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Headlight bulb blowing

Windmill John

Veteran Member
Joined
Jun 4, 2022
Total Posts
446
Total likes
64
Location
East Sussex, England
Just any usual suspects here? Vibes, excessive current/voltage or just a crappy bulb.

CB250K0. Dip beam blew within days. Due to low power, I’m using high beam rather than just binning bulb.

I might check power whilst running, just wondered an thoughts.
 
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Just in case, you should check the max voltage of the system while riding at continuous rpm above 4000 to 5000. If the bike still has the original rectifier (and separate regulator if present, some did not have it back then) it could be overcharging significantly contributing to the blown filament. If it's above 15v max you should put a modern rec/reg combo on it like this one - http://www.sparckmoto.com/Products/Detail/7 - and check the electrolyte in the battery if it has a lead-acid version, it could also be boiled down a bit
 
Purely an update for closure. Went for a ride, gave him some beans and got a max of 14.8 volts charging.
According to the manual, that’s spot on :)

I’ve been riding on full beam for the last couple of weeks rather than replace bulb and all good. That’s only, I think, 10 watts higher.
 
If it reads 14.8v after you stop on the side of the road or back home in your garage, it's likely exceeding 15v while riding and that's probably what blew the bulb. I'd be replacing the separate components with a modern rec/reg combo unit from Sparck Moto or an equivalent of good quality from your side of the pond. Modern AGM battery or lead acid? If it's a lead acid battery you'll be adding water often at that charge rate if you ride the bike a fair amount, and especially if you go on a long ride with continuous rpm level above 4000
 
Maybe I didn’t post clearly. At the side of the road, revving up to 5000 rpm plus gave me the 14.8 volt reading.
Can’t recall exactly what it was at tick-over, but I think about 12.8 V or so.
 
Okay, but if it gets that high on a short rev roadside, it might get higher than that while held steady at the same rpm for a few minutes or longer. At tickover you'd expect 12.8 or lower if it sat at that rpm for a while, since they actually discharge below the break-even point of around 3500 to 4000. If it were mine, I'd either put a voltmeter on it to verify while riding or just cut to the chase and replace the components with the modern unit so you'd be assured of no more blown bulbs or boiled batteries.
 
Well, now the snow has gone, just had a blast and even in the ancientdad rev range, never got above 14.9 volts.
so, it’s either hunt the vibe or crappy bulbs.

I’d been using high beam since low blew. Then that went. Rode home from work with my phone’s light sticking out of a pocket! Had a few cars flash me.
 
I wonder if your CB250 is the same as the UK spec CB175, in that we didn't get the separate voltage regulator found on the US spec bikes, just the old style rectifier ? My original CB175 used to eat tail light bulbs, also boiled the battery once or twice, and in retrospect I put that down to the lack of a separate voltage regulator. I didn't, and still don't, run the headlight in daytime.

If so, easily rectified <groan> by fitting a modern combined regulator rectifier, available as generic 12v units on Ebay for literally a few pounds. All three of my 175s run these reliably, although they are so cheap I have a couple of spares stashed away just in case.

For example, first one that came up on a search.

Universal 4 Wire Full Wave Motorcycle Regulator Rectifier for 12V DC Bike Eh | eBay
 
Actually, just checking the manual, we could be at 15V at 10,000rpm. This could be shoving out 4A.
So, P=VxI etc, I could be sticking 48 Watts through my 25/35 Watt bulb…

As I’ve never seen this offset bulb fitment, if someone made a 55/65 Watt version I’d probably be okay.

 

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OR, you could just put a modern rectifier/regulator on it and call it a day... and no more blown bulbs. If you don't really ride at night the headlight brightness isn't a factor.
 
Just wondered what’s happening. If the book says the charging coils can dish out 15V, does the new reg/rec just keep it down to a non bulb blowing level?
 
... just "spitballing here" but is it possible there is a poor ground on the bulb circuit causing the filament to overheat when on?
 
Just wondered what’s happening. If the book says the charging coils can dish out 15V, does the new reg/rec just keep it down to a non bulb blowing level?

Yes, most of the good ones cut the voltage off at 14.5 or so. The (previously installed) Oregon Cycle rec/reg combo on my 450 tops out at 14.6v
 
Looks like the same unit sold by CMC and, unsurprisingly, for a fair amount less than their price.
 
Mine was £57, theirs is $65.

But…. mine was 24 miles of petrol in place of carriage and I was back home well within the hour. It was a very windy cross country some single track trip.
 
Some only realize that the voltage regulator when the low output fails. (Dim bulbs, weak or no spark, battery is not charging.) Yet the high end output can also fail. Leading to very bright bulbs, starter problems, hot to the touch controls on the handle bars, very hot or melted wires. I know a bad rectifier/ voltage regulator can allow 18 plus volts to run through an electrical system. (tried mounting a voltage meter on my bike, thought the meter was faulty when it pegged out on the high side, yup bad regulator...)
 
Mine was £57, theirs is $65.

Interesting... this is what I see when I go to the link for what you bought.

Regulator Rectifier | Honda | CB250 | CJ 250 | CB350K | CB450 | CB500

£47.92 Incl. VAT

Obviously may not include local taxes if any, our prices (like CMC's $65 price) are before applicable state taxes, of course
 
It’s a retail site, so the £57.50 I see is inclusive of VAT. So I paid in cash £57.50. Delivery was £6.95, but as mentioned, I’m very close so picked it up.

Day444, whilst I’m not 100% sure of the Honda, the reg/rec shouldn’t affect spark, unless battery was very dead. The ignition system should just be key, wire, coil/condenser/points, HT leads and plugs.

Thats how it is on BMs I’ve had.
 
If you do have a voltage regulator fitted, when you remove it remember to connect the redundant green wire to frame ground. Black and yellow wires can simply be blanked off.

And I do wonder if that expensive new reg rec is actually any better than the cheap ones I'm using .....
 
And I do wonder if that expensive new reg rec is actually any better than the cheap ones I'm using .....

It's a valid question. I know the Oregon Cycle rec/reg that was already installed on my 450 was more expensive than the Sparck Moto unit ($37.50 US), they're priced at $96 currently and most likely do not do any better job of voltage regulation. I'd suspect the more expensive models could be better at filtering out AC waveform from the DC current but testing would be required to verify that, of course.
 
If you do have a voltage regulator fitted, when you remove it remember to connect the redundant green wire to frame ground. Black and yellow wires can simply be blanked off.

And I do wonder if that expensive new reg rec is actually any better than the cheap ones I'm using .....

Thanks Richard. And re the price, leave me alone! :) You might be right. What put me off the one you listed, was the line about they may be up to 10 to 20mm different in size. This is itself shouldn’t be an issue, but it made me wonder about the innards. And plus it’s an example of how silly I can be with money!

And, if yours is as good as mine, keep it to yourself ;-)

I do ride in all weathers and lighting conditions.
 
Agreed, you need something reliable if you ride in all weathers, night and day. My 175's are really just fair weather toys.

On my CB600 I've dumped the unreliable OEM Honda reg/rec, and fitted a massive ( and expensive ) Shindengen mosfet unit, originally intended for a Yamaha.

vi3JV0G.jpg
 
Yes, they are notorious for reg rec problems, some of which are caused by corroded connector blocks which then cause the reg rec to fail. Cam chain tensioners are also an issue. MY CB600 has had both problems, and I like to think that mine is reasonably well looked after. Also affects Fireblades and VFR800. My friend had his VFR reg rec fail.

I originally just replaced my reg rec with a part from David Silvers, but in the end fitted the better Yamaha part and also replaced the wiring with heavier cables direct from stator to reg rec and thence direct to battery.
 
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