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MG Midget and Sprite Technical - Relay questions

I've been trying to figure out the proper relays to use for headlights (without buying an expensive kit) and the more I read the more I get confused.
30 amp or 30 amp with load open (40 amp)?
4 pin or 5 pin?
With diode or without diode?
SPST or SPDT?

And what would be used in other applications - horn, brake lights, cooling fan, etc.?

I've attached a link to a site that sells relays if it helps...
http://www.keefeperformance.com/kprelay.html

Thanks,
Bud
Bud K

As I posted on BCF:

http://www.danielsternlighting.com/tech/relays/relays.html
Trevor Jessie

great artical treavor, vary informative,


hey Bud, I dont know why but that site wont let me "create a shortcut" (funtion disabled) I have found to be leary of websites that have website problems, its a reflection of who they really are.

prop
Prop

Prop,
Perhaps "who they are" is a buncha car guys rather than a buncha web-heads? Which would you rather get car advice from?

Bud,
What you are really trying to do is to use the high-beam and low-beam feeds between the dip-switch and the actual headlights (along the right fender) to turn the relays (one for high and one for low) on and off. Pull power from the battery feed at the solenoid (nice and close on a 1275, dunno about the 1500s), fuse it if you like. I used bullet sleeves and connectors so that I can return it to normal if a relay were to fail. Not hard at all.
David "relaying info" Lieb
David Lieb

Most application will only require a single pole normally open (SPST) on/off apart from ie. (SPDT) headlight switching when going from main to high beam and a second relay to allow for flash that will allow both elements of the bulb to operate at the same time, this is of course normal controlled via the high low switch.

Size the relay to the rated current of the devise being switched as the inrush current (mainly only motors) is calculated into the relay size, ie a relay rated at 30 amp will handle 60 amp on switching for a short time.

It is always best to fit diodes when switching DC due to the way the DC field collapses.
Alex Sturgeon

Cant see any reason not use the basic 4.99 realy from that site

electrical relay 40 AMP - Tyco / replaces Bosch 0 332 209 150


My setup fwiw...

http://www.eatworms.org.uk/album/album2.php?album=midget-Dash&mode=page&index=9
Dean Smith ('73 RWA)

Alex,
Sounds needlessly complicated to me. The method outlined by the Daniel Sterns link above is pretty much identical to the way I did it. One relay to operate the high beams, one relay for the low beams and no need for diodes. Eliminates the load on the dip switch and the headlight switch, since the only power going through them is the minimal amount necessary to operate the relays. If you pull the lever for the flash, both relays are on. No big deal.
David "keepin it simple" Lieb
David Lieb

David

Yes agree with you, I would only use a relay for big spots and think the high / low on the stick works fine (mine is 38 years old and still going), only used the headlight application as an example of why a SPDT relay would be used, as to Bud's question.

As to diodes, quality relays will have diodes fitted as a matter of course inside the body of the relay and would not be obvious to the user, this is the difference from the unbranded relays and say Bosch, the two will look the same from the outside but inside is a complete different story
Alex Sturgeon

With halogen conversion (and uprated bulbs) I went through 2 full/dip stalks in quick succession - hence the relays on both main and dip. No need for that sort of current to be going through the stalk (imho).
Dean Smith ('73 RWA)

John Twist of University Motors recently posted a video on YouTube describing relay installation in an MGB, and the theory is identical. He draws schematics and everything:

http://www.youtube.com/profile_videos?user=Universitymotorsltd&p=r

Just look for the appropriate title.

-:G:-
Gryf Ketcherside

Dean, though I wholeheartedly agree with your use of relays and the tidy way you have mounted them, I can't say the same about a couple of things on your car that worry me a little.

First, I really hate Scotchloks, they are no more than a problem lying in wait for you to have electrical failures in the future. (always at the least convenient time too) The blades often cut strands of the wire as they cut across the insulation layer and thus reduce the effective size of the wire.
They let corrosion start out of sight too. I have an AA type picture and article some place, I'll look it out.

Secondly the battery terminal on the picture needs to be opened out and after cleaning the almost certain oxidation from its inner surface and the battery post, clamped fully down the post so that all the contact surface is in contact with the post. Then given a coat of Vaseline or a di-electric grease if you can find one

You could be losing a quarter of the current flow-ability of that clamp like that. Winter time needs fully efficient battry operation after all.

I know this sounds like a preaching session but have seen so many problems caused like this I feel I have to mention it.


best get myself into the corner again huh...
Bill

bill

thats the only scotchlok on the car ... and whilst they are (by a long way) my least preferred way of joining into the loom. that one was a necessary evil at the time. In fact a good part of the reason for redoing so much of the wiring was to clean up some of the assorted scotchlok'd additions fromt he last 15 years.

its actually there to take a switched ignition feed to a new relay that then feeds as many of the accessories as possible. so whilst it may have reduced the capacity of that bit of wire...its reduced the demand by far more.

the battery post is clean - that pictue was taken mid winter jobs, shortly after a lot of filler had been sanded - hence the dust everywhere. that was all cleaned up later. i suspect in that picture the cable is not even clamped fully.

I will have anotherlook at that scotchlok though....now you've mentioned it its going to keep looking at me.... ;-)
Dean Smith ('73 RWA)

Yo Dean

I was only concerned, is all

I wish Lara was even a bit that nice underbonnet, but she aint and barring the rewire in plan for about the next twelve months, she isnt going to be either

I have put Lara's relays along the o/s inner wing panel 'cos they only operate the cooling fan and the brake lights at present.

Headlights will be a separate issue later but even running halogens I havent had issues with them yet

Scotchloks, well I just prefer to cut in, solder and heat sleeve any taken-off power sources, may look ovious but always carries the load safer.

(can I come out of the corner? Gotta go to the Green Man tonight...)
Bill

Anything connected with auto electrics usually sends me scurrying into the undergrowth.

However this thread has raised a potential problem for me. Dean's post about his halogen upgrade causing him to replace two dip-switch stalks has got me worried.

I have bought a pair of halogen headlights but not yet fitted them. Does this mean that it will be necessary (or advisable) to fit a relay?

Dave
Penwithian

Dave,

If the wattage of the halogens is the same as standard then the current seen by the switch will be the same so no change. Dean did mention he had fitted uprated bulbs, wattage I presume, so the switch will see an increased current load and that can often have a snow ball effect where the increased heat in the contacts causes increased oxidation and resistance so increased heat, etc, etc.

Keep in mind that not all halogens are created equal. I bought a Lucas set years ago and they were not a patch on the same wattage Cibies that a mate had so I replaced them with Cibies.
David Billington

Dave

At the time It was my only car so I was doing pretty high mileages and I was running 100W bulbs at the time (off-road obviously!)....The contacts in the switch were just burning out.

(it was great having better lights on the midget than most people have on their euro boxes though !)

Dean
Dean Smith ('73 RWA)

Dean,

Which Dave ?.

Dave
David Billington

Yes, IF the bulbs have the same actual wattage, they will have the same effect on the switches. However. please bear in mind that these switches have all exceeded their designed life expectancy years, if not decades, ago. If you implement a pair of relays, you reduce the load on those very expensive switches (bearing in mind that the replacements you are likely to get today are greatly inferior to the original ones) to virtually nothing. With the load of merely driving a relay, those switches will last longer than you will. That is why I chose to install them.

Add to that equation the fact that the factory wiring for the headlights ran from the battery to the solenoid, then to the headlight switch, then to the dip switch and then to the headlight filaments, thence to ground and back to the battery, and you can see thatyou have some very tired electrons. By installing relays, the current lighting my headlights goes from the battery to the solenoid through a fuse to the relay then directly to the headlight. Larger gauge of wires and MUCH shorter runs resulting in significantly brighter lights as well. What's not to like?
David "ever wonder why all the moderns use relays?" Lieb
David Lieb

I know of someone with a Midget who did not have his halogen headlights switched with a relay and again went through two stalks in quick succession second time with added smoke for extra effect!!!!

I would advise fitting a relay!!

Shaun
Shaun

I've been thinking of doing this for some time and you lads finally got me off my duff and into the garage.

Pulled a couple of relays out of my spare parts box and a little wire and some bullet connectors and I'm all set.

I mounted the relays on the inside of the front fender/wing ala John Twist's video. I did not have to cut into the harness.

The headlights are NOTICEABLY brighter than before!

Next step is to do the heater fan, brake lights, horn and, soon to be installed, electric radiator fan. Yikes, that will make six relays!

A worthy upgrade.

Lee
L Fox

I'll be fitting relays when I rewire my engine bay. I've been trying to put together a list. From what's been said recently on here then there's a good case for fitting them to:

1) headlamp dip
2) Headlamp main beam
3) Brake lights
4) Horn

That reduces load on the main/dip column switch, the brake light switch and the horn push, and also allows higher rated halogen headlamps and an air horn.

Any more worth doing? Such as:
- Protect the ignition switch by relaying the fuel pump? Or more generally have a relay for position 1 (aux) power and a relay for key position 2 (ignition) power and therefore take everything off the ignition switch? What about the solenoid load?
- Protect heater / wiper / headlamp switches?
- Protect indicator stalk switch? (2 relays?)

The list could go on and on.
Ant
Ant Allen

Ant-
Since I started this discussion I've done a lot of reading on different sites and looking at different set-ups and most recommend relays being used on electric radiator fans and fuel pumps, and one or two show brake lites being done. Since I'm installing new after market switches I'm drawing the line at the four you show.
Bud
Bud K

I'm thinking that a high current ignition feed for the fuel pump would be useful, not least as I have a non-original pump on my car.

I can see that the chances of burning out a dash toggle switch are minimal, and they're not too expensive to replace. The indicators worry me more as that's on the stalk and they're expensive. Trouble is it's an extra two relays. And then I need to get a hazard switch in there somehow.

Oh and I've also heard that brake light relays add a small delay which is crutial in avoiding rear end impacts. That's probably not an issue with 1971 era braking but is an issue on performance or track cars (mine is neither!)

Ant
Ant Allen

two things Ant

1: KISS. do not add complication in circuits that dont have a need for them. Relays off the ignition switch circuit? No chance. Most loads are and always have been designed for. Electricity was around when Spridgets were designed and except for certain specific (read UPRATED LOAD) areas such as brake lights (poor quality pattern switches) and headlights or electric fans, need no messing about with. The addition of relays everywhere simply adds to the places that failure can occur (Having spent most of the last thirty years as an AA patrol, I am sure that you need less risky places not more in vehicle wiring)

Extra wiring on the fuel pump circuit (as easy a circuit as you could ask for just means more risk of lying under the axle wondering "Wot went wrong?" this time.

2: (bet you thought I'd forgotten) I have a relay on my brake lights, needed because I am on switch number two or three, I lost count. I have no noticeable delay when stepping on the pedal. I do not use the switching supply as the lamp supply though I take a direct feed off the solenoid live, just using the ignition fed supply as a switching signal.

I think I have a picture, ah yes. The power in on pin 30 is direct from the solenoid live and the switching is simply done by pins 85 and 86 and gives me no delay putting on the lights.

This has been an interesting thread, Bud K and as a result I will be relay protecting my halogen headlights.


Bill

Thanks lads,

There seems to be some difference of opinion regarding fitting a relay for a halogen (do you remember when they were called Quartz Iodine?)upgrade on the headlights.

Having just returned from my -6 degree centigrade garage, I have established that my yet to be fitted halogens are main beam 65w and dipped 55w.(Wipac)

In view of what Bill said, I probably won't fit a relay (until I've burned out a couple of switches, that is)

Dave
Penwithian

Dave dont let me stop you mate but I just gave a warning against excess

I may actually fit relays for the halogens myself, there is some potential for a problem when the originals were summat like 60/45s werent they?

Not a huge increase but worth a thought

Were QI not different to Halogens then?

Bill

Read my previous post carefully. Even with the standard bulbs the switches wear out. They are a pain to replace(!) and the new ones are not as good. If you properly install a pair of relays, you can reasonably expect the existing switches to outlast your interest in Spridgets, especially if you were to clean and lube them.
David "not fond of disassembling steering columns" Lieb
David Lieb


Plus by adding relays, you can use a heavier gauge wire for the power feed, and that with the shorter cable run means less power drop, which equals brighter lights.

I'll be doing it, as I've done on most old cars I've owned when I fit my Cibe's.

I run a larger cable to a secondary fuse mounted near the front and this in turn provides power for the headlights, air horn and fan motor.

By doing it this way I only add one wire to the under bonnet area, then a small extra loom from the fuse box to the lights etc., keeps all the wiring neat and tidy.

The fuse box is the type which has one feed in and 6 out, but with 6 fused circuits.

Andy
a borris

Andy,
Sounds like you might have me beat for added fuses in a Spridget. Last I chaecked, I had seven non-original fuses in my 72 ;-)
David "no fun when blowing the horn takes out the headlights at night on a busy expressway" Lieb
David Lieb


I usually have the dip (low) beam un-fused and the main (high) fused, but the dip is on at the same time, so if the fuse does blow, you've still got lights.

And because it's all new wiring and from a single source (usually starter solenoid), it's pretty reliable. And if the worst happens, because the original wiring is still intact, you can even bypass the relays.

AndyB
a borris

This thread was discussed between 06/01/2009 and 11/01/2009

MG Midget and Sprite Technical index

This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.