I decided to pop this out of my build thread, to get more traffic. I'm considering the Mtroniks brushless WATERPROOF 30Amp esc. Here is an excerpt from my discussions with mtroniks..... JS> So if the current is LIMITED to 30amps, and the motor "requests" more.... What happens? Does the motor will just slow down? Or will it just suddenly stop? What happens if the prop is fouled? The current demand from the motor will spike... What will the esc do then? Mtroniks> The controller will hold drop the power back to just below 30Amps, it won’t just stop. the prop is fouled the controller will do the same. Mtroniks>There is no need for a fuse although you can never have enough protection! We do advise fitting a fuse as a backup but this is up to you! Mtroniks>It will run at 30amp continuously or until it reaches its thermal cut off protection. Mtroniks>The Hydra 30 brushless ESC has instant reverse and symmetrical power in each direction. Mtroniks>You can use any sensorless brushless motor and prop combination So... I'll be able to apply a 30 AMP load to my motor without worrying about burning out the ESC, or popping a fuse!!!! That alone is the reason I'm shifting to brushless... Never saw a brushed solution capable of this.
the internal thermal cutoffs are dubious at best. If mtronics is current limiting via thermal means, there will be a transient time where the current will be too high prior to the thermal limit activating. this time is short to us, but long to electronic circuits, typically, and I would not trust it to protect the ESC. (not that a slow blow fuse would necessarily be any better, mind you. Fast blow would be). The only way to be certain would be to know very detailed design specifics on the components that would fail first due to over-current and compare the transient time to failure at various overcurrents to the time it takes to activate the thermal overcurrent. If they directly measure the current, however, or are suitably derated such that the components will hold a decently higher current than the current the thermal overcurrent circut detects, it would possibly be suitable. All of these hinge on the details of the design
I think you are reading it wrong, he is saying it will limit current at 30amps indefinately.... Or until the thing gets too hot, in which case it'll shut off. So my guess is if submurged, it wouldn't cut off... It'd just stay @ 30amps ouput. Unless the heatsink is quite lossy; such that the component is significantly hotter than it's sink. Just switch your fets such that the ave voltage is what is needed for 30amps@ given resistance.
We will see when you get one . Think transient. Think fast rate of change with time. The issue with a thermal switch or thermal limiting is the time lag between an overcurrent situation and when the temperature rises enough to cause the current limiting circuitry to work. If you have a large enough spike current that spikes quickly enough, you will cook components before the temperature rise will be sufficient to activate the limiting circuitry. Without considering detailed designs, it is impossible to know what the value and time scale for that current will be, but if they use thermal detection means, there will be a current/time spike (possibly not physically realistic, if sufficiently over-designed) that will kill it without engaging the limit. the issue with the "resistance" is that the resistance is not a fixed value, and changes with motor load & speed due to the interaction with the magnetic field produced by the rotor. If you were to limit the voltage supplied so that you could never exceed 30A even with a stalled motor, you would never go anywhere, as the resistance has to decrease with increasing load, as the current is ~a minimum while the motor is free spinning with little load.
That being said, I don't usually run fusing/breakering (although I think I probably should) I tend to oversize controllers such that I don't think there is any real way to cook them (but I have been wrong on the cook them account, particularly with bec's in the past).
Again, you are assuming the circuitry is current sensing based on heat. I'm assuming they have a .00000000001ohm resister on the +terminal and are measuring the voltage drop.... therefore, making current sensing simple math. >If you were to limit the voltage supplied so that you could never exceed 30A even with a stalled motor, you would never go anywhere, as the resistance has to decrease with increasing load, as the current is ~a minimum while the motor is free spinning with little load. Sure, but it is obviously a switching ESC... which means there is a micro controller in there. You check current (see above) at a frequency of a hundred microsecond or so, and the system should be pleasantly protected. ---> Admittedly, I don't know their designs... but to make the promises they are advertising acutally work, heat sensing is probably the worst way possible for detecting current. It is a good way of, well, detecting failure due to heat.
I could have sworn they said thermal in one of the emails. I would be immensly curious at what they are actually measuring and how. I am very curious what they are actually doing, particularly if they have gone away from the "thermal" approach. Let me know if you find out.
They said: "It will run at 30amp continuously or until it reaches its thermal cut off protection." At least it has a 2 year warranty... or something like that. Unfortunately, that puts me back in the boat I'm in now.
Yep. I shot them an email asking some techical questions. If it actively current limits, as implied, that would be a wonderful feature.
From mtroniks: The Viper Marine range of controllers work with an absolute current limit system. What I mean by that is as soon as the motor tries to pull more than the stated current limit of the controller it will limit the current to that controllers stated limit. So, for example, a 25Amp controller will allow no more than 25Amps ever, under any condition. The current limit on the controllers watches the actual current that the motor is pulling from the battery pack through the controller. Each controller will happily sit on its current limit indefinitely. The controllers also have a thermal cut off so if the unit is stuck in weeds and the customer doesn’t let of the throttle (?) the controller would sit in current limit until it shut down safely due to the thermal cut off. This method of current limiting also detects spikes as soon as they occur so the customer has nothing to worry about.
It sounds like the ones for brushed motors do the same. That is good to know and must be a newer feature they designed after the old models kept burning out. I still have a fuse as recommended by their instructions but now can rest a bit easier.
If this is true then why to so many of these units burn out? I heard of another one that died over the weekend.
That's a very good point. I just emailed him (again) asking if this is true for the brushed versions, if its a new change, and if it is... how do we identify if an ESC has or does not have this feature.
Mtroniks: The brushed versions have the same current limit detection system, they are 100% safe in a stalled motor. We sell 1000’s of the brushed marine controller monthly here in the UK. They are the No1 marine controller in most of Europe because of this. My reply: Then why did mine burn up? More over, as a community we've lost many mtroniks escs to a stalled prop.
Now, I have to admit; my esc did put up quite a fight before it con-k-d out. I'm sure I was running it for quite a while with a dieing motor (without realizing it). My memories: I could tell something was wrong with my boat for a few minutes; as it was slowing down. I figured the motor was overheating; so I put a water on it. The water immediately steamed. I decided I just had a hot motor, and put more water into the boat and sent it back out from port. I could see the steam as the water sloshed around in the boat. A few minutes later, the type of steam changed color... it became 'darker'. I decided I probably had a problem, and I should bring her back in. She made it back to port and I pulled off the SS. Everything looked normal and the steam was coming from the motor; so I figured (incorrectly) that as the water was pretty mucky... it was probably just water or something in the water burning off. I decided to shut it off and wait for a little. A few minutes later, I switched it back on... because I wanted to know if I had a heat problem or if the motor was giving out. Everything looked OK; so I sent her out. 3 feet from me I saw some sparks and heavier smoke. I jumped into the water and cut power. I took her back to short and decided (I don't know why) to see what exactly had happened. Was the ESC OK? Was it just the motor? The motor immediately went into fireball mode, flames, sparks, the whole deal... And to my horrified eyes, a small but potent spark flew 4 inches from the side of my poor esc. It was like a small private sad fireworks show. I pulled the motor apart back @ my bench, one winding's protective coating had completely melted off and the winding itself had burst and grounded against the casing. So my best guess is the 'dark smoke' I saw was the protective coating vacating. And the fireworks was probably the winding giving way. This is admittedly probably a worst case scenario from the ESC's perspective. But the ESC did make it through the first motor failure mode, which was probably 45 seconds total. I'm starting to believe the ESC really gave out because the motor was destroyed @ startup & the ESC didn't have the chance to boot completely.
