Did my stereo kill my alternator?

[Hyde]

Hey guys, after the fun yesterday of pulling my carbs and doing fuel and air tube o-rings I set off hoping for some trouble free miles. Well I made it about 10, first my tach stopped and started going goofy, then my turns weren't working right. Stopped at a gas station for some caffeine and it wouldnt start, I thought it may be the common start switch so I roll started it and headed to a buddys shop.

Pulled my start button apart, didnt look too bad but cleaned it anyway, test light showed I was getting power at the relay. There was some corrosion on the plug for the starter relay, cleaned it up and hit it with some dialectric grease. Finally jumped it and got it to start, 9 volts running, battery voltage at the alternator post, battery voltage at the excite wire.

Well I've been needing to replace the battery so I bought a new AGM and rode it home.

Now I told that story to tell this story, I have a stereo with two 6x9s and a 350 watt amp, could all of that have killed my alternator? Bike only has 16k miles, if thats too much for the factory alternator I have seen on here the Goldwing one will fit with some slight modification and there are various high-output options.

[Blackduck]

Doubt the stereo would have killed the alternator unless the load burnt out the brushes.
The stock alt is over 500 watts, should have ended up with a flat battery first if the alternator could not keep up.
Pull the alternator and check the brushes and the rotor windings for continuity. Common for the wire in the rotor to break.
Cheers Steve

[Gryphon Rider]

It's not uncommon for 2000 (2001?) and earlier Valkyries to have their alternators fail.  The wires to the coils on the rotors aren't sturdy enough.  The replacement rotors (or complete alternators) from Honda are much more reliable.  That being said, if you are going to do other than replace the whole alternator, be sure to use the diagnostic procedure in the service manual so you know you are replacing the right parts.

It might also be caused by a bad connection within the charging circuit (connections and wiring between the alternator, battery, and engine ground).

[Hyde]

Mine is a 99, I checked all the external working and it tested ok. Went ahead and ordered an 85amp, so whether it was the stereo or not it should be ok now! I didn't know alternator failure was that common on earlier ones. Makes me more confident in the diagnoses though!

[Gryphon Rider]

Mine is a 99, I checked all the external working and it tested ok. Went ahead and ordered an 85amp, so whether it was the stereo or not it should be ok now! I didn't know alternator failure was that common on earlier ones. Makes me more confident in the diagnoses though!

Now you're going to have to upgrade your battery, as doubling your alternator output is going to put out more current than your battery can handle.  You're also going to have to, at minimum, replace your dogbone fuse with a higher current fuse (stock is 55A), and possibly upsize your charging circuit wiring as well.

[The emperor has no clothes]

Mine is a 99, I checked all the external working and it tested ok. Went ahead and ordered an 85amp, so whether it was the stereo or not it should be ok now! I didn't know alternator failure was that common on earlier ones. Makes me more confident in the diagnoses though!

Now you're going to have to upgrade your battery, as doubling your alternator output is going to put out more current than your battery can handle.  You're also going to have to, at minimum, replace your dogbone fuse with a higher current fuse (stock is 55A), and possibly upsize your charging circuit wiring as well.

Ive been running a 85 amp one for a couple years now with no battery or dogbone issues. Isn't there a regulator that keeps it from overcharging ?

[Gryphon Rider]

Mine is a 99, I checked all the external working and it tested ok. Went ahead and ordered an 85amp, so whether it was the stereo or not it should be ok now! I didn't know alternator failure was that common on earlier ones. Makes me more confident in the diagnoses though!

Now you're going to have to upgrade your battery, as doubling your alternator output is going to put out more current than your battery can handle.  You're also going to have to, at minimum, replace your dogbone fuse with a higher current fuse (stock is 55A), and possibly upsize your charging circuit wiring as well.

Ive been running a 85 amp one for a couple years now with no battery or dogbone issues. Isn't there a regulator that keeps it from overcharging ?

The maximum current going through a battery is determined by its internal resistance and the difference between the battery's voltage and the charging voltage.  A battery can only convert electrical energy to chemical potential energy at a fixed maximum rate, based on the size of the battery.  Any energy not used to make the chemical reaction gets converted to heat.  If a battery is deeply discharged, its voltage is significantly lower than the alternator's, and thus will draw a significant current, taking the maximum that the alternator will produce.  The end result is that a deeply discharged battery with more power available than it's chemistry can absorb, will heat up.  The greater the alternator's output, the hotter it will get, and the greater the chance of damage from that heat.  A larger battery can use more of the available power to feed the chemical reaction than a smaller one, and thus less heat is produced.

Perhaps you haven't discharged your battery deeply enough, enough times, to cause it to fail.

[The emperor has no clothes]

Mine is a 99, I checked all the external working and it tested ok. Went ahead and ordered an 85amp, so whether it was the stereo or not it should be ok now! I didn't know alternator failure was that common on earlier ones. Makes me more confident in the diagnoses though!

Now you're going to have to upgrade your battery, as doubling your alternator output is going to put out more current than your battery can handle.  You're also going to have to, at minimum, replace your dogbone fuse with a higher current fuse (stock is 55A), and possibly upsize your charging circuit wiring as well.

Ive been running a 85 amp one for a couple years now with no battery or dogbone issues. Isn't there a regulator that keeps it from overcharging ?

The maximum current going through a battery is determined by its internal resistance and the difference between the battery's voltage and the charging voltage.  A battery can only convert electrical energy to chemical potential energy at a fixed maximum rate, based on the size of the battery.  Any energy not used to make the chemical reaction gets converted to heat.  If a battery is deeply discharged, its voltage is significantly lower than the alternator's, and thus will draw a significant current, taking the maximum that the alternator will produce.  The end result is that a deeply discharged battery with more power available than it's chemistry can absorb, will heat up.  The greater the alternator's output, the hotter it will get, and the greater the chance of damage from that heat.  A larger battery can use more of the available power to feed the chemical reaction than a smaller one, and thus less heat is produced.

Perhaps you haven't discharged your battery deeply enough, enough times, to cause it to fail.

I see  you are probably right, it never gets drained much.

[gordonv]

Finally jumped it and got it to start, 9 volts running

Where was the 9v at running?

Battery voltage should be like 12.8v, so you have this voltage, but couldn't start your bike?

battery voltage at the alternator post, battery voltage at the excite wire.

So you have 12.8v with the running motorcycle at the alternator post? What RPM?

What is the excite wire? Exit from where?

[Hyde]

9v at the battery after I jumped and removed the cables. The excite wire is what tells the alternator to charge essentially, I also had 9v there, and the charge post at the alternator was at 9v. So the whole system had battery voltage at the time of testing. Which was 9 volts. I'm an automotive technician by trade, most things transfer over but I like to check here for known problems.

Also I don't see where a higher than stock amperage alternator will harm my system, the alternator has the potential for 85 amps but in this system will never see close to full load.

[Gryphon Rider]

9v at the battery after I jumped and removed the cables. The excite wire is what tells the alternator to charge essentially, I also had 9v there, and the charge post at the alternator was at 9v. So the whole system had battery voltage at the time of testing. Which was 9 volts. I'm an automotive technician by trade, most things transfer over but I like to check here for known problems.

Also I don't see where a higher than stock amperage alternator will harm my system, the alternator has the potential for 85 amps but in this system will never see close to full load.

Say you put in your 85A alternator, boosted the bike from a car battery to get it going, then immediately pulled off the booster cables and went for a ride to charge your battery from it's current 9V.

Lets assume your alternator puts out 14V, and the bike uses 140W for your lights, ignition, and killer stereo at low volume.  That's 140W ÷ 14 = 10A to run, leaving 75A for other stuff.

Your battery has approximately 0.007Ω internal resistance (the only internal resistance data I could find is from here: http://ultracell.net/datasheets/YTX14-BS.pdf), and the voltage differential is 14V-7V = 7V, so until the battery's voltage starts to increase as it charges, it could draw as much as 7V ÷ 0.007Ω = 1000A if the current were available.  But it only has 75A to work with, which is good because 1000A would destroy the battery.

As it is, your 75A x 7V = 525W is being used by the battery, with only a small portion of it being used to actually charge the battery, the rest being turned into heat, which your auto tech experience will tell you is bad for the battery.

If you are going to use the 85A alternator without modifying anything else, I suggest you give the battery a full charge before starting the bike, and be sure not to run down the battery when the engine is off.

[Hyde]

I generally try not to charge flat batteries with the alternator unless Im stranded somewhere and thats the only option, I have a maintainer on it if it will be sitting for extended times. Also unless Im being forgetful I dont leave the stereo powered up when the bike is not running. Got the new alternator installed this morning though, thanks for the help everyone!