6V -> 12V @ 25 watt

[Dan East]

I've done a lot of searching through the forums, and couldn't find a suitable solution for what I'm looking for.

I have an older motorcycle that is 6V. The headlights for this bike are expensive, and are based on old technology. I want to use a 12V headlight so I can utilize modern higher efficiency technology as well as save money on replacement bulbs. So I want to go from 6V 25 watt lamp (4.2 amp) to 12V 25 watt (2.1 amp).

What type of circuit would work for this, and how efficient would it be?

PS, does anyone have really annoying problems when typing a message in this forum when using Firefox? It keeps missing the spaces I type.

Dan East

 

[things]

what type of bulb are you planning on using? eg; halogen, led's

 

[mvs sarma]

I've done a lot of searching through the forums, and couldn't find a suitable solution for what I'm looking for.

I have an older motorcycle that is 6V. The headlights for this bike are expensive, and are based on old technology. I want to use a 12V headlight so I can utilize modern higher efficiency technology as well as save money on replacement bulbs. So I want to go from 6V 25 watt lamp (4.2 amp) to 12V 25 watt (2.1 amp).

What type of circuit would work for this, and how efficient would it be?

PS, does anyone have really annoying problems when typing a message in this forum when using Firefox? It keeps missing the spaces I type.

Dan East

Hi,
if the 6V bulb is drawing 4.2amps , the 12V converter will have an efficiency of 80% and thus it will draw more current at 6v as finally the load is measured at 6V battery point.
instead better have 6V halogen bulbs where the illumination efficiency is better. it may perhaps be little more costly. but these are more durable.

as regards missing characters, check your keyboard and typing habbits.-- for eg i am so poor that i use two fingures. the procedual typeing practice, like'asdfgf--;lkjhj ' etc i neverhad. so itoo face the problems of mis spells and missing characters.
perhpas firefox has nothing todo -- as i am right now Firefox

 

[bananasiong]

Hi,
I'm using Firefox too and I'm satisfied with it. Especially the spelling checking features. Maybe your keyboard is not functioning well.

 

[Hero999]

Perhaps you need to clean your keyboard.

Is it 6VAC or 6VDC?

mvs sarma is right that the input current will need to be slightly more than the output current to make up for the power los in the e converter but it shouldn't matter as the alternator is probably oversize slightly anyway, I assume it'll be alright up to 5A.

If it's 6VAC then I would use a 1:2 transformer; for this I would either use a 1:1 audio isolation transformer with the winding connected in series forming an an auto transformer or a 6V-0--6V mains transoformer secondary as an auto transformer. Also make sure the transformer is rated for at least 5A to match the input current, not the output current.

 

[Blatman Bond]

If you choose DC-DC converter and make it by yourself, charge-pump (doubler) method provide better efficiency than boost converter.

 

[Hero999]

That's a good idea, if it's AC then it's even simpler, a diode and capacitor voltage doubling network will give 14V which most automotive lamps are designed to work from anyway.

 

[CheapSlider]

I agree with Hero about using a transformer or Blatman Bond using a voltage doubler. Either would be easier than a converter.

Your particular bulb may not be the cheapest available but you may have to spend a disproportionate amount in order to be able to fit a cheaper bulb. (If you're having to change your headlight bulb so often, then you may be better off looking at your bikes electrics - is your regulator working properly?)


Have you considered the physical aspects of actually fitting a different type of bulb base into your headlight ?


Can it fit into the existing reflector?
Will it need a bulb holder adapter?
How will the beam pattern be* ?


*You haven't given your area, but some places (EG Europe or USA) can be very strict about headlight beam patterns (though I doubt they'd be too worried about a 25W lamp)

 

[Thunderchild]

if AC then a voltage doubling rectifier will be best

 

[mvs sarma]

capacitor rectifier combination might give rise to initial spike which may accidentally fuse the bulb filament.

even otherwise it requires a lage cap and high current diode to meet 25watts power demand. best may be to wind a auto transformer to double the voltage and use it if filament bulb could not be procured.

perhaps one might change the alternator winding and the circuitry to convert it to 12v model. automobile cos may be selling such conversion kits.

 

[Thunderchild]

perhaps a very low value resitor in series and a hefty zener diode in parallel ? be also warned that if we are talking a sine wave of 6 V RMS this will come out rectified as 6 X 2 X 1.41 so like 18 volts

 

[mvs sarma]

Please consider the power requirement. i believe passive component like 1:2 transformer,is better. or retain back at 6V bulb by somehow procuring a few from other countires and be done with it.

afterall if the bulb fails enroute a journey due to design flaws etc, it is a risk.

 

[Hero999]

perhaps a very low value resitor in series and a hefty zener diode in parallel ? be also warned that if we are talking a sine wave of 6 V RMS this will come out rectified as 6 X 2 X 1.41 so like 18 volts

No, you've forgotten the 1.4V diode voltage drops which are subtracted from the peak AC waveform before it's doubled;
[latex]V_{OUT} =2 (6 \sqrt{2} - 1.4) = 14V[/latex]
Also 14V is the peak DC waveform, the RMS DC waveform will be a bit less so you won't blow the lamps.

 

[mvs sarma]

No, you've forgotten the 1.4V diode voltage drops which are subtracted from the peak AC waveform before it's doubled;
[latex]V_{OUT} =2 (6 \sqrt{2} - 1.4) = 14V[/latex]
Also 14V is the peak DC waveform, the RMS DC waveform will be a bit less so you won't blow the lamps.

thanks Hero999-- You are right

 

[Nigel Goodwin]

I think you're all really missing the point?, voltage doublers are really only suitable for low currents, not headlight bulbs. Switchmode systems could work?, BUT probably not for this application.

It's been mentioned that 25W isn't a very bright headlight, so it's obviously off a pretty naff 'motorbike', only a moped or something similar?. These normally feed the headlight directly from the alternator, so the voltage changes with the speed of the engine, and so does the headlight brightness. The alternator itself is designed to 'self limit' it's voltage output, so once you get to a certain speed it doesn't go any higher.

These don't seem very good conditions for a switchmode converter?.

I used to have a Yamaha DT400 (400cc trail bike), this had similar crappy 6V lights direct off the engine - I thought long and hard about how to improve it, but never actually did anything about it. My thoughts amounted to this:

1) convert the entire electrical system to 12V.

2) fit a MUCH larger 12V battery in place of the puny 6V one.

3) rewind the alternator to provide a higher power 12V, without the speed limit on it.

4) build an electronic charging system to prevent overcharging of the battery.

5) feed the headlight from the battery, like sensible lights.

The sticking point really is rewinding the alternator, particularly for me, as at the time it was my sole means of transport - so I couldn't afford time to mess about with it.

 

[Thunderchild]

well then charge a 12 volt battery thru a doubling rectifier with a proper charging controller and you can then feed the headlight a stable 12 volts

 

[Nigel Goodwin]

well then charge a 12 volt battery thru a doubling rectifier with a proper charging controller and you can then feed the headlight a stable 12 volts

I'm sure a moments thought will show you the flaw in that!.

 

[Hero999]

Not even a diode doubler using 10,000:mu:F capacitors?

I have a Honda CG125 and the headlights are powered from the alternator and I have a feeling that this is also the case on my CB500. The CG125's headlights are a bit dim but the CB500's are bright enough. I think having a bigger bike makes sense in lots of ways and safety is probably the main one as the brakes, lights and tyres will all be better. Having said all of that, I don't see the point in getting a really big bike (over 600cc) as it costs more to tax, insure and it drinks more fuel. There again, I suppose I would say that as I'm more of an A to B persone than someone who rides for the fun of it.

 

[Dan East]

Nigel, you're awfully close to the mark. It's a like-new (2000 miles) 1978 Yamaha DT175.

https://www.bikepics.com/pictures/564302/

The headlight was actually pretty good, until both high and low beams finally burnt out. Replacements bulbs are expensive, and like with an older Suzuki I have, once the stock of OOS parts runs out you're pretty much screwed on a bike like that.

Converting the entire system to 12V is beyond what I want to do right now. As you also predicted, the battery has nothing to do with the headlight - it only helps out with the turn signals and brake light.

At some point I would like to replace the turn signals and tail lamp with LED, but that will be a different project.

Dan East

 

[Hero999]

I've done a quick Google
https://www.bikez.com/motorcycles/yamaha_dt_175_2004.php

It looks like it's still being made!

Perhaps you could upgrade the entire electrical system to 12V by replacing the alternator and all the fittings.

It doesn't look like a bad bike for a nube biker.