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 Post subject: Electrical short
PostPosted: Sat Nov 11, 2017 11:05 am 
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Still in the Driveway

Joined: Tue Nov 07, 2017 3:25 pm
Posts: 3
Country: Portugal
Bikes owned: GP125, GT380
I need some help with what I think may be a short on my GT380 (1976). The bike has been standing for some time due to an engine breakdown. I work abroad so have limited time to work on it. The bike is now complete but wont start at all.
I purchased a Newtronic ignition a few years ago and decided to installed it whilst undertaking the repairs but the following happens and am at my wits end as to the cause.
a) With the ignition in the ON position & the RUN/OFF switch in the OFF position there is around a 1Amp draw from the supply.
b) With the ignition in the ON position & the RUN/OFF switch in the ON position there is around a 5Amp draw from the supply.
c) If the white connector is unplugged at the Newtronic unit the system all seems ok but once connected reverts to a large current draw which doesn't seem correct.
The following has been checked and gives the correct readings:
a) All wiring harnesses checked for short circuit.
b) Coils, Rotor & Armature impedances checked.
c) Good earth between motor & chassis.
d) There was a spark at the first time of testing.
The Regulator & Rectifier have been replace for a unit combining both as the original rectifier had a dead diode which I think may have occured when the bike was first switched on & attempted to start.
The Newtronic unit was replaced with the points/condensor unit but this didn't solve the problem.
During the second time of testing I didn't connect the Regulator/Rectifier unit to avoid frying the new item.
Any ideas and possible solutions as to what may be the cause are greatly appreciated.

Thanks
Carlos


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 Post subject: Re: Electrical short
PostPosted: Sat Nov 11, 2017 11:34 am 
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To the on ramp

Joined: Wed Jul 10, 2013 12:04 pm
Posts: 431
Country: England, UK
Bikes owned: FZ50, GP100, RG125 Gamma, GT380, Bandit 1200S
CFS wrote:
I need some help with what I think may be a short on my GT380 (1976). The bike has been standing for some time due to an engine breakdown. I work abroad so have limited time to work on it. The bike is now complete but wont start at all.
I purchased a Newtronic ignition a few years ago and decided to installed it whilst undertaking the repairs but the following happens and am at my wits end as to the cause.
a) With the ignition in the ON position & the RUN/OFF switch in the OFF position there is around a 1Amp draw from the supply.
b) With the ignition in the ON position & the RUN/OFF switch in the ON position there is around a 5Amp draw from the supply.
c) If the white connector is unplugged at the Newtronic unit the system all seems ok but once connected reverts to a large current draw which doesn't seem correct.
The following has been checked and gives the correct readings:
a) All wiring harnesses checked for short circuit.
b) Coils, Rotor & Armature impedances checked.
c) Good earth between motor & chassis.
d) There was a spark at the first time of testing.
The Regulator & Rectifier have been replace for a unit combining both as the original rectifier had a dead diode which I think may have occured when the bike was first switched on & attempted to start.
The Newtronic unit was replaced with the points/condensor unit but this didn't solve the problem.
During the second time of testing I didn't connect the Regulator/Rectifier unit to avoid frying the new item.
Any ideas and possible solutions as to what may be the cause are greatly appreciated.

Thanks
Carlos

So let me get this straight.. You have 5 amp current draw when you activate the circuit supplying the coils?
Try this; disconnect the low voltage side of the ignition coils. Then check to see if you have a 5 amp draw still. If the problem has gone, maybe you have a faulty coil.
However... a common fault, after working on the bike, is to accidentally clamp a wire to earth. Check you have no wires clamped either at the handlebars or the engine casings/covers. Another possible is that your solid state regulator/rectifier has a couple of wires transposed. They are often universal type things and sometimes you need to verify that they have put the multi-plug on correctly for your bike.


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 Post subject: Re: Electrical short
PostPosted: Sat Nov 11, 2017 1:04 pm 
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Moto GP
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Joined: Mon Dec 13, 2010 4:32 pm
Posts: 2948
Location: southwestern Pennsylvania
Country: USA
Bikes owned: 69 T350 thru 75 GT750
1) With ignition on & run/off in off, you are powering the alternator rotor.

See page 15 of http://www.ozebook.com/compendium/suzi/suzidata1.htm
The Nippon Denso alternator rotor has a resistance of 10 to 20 ohms.

12V & 12 ohms gives you a 1 amp current.

So your 1 amp current looks like it may OK.

2) With ignition on & run/off in on, you are powering the alternator rotor & the ignition coils.

On the GT380 with points ignition, either 1 or 2 coils are powered at any given degree rotation of the crank.
Coils are around 4 ohms. (3 to 6 ohms per page 15)
5 amps out of the tiny GT380 battery will cause the voltage to drop.
You can have an additional 1 volt drop in the wiring between the battery & the coils.

9V at the coils & 4 ohm coils gives you a 2.2 amp current. And 2 powered coils gives you 4.4 amp. Reduced voltage for the alternator rotor gives you 0.75 amp.
For a total of 5.15 amps.

So your 5 amps looks like it may be OK.

3) what to do next.

Charge up the battery. Check for spark.
Your starting problem may be fuel related, so check to see if the plugs get wet.

Once you have the bike running, check the voltage at the battery with the motor at revs. Post the results.
You may actually find the results ok.
You might also find the the voltage running at revs is actually too high. (High voltage can damage modern sealed batteries.)

_________________
BAS (Bike Acquisition Syndrome) - too many bikes but have room for more

Suzuki:
GT750 2x75
GT550 72 project & 75
GT380 72
T500 73 project
T350 69, 71 & 72 project
T250 72
Honda 85 CB650SC & 86 CB700SC
Yamaha 75 XS650
09 Triumph Bonneville SE


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 Post subject: Re: Electrical short
PostPosted: Sat Nov 11, 2017 2:01 pm 
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Still in the Driveway

Joined: Tue Nov 07, 2017 3:25 pm
Posts: 3
Country: Portugal
Bikes owned: GP125, GT380
Thank you all for the prompt reply and all the advice/help.

Sportston
I have measured the coils impedance - would this not have detected a faulty coil? All the coils measured around the 4.4 ohm mark.
Can you be more specific as to the low voltage side of the ignition coils - where to check.
After this happened at the first attempt all the wiring and connectors were disconnected & re-checked. I didn't find any short.

Moto GP
At the first time of trying there was spark at all cylinders and the plugs were wet. The carbs had been cleaned and re-set.
What I forgot to mention was that when the circuit was activated (ignition on & run/off on run) the neutral light dimmed considerably which has led me to suspect an electrical short. This never occured previously (before the breakdown).

Please note that electrical issues are not my strong point.

I will take all the information/advice given on board and check/attempt when next at home.

Thanks


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 Post subject: Re: Electrical short
PostPosted: Sat Nov 11, 2017 7:07 pm 
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Moto GP
User avatar

Joined: Mon Dec 13, 2010 4:32 pm
Posts: 2948
Location: southwestern Pennsylvania
Country: USA
Bikes owned: 69 T350 thru 75 GT750
These bikes can be a real PITA (pain in …) to start the first time you kick start after major work like a rebuild.
We gave up the first time we tried to start our GT250 cafe build. A few days later we tried again & got it going. Now it starts easy.

Fully charge the battery & use a new set of plugs.
Check the battery voltage with the ignition on & run/stop in on.

_________________
BAS (Bike Acquisition Syndrome) - too many bikes but have room for more

Suzuki:
GT750 2x75
GT550 72 project & 75
GT380 72
T500 73 project
T350 69, 71 & 72 project
T250 72
Honda 85 CB650SC & 86 CB700SC
Yamaha 75 XS650
09 Triumph Bonneville SE


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 Post subject: Re: Electrical short
PostPosted: Tue Nov 14, 2017 11:54 am 
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To the on ramp

Joined: Wed Jul 10, 2013 12:04 pm
Posts: 431
Country: England, UK
Bikes owned: FZ50, GP100, RG125 Gamma, GT380, Bandit 1200S
CFS wrote:
I have measured the coils impedance - would this not have detected a faulty coil? All the coils measured around the 4.4 ohm mark.
Can you be more specific as to the low voltage side of the ignition coils - where to check.
After this happened at the first attempt all the wiring and connectors were disconnected & re-checked. I didn't find any short.


Ok sounds good. When I said the low voltage side I meant the skinny wires, not the thick one. The coils have two windings inside, one is the low tension/voltage input side of the coil (12v) and the other is the high tension/voltage output side of the coil (approx. 40,000 volts). If you had a short it would usually be the low tension side of the coil causing a problem. However, I do not think this is your problem.
Follow these instructions carefully;
1. First make sure you do NOT have a regulator plugged in.
2. Next... You should have a multiplug that supplies your ignition coils (it will probably have about 3 orange and white wires, 1 black wire, 1 white wire and one black and yellow wire). Unplug this multiplug.
3. Check to see if you still have 5 amps draw when you have the kill switch in the RUN position and 1 amp in the KILL position.

If you still have 5 amp draw in the RUN position then you have a wiring loom fault. If so you will need to repair or replace the orange and white wire which goes to your coils and regulator.

If you DON'T have a 5 amp draw will kill switch in RUN position anymore follow these instructions;
4. Plug the ignition coil multiplug back in again.
5. Check if you have a 5 amp draw again.
If you have a 5 amp draw again, then you either have a fault with the coils or wiring between multiplug and coils.

Report back and let us know what you find.
This is not a definitive diagnosis table. I have tried to keep it fairly simple and give it to you in small chunks. The next step, depends upon what you find. I have had to rely upon wiring diagram info for the 1977 model as I am on holiday at the moment and don't have access to my Haynes manuals. If you find the colours are not the same, let me know.


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 Post subject: Re: Electrical short
PostPosted: Sat Dec 02, 2017 12:01 pm 
Offline
Still in the Driveway

Joined: Tue Nov 07, 2017 3:25 pm
Posts: 3
Country: Portugal
Bikes owned: GP125, GT380
sportston
I have tried what you recommended but had to use an electronic power supply as the battery is a total loss and needs replacing. Again this was checked using the Newtronic ignition and not a points & condensor ignition.
My findings are as follows:
a) With the coils multiplug disconnected and the regulator disconnected I measure 0.6 Amps in the kill position and no change in the run position.
b) With the multiplug connected and the regulator disconnected I measure 0.6 Amps in the kill position and 5.5 Amps in the run position.
I didn't get an opportunity to re-check the wiring loom for faults but when checked the first time none were found. I will re-check the loom when back home over the Xmas break.
I re-checked the colis and they all measure in the 4.4 ohm range.
As this was never noticed before I replaced the points & condensor system for the Newtronic ignition I contacted the supplier with the same query as I thought the ignition may be at fault. Their reply was that when the engine is not running there will always be one coil drawing current but depending on the position of the rotor blade there may be two.
The static draw current for a single coil may be up to 4 Amps and that in their opinion it would appear to be normal for the ignition circuit to draw 5 Amps when in the run position. They have implied that the fault could be from the battery.
Any further testing/checks you think I should carry out?

jabcb
As mentioned above the battery is of no use and needs replacing.
Using the electronic power supply I re-checked for spark and this is present.
I have removed the carbs for re-cleaning and re-calibrating.
When back home for the Xmas break I will purchase a new battery and attempt to start it again with new spark plugs.
The recommended battery is a 12V7AH which you previously said was a tiny battery. As I have to purchase a replacement would it be a benefit to purchase a larger capacity unit and if so what would a recommeded size be?

Many thanks to both for all the help given thus far. I will keep you posted of my findings as they occur.


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 Post subject: Re: Electrical short
PostPosted: Sat Dec 02, 2017 12:40 pm 
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Moto GP
User avatar

Joined: Mon Dec 13, 2010 4:32 pm
Posts: 2948
Location: southwestern Pennsylvania
Country: USA
Bikes owned: 69 T350 thru 75 GT750
I have a standard-size AGM battery in my GT380. It will work out fine once you have this problem sorted.
Just charge the battery up from time to time while you work on this problem.

_________________
BAS (Bike Acquisition Syndrome) - too many bikes but have room for more

Suzuki:
GT750 2x75
GT550 72 project & 75
GT380 72
T500 73 project
T350 69, 71 & 72 project
T250 72
Honda 85 CB650SC & 86 CB700SC
Yamaha 75 XS650
09 Triumph Bonneville SE


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 Post subject: Re: Electrical short
PostPosted: Mon Dec 04, 2017 1:01 pm 
Offline
To the on ramp

Joined: Wed Jul 10, 2013 12:04 pm
Posts: 431
Country: England, UK
Bikes owned: FZ50, GP100, RG125 Gamma, GT380, Bandit 1200S
First off....ditch the power supply and use a new battery instead.
A slightly heavier duty one will be ok, but you don't need a huge one on a bike without an electric starter. You just need a good one. A gel battery will hold its charge for longer and last longer without the need for topping up. But an old style liquid acid type is fine for a few years use if looked after well.
As Jab has done the math, it looks like you might not have a short, just the bike wont run.
So you probably need to try starting the bike with a new battery.
If it won't start, check if you have three good sparks or not


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