Brian
just wondering if you could give us a run down of how you think lipo perform in a boat - advantages and disadv's or limitations ?
Please remember I'm the newest of the guys running LiPos, there are quite a few guys with tons more time with them than I've got. Here's my take, for what it's worth.
The short answer is:
Once we have LiPo classes I'll never buy another NiMH cell,
period. With my history with NiCd/NiMH cells that's saying something (you should see the amount of garbage I've got in the shop to support those chemistries; matchers, zapper etc).
The longer answer:
They worked great. No failures, no fires, no charging incidents. I ran them in the small Offshore class and they worked perfectly, even charging between heats. 4+ minutes running at sprint race speeds, I like it.
I also ran them in my 12 cell rigger for a demo/test, the performance gain was scary (call it 20%+, about what you'd expect when you take into account the voltage depression for the NiMH packs under load). The boat was easily into the 70+mph range, ask the witnesses (felt like running one of my SAW sport boats, except it turns). I ran 10 very wide laps (turn fin and bracket need an upgrade) on the 1/8 mile oval, nothing particularly hot so 1 mile heat races would be no problem. With a bit of tuning on this boat I'd love to try and run with the smaller nitro classes. The end result is I think my 30" 12 cell rigger is too small for that system, a ~35" boat would be more fitting.
The setups were as follows:
N3 Offshore (what we dubbed the 7.4V LiPo class); DH 26 mono, Neu 1512/1.5D, Schultze 18-149, 2S2P 5000mah (10,000mah total) Poly RC (I got them from CheapBatteryPacks.com, but there are lots of sources for cells), X640. This is just about the right setup, nothing is getting pushed real hard. It's every bit of fast (faster than the same boat on 8 NiMH with a power system that's at its limit) and it does it for 4.5 minutes. Making it a 10 minute sport boat that's 80% of the speed is only a matter of tuning.
12 cell rigger; Raptor/Crumgrabber, Neu 1515/1.5D, MGM 16024-3 ESC, 4S2P 4350mah (8700mah total) Poly RC pack, modded X645. This one isn't even close to its limit, just a safe setup for testing.
Rough LiPo guidelines:
Here are some of the recomendations that came up over dinner saturday night (Most of the avid LiPo guys were sitting around the table):
-Figure on using double the capacity you would normally use with NiMH at a minimum (4200mah NiMH-->8400mah LiPo).
-Use 20C continuous discharge cells at a minimum (2nd gen. cells or newer).
-Use the larger capacity cells to minimize paralleling (many fewer connections to fail).
-Don't pull out more than 75% of the cell capacity (treat those 20C cells as 15C).
-Don't get the cells above 140F (mfgs say 160F but the guys with lots more experience than I say 140F max will extend cell life significantly).
-Use proper chargers with balancers (I'm using Hyperion 7i chargers and ballancers, I charge through the ballancer every charge. Also great for NiMH).
-Charge cells out of the boat and in some sort of fire proof, vented container just in case (I'm using LiPo sacks, we purposely tested one at the race and the containment was impressive).
-Keep a bucket of sand and a fire extinguisher on hand just in case (sand is for the LiPos and the FE is for anything that catches surounding it).
-Don't try to use cells that have been damaged in a crash (ask the airplane guys about this one).
-Take a little more care with the cells, the packaging isn't quite as tough as the metal cans we're used to.
-TEST YOUR SETUPS (start very safe and work up to the safe max performance, this goes for NiMH as well).
You have to take safety precautions, just like we should with our other cells (and generally don't). The only things that litterally blew up all weekend were NiMH's and Capacitors (someone dead shorted some fresh charged 4200's by mistake and they did explode, split cans and blown out possitive caps. sounded like big firecrackers in the pits).
The reality is the Li chemistry cells will allow FE racers to go compete with the gas/nitro racers on an even footing. The response from the Gas/Nitro guys from what I've seen has been; come on out, we'd love to have you.
I will say the guys running LiPos were more attentive when dealing with charging the packs. I found myself becoming instantly less attentive when going back to NiMH packs (not a great practice).
Thanks to Alan Nayman for setup help (and the charger recomendation), that was a crash couse on LiPo tech. Paul, did really have to let me drive that cat (Open Mono, Cat and Hydro at the master next year, do they run open sport?). Mike at CBP for getting me loose cells so I could learn how these things really go together.
