Battery question

[Spuds1234]

Out of curiosity (and a bike thats not working right), would a bad battery thats not holding a charge cause the tail light bulb to blow consistantly while the engine is running?

[YellowDog]

Out of curiosity (and a bike thats not working right), would a bad battery thats not holding a charge cause the tail light bulb to blow consistantly while the engine is running?

No

[onearmedbandit]

Shouldn't do. Your charging system is providing the power for lights etc.

[davereid]

Out of curiosity (and a bike thats not working right), would a bad battery thats not holding a charge cause the tail light bulb to blow consistantly while the engine is running?

Most bulbs can run quite a significantly higher voltage than the nominal voltage of your bike. So even if the battery was duff, a single light blowing lots is likely caused by vibration.

Lose earth rattling, tail light not mounted securely, look there first. Plus, its cheaper to look there than it is to buy a battery.

[YellowDog]

If you get yourself a battery tender for about $50 on TM, you can keep your battery topped up and save it getting discharged to a state of damage where it will no longer hold charge.

You blowing tail bulb is likely to be realted to short of some kind, though they really don't like a flickering voltage going through them, which is what your duff battery is doing.

Good luck.

[Spuds1234]

Swell.

A quick check of the multimeter accross the battery terminals tells me the battery is charging, so I guess I'll have to delve a bit deeper.

If there was a short to earth wouldnt that blow a fuse first. Although the tail light is on the same circuit as the starter motor so its fused with a 20A fuse. There are no issues with anything else on that circuit (except for a flat battery not being able to start the bike).

What are the most likely causes of this?

[Spuds1234]

Wow not sure how I missed 4 replys to this thread this morning.

I dont need a battery tender, I ride my bike every day.

Why would tail light bulbs suddenly start to go from vibration? Its never been a problem before on this bike (since new). Now suddenly the battery wont hold a charge and its blowing bulbs.

Oh well. I have a new battery arriving today so I'll see how that goes and replace the tail light bulb again and see what happens when the engine is running.

Thanks for the replies guys.

[Juzz976]

Did u check the AC component of your charge voltage, generally your going to have an AC waveform superimposed onto your DC. as more load is taken the regulation of the DC output reduces (increase in AC fluctuations).

Its posible your regulator is either allowing transients (surges/spikes) or the Alt AC peaks to go through on 1,2 or maybe all of the phases from the alternator to the DC distribution.

If your battery plates have sulphated then the internal resistance is higher giving less charge at float voltage and also less ability to soak up or drain off these peaks.

Esle a bad connection in the socket or wiring close to the lamp could be heating up, now this is not enough to burn out the filament but its reduces to thermal conduction of the conductors supplying the filament, thus the filament is running hotter and may be making it go brittle and melt. <- more likely as only 1 lamp is blowing come to think of it. Also loose connection could cause thermal creep from constant contraction and expansion of filament from the repeated on off.

[Spuds1234]

Lol I was testing the ac side of the rectifier this afternoon and my multimeter ran out of battery. Before it went flat it was putting out a steady 25Vac.

I think I was testing the right wires, although there were 4 wires rather than the 3 I was expecting.

Im going to retest everything when I get my new battery and see whats up then.

The lamp holder itself is fine. No signs of damage at all.

[Juzz976]

and the connector?

Maybe u just got a bad batch of lamps

make sure there isnt too much AC voltage at the battery when charging, check at idle and at rev.

[Spuds1234]

Do you mean DC voltage at the battery?

Its at about 14.6Vdc at idle and 14.8Vdc at 5000rpm.

I would have thought that the idle value should have been lower but according to a electrical diagnosis flow chart its ok.

[Juzz976]

No I mean AC, a meter will determine a DC voltage based on an average.

A small amount of AC may come through the regulator as well

|12V ---------- 12V DC ~~~~~~ 12VDC with 0.5V AC Ripple
|
|
|0V -------------------~~~~~~ AC Volts (say 0.5V)
|
|
|-12V -------------- -12VDC

The more ripple VAC divded by VDC = % Regulation as load increases regulation falls.

The rectifier gives out a pulse DC, the regulator limits the peaks and a battery or capacitor is used to filter out any residual AC waveforms.

[Spuds1234]

I'll check it out once the battery is charged again lol. Its on charge now, should be right in an hour or two.

[Juzz976]

This is DC with AC Ripple, the reverse is AC Voltage with DC offset.

the meter reads the average voltage in DC mode and measures peak to peak on AC mode.

If you AC component is as much as your DC..... 12V DC with 12V Ripple, your peaks will be
+28.97V and -4.97V (peaks are √2 (1.42) x the rms value). and in DC will only show the offset of 12V.

[Spuds1234]

So I should measure the AC voltage across the battery while the bike is running if Im following you correctly?

I did this and it read 32Vac. I switched the meter leads around and it read 0. Im real confused lol.