GT550A Charging Troubles

[jonathanblair]

I recently added a GT550A to my garage. Bike has about 13,000 miles and is in VGC overall. After a recent 2-hour run on a warm day, I noted that the bike almost didn't want to restart, even though I had put in a brand new, freshly-charged battery. Also noticed that the alternator cover was too hot to touch - much hotter than the engine. I got a meat thermometer from the kitchen. The ram air cover measured about 115 degrees F. while the alt. cover was over 135 degrees. After a weekend of testing stuff, here is what I found:

Charging voltage is 13.5-14.5 at 3-4000 rpm when engine is cold. Voltage drops to 12-12.5 when engine is hot. Charging system will charge at up to 10 amps when cold, but only -1 to 1.5 amps when hot.
Field coil and stator coil resistance and continuity checks are all factory when cold or hot. VR checks out. Rectifier checks out fine cold, but some of the diodes allowed current flow in both directions when rec. was hot. Readings returned to normal as soon as rectifier cooled down.

Checked all wiring related to battery, fuse, ignition switch, charging etc. All wires and connectors are clean and solid and tight. Checked each wire for high resistance. Checked load on the battery (lights, field coil, ignition coil, recifier, VR, etc.) Each load seems accurate and appropriate. Loads are consistent - no change whether bike is hot or cold. Total draw is about 9.5 amps. The only non-stock loads on the system - H4 headlamp (about 10 watts over stock) and two additional tailights (8 watts each) I performed all of the tests with the extra taillights unplugged and it didn't seem to make a difference. I even did the hot tests with the lights off and the system still couldn't charge.)

I performed the Suzuki factory manual tests with the bike load off line, and the VR unplugged. Both cold and hot, the alternator put out the specified volts and a good bit more.

I replaced the faulty rectifier and the VR with brand new single rec/reg unit from Electrosports this weekend. Rain let up today so I could test ride. Cold, the voltage is 13.5-14.5 depending on rpm, lights on or off. Hot, voltage is 12- 12.5 with the lights on, 13-13.5 with the lights off. Alternator cover is not as hot as before. So the new Rec/Reg helped, but not enough.

Am I ready for a new alternator? Any other suggestions?

Thanks!

[jabcb]

Resistance checks only locate some problems. Also not sure what Suzuki manual test you did.

But it looks like you have a bad stator.

If you had a rotor that goes bad when its hot, I would expect it to reduce alternator output without creating a lot of current in the stator & without causing a lot of heat. Same goes for problems with the brushes.

Suzuki used two brands of alternators for the GT380/GT550. Parts are not interchangable. Its easy to tell which one you have based on the layout of the brushes.

For your load, the Kokusan alternator should start charging around 2k rpm & the Nippon Denso should start charging around 1,500 rpm. See page 18 of: http://www.ozebook.com/compendium/suzi/suzidata1.htm

[jonathanblair]

Thanks for your response. I think you're right - stator coil is the next place to look. In my experience, electrical problems that get worse when the engine heats up are usually related to a coil that is expanding with the heat.

Do you think a 9.5 amp load is about right?

I am hoping I don't have to pull apart every single wiring connector looking for green copper... I know that the battery connections, ground wires, starter wires, ignition switch, and all the leads to the alternator, rect. and reg, are all good.

I will check back in when I get a new coil installed.

Thanks!

jbl

[jabcb]

9.5 amp is reasonable.

Coils are around 4 ohms & dwell is around 180 degrees. So the coils draw around 4.5 amps.
Lights draw about 5 amps (55W headlight + 8W taillight)
You have a few more lights, but the current draw is reduced a little by voltage drops in the wiring.