ESC Amps verses power of batteries and motor

[sprintkat]

Lets see if i got this right --- if i have a 4500mah 45-90c discharge battery, ill have 202 amps minimum and 405 amps maximum. leopard 4092 - 4000 watt motor on 5s - 18.5 volts, will need 216 amps from the batteries at full power. so a proper esc would be a 220amp minimum and 250amps surge.
am i figuring this right ???

[Fluid]

Not quite. Modern packs can deliver over 400 amps for a short period. You can put a big enough prop on that Leopard to pull over 300 amps. The more amps you draw the shorter the run time. You need to use the experience of others or your experience to choose the ESC rating. For most uses a 220 amp ESC is enough if you use good sense and don't overheat your electronics.

ESC rating is really based on heat, not amps. I have safely pulled over 350 amps through a 200 amp ESC many times without damage - but total run times were under half a minute each so heat buildup was relatively low.






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[keithbradley]

The majority (if not all) lipo packs are vastly over-rated. I've never actually seen a pack that can discharge 45C constant without damage or at the very least a very short life span. Motors don't pull the power that they are rated at, they pull current relative to load. If the load is beyond the motor's rating (if it's an honest one) it can still pull more current, but efficiency (output relative to power drawn) will be greatly reduced. If the load is below the motor's rating, it will pull less current.
ESC current capacity varies relative to voltage and run time. For example, the Swordfish 8s/200A ESC is rated at 200A on 5s lipo. If you were to run that ESC on 8s lipo with a 200A current draw, you are far exceeding the ESC's ratings. Also, not all ESCs are created equal. For example, the old Schulze 40.160 ESCs are rated at 160A, but known to be more capable than some ESCs rated almost twice that (or in some cases, even some ESCs that are rated higher).

I know that's not a clear cut answer on what you need, but the truth is that you won't find one working it out on paper (using manufacturer's specs alone). If you can find data on another setup (prop, hull, rpm, etc.) similar to yours, you will have more relevant information. You could also post all of those details in regards to your own setup and see if anyone has experience that will help (the "has experience" part is important).

[sprintkat]

Thanks for the input. yea,, i found out the hard way about battery output. leopard 4082 with 5s 4500mah 45-90c in a 29 inch sprintcat runing a x447 prop. run after run everything stayed cool to the touch. jumped a wake and went nose first into about 3 feet of water and hit the bottom and the impact shorted the esc and it stayed on, that put (according to battery discharge rate) approx 405 amps into a 120-240 amp esc and literally blew it up. didnt hurt the motor or the batteries at all. im just trying to size up a different esc for a leopard 4092.