So most of us know that C ratings are quite often exaggerated, but what about claimed ESC amperage ratings? What sort of “safety margin” should be factored in, in terms of percentage, in order to minimise any overdrawing issues?

ESC amps = motor amps + 20%?
Battery amps = ESC amps + 100%?

i.e. a brushless motor that draws 50A constant would be well matched with a (claimed) 60A ESC, which would be well matched with a (claimed) 120A battery.

Thoughts?

ill add what i know. but first my back ground. i am a union electrician for over 10 years and how i was the measures amps and watts is for a unit duration of 1 hour. so these measurements the rc industry uses always confused me. because if we used this batteries, esc and motors at amp levels I've been taught are batteries spontaneously combust, ESCs would let out all the magic smoke, Motors would be nothing but liquid metal. which leads me to my next train of thought there measurements must not be based on a full hour duty cycle. if this is the case then there 50a, 60a rated number. could be over inflated to what ever the manufacturer desired. because what one company rated as 2 a sec constant would be dwarfed by another company reading theirs as 1/10 of a second constant.

how i select my setup. i get my motors true unloaded current, i take that to 10% of my esc rated current and then select the capacity battery at half unload motor current.
example:
my motor pulls 2 pole brush-less motor pulls 5 amps @ no load. i will select an esc no less then 50a as minimum and i may go to 60a 2%for extra over head.

5(amp motor)=10% * 50a (esc), 5(amp motor)=12% * 60a (esc)


i then select a battery atleast 50% of my motors no load draw as a minimum capacity battery.( i don't give c rating much pull,i give it to capacity)

5(amp motor) *50%= 2.5 (amp battery minimal)

i have given this much though on 4 pole motor esc selection and i always when with the largest battery i could find.
i haven't given it any though on 3S or more cell batteries so i don't know how it may if at all scale.

not sure is then in for worth 2 cent or the time it took to type

It is very hard to determ such limits, and calculating such current draws.

While recently running into high current issues with my 4WD SCT, I am starting to appreciate the need for a data logger and current limiter which are not included in my ESC.

While my motor and ESC temps are normal, 140° and 100° respectively after an 8 min main, I have recently been experiencing excessive current drain which have un-soldered my battery terminals at both the positive and negative terminals, the heat has also deformed the plastic around the terminals:



I regularly maintain my truck by cleaning the bearings and making sure there is no binding anywhere in the system. The battery is about 6 months old with IR around 5mΩ respectively for each cell. in the pack. I made no changes to the setup which worked fine for the past 6 months and then mysteriously started drawing excess current.

I have been trying to mitigate the issue by reducing the punch from 9 to 4, increased the expo on the throttle from 0% to 25% and decreased the EPA from 100% to 90% and now I can make it through a race without unsoldering the terminals anymore, but my battery temps are still higher than normal where in the past 6 months the battery would average around 100° but now it's in the 130° range after a race

That said the pack is way over rated for the specs and it worked flawlessly for 6 months, but now there is some sort of gremlin that I am chasing down. I am thinking there is a problem with the ESC which lacks a "current limiter" feature which I believe would prevent this problem of excessive current drain on my battery.


***
Because I am cheap, and the track in my area does not enforce ROAR, I plan to resolve the issue by replacing the 3660-4300KV motor with a 3660-3200KV motor (26% reduction in KV) and running it on 3S (33% increase in Voltage) which will be more cost effective than investing in a new ESC with a current limiter... by switching to 3S, I will reduce the current draw by 30% (averaging KV and Voltage changes) and should be able to keep the same gearing and increase my EPA back to 100% and get roughly the same net power draw as before.

Wow, that melted plastic does not look good at all!

Bill, melted plastic around the bullet plugs suggests a problem with the connections. Have you replaced the bullet connectors on your ESC? After so many insertions, they can get dirty/loose, and lose their contact force. If there is excessive electrical resistance in the connectors, they will generate a lot of heat at the plugs.

They are still a nice tight/snug fit, but yes, the 5mm slotted bullets are 6 months old and no longer have a shiny gold plated finish to them anymore. Looking inside the female slots of the battery also show signs of dark corrosion suggesting that the internal connectors on the battery pack itself has also degraded.

I have since ordered the following:

3660-2500KV motor which is 58% of 4300KV (this is reduction of 42% less current draw)
2S --> 3S = 33% increase in voltage

The net speed difference should be (3S/2S) x (2500KV/4300KV) = 87%
So to get the same speed I will need in increase my 15T pinion +13% = 17T pinion with the new setup to get roughly the same speed, while reducing the current draw by 42%

*** EDIT
The 3S battery I have chosen to order is a 6Ah pack which will produce 75.6Wh
The 2S battery I had before was a 7.7Ah pack which produced 64.7Wh

So I should increase my run time by at least 75.6Wh / 64.7Wh = 17%

1st you can never believe any said or printed amps, C, or watts on anything we use in RC.. from rx to batteries..

billdelong

the best current limiters shorten the duty cycle (PWM). that is the main thing you ESC does. its is a current limiter. if you want to limit it more then set the end point shorter.

you have 1 of 2 problems and I’d start by isolating the two systems to figure it out.

1-you have an electrical resistance problem
2-you have a mechanical binding problem.

if its electrical, measure the voltage before and after the hotspot while under load. this will tell you dynamic resistance (and its a very cheap method to measure very low resistances that a high dollar LCR would measure). a big drop on the output side (voltage) without much of a drop on the input is resistance (you can measure current to have all the values in ohms law but even using a guess is fine). if the drop is close to equal then look at mechanical.

if its mechanical start isolating components. left, right, front, rear. A dif checker does pretty good at checking specific points for friction. you can also use weight an a lever arm at a know distance. once you get it in good running order measure the current at the motor at say 5000 rpm. keep that number handy because you can use it to check friction over time.

Billdelong... I experienced the same problem... melting the solder on my bullet plugs/ wire. Kept re-soldering thinking that was the problem only to experience the problem again. Changed the bullets and problem went away.