Newbie question about lipos & esc

[ezhitz]

Hi I was wondering does the mah rating effect the size of ecs i should get
or is it the max amps of the motor.I'm thinking of buying a couple
turnigy 2s 30c 5000mah pack.I will be using it in a 24"rigger with 7s and I will buy hydra 120
if thats all I nead.
thanks for your time.

[soulreaper]

Amps of the motor affect the esc more. It is the amp draw that you are really concerned about. For example. If a motor draws 60 amps. you want an esc that at the least is 60 amps, nothing less. Then you want to make sure the lipo batteries you are going to use can provide the needed amps. This is how you tell what the battery can put out.

LOWEST C Rating X Mah. Example your above listed battery 30C x 5000 Mah =150 amp.

Reaper.

[ezhitz]

How do you know what amps the will draw before you run it?I see on the feigao list max
amps for a 7s is 93.So do i want a esc where that number would be 70% of it peak output.
I understand that there are factures in the setup that will affect the draw like prop size,boat weight.Thanks for your reply again sorry if these question sound stupid.

[Flying Scotsman]

They are not stupid qustions, they are very valid. I am not familiar with rigger setups, so I can not comment on your choice of motor. The Feigao chart will not reveal the amp draw your setup will require. Their is only one way to find peak amp draw, you have to use a measuring device such as an Eagle Tree. The 7S motor will be spun to 40,000 rpm, which is SAW levels and very short runs, a large prop will increase the amp draw way over 90 amps. I trust that someone with rigger experince will chime in to help you on the motor choice, off the cuff I would have thought an L series motor or higher turn S series might be a better choice, dependant on your goals

Douggie

[questtek]

How do you know what amps the will draw before you run it?I see on the feigao list max
amps for a 7s is 93.So do i want a esc where that number would be 70% of it peak output.
I understand that there are factures in the setup that will affect the draw like prop size,boat weight.Thanks for your reply again sorry if these question sound stupid.

I certainly agree with the last reply on using the Eagle Tree. You can buy them on this forum host site and I believe they are one of the best investments going. I own 3 of them!

To answer your specific question I refer to a previous post I made under the ECS cooling topic. Here is a shortened version.......... Hope it helps but it is an 8X motor I was using.


I did the baseline tests with my Mean Machine. This baseline configuration used my modified Mystery 100 amp controller with large copper heat sink and two tube cooling. The boat was set up with a 540 XL, x8 that has a 2084 KV. I used 4S, 40 C, 5000mAhr Lipos. The running gear was stock and not tweaked in the least bit. The prop was an old beat up plastic pile of crap I just found on my workshop floor...good enough for the baseline since I am not looking for performance, (at least not now). I used the latest V3 Eagle Tree data logger with GPS sensor, brushless RPM sensor and thermistors on the ESC FET's and on the motor just in front of the water jacket but in direct contact with the case.

The lake water was about 77F. The initial EXC and motor temps were 76.9 and 77.4F

For the 4 minute run which just had bursts of speed and only modestly fast turns...
Max amps 82
Max watts 1156
High RPM 29,880
Max GPS SPeed in MPH 29
Final ESC temp 101.3
Final Motor temp 102.9

[Xzessperated]

Hi I was wondering does the mah rating effect the size of ecs i should get
or is it the max amps of the motor.I'm thinking of buying a couple
turnigy 2s 30c 5000mah pack.I will be using it in a 24"rigger with 7s and I will buy hydra 120
if thats all I nead.
thanks for your time.

You have no way of telling what the Amp draw will be until it is on the water so the Eagle Tree Data Logger is a very good suggestion. As you said there are variables that will affect Amp draw.
What do you want to do with this boat? As Douggie said it is really a SAW setup. If you are going to run at 40,000 rpm it will not be suitable for long run times. I also would have gone for an L motor. If you want to do circuit (oval) racing then go for a motor with less kv and will spin at about 30,000 rpm on your Lipo.
I have run the old CC Barracuda 120 esc's on hotter SAW setups without water cooling but in the end I have cooked them all.
I would go for the best esc you can afford. The Hydra 240 is a good price at the moment.

Q. Why buy Castle?
A. Because for about $70 they fix it if you fry it.

In the end the decision will be yours but my advice is to buy one bigger than you need and one that has good after sales service. For oval racing use good water cooling on both motor and esc. Start testing with small props and monitor the heat of battery, motor and esc. If you can afford it get the Eagle Tree Data Logger.
I hope you let us know how the rigger runs when you get it on the water.

[ezhitz]

thanks for your answers i should say the boat was just something to try I'm not looking for
ultimate speed and i'm not racing it .i have a nitro 12 to run when its cooling down and recharging.i won't have it ready before winter comes so it will next spring when i can run it.This way i can save up my money and get a data logger and go for the hydra 240.

[andym]

In a 24" rigger i would be more inclined to go with a 6L (4116 Kv) on 7.4 volts. more torque to push a suitable prop for the size of hull and it would be very quick.

[ncornacchi]

Q. Why buy Castle?
A. Because for about $70 they fix it if you fry it.

I didn't know that they'd do that !

[duckbum]

I'm fairly new at electric boats...even though I own quite a few of them...sometimes I can't repair them...especially have trouble getting throttle/radio maanual programming for speed control/esc...

Is there a basic BOOK available for Electric Boats???

[video200]

Q. Why buy Castle?
A. Because for about $70 they fix it if you fry it.

I didn't know that they'd do that !

if no warranty it is a flat rate to fix a hydra 240 is $150

http://www.castlecreations.com/support/flat_rate_repair.html

all the way down on that page.