Last Friday I had my third attempt of riding the board. After 1 minute of full throttle (in water without foiling) the motor stopped and the ESC began to catch fire. To my setup:
I have a SSS motor with the Seaking 130A and two 6S battery’s in series. The ESC is directly water cooled with lake water. The electric box on top of the board was perfectly dry.
One motor-ESC cable got loose at the bullet connector at ESC side because of the heat as well at the XT90 connector of the series cable adapter. Everything is working (batterys, motor, etc) except of the ESC.
The two reasons why the big fire may occurred:
I used 12 AWG cable (1,5m)
In the propulsion system was a lot of water which get in touch with the motor.
To my question:
to 1) Could it be that the ESC burned because of the too small cables? But if so, wouldn’t react the cables as a fuse and safe the whole system? BTW, I didn’t have a fuse.
to 2) Is it possible that there was a short cut because the motor saw to much water? Or can I run a brushless inrunner like an outrunner under water?
Sorry to hear! “Big fire” doesn’t sounds good. What exactly caught fire? Maybe you can post some pics. You can definitely kill the ESC (likely the MOSFET driver) when you short out the motor phases. The inrunner itself can run wet since the copper winding are isolated. You might have shorted it where you connected the cables. Best use waterproof shrink wrap down there, no plugs. Did you have an amp meter?
I have a similar problem with same motor/esc combo. Was riding today and esc cut out. Then the motor would only cog back and forth. Any idea if this is a fried esc or a bad motor? Was pulling 75 amps around the time this happened using 12s batteries, 8awg wire. Nothing appears to be visually damaged.
@pacificmeister Perhaps we should update on our parts list that we have an ESC, but modified for 8 awg cables? I would hate to see others getting into trouble like this if that were a cause.
We have been running 12 awg wires no problem but will upgrade them for our production version. My initial problems with these issues in the early days were the bullet connectors. The small common 3.5mm bullet connectors are not rated for the current that we are using so they end up acting as resistors. The male section gets hot, looses it’s coating and shrinks and it gets worse until solder starts melting and things get very hot. We have only ever used a much more powerful 300amp ESC so no experience with ESC fires. I know @pacificmeister has been using the Sea King OK? I have shorted esc’s before from the phase wires touching. Also think about your battery capacity. You need enough capacity in parallel to share the current across the cells. The bigger the battery the less issues you will have with battery heat. I think the only viable long term solution is moving to 18650 cells with a BMS, but BMS that can handle the current is hard to find (or impossible?) so likely needs to be custom.
The fire was at the motor-phase-side of the ESC. Luckily the batterys and motor survived.
I thing Pacificmeister is right that I shorted the phases inside the motorhousing at the bullet connections which were not secured against water…
To prevent water next time I print a adapter with a 1/4" thread with a festo coupling which is connected to a ball pump. I put the motorhousing under water and but positiv pressure on it. The bubbles should show me the leakages.
We have also been riding with long 12 awg to the motor without any issues. We soldered everything (no bullet connectors). We got 5.5mm bullets that are rated for 150A now, so should work I suppose.
I guess, those poor tiny Fets in the ESC just burned up cracking and spitting plasma as normal response to overheating and to high current, wonder they resisted repeated hammering with loaded startup current. Topology and packaging of those ESC does not allow any reasonable cooling due to lack of thermal mass and thermal path. They are extremely overrated in their current handling and usually have no protection mechanism against over current, like phase current limiting nor even parallel Fet current sharing or any advanced control algorithm. It is a good practice to at least divide the sticker rating of ESC by 2 and use it as maximum value for phase current. Then choose load value accordingly and you should have not reliable but at least mediocre system.
In short, if you need 150A, seek for 300A sticker.
I opened up today the ESC and some MOSFETs were burnt and cracked. But the cooling mechanism looks -for my understanding- pretty forward. I will post a picture tomorrow.
@ tylerclark You mentioned you modified the SeaKing 130A HV ESC to 8AWG. Did you desolder the stock 12AWG wires off the board, solder on 8AWG and then re-pot the cables?
I’ll let @jclark chime in here, but we weren’t able to modify it down to the board. So instead we cut the wires down as much as possible and use bullet connectors to then switch to the 8AWG. If I see someone who has successfully done it, maybe we’ll do it too. Just seemed too risky.
We dissassembled the seaking and changed the wires. Not worth the trouble!! nearly killed the esc, but It works now (can’t get contact with the program card for some reason tho).
Better to take the wires down. Altho you might damage it by soldering close to the esc due to excessive heat from the solder.
