Classic cars forum & vehicle restoration.

[Ray White]

I have installed a positive earth Dynamater (alternator that looks like a dynamo) and it came with a wiring diagram that I am posting here.
http://www.accuspark.co.uk/InstructionsPDF/Dynamator%20Positive%20Earth%20Instructions.pdf

I have a relay wired as shown but what I need to know is...do I have to fuse it somehow? If so, where does a fuse go?

[ukdave2002]

Hi Ray ,what do want the fuse to protect? I think you have everything that the alternator supplies fused anyway, as someone mentioned the other day every time you add a fuse its another point of failure/ reliability.

My 1967 Bedford CA has a single fuse and a thermal cut-out integrated to the light switch!

Dave

[Ray White]

Good point Dave.

I think I shall leave it as it is.

I just had it in my head that every relay should have a fuse with it; regardless.

[Bitumen Boy]

I have a vague memory of relays that had an integral fuse; whether they were intended for car electrical systems I don't recall.

[Ray White]

[ukdave2002]

[Ray White]

[petelang]

Ray, the ignition warning light is only illuminated when not charging, ie ignition on, engine static. Even at low charge rates there will be an opposing voltage coming from the field to dim it so the chance of it melting the indicator bezel is slim to the extreme.

Go and worry about fitting the wings and stop getting stressed over the electrics. You'll never sleep at night.
Having said that, I'm not getting a lot of kip at present as I'm learning to mig welder my Armstrong Siddeley wings and they're compley shape patches so it all goes round in my head when it reaches the pillow and I have those "eureka" moments at about 2.30 am, but have forgotten it again in the morning!
Peter
_________________
Daimler Fifteen 1934
Armstrong Siddeley 15 Long 1933
Daimler V8 250 1969

[Ray White]

Good advice Peter. Without getting enough sleep I can't think straight !

Originally, the low level petrol warning light and matching ignition warning light used the same 2.5 Volt 0.5 Watt bulbs with a resistance coil wrapped around the bakelite bulb holder. I don't know for sure but I wondered if this also had something to do with the earthing of the sender unit in the presence of petrol?

Sometime in the distant past, I presume the resistor wire failed and a previous owner fitted a 12 volt 2 watt bulb to the low level petrol warning light and slightly 'melted' the plastic lens. I have been able to rescue the lens but I don't want the same thing to happen again.

I researched the problem and found that the same can happen with the ignition warning light. Modern replacement lights have the resistance coil wire but they cannot be relied on. They are also fitted with a 12 volt 2 watt bulb but as other owners have found, even they can generate enough heat to melt the plastic lens!.

As I said in my previous post, I can perhaps fit a low voltage, low wattage torch bulb and maybe a stand alone resistor which I have in stock.

I have had to rebuild all my dash lamps and in doing so tried - with the aid of a weak coil spring - to leave an 'air gap' between the bulb and the lens.

As you say, I should be getting on with the bodywork. I need to paint the tub and scuttle but I can't do that until I have all the electrics done because the dashboard will have a leather covering and I can't do that until I have the dashboard electrics finished.

I realise I am my own worst enemy because I have embarked on so many upgrades instead of sticking to the simple and basic.

[ukdave2002]

The coils wound round warning lamps are just electrical resistance, the resistance limits the current to the bulb, in essence the bulbs are never operated at their "normal" voltage and current thus extending the bulb life. Also in the day the most robust filament bulbs were those used in hand torches, hence the 2.5v

Why do this? simply because they are warning lamps and they don't fail "safe", so you want to protect and maximise their life.

I suspect they were discontinued because Lucas had more failure with the delicate fine wire used for the coil! not to mention the cost.

Dave

[Ray White]

[ukdave2002]

Bulb and resistance coil are wired in series, doesn't matter which side of the bulb the coil is, the current will be the same in both components.

[Ray White]

[ukdave2002]

[Ray White]

I guess it wouldn't light up at all..?

I suppose what I am asking is why there isn't a resistor on BOTH sides of the bulb?