Mosfet optocoupler cant handle pump

Projects General Guidance
1

I'm trying to run a 3.7v pump (https://aliexpress.ru/item/1005007462476619.html?sku_id=12000041172228789) using following Mosfet Optocoupler module https://aliexpress.ru/item/1005005933522519.html?sku_id=12000034909573598 (FR120N)
Optron is controlled by wemos D1 mini through a web page, and when testing the whole circuit with pump replaced by LED - no issues raise, all is working correctly (enabling led by schedule, manually, manually with PWM).
However when led is replaced by Pump - pump just fails to start. There is small led on the mosfet optocoupler so when optron is closed - it is burning red. However when pump is enabled this small led just blinks slightly on start and immediately switches off.
When pump is connected directly to battery - it starts without any issues, but through an optocoupler it just does nothing. When PWM is lowered to any value below 100% I just hear peep sound from the pump.

What am I doing wrong? I have 3 same optocoupler mosfet modules, issue is the same for each. Mosfet seems capable of starting this pump, but still nothing.

Battery is connected to + and -, pump (or LED as on the photo) is connected + to + and - to Load.

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2

I don't see any detailed specs or application data for either part. The MOSFET might need more gate voltage to operate properly.

Here is a MOSFET driver circuit if you want to build one yourself. But a logic-level MOSFET normally needs 5V at the gate to turn it fully-on so it might not work if you only have 3.3 or 3.7v.

A regular bipolar transistor turns-on with less than 1V. They generally can't handle as much current as MOSFET but the right transistor can probably drive that little motor. (The driver circuit would be slightly different.)

3

Hi, @crztsr

Can you please post a copy of your circuit, a picture of a hand drawn circuit in jpg, png?
Hand drawn and photographed is perfectly acceptable.
Please include ALL hardware, power supplies, component names and pin labels.

Do you have a DMM? (Digital MultiMeter)

Thanks.. Tom.. :smiley: :+1: :coffee: :australia:

4

FR120N
FR120N788×399 36.9 KB

5

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Wemos is powered separately, didn't mention it on the picture.
Yes, I have DMM, once optron is triggered I have same voltage on the pump powerline as on the battery (4.1v). However if I connect the pump to this powerline - voltage drops to 247mv.
Looks like some kind of "protection" to me

6

That MOSFET module need at least 9V to operate a high current device like a pump. 3.7 is too low.

8

True. Not sure if 9v is really required, but 5v did the trick and it start working as expected

9

5V might be OK, it depends on the pump current. Check to make sure that the MOSFET is not getting hot when the pump is on