Matthew_1
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| posted on 10/11/04 at 12:46 PM |
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Relays or not ?
I'm in the process of doing the electrics now and wondered if relays are needed for the lighting or not?
All the mini's I've ever worked on don't have them, yet the Sierra and Mondeo Haynes manuals both show relays in the circuits.
I assume its to reduce current/heat draw etc in long cabling runs and where you have lots of things which draw current from the same cable,?
Anyone any thoughts on if I should wire in relays ?
Cheers
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craig1410
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| posted on 10/11/04 at 12:56 PM |
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Matthew,
It depends to a large extent on what the current rating of your lighting switch is. As a rule of thumb I'd say that, if the donor vehicle (donor
of the light switch/dip-main switch that is) uses relays then you should as well.
I'm using Sierra column stalks and switches and thus I am using a pair of relays - one for main beam and one for dip beam. The side lights are
driven directly from the column stalks and I have split the left and right hand side with separate fuses. You should also use split fuses for both the
main beam and dip beam by putting the output from you r relays through a pair of fuses. That way if one bulb goes and causes a surge, blowing the
fuse, you will still have one good headlight. I once had a Mini which had complete lighting failure at night on country roads while I was learning to
drive. It is very very scary indeed as you get plunged into pitch black with only a memory of the road ahead to guide you safely to a halt!
Cheers,
Craig.
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Petemate
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| posted on 10/11/04 at 02:37 PM |
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Hi Guys.
Craig's views fully endorsed - any Ford with relays is a Ford with fragile contacts in the column stalks; they do not last long without relays
especially if you decide to up the wattage of the bulbs. Better safe than sorry, also a very good idea to run separate fuses for each side - total and
sudden darkness is NOT good when going at a fair lick!!
Petemate
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nick205
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| posted on 10/11/04 at 03:04 PM |
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As above and I can confirm thast the later Sierra column switches will start to smoke in an unhealthy manner when faced with too much current.
Luckily the fuse went first and my switches were OK!
HTH
Nick
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splitrivet
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| posted on 10/11/04 at 04:33 PM |
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I'm with all these guys,Mini's if my memory doesnt fail me had toggle switches rated at about 25 amp.Ford stalks will carry bugger all
juice, if your using ford stalks youd need relays for sure, if not toggle switches will do it but then your into SVA territory.
Cheers,
Bob
[Edited on 10/11/04 by splitrivet]
I used to be a Werewolf but I'm alright nowwoooooooooooooo
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Hellfire
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| posted on 10/11/04 at 04:39 PM |
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Endorsement
Ditto the above comments but adding:
If the mini switches handle 25 A it's obvious it can handle 100W (16.7A) headlights? (Amended  Thanks PioneerX)
I'd consider it imperative to use relays on an open top car - just incase they get wet. That way the fuse blows much earlier and not frying you
or the car!
[Edited on 10-11-04 by Hellfire]
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PioneerX
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| posted on 10/11/04 at 04:49 PM |
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Hellfire,
I think you read it wrong. Mini switches are 25A not (watts) therefore there power tolerance would be 300watts.
Either way I decided to go for relays as it just adds an extra level of protection should the column get wet. Fuse & relay are far cheaper than
replacing a burned out loom.
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Deckman001
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| posted on 10/11/04 at 05:46 PM |
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So have many people put fuses in-line to the lights, I'm using a premier loom and thought their fuses were enough ? or have i got the wrong
end of the stick and you are all using home made looms ?????
Jason
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Surrey Dave
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| posted on 10/11/04 at 07:53 PM |
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I used a Premier loom on my build with Sierra stalks . came with relays and fuses, no probs ,and Alan at Premier is a very helpful guy.
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Hellfire
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| posted on 10/11/04 at 09:50 PM |
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Fuses are fine - it just means using heavier capacity switches and cabling usually!
quote:
Originally posted by Deckman001
So have many people put fuses in-line to the lights, I'm using a premier loom and thought their fuses were enough ? or have i got the wrong
end of the stick and you are all using home made looms ?????
Jason
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craig1410
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| posted on 10/11/04 at 10:57 PM |
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Guys,
I am with you all 100% on using relays to reduce the loading on the column stalks, lighting switch and ignition switch but I don't believe that
you will get any extra protection from relays if the electrics get wet! Remember we are only dealing with 12 Volts which won't cause much
current to flow through pure water which is not a good conductor. Obviously the water which falls from the sky isn't pure (sadly) but even so
you would be hard pressed to push enough current through it to cause a loom to melt.
In fact, due to the fact that the relay is acting as an amplifier but taking a small control current to switch a large load, you might find that
having relays is actually a disadvantage. I say this because it is "possible" that the water might flow enough current to activate the
relay unintentionally and thus switch on your headlights or horn or something. I wouldn't lose any sleep over this mind because the chances of
it happening with anything but the most salty water would be very slim. My relay boxes which I bought from Vehicle Wiring Products (P/N RB4U) have an
o-ring seal on the lid so assuming I don't end up upside down in the rain (possible!) or submerged (less likely) then my relays should remain
dry.
Just for info, I have a 16 fuse and 8 relay setup on my locost. I'm not using all of the relays initially as I don't intend to have a
windscreen for SVA but eventually the relays will control: Main Beam, Dip Beam, Horn, Radiator Fan, Fuel Pump, Ignition Relay (To feed wipers,washers
and heater blower) and two spares for stuff like front fog lights or driving lamps or of course my electric hood
Cheers,
Craig.
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Hellfire
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| posted on 13/11/04 at 08:51 PM |
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quote:
Originally posted by craig1410
Guys,
I am with you all 100% on using relays to reduce the loading on the column stalks, lighting switch and ignition switch but I don't believe that
you will get any extra protection from relays if the electrics get wet! Remember we are only dealing with 12 Volts which won't cause much
current to flow through pure water which is not a good conductor. Obviously the water which falls from the sky isn't pure (sadly) but even so
you would be hard pressed to push enough current through it to cause a loom to melt.
In fact, due to the fact that the relay is acting as an amplifier but taking a small control current to switch a large load, you might find that
having relays is actually a disadvantage. I say this because it is "possible" that the water might flow enough current to activate the
relay unintentionally and thus switch on your headlights or horn or something. I wouldn't lose any sleep over this mind because the chances of
it happening with anything but the most salty water would be very slim. My relay boxes which I bought from Vehicle Wiring Products (P/N RB4U) have an
o-ring seal on the lid so assuming I don't end up upside down in the rain (possible!) or submerged (less likely) then my relays should remain
dry.
Just for info, I have a 16 fuse and 8 relay setup on my locost. I'm not using all of the relays initially as I don't intend to have a
windscreen for SVA but eventually the relays will control: Main Beam, Dip Beam, Horn, Radiator Fan, Fuel Pump, Ignition Relay (To feed wipers,washers
and heater blower) and two spares for stuff like front fog lights or driving lamps or of course my electric hood
Cheers,
Craig.
Craig - I've never read so much bollox in all of my life!
Water is an excellent conductor of water - for a start!!!! That's why there are no flickable light switches in a bathroom! AND all of the
bathroom accesories and metal objects need to be earth banded!
It isn't volts that kills you - the AMPS do the killing of which there are plenty in a car battery - hence the 10mm^2 wire from battery to
starter motor and earth strapping. 
I am absolutely flabbergasted that you give scant regard to the apparent innocence of a electricity supply.
Did you realise people die through touching a fully charged PP9 battery on thier tongue???
I don't envy anyone driving in your car if you have done the wiring my friend with your attitude towards electricity. Electricity is a killer -
make no mistake!!!!
THIS ATTACHEMENT IS NOT FOR THE SQUEAMISH OR WORKSAFE
It is of a malasian man who wired in his own shower - incorrectly. He was holding the plastic shower head at the time - water conducted the
electricity!
YOU HAVE BEEN WARNED
ELECTRICITY KILLS
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Hellfire
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| posted on 13/11/04 at 09:14 PM |
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Sorry if I went overboard - I just couldn't believe what I just read.
No offence. 
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JoelP
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| posted on 13/11/04 at 09:17 PM |
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i think craig is right, myself. 12v isnt enough of a potential difference to flow thru flesh, unless you do the tongue trick - and if your tongue is
that big, you deserve a shock!
amps kill indeed, but there are only so many amps thru the starter wires cos the resistance is so low.
if you touch both terminals of a battery, you dont get a shock. 24v is a tingle. 50 is a bit more.
remember v=ir. since there is a lot of resistance between your finger tips, current is negligable at low volts.
not saying that electricity is harmless, obviously, cos it isnt. but i think craig isnt too far off the truth.
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Hellfire
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| posted on 13/11/04 at 09:40 PM |
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The reason you don't get a shock when holding both terminals is due to the resistance of your hands being dry.
Lets draw a mental picture:
On a pootle drive one Sunday afternoon, the weather turns a little inclemant. The rain falls into your lap, wets your jeans and proceeds to run
between your legs and gradually fills up your lovely GRP seat. Unbeknown to you the main feed to your headlight relay has fallen off and is dangling
precariously low to the shiny aluminium/steel floor.
The rain and dampness begin to everso slightly fill up the metal bath you curerntly sit in... which so by happens to be connected to the negative side
of the battery! The positive wire which has detached itself from the connector is waivering dangerously close to the floor which is now slightly wet.
But we're going slightly uphill which means the water puddle is towards the back of the car.
At the top of the hill is a level T Junction where we will be applying the brakes and the slurry of water will head towards the live naked headlight
wire....
The floor is wet - you are wet, you will become part of the electrical loop - you guess what happens...
Not scaremongering - just worried!
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dmottaway
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| posted on 13/11/04 at 11:24 PM |
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I am a telephone repairman and work outside in all sorts of weather. The voltage on the line is usually in the neighborhood of 24v DC and in 30 years
of working on lines in the rain I have never even felt the slightest tingle. Except, of course, when the line is ringing! Then it is 110v AC, and
that wakes me up.
dave
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Hellfire
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| posted on 13/11/04 at 11:36 PM |
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Thanks for that Dave - I'm glad you agree with me.
USA phone systems have only 20mA current normally at 40V though varies up to 150V. Using the negative 40V your system has proves my point nicely...
Don't want to put a spanner in the works but you ought to read up!
http://www.hut.fi/Misc/Electronics/circuits/telephone_ringer.html
[Edited on 13-11-04 by Hellfire]
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craig1410
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| posted on 13/11/04 at 11:38 PM |
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Hmmm...
Not quite sure where to start with the defense of my point of view or indeed whether I can be bothered but I feel I owe it to mankind (or at least
this forum) to at least try. Hellfire, I don't wish to be disrespectful but it seems clear that electricity is not your strong point matey. I
also don't want to be a smart arse but I have a degree in electronics and electrical engineering as well as 20 years+ of practical experience in
the subject. I also used to design engine management systems for Lucas Automotive.
1. Agreed - current kills not voltage and the CAPACITY of a car battery to produce amps is very large. 20mA can stop your heart and a car battery can
produce somewhere in the region of 500A which is 25000 times the lethal current level.
2. Ohms law states that V=IR or I=V/R if you prefer. Therefore the current flowing through an object of a given electrical resistance (cable,
filament, starter motor, human body) is proportional to the voltage applied across that object and inversely proportional t the resistance of the
object.
3. Resistance of a material (steel, rubber, skin) depends on the cross section through which the current flows. In simpler terms, if you grab a little
skinny wire with your finger tips then a smaller current will flow than if you lie flat out naked on a copper plate with another copper plate on top
of you... (As you do...)
4. Human skill resistance is usually somwhere in the 100's of KOhms to 1MOhm range and thus with only 12 Volts to drive the current through this
very high resistance only around 12uA (microamps) to 120uA would flow and according to scientific studies this is likely to be below the perception
threshold of a typical human, never mind dangerous!
While confirming my values for skin resistance on google, I found this article which I
think is a good balanced piece. Note that at the end of the article the author says that 12V can in fairly specific and unusual circumstances produce
a "sensation" but is not in itself dangerous. I'd refer you to point 4 above where large contact areas can reduce resistance.
Getting back to the original argument, relays will not in any way that I can possibly imagine, protect you better if they get wet and, Hellfire, your
comment that the fuses will blow earlier if relays are fitted and they get wet is highly unlikely to say the least... A fuse will only blow if the
current flowing exceeds the rating of the fuse (ignoring vibration fatigue of course).
By the way, thanks to JoelP for backing me up on this.
Cheers,
Craig.
ps. Here are a few gratuitous 's just to keep Hellfire happy!
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craig1410
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| posted on 13/11/04 at 11:41 PM |
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quote:
Originally posted by Hellfire
Thanks for that Dave - I'm glad you agree with me.
The way I read it he didn't agree with you!
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Hellfire
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| posted on 13/11/04 at 11:55 PM |
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Craig - graduate or not.
Water is a poor conductor of electricity?
I would never smirk in the face of an educated person - and no electricity is not my strong point I admit freely. However, I would rather have a 5A
fuse blow on the secondary switching feed to the relay rather than a 20A fuse for the primary.
As for reaction speed - how quick can you undo a safety belt and jump out of a car?
I am not being synical or clever - a little knowledge is a dangerous thing, I understand that in it's most humbleness... I have the greatest
respect for electricity thats all. I know the basic's, maybe a bit more and that's about it. I'm not into a sh!t throwing contest -
please don't read it as such.
JoelP may have altered his opinion a little by now.... I believe
Your quote:
Getting back to the original argument, relays will not in any way that I can possibly imagine, protect you better if they get wet and, Hellfire, your
comment that the fuses will blow earlier if relays are fitted and they get wet is highly unlikely to say the least... A fuse will only blow if the
current flowing exceeds the rating of the fuse (ignoring vibration fatigue of course).
Being as there should be two fuse's that feed a relay (primary and secondary) - wouldn't the smaller of the two fuses blow first? Thereby
protecting your treasures. If there was no relay you would have a direct main feed of 20A or more... surely this would have caused much more damage
than the 5A blowing first?
I don't mean to sound direspectful but are you sure you graduated, bearing in mind your simple mistakes?
Teach me - I may learn something, but don't shout or I learn nothing!
[Edited on 14-11-04 by Hellfire]
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craig1410
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| posted on 14/11/04 at 12:27 AM |
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quote:
Craig - I've never read so much bollox in all of my life!
Hellfire, I didn't start the shouting I think you will find but I suppose you did at least apologise for your outburst a bit later. No offence
taken in any case.
If you read my original posting you will see that I said that "pure" water was not a good conductor and if you check scientific datasheets
you will see that this is 100% correct. According to the first website I found from google it has a resistivity of 250000 ohm-meters compared to
copper which has a resistivity of .00000001724 ohm-meters (A difference in the region of 14.5 million million times)
However, as I also said, pure water is hard to come by and impurities such as salt in water radically change the resistivity. A typical value for
seawater would be 0.23 ohm-meters which is still over 13 million times poorer than copper. Hopefully you will see my point.
Anyway, of greater concern to me right now is your last statement:
quote:
I would rather have a 5A fuse blow on the secondary switching feed to the relay rather than a 20A fuse for the primary.
Are you telling me that you are placing your fuse in series with the relay coil rather than in series with the relay contacts? If so then you have a
bigger problem to concern yourself with than getting your relays wet! While there is nothing fundamentally wrong with fusing the relay coil circuit I
really really hope that you have ALSO placed a suitable fuse in the circuit between the relay and the load or alternatively between the relay and the
battery positive terminal. If not then you have little or no protection against electrical shorts and are likely to end up with a melted loom at best
or fire at worst.
Let's hope you do have swift reaction times and can unbuckle your belt and get out quick should the worst happen. In all seriousness if I have
picked you up correctly then you really should get an auto-electrician to take a look or seek some help on the forum here. I'd be happy to help
if we are still on speaking terms after all this...
Cheers,
Craig.
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craig1410
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| posted on 14/11/04 at 12:44 AM |
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Hellfire,
Just saw your edited posting:
quote:
I don't mean to sound direspectful but are you sure you graduated, bearing in mind your simple mistakes?
Oh dear we are getting petty now aren't we?? What simple mistakes would that be? The only mistake I made was getting drawn in to this thread in
the first place!!
...besides, this stuff is elementary high school physics which, as it happens, I was already familiar with when I went to primary school from playing
with Tandy / Radio Shack electronics kits as a kid.
Anyway, this argument has eroded my will to live so I'm off to grasp my car battery terminals with wet hands - Speak to you again tomorrow I
suspect...
Craig.
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Mr G
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| posted on 14/11/04 at 12:52 AM |
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More tea vicar ???
G
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Hellfire
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| posted on 14/11/04 at 01:19 AM |
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I hope we can speak after this - afterall I am learning more this way! I'm not being petty - well not intentionally anyway. You didn't use
a comparator such as copper (or silver dare I add!) in your previous posting's Craig regarding conductivety.
Anyhow - this all makes for a light hearted discussion on a Saturday Night - beats watching the X-Factor anyday! IMHO
I'd love a cup of tea - BTW! Maybe when I'm in Scotland next Scotlad (oh no - not again!), yourself and I could chat over a pint or
three?
So you do agree with relays then Craig All the best.... end of postings! You bite so easily!
[Edited on 14-11-04 by Hellfire]
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Peteff
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| posted on 14/11/04 at 10:10 AM |
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Yes please....
1 sugar, not much milk thanks.
yours, Pete
I went into the RSPCA office the other day. It was so small you could hardly swing a cat in there.
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