What causes an ESC to fry if batts are left connected?

[BrianG]

I know you aren't supposed to ever leave your batteries connected to the ESC, but I've seen several instances where someone has accidentally left their batteries connected and eventually the ESC fries when it's just sitting there (switch is off). What would cause this?

[magman]

would it be that the switch on or off still allows a small amount of constant current through and being left on for an extended period wear circuits out causing them to fail leading to a meltdown?

[BrianG]

Maybe. The quiescent current being drawn has to be pretty small; I would assume under 0.5A. Even at 6s, that's around 12w (assuming 0.5A), and the heatsink/PCB should be able to handle that kind of thermal load. With the switch "on", the fan should auto kick on if the ESC got too hot.

The only way I can think of for the ESC to overheat in this situation would be if the switch is "off" (where the fan can't come on), but again, I would guess the HS should be able to handle it. Again, I am assuming a ~0.5A quiescent current draw - it could be higher or lower which would make a difference.

And, even if the HS did get hot, I would think that as temps climb, there would be a point where the rate of dissipation exceeds the rate of heat (due to differential between HS temp and ambient temp), and that temp point would be under the catastrophic failure threshold?

[Semi Pro]

brian brian brian

we all know esc's have certain level of black smoke in them, as you use them for hours and hours the smoke slowly escapes and often goes unnoticed until it all runs out or it escapes in a rapid dramatic fashion. if the battery is left plugged in the smoke keeps escaping the whole time until the battery dies, this usually causes the esc to become depressed and it will often, in a very emo fashion, go off and die quietly in a corner some ware by it's self due to lack of attention, love or what ever it is emo's are always crying about.



case closed, the end

[snellemin]

Such Wisdom Semi.

[hemiblas]

I cant help with why, but I had this happen with one of the original novak brushless controllers that came out for the SS series motors. That was a long time ago.

[hashemio]

The small amount of current that flows to the ESC probably either makes something too hot or maybe shorts something out.

[BrianG]

So, no word from Castle on this? We can all speculate, but it would be nice to get an expert's point of view...

As said, it's not just a Castle issue, but something that can happen to various ESCs.

[Pdelcast]

Originally Posted by BrianG

So, no word from Castle on this? We can all speculate, but it would be nice to get an expert's point of view...

As said, it's not just a Castle issue, but something that can happen to various ESCs.

Honestly Brian -- I don't know. We test our ESCs all the way down to 0V, and I've personally never heard (before this) of an ESC failing when left connected to a battery.

[BrianG]

Thanks for chiming in Patrick.

Now that I think about it, I think I have it happen to me too with a MMMv1. But since it was a V1 (and modified to remove the BEC because of the issues back then), I'm not sure what the actual cause was. All I know I was running around at the LHS. Someone came over to chat, so I just let it sit, and about 5 minutes later it started smoking. Batts were fine and still plenty charged.

Like I said, the only thing I can think of is if the ESC is drawing enough quiescent current that at higher voltages, the resulting power loss is too much for the heatsink and it just overheats until poof. But I think that's reaching.

I'd like to experiment with this a bit more, but don't have the disposable cash to replace ESCs if/when the fry.