Here's a degree level P6 question...

NickDunning

Active Member
Folks

I've recently supplied a couple of good main beams to Rodger Murphy, owner of Rodger's Rocket, one of my favourite cars (A June 1964 'A' suffix Sharkstooth 2000)

We have a query though - on taking his blown main beam off Rodger discovered it to be a mere 37.5w, not the 50w I thought all cars up to 1971 had.

It appears, looking at books I have, that 50w main beams were not introduced until early 1965. I'm still trying to confirm this.

Question is: Can Rodger put a 50w main beam on - does anyone know if there's any reason why not with the early loom?

Told you it was a difficult one. 37.5w main beam? candle power :)
 
harveyp6 said:
If you're worried, just fit relays. Any possible problems solved.

Thanks Harvey.

Rodger is talking about getting the local auto electrician to him to have a look at the car, sounds sensible, he'd have more illumination at night.
 
Interesting Nick :? I didn't know there was a difference.

I put 50w lamps in my April '64 2000 & have tried them without issue, but I've not had them on for long. Come to think of it, my car had a varied collection of (non Lucas) lamps in when I got it which would have been 50w, so presumably they worked safely enough.
 
Nick

I've been in discussion with Rodger on this via Facebook and told him that the wiring will more than likely handle the extra 2 amps difference between 37.5W and 50W inners. Here's the science bit:

I = P/V

Where I = current in Amps, P = power in Watts and V = Volts

For the 37.5W inners, assuming 14V from the dynamo, that gives a total current draw of (2x37.5)/14 = 5.36A

For the 50W inners that gives (2x50)/14 = 7.14A

That's a difference of less than 2 Amps, which the wiring whould be able to handle comfortably :D

The main issue will be the sidelight switch as it carries the entire load for all of the lights when they are on. Even so, the extra 1.78A should not cause any significant issues there. If Rodger has any concerns he should fit a relay as I did in Lady C.

Dave
 
Did the early cars have a dynamo and did the change to alternators coincide with the change from 37.5w to 50w?

Colin
 
arthuy said:
Did the early cars have a dynamo and did the change to alternators coincide with the change from 37.5w to 50w?

Colin

No - Dynamos didn't become standard on a 4-cylinder until Series 2, believe it or not.

What it appears to be is that Rover uprated the main beams from 37.5w to 50w in approx March 1965. I don't believe any alterations were made to the loom at all at this point. I was unaware, until Rodger told me, that his car had 37.5w main beams.

This must mean also that my car has - I will check this out.
 
I think it was fairly typical of Lucas in the 60's that they would produce a ludicrously low power 'Main' beam lamp.
They were addicted to the lowest possible standards they could get away with, and it was road-users who suffered.
Their slogan "Lucas, King of the Road" was rendered by fed-up consumers as "Lucas, Prince of Darkness"
John
 
Dave,

Your calculation is correct and it will not harm the wiring harness much but the weakest link is the switch. So i agree with Harvey and simply fit a relais. When i restored my MGB, i fitted relais for the high and main beam, the cooling fans and the horns. I haven't renewed the switchend and never had any problems with the electrics.
I also adder an extra " return" wire because a lot of "users" had the same return line and this caused a severe voltage drop of more then 1 volt. You saw that the light were more powerfull after installation of this additional return line. I don't know what the electrical system of the P6 looks like, maybe it has more return lines.

Peter
 
my rover had 37watt headlamps(1965) but put in lamps from a series2--no problems-just plug and play--as they say now
 
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