Solving Power Delivery Issues in a 5V Series Circuit with a 1.5V Rated Relay

[shushi_boi]

TL;DR Summary

When using a relay (coil) in operating voltage at 1.5V, but the minimum operating amperage is rated differently from different components in the circuit that require 20mA, whereas the coil requires 93.8mA, can all components function together?

Hello, I'm using a "TQ2SA-1.5V Panasonic 2 Form C AS Single side stable, 1.5VDC 2A DPDT NON-LATCHING SMD Relay" (specifically the coil side of this relay) that is rated for 1.5 volts that is connected in series to this circuit (as the last device in this circuit shown below), which in this series 5VDC circuit, the main voltage supply dropped from 5V to 1.5V once it reaches the relay (hopefully my math is correct up to that point ).

Here are the links to devices that I'm using in this circuit for more information about them as well as a PDF file I'll include that I will be referencing for the Relay device, specifically its coil's electrical characteristics.
https://www.mouser.com/ProductDetail/769-TQ2SA-1.5V
Link to LED switch
https://www.amazon.com/gp/product/B00OT74FIS/?tag=pfamazon01-20

As shown in the image above, the circuit is being fed from a 4 Port Charging USB Hub through a USB jumper cable, which the other ports consume a total of 0.2545 amps, reducing the 1.48 amps supply to 1.23 amps for this port (which is capable of supplying up to a maximum of 2.4 amps) that I'm working on here. So I know that the total volts in this circuit would be 5 Volts, but not knowing the total resistance or total amperage of this circuit, I decided to use Ohms law to figure out the resistance, voltage drop and amperage of this circuit and of the components that I want to use.

having done further research on each component, such as the green LED switch (which the datasheet referenced in the image below shows that it's resistance is 105 Ohms when one divides Foward Nominal Voltage [or voltage drop] 2.1 by Forward Current 0.02 Amps), or the 1N4001 diode (which I couldn't find a forward resistance value online but read that it's forward voltage drop is always 0.7 volts, although I used my digital multimeter at home and on average most of these diodes that I have at home measured around 280 kiloOhms, which didn't make sense with the forward voltage drop which I divided the forward voltage drop by the 0.02 Amps value that I got from the LED switch which got me a calculated 30 ohms of resistance which was the value that I used) I was able to come up with some resistance and voltage drop values for these components (which I based the Forward Current value from the LED switch as the basis of this circuit's current), which having reached to the final component, which was the relay's coil which needed 1.5V to operate, I was able to drop the circuit's voltage up to 1.5 Volts, which is the minimum operating voltage for this coil by using X1 LED switch and X2 1N4001 Diodes. But as the image above indicates, from the datasheet (page 5) of the relay, the coil's minimum operating current is 93.8m Amps and 140m Watts, but having calculated to total current based off the resistance of all the components together my calculated total amperage is 20m Amps and 30m Watts (from calculated 191 Ohms total resistance).

My knowledge with circuitry is very basic and I am self taught for the most part so I'm not sure if I made mistakes in my calculations or how I would go about to correct them. But I understand that these graphs that I made are really messy so I tried to redraw a basic outline of this circuit down below.

Having calcuted these resistance and voltage drop values for these components, how can I fix this circuit so that the Coil Relay receives enough amperage to reach the 140mW goal? If all the other earlier ports from the USB charging Hub leave this circuit with a total current of 1.23A to work with, will this circuit draw more than 20mA in order to get the highest current consuming component to work (which would be the 93.8mA hungry relay coils)? If this happens, would the other components with the same voltage, but added amperage and wattage fry them like the LED switch? What would be the total amperage in this circuit and resistance, since most of these components would probably change in resistance value (which I'm guessing happens since the datasheets seem to imply this)? And are all of my questions close to the right answer or am I way off?

I'm sorry for asking too many questions about this circuit or if I asked questions that aren't relevant or are completely wrong, I'm sort of thinking more and more about this issue and trying to think of different possibilities

I feel that I made a lot of mistakes or that I have a lot of faulty assumptions behind my calucations and reasoning, but the part that is killing me the most is that I can't figure out what it is, I hit an empass and I feel a bit disapointed

I try not to ask too many novice questions, but I do appreciate the time and everyone's efforst to assist others in need, the answers that I've personally learned from this forum have been enlightening a very indespensible to me so from my end I'd like to thank everyone's continued assistance for others which continues to be very educational for many aspiring engineers such as myself

 

[gleem]

Is this circuit a schematic representation of your circuit?

 

[shushi_boi]

Yes it is, but it's a simplified version, the first two top images are a more detailed representation of the same circuit, although I just used the same resistor symbol for all of the components to simplify the circuit further for myself, but the first resistor in this circuit an LED, the next two are 1N4001 Diodes and the last one is the coil side or control side of a relay

 

[gleem]

Well isn't the current through all the components the same? I do not know how the LED is incorporated into the switch. Presumably it is green when the switch is passing current and being a switch should have zero resistance so the LED should not figure into the current calculation.

One curious point is that the diodes are reversed biased is this intended? What is their function?

 

[Rive]

You are on the right track with substituting the components, but it's still messed up. Diodes does not work like that and the switch itself is not OK.

The switch has two circuit: one for the LED and one for the switch. Since the required current on the LED is smaller than the current needed to operate the relay you can't connect them in series, only in parallel. The LED needs a current limiting resistor, value according to the datasheet.

The relay needs 1.5V = the voltage drop from 5V is 3.5V. Drop it with resistor: it is easy to calculate the value given the current required by the relay. Mind the power rating!

 

[shushi_boi]

You are on the right track with substituting the components, but it's still messed up. Diodes does not work like that and the switch itself is not OK.

The switch has two circuit: one for the LED and one for the switch. Since the required current on the LED is smaller than the current needed to operate the relay you can't connect them in series, only in parallel. The LED needs a current limiting resistor, value according to the datasheet.

The relay needs 1.5V = the voltage drop from 5V is 3.5V. Drop it with resistor: it is easy to calculate the value given the current required by the relay. Mind the power rating!

Thank you for your informative insight and for pointing me towards the right direction. In actuality I had overlooked the fact that in Parallel circuits, the amperage splits up depending on the different resistance values in each branch or leg!

Having revised my schematic to include this,

I included the diodes again for the Coil relay branch just so that any back emf doesn't damage the circuit, and I feel that this circuit actually works better and fits in better with the different Amperage or Current needs of the different components. For the Green IDEC LED switch, I wanted the LED to light up when it is switched on, which causes the relay to activate and turn on two separate circuits, specifically I wanted to light up different luminescent components. But as for the non-LED circuit that this switch turns on or closes, that where I have the IDEC hooked up to a Teensy++ that also sends the luminescent signal to the Raspberry Pi which notifies the program that runs the Pi and the entire device that I'm building.

But having fixed the first issue, I just realized that in this parallel circuit, the LED switch does not control relay as the relay will be switched on or closed the entire time.

I guess I just realized the best solution to all of this, which I have overlooked the entire time, which is to switch the legs of this switch where the LED and is hooked up to the Teensy, and the non-led switch is hooked up to the relay so that I could entirely remove one of the parallel branches and just keep the relay coil branch as I demonstrate down below,

It seems that as long as the power supply for the Teensy 2.0++ is 5V, that the voltage should be 5V, the current should be 0.02 Amps, which means that I can use the same resistor that the data sheet recommends for the LED portion of the IDEC switch, which means that everything should work fine.

My only question at this point would be that if the RavPower 4-Port USB Charger Hub is being fed 1.48 amps and all of its ports combined only use up to 0.3 amps, leaving an excess of 1.18 amps, could this cause this hub to overheat or blowup? I once heard an instruct say that the resistance of a circuit along with the voltage being fed is what will determine amperage, so I don't that the extra amperage will leak over to the four ports, but is this really a concern worth worrying about, or does the Hub have an intellegent system that protects it from being overfed and overheating due to excess current?

Thank you again for all of your help!

 

[gleem]

Your switch does not control the relay. The relay is always energized.

 

[shushi_boi]

Well isn't the current through all the components the same? I do not know how the LED is incorporated into the switch. Presumably it is green when the switch is passing current and being a switch should have zero resistance so the LED should not figure into the current calculation.

One curious point is that the diodes are reversed biased is this intended? What is their function?

Thank you gleem for your input! The IDEC switch is a pretty neat device that has 2 separate circuits that allows it to control both on and off, one of them is with the green led and the other switch is just a regular switch.

As for the diodes, I'm still a bit new to it them, but I learned that they have a forward voltage and resistance/voltage drop and a reverse resistance, and their main function in this set up is to help block out the excessive 50 volts that is produced from the collapsing coils from the relay which flows backwards rather to ground since ground would be cut off from the circuit so these 1N4001 are perfect for that job (the higher valued ones are meant for bigger relays and higher voltage circuits). Here's a link to more in depth info on these diodes, you may use them on a variety of different projects
1N4001 Info

 

[gleem]

Thank you gleem for your input! The IDEC switch is a pretty neat device that has 2 separate circuits that allows it to control both on and off, one of them is with the green led and the other switch is just a regular switch.

I think your second schematic is in error. The second schematic shows that the LED is always lit.

 

[shushi_boi]

I think your second schematic is in error. The second schematic shows that the LED is always lit.

I think you are right! My drawings are a bit bad, or ambigious sometimes, but I think this new design should work better I think

 

[gleem]

I think I may see the problem that I have. What is the schematic for the switch?

 

[shushi_boi]

I think I may see the problem that I have. What is the schematic for the switch?

I can't find the schematics, but this seems to be the best data sheet about these switches (the A8 series) that I could find online.
The Link

I own a few of these, including the green round sustain push button one, which I was able to figure out the schematics and function of this switch by using my multi-meter on its 5 terminals to figure out which pins corresponded to the LED circuit, and which ones were just the switch alone.

 

[gleem]

I do not understand why they do not show the actual electrical schematic with pins identified. Will you show me what you think the schematic is?