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I have Yamaha RX100 1996 model which has 6 V power supply.

This 6 V power supply is the main drawback for the headlight, where the circuit diagram is shown in these images:

Wiring diagram - schematic

Wiring diagram - legend

The official bulb requirements are given below:

Bulb specification

For further details about the circuit diagram open the link below (page - 63): Yamaha-RX-100-Workshop-Manual.

I plan to convert 6 V 25 W to 12 V 36 W using either this boost converter:

Is it possible or not?

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  • \$\begingroup\$ Why do you think the 6V supply is limited to 4A? If you want a more powerful headlamp, then you draw more power. \$\endgroup\$
    – Pete Kirkham
    Commented Apr 25, 2019 at 12:51
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    \$\begingroup\$ You need to google what power is then you'll have your answer. \$\endgroup\$
    – Andy aka
    Commented Apr 25, 2019 at 12:53
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    \$\begingroup\$ The suggested product has a maximum output of 12 V, 3A. I guess you want to use it for some time at 3A. I would not recommend that as it is too close to the limits of the converter. Such cheap products from China often aren't designed very well and aren't robust. Using it at 3 A will mean it will break soon. Get a 12 V, 5 A converter so it has somewhat more power than needed. \$\endgroup\$
    – Bimpelrekkie
    Commented Apr 25, 2019 at 12:54
  • \$\begingroup\$ It is possible to work and also possible to burn out the fuse or converter and drain 4Ah battery a bit faster. as the surge power on cold lamp is 10x so 360 W \$\endgroup\$
    – D.A.S.
    Commented Apr 25, 2019 at 13:06
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    \$\begingroup\$ In theory, you can't "covert" 24 Watt into 36 Watt, it contradicts the basic law of Physics - the Law of Conservation of Energy. \$\endgroup\$
    – Ale..chenski
    Commented Apr 25, 2019 at 14:25

3 Answers 3

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No. To put it quite simply, you cannot have more power out than you have going in. You can increase the voltage available, you can increase the current available, but you cannot increase the available power.

25W going in means a maximum of 25W out.

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IF your question was about power supply conversion, the answer WOULD be a solid "No". But...

25 W is the power consumption of the bulb, not the power supply output. You could step up the power as you asked IF you checked all the components involved in that bulb's circuit (including wiring, connectors, etc) making sure they can handle the extra power you push through them. That sounds like a lot of pain, but possibly doable.

In case the above path isn't feaseable, you could try using the original circuit to control a relay powered directly from the battery (fused!).

Also, the increased bulb power output would put out more heat than the orignal one and could damage it's housing, reflector and connector.

Maybe it would be best to check for a compatible 6V bulb.

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If you look at the connections in the light switch, only the park light is fed from the battery supply (brown wire), the other lighting is fed from the Y/R wire from the magneto coil, so the headlight supply is AC. That precludes the use of a DC-DC converter, unless you rectify it first - and with half-wave rectification you won't get the same power out of the magneto.

The coils on these magnetos are often wound with a specific load in mind, so the terminal voltage is determined by that load - put a lower current bulb in the circuit and the terminal voltage will rise, though probably not by enough to successfully run a 12V bulb - but the total power available is likely limited by the magneto coil.

There's a separate winding (or maybe a tap) that goes through the rectifier/regulator to charge the battery. The regulator is typically a shunt type - essentially a large Zener diode that holds the maximum voltage down by dissipating the excess generated power as heat. One possibility might be to find an LED bulb you can power from this circuit, either directly or through a DC-DC converter if you're looking for more light output, but you're unlikely to be able to get more out of the magneto to get a brighter incandescent bulb. Running a DC-DC converter from the battery to power a 36W bulb will likely result in a flat battery.

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