Model Boat Mayhem - Forum

Mess Deck: General Section => Tugs and Towing => Topic started by: gman on October 30, 2017, 09:31:25 PM

Title: Relay Question
Post by: gman on October 30, 2017, 09:31:25 PM
Hello, I was looking through some wiring diagrams and have a question. In the pic below, what is the relay switch used for and what type are used? The relay is located at the bottom of the pic past the fuse.
Title: Re: Relay Question
Post by: Starspider on October 30, 2017, 10:09:09 PM
It would appear that the relay is acting as the main isolating "switch" for the main power circuit, making it live as the 4.8v line is switched manually to the receiver.
But I am no expert  %)


Colin
Title: Re: Relay Question
Post by: Time Bandit on October 30, 2017, 10:11:03 PM
The relay is used as main switch for the battery.

It has to be a 5V version (coil is powered by receiver batt) and should be able to switch at least 20A considering the 20A fuse.
IŽd personally use a relay with 25A+
Title: Re: Relay Question
Post by: gman on October 31, 2017, 12:30:15 AM
So in this case the relay is reducing the power from 6v to 4.8v?
Title: Re: Relay Question
Post by: roycv on October 31, 2017, 05:30:33 AM
Hi gman, the relay is made up of 2 parts inside a plastic case, one part is a coil and when a current goes thru' it, it becomes magnetised and this then attracts the other part which is a small lever system that operates a switch, all inside the relay. The electrical contacts of the switch are brought outside the plastic case so they can be connected into a circuit.
 
So in this circuit the relay coil is  powered by the receiver 4.8 volt battery, the quite separate switch in the relay has been wired into the circuit with the 6 voly battery. 
When the receiver is turned on the relay coil gets magnetized and this attracts the lever system which turns the switch to the on position and the switch in the relay powers up the 6 volt battery circuit a moment later.
The relay isolates the 2 circuits from each other, so if anything goes wrong in the 6 volt circuit, it does not affect the receiver.

You can see that in a different set up you could have a low voltage operating the relay coil and the relay contacts switching a much higher voltage but they remain quite separate from each other.

Relays come in different types and sizes.  You choose one that has a coil suitable for the coil voltage you wish to use and contacts that can handle the current you want to switch.
There are electronic equivalents called solid state switches and these are typically used by having the coil in a digital (5 volt) circuit but the switching part in an AC mains 240volt circuit and the solid state relay keeps them form interacting,

Hope this helps and not TMI,
kind regards Roy
Title: Re: Relay Question
Post by: CGAux26 on October 31, 2017, 01:48:15 PM
I don't understand why a relay is necessary at all.  I have built my boats with up to 25 A ESC's and just a main switch rated at least 25 A.  Somebody educate me, please. 
Title: Re: Relay Question
Post by: roycv on October 31, 2017, 02:04:01 PM
Hi, I do not disagree, but this is being very careful, that is all.
regards Roy
Title: Re: Relay Question
Post by: Netleyned on October 31, 2017, 02:45:42 PM
Could be just to facilitate the use
of a lower rated switch i.e
 smaller, which needs to be hidden in a deck
locker or suchlike.


Ned
Title: Re: Relay Question
Post by: JimG on October 31, 2017, 09:21:28 PM
The relay keeps the 4.8V and 6V supplies seperate and switched from a single pole switch. An alternative would be to use a double pole switch with each supply on a seperate pole.

Jim
Title: Re: Relay Question
Post by: gman on October 31, 2017, 09:40:15 PM
Still confused.  The 6v power supply goes to the fuse and to the relay. From there is where I confused. Why would the relay be necessary? The power to the switch is from the 4.8 v power supply, right? So I don't understand why the relay is being used?  I researched this vid ...


https://m.youtube.com/watch?v=UAeKTlieYhw


Thanks everyone on their feedback.
Title: Re: Relay Question
Post by: Starspider on October 31, 2017, 10:14:06 PM
I think your confusion maybe caused by the fact that it is a relay. If you replace the relay with a simple switch that is manually switched you have two circuits that are independent of each other, one is low voltage and low current the receiver 4.8v side. The other is still low voltage but high current the motor and its control. This works fine but you have two small problems 1 you have two switches to hide on your boat truck etc one of which needs to be a heavy current switch which tends to make it larger. The second problem is control with 2 separate switches you can turn on the higher current circuit the motors etc before the control circuit circuit the receiver and servos etc in some instances the motors may startup if your fingers are in the way it will hurt. So if you replace the high current switch with a relay that is triggered by the control circuit you gain a safer circuit and you only have to hide one smaller switch. Hope that helps, I need a lay down now. Lol.


Colin
Title: Re: Relay Question
Post by: roycv on November 01, 2017, 11:48:08 AM
Hi gman, was my explanation gobbledegook to you? Sorry if it was but one never knows at what level to start, I should add that I give up on programming now, I just let it pass me by!
Have another read of para 3 in my explanation.  There is no mystery here just a low rated switch operates the relay which has high current switching ability.  It is a reasonable way to wire things up and give yourself a bit of belt and braces.
regards Roy
Title: Re: Relay Question
Post by: grendel on November 01, 2017, 12:33:36 PM
it would also mean that if the radio battery went flat, the power circuit would switch off too.
Title: Re: Relay Question
Post by: gman on November 01, 2017, 11:58:22 PM
I think I have a better understanding of the relay. So I don't understand how it all works in the pic above. 6v go to the relay, and back out of the relay to the components at the top? Correct?  So if the switch above left of the relay has power from the receiver batteries why is the switch connected to the relay?
Title: Re: Relay Question
Post by: Umi_Ryuzuki on November 02, 2017, 07:40:10 AM
I would guess that the  P80 does not have a BEC, so none of the power from the esc goes to the  Receiver.
If the relay wasn't activated, the receiver would get power from the switch, but no power would go to the ESC or motor.
Title: Re: Relay Question
Post by: C-3PO on November 02, 2017, 08:55:04 AM
Two sides of relay circuit - 4.8v switch to energise coil. Other side (circuit) of relay the supply load - in this case 6v
Title: Re: Relay Question
Post by: Corposant on November 02, 2017, 10:40:44 AM
Hi Gman,

I think the wording of your post yesterday should be changed (in your mind!) from "6v go to the relay and back out of the relay to the components at the top" to: The 6v supply goes to the relay contacts and is thus connected to the components at the top.

In answer to your question: "why is the switch connected to the relay?" - To switch it on!

As has been pointed out, the relay (i.e. electrically operated switch) is being used in the circuit to ensure that the 6v supply can only be switched on if the receiver is switched on also.

Regards,
             Mike
Title: Re: Relay Question
Post by: chas on November 02, 2017, 02:26:22 PM
To put it another way, the single switch switches on the radio and the relay. The purpose of the relay is to isolate / switch on and off the drive batteries, which is a very sensible and safe thing to do.
   A relay in this case is just a switch worked by electricity instead of a lever.
     Earlier answers mentioned this, but might have confused someone new to the principle. I think it's an elegant  idea some of which harks back to the early days of radio control.
Chas.
Title: Re: Relay Question
Post by: gman on November 02, 2017, 10:50:59 PM
So I watched several you tube vids and with the explanations here, and I thank everyone for the feedback. I believe I finally have it. So is using relays old school then? Anyone use them still?


Thanks for the efforts.
Title: Re: Relay Question
Post by: chas on November 02, 2017, 11:13:34 PM
Not really old school. An existing, proven, reliable and robust technology still very much in use for the right application such as your example.
Chas
Title: Re: Relay Question
Post by: david48 on November 02, 2017, 11:57:52 PM

There is every chance that there is a relay operating your  car head lights . They are used  to switch on spot lights so that a heavier load can be switched and it does not burn out the contacts on the light switch . Have a look under the bonnet near the battery there might be a box with big rated fuse and some small black cubes a bit bigger than a  oxo cube or they might be green they are just pushed in there might be one for the air con as well if fitted .  All that is just to say that they are still in everyday use .
David
Title: Re: Relay Question
Post by: Brian60 on November 06, 2017, 07:35:09 PM
So I watched several you tube vids and with the explanations here, and I thank everyone for the feedback. I believe I finally have it. So is using relays old school then? Anyone use them still?


Thanks for the efforts.

Of course. They are very big in the robotics field where switching high current with micro controllers like Arduino and Raspberry Pie etc are common place.

Here's a 4 bank for such situations, this particular one comes in 2,4 and 8 relay boards, I have a 4 and an 8 board lined up for my current project, but I'm also exploring other options.
Title: Re: Relay Question
Post by: gman on November 07, 2017, 01:00:33 AM
Nice, care to share how you are going to wire it up and for what components? Where did you get this?

Title: Re: Relay Question
Post by: Brian60 on November 07, 2017, 02:51:48 PM
Nice, care to share how you are going to wire it up and for what components? Where did you get this?

As I said these banks are for use with micro controllers, in my case these will be connected via a Arduino Mega. The arduino provides the switching signal to trigger the relay's, the relays are the switch for heavier currents which connect to them via the blue terminals on the board edge.

Freely available via ebay or the many robotic supplies shops that proliferate now.
Title: Re: Relay Question
Post by: tsenecal on November 07, 2017, 05:50:37 PM
most of these "things" now-a-days will use a FET instead of a relay, because the FET is much smaller... but a relay would work fine...

http://www.electronics-tutorials.ws/transistor/tran_7.html (http://www.electronics-tutorials.ws/transistor/tran_7.html)

FETs are also easily available on ebay...   

https://www.ebay.com/itm/15A-400W-MOS-FET-Trigger-Switch-Drive-Module-PWM-Regulator-Control-Panel/172521969293?_trkparms=aid%3D222007%26algo%3DSIM.MBE%26ao%3D2%26asc%3D41376%26meid%3D2cd21a1bf7d54cb19c0728097d70365f%26pid%3D100005%26rk%3D3%26rkt%3D6%26sd%3D291780392225&_trksid=p2047675.c100005.m1851 (https://www.ebay.com/itm/15A-400W-MOS-FET-Trigger-Switch-Drive-Module-PWM-Regulator-Control-Panel/172521969293?_trkparms=aid%3D222007%26algo%3DSIM.MBE%26ao%3D2%26asc%3D41376%26meid%3D2cd21a1bf7d54cb19c0728097d70365f%26pid%3D100005%26rk%3D3%26rkt%3D6%26sd%3D291780392225&_trksid=p2047675.c100005.m1851)