# HAKRC HK1S ESC FET identification

I'm trying to find the part numbers for FETs used in a 4in1 quadcopter ESC.

• brand/model: HAKRC/HK1S
• voltage 1-2S Lipo or 1-2S HV Lipo, which translates to roughly 3.3 - 8.7 V
• current: 10 A continuous, 12 A for 5 seconds
• firmware: BLHeli_S O_L_05

The firmware variant ("O") points towards a pair of P- and NFETs for each phase, but that's not 100% sure.

Microscope pictures:

There are three chips marked "SP1 645" and three chips marked "AKW 3FAB" per phase.

Doubts have come up regarding the max voltage rating, because the MCU might not be able to pull a PFET's gate high enough to fully switch it off. FETs were reported to blow up when a 2S LiPo is connected. This seems plausible because there is no additional circuitry present to drive the high side FET's gate, unless the chips aren't ordinary FETs.

EDIT:

# I was able to trace some signals and here are my findings.

The chip labeled "SP1 645" in the first picture has direct connections to

• Bat+
• a motor phase output and
• the EFM8BB1's pin 8, which is P1.5. In BLHeli_S terms that's "Cc", or "phase C com FET gate output".
• -> it's probably a PFET.

The chip labeled "AKW 3FAB" in the third picture, next to the black lead has direct connections to

• Bat- (or Gnd),
• the same motor phase output as the chip described above
• the EFM8BB1's pin 9, which is P1.4. That's "Cp" or "phase C PWM gate output" in BLHeli_S.
• -> it's probably an NFET.

The EFM8BB1 is directly powered from Bat+. The absolute maximum for this chip is 4.2 V, which is pretty much exactly a fully charged LiPo. The SOT-23-6 part is apparently a boost regulator because

• it sits opposite to a large inductor labeled "100" and a diode labeled "K34"
• the ESC has 5 V output on a pin labeled "5V" even if it is only supplied with a lower voltage through Bat+

The connections found so far support the impression that this ESC can't handle anything above 4.2 V. The FETs might be able to, but the whole ESC can't.

• "the MCU might not be able to pull a PFET's gate high enough to fully switch it off." - is the MCU powered directly from the battery, or through a voltage regulator? If the latter then it should have level shifters for the upper FETs. Can you trace enough of the circuit to verify that? – Bruce Abbott Mar 1 at 21:46
• @BruceAbbott the MCU (EFM8BB10F8G x 4) can only be powered from 3V3, and there's an SOT-23-6 part that might be a linear regulator - it's the only part left on the PCB that could do anything like that. However, the I/Os are 5V tolerant. I'll try to trace some more. – Christoph Mar 1 at 22:20

brand/model: HAKRC/HK1S
voltage 1-2S Lipo or 1-2S HV Lipo, which translates to roughly 3.3 - 8.7 V


... The EFM8BB1 is directly powered from Bat+. The absolute maximum for this chip is 4.2 V

As I suspected, the 'as advertised' information is incorrect - this is a 1S only ESC! Which is probably why the part number is HK1S, and it is designated "HK 1610 1S" on the PCB.

The SOT-23-6 part is apparently a boost regulator because

it sits opposite to a large inductor labeled "100" and a diode labeled "K34" the ESC has 5 V output on a pin labeled "5V" even if it is only supplied with a lower voltage through Bat+

If it is a boost converter then the inductor should be connected between the battery and the chip, and the diode should be between the inductor/chip and 5V pin.

The mosfet marked with SP1 645 is possible to be "SSM6J501NU P-channel 10A FET" - this is what google has found and it seems to be in the same package as the one in your photo. You could try to search for it's pair, filter on a supplier website 10A N-channel mosfets in that package and see what you get.

I also damaged the same ESC by connecting it to 2S battery as it was advertised, I plan to fix it, if I find the N-channel part number meanwhile I will edit this post.

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