Blown bulbs

[Hugo]

I have a 250c, just went to check for mot and all the bulbs have blown! Any info welcome.
Also what do I need to convert to 12v? Thanks

[julianharty]

It sounds like your regulator isn't working correctly, which lead to excessive DC voltage toasting the various bulbs. I don't know if the headlight is powered by AC or DC on this model, nonetheless it sounds like it was similarly affected from your brief message. It should be doable to diagnose the cause with a combination of a multimeter (to measure volts and amps) and some new bulbs. Does the bike have a viable battery fitted? If so, do the new bulbs shine with the expected brightness when powered by the battery? with the engine running how does the brightness vary as you increase and decrease the revs? what is the measured voltage when measured at the base of the light bulbs?

I don't actually know how to convert your bike to 12V, I've not owned any of the 250's (yet) and haven't worked on one, nonetheless I have been led to believe the conversion may be relatively simple. Something along the lines of:

• Fit a combined 12V combined regulator rectifier, such as pattern ones sold for Honda Superdream 250's

• Fit a 12V battery that fits in the space vacated by removing the 6V battery

• Replace all the bulbs with 12V ones and also replace the 6V flasher unit with a 12V one

Personally I'd start by measuring the outputs of the alternator when the bike is running, this should be AC voltage, and at least 30V AC. To do so I'd disconnect the wires that come from the alternator so they're no longer connected to the rest of the bike's wiring. Then I'd connect the alternator outputs to the AC side of the regulator/rectifier and the DC side to a 12V battery fitted with a low rated fuse in the circuit (no more than 10 amp rating) to try to protect anything electrical from cooking and measure the output from the regulator/rectifier when the engine is running, aiming to see somewhere around 14V DC when the engine is running.

There are likely to be various nuances and my first approach probably needs refining based on the actual design of the alternator. I hope someone who knows these bikes far better than I do can and will comment with more accurate details.

[mbmm350s]

Hi Hugo

The 250 2C was originally 6V d.c so charging voltage would be circa 7.2V
did you check the inline fuse, to the battery.
Sometimes its in the earth side of the battery.

Julian's description of how to change to 12V is well written and concise.

As for regulator
https://www.modernmotorcycle.co.uk/coll ... or-3-phase
Theis or similar has been used by quite a few on this forum so far for both 6V to 12V conversions and as replacement for failed regulators.
It will fit in the 250 2C, though new connectors will be needed. While at it you should upgrade the fuse holder to a modern type.

When you use this regulator - the red wire from the alternator must not be connected and must be taped up to prevent it shorting out.
To be clear the alternator does not need to be changed and is identical to 350 alternators
If you have a Bosch bayonet fitting in the headlight you can fit a LED headlight (which is legal in the UK for bikes of this age).

You might want to fit a 12V horn.

Cheers Mark

[Hugo]

Thanks for advice I have decided to go the 12 v route as the bulbs and battery need replacing, I have bought the recommended rectifier but not sure how to wire it, could someone help please.

[julianharty]

Hugo,
I don't know exactly how to wire it in. Can you provide some details on the wires and their colours that come from the alternator and the wires and the colours on the regulator/rectifier you've obtained. These may help me and/or others to help you with working out the wiring connections.

[Hugo]

Hi, Justin, the existing wiring is standard 250c, the new 12v one has green ,black ,red and 3 yellows

[mbmm350s]

Hello Hugo,

The new regulator is suitable for three phase, you will only have a two phase, so one yellow is not used.
hopefully I don't need to remind anyone to disconnect battery negative lead first!!!
Remove old regulator noting the wires that go to it, particularly the brown and 2 or 3 reds.

1. one of the yellow wire of the regulator should be taped up and insulated
2. The red wire coming from the stator to the regulator should be taped up and insulated, don't connect it to anything.
it might have been commoned so may need to be cut.
3. Connect two Yellow wires from stator to remaining two yellow wires of the regulator.
4. Connect the red wire of the regulator to the battery feed AND to the red feed wire to the ignition switch .
You will need to make a custom connector.
5. Connect the black wire of the regulator to the brown wire of the loom that was connected to the old regulator (this is switched 12V)
on some bikes I have seen different colour for this.
6. Connect the green wire of the regulator to a common earth point (i.e the regulator mount point) and make sure the battery negative is connected there or nearby, and that earth continuity exists, if necessary clean the area and even remove some paint.
7. Reconnect battery negative lead.
8. when happy make sure that all cables are secure with cable ties to prevent chafing

Note the green wire from the alternator remains connected as it was to the transducers it is not to be changed.

I use 6.4mm (1/4) terminal blades so as not to change the alternator connections and keep the possibility of reverting back to standard regulator.

First check is to make sure that when the ignition switch is ON that 12V is present on the red wire AND on the black(brown) wire
Now make sure to check the charging voltage as per the manual. It is 14.4V. You should see that at fast tick-over into a fully charged battery.
It should never exceed 15V
These points and how to check that the alternator/regulator can supply the load are given in the manual.
But it easy to check that the lights should get brighter at fast tick over, also check that with front brake on and lights on that the indicators still function.

Hope that makes sense.

Mark

[Hugo]

Thanks Mark, does It matter which yellow wires are connected ? Also do you know which 12v battery fits the tray it's only 60mm wide? Regards Hugh

[julianharty]

Thanks Mark, does It matter which yellow wires are connected ? Also do you know which 12v battery fits the tray it's only 60mm wide? Regards Hugh

The yellow wires are interchangable, the AC voltage is generated across any pair of them (I think you only have one pair). The rectifier in the regulator unit processes the AC to generate DC, the regulator then limits the DC voltage so it can charge the battery and power things that need 12V (DC) without blowing them up.

You'll find a wide variety of batteries available from many stockists. Some provide the dimensions, for instance when I buy mottbatt batteries I look at the physical dimensions and the locations of the +ve and -ve terminals to decide which battery would suit my bikes. Typically I'd buy one of the larger (i.e. more powerful in terms of capacity) batteries that fits within the dimensions of the battery tray. You'll find at least one that fits as I use a much narrower one on my Kanguro X model which I converted to 12V.

[mbmm350s]

Thanks Julian

For 250 2C I last converted to 12V I used a Moto batt AGM, terminals are a doddle on those.

This is what I used:

MB5U Motobatt AGM Motorcycle Battery 12v 7Ah 90CCA (YB5L-B, 12N5-3B)

Its a bit cramped for space in the 250 2C

Mark

[Hugo]

Thanks Mark and Julian, I shall have a go ASAP. Regards Hugh