connecting 5v relay with 3.3v nodemcu pin

[ravi.2k17]

hi all,

i want to power up 5V 2-channel relay module with 3v3 pin of nodeMCU. Can it be directly connected or do i need some thing to step up voltage?
nodemcu is powered with 5v micro-usb cell charger. i do not want another/dedicated power source for relay module.

2-Channel 5V Relay Module(Black) : rhydoLABZ INDIA

rhydoLABZ INDIA 2-Channel 5V Relay Module(Black) - 2-Channel 5V Relay Module is a relay interface board, it can be controlled directly by a wide range of microcontrollers such as Arduino, AVR, PIC, ARM and so on. It uses a low level triggered control signal (3.3-5VDC) to control the relay...

www.rhydolabz.com

.


thanks

 

[danadakk]

Its description appears to indicate it requires a supply of 5V to operate
the coil of the relay, and will take a signal to turn on of 3.3V to 5V from
a processor. I do see 5V on top of relay so that seems to confirm.

If you can get a schematic of board, you can confirm the processor
interface. I cannot see any driver transistor to implement the processor
interface. Or ask seller for this info.

You could use a boost regulator to generate the 5V. If yoiu are powering
to the pin that runs part off 3.3 then you will need that. If you are running
NodeMCU from USB or 5V directly then that will supply power for the relay.


Regards, Dana.

 

[FvM]

There are drivers in DIL-4 package on the module, may be e.g. MOSFETs. It's as said, you need 5V supply to the relays module, logic signal can be 3.3V.

 

[c_mitra]

If the relay coil is rated for 5V, it will very likely to work at 4V or even 3.5V. But you may have to sacrifice some reliability.

The coil is likely NOT directly driven by the logic signal. The driver may drop some voltage applied to the relay coils.

If you try to drive the relay coil power supply at 3.3V, the actual voltage the coils may get is perhaps 3V. It may or may not work.

At lower voltage, the speed may also be affected and that may in turn damage the contacts.

As others have suggested, better to get a 5V supply for the delay driver. Current demand is likely to be modest.

 

[KlausST]

Hi,

In the end: If you run a circuit without datasheet ... all you can do is guess and hope.

Klaus

 

[ravi.2k17]

can we some how increase the voltage from 3V3 pin to 5v and use this powering up relay?
i see somewhere about logic sifter (3.3v -> 5v). it seems this is being used to step up voltage for sensor signalling purpose.
can this be also used to powering up relay?

some online seller do not give proper datasheets for there breakup boards hence become difficult to know there boundary conditions.
now here i want to avoid these boundary situations by stepping up voltage.

--- Updated Nov 20, 2020 ---

Its description appears to indicate it requires a supply of 5V to operate
the coil of the relay, and will take a signal to turn on of 3.3V to 5V from
a processor. I do see 5V on top of relay so that seems to confirm.

If you can get a schematic of board, you can confirm the processor
interface. I cannot see any driver transistor to implement the processor
interface. Or ask seller for this info.

You could use a boost regulator to generate the 5V. If yoiu are powering
to the pin that runs part off 3.3 then you will need that. If you are running
NodeMCU from USB or 5V directly then that will supply power for the relay.


Regards, Dana.

are suggesting something like this?

https://robu.in/product/mt3608-2a-max-dc-dc-step-power-module-booster-power-module/?gclid=CjwKCAiAzNj9BRBDEiwAPsL0d8RX3DeNmMERhBbKRc33Br8VBQJ4T8Gad0AjZzMkfH3KBlUvqznnAhoCtOsQAvD_BwE

 

[KlausST]

Hi,

Then why not simply use a bare relay
* and a bjt 1 or 2 resitors and a diode.
* or a dedicated relay diver
* or general low side driver like ULN200x

All come with a datasheet. Cheap, simple, reliable....done many million times. No guessing. No uncertainties.
Schematics, calculations, examples, descriptions, even videos can be found in the internet, too. Million times.

Just do a search in your own.

Klaus

 

[BradtheRad]

Most likely the 3.3v pin cannot provide sufficient power (even stepped up to 5V) to activate a relay.

It sounds as though you have a 5V supply available. A transistor is a cheap and easy way to send supply voltage to a relay coil (as suggested in post #7). Bias is 3.3v @ 2 mA drawn from the micro controller.

Recommendations advise to put a catch diode across relay coil as shown below.

 

[FvM]

You tell the circuit is powered by a 5V USB power supply. Why it's not possible to feed the 5V to relays module?

Consider that the relays have a coil resistance of 70 ohms each, the relays module will draw about 140 mA from 5V. Supplying it by a 3.3V to 5V boost converter raises the 3.3V input current to at least 250 mA, probably more. Not sure if the 5 to 3.3V voltage regulator of the nodeMCU can provide it.

 

[danadakk]

can we some how increase the voltage from 3V3 pin to 5v and use this powering up relay?
i see somewhere about logic sifter (3.3v -> 5v). it seems this is being used to step up voltage for sensor signalling purpose.
can this be also used to powering up relay?

some online seller do not give proper datasheets for there breakup boards hence become difficult to know there boundary conditions.
now here i want to avoid these boundary situations by stepping up voltage.

--- Updated Nov 20, 2020 ---

are suggesting something like this?

https://robu.in/product/mt3608-2a-max-dc-dc-step-power-module-booster-power-module/?gclid=CjwKCAiAzNj9BRBDEiwAPsL0d8RX3DeNmMERhBbKRc33Br8VBQJ4T8Gad0AjZzMkfH3KBlUvqznnAhoCtOsQAvD_BwE

Yes that should work. Note the Nodemcu, depending on manufacturer, board version,
use a reg (no heatsink) NCP1117. That takes USB 5V and translates to 3.3. Its capable of 1 A,
but the thermals would be of concern. So if you have 3.3V supply and not using the onboard
3.3V reg should work fine. Otherwise you will have to do a power/load/thermal analysis to
use the onboard 3.3 as source to boost for relay.

I do not see any min load requirements for the DC/DC, you might want to check into that.
Also use the turn off clamp diode applied to the relay to protect DC/DC. Also check the
transient response of DC/DC to make sure when relay is turned on it does not "chatter"
because its supply (DC/DC output) is dropping due to the DC/DC control loop transient.

Regards, Dana.

 

[KlausST]

increase the voltage from 3V3 pin to 5v and use this powering up relay?
i see somewhere about logic sifter (3.3v -> 5v).

ravi isn´t clear whether a DCDC is expected or a logic level shifter.
I assumed a logic level shifter. On the other hand a logic level shifter does not "powering" up the relay.

Klaus

 

[FvM]

There's no purpose for a level shifter in the project. It can't supply the relays (70 mA operation current each) and isn't required by the relays module logic input which accepts 3.3V level according to specification.