Flipsky 75200 - Same Amp Setting Required After Increasing Voltage - 8s to 14s

Build, Repair & Mod
1

I changed my batteries from two 8s in parallel for 8s to one 8s and one 6s in series for 14s.

In VESC Tool (VT) I reduced the motor amp limit for the same watts from 70 to 40, but I had reduced max power from before.

I then changed the motor max back to 70 amp and the throttle power was exactly the same as when I had 8s, but now on 14s.

I did a run of just over 4 km and the batteries were at the value expected at just under 60% each.

So full throttle is actually providing 40 amp, but the setting in VT is 70 amp, and based on battery use there is no lost power anywhere.

No other settings were changed, and I thought the BMS in the 8s battery was the problem, but wired it so it wasn’t.

Any ideas.

2

I am no expert, but what exactly is your issue?

If the prop does reach full ERPM with 40A current, it will not go any higher.

3

Good point, that it works.

My issue is that there is something not right that I hope is not going to cause me problems in the future.

But you are right, many people here have problems and something that doesn’t work, and my board works great.

4

That is what I was asking.

What do you expect to behave differently?

The AMP settings are a maximum limit. If the maximum RPM is reached without reaching the AMP limit, the AMPs will not go any higher.

That is exactly as expected.

5

The erpm limit is not restring the power.

The throttle range is performing the same as before, but with a voltage increase.

Anyway, it doesn’t matter now my ESC has died.

6

You always need to consider the input (battery) and output (motor) side of a ESC or vesc separately.
On motor side: current=torque, voltage=Max speed
No matter what you do on the battery side, the torque you need to get started is only dependent on the prop you have and the resistance the eFoil has in the water. If you lower your current it’s like trying to get going in a car in 4th gear. Sure you now have the voltage (top speed) raised, but you will never reach that speed with little torque.

On battery side, for same output (motor) power, the voltage influences the current like you expected. So even though the motor / output is still drawing the same current, the battery will now see less current at higher voltage.

If you want to lower motor current wou will have to change the Motor to a motor with less kV or use a propeller with less pitch. Or just accept the 70A and be happy that at least your battery now uses less current.

7

Thanks for the response and explanation, I don’t think the situation is clear, for me at least.

The motor is not using the amps set in the ESC, based on speed, battery use and increased voltage.

I would expect that if you have 8s with 70 amp motor limit, then only increase the voltage from the battery to 14s, the response from the throttle range on the remote would increase 14/8 or 1.75 times more power, or watts through the motor.

However I have the exact same speed range from my remote throttle range with 8s and 14s with the same ESC motor amp setting of 70 amp.

8

In your case the current seems to be your limiting factor, even before Max. Voltage limits your rpm. So if you limit to 70A, no matter what battery you attach, the remote throttle range will always be 0 to 70A. And if at 70A you don’t reach the max rpm for 8S, you also won’t reach it for 14s.
2 options: increase current or use a propeller with less pitch
The lower pitch propeller will take less torque (current) at same rpm or will have a higher rpm at same torque (current).

Again, a Ferrari with 800hp will never come up to speed if you only use the 5th gear. You need to shift down to have more torque, and later the 800hp come into play for top speed
(In this analogy gear/torque= current, horsepower= battery voltage)
In case you have a way to log/monitor data (Bluetooth module or metr/voyage system module) upload some log here so we can further investigate

1 Like
9

The values in the VESC tool are simply limit values to protect your motor and battery.

If changing the limits does not affect the result, then you are not hitting those limit values.
Either because you have another limit somewhere or your hardware does not allow it.

I.e. if you set battery limit to 100A and your battery can only provide, 80A, changing that limit to 150A would not alter the result.
Or if you limit motor current, but your wires can not actually handle that phase current due to wire size or connection problems, changing that limit will not do anything.

10

There is some limit somewhere I can’t find, and everything else is at 100 amp. It isn’t a limit as such, but more of a multiplier, 40 amp range of performance, but with a setting of 70 amps for 14s.

It just seems strange, same performance, but higher volts and same motor amp limit.

There was a slight performance improvement as expected with higher volts.

I will see what happens when I use a new ESC.

11

What kind of battery are you using?

12

FD Assist plus 8s 12.6 ah and Turnigy 6s 12 ah in series.

The FD has a BMS so it is wired negative to load. I had it the other way around but didn’t make a difference.

I was previously running two FD batteries in parallel.

13

Is that a special model?
On the hobbyking website the highest 12ah 6s batteries go is 15C discharge.
With peak discharge of 30a.

That would surely not provide 70a to your system.

And while I am no expert there either, I find it pretty unlikely mixing lipos and li-ion cells is a good idea.

14

Correct, it doesn’t provide 70amp, that is the point of this post, it is providing 40 amp max which is 3.33 C, being a 12C battery capable of 144 amps.

If it was providing 70 amp, most of my time is on half throttle and my battery range would be just over half of before.

It is as if my motor max changed to watts instead, but in amps. Maybe I’m wrong on how to configure an ESC.

Again, I increased volts, but amp setting is the same, performance the same, battery use the same.

15

Yes, sorry for the non-sense.
Battery should be ok, I guess.

Would have been the easy explanation for your issue though.

A VESC log should help.

16

I tried to use my phone to look at real time but Bluetooth kept disconnecting, it worked before, and then the ESC died most likely from some water that got in the useless box…

Not happy at the moment and should delete this post.

A new ESC and the VESC Tool setup should solve this issue.

Thanks for the reply.

17

To close off another post, it was my mistake.

Due to how motors work, they need current, and the motor amp limit setting is not impacted by battery voltage.

It didn’t make sense to me, but ChatGpt explained how the ESC controls voltage for current and torque.

I incorrectly assumed a motor was like a battery with matched volts and amps, and then realised it was obvious as I forgot about how magnetic fields work.

Change the battery voltage, same motor amps for similar performance.

I’m slowly learning.

1 Like
18

May I ask how ChatGPT explained this in a good way?
I also tried to explain this concept in my replies above but apparently I failed in making it easy to understand :smiley:

1 Like
19

Your reply implied that I had limits, needed to change things, not that it was normal.

In answer to why I didn’t need to change anything after increasing volts from ChatGpt:

"So Why Performance Feels the Same at Same Motor Amps:

Motor torque is almost entirely a function of motor current, not voltage.

As long as the motor sees the same current, it produces the same torque, regardless of how high the battery voltage is.

You’re seeing identical motor-side electrical conditions, just sourced more efficiently from a higher-voltage battery."

I asked for a calculation to demonstrate this with the difference of motor and battery current when I start to get on foil, and when on foil at just under half throttle.

Take off is motor 80 amp, battery 40 amp, cruise on foil is 35 amp motor and 30 amp battery.

20

(post deleted by author)