Another disturbing noise from Ruby

[Denis Sweeney]

John, I do have a simple meter that will check circuits and will measure voltage across the battery, please excuse my ignorance, but is it as simple as taking a reading across the terminals whilst turning the stater motor on the switch and noting the change?

[John Cornforth]

Yes, monitor the voltage whilst operating the starter.

To eliminate the cables and starter switch from the picture, you could also monitor voltage between the casing of the starter and the "downstream" side of the starter switch if you can access it with your probe.

[John Mason]

Denis, For how long it takes would have a look a the brushes and commutator. Make sure they are clean and free of any oil and grease and that the brushes have not worn to short thus taking the pressure off the brush springs. You can possible do this through the opening in the starter motor. Brake cleaner and a clean rag on the end of a screwdriver should do the brushes.

John Mason

[Denis Sweeney]

John C, garage has been OOB for the weekend but just put the meter across the terminals and registered 6.3 bolts, tried the starter motor and the reading dropped to just 2 volts. I am putting this back to yourself and others as electrics are a bit of a dark art to me, is that good or tragic??
I did also check the reading at the ends if the cables at the connection to the engine and starter switch and that is the same as the reading across the terminals, 6.3 volts.

[John Cornforth]

Hi Denis

6.3 volts is normal for a charged battery off load. If the terminal voltage drops as low as 2 during cranking, it suggests that the battery is on its last legs. However, before condemning the battery, make sure you have the meter probes on the actual posts of the battery rather than the cable clamps, just in case there is a bad joint between clamp and post. The latter is however unlikely as you would have spotted trouble whilst recently connecting and reconnecting different leads. Another trouble spot can be the joint between cable clamp and cable, if it is the "two screw" type rather than soldered or factory crimped.

The off load reading at the far ends of the starter cables doesn't really tell you much apart from the fact that they are connected.

You could try charging the battery with a 10 amp (or more) battery charger, rather than a low current trickle/maintenance type. However, your best bet would be to borrow a good 6V battery from another Sevenner.

In my experience, car batteries can quite easily "die" over a short space of time rather than deteriorating gradually. I have no idea what the mechanism is for this.

[Denis Sweeney]

John, as I noted in an earlier post, I had the battery checked by the supplier and he had advised it was all ok.
So have just checked again making sure the meter probes were made directly to the battery posts and there is virtually no die off at all, reading 6 volts when trying to turn the motor.
However anywhere downstream of the terminals and this falls to 2 volts when the starter switch is engaged.

[Ivor Hawkins]

I had a similar problem and replaced the leads with new HD copper cables. That extra bit of oomph was all that wa needed to turn the engine over.

[Denis Sweeney]

I have now isolated it down to the jump lead section on each cable. The voltage drop is negligible until it reaches the extension part of the temporary cable to reach the test rig and at the end of that cable it drops from 6 to 2 volts from one end of the temporary copper wire to the other measured on the copper itself and not the connectors.

[Nick Lettington]

The current in a 6V system is higher than in a 12v system... If you have used budget jump leads (quite sufficient at 12v), you may find the cross sectional area of the cable is quite a bit less than the battery leads on your Ruby... I used heavy duty cables when I did something similar. Shortening and/or doubling up the wires on the extension sections may help!

[Reckless Rat]

Best solution Denis, is two new cables, one from the battery POSITIVE lead through to a suitable bolt on the crankcase, and another one from the battery NEGATIVE terminal to the Starter solenoid, and a back up earth strap from the front of the crankcase to the nearside cow horn. My 6v starter spins like a good 'un since I did this.