How to change the Rover torch bulb to LED/CREE [Archive]

View Full Version : How to change the Rover torch bulb to LED/CREE

CDTi

8th January 2009, 22:23

Following on from here (http://the75andztclub.co.uk/forum/showthread.php?t=29895&highlight=cree), I decided to change the bulb in my torch to something a bit more powerful. I purchased a BMW unit as a spare some time back so I used this.

Step 1: obtain the new bulb.

I looked for direct replacement bulb but couldn't get a suitable one so I bought this torch (http://dealextreme.com/details.dx/sku.12849).

http://www.the75andztclub.co.uk/forum/imagehosting/33496656f308eb6.jpg

The eagle-eyed among you will notice that this bulb is only rated to 1.5 volts, and our torches run at a higher voltage (2.4 nom). However this seemed to be the only size that would fit into torch and most CREEs have a reasonable tolerance for a bit more juice :D. I have since used the bulb in the Rover torch for about an hour in total and it hasn't burned out or over-heated.

Step 2: Open the Rover torch.

Thanks to Greeners for this

link (http://www.bimmerboard.com/forums/posts/137453)

Here is a pic of our torch opened:

http://www.the75andztclub.co.uk/forum/imagehosting/334966570d98a0b.jpg

Step 3: Remove the new bulb.

First unscrew the bulb from the torch:

http://www.the75andztclub.co.uk/forum/imagehosting/33496656f3425f6.jpg

and then remove the bulb from the holder:
http://www.the75andztclub.co.uk/forum/imagehosting/33496656f370065.jpg

Removing the bulb isn't a pretty job. I used a combination of a hacksaw, snips and BF&I.

Step 4 - Modify the new bulb.

The job would have been much simpler if the existing bulb polarity wasn't the reverse of what is considered "normal" i.e. the tip of the bulb should be positive. So I had to solder a piece of wire onto the tip of the new bulb and bend it around the bulb so the switch could make contact with it. I used a paperclip as its rigid and the switch will be making contact with it. I also used a bit of yellow heatshrink for obvious reasons;):
http://www.the75andztclub.co.uk/forum/imagehosting/334966570e08a94.jpg

Step 5 - Enlarge the existing bulb holder.

The CREE bulb is bigger than the original so the holder must be enlarged. I did this with a Dremel

Step 6 - Fit the new bulb.

I used double sided tape to hold it in place:
http://www.the75andztclub.co.uk/forum/imagehosting/334966570e6cea4.jpg

http://www.the75andztclub.co.uk/forum/imagehosting/33496657480e844.jpg

http://www.the75andztclub.co.uk/forum/imagehosting/33496657479999a.jpg

I had to modify the switch a little so it makes good contact with the newly soldered and bent paperclip. I also soldered the red wire for the negative pole of the bulb. I obviously did lots of testing at this point to make sure that all was working correctly and reliably.

Step 7 - Re-assembly.

I used superglue to glue the 2 parts back together again and it worked very well indeed:
http://www.the75andztclub.co.uk/forum/imagehosting/3349665e537e54b.jpg

I also stuck the reflector from the CREE torch to the white reflector bit from the MGR torch:
http://www.the75andztclub.co.uk/forum/imagehosting/33496664a79d231.jpg

http://www.the75andztclub.co.uk/forum/imagehosting/3349666681616b6.jpg

http://www.the75andztclub.co.uk/forum/imagehosting/3349666681ec157.jpg

Step 8 - Comparison!!

A picture tells a thousand words:

http://www.the75andztclub.co.uk/forum/imagehosting/3349666421227df.jpg

http://www.the75andztclub.co.uk/forum/imagehosting/334966646629eb2.jpg

I haven't got a lux meter but the finished product is much, much, much, much, much brighter than the original :D

scgfull

9th January 2009, 08:48

CDTi

9th January 2009, 09:12

but what difference does it make to a bulb if the polarity is reversed? I just wondered why you needed to go to the effort of changing it (the polarity thatis).LED/CREE bulbs are polarity sensitive. Filament bulbs are not.

So even if you got a direct LED replacement for the original bulb it would not work.

scgfull

9th January 2009, 10:44

Ah ha, that answers that - Thanks

NikTheGeek

12th January 2009, 19:21

Thanks very much for that CDTI, an excellent guide.

Just one query and please forgive my ignorance, but what difference does it make to a bulb if the polarity is reversed? I just wondered why you needed to go to the effort of changing it (the polarity thatis).

LED = Light Emitting *Diode* - ie it will only allow electickery around in one direction. Try it the other way and it will burn out...

CDTi

12th January 2009, 19:36

Try it the other way and it will burn out...Ah.....no. Its a diode so it will only allow current flow in one direction only. An ordinary LED will not burn out if connected up the wrong way around. I don't know if the CREE is different.

Harrygsi

14th January 2009, 11:39

..........just to hi-jack the thread, on another matter relating to lights have you read the PM I sent the other day please?

Cheers
Peter

CDTi

14th January 2009, 12:02

..........just to hi-jack the thread, on another matter relating to lights have you read the PM I sent the other day please?

Cheers
PeterRead and replied.

lowedb

16th January 2009, 16:23

Ah.....no. Its a diode so it will only allow current flow in one direction only. An ordinary LED will not burn out if connected up the wrong way around. I don't know if the CREE is different.

Depends on the voltage. They can only take a fairly small reverse voltage before the junction breaks down (just looked at a typical red LED and it's max reverse voltage is 5v), unlike a normal rectifier diode with a fairly high reverse voltage in the 100s of volts usually.

Not a problem in our case with only 2.4v, but can be a problem particlularly in 12v designs.

CDTi

16th January 2009, 16:54

Depends on the voltage. They can only take a fairly small reverse voltage before the junction breaks down (just looked at a typical red LED and it's max reverse voltage is 5v), unlike a normal rectifier diode with a fairly high reverse voltage in the 100s of volts usually.

Not a problem in our case with only 2.4v, but can be a problem particlularly in 12v designs.Its been a while since I played around with LEDs but the ones I used were all low voltage with a voltage dropping resistor in series. So the effective voltage was always low (about 1.7V?)

I don't doubt what you are saying, though ;).

Colin.Tinker

16th January 2009, 20:40

NOCTURNAL

17th January 2009, 11:47

LED Life withstanding... NICE JOB :)

CDTi

17th January 2009, 16:39

I thought I'd mention that the LED torch that has been used in this modification has a voltage increasing circuit in the cap that the LED is mounted on. The torch is designed to run off a 1.5 volt battery. The electronics then boost the voltage to over 3 volts to run the LED. Since the modified unit is now running from a battery voltage in excess of 1.5 volts it will be overdriven and consequently have a shorter lifespan.I agree - its never a good idea to run any kind of electronics on a higher voltage. Sometimes even a lower voltage can damage equipment.

I have run the torch for a few hours at this stage and there is no sign of any problem as yet and the bulb doesn't get hot. I also noticed during the modification process that the battery voltage dropped to about 1.7 volts under load when the bulb was on.

lowedb

23rd January 2009, 15:53

Its been a while since I played around with LEDs but the ones I used were all low voltage with a voltage dropping resistor in series. So the effective voltage was always low (about 1.7V?)

I don't doubt what you are saying, though ;).

To explain why it's as it is:

Yes the voltage is low (2v is fairly typical depending on colour) but as Mr ohm says, the voltage is only dropped in the droppoing resistor when current is flowing. So when you apply it in reverse, no (or next to none) current flows, and hence the full voltage is applied across the LED until it breaks down. Then the resistor starts to reduce the voltage, but it's too late then.

Interestingly, was working with some white LEDs this week and they've put a zener inside the package to prevent this. Didn't half cause some head scratching as the package anbd die are also unusual in that the flat was Anode which is normally cathode.

CDTi

23rd January 2009, 17:32

To explain why it's as it is:

Yes the voltage is low (2v is fairly typical depending on colour) but as Mr ohm says, the voltage is only dropped in the droppoing resistor when current is flowing. So when you apply it in reverse, no (or next to none) current flows, and hence the full voltage is applied across the LED until it breaks down. Then the resistor starts to reduce the voltage, but it's too late then.

Interestingly, was working with some white LEDs this week and they've put a zener inside the package to prevent this. Didn't half cause some head scratching as the package anbd die are also unusual in that the flat was Anode which is normally cathode.You obviously know your LEDs :D - and there is no escaping V=IR.

The addition of a zener is interesting but why would they change the conventional leg shape :confused:

lowedb

23rd January 2009, 19:14

You obviously know your LEDs :D - and there is no escaping V=IR.

The addition of a zener is interesting but why would they change the conventional leg shape :confused:

Dunno.

Certainly caused some head scratching though. Trainee wired it up, connected it, no light. 1 and a bit volts across it, 11 across the resistor.

'You numpty you've wired it the wrong way' says my colleauge and looks at it, then decides it's OK. Several minutes with a meter and still no light. Things are a bit confusing as we'd never come across the zener before.

So I get back into the office. 'You numpty's you've wired it the wrong way' says I. Then I look, and it seems OK. So I check the part number and start to look at the data sheet, because it can't be that hard and I have seen wierd stuff like this before. This had obviously prompted our trainee to do the same, and that made him spot his mistake. Switched the wires, and off we go.