic casing. It seems to me that a hard pack LiPO would be as safe as an SLA as long as the LiPO does not go nuclear when put in water. Besides I heard that LiPO should be stored in those fire proof bags anyway. My understanding is the LiFE batteries are less volitale when charging, not so much that they are less susceptible to water. There is one hard pack LiFE at tower which is 4ah for 89. I am sure the prices will drop soon. Any thoughts on that?
I heard that Lou tried Lipo's down here in region 3. On the MWC site these is a picture if you look through them all, where his boat is smoking, and on fire due to the batteries. I don't know the whole story, on how many times he used them.
I do take issue with some of this... the physical weakness is the least of the concerns with lithium, and can be readily dealt with by enclosing in plastic, e.g. armoring it. there are plenty of things in the boats that need protection from the cannons, particularly the larger big gun calibers. The big kicker if you use lipo's is to watch them like a hawk, particularly when charging, as if they are going to cook off, odds are, it will be durring charge. Take a measurement on their thickness when new, if they baloon up, stop using them immediately, and dispose of them by fully discharging them. Same goes if there is damage. What I have done for years with damaged lithiums (and I have smashed a number of them from aircraft, and never had one cook off) is to set them in a metal tin full of salt water, and let them fully discharge for a day or two (tin placed outside, away from anything important). I generally transport them and charge them in a metal ammo can, just for the sake of my own paranoia. heck, I've tried to blow up damaged cells by short circuit and never succeeded (never tried sevear over-charging, mostly due to lazyness, and the knowledge that if properly overcharged they will blow up)... the only lithium's I've had success turning into a fireball are lithium ion packs. My 2 cents on them is that if you are an anal retentive fellow who always removes them and puts them in a fire proof container for charge or transport, and you armor the cells, the odds that you will have issue are few... if on the other hand, you never look at them, don't know what a bloated or damaged pack looks like, and don't check, you are playing with fire. I note that I only use them when a Nimh pack just won't fit with the capacity I want... Although I would note that it would be useful to make sure the batteries you are buying have passed the linked to tests, as those are rather harsh, and far worse than what we would do to a pack. testing req's There is also a nail penetration test that reputable manufacturer's use, I am trying to find the spec, but the gist of it is that there should be no smoke, explosion, or fire after penetrating a charged pack with a nail.
The overriding issue with most of the lithium battery chemistries is thermal runaway. If the battery gets too hot during charging, the lithium reacts which further builds up heat. The same goes for shorting the pack. If the battery is dented or pierced, it shorts the internal foil, again leading to thermal runaway. The lithium in the LiFePO4 cells is bonded more strongly, so that the cell does not go into thermal runaway until well past 500 C. If your ship hits temperatures like that, the batteries will be the least of your problems. There are some great videos out there of testing li-ion and LiFe cells via piercing, crushing, shorting. A fun (but promo) video is http://www.valence.com/technology/battery_safety/battery_safety_video . Here's another video of someone running a large cell of the specific chemistry I stock through a metal shear: http://www.youtube.com/watch?v=zwIl8f3WI0s . They have a bulb and voltage meter hooked up to the cell as the test continues. I have been working with a battery manufacturer this last week about battery protection circuits for LiFePO4 cells. It looks like they are not recommended IF you are using a smart charger. The PCB and smart charger work against each other when charging, and causes faults with the charger. But, if using a dumb charger, you definitely want the PCB to protect from overcharging. On the other hand, you do need to make sure that you do not overdischarge the cells if you do not have the PCB (the PCB cuts off the battery if the voltage drops too low). LiFePO4 cells have a very quick drop-off in voltage at about 85% to 95% of discharge. Until then, the voltage is extremely flat. If you overdischarge the cells, you will shorten the life of the cell. As for shorting the packs in a boat, I highly recommend using a fuse somewhere close to the cells. I've seen a few ships that shorted out packs with less than desirable results. To give some idea as to energy density, I have a 5 Ah pack at 6.4 volts that is just under 1 pound. I also have an armored cell (flat, with a stainless steel case) that is 10 Ah at 3.2 volts that is also just under a pound. A 4 pack of AA cells also works really well for driving solenoid valves (12.8 volts). I will have batteries and packs up on the web site this weekend. Thank you, Stephen Morgret Strike Models www.strikemodels.com
According to what I have been reading, although the PCB does not work well with the smart charger, it should still be used in the ship to prevent discharging the battery too low, correct?
I used my set of LiFePO4 this weekend. I got the 20 amp, 3.2 volt cells, and hooked them up in series in the boat. Ran them 2 sorties with no problem in my Iron Duke. I got a single 6 amp charger made just for LifePO4 cells, so when the single cell is charged, it cuts off. They were only down less than 10 amps, since they both charged in less than 1 1/2 hours each.
what type did you get and where? Did they include the PCM to prevent over-discharge? If not how are you keeping track of that?
aah:cry:, just last week i was down at my LHS/track drifting my rc car and a guy had this happen, the pack was at least twice the size that it should be, and he kept racing with it hooked up to his car:blink:, he checked the pack three times over a 30min race and didnt seemed to bothered about it melting is grand and half car to the track, dont know if he knew to stop using them once this happens or not, oh and also the lipo packs will react with water (asked my chem lecturer), although Kotori seems to have the exact oposite infomation(not saying you are wrong just that the info is opposite), so now i dont know what to believe, but my lecture recons the water will not put out the pack if it starts to spit flames, instead it will just make the fire burn quicker and hotter, sort of like how magniesium burns in water, it just aides the fire, he said you cant really stop it from burning, just dump a pile of sand on it and wait till it stops smoking.
20AH LiFE cells? Nice find Dave! The 10Ah LiFE cells I ordered weeks ago finally arrived the other day. Each cell is 3.3 volts, 10Ah. In series, they'll give 6.6 volts, 10Ah ... more than enough for small ships. Even nicer, the LiFE battery pack weighs 6 ounces less than the D size, 5 cell, 10Ah NiMH packs I'm running now. The Omaha might need that extra 6 ounces of weight savings.
Yep the 2, 20 amp together weigh about 1/3 more, 3 pounds vs 2 pounds for a D-cell pack, but twice the power. Also they are 3C, so can put out 60 amps without a problem.
