6v to 12v Step-up convertor for headlamp?

[Greybeard]

Thanks for all the posts. I have a new Westco 6V AGM battery from Goffys, (http://www.norbsa02.freeuk.com/goffybatteries.htm) that I don't want to throw away. I don't want the expense of converting to a belt driven dynamo, (to achieve 12v output). I have excellent 6v LED tail & brake lights. My thoughts were that if the 6v to 12v converter could be used just for the headlamp,(incandescent) I could easily hide it in the cowling or shell. Later I thought it might be possible to power my SatNav from it as well.

After reading Paul Goffs criticism of LED headlamps I was looking for a real bulb solution.

I see other Step-up converters on Ebay that cover a wider range of voltages. This implies that I could get more than 12volts to my headlamp bulb. Can you sparky type people give me your opinion on that idea please.

[Triton Thrasher]

If you're first to try it, you'll be first to know for sure, but....

85% of 60W is 51W. 

The dynamo only makes 60W at rated speed (3,000 rpm?).  Unless it's a 45W dynamo!

There are losses in the wiring and switches.

The tail lamp draws a little bit too.

Seems like a 60W headlamp bulb will be too much. The light will be dim and the battery will go low.

A 45W bulb may be borderline.

[Greybeard]

Thanks for replying TT. I'm thinking I may take a punt and buy one of these gizmo's to give it a try on my bench.

[Johnny J]

He's not the first, for me it works fine! (with all LEDs). 

[Greybeard]

I have just ordered one of these: http://www.ebay.co.uk/itm/281641111105

The output voltage can be adjusted and it states a power output of up to 400W!

It's coming from China so will probably take weeks to arrive 

When it arrives I'll have a play and let you know how I get on.

I measured the current on my 6v machine. Engine not running, with all lights on my multimeter shows less than five amps. Does that sound correct?

[Triton Thrasher]

I measured the current on my 6v machine. Engine not running, with all lights on my multimeter shows less than five amps. Does that sound correct?

Does it charge the battery to about 7 volts with lights on and engine running at road speed? That's the important thing.


5 amps at 6 volts would be 30 watts. Did the battery show at least 6 volts across the terminals while the lights were on?  If the battery is getting a bit low, the current drops.


What wattage headlight bulb is in it now?

[Greybeard]

I'll check that when I get a chance. Thanks again TT.

[Viking]

Keeping enough electric power for running around town at night or with the light on, is a struggle for the old dynamo system.
The engine need revs. To charge and feed the electric consumption.
If you fit a step up unit you lose even more power. Please bear in mind that the voltage step up unit need cooling, and air circulation inside the headlamp I not “impressive”.
The way to 12 volt is a new 12 volt armature and 12v regulator. ( or Alton generator ).

Why not fit a 6 volt LED headlamp, and 6 volt LED rear light bulb. To ease load on the feeble dynamo system.

[Greybeard]

My voltage converter arrived from China today, (http://www.ebay.co.uk/itm/281641111105?ssPageName=STRK:MESINDXX:IT&_trksid=p3984.m1436.l2649)

First thing; it's a bit bigger than I was hoping for; half of it is a huge heat-sink. I don't think it's going to fit inside the headlamp shell or the headlamp cowl. Might have to put it under the saddle or maybe remove the heat-sink and fix the device to the metal inside the toolbox instead. As it's an open circuit board I need to think about protection from the wet so the toolbox sounds good but then I'd have to make my tool roll slimmer!

I've been in the man-cave carrying out some initial experiments on the bench.
I've connected a 12v bulb into the output terminals and my 6v motorbike battery is connected to the inputs, (via my multimeter set to Amps).
The gizmo is programmable, (no instructions came with it though!). Anyway, I've managed to set an output voltage of 14v, (as advised by,  (I think) Triton Thrasher) for the bulb. The bulb is lovely and bright. The input current from my 6v, (13 AmpHour)  battery is 5.7 amps.
Given that my tail lights are LED's my thinking is that if the battery had no charging it should provide about two hours of light. Does all this sound ok to you electrical guru's?

[bsa-bill]

definitely not a guru but if your battery is 5.7 a/h then double voltage would half the amps required so should that be 4 hours or have I just solved the worlds energy crisis

[Triton Thrasher]

In theory, it should provide 6 amps for about two hours, but I've never seen a motorbike battery power a headlamp for anything like that long.

6 V x 5.7 A gives a nominal total of nearly 35 W. 15% is lost in the stepper-up, so your headlamp bulb is consuming about 30 W of power. Seems a bit low. Can you measure 14 V across the bulb terminals with your meter?

You've gone this far- you may as well try it on the bike.

[Johnny J]

To make it more complicated, lead-acid batteries suffers from a thing called "Peukerts effect".
Normally the 13Ah is true if you discharge the battery with a load of 650mA for 20 hours.
If you apply 5-6A you will not get the 13Ah, but maybe only 8-10Ah.

So the higher the load, the less total energy available...

[Greybeard]

In theory, it should provide 6 amps for about two hours, but I've never seen a motorbike battery power a headlamp for anything like that long.

6 V x 5.7 A gives a nominal total of nearly 35 W. 15% is lost in the stepper-up, so your headlamp bulb is consuming about 30 W of power. Seems a bit low. Can you measure 14 V across the bulb terminals with your meter?

You've gone this far- you may as well try it on the bike.

Yes, I get 14v at the bulb, (or any other voltage, up to the designed maximum).
I should have said I'm using an indicator bulb; I think they are probably 21w; a headlamp bulb, (35w?) will of course need more power.
I'll update when I get a chance to play again.

[Triton Thrasher]

Ah- I assumed it was a headlight bulb.

[Dynamo Regulators Mike]

That may seem like very low efficiency of about 60%, but this does make sense for this type of unit.

The converter here is 400 W rated. The efficiency figure provided will almost certainly apply to somewhere near full output power. Because of the standing power consumption of the converter (regardless of load it will draw current for internal consumption) the efficiency falls at lower output levels.

This can be compared to the old truism that all engines are at their least efficient at idle. No useful output, but some fuel burnt in running the engine.