Cruisers Forum
 


Reply
  This discussion is proudly sponsored by:
Please support our sponsors and let them know you heard about their products on Cruisers Forums. Advertise Here
 
Thread Tools Search this Thread Rate Thread Display Modes
Old 05-03-2021, 22:15   #1
Registered User
 
Peel's Avatar

Join Date: Nov 2020
Location: Salish Sea
Boat: Contrast 33
Posts: 54
120V switching 12V relay?

Usually relays have a low amp line that switches a high amp device that has larger gauge wire. Or a low voltage line that switches a higher voltage circuit. Does there exist a relay that does the opposite? I want to have my 120V shore power switch a 12V line so that I can put a low voltage indicator LED on my switch panel without running 120V into that area of the boat. Searching my local boat supply store's website, Amazon, and general Googling doesn't seem to yield anything (maybe I'm just using the wrong search terms)

Or is there a better way to accomplish this without a relay? Again, I don't want to introduce 120V into the switch panel area that is currently exclusively 12V.
Peel is offline   Reply With Quote
Old 05-03-2021, 22:21   #2
Certifiable Refitter/Senior Wannbe
 
Wotname's Avatar

Join Date: Jan 2008
Location: South of 43 S, Australia
Boat: C.L.O.D.
Posts: 12,354
Re: 120V switching 12V relay?

There are plenty of AC relays. Provided the relay can be operated by 120VAC, the contacts can be used to switch a 12V LED assuming you have a 12V source near the relay location or are willing to run a 12V supply to that area.
__________________
All men dream: but not equally. Those who dream by night in the dusty recesses of their minds wake in the day to find it was vanity: but the dreamers of the day are dangereous men, for they may act their dreams with open eyes, to make it possible. T.E. Lawrence
Wotname is offline   Reply With Quote
Old 05-03-2021, 22:34   #3
Registered User
 
Peel's Avatar

Join Date: Nov 2020
Location: Salish Sea
Boat: Contrast 33
Posts: 54
Re: 120V switching 12V relay?

Quote:
Originally Posted by Wotname View Post
There are plenty of AC relays. Provided the relay can be operated by 120VAC, the contacts can be used to switch a 12V LED assuming you have a 12V source near the relay location or are willing to run a 12V supply to that area.
So something like this (Amazon Link) that only mentions 120VAC would work?

Click image for larger version

Name:	719dB+RxPVL._SL1500_.jpg
Views:	32
Size:	151.6 KB
ID:	233930
Peel is offline   Reply With Quote
Old 05-03-2021, 23:21   #4
Registered User

Join Date: Apr 2007
Location: Australia
Boat: Island Packet 40
Posts: 4,516
Images: 7
Re: 120V switching 12V relay?

Small transformer, diode, resister and a LED.
__________________
Satiriker ist verboten, la conformitť est obligatoire
RaymondR is offline   Reply With Quote
Old 06-03-2021, 00:38   #5
Registered User

Join Date: Jun 2013
Location: canada
Posts: 3,511
Re: 120V switching 12V relay?

The coil will 120v on a 120v relay. . You can put whatever you want though the switch. The amp rating will vary with what you put through.
smac999 is offline   Reply With Quote
Old 06-03-2021, 01:48   #6
Certifiable Refitter/Senior Wannbe
 
Wotname's Avatar

Join Date: Jan 2008
Location: South of 43 S, Australia
Boat: C.L.O.D.
Posts: 12,354
Re: 120V switching 12V relay?

With respect Peel, if you are having to ask this question, I'm not convinced you should be messing with the 120VAC.
__________________
All men dream: but not equally. Those who dream by night in the dusty recesses of their minds wake in the day to find it was vanity: but the dreamers of the day are dangereous men, for they may act their dreams with open eyes, to make it possible. T.E. Lawrence
Wotname is offline   Reply With Quote
Old 06-03-2021, 01:48   #7
Senior Cruiser

Cruisers Forum Supporter

Join Date: May 2013
Location: Oregon to Alaska
Boat: Wheeler Shipyard 83' ex USCG
Posts: 3,026
Re: 120V switching 12V relay?

Look for relays with a 110v coil. One shown is as cheap as $2 on ebay. Some come with base, some sell base separately and some are all in one.
Attached Thumbnails
Click image for larger version

Name:	Coil and Base_sm.jpg
Views:	25
Size:	75.3 KB
ID:	233934  
Lepke is offline   Reply With Quote
Old 06-03-2021, 08:55   #8
Registered User
 
Peel's Avatar

Join Date: Nov 2020
Location: Salish Sea
Boat: Contrast 33
Posts: 54
Re: 120V switching 12V relay?

Quote:
Originally Posted by Wotname View Post
With respect Peel, if you are having to ask this question, I'm not convinced you should be messing with the 120VAC.
Iím actually quite familiar with 120VAC systems having rewired my home, and am also comfortable with 12VDC systems, but have never interfaced the two other than installing a battery charger and inverter.
Peel is offline   Reply With Quote
Old 06-03-2021, 09:43   #9
Registered User
 
Lancerbye's Avatar

Join Date: Mar 2007
Location: Ladysmith,BC, Vancouver Island , Canada
Boat: Lancer 44 Motorsailer
Posts: 1,839
Images: 38
Re: 120V switching 12V relay?

Any 120 volt relay will do the job . The coil only has to be rated for 120 volts. The contacts have to be rated for the current going through them. Look at electronic stores for supply. I shop online with Digi-key. Fast response
__________________
The basis of accomplishment is in never quitting
Mengzi Meng-tse
Lancerbye is offline   Reply With Quote
Old 06-03-2021, 09:44   #10
Registered User

Join Date: Sep 2017
Location: Langley, WA
Boat: Nordic 44
Posts: 1,620
Re: 120V switching 12V relay?

Quote:
Originally Posted by Peel View Post
Iím actually quite familiar with 120VAC systems having rewired my home, and am also comfortable with 12VDC systems, but have never interfaced the two other than installing a battery charger and inverter.
Well apparently you do not understand the concept of a mechanical relay. The contact ratings are maximums, there are no minimums.
stormalong is online now   Reply With Quote
Old 06-03-2021, 10:32   #11
Registered User

Join Date: Mar 2016
Boat: McCurdy & Rhodes Custom 46
Posts: 1,047
120V switching 12V relay?

Quote:
Originally Posted by stormalong View Post
Well apparently you do not understand the concept of a mechanical relay. The contact ratings are maximums, there are no minimums.


There are minimum load currents specified for relays. This is because without an adequate load the contact materials used will slowly build up oxide layers until the contact resistance becomes quite high.
Relays designed for small signals typically use precious metals in the contacts instead of silver or silver alloys.

https://www.te.com/commerce/Document...=CS&DocLang=EN

In addition certain types of solid state relays require AC loads and a minimum load as well.

If it were me Iíd use any old 120v mechanical coil relay and not worry much. It may fail some day but if itís not a critical application thatís ok.
Use a sealed relay if you find one cheap to help avoid the oxidation on the contacts.
dfelsent is offline   Reply With Quote
Old 06-03-2021, 10:58   #12
Registered User

Join Date: Apr 2020
Location: Marseille
Boat: Superchallenger 29.6
Posts: 9
Re: 120V switching 12V relay?

To decouple the 120V and limit the current, you can put a 220 nF capacitor on each wire connected to the 120V in series with a high brightness LED. It takes capacitors sized for 250V and install them between the 120V and each wire connected to a terminal of the LED. The maximum current supplied to the LED will be approximately 5 mA. It will light up every second alternation but it will already be very bright if the diode is at high brightness (L-1154ZGW, L-1503CGDK or L-57SRSRD at Radio Spares). The two 220 nF capacitors in series are equivalent to a 24 Kohm resistor at 60 Hz.
Marc13 is offline   Reply With Quote
Old 06-03-2021, 11:05   #13
Registered User

Join Date: Mar 2020
Posts: 16
Re: 120V switching 12V relay?

If I get what you're saying that you just want an indicator light to come on when your shore power is on then don't listen to any of the advice you've received so far. Just wire in a 120Vac indicator lamp.
RigBig is offline   Reply With Quote
Old 06-03-2021, 11:09   #14
Registered User
 
Cadence's Avatar

Join Date: Dec 2008
Location: SC
Boat: None,build the one shown of glass, had many from 6' to 48'.
Posts: 9,492
Re: 120V switching 12V relay?

Quote:
Originally Posted by Peel View Post
Usually relays have a low amp line that switches a high amp device that has larger gauge wire. Or a low voltage line that switches a higher voltage circuit. Does there exist a relay that does the opposite? I want to have my 120V shore power switch a 12V line so that I can put a low voltage indicator LED on my switch panel without running 120V into that area of the boat. Searching my local boat supply store's website, Amazon, and general Googling doesn't seem to yield anything (maybe I'm just using the wrong search terms)

Or is there a better way to accomplish this without a relay? Again, I don't want to introduce 120V into the switch panel area that is currently exclusively 12V.
Sounds like you want a 110v coil and 12V contacts. They are readily available.
DC contacts are different than AC contacts so current rating is not the only thing, however I doubt you will find AC contacts in 12V. anyway.
Cadence is online now   Reply With Quote
Old 06-03-2021, 11:10   #15
Registered User

Join Date: Apr 2020
Location: Marseille
Boat: Superchallenger 29.6
Posts: 9
Re: 120V switching 12V relay?

Yes, but he wants to limit the risk of wires with 120V on his 12V electrical panel. It is safer with the capacitors at the start of the wires of the LED.
Marc13 is offline   Reply With Quote
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Remot-a-boat! Remote monitoring and relay switching by text Poey50 Marine Electronics 0 27-02-2021 12:43
12V vs 120V sailingharry Electrical: Batteries, Generators & Solar 5 10-10-2017 16:27
TV: 12v vs 120v Macblaze Marine Electronics 18 12-03-2017 10:29
For Sale: Newmar HDM 30 Battery Charger/Converter 120v AC shore power to 12v DC redpointist Classifieds Archive 0 18-01-2016 11:25
12V/120V Refrigeration? lifeofreilly57 Construction, Maintenance & Refit 5 05-01-2015 23:40

Advertise Here


All times are GMT -7. The time now is 14:26.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2021, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2021, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.