Author Topic: Troubleshooting blown headlight bulbs - high voltage? (Read 6686 times)

brandEn · « **on:** November 12, 2013, 07:43:46 PM »

1978 CB750F3
Ricks Reg/Rec unit
H4 headlight bulb
Yuasa sealed battery/non gel
Light is running directly from battery via relays. One for hi, one for low beams.

So I have blown two H4 bulbs now. The first time it was the lo beam so I replaced the bulb and after a short run yesterday the hi beam portion of the new bulb blew. I checked the voltage at the plug for the reg/rec and it reads 15.23 VDC at RPM's above 3000k. Is this voltage high enough to blow bulbs ya think? I am positive I have good grounds and all the connections are good so I immediately suspected voltage or possibly vibrations killing it. Thoughts? Any thing else I can check to verify an issue?

scottly · « **Reply #1 on:** November 12, 2013, 08:18:01 PM »

15.23 volts is too high; should be 14.5 max. What is the voltage actually delivered to the headlight through the relay?

david 750f · « **Reply #2 on:** November 12, 2013, 08:22:06 PM »

Agree with Scottly, check the voltage at the headlight

brandEn · « **Reply #3 on:** November 12, 2013, 08:30:32 PM »

Its the same.

scottly · « **Reply #4 on:** November 12, 2013, 08:33:00 PM »

That's too high.

brandEn · « **Reply #5 on:** November 12, 2013, 08:33:58 PM »

Thanks scottly, Looks like I need to order some parts

david 750f · « **Reply #6 on:** November 12, 2013, 08:38:21 PM »

brandEn, the voltage is a bit high. Running stock Honda Voltage/Regulator or aftermarket? I have had a problem running H4 car bulbs. I now run the Heavy Duty motorcycle bulbs, not sure if its a scam but haven't had any issues since.

i'll find the link for the bulbs I run.

scottly · « **Reply #7 on:** November 12, 2013, 08:42:01 PM »

You need to look at the regulator; it's purpose is to limit the maximum voltage. You didn't happen to get a unit designed for the 650s and DOHCs? If one is used with the sohc wiring scheme, it will run the charging system in the "full on" mode.

brandEn · « **Reply #8 on:** November 12, 2013, 08:52:31 PM »

I am running a Ricks regulator rectifier combo unit. As far as I know it is designed for the CB750 SOHC and I got it from Bike Bandit. I have the receipt someplace.

I saw some PIAA Motorsport anti vibration bulbs. They are $40 a pop.

brandEn · « **Reply #9 on:** November 12, 2013, 08:53:42 PM »

I think the unit is sealed and non adjustable. I will look into it.
Thanks for help guys. Keep the suggestions coming if ya got one.

david 750f · « **Reply #10 on:** November 12, 2013, 08:59:43 PM »

Email Ricks to see if it is adjustable. He may agree that the voltage is too high and do an exchange.

If not, Oregon Motor sports is an option.

http://www.oregonmotorcycleparts.com/SOHCfours.html

scottly · « **Reply #11 on:** November 12, 2013, 09:00:56 PM »

IIRC, the Rick's DOHC reg/rect has one or two more wires than the Rick's SOHC reg/rect. The DOHC unit will work with an SOHC charging system by making some simple changes to the wiring of the field coil.

dave500 · « **Reply #12 on:** November 12, 2013, 11:26:30 PM »

those vibration resistant bulbs might be for harleys or other very vibratey bikes or off road enduro use?40 bucks is too much to burn out while testing,you can get real cheap h4s.

TwoTired · « **Reply #13 on:** November 13, 2013, 12:02:23 AM »

How is the headlight mounted? On stock fork ears?

brandEn · « **Reply #14 on:** November 13, 2013, 05:24:22 AM »

No, the headlight is mounted on custom made brackets and has no rubber isolaters. I have not had a problem until the last week though.

Bodi · « **Reply #15 on:** November 13, 2013, 05:50:55 AM »

If an accurate reading, that voltage is too high and would explain short lamp life. The other bulbs will probably burn out quickly as well. Halogen lamps are sensitive to overvoltage a bit more than "normal" lamps, the process of evaporation and redeposition of filament tungsten is upset since redeposition stops on the overtemp filament areas and the tungsten is only redeposited at the cooler bits - thinning the hottest area and accelerating the process.
Possibly the regulator has competely failed, or the sense voltage to it is low due to parasitic losses in the wiring harness. That's quite likely if you have added a headlight relay sending battery power directly to it, the regulator will still be on the main harness and if there's a voltage drop in there, if the regulator may be seeing 12V while the actual battery (and headlight) voltage is at 15+V. Measure the voltage at the regulator black wire to ground. It should be within ~1/2V of the battery voltage. Voltage drops happen from the resistance of the harness bullet connectors and switch contacts, the bullets particularly corrode over the decades and need a good cleaning every 10 years or so. The switches should clean themselves every time they're used but can get worn and loose with use, and then the contact resistance goes up.

brandEn · « **Reply #16 on:** November 13, 2013, 06:43:02 AM »

Thanks Bodi I will check that tonight.

brandEn · « **Reply #17 on:** November 13, 2013, 08:02:18 AM »

So I emailed Ricks electrics and got this reply. Does this sound right?

Hi Branden,

Thank you for your email! The set point on our rectifier-regulators is not adjustable. Your battery charge should be 13.5-14.5 DC Volts. Most likely you have a faulty rec-reg but you should check your rotor (field coil, 7 ohms +/-.5) as well before installing a new rec-reg.

Hope this helps!

Best regards,
Maria

Jerry Rxman Griffin aka MuthaF'er · « **Reply #18 on:** November 13, 2013, 08:16:40 AM »

I would like to have thought they may offer a replacement. How would it create overvoltage if it wasn't faulty to begin with. How often do they go 'better' output vs just frying?!

brandEn · « **Reply #19 on:** November 13, 2013, 08:21:26 AM »

Yea I was hoping for a replacement but they only offer a year warranty. Gonna get the adjustable one from Oregon. Put that on my K4 and it's better quality for sure. Plus the warranty is much better.

Which one is the field coil? The smaller one that mounts with the three bolts from outside the cover ?

TwoTired · « **Reply #20 on:** November 13, 2013, 10:47:12 AM »

Quote from: brandEn on November 13, 2013, 05:24:22 AM

No, the headlight is mounted on custom made brackets and has no rubber isolaters. I have not had a problem until the last week though.

Well, that does fit within the definition of random. So tire pressure and road roughness are able to translate to sharp bulb filament shock at any time.

However, the regulator may be just fine and providing over voltage because it's connection to the battery is faulty.

Turn everything on with the new bulb, and measure the voltage drop between the battery POS terminal And the vreg power in terminal. You should do the same between the battery NEG terminal and the Vreg GND terminal. The sum of these voltage losses is the misrepresentation of the battery's true status. The Vreg can't do a proper job if the it doesn't know true battery voltage. If it thinks the battery is a volt or two low, it will try to boost what it sees.

There could easily be a problem with the the key switch losing voltage as the power passes through it.

The field coil has white and green wires going to it.

brandEn · « **Reply #21 on:** November 13, 2013, 10:59:02 AM »

Thanks! I will check all this stuff ASAP

brandEn · « **Reply #22 on:** November 13, 2013, 05:01:11 PM »

So I was able to make a few checks before Things went south....

My field coil measures approximately 7.6 ohms

Battery Voltage with engine off measured at the battery POS and NEG terminals = 12.88 VDC
Battery Voltage measured at terminals with engine off Headlight ON LO = 11.92 VDC
Battery Voltage with engine at idle and headlight light on LO = 12.23 VDC
Battery Voltage @ 4000 rpm = 14.67

Voltage Regulator power in (red & white wire) and battery ground @ idle = 12.4 VDC
Voltage regulator measured between GND and PWR (voltage regulator green and red wires) @ idle = 12.6 VDC

I did find a problem with one of the yellow wire bullet terminals under the sprocket cover. It was totally black and melted. Not sure if this IS the problem or the result of a problem. Unfortunately my bike is down for the count at the moment until I get this buttoned up and a new gasket ordered.

Didn't see voltage above 15VDC during my checks today because I didn't get that far along....

brandEn · « **Reply #23 on:** November 13, 2013, 05:05:32 PM »

I should note those terminals were brand new and replaced by me 5000 miles ago in 2011...

TwoTired · « **Reply #24 on:** November 13, 2013, 05:53:30 PM »

Do yourself a favor and measure the voltage drop for the power path and the return path to/from the Vreg and a Battery terminals.

Turn everything on and put the voltmeter probes on the battery POS terminal and the vreg voltage input. The meter will read directly the voltage lost in that path. Do the same with the battery NEG terminal and the vreg GND terminal. Add the two measurements together to find out how the bike's distribution wiring is lying to the Vreg. Anything more that 0.5V total loss requires and investigation to track down the cause of the losses .

Your field coil is fine.

As you have seen the system voltage varies with RPM and battery charge state. As soon as the battery drops below 12.6-8 Volts it is depleting and losing charge state. When the voltage rises above that, the battery is recharging. Depletion and recharging are not instantaneous functions. They both take time and voltages are transient during both processes. So, not only is the voltage report required, but also the test sample conditions and voltage change trends, as well, in order to make proper diagnoses and offer guidance.

Do fix the yellow wire connections. The blackness is due to overheating from the charging currents passing through connections with resistance. Poor crimping and/or poor contact to contact grip can both cause the blackened connectors.

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Author Topic: Troubleshooting blown headlight bulbs - high voltage? (Read 6686 times)