Max amps: is it dependent on how many cells?

[SrC]

The lower the voltage, the higher the amp draw is. If you’re borderline, then 4s would be the way to go if you can. 3s, all other factors being equal, will draw more current than 4s.

+!

The motor is in the lead; it pulls whatever amps it needs (Watt=amps x volts) from the esc, which in turn pulls them from the lipo’s. A 150a esc doesn’t limit that at 150a, the 150a is an indication of what it ‘safely’ can deliver for a certain amount of time.
If your lipo’s can’t deliver the amount of amps the motor is asking for, your lipo’s will go bad (puffing). If your lipo’s can deliver the amps, but it’s above the esc specs, your esc will overheat and either go on thermal shutdown or burns down .
Based on the motor power specs (Watts) you can calculate, based on on how many volts you will be running the car (3s, 4s etc.), an indication of the esc amp specs you should be looking for.

+!
Proper Gearing is always part of this equation.

 

[jkflow]

Would running 3s have lower max amps than 4s? Seems like that would be ok but not sure.

Back to OP and I stand by my statements, use a logging ESC and you will see I'm right.
3S will use fewer amps vs the 4S, if nothing else changes.

 

[LibertyMKiii]

To go a certain speed you need a certain amount of power. In our cars that power is watts of electricity

Simple math here.... Lets say for example you need 2000 watts to reach the speed you want.

3s example:
11.1v * amps = 2000 watts (amps = 180)

4s Example:
14.8v * amps = 2000 watts (amps = 135)

 

[Dan B.]

Back to OP and I stand by my statements, use a logging ESC and you will see I'm right.
3S will use fewer amps vs the 4S, if nothing else changes.

Ain‘t buying it. Prove it.

 

[jkflow]

Ain‘t buying it. Prove it.

Prove your statement instead

I would, but I do not have logging ESC's on my cars.
If you have one, just run a 4S followed by a 6S on your car, change nothing else and current will be lower on 4S, if not I'll buy myself a beer and call it a day

I will be able to try it on my boats next week, patience, can't do it until Saturday.

 

[Dan B.]

Prove your statement instead

I would, but I do not have logging ESC's on my cars.
If you have one, just run a 4S followed by a 6S on your car, change nothing else and current will be lower on 4S, if not I'll buy myself a beer and call it a day

I will be able to try it on my boats next week, patience, can't do it until Saturday.

You might as well just go buy yourself a beer without further ado. I don’t know squat about RC boats, but the physics are the same. You’ll pull less amps with higher voltage.

 

[Hector_Fisher]

Prove your statement instead

I would, but I do not have logging ESC's on my cars.
If you have one, just run a 4S followed by a 6S on your car, change nothing else and current will be lower on 4S, if not I'll buy myself a beer and call it a day

I will be able to try it on my boats next week, patience, can't do it until Saturday.

Still, the problem is the matter of loading. Unless all things can be controlled as the same, then your demanded load could change between the two situations.

If your truck is geared for 50mph on 4s, and you then pop in a 6s lipo, you've "effectively" geared for 75mph. If you are unable to match your typical throttle inputs exactly the same as on 4s, then you can't expect valid results. Odds are that for the majority of cases, you will not be able to use all XX% of the extra speed (~50% in this case). So by using less throttle, you would likely skew the results.

Though for speed running, you could theoretically hold all else the same. Full throttle is full throttle. However, I don't think that speed running is representative of typical RC loading. And especially in this case considering OP is using a max10 sct.

 

[Dan B.]

Still, the problem is the matter of loading. Unless all things can be controlled as the same, then your demanded load could change between the two situations.

If your truck is geared for 50mph on 4s, and you then pop in a 6s lipo, you've "effectively" geared for 75mph. If you are unable to match your typical throttle inputs exactly the same as on 4s, then you can't expect valid results. Odds are that for the majority of cases, you will not be able to use all XX% of the extra speed (~50% in this case). So by using less throttle, you would likely skew the results.

Though for speed running, you could theoretically hold all else the same. Full throttle is full throttle. However, I don't think that speed running is representative of typical RC loading. And especially in this case considering OP is using a max10 sct.

All else being the same, higher voltage=fewer amps.

 

[jkflow]

Doesn't someone have a Kraton or rig with a castle and can run 3S vs 6S? or 3S/ 4S and post logs?

With all else being the same, with @Dan B. logic the 3S would be overloaded with ~ 300A vs 6S ~150A (typical stock)
With my logic, you will get half the speed and lot less power = less current.

Note:
Boats are actually bad example after thinking about it, with less speed there will be more drag, i.e. not the same, different with cars. I'll still try if it hasn't been settled.

 

[Hector_Fisher]

All else being the same, higher voltage=fewer amps.

But that's what I'm trying to say. Except for simple cases, something like speed running, it's easier said than done to keep all things the same.

For example, my MT410 runs MMX. I could pull the data logs. The only problem is that I could hit full throttle all day long on 4s. I can't go near full throttle with a 6s pack. 1) I can't lay down the power fast enough. 2) it's genuinely just too fast.

When I compensate by easing up on the throttle, then I'm not keeping all things the same. Which is why I believe speed running might be the only relevant example here.

 

[Dan B.]

Doesn't someone have a Kraton or rig with a castle and can run 3S vs 6S? or 3S/ 4S and post logs?

With all else being the same, with @Dan B. logic the 3S would be overloaded with ~ 300A vs 6S ~150A (typical stock)
With my logic, you will get half the speed and lot less power = less current.

Note:
Boats are actually bad example after thinking about it, with less speed there will be more drag, i.e. not the same, different with cars. I'll still try if it hasn't been settled.

No, that ain’t what I said. Not talking speed, RPM’s, UFO’s, ESC’s, or WTF’s. All I’m saying is, run a truck balls out on 3s. Then run the same truck balls out on 4s. The 4s will pull less amps.

 

[dure16]

Alright y'all, I decided to bring my Talion along for a speed run to test out this theory.

All three speed runs were on a long, smooth road with full throttle held for a long time. I was surprised to see current decrease from 3S to 4S, but then increase from 4S to 6S.


Talion V4
Castle MMX6S ESC
Tekin 4274 1550kv motor
Method belted mojave tires
22/50 gearing (static for all runs)
Zeee batteries for all three speed runs

3S Speed Run
Max current: 53.8 amps
Max power: 631 watts
Max speed: 29 mph

4S Speed Run
Max current: 47.5 amps
Max power: 742 watts
Max speed: 38 mph

6s Speed Run
Max current: 76.3 amps
Max power: 1788 watts
Max speed: 56 mph

6S Bash (just for kicks)
Max current: 172.5 amps
Max power: 3370 watts

 

[jkflow]

Very interesting and I owe @Dan B. a beer.
On original question is 3S lower than 4S - NO! it's higher

My logic kicks in after that, there must be something going on I haven't taken into account.

 

[Dan B.]

Very interesting and I owe @Dan B. a beer.
On original question is 3S lower than 4S - NO! it's higher

My logic kicks in after that, there must be something going on I haven't taken into account.

You were just mistaken.
Amps=watts/volts
So in any application the lower volts will result in higher amps based on the same amount of watts to the motor.
So, just to use arbitrary numbers, 11.3v (3s) running a 1000w motor will result in 88.5 amps.
14.8v (4s) running a 1000w motor will result in 67.6 amps.

My logic kicks in after that, there must be something going on I haven't taken into account.

I guess it’s possible that if one were to see higher amps on 4s vs 3s then something (a super crappy or very low C-rated battery under very heavy load for example) was causing voltage sag to the point where the 4s dropped the voltage to below even what the 3s was running.

 

[parcou]

Wow!!

Although lost in all this, I will read this about 5x times so I can somewhat understand. I still do not understand AMPS. I had this same question when I flipped my stock Talion EXB over to an XL

Batteries: 2x 3S ChinaHobby 5200 90C

Stock Spectrum 150A ESC
2050kv stock motor
15T pinion

Then I flipped it to:
Max6 ESC
Hobbystar 4082 2000kv motor
17T pinon

I can figure out RPM and on paper to get my speeds, but I cannot determine how you figure out AMP to the ESC. It's a safe motor others use and a safe ESC over the crapy 150A stock, but how do I calculate AMPs I am putting it under with the change in pinion?

It's fast bashing, and temps are low I can measure, but that does not tell me AMPs

 

[dure16]

My logic kicks in after that, there must be something going on I haven't taken into account.

Yeah I’m completely lost on why amps went down from 3S to 4S, and then up from 4S to 6S.

 

[Jerold]

I think "Watt" you are seeing is the effect of the gearing. The tops speed is pretty linear, but is mostly unrelated to the max current unless you have something that regulates/limits the current real time.

For instance you burn 2x the watts bashing as you did speed running. So unless your max current is at the final plateau before you brake it's throttle control creating max current.

The Amps 4S dip is interesting and probably because that gearing works better with that motor ESC combo. I need to ponder this more.

The Watts makes sense because Power (W) = Voltage (V) * Current (A). The only thing you really can change there is amps, with your throttle control. Yes the battery voltage droops to, but that it relative to your load requirements and a bunch of stuff you can't control.

Your MPH/Amp is much better with 4S, it's is the best choice for speed runs with the current gearing. 6s gets you more speed but it's a big hammer approach to getting speed.

You might try some different pinions and see what you get. The 6S run may not have reach full RPM yet?

 

[parcou]

At least I am not lost alone....just deeper in the woods

 

[Garcbomber]

Pretty easy calculation

 

[Jerold]

I think the math is straight up but I think the concept is lost. These are Si Units and you can see the ugly math on Wikipedia if you like, but this is the one liner.

Voltage is the amount of potential something has. Like a bucket pouring water in to a pipe. The higher the bucket the more potential it has.
Current is like the size of the pipe. If you have a giant pipe it will drain the potential quickly.
Power is just multiplying the two. Says how much power can you have from your bucket and pipe.

High potential with skinny pipe is the same as low potential with fat pipe. How much water can you get down there at one time?

So
5V*1A is 5W
5V*.5A is 2.5W
10V*.05A is 5W

So you can have higher voltage and lower current, which is generally more efficient.

You can take power and dice it up and compare it to other things like MPH or RPM to optimize what you want

It's a bizarre thing, I know.