6S or 8S? I need some help deciding which way to go.

[Switch]

OK well got my self way in over my head (and probably over my budget) got a 40" TT outlaw in trade and through the research and advice of friends. I thought I would set it up to run in "open gas mono" since we have no FE class in my area big enough for my hull. The goal is 60-65mph planned on running it on 8S with either a TP, Leo, or Neu (havent decided yet) some where around a 1000kv setup maybe a 4092 for example. In my newbish way of thinking I planned on running two 4s packs in series. but that will drop my mah to 5000 total, is this enough for a race even? Then I checked the price on going with two 8s packs and about wanted to have a heart attack $$$(now I understand why P spec classes are so awsome, keeps you out of the hot seat with the wife). A set of 6s batteries is alot more affordable and easier to put in the hull I was really just hopeing to keep the voltage up and the amp draw down with the 8s setup. So is 5000mah enough? what would my amp draw be on a 8s setup? do I need a 240Amp speed control? feeling a little overwhelmed right now. I should have just stuck to plan and built a P-spec rigger

[jcald2000]

5000 is not enough!
I have a heavy (rough lake) 40" sport hydro I run on 8s 2p at mid to upper 60's and use 6600 mah.

[BHChieftain]

There are 3 ways to skin this cat. You are gonna want a 2P setup for 10,000mah capacity

I pick my configs so I can run my lipos on as many boats as possible so the right answer depends on if you plan to run your other boats on 6S power or 4S power. I've standardized my boats to run on different configs of 2S 5000 packs (either 4S1P or 4S2P).

1) 2 x 8S packs for 8S2P. Not very practical...
2) 2 X 6S packs for 6S2P. Ok if you plan to run other boats with your 6S packs. In this case you'd want to increase the motor KV to around 1500 or so.
3) 4 x 4S packs for 8S2P (wire up 2 sets in serial, then put those 2 sets in //. I do this with 2S packs for a 4S2P config). Good if you plan to run other boats with 4S config. This is probably the most cost effective and flexible option, unless you plan to run your other boats on 6S. The other nice thing is if you have a cell go bad in a pack, you don't have to trash as many "good" cells-- you can just replace on of the 4S packs.

On the ESC I would definately go with at least 240A.

Chief

[Switch]

Cheif that is some great advice I never thought about running 4 x 4s Thats alot of battery to tuck but that would be fine no less than anyof the other options. That would drive my battery cost down big time and alow me to run 4s on my other models which would be sweat! WHat other options are there for a good 240+ amp esc? I know there is a swordfish 300A out but do I really need one that big?

[Fluid]

If you want to go with 8S2P - this works although amp draw is higher - then consider the Castle 2028 motor. This one is strong enough to swing gas props (65-72mm) on 8S without trouble, and is available for under $300 new on OSE. Much higher quality and efficiency than the TP or Leopard and less $$$ than the Neu.

That said, all the guys running large FE boats in my District run 10S. That either results in higher speeds or longer run times versus 8S. You can run 2x6S and 2x4S packs for 10S2P. Room for packs is seldom an issue in these large boats. The Castle 2028 works well for 10S too, just run a slightly smaller prop (57-62mm). Either way will get you where you want to go.

I simply do not understand the fascination some have with high-amp ESCs with high voltage setups. No one (sans SAW) needs a 300 amp ESC for a 8s or 10S boat, these get their power (watts) from voltage. Using voltage for power means lower ESC temperatures and longer run times. High amp draw has plenty of drawbacks. Most of the big FE boats in my District pull under 170 amps continmuous and are plenty fast (60s to 70s) - too fast to stay on the rough water we run in if they prop up. A 200 amp controller like the Castle is ample for most 8S/10S uses - many of us have been running the Schulze 160 amp controller on 10S for years with zero issues. There is nothing wrong with having some head room in an ESC, but there is no reason to try to run more amps in a 10S setup than in a 4S setup for an oval racer. There is plenty of performance at 6000 watts unless the hull/setup is a real dog.




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[Switch]

Thanks Fluid! It was kind of my goal to get away from the 240A esc just due to the price. I figured 8S would help ease the amp strain eleviating the need for a big esc. Would like to be around $400 for a motor and ESC. Might just have to wait and watch for a good used one. If I am going to mix cell counts on my packs do I just need to make sure they are of similiar discharge rates and mah capacity? Id probably try and get the same brand as well. 10s is definately again something I haddent considered but will definately think about. I dont think anyone in my district is running an FE with this much power so idk it will be interesting. Cant wait to get out there and try to put a hurting on the open gas mono guys!

[Fluid]

Mixed-cell-count packs is no problem, but all the packs should be the same - same brand, version, capacity and 'C' rating. Running 10S in a 40" boat works and gives longer run times, but 8S is a bit less costly from a battery standpoint. The ESC should be capable of at least 10S for use in an 8S setup - don't try running any ESC at its maximum voltage rating. $400 for a motor/ESC is certainly possible, but watch for reliability issues. And do what you can to keep the wire lengths as short as practical, that will help the ESC to survive.




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[bill34207]

I'll back up what Fluid has already said. My 41" Falcon cat runs an average of around 110 amps on a 6 lap run. However, it does spike close to the 200 mark and sometimes a hair over spinning an Octura X460/3 on 9s 2p. The Swordfish 240 HV is a good reliable esc as long as it doesn't get wet (less expensive than the Castle Hydra Ice 200) and it does not hurt to have some wiggle room for current.
I own 2 SF 240's and an Ice 200. Both of the SF esc's are over a year old now and no issues so far. The data logging from the Ice is nice for setting up and seeing how much room you have and the throttle has a little better feel (IMO) but the SF is still a better bang for the buck option.

[Switch]

sounds like a plan. Having a 240A speed control would definately give me some more room incase my first attempt at a motor choice didn't achieve my goals and would probably be a better investment in the long run espically if I can only go with a 6s2p setup. Now I just gotta watch the for sale thread like a hawk and find a good used one. 10s would be awsome but I'm gonna have to build up a battery surplus first

[gyrotron]

Mixed-cell-count packs is no problem, but all the packs should be the same - same brand, version, capacity and 'C' rating. Running 10S in a 40" boat works and gives longer run times, but 8S is a bit less costly from a battery standpoint. The ESC should be capable of at least 10S for use in an 8S setup - don't try running any ESC at its maximum voltage rating. $400 for a motor/ESC is certainly possible, but watch for reliability issues. And do what you can to keep the wire lengths as short as practical, that will help the ESC to survive.




.

Fluid,

Can you elaborate more on the wire lengths and ESC survival? Why is this so?

Thank you