Electrical issue . I am baffled!

[petergarth]

I'm busy reinstalling my Volvo Penta 2002 after a rebuild and posted several times.
Going reasonably well but all of a sudden an unrelated problem.

I'd re connected the electrics to the engine and switched on the DB.
I have two main battery switches, one for each battery bank (house and engine) but won't go into detail on this.

All fine (listernin g to music while making progress) when suddenly all power goes down.
NO voltage at the starter motor circuit and no power at the DB.

I trace the power from batteries through earth leakage etc etc. all the way but at the board no power.

After disconnecting +ve to starter motor (thinking this might be a problem), no change.

Then I notice I have power at the DB.......BUT it's only about 2.5 volts. Just enough to like a few CB LEDs.

Battery banks both showing full charge, solar panel working, all good!

Switch off all circuit breakers at the board. Switch off battery and DB main switches.
Switch back on and power at the board shows normal ( same voltage as measured at the MPPT on the solar panel)

Now here is the baffling bit.

As soon as I turn on ANY one of the circuit breakers at the DB, the voltage immediately drops back to around 2.5 to 5 volts.
If I replay the procedure it happens each time.
As soon as I switch one a CB the voltage drops.

What can be doing this???
I am stumped.

Any ideas from the forum experts will be greatly appreciated.

 

[pvb]

Check the main switch on the house battery circuit. You could disconnect one side and temporarily connect it to the other side of the switch to take the switch out of circuit.

 

[MikeCC]

Fault in switch panel? What happens if you connect panel feed (or separate wire from battery) directly to a switch/breaker?

 

[Daverw]

Sounds like a bad neutral, when the switches are on mine can do this through the feed back from the indicator bulbs

 

[NorthUp]

You probably have a corroded connection or wire, either in a crimp or possibly a main battery wire- all it takes is a crack in old insulation and the water gets in. Flex the main cables and see if one bit gives more than the rest.
Or as above- a corroded master switch

 

[halcyon]

Lost earth ? was it all connected via, or not via the old engine, loose earth, breaks down under load.

Brian

 

[VicS]

What can be doing this???
I am stumped.

Any ideas from the forum experts will be greatly appreciated.

Almost certainly a bad connecion somewhere, or a bad switch

A bulb on a couple of leads is often better than a multimeter for locating this sort of thing because a digital multimeter draws so little current that it will often give a normal reading through a bad connection and is guaranteed to make a fool of you sooner or later

 

[Stemar]

The first thing I'd do is clean all the battery terminals and connectors. A similar problem on Jissel resulted in a new battery connector. Then I'd work my way through the cables and switches up to the domestic panel and through the starter system. Put a load on the circuit and then trace the voltage drop. Where you get a drop where there shouldn't be one is where you have the problem. Put the -ve terminal of your voltmeter on the battery post itself, not on the clamp.

 

[petergarth]

Hi All
Thanks for the suggestions as to the electrical problem.
I have sorted it and thought it may be helpful to explain.
The reason for the voltage drop was that I had failed to connect one of the main earthing straps to the motor.
Apparently this causes the system you use one of the other smaller gauge earth wires to return to the battery. As soon as a load was applied at the DB it failed.
Once this was done it all returned to normal.
Hope this is useful feedback.

 

[pandos]

Thanks for the feedback..(so many threads do not have a conclusion or an acknowledgement of what was the correct theory about a fault).

I am about two steps behind you in terms of putting my Md21b back into action and this morning was reminding myself to not forget the negative connections at the block...

(Obviously I will now have a different problem...)