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[Marks DTM Calib]

.....which might be of interest to some.

Wondered where the lack of light output on the projector lamps was and why it was occuring.

Today I made some measurements on the electrical feed to the bulbs with the engine not running (lower voltage so worst case scenario)

Battery voltage - 12.6V
Bulb Voltage - 11.1V
Bulb resistance - 3 ohm
Calculated watage - 41W!

Its clear that we need to address these volt drops to get max light output as the bulbs are running at 23% less than thier rated amount!!

So, on the 0v side I found a volt drop of 470mV when measured between the bulb body and 0V terminal of the battery. I looked further and 300mV of this is lot across the lucas style terminal that connects the 0V feed to the bulb mount!

So I soldered the terminal to the body and we got:

Battery voltage - 12.6V
Bulb Voltage - 11.4V
Bulb resistance - 3 ohm
Calculated wattage - 43.3W!

Next stop was to look at the positive side.....the volt drop here was close to 1V!

Again, 200mV of this was across the lucas type connector to the back of the bulb.

This cant be soldered as it would affect the ability to change the bulb so I removed the connector and fitted a nice tight new one.

Battery voltage - 12.6V
Bulb Voltage - 11.6V
Bulb resistance - 3 ohm
Calculated wattage - 45W

The rest of the volt drop is clearly a result of the wiring and switch so I may try adding a relay switched feed to the headlights.

Key thing here is though that a small amount of work has yielded a 10% increase in theoretical light ouptut!

[dispondent 1]

 

[dieseldean]

without having to fit overated illegal bulbs nice one

[dispondent 1]

i got some ov them, 100 watters   is that common practice?

[Pitchfork]

i got some ov them, 100 watters   is that common practice?

No & it's very naughty!

[HGV mechanic]

.....which might be of interest to some.

Wondered where the lack of light output on the projector lamps was and why it was occuring.

Today I made some measurements on the electrical feed to the bulbs with the engine not running (lower voltage so worst case scenario)

Battery voltage - 12.6V
Bulb Voltage - 11.1V
Bulb resistance - 4 ohm
Calculated watage - 44.4W!

Its clear that we need to address these volt drops to get max light output as the bulbs are running at 10% less than thier rated amount!!

So, on the 0v side I found a volt drop of 470mV when measured between the bulb body and 0V terminal of the battery. I looked further and 300mV of this is lot across the lucas style terminal that connects the 0V feed to the bulb mount!

So I soldered the terminal to the body and we got:

Battery voltage - 12.6V
Bulb Voltage - 11.4V
Bulb resistance - 4 ohm
Calculated wattage - 45.6W!

Next stop was to look at the positive side.....the volt drop here was close to 1V!

Again, 200mV of this was across the lucas type connector to the back of the bulb.

This cant be soldered as it would affect the ability to change the bulb so I removed the connector and fitted a nice tight new one.

Battery voltage - 12.6V
Bulb Voltage - 11.6V
Bulb resistance - 4 ohm
Calculated wattage - 46.4W

The rest of the volt drop is clearly a result of the wiring and switch so I amy try adding a relay switched feed to the headlights.

Key thing here is though that a small amount of work has yielded a 5% increase in theoretical light ouptut!

please correct me if wrong ,,, but would you not gain more wattage if the volts were at alternator output, i.e 13v ish?  :-?

[RichB]

.....which might be of interest to some.

Wondered where the lack of light output on the projector lamps was and why it was occuring.

Today I made some measurements on the electrical feed to the bulbs with the engine not running (lower voltage so worst case scenario)

Battery voltage - 12.6V
Bulb Voltage - 11.1V
Bulb resistance - 4 ohm
Calculated watage - 44.4W!

Its clear that we need to address these volt drops to get max light output as the bulbs are running at 10% less than thier rated amount!!

So, on the 0v side I found a volt drop of 470mV when measured between the bulb body and 0V terminal of the battery. I looked further and 300mV of this is lot across the lucas style terminal that connects the 0V feed to the bulb mount!

So I soldered the terminal to the body and we got:

Battery voltage - 12.6V
Bulb Voltage - 11.4V
Bulb resistance - 4 ohm
Calculated wattage - 45.6W!

Next stop was to look at the positive side.....the volt drop here was close to 1V!

Again, 200mV of this was across the lucas type connector to the back of the bulb.

This cant be soldered as it would affect the ability to change the bulb so I removed the connector and fitted a nice tight new one.

Battery voltage - 12.6V
Bulb Voltage - 11.6V
Bulb resistance - 4 ohm
Calculated wattage - 46.4W

The rest of the volt drop is clearly a result of the wiring and switch so I amy try adding a relay switched feed to the headlights.

Key thing here is though that a small amount of work has yielded a 5% increase in theoretical light ouptut!

please correct me if wrong ,,, but would you not gain more wattage if the volts were at alternator output, i.e 13v ish?  :-?

I think the reason he has done the test without the engine running is to highlight the areas with voltage drop.  Obviously with the engine running the voltage drop will still occur, but will be more difficult to identify the problem areas.

[Marks DTM Calib]

I need to work with a minimum number of variables.

The resistance of the wires will be constant and wont change with the engine running (which is what we are checking effectively here).

It would appear from the measurements that to get max rated wattage out the bulbs you need about 13V across them.....we are still a little short of this!

[TheBoy]

I need to work with a minimum number of variables.

The resistance of the wires will be constant and wont change with the engine running (which is what we are checking effectively here).

It would appear from the measurements that to get max rated wattage out the bulbs you need about 13V across them.....we are still a little short of this!

Even at running voltage of 14ish, your not going to be much over 12v at the bulb, which isn't that great.

I'm guessing that as most 12v cars are going to be running at 14v, the bulbs are actually designed for 14v running?

Anything to get less loses in the wiring and better voltages at the bulb have got to be

[dispondent 1]

i got some ov them, 100 watters   is that common practice?

No & it's very naughty!

  oh well

[HGV mechanic]

I need to work with a minimum number of variables.

The resistance of the wires will be constant and wont change with the engine running (which is what we are checking effectively here).

It would appear from the measurements that to get max rated wattage out the bulbs you need about 13V across them.....we are still a little short of this!

Even at running voltage of 14ish, your not going to be much over 12v at the bulb, which isn't that great.

I'm guessing that as most 12v cars are going to be running at 14v, the bulbs are actually designed for 14v running?

Anything to get less loses in the wiring and better voltages at the bulb have got to be

my thoughts too, - im thinking there designed to operate at typical running voltages, and the designes resistance, i.e wire diameter/fuse rating

[Mr Skrunts]

i got some ov them, 100 watters   is that common practice?

No & it's very naughty!

Maybe so.  But before HID etc police sars used to fit 130 watt bulbs, so I dont understand, if it's ok for plod, then why not for all road users.


Lets face it, rules is rules.

[Marie]

well done mark, i might have to have a look at doing mine too.

cheers

[Marks DTM Calib]

For info....it would appear that most manufacturers use a test voltage of 13.2V....this also ties in with the measured resistance!

So you only get 55W output at 13.2V at the bulb terminals

[Marks DTM Calib]

Here is a little graph to show how a small drop in supply voltage has a big effect on bulb operating wattage (I²R)