Battery volts drop when trying to start - Triumph Forum: Triumph Rat Motorcycle Forums
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post #1 of 19 (permalink) Old 10-09-2019, 11:10 PM Thread Starter
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Battery volts drop when trying to start

Hi all,
Carby Thrux has been running (5-10km) after a recent makeover but does not have a consistent start.

Checked the specs on their website http://www.linkint.com.au/ and purchased a MOTOCELL LITHIUM GOLD LiFePO4 Battery 12.8 Volt Series - MLG14B 48WH.
Charges up to around 13.2v, hit the starter and sometimes it kicks over but more times just a click and whir of the engine trying to spin up but feels not enough oomph to get it to start.
Placed a multimeter across battery terminals, hit the starter and it drops to around 5-6v, no start, then it bumps back up to high 12s.
Swapped over and utilised a larger battery from another bike with same result.
New coil and plugs.
New wiring throughout using m.unit with two wires utilised from starter solenoid to START terminals on unit, this is the way many others also connect this circuit.
New R/R, recently purchased by Ricks for my set up.
Stator tested by checking resistance (20ohm) between each pin (1-2, 1-3, 2-3) whilst bike is off with no battery and reads starting at OL. to 0.00 after contact.
There is continuity between any of the three (1-2, 1-3, 2-3).
No resistance reading between any of the 3 pins to earth, checked with other earths.
Both connectors between rectifier and stator looks good.
Also noticed the battery earth cable gets quite hot to touch when attempting to start a few times.
Earth cable runs from battery to frame .5M and is around 6mm conductor diameter, no kinks or connectors.
Earth cable from starter motor to starter solenoid is 1.5M and again is around 6mm conductor diameter no kinks or connectors.
Seat not touching Ignitor.

If the bike does not start, I’ve also tried to rock bike in gear and reattempt, with some luck but not a lot.

Edit, altered text from relay to ‘starter solenoid’

Cheers
Daz

Last edited by Dazzzz88; 10-10-2019 at 06:05 PM. Reason: Changed ‘plugs’ to ‘connectors’
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post #2 of 19 (permalink) Old 10-10-2019, 12:27 AM
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Maybe you should isolate the starter motor and bench test the motor. If a different battery does the same thing and you are sure of the wiring and correct connections, then I would test to eliminate the starter. Might be pulling too many amps.
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post #3 of 19 (permalink) Old 10-10-2019, 01:29 AM Thread Starter
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Thanks, In there a procedure for testing a starter, what am I looking for?

Also just removed the spark plugs and bike spins up a lot easier, put them back in and no change, will move on to Felonyís response.

Cheers
Daz
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post #4 of 19 (permalink) Old 10-10-2019, 03:15 AM Thread Starter
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Haven’t yet got to the starter motor, but I tested resistance between the two spade terminals on the starter solenoid and I get .003 at 2k.
Search goes on.

Cheers
Daz

Last edited by Dazzzz88; 10-10-2019 at 04:41 AM.
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post #5 of 19 (permalink) Old 10-10-2019, 01:55 PM
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Try a voltage drop test. Connect one lead of the volt meter to the battery + terminal and the other to the battery cable stud on the starter. The meter should read .0. With the meter connected this way try to start the engine, the meter should read less than .5 volts. If the reading is higher you have a resistance problem in the cable, solenoid, or a bad connection in the circuit. Check the ground side the same way. Connect the volt meter to - battery terminal and starter housing, engage the starter and read voltage drop, should be less than .5 volts.
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post #6 of 19 (permalink) Old 10-10-2019, 06:00 PM Thread Starter
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Quote:
Originally Posted by rweb View Post
Try a voltage drop test. Connect one lead of the volt meter to the battery + terminal and the other to the battery cable stud on the starter. The meter should read .0. With the meter connected this way try to start the engine, the meter should read less than .5 volts. If the reading is higher you have a resistance problem in the cable, solenoid, or a bad connection in the circuit. Check the ground side the same way. Connect the volt meter to - battery terminal and starter housing, engage the starter and read voltage drop, should be less than .5 volts.
I’ve disconnected the starter motor. Cable looks good and connection was clean and solid. Cable left off at starter motor for tests above.

0v with both tests and just the sound of a single click from the solenoid.
Battery fully charged.

Edit
Connected starter motor back up and conducted same tests
.08 with the + side and
.1 with the - side.

Cheers
Daz

Last edited by Dazzzz88; 10-10-2019 at 06:23 PM.
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post #7 of 19 (permalink) Old 10-10-2019, 06:37 PM
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Quote:
Originally Posted by Dazzzz88 View Post
Iíve disconnected the starter motor.

Edit
Connected starter motor back up and conducted same tests
.08 with the + side and
.1 with the - side.
Every thing has to be connected as normal to conduct the test. Removing the cable tells you nothing. When you did the test (with cable connected) did the engine turnover normally or you just got a click? Have you tried using jumper cables from a car to see how it acts?
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post #8 of 19 (permalink) Old 10-10-2019, 06:45 PM Thread Starter
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Quote:
Originally Posted by rweb View Post
Every thing has to be connected as normal to conduct the test. Removing the cable tells you nothing. When you did the test (with cable connected) did the engine turnover normally or you just got a click? Have you tried using jumper cables from a car to see how it acts?
Maybe 4 out of 5 attempts I just get a click. The starter motor does spin sometimes, but usually only a few turns.
I haven’t tried jumper cables, but I did try a much larger battery with the same results.

Cheers
Daz
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post #9 of 19 (permalink) Old 10-10-2019, 07:13 PM
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Sounds like a bad starter or battery. Try the jumper cables, that will eliminate the battery if it turns normally. You can also try hooking a good jumper cable from a known good battery from positive terminal to the cable stud on the starter. With a cable from the negative battery post momentarily touch the starter housing. This is direct to the starter bypassing all else. Make certain the trans is in neutral and ignition is off.
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post #10 of 19 (permalink) Old 10-10-2019, 07:21 PM Thread Starter
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I will remove and bench test the starter motor (thanks Felony and wreb) then move on to jumper cable set up.

Cheers
Daz
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