# Voltage question

#### sikter

Joined Jan 25, 2012
23
(2,4 gHz) in my simple circuit to operate 4 relays.
Reciever initially came from RC helicopter with
3,7 V battery.
How much can I vary the voltage without
I got planty 5V DC relays which I would like to
use. All relays are of momentary type and they'll never
be engaged longer than a split second at the time.

#### mcgyvr

Joined Oct 15, 2009
5,394
A 5V relay won't switch at anything lower than maybe 3.8V (pick up voltage)
I'd suggest 3V relays or switching a transistor/5V supply to use the 5V relays.

#### Mark_T

Joined Feb 7, 2012
47
You will not damage a 5V relay by switching it with 3.7V, its just that it may not switch because the field strength is to weak. If you only have 3.7V then try them if you can put up with them not being 100% reliable then ok. Chances are they will either work or not. Also, be aware that if the battery voltage falls they will at some point stop functioning.
If not then get lower voltage ones or boost the voltage.

#### BJT_user

Joined Oct 9, 2011
35
If you power your receiver wtih 5 volts, you will likely fry it, however, if you try to switch your relays with 3.7 volts, then they probably won't activate. I would suggest using a 6 volt power source (only because it's easy to produce VIA 4 alkaline batteries) and a LM317 variable voltage regulator to reduce the voltage to 3.7 volts on your receiver. Of course you'll have to use a simple voltage amp (single transistor and base resistor) to activate each relay, as well. It's a bit of a complex solution, but workable.

#### sikter

Joined Jan 25, 2012
23
Thank you!

Last edited:

#### Von

Joined Oct 29, 2008
65
How are you planning to drive these relays coils?

#### sikter

Joined Jan 25, 2012
23
How are you planning to drive these relays coils?
I'm going to have 4 momentary switches on my radio transmiter!
When reciever gets a signal from the radio it will engage
one of my 4 ralays. The relay is momentary too and it
will close my main circuit for a just a moment.
That's all I need. The other three ralays work same way.
They are connected to other 3 channels.
I have already connected this sistem and it's working but with 2 channels radio.
Receiver has 6 V Power supply and my relays have 5V coils.
works on 6V. So I am checking my other options!

#### Von

Joined Oct 29, 2008
65
Cool!

What I mean is what are you using to convert the PWM to a DC voltage for relay coil activation. I have seen devices for about $20 to do this but am interested in your design concept. Thread Starter #### sikter Joined Jan 25, 2012 23 Cool! What I mean is what are you using to convert the PWM to a DC voltage for relay coil activation. I have seen devices for about$20 to do this but am interested in your design concept.
Sorry I wasn't paying enough attention lately.
I don't know what PWM is, but it's probably something what's already integrated into my receiver. I measured the voltege on the circuit card while pushing joystick on the remote controler. I found points where I have to solder the wires what lead to my relays. That's all, I don't know anything about things on the circuit card.

Can you post a linkt to those 20$devices? I can't find it. Reason that I made my own is because devices I found on the marked were very expensive. I spent about 30$ to bulid my own device

#### Von

Joined Oct 29, 2008
65

#### sikter

Joined Jan 25, 2012
23
If the R/C receiver outputs are intended/designed to drive a R/C servo than you cannot just simply hook up a relay and expect it to work.

As far as a device to operate a relay with an R/C system,
look here: http://www.dimensionengineering.com/PicoSwitch.htm

You will need to supply the voltage to operate the device connected to the relay separately (i.e they are 'dry' contacts).
Thank you very much,
I am glad I didn't read this earlier, this would stop me of even trying.
But I tried and it worked. After reading this one more time my explanation is that those pulses from receiver give enough voltage to engage my relay just for a moment (which is what I needed in the first place)

"Picoswitch" you showed me is real thing for this job but it would be more expensive solution. (I would be needing four picoswitches which would cost me 80$+ radiotransmitter) I payed 35$ for my 4 channel radio, 4 channel receiver and 4 relays.

It looks that those radio receivers are very flexible regarding the voltage.
I run it on 4.5V, 6V, 7.4V and 9V. It worked regardlessly, which gave me more flexibility to select the relays.

Off course, the time will show how close to its limits I've been pushing it.

#### Andreas

Joined Jan 26, 2009
86
If the R/C receiver outputs are intended/designed to drive a R/C servo than you cannot just simply hook up a relay and expect it to work.