1975 Suzuki GT380 battery charging issue??

[wavehog33]

I recently purchased this 1975 GT380 and then tore it down for a frame up restore/rebuild. I do not know 100% if this problems existed prior to the tear down as I only rode the bike for 5 miles. On the first 20 mile ride, after the rebuild, I started losing my lights, horn, flasher etc and noticed my battery was going dead. Made it home then hooked the 6 amp charger and brought the battery back...so I thought.
Thought my voltage regulator must be faulty? I checked my reading on the full charge battery-13.5 volts, when I run the bike at 5000rpm I read 12.3 volts on the battery. My research has shown the reading should be 13.5-14.5 when at 5000rpm. However all 3 regulator/rectifiers that I tested had similiar low readings? Unlikely that 3 regulator/rectifiers are all bad, more likely I have something else going on. I also do not believe my alternator is faulty. Part is in far too nice of condition and the bike only has 4900 miles...practically still new
My battery during charging with the 6amp charger would show charger needle about 7 amps when first connected, then fully charged would show around 3-4 amps. Never getting much lower. I had the battery checked at local autoparts store and at 75% charge and 200 cold crank amps, the battery showed faulty? My new battery when filled with fluid and hooked to charger gets a charger gauge reading of 2-3 amps and after about 8 hours charging, the reading is down to approx 1 amp. Does this mean anything???
Is it possible that the 6amp charger will charge my old battery but the bike will not charge during running because it is not designed to put out enough amps that the "bad" battery is requiring??? Any ideas??? Thanks! Pics are before the pipes.

[felkman]

First let me say beautiful bike, you did a great job!

One question I always have when trying to figure out an electrical problem is, have you changed the headlight to a brighter bulb, this can really put a strain on the system if your headlight is using more amps than the system is putting out.

Is the "good" battery completely charged when you are testing. You have to remember that the charging system is not designed to charge a battery, it is to maintain the charge. Yes, a charging system on a bike can and will bring up a charge of a battery but it takes a while of riding it.

I would not rule out the alternator just because it only has 4,900, it is still a 37 year old bike and just like everything else, it to can need some work. There was a reason you did a frame up restoration on such a low mileage bike, it must have needed some work. Is there a way to check the alternator on a GT380 while it is on the bike?

Last thing, This may sound stupid, but, have you checked all the connections?

I am guessing these are all things you have thought of but just thought I would throw this out there. Again, You have one beautiful two stroke wheelie machine!

[wavehog33]

Checking through all the connections one more time. Pretty sure I got them all though. I am checking on another vintage forum about metering the alternator while on the bike. The headlight is a sealed unit, the bulb cannot be replaced alone. I believe the headlight to be original. Thanks for the compliments about the bike.

[felkman]

I just reread your first post and your new battery has dropped amps after charging? How many volts does your new battery show when fully charged and when it is not connected to the bike? I think it should be 12.4 - 12.6. I am kind of thinking your new battery may have an issue! Your battery will last longer if charged on the 2 amp setting instead of 6

[cb500bobber]

Another thing did you make your own harness or use the old one

[williamc89]

ok when you put the battery in the bike start the bike and hook ur - + of a volt meter up and check ur volts at idle you should be 13 or more just at idle that is how all chargeing systems work,, and as far as ur charge if im right when its charged it should go up in amps not down, remember ur putting power into the battery so the amps go up not down,,,, my charger goes up when its chargeing,,, also check the ohms in ur main chargeing wires ,,

[tango911]

its the original harness, its in good shape. we have it narrowed down to the bad battery, or possibly the stator.

[wavehog33]

Just an update on the GT380 progress. I am becoming experienced with a multimeter! Checked resistence from alternator, rectifier and regulator. Everything checked except one line from the alternator. Turns out the brush assembly had come loose and one of the leads inside the brush housing was not making contact showing and open circuit. Replaced with brushes from a parts bike I have and BAM, checks out perfect now. Battery at 13.3 volts and charging at 14.5 at 5000RPM. Looks like I am branching into the streetbike world!!

[felkman]

Glad you got it figured out and it didn't cost you anything. Hope to see you riding it this summer!

[williamc89]

thats great it was something easy

[550fi]

Really nice restoration,glad its fixed.

[tango911]

i got to ride that beast the other day and man its quick.

[bluebeard]

Good looking bike. Where's the exhaust?