what is the best high level brake light for new style FIA bar

[Roger Ford]

Quoting Willie.: 

What's the purpose of the resistor; is it to drop the voltage to stop the LEDs popping? I tried mine on the car battery (Not running) and it was lovely and bright, compared to the 9V battery, which was quite dull in comparison.

Yes, it's to limit the voltage, and therefore the current. The "forward voltage" is descibed on the Maplin web page as "9.6V (11.2V) ". I assume 11.2 is the maximum it can take. Any LEDs can be overdriven, but the current taken (and therfore power usgae) increases rapidly with voltage. You can get away with a lot of extra voltage for a short time, or a little extra for a long time, but eventually it will overheat and burn out. You can probably get away with 12v from a static battery, but you won't get away with the 14.4 volts that you'd get out of your alternator for very long (been there - when I first fitted one I had no resistor, about half the LEDs had gone after one session).

 

I showed the calculation for the resistor here. You could redo that calculation for 11.2v rather than 9.6v, and perhaps with the alternator output as 14.4v rather than 14.7. The current would increase - we don't know how much by, but perhaps assume 300mA.

 

That gives us a voltage drop across the resistor of 3.2v, and current 0.3. R= V/I = 10.66 ohms.

Maplin do W10R, W15R and W18R. If you want to live dangerously, 10R might work, or it might blow out. 15R or 18R are probably pretty safe and should be significantly brighter than the 22R. If I was doing it again I'd probably use 18R.

 

 

 

[Roger Ford]

Actually looking at the specs again, I think it's 200mA at 9.6v and 250mA at 11.2v. So that gives us a "minimum" resistance of 12.8 ohms, so 10 is definitely dangerous. I might have to take mine off and connect it to the bench power supply to check those figures.

[Willie.]

Hi Roger, thanks very much for the reply and extremely helpful explanation. I've no idea about electronics but keen to get a handle on it, so that really helps.

 

Just measured, so the 9v battery is showing 8.8v and the car battery is 12.8v. There was a significant difference between these two, so the brighter I could run it the better. Have looked at your calculation and reckon taking alternator output as 14.7v and light at a "safe" 10v, again assuming your 0.3a, 4.7v/0.3a = 15.6r

 

Increasing the light to the full 11.2v (With 14.7 alt output) gives 11.6r, so I reckon I should be ok to try the 15R one.

 

On the power side; 4.7v x 0.3a = 1.41w and 3.5v x 0.3a = 1.05a, so again the 3watt should be fine.

 

Given that this is the first time I've even thought about this stuff; does that make sense to you? Don't worry, if I blow it up with the 15R I've only myself to blame, but just checking I did the sums correctly.

[Roger Ford]

Pretty much. On your "safe" 10v calculation, the current is going to be lower than the maximum 0.3A, so let's assume 0.26A, in which case it's 4.7/0.26 = 18 ohms.

 

I think you ought to be safe with 15R, but would suggest getting that and 18R, and measuring the current draw with a multimeter (you do have one, right?). If it's much more than 0.3A with the 15R, use the 18R instead. Do this with the engine running, and rev it a bit first (for some reason that I've never figured out, my alternator doesn't "kick in" at 14+ volts until it's been revved. At tickover from startup it still measures battery voltage. After revving it I get 14+ volts even at tickover).

 

If you don't have a multimeter, add one of these for £8.99 to your Maplin order, or what looks much the same, one of these for £3.45 delivered from ebay.

[Willie.]

Thanks very much Roger. I have a multimeter, just not a great deal of knowledge on how to use it. I'll get the 15R & 18R and do as you say. I'll report back on the results.

 

Showing the extent of my ignorance now, but is it current that requires you to put the multimeter in series with the light?

[Roger Ford]

Yes. And try not to leave the multimeter in "current" mode when you check the voltage of the battery - it tends to let the smoke out.

[David aka Blue7]

Quoting Roger Ford: 

Quoting Willie.: 

What's the purpose of the resistor; is it to drop the voltage to stop the LEDs popping? I tried mine on the car battery (Not running) and it was lovely and bright, compared to the 9V battery, which was quite dull in comparison.

Yes, it's to limit the voltage, and therefore the current. The "forward voltage" is descibed on the Maplin web page as "9.6V (11.2V) ". I assume 11.2 is the maximum it can take. Any LEDs can be overdriven, but the current taken (and therfore power usgae) increases rapidly with voltage. You can get away with a lot of extra voltage for a short time, or a little extra for a long time, but eventually it will overheat and burn out. You can probably get away with 12v from a static battery, but you won't get away with the 14.4 volts that you'd get out of your alternator for very long (been there - when I first fitted one I had no resistor, about half the LEDs had gone after one session).

 

Thanks for your very good explanation Roger I have just bought and fitted one of these 12 v. led rain lights from Car Builder Solutions here

 

I emailed them to enquire if I needed to wire it through a resistor like their Respak2 25 watt here and they replied saying it was unnecessary and to just wire it into the brake light circuit.

 

Your comments have made me think that I maybe should wire it through a resistor but the Maplin one you are discussing seems to be 9.6 v. whereas this one is 12 v. ?

 

Incidentally, I was not looking forward to trying to split the junction box to fit the CC spur into the brake light loom, having done so on my last 7 it is so difficult to split the box with one hand and just about impossible for me to get both hands to it. However, I discovered 2 unused female spade connections close to the junction box on the loom so I tried connecting to these and to my delight and relief they provide a connection for a 3rd brake light

[Roger Ford]

The Car Builder Solutions one probably has a built-in resistor, or possibly even a solid-state driver circuit that provides a constant current.

[David aka Blue7]

Quoting Roger Ford: 

The Car Builder Solutions one probably has a built-in resistor, or possibly even a solid-state driver circuit that provides a constant current.

Thanks Roger

[SUPERLIGHT91]

Some good tips there on wiring up and various lights thanks.

 

Have people seen these products: here

http://www.ebay.co.uk/itm/130869301284

 

and add a fast flasher to catch people's attention when the light first goes on.

cheap example product herehttp://www.ebay.co.uk/itm/Flash-Strobe-Controller-Flasher-Module-for-LED-Brake-Stop-Light-12V-/370731798859?pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item565156514b

 

demo video

 

[David aka Blue7]

Having just fitted one of these and ensured it was working, I discovered yesterday that both brake lights and new led light were not working. I thought it might be the fuse at first but that was still intact.

 

I removed the cover to expose the brake light switch, disconnected the new led light and flicked the brake light switch plunger a few times and eventually the brake lights operated again. However, as soon as I try to reconnect the new led light both brake lights go out again. So back to flicking the brake light switch plunger in and out and brake lights operate again ... until I reconnect the led light and off they go again 😔

 

This car is only a year old so it is not exactly an old switch in need of replacement. It suggests to me that switch contacts are faulty and not able to take the added load of the led light ... unless I am missing something?

 

 

Edited by - Blue7 on 20 May 2013 14:14:48

[Jonathan Kay]

It sounds more like a wiring problem than the switch being unable to supply the extra current.

 

I'd check the wiring and then either:

* Measure the voltage at the old brake lights as you close the brake lights, or

* Temporarily fit the LEDs directly to the switch and earth and retest

 

Jonathan

[Roger Ford]

Take the brake light switch out of circuit by pulling the two spade connectors off it.

 

You can then short the connectors out to make the connection - if you've got the wherewithal, you can make a short lead with a male spade at each end to do this reliably.

 

That way if it still does it you'll know it's nothing to do with the switch.

 

Must say your symptoms don't make a lot of sense. I presume you have conventional fuses, and not some sort of self-resetting thermal circuit breakers?

 

[David aka Blue7]

Quoting Roger Ford: 

Take the brake light switch out of circuit by pulling the two spade connectors off it.

 

You can then short the connectors out to make the connection - if you've got the wherewithal, you can make a short lead with a male spade at each end to do this reliably.

 

That way if it still does it you'll know it's nothing to do with the switch.

 

Must say your symptoms don't make a lot of sense. I presume you have conventional fuses, and not some sort of self-resetting thermal circuit breakers?

 

Roger / Jonathan

 

Conventional fuses for CSR Duratec and I agree, it doesn't make a lot of sense to me either I have connected up another HL led brake light, which I had fitted to my last 7 seen here This operates ok, comes on with the brake lights and the brake lights stay on. This has 48 leds compared to present one which has 72.

 

I carry a spare CC brake switch so I have just wired that up to the new 72 led light and it operates the light ok. I was just going to fit this in place of the existing switch but I can't remove the spade connectors because they are hard up against the bulkhead so I will have to remove the switch first and it looks like I will have to bend the bracket it is attached to in order to remove it. It also looks like the new CC switch is too long for a straight forward swap and looks like it has to have the plunger and casing cut down to size?

 

My brake lights are CC supplied red led bulbs to compliment the clear lenses.

[David aka Blue7]

Well I have fitted the new CC brake light switch and now when I open the circuit it blows the standard 15 amp fuse. So I have increased the fuse rating to 20 amp and it blows that fuse also.

 

I am a bit reluctant to go the a 30 amp fuse so I removed one of the led brake light bulbs and replaced it with a standard brake light bulb, connected up the rain light and result is no blown fuse but no brake or rain light either. So disconnect rain light try again and nothing until I push the brake light plunger in and out and then brake lights operate again.

 

I have connected the rain light direct to the battery with a 10 amp fuse and it doesn't blow the fuse.

 

Seems to me that the switch can't cope with the additional load so I could either take another power supply for the rain light and fit a relay operated by the brake light switch ... or remove the rain light and fit another HL break light similar to my old one (which works ok), which uses less load.

 

Probably should have just left well alone 😔

[Jonathan Kay]

Do you mean close the circuit? If not more details please.

 

Jonathan

 

PS: it's a wiring fault

[David aka Blue7]

Quoting Jonathan Kay: 

Do you mean close the circuit? If not more details please.

 

Jonathan

 

PS: it's a wiring fault

 

Yes sorry close circuit by switching on completing the circuit to supply power to brake lights.

 

If it's a wiring fault I can't understand why my old HL brake light operates ok when connected up to the same terminals?

[Jonathan Kay]

Sorry, should have said "fault with wiring or the LED lamp fitting". But the problem doesn't occur when you you have the lamp fitting connected to the battery rather than the additional wiring. It sounds as if as long as the additional rain lamp wiring and lamp housing and LEDs are open circuit there is no problem, but when they aren't there is.

 

Jonathan

[Roger Ford]

Sounds like a short-to-earth problem somewhere in the connection to the rain light.

 

Have you checked the current going through the rain light when connected directly to the battery? I'd be very surprised if it was more than 1A at the very most - more likely to be around 0.5A or less. The existing brake lights will be 21w each, so that's nearly 4A, so the rain light shouldn't add significantly to the load.

[David aka Blue7]

To rule out the possibility of defective switch I have connected the 2 brake light spade connections to a toggle switch, strangely one spade connector has insulation tape wrapped around it? There are 3 green and maybe purple wires attached to this spade terminal and on closer inspection if I move the wires around a bit the brake lights are flickering on and off, which suggests to me that it is a broken or damaged connection to the spade terminal and whoever wired it up at CC wrapped insulation tape around it to keep it as rigid as possible thereby maintaining a connection. I assume this connection must be breaking down with the extra load?

 

Re bad earth I have already tried just connecting the rain light to the positive feed and earthing the rain light's negative wire direct to the chassis but still the same problem.

 

There isn't much cable to play with at the dodgy spade terminal so I will have to decide whether to just revert back to normal brake lights or attempt a repair with connections to a new spade terminal.

 

The led brake light bulbs have a sticker behind them indicating P521 / 5w. I don't have any instrumentation to measure the rain light amps.

[Roger Ford]

I don't have any instrumentation to measure the rain light amps.

 

FFS. If you don't own a £5 multimeter, stop messing around with electrics. Order one of these and come back when it's arrived.

[David aka Blue7]

Quoting Roger Ford: 

I don't have any instrumentation to measure the rain light amps.

 

FFS. If you don't own a £5 multimeter, stop messing around with electrics. Order one of these and come back when it's arrived.

 

Roger

I'll see if I can get one locally tomorrow at Autoparts, it would certainly be interesting to discover the amount of current going through the rain light.

 

Meantime I have wired the rainlight through a relay using the spur from the brake light circuit to operate the relay and as a temporary set up taken power for the relay 87 / 30 terminals from a spare battery to power the rainlight ... and it works Stepping back to look at it, the rainlight is incredibly bright and puts my normal led brake lights in the shade so it is obviously taking a large current. Incidentally, I have gone back to the standard 15a fuse, which is not blowing.

 

I will get the multimeter tomorrow and report back on my findings but meantime here is a photo of the rainlight, it doesn't really do it justice but pales the standard lights into insignificance and they are fitted with led bulbs and the reflective lens enhancements

 

http://i1211.photobucket.com/albums/cc428/Blu-7/Rainlightsm_zpsa5cf328e.jpg

[Ozzy]

FFS. If you don't own a £5 multimeter, stop messing around with electrics. Order one of these and come back when it's arrived.

 

Can't believe the price of that. Somewhat cheaper than my Fluke! Are you sure it's not a chocolate one 😬

 

 

 

[Roger Ford]

Yeah, I've got one - as well as a couple of more expensive ones - and it works fine. Never going to be up to Fluke standards, but anything better than 5% accuracy is fine for most jobs.

 

[Ozzy]

Truly staggering what you can get for a fiver these days!

 

I've actually still got my old AVO analogue multimeter, which I must have had for 30 years! Still works fine, and came in a nice leather case. That's probably not worth a fiver now, and it probably cost me a weeks wages back then!

 

Oz