Electric Surf Board

srn said:
I dont understand the issue with cable length. I understand that long cables have high resistance, but how about the current peaks at long cables from battery to controller ? Can someone explain this ? And is it really better to have longer cable from controller to motor than from battery to ESC ?

Thank you for further explanation and best regards,

Soeren

Yes, the longer the battery wires the higher the resistance, but thats not the problem. The problem is the inductance.
The Mosfet's can be seen as a switch that turns on and off very quick.
Lets say one bank of FET's is in on stage and 200A are flowing into the motor at 60V.
At the moment when this bank of FET's turns off (and another bank turns on eg), there will occur voltage spikes which can be much higher as the battery voltage itself.
The higher the inductance of the battery wires incl. the bus bars in the controller, and the higher the motor current (which will be always abruptly interrupted by the FET's), the higher the voltage spikes will be.

The caps are now there to smooth out those spikes keeping them below a level which would be dangerous for other electronic components.
If you now have very long battery wires, the caps have lots of work (current ripple) and they can get hot and swell.
If the caps (partial)fail, the voltage spikes will kill the FET's.

Longer motor wires are absolutley no problem assuming the cross section is large enough so they can handle the amps :wink:
Twisting the battery wires or put them as close as possible beside each other helps to reduce the inductance in the supply line.
 
Nice simple answer to a complex question.

Much more useful than a complex answer to a simple question.
.
.

Complex vs Polar.png

When we learned it in trade school it started out as cranking out conversions between polar and complex notation on fairly complicated LRC circuits. All those omegas and Zsubs scare most people off.

In trying to teach a 5yo (by starting off teaching my CPA) I focus first on believing/understanding the most basic Boost Circuit, then by completely understanding

T = 0 and
T = Steady State

First for caps and then for inductors

At some point it clicks for many people, but to expect a higher order concept to click on top of minimal mathematical foundation begs for faith instead of confidence... and I dont support faith based conclusions... so I dig deeper and deeper back into simple proofs backed by experiment.

I would ask - what is the ratio of the inductance of the System Configuration A vs the inductance of system configuration B, by isolating the motor and measuring, isolating the wiring and measuring. Then we can prove it without any trust involved.

-methods
 
ahhh... lost my response.
the punch line:

If you stack out capacitance at the load input it will eliminate the root cause of the inrush currents flowing thru the parasitic inductance in the long cabling by - effectively filtering the high frequency content and leaving only nice slow content running down your long cable.

The byproduct of this seemingly perfect fix (which will allow you to run a mile of DC power cable) is that Inrush at T=0 will become nasty - so you have to deal with that by adding additional R

(where did my damn first response go... arg...)

So as the poster said - you can navigate any issues you find by:

Adding L
Removing L

Adding C
Removing C

Adding R
Removing R

Or using active circuitry that changes thru time.

There are no works or does not work - only different ways to make what you want work.
(and lots of rules of thumb)

-methods
 
madin88 said:
fabianpusch said:
Hi & good morning

Longtime full load is about 240 Amps for 5 seconds.
Not too much - I think the problem will be the cable lengths from the battery to the controller.
There are indication high internal peak currents (about 600Amps) and this is too much for the caps.
Install the controller as close as possible to the battery and twist the wires. This will reduce the inductance and lower the stress on the capacitors (less voltage and current ripple). Long motor wires are not a problem, more the opposite, but long battery wires are!
Maximum temperature was about 105°C of the ESC, I think the problem ist that I have used some speeds of 70% - and that is not too good fort the FETs.
At the moment I am waiting for an answer of MGM if I can go on or have to stop testing...
105°C is quite high for a controller and the caps don't like this as well.
Speeds of 70% should be no problem if it has the so called "active freewheeling".
Only the very first or cheapest BLDC controllers don't have this.

From the specs the MGM controllers are not impressive.
They have no FOC control or other new stuff which you would expect in view of the high price.

Kontronik Kosmik ESCs for instance have FOC control with current measurement on each phase and outstanding efficiency, but unfortunately the largest model can only do 14s max and 200A. Otherwise i would suggest to try out a kosmik.

What about these Flier ESCs?
This one seems crazy to me
http://www.fliermodel.com/en/prc-show.asp?id=684
22S and 800A are still 31kW if we divide the specs in half

Or this one
https://www.ebay.es/itm/400A-Boat-ESC-Waterproof-16S-Flier-USB-for-electric-jetsurf-hydrofoil-sss-motor/262586955187?hash=item3d2366f5b3:g:FRcAAOSwzJhZ0Rgt
Is still 11kW with the same specs halved
 
bigbore said:
What about these Flier ESCs?
This one seems crazy to me
http://www.fliermodel.com/en/prc-show.asp?id=684
22S and 800A are still 31kW if we divide the specs in half

Or this one
https://www.ebay.es/itm/400A-Boat-ESC-W ... SwzJhZ0Rgt
Is still 11kW with the same specs halved
I think, Luke tried 22s 400A ESC from alien and it could hold 50A and 100A for few seconds before plasma, spinning propeller and it was called an outstanding performance for ESC at the end.
Maybe better divide by 8 ?

EDIT:
P.S. Finally found the tread, it was "24s 420A" ESC, here is the result of this long story: https://endless-sphere.com/forums/viewtopic.php?f=2&t=44897&start=650#p1236920
 
Hello,

my board is finally running (atm only dry for testing).
Now I am thinking about cooling. I have the watercooled Torqstar 3 and the watercooled MGM 40063.

How do you get cool water into your Motor and ESC ? Do you use external water or maybe a closed internal water circle with pump ?
 
bigbore said:
The water is generally drawn through the outlet nozzle with a radial outlet

How about salt water, sand and dirt ? Anyone who had problems with direct cooling from nozzle water ?
 
srn said:
bigbore said:
The water is generally drawn through the outlet nozzle with a radial outlet

How about salt water, sand and dirt ? Anyone who had problems with direct cooling from nozzle water ?

If you have sand or dirt sucked in the jet drive you will have bad problems with impeller far prior of cooling problems. I saw a Lampuga Boost stopped by a fisherman's line with a consequent replacement of both the stator and impeller.
 
Hi Srn.

I would do it like in the image I attached you. For the dirt I would put a tank filter like the one used in nitro rc cars.

link: https://www.ebay.de/itm/L11517-1-5-Mas-Rc-Nitro-Lokomotive-Kleiner-Inline-Legierung-Fett-Benzin-Filter/332728893087?hash=item4d782ffe9f:g:JPwAAOSw5cNYXTti

For the salt water: just clean after every use your cooling system by puming clean tab water in it.
 
In my board I have started to use the water going out from the nozzle/delivered by the jet.
But after a run there is a lot of heat remaining in the whole system.
So my next improvement will be an update with an additional cooling pump, a filter and a reed switch to switch on or off.
The f***ing heat is really a problem.
For a first step use a water bottle (PET), add a hole and put in a tube which fits into the outlet of the water.
So you have eliminated both together, the post cooling and the fresh water flushing of the system 🤪
 
Hi Fabian. Can you add some pictures of that bottle system? I kinda didn't understand what you men with that. :oops: :p
 
Hello guys,
here some updates of my project:

Today I made first water tests in a small pool (after fixing all sealing issues last days).
It worked very well, also the water cooling, which I made according to Frizzo's suggestion.

IMG_3577.JPG

Here two log files of my controller. The peak current looks high, while the max power of 1,5kw at 6000rpm is quite moderate I think.

Controller 2 history 2018-08-07 21-33-45.jpg
Controller 2 history 2018-08-07 21-34-03.jpg

Tomorrow I will slowly increase the speed and check power consumption and efficiency.
 
The graphs are definetely not good.
What about the voltage of the battery.
Normally I have 450/500 peaks when the engine ist running on 250A.
And the peaks are occuring only at the acceleration phase...please drive a ramp.
From 0-25-50-100 throttle Input.
 
Hello Fabian,

do you know why this peaks can occur ? You see on following graph, that the average input current is 10 - 20 A.
Peak current is at motor side, maybe I have too fast acceleration ? I will reduce it and try again.

 
If motor current is larger as the battery current by such a big factor (10A battery and 100A phase around 50s) than it's normally a sign of overload.
Is the size of the propeller correct and what about the motor kV? If you would use a motor with way too high kV it could look similar..
 
The Impeller should be too small (60mm) for the Lehner Torqstar 7050 275kV.

I found that there was high tension on the shaft. Will adjust it again and do another try.
 
Srn, I have a question about the torqstar. Did you remove the anodized purple color? Do you have a picture of it with the acrylic shield off? Thanks!

I have the same combo coming, torqstar 1 with the 60023 so very interested in seeing how you get your setup working without the peaks.

—Michael
 
Hello Mgivens,
my motor looked already like this when i got it. I also wondered, because i expected black-purple. Dont know but i dont need color on it.

 
Thank you. That is strange that it is silver. Did you order directly from Lehner? The back looks different too, wonder if the design has changed...
 
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