classic car forum header
Classic cars forum & vehicle restoration.
 FAQFAQ   SearchSearch   MemberlistMemberlist   UsergroupsUsergroups 
 ProfileProfile   Log in to check your private messagesLog in to check your private messages   Log inLog in 
Register     Posting Photographs     Privacy     F/book OCC Facebook     OCC on Patreon

Fitting relays.
Goto page 1, 2  Next
Post new topic   Reply to topic    Classic cars forum & vehicle restoration. Forum Index -> Electrical Restoration
Author Message
Ray White



Joined: 02 Dec 2014
Posts: 6286
Location: Derby

PostPosted: Sun Oct 18, 2020 9:32 pm    Post subject: Fitting relays. Reply with quote

I have been reading about how in days gone by cars were not expected to be drawing much power from their electrical systems hence ignition/light switches were not designed to carry much more than 13 or 14 amps. Apparently, running too much power through these old fashioned switches can easily burn them out.

I have been advised that the answer is to fit relays. This is not something that I know anything about but I am willing to learn especially as I am fitting several extra gauges and halogen headlamps. How do relays work?

With the high cost of new ignition switches I had better learn...and fast.!

Please can someone give me a few tips on how and what I need to do.
Back to top
View user's profile Send private message Send e-mail
Penguin45



Joined: 28 Jul 2014
Posts: 381
Location: Padiham

PostPosted: Mon Oct 19, 2020 10:37 am    Post subject: Reply with quote

Hi Ray.

They're really just a heavier duty switch. You can use the original circuit (say, headlight) to operate a coil in the relay, which operates a switch in the relay to power the light. Think starter solenoid, but a lot more compact. It allows you to use heavier wiring which is perhaps more suited to the continuous load.

Relay diagram by Penguin 45, on Flickr

Basic wiring diagrams for a circuit with and without relay. If you click the pic it'll blow up nicely for extra clarity.

Chris.
_________________
'67 Wolseley MkI 18/85, '70 Austin MkII 1800 The Landcrab Forum.
Back to top
View user's profile Send private message
Ray White



Joined: 02 Dec 2014
Posts: 6286
Location: Derby

PostPosted: Mon Oct 19, 2020 12:44 pm    Post subject: Reply with quote

That's helpful!

So each relay needs it's own earth wire?

I see how the relay fits into the circuit but how does it protect the switch? Will the fuse only protect the accessory?

(You see,,,I am really not very bright when it comes Ito sparks. Rolling Eyes )
Back to top
View user's profile Send private message Send e-mail
badhuis



Joined: 20 Aug 2008
Posts: 1390
Location: Netherlands

PostPosted: Mon Oct 19, 2020 1:03 pm    Post subject: Reply with quote

Excellent simple diagram.

Without a relay, all current needed for example for the headlamps would go through the switch. This will have an effect on the contact points within the switch, they will erode faster, get warm and ultimately melt. On a holiday in France I had this exact problem, the headlamp switch melted on my Citroen CX.

With a relay, only a small current is going through the original switch. No fear of melting. This then provides current to the relay where the "heavy" current wire from the battery / fuse is connected to the headlamps.
_________________
a car stops being fun when it becomes an investment
Back to top
View user's profile Send private message
Ray White



Joined: 02 Dec 2014
Posts: 6286
Location: Derby

PostPosted: Mon Oct 19, 2020 1:22 pm    Post subject: Reply with quote

I am amazed that happened on a CX. I always thought they were a marvel of electrical complexity!
Back to top
View user's profile Send private message Send e-mail
Bitumen Boy



Joined: 26 Jan 2012
Posts: 1733
Location: Above the snow line in old Monmouthshire

PostPosted: Mon Oct 19, 2020 1:50 pm    Post subject: Reply with quote

Ray White wrote:
That's helpful!

So each relay needs it's own earth wire?

I see how the relay fits into the circuit but how does it protect the switch? Will the fuse only protect the accessory?

(You see,,,I am really not very bright when it comes Ito sparks. Rolling Eyes )


Each relay will need its own earth wire, but the mounting point for the relays is usually a convenient earth point so you're not necessarily looking at a great deal of extra wiring.
Back to top
View user's profile Send private message
alastairq



Joined: 14 Oct 2016
Posts: 1950
Location: East Yorkshire

PostPosted: Mon Oct 19, 2020 2:34 pm    Post subject: Reply with quote

The current needs of the relay [solenoid switch]...will be quite low....your light switch [for example?] will simply operate the solenoid in the relay switch...instead of the lights directly. thus, the live wire goes into the relay , and the other connection goes to earth. You will have replaced the lights [power hungry] with a small electromagnet, inside the relay.
When operated, the contacts are worked in the relay..making the heavy duty circuit to the lights.
Saves having a switch on the dash like a Dungeness circuit breaker?
Or, all that heavy duty[high amperage] wiring all over behind the dash?
Relays come in lots of shapes and sizes...[the size really depending on the heavier load it has to switch?]
Some relays are normally-closed [so your switch will open the relay ..turning it off, so to speak]......or, most are ''normally open..''
Some are single pole, some or double or triple [or more] pole....double throw.....
All this refers to what the relay operates. IE what it does to the main circuit[s] it switches.
For that is what a relay is.......an electrically operated, electrical switch.

My Dellow..being 'sorted out' for racing in the USA, whilst it has most of its original electrics in situ [where they were sound]....the owner had a complete self-contained box of tricks mounted [under the dash]....from Painless Performance Products, of Ft Worth, Tx...a couple of hundred dollars worth in fact...this below, or nearly so

https://www.painlessperformance.com/wc/30001

Everything built into the one compact package..all I have to do is connect the live feeds for whatever, to the marked terminals..hence for the Dellow, if I connected the live feed for the reversing spotlight, to the hazards terminal..the light flashes!!
Not that I left it thus, you understand...just trying the thing out really...gives me backache going under the dash.
_________________
Dellow Mk2, 1951 built, reg 1952.
Fiat 126 BIS
Cannon special [1996 registered. Built in 1950's]
----------------------------------------------
Ford Pop chassis, Ashley 1172 bodyshell, in pieces.
Back to top
View user's profile Send private message
Ray White



Joined: 02 Dec 2014
Posts: 6286
Location: Derby

PostPosted: Mon Oct 19, 2020 7:39 pm    Post subject: Reply with quote

Thank you Alastair. A most fulsome explanation.

Electronics... it kind of scares me.

Very Happy

Actually, that looks pretty neat. Is it just a fuse block or are the relays built in?
Back to top
View user's profile Send private message Send e-mail
Ray White



Joined: 02 Dec 2014
Posts: 6286
Location: Derby

PostPosted: Mon Oct 19, 2020 10:27 pm    Post subject: Reply with quote

I found this.......??

https://www.ebay.co.uk/itm/Universal-fuse-box-kit-car-hot-rod-relays-etc/193611588007?hash=item2d142661a7:g:i2IAAOSwtVpesHnG

It is little wonder your 'painless' fuse box places the emphasis on "easy read". Smile
Back to top
View user's profile Send private message Send e-mail
MVPeters



Joined: 28 Aug 2008
Posts: 822
Location: Northern MA, USA

PostPosted: Tue Oct 20, 2020 3:04 am    Post subject: Reply with quote

Ray
I think the only place you'd use a relay on the TC is for the headlight circuits.

A standard relay & socket from your local parts store is very few dollars; you can get dual-circuit ones (hi & lo beams) & ones with built-in fuses.
Wiring is simple - run 12V to the relay #30 from the battery, connect the h/l low beam switch wire to one side #85 of the relay & the low beam h/l wire to the other side #87. Earth is #86 & usually under the mounting screw. Same for the hi beam.

To put it another way, you simply cut the headlight wires & 'insert' the relay into the circuit. The only new wire is the 12V feed from the battery.
_________________
Mike - MVPeters at comcast.net
2002 MINI Cooper 'S'
Back to top
View user's profile Send private message Send e-mail Visit poster's website
Ray White



Joined: 02 Dec 2014
Posts: 6286
Location: Derby

PostPosted: Tue Oct 20, 2020 8:22 am    Post subject: Reply with quote

Hello Mike. Your reply is appreciated. You are focusing on what I need to do for the TC which is what I need to do. Focus on the job or risk getting side tracked.

You rightly say the headlights need a relay. This would presumably protect the rather fragile ignition/light switch. What about the horn and the indicators? Then there is the fog lamp.

One unknown quantity is the draw from the (new) proposed hydrostatic fuel pump sender unit.

I am unsure which things need a fuse; a relay or both.?
Back to top
View user's profile Send private message Send e-mail
alastairq



Joined: 14 Oct 2016
Posts: 1950
Location: East Yorkshire

PostPosted: Tue Oct 20, 2020 12:42 pm    Post subject: Reply with quote

I suggest, if concerned, fuse everything? {Separately if possible...but perhaps not always possible?]
It can do no harm...aside from introducing yet another set of contacts into the circuit....to become corroded or gungy?
A long time ago I had to 'invent' a wiring circuit for my old Cannon, when it was road-registered.
I tried to run everything through a fuse...I ran out of fuse positions very quickly...I only had a freebie old Lucas fuse box to play with..without actually going and spending real money on the thing?
Working out the fuse sizes was the hardest par..ther ewas always one circuit that wanted a slightly heavier fuse...So I also ended up with some 'inline' fuses... Relays for the headlamps...and, when it eventually got one, the wiper motor [one wiper, ex-polo rear window item]
_________________
Dellow Mk2, 1951 built, reg 1952.
Fiat 126 BIS
Cannon special [1996 registered. Built in 1950's]
----------------------------------------------
Ford Pop chassis, Ashley 1172 bodyshell, in pieces.
Back to top
View user's profile Send private message
ukdave2002



Joined: 23 Nov 2007
Posts: 4100
Location: South Cheshire

PostPosted: Tue Oct 20, 2020 2:56 pm    Post subject: Reply with quote

alastairq wrote:
I suggest, if concerned, fuse everything? {Separately if possible...but perhaps not always possible?]
It can do no harm...aside from introducing yet another set of contacts into the circuit....to become corroded or gungy?
A long time ago I had to 'invent' a wiring circuit for my old Cannon, when it was road-registered.
I tried to run everything through a fuse...I ran out of fuse positions very quickly...I only had a freebie old Lucas fuse box to play with..without actually going and spending real money on the thing?
Working out the fuse sizes was the hardest par..ther ewas always one circuit that wanted a slightly heavier fuse...So I also ended up with some 'inline' fuses... Relays for the headlamps...and, when it eventually got one, the wiper motor [one wiper, ex-polo rear window item]
The fuse is there to protect the wiring, so its not too complicated to figure out what size to use.
It gets messy when folk start mixing cable sizes up a case in point:

I moved house not so long ago, the garage was fed from the consumer unit by some 4mm twin and earth, protected by a 32A breaker in the consumer unit dedicated to the garage spur, in the garage the 4mm T&E splits in to 2 separate circuits, one providing power to the sockets using 2.5mm T&E and the other for lighting using 1.5mm T&E. Now whilst the cable for the lighting and sockets is the correct size, the only protection is the 32A breaker in the consumer unit; 1.5mm T&E is rated at 15A, meaning in the case of a fault in the lighting cable , the cable could overhead before the breaker activated, a genuine fire hazard.

Sadly its not an uncommon arrangement when garage or shed has been DIY wired.

Dave


Last edited by ukdave2002 on Tue Oct 20, 2020 3:19 pm; edited 1 time in total
Back to top
View user's profile Send private message Visit poster's website
MVPeters



Joined: 28 Aug 2008
Posts: 822
Location: Northern MA, USA

PostPosted: Tue Oct 20, 2020 3:07 pm    Post subject: Reply with quote

Ray White wrote:
Hello Mike. Your reply is appreciated. You are focusing on what I need to do for the TC which is what I need to do. Focus on the job or risk getting sidetracked.
You rightly say the headlights need a relay. This would presumably protect the rather fragile ignition/light switch. What about the horn and the indicators? Then there is the fog lamp.
One unknown quantity is the draw from the (new) proposed hydrostatic fuel pump sender unit.
I am unsure which things need a fuse; a relay or both.?

Ray
Just for reference, early cars generally only had 2 fuses on the control box - one for ignition-switched devices & one for not. Lights & horns were not fused. Switches & wiring were designed to carry the necessary currents of the time.
The primary purpose of relays is to make sure the end device gets the full 12V & adequate amps.

For your car, I think I'd fit 3 or 4 relays, 2 for headlights, one for fog & maybe one for the horn, although that particular horn shouldn't draw much current.
Run a heavy wire from the battery to all 4 relays & continue the original wiring from there.
You could add a 4-position fuse box on the output side of the relays if you wish.

(Also for reference, my '02 MINI has 50 or more fuses!).
_________________
Mike - MVPeters at comcast.net
2002 MINI Cooper 'S'
Back to top
View user's profile Send private message Send e-mail Visit poster's website
Ray White



Joined: 02 Dec 2014
Posts: 6286
Location: Derby

PostPosted: Tue Oct 20, 2020 4:43 pm    Post subject: Reply with quote

Mike you say run a heavy wire from the battery to all four relays. There is no wiring in the car at all at present but I have bought an expensive new wiring loom. Is this insufficient?

I had also forgotten the wiper motor. Originally this would have been operated by the switch on the unit itself but I will have it operated from a switch on the new dash. When I decided to move the ignition warning lamp I had a space available and that seemed like a sensible idea.
Back to top
View user's profile Send private message Send e-mail
Display posts from previous:   
Post new topic   Reply to topic    Classic cars forum & vehicle restoration. Forum Index -> Electrical Restoration All times are GMT + 1 Hour
Goto page 1, 2  Next
Page 1 of 2

 
Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
OCC Merch link
Forum T&C


php BB powered © php BB Grp.