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Low output voltage on DRV8838

I have a DRV8838 in usage that is supposed to trigger a solenoid. The logic circuit is powered with 3.3V and controlled by an ESP32 which all works fine (i can see voltage raise and fall for PHASE and ENABLE pin as the ESP32 triggers HIGH and LOW)
The motor circuit is powered with 9V (originating from an S10V3F9) and i can measure that voltage alright at the VM pin. But Vout1 and Vout2 only give me stable 3.05V (i can see that also they drop to 0V if the ESP32 triggers the ENABLE PIN)

If i replace the DRV8838 with a second one i have it gives me 0V for Vout1 and Vout2.

What could the source for that problem (not getting expected 9V)? (i did not really pay attention in school when it came to theory of electricity so i am wandering in the dark here)


Can you post some pictures of your setup as well as information about your solenoid and power supply? Also, can you measure the output of your power supply and regulator to confirm that they are working and that the voltage is not dropping when the solenoid is activated? If it does drop, that could indicate your circuit isn’t able to supply enough current for the solenoid.

- Patrick

This is the schematic from which i built. Though i replaced the ESP-07 with an ESP32 and did not wire in the debug part to the left of the ESP-07

Gardena1251-Controller-H-Bridge-Schematic.pdf (103.8 KB)

Power source is a Li-Io 18650 3.7V (measuring 4.1V since its still charged). The LDO gives me constant 3.3V (logic voltage) and the voltage regulator Popolu S10V3F8

measures constant 9V at Vout (supposed for motor/solenoid voltage)

and Vout1/2 only give me around 3V

The solenoid is latching.

Please note, our company name is “Pololu”, not “Popolu”.

My main concern right now is that your soldering does not look great, and there are two pins on your driver that are not soldered at all which can cause intermittent connections and potentially damaging voltage spikes. You might check out the Adafruit Guide to Excellent Soldering, which is a useful soldering reference.

In the schematic, the driver is powered through the VM pin, but then in your pictures, nothing is connected to that pin. You do have a jumper wire connected to the VIN pin, and it would be fine to power your DRV8838 from either VIN or VM, but your VIN pin is not soldered. Given that error, it might also be wise to go back and double check that all of your connections match your schematic.

- Patrick

Sorry, for the getting the company name wrong.
Usually i have the VM pin connected like in the schematics but when i took the picture i had it connected to VIN just to try if something was off with the VM pin. But its the same behavior.

Thanks for your thorough investigation with the schematics. I’ll redo my soldering with the guide you provided me and hope that this is just due to bad soldering by a newby :slight_smile: