Confused by these amp ratings

[dure16]

Can someone dumb these specs down for me?

Looking at the max wattage of 4200w, I’d expect the max amps to be much higher than 123. For example, 4200w/25V = 168 amp draw on 6S.

What am I missing?

http://www.tppowerusa.com/index.php?route=product/product&product_id=424

 

[Cheez]

Hopefully this helps. https://www.wikihow.com/Calculate-Wattage
123 amps is enough to kill a herd of bulls , and set your home on fire .

 

[The Bean]

Can someone dumb these specs down for me?

Looking at the max wattage of 4200w, I’d expect the max amps to be much higher than 123. For example, 4200w/25V = 168 amp draw on 6S.

What am I missing?

View attachment 229425

http://www.tppowerusa.com/index.php?route=product/product&product_id=424

It can take more than 25V (up to 37V).
The max amps (123A) × 37V = appx. 4500W.
This also means it can't take max. amps and max. volts at the same time.
The max. wattage isn't the "wattage at all times", but only at short bursts in the right conditions. You need more volts for that if you really want the max. performance out of that motor, but I don't think you'll need it.

 

[Diem Turner]

Can someone dumb these specs down for me?

Looking at the max wattage of 4200w, I’d expect the max amps to be much higher than 123. For example, 4200w/25V = 168 amp draw on 6S.

What am I missing?

View attachment 229425

http://www.tppowerusa.com/index.php?route=product/product&product_id=424

Divide the wattage by the max voltage and you get 113A. If you divide the wattage by 33.6V (8S, which is what I assume they did) you get 125A.

It can take more than 25V (up to 37V).
The max amps (123A) × 37V = appx. 4500W.
This also means it can't take max. amps and max. volts at the same time.
The max. wattage isn't the "wattage at all times", but only at short bursts in the right conditions. You need more volts for that if you really want the max. performance out of that motor, but I don't think you'll need it.

It doesn't have to because as voltage rises, amps drop inversely in accordance with Ohm's law.

 

[dure16]

Divide the wattage by the max voltage and you get 113A. If you divide the wattage by 33.6V (8S, which is what I assume they did) you get 125A.

Okay that makes sense. Would you expect the motor to pull more amps at lower voltages?

I’m trying to figure out how much ESC I need in order to run that motor on 6S or 4S.

 

[The Bean]

I'd just run it on 6s, and use the throttle limiter to reduce the speed if necessary. It's less lf a hassle.

 

[Diem Turner]

Okay that makes sense. Would you expect the motor to pull more amps at lower voltages?

I’m trying to figure out how much ESC I need in order to run that motor on 6S or 4S.

Yes. Ohm's law will always apply. It's a law, not a suggestion or possibility

 

[LibertyMKiii]

I play this game alot. I setup my 1/7 hobao vte2 to run 99 mph on 2s and recently hit 124mph on 3s.
Lower voltage will pull more amps for the same given wattage needs, but RC cars its never that simple....

The question is what are you using it for? Low RPMS on a lower KV setup work fine, but only to some extent....
This setup you are looking at seems fine. The 1680kv on 6s would net something like 25-33k rpms which is a very efficient power band for the motors.

 

[dure16]

Using it in a tekno and the truck's transmission ratio is unusually high. The sweet spot for 6S is around 1500kv from a gearing perspective.

 

[Hector_Fisher]

In my opinion, max power rating (and thereby max amperage, related per Ohm's law) is not necessarily a physical limitation but a guidance for how much heat generated the motor can handle within a specific amount of time. Higher amps will cause increased temperatures, but all of this is dependent on the amount of time that amperage is applied. 123amps when applied for 0.01 seconds will not heat up the motor very much. So it stands to reason that an amperage higher than 123 amp when sustain only for a reasonable amount of time should be fine. Same goes for ESC's. There isn't any sensor on the ESC that determines amperage and shuts off the ESC, only thermal protection if temperature rises too high. As long as you can manage heat, the "max amperage" is only a calculated result. I assume this is an MT410. I run the spektrum 4074 2050kv motor (with motor fan) and a 130a motor on 4s and the setup works well. The fan is currently broken on the esc, but temps have not been excessive.

 

[Diem Turner]

In my opinion, max power rating (and thereby max amperage, related per Ohm's law) is not necessarily a physical limitation but a guidance for how much heat generated the motor can handle within a specific amount of time. Higher amps will cause increased temperatures, but all of this is dependent on the amount of time that amperage is applied. 123amps when applied for 0.01 seconds will not heat up the motor very much. So it stands to reason that an amperage higher than 123 amp when sustain only for a reasonable amount of time should be fine. Same goes for ESC's. There isn't any sensor on the ESC that determines amperage and shuts off the ESC, only thermal protection. As long as you can manage heat, the "max amperage" is only a calculated result.

FWIW, Castle ESCs do have an "excessive load" warning. So there is more than just thermal protection.

"The ESC detected very high current spikes. Causes may include damaged wiring leading to, or inside, the motor, the use of too large a motor for the controller, excessive gearing, or improperly soldered motor connections. If multiple Excessive Load errors are detected, beeping will be disabled to protect the ESC. If the error continues, contact Castle Tech Support"

 

[Hector_Fisher]

FWIW, Castle ESCs do have an "excessive load" warning. So there is more than just thermal protection.

"The ESC detected very high current spikes. Causes may include damaged wiring leading to, or inside, the motor, the use of too large a motor for the controller, excessive gearing, or improperly soldered motor connections. If multiple Excessive Load errors are detected, beeping will be disabled to protect the ESC. If the error continues, contact Castle Tech Support"

Interesting.... That's the big draw behind castle esc's for me, the amount of data available. I agree that large current spikes are indicative of something off, like castle states. But I think there are two cases here to explore, high/narrow spikes and peaks in amps vs slightly higher flattened hills. I'm more referring to the latter. If the motor has a 123a limit, and you pull 150a for a few seconds during a hard pull, then take a break for a few minutes to cool down, would that be a problem?

 

[Diem Turner]

Interesting.... That's the big draw behind castle esc's for me, the amount of data available. I agree that large current spikes are indicative of something off, like castle states. But I think there are two cases here to explore, high/narrow spikes and peaks in amps vs slightly higher flattened hills. I'm more referring to the latter. If the motor has a 123a limit, and you pull 150a for a few seconds during a hard pull, then take a break for a few minutes to cool down, would that be a problem?

Short answer, no. That wouldn't be a problem at all. Just to illustrate how meaningful/meaningless the max amp value of a given motor is, look at the actual max amperage my 4080 pulled on 6S in the data log below. It's geared fairly tall at 30/31T:

TP 4080 CM 2022 kv BRUSHLESS MOTOR (UP TO 8s)
WIND: D
KV = 2022
MAX AMPS = 324

Now compare that to amp draw on 4S at 20/46T gearing. Peak RPM was, near as makes no difference, the same:

 

[dure16]

Short answer, no. That wouldn't be a problem at all. Just to illustrate how meaningful/meaningless the max amp value of a given motor is, look at the actual max amperage my 4080 pulled on 6S in the data log below. It's geared fairly tall at 30/31T:

TP 4080 CM 2022 kv BRUSHLESS MOTOR (UP TO 8s)
WIND: D
KV = 2022
MAX AMPS = 324
View attachment 229520

Now compare that to amp draw on 4S at 20/46T gearing. Peak RPM was near as makes no difference, the same:
View attachment 229521

That’s nuts! And it answers my big question here - as suspected, that max amps rating shouldn’t be relied on as an actual maximum.

 

[Diem Turner]

That’s nuts! And it answers my big question here - as suspected, that max amps rating shouldn’t be relied on as an actual maximum.

I think the spec "max amps" is incorrect, or more accurately, incomplete in it's labeling. I think "max continuous amps" would probably be more accurate as to what they mean.

 

[Hector_Fisher]

And that would be "Max Continuous Amps**" with the asterisk. If you increase cooling any amount beyond what the manufacturer used for their testing (which I assume would be passive cooling), then you could arguably be okay with higher sustained amps.

 

[LibertyMKiii]

TP does a pretty good job of saying peak specs for 10 sec duration. Those graphs you can see that spike only occurred for around 0.5 seconds.
The issue would be if you held that amperage for 30 seconds like in the situation of an RC boat. RC cars can almost never hold full throttle for that long with the limitations of the roads, obstacles, and speeds they go.

 

[dure16]

The question is what are you using it for? Low RPMS on a lower KV setup work fine, but only to some extent....
This setup you are looking at seems fine. The 1680kv on 6s would net something like 25-33k rpms which is a very efficient power band for the motors.

That kv range works well to accommodate either 4S or 6S in the MT410 from a gearing perspective. And I like the idea of easily switching 4S/6S with a simple pinion swap.

But would that motor’s RPM be too low on 4S? What problems might that cause?

 

[The Bean]

But would that motor’s RPM be too low on 4S? What problems might that cause?

It has a very low kv, yes. It'd feel sluggish on 4s

 

[dure16]

It has a very low kv, yes. It'd feel sluggish on 4s

Even if I change the pinion for a similar top speed as 6S? I’m trying to understand motor behavior.