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I’m trying to build an elecyronic speed control (ESC) for a boat that requires a massive amount of continuous current flow. I’m trying to also design the ESC my self.

I need to supply 50 V and 300 A to the motor continuously,but when researching MOSFETs, I can’t seem to find any that can handle anything close to that load. Yet I see 50 V 300 A ESCs on the market.

How do they do it?

Do they wire multiple MOSFETs in parallel? Do they use massive capacitor banks? Do they just have massive MOSFETs? I’m slowly figuring this out, I just need some clarification on how those massive ESCs supply that amount of power.

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  • \$\begingroup\$ Do the commercial offerings have (or can they accommodate) wires large enough to carry 500A continuously? \$\endgroup\$ Commented Jun 20, 2022 at 2:55
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    \$\begingroup\$ Parallel MOSFETs. But a brushless ESC of any kind is not a beginner project. let alone a 300 amp one. Try building a 3A one first. That will already be several times more than a newbie can handle. Go slow and you will probably make a non-working one 2 or three times in the best of cases. Then start learning the special stuff needed for a 300A one. \$\endgroup\$
    – DKNguyen
    Commented Jun 20, 2022 at 3:40
  • \$\begingroup\$ Check out specs for BESC-G2 specs. It will meet your needs, but your biggest problem is getting parts. As DKNguyen says, a 15kW ESC is not a place to start. 24 FETs means 4 FETs running in parallel. \$\endgroup\$ Commented Jun 20, 2022 at 11:16
  • \$\begingroup\$ Yes I am fully aware this is not a beginner project, however, I am not a complete noob, I am already working on a much smaller esc as a starting point, but I want to eventually build a much larger on once I have mastered the smaller ones. This does clear everything up though, so thank you very much for the explanation. \$\endgroup\$ Commented Jun 20, 2022 at 15:02

2 Answers 2

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Well, MOSFETs have a special property (you can't do that with BJTs). You can parallel them. It's not unusual to see 5-10 or more MOSFETs in parallel for each branch of the bridges.

However there are still some issues:

  • You need to somehow carry all of that current, which usually means custom laminated busbar;
  • You need to keep the MOSFETs cool, if you look at the datasheet they are often specified with the case at 25°C. Good luck with that
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  • \$\begingroup\$ Haha, yeah cooling seems like an issue, but definitely solvable (maybe not to 25c though) but thank you for the clarification. \$\endgroup\$ Commented Jun 20, 2022 at 15:07
  • \$\begingroup\$ 300A are not really so much, it's doing quite often in electric mobility with lead batteries \$\endgroup\$ Commented Jun 21, 2022 at 7:58
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A quick search on Digikey shows MOSFET up to 1900A

Here is one 75V - 520A.

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    \$\begingroup\$ That spec is kind of a joke: It's 520 A for the silicon, IF you can keep the case at 25 C. But the leads can only handle 160 A. So unless you immerse it in liquid helium the practical rating is much lower than 520 A. There are power modules made up of many FETs in parallel for handling higher current, or you can parallel them yourself. \$\endgroup\$
    – John D
    Commented Jun 20, 2022 at 5:14
  • \$\begingroup\$ Perhaps, but regardless there are many in the list provided a quick search. Also ESC are usually 3 phase full bridge, so the current is split over 2x3 MOS, so the average current load will be about a third of nominal rating. \$\endgroup\$
    – Damien
    Commented Jun 21, 2022 at 7:05
  • \$\begingroup\$ Sure, not arguing your point, just pointing out how ridiculous MOSFET specs have become. All the data you need is still there, but the marketing people want to put 520 A on the front page when nobody will ever get near that with the part (except maybe for a short transient.) \$\endgroup\$
    – John D
    Commented Jun 21, 2022 at 16:52
  • \$\begingroup\$ Agreed on that @JohnD, and sometimes they don't even hold their specs. \$\endgroup\$
    – Damien
    Commented Jun 23, 2022 at 8:04

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