Strange diagnostics please help

[Datunrestricted]

G’day all new member so I’ve got a 2000 busa charging problem new battery, with the bike running and battery connected no charge with the bike running and battery disconnected shes on 13.8/14 volts so it’s making power but reconnect the battery and multimeter drops 12.8 ffs spoke to the bike shop there saying new alternator but without the connected battery alternators fine just about to replace rectifier hoping for some advice before thanks in advance for any help

 

[Hayabusa Wannabe]

Welcome to the forum @Datunrestricted. I am sorry to hear of your problems but I am sure with the help here you will get them sorted quickly. Did you just purchase this bike, as I noted you are looking for a seat as well?

with the bike running and battery connected no charge

Do you have the service manual which has several tests? Measure the alternator AC voltage, before the rectifier converts it to 12.8V DC, as specified in the manual, at idle and 5,000 RPM. Let it idle first so that the alternator is hot as it can internally short circuit when it is hot, ergo working fine when cold but dropping power when hot. Also from the manual, test the resistance between each alternator coil. If there are any short circuits, that is another verification that it would need replacement.

You also want to test for short circuits on the bike which could cause all of this and burn up the rectifier/stator/battery, especially if the bike is new to you. The manual calls this a "leakage test." The bottom line is that the current draw when the bike is off should be .03A/3mA or less.

 

[VNE]

Get one of the new rectifiers that use Mosfets instead of the standard silicone diodes.

As a 2000 model, your Aluminium electrolytic reservoir and filter capacitors are now 23 years old and they work really hard because of the pulsed DC that hammers them. Electrolytic caps begin to leak DC after a decade (give or take) depending on the climate, hours used, equivelant series resistance (ESR) and build quality.

Capacitors are the main failure point in a rectification circuit (AC to DC) and usually fail to short. When a battery is connected, they drop voltage because it's drawing more current as voltage is proportional to current.

The heat produced by the OEM rectifier doesn't help its health either. If you get a new one, maybe reloate it here.

Some of the better aftermarket rectifiers use more effective heatsinks and better bridge rectifiers. They run cooler, are more efficient and will have new capacitors. It's certainly due for a new one.

Working in the electronics industry, I know that any appliance will only last as long as the roll of the dice because there are too many variables to contend with that can predict the life of a passive component. Anyone with a 24 year old rectifier that swears it's still going great is living on borrowed time lol.

I just fixed a friend's living room 7.1 surround sound amplifier, and sure enough it was the rectifier power board. Always the first to go especially with those cheap flat screen TV's. The TV's are always fine! It's the filter caps that clap out. $10 later and it's good as gold. Repair men won't tell you that though.