Intermittent earth?

[cushers]

Hi All,
Is there, with respect to LBs, SBs and SVRs, such a thing as an intermittent earth?

My reason for asking is that over the last month the Power Management 3 system in my conversion has been indicating a deteriorating battery condition for both the LB and SB.

I checked both batteries with a multimeter and they were healthy, giving good readings when the engine was off, running and under load.

Today the LB which really only runs the radio died at approx 9.4 V. With the engine running the Volts didn't increase. When checking the earth it seemed more difficult to register a "beep" on the multimeter than one would normally expect. My mechanic friend tested across both batteries and all of a sudden the next check of the LB registered at 13.9 V with the engine running. The Power management 3 unit in the conversion jumped to green on the battery condition for a short while then dropped to red again,

So, Is it the earth, the LB itself, the charging relay or the PM3?

Yours in anticipation
Graeme

[g8dhe]

Any problem with the earth to the battery itself or the relay will cause those problems.

[cushers]

Thank you Geoff. Hopefully a simple fix. Even for me.
Graeme

[cushers]

So I cleaned off the terminal and the earth. I think that is a big step towards the final solution but maybe a suspect LB now too. The PMS 3v system sometimes now reads a good condition on the LB and SB but not all of the time. Interestingly, whatever the condition the LB (van battery) shows, SB (car battery) shows the same.

Will let you know how this transpires.

Graeme

[g8dhe]

Its probably worth inspecting every connection point and fuse blade, they tend to get left for many years and slowly they deteriorate nothing dramatic, but slowly there is more and more resistance at each and every point which all adds up to lowering the current, extending the charging time and generally making for odd problems. Its a tedious job but for once every year or two it saves a lot of mucking around when a fault becomes obvious!

[cushers]

That'll keep me busy. Thank you

G

[windywatson]

I would personally be checking the connections at the PMS. If the voltages checked at each battery are good but you are getting spurious readings at the PMS then look there first. Also depending upon the type of split charger being used to charge the LB there may be a shared earth at the split charger that would be in common.

[cmm303]

Cushers, you mention not getting a "beep" on the multimeter. Suggests you are measuring continuity. If a high resistance connection is suspected, try measuring volts between specific points along the circuit to identify where the volts are being dropped. Won't work though if the circuit is completely broken somewhere unless you happen to be measuring across that break.

E.g. 9.4v across PMS terminals and 13.6v across battery posts. Measure + post to positive PMS terminal. Measure - post to PMS ground. The sum of the last two measurements should equal 4.2v (13.6v - 9.4v) and show if it's the earth or supply that's the problem.

[cushers]

Thank you.

Much food for thought. May get a professional to have a look.

Graeme