Ok, after nearly hijacking another thread, I thought it would be a good idea to start another one to hopefully get more in depth on the subject of pros and cons for each battery type. I'm mostly interested in the LiPo batteries, and how they fare in in our hobby, but all discussion is encouraged. So lets have it... What kind of batteries does everyone use, and why. What are the problems associated with each type? And if anyone has run the LiPos, how are they working?
I am probably the only person who has used Lipo batteries in combat. I used a pair of 3200mah 2S1P packs from venom racing in my karlsruhe. I originally used round cells (2400 mah nimh, 6 cell) but they would loose too much juice over the course of a sortee to keep it at speed for fast gun (or if I jacked it up so that I was at speed at the end, I was radically over-speed in the beginning). I switched to the lipo's and was able to hold a nice consistent speed for ~2-3 sortees without recharging. I could have gone more but I would have had to adjust the end points to bring me back up to speed for the 4th. Also got me a bit of reserve buoyancy that I did not have before and a skosh more stability. Allowed me to run a 3.5oz co2 tank in that tiny light cruiser without tipping problems. They spent more than a day underwater on my deck, as a test, in a 5 gallon bucket. They then spent about an hour and a half at about 12-15 feet down (I found the one deep spot in the pond). And survived countless other less deep sinks. I had zero trouble with them. I did waterproof them with electronics safe silicon. that being said, I only used them for their discharge characteristics and light weight. on all my other ships that had the space/weight available, I have used and will continue to use SLA's.
For my cruisers I am seriously considering going to NiHM type batteries. It's an option I might look at for my capital ships as well.
SLA's are bullet proof (figuratively) are very inexpensive, provide good ballast in larger ships. The cost of 4 6V 12AH gel cells was less than the cost of the two 8.4V (fully charged) 3.2AH lipoly packs. They do not require as advanced a charger, although with chargers like the http://www.venom-group.com/itemdesc.asp?ic=VEN%2D0657 it isn't that important (does everything I charge, and well). They also are not harmed (as much) by going under voltage on them. They are, in general, a more robust chemistry. There is always a greater risk of fire with lipoly packs, although that being said, the cells are much better than they were 5 years ago... and I have been unable to create a non-absurd condition and get a pack to fireball. (absurd condition = hooking battery leads to high current charger and leaving for a very long time). The cells seem well sealed against water by themselves, but the pack itself should be waterproofed IMO.
I use some LiPolys in my airplanes, my major gripes about them are the voltage and the price. The voltage seems to be OK if you run brushless motors, but for the cheapo motors I like to put in my ships, I'm not sure if they're the best choice. If I ever build a SMALL ship though, I think LiPolys are the probably the best way to go.
I should add another caveat to lipoly: make certain your esc has a correct voltage cutoff for them. I ran a castle creations mamba esc on my karlsruhe with a brushless outrunner. There is another thread somewhere about using brushless motors that I started.
one thing I learned was that you can run a ship with a much smaller motor to fast gun speeds and specs with brushless. I ran my karlsruhe off of a single eflight park 400 outrunner, that would have easily run my tirpitz... the writeup is here http://www.rcnavalcombat.com/rcnavalcombat/FileManager/ViewFile.aspx?id=519 http://www.rcnavalcombat.com/rcnavalcombat/forum/topic.asp?TOPIC_ID=988
At Nats this year, a fellow with a Baltimore was having weight issues, and control issues, so I loaned him a set of my Nimh battery packs to try out. I sank him when he passed behind me making a tight turn, I hit him with 7 belows and numerious other holes, but somthing shorted out in the process, and one of the Nimh packs I loaned him went off like a gun shot. He got it back in, and the packs were very hot, and the one cell had exploded, the end was completly blown off. I had no issues with them in my Kumano, they ran great all week for me. I guess I learned a lesson, never loan a Allied your battery packs.
A new Rookie captain, Mike Cucchiarella, he scratch built it. Actually we had another rookie with one also, Andy Terpstra also scratch built his. Both of them had a flat stern like the Des Monies. Tyler Helland also scratch built a New Orleans class, he won Rookie of the year honors with it. All 3 of them went to the bottom at least once, and some a few times.
Greg- How did your brushless motors handle water? It might be worth experimenting with them on my Salt Lake City. She's not as quite as light as a K class, but I'm willing to do anything I can to keep weight down, as I have concerns about regulator weight. Did you run one motor or two through a gearbox? Plus, the idea of putting cutting edge technology in a nearly 30 year old combat ship (yes, she was built in 81 or 82) brings a smile to my face.
I still haven't had time to sit down, read, and comprehend the entire write up on the brushless motors yet, but I gotta say thanks Greg, what I've read so far is excellent. I'm really interested them! Is anyone else experimenting with them?
They handle water just fine. They do slow down in water when submerged (as all motors do), although the outrunners slow down more since the outer housing moves, giving the water more drag, so I just made a gearbox that kept the motor out of the water till my decks were roughly awash... I see no significant rust/corrosion and the bearings were great after the first year. feel free to give me a call some evening to chat. drop me an email if interested and I'll shoot you my phone number
For my larger ships, the SLA's purpose is ballast. They just accidentally provide power in the process. On my Heavy Cruiser Dallas, I switched from a total of 7.8ah of SLA to 15AH of high discharge NIMH packs, AND still saved enough weight to go from 6oz tank to a 9oz tank. For fun, I've sometimes sailed with 18AH onboard just for a little extra reserve. But for working with the big Battleships, instead of trying to save weight whereever I could, I'm trying to put more weight on whereever I can. SLA's are brilliant for solving a ballast issue and provide ship's power as a happy side effect. For the smaller ships, really small high discharge NIMH packs or high discharge LiPO are life savers for making a combat effective ship that can stay out on the water for longer than a single flit around the pond. But both of these require better electrical building skills, and precautions. Well actually they require roughly the same wiring skills as SLA, but SLA's just so darned tough that you can get away with being sloppy.
Need to make sure the positive ends of the cells are coated in Skotchkote or similar (something that will protect, but can be displaced later for reasons about to be given. NIMH (and NiCD) has vents on the positive pole that if the cell gets over stressed and starts building pressure, it'll vent safely rather than explode. From the sound of it, your vents had rusted shut, and that Baltimore probably had electrical issues, or bad or just plain oversized motors without fuses. But yeah, lending expensive packs to a ship that you haven't directly been involved in the construction of, is probably a bad idea.
The ends were coated with scotchcoat, and they were brand new batteries. But when we got them out of his boat, they were burning hot. They were 4500 mAh 10C subC cells.
Did you put anything between the cells? The first pack I made for a guy up here had a shorth between the cells. After we scotchcoated the ends we saw it spark from cell to cell. The plastic covering from the cells had moved and the cases were shorting. We put some rubber inbetween the cells and it has not been an issue since. After the first time I started either putting extra heat shrink around the cells or rubber in between them before they were heat shrinked together. It also could have shorted between the tab on the + side and the case as the case is -. He would have had to overload his motors to blow the battery. Motor overload was not one of his problems. Do you have a photo of the bad pack to see where it shorted out at?
