12 v socket wiring - double checking

[PD1964]

Is your battery charger switched on and is producing charge? I would take all readings with all charging switched off so you get a genuine battery voltage and amp reading from the batteries only.

Edited January 23, 2022 by PD1964

[Tony Brooks]

10 minutes ago, PD1964 said:

Is your battery charger switched on and is producing charge? I would take all readings with all charging switched off so you get a genuine battery voltage and amp reading from the batteries only.

 

No use doing that if the circuit is not driving its designed load. with everything turned off the current flow will be zero so the volt drop will also be zero. testing voltage with no load is arguably the most common way ordinary boaters fail to recognize volt drop faults.

[Alan de Enfield]

28 minutes ago, RickS said:

Why are they the same if there is voltage drop - I know no load is being applied at the moment but the voltage is there to be used ?

 

Presumably you have a battery charger switched on to be showing 13.4 volts.

 

As I explained - volt drop is a function of 3 criteria Voltage, copper cross sectional area and current.

 

If you have zero current flowing then you have zero volt drop.

 

Put a test meter on your starter battery and take a reading, leave the tester connected, turn your engine over and watch the voltage drop to (maybe) 11 volts as the starter motor draws a large current.

 

Amps drag down voltage.

Edited January 23, 2022 by Alan de Enfield

[PD1964]

18 minutes ago, Tony Brooks said:

 

No use doing that if the circuit is not driving its designed load. with everything turned off the current flow will be zero so the volt drop will also be zero. testing voltage with no load is arguably the most common way ordinary boaters fail to recognize volt drop faults.

Why would you test a circuit for voltage with your battery charger switched on charging the batteries? Surely this would not give the genuine battery voltage but the voltage being produced by the charger, the charging voltage.

  I said to switch charger off only so you get the battery charge not a bulk or float charge from the charger.

Edited January 23, 2022 by PD1964

[TheBiscuits]

1 minute ago, PD1964 said:

Why would you test a circuit for voltage with your battery charger switched on charging the batteries? Surely this would not give the genuine battery voltage but the voltage being produced by the charger, the charging voltage.

 

To measure the voltage drop along the cable run.

 

 

He's not trying to measure the battery voltage, so the difference between 12 and 14 volts (charger off or on) is irrelevant.

 

[PD1964]

10 minutes ago, TheBiscuits said:

 

To measure the voltage drop along the cable run.

 

 

He's not trying to measure the battery voltage, so the difference between 12 and 14 volts (charger off or on) is irrelevant.

 

I know he’s not measuring the battery voltage, but surely with the charger switched off and not making charge would give a better indication of batteries and more genuine results.

Edited January 23, 2022 by PD1964

[Tony Brooks]

12 minutes ago, PD1964 said:

Why would you test a circuit for voltage with your battery charger switched on charging the batteries? Surely this would not give the genuine battery voltage but the voltage being produced by the charger, the charging voltage.

  I said to switch charger off only so you get the battery charge not a bulk or float charge from the charger.

 

It depends what you are trying to measure/discover. If you want to know the rested voltage of the batteries then I would agree with you apart from measuring in the end of a circuit rather than at the batteries invites errors.

 

If you want to know if you have voltage at the ends of the cables 12, 14, or 14.5 volts makes no difference apart from the fact with the circuit not drawing load gives a meaningless reading.

 

 

 

 

3 minutes ago, PD1964 said:

I know he’s not measuring the battery voltage, but surely with the charger switched off and not making charge would give a better indication of batteries and more genuine results.

 

Not if it a volt drop issue and you make the measurement with no load.

[PD1964]

9 minutes ago, Tony Brooks said:

 

It depends what you are trying to measure/discover. If you want to know the rested voltage of the batteries then I would agree with you apart from measuring in the end of a circuit rather than at the batteries invites errors.

 

If you want to know if you have voltage at the ends of the cables 12, 14, or 14.5 volts makes no difference apart from the fact with the circuit not drawing load gives a meaningless reading.

 

 

 

 

 

Not if it a volt drop issue and you make the measurement with no load.

I know what your saying, but I would do it without a charge voltage going into the batteries.

[cuthound]

2 hours ago, Alan de Enfield said:

 

Ok. Volt drop (what voltage comes out of the cable compared to what goes in) is affected by Voltage, current drawn and cable copper cross sectional area (size)

The 'normal acceptable volt drop is a maximum of 4% and nearer 2% is the target.

 

Taking 12m (one way) at 12 volts.

You will be using around 7.5 amps, lets call it 10 amps just in case you plug another phone onto charge somewhere in the circuit.

 

The wiring already existing is quite likely to be 1.5mm2 or at best 2.5mm2 so what would be the volt drop on these :

 

1.5mm2 will give 3.04 volt drop (25.4%)

2.5mm2 will give 1.80 volt drop (15.2%)

 

You need to go to 10mm2 cable which will give you a 0.44 volt drop (3.64%) just below the maximum 4%

 

 

 

You may find that it will not fit into your terminals so 'work will be needed' to fit it.

 

 

 

To fit large cables into smaller terminals use reducing lugs like these.

[ditchcrawler]

4 hours ago, blackrose said:

 

I also knew a guy who did that. He lived aboard but knew nothing about boats and didn't realise that a mains supply would sink his boat in the event of a plumbing leak while nobody was onboard.  

One on the Thames did sink

 

4 hours ago, RickS said:

OK thanks Alan. I am going to sound quite dim now but going to ask anyway 🙂 At the moment, the cable carrying the current that was supplying the extension lead debacle is showing 13.4 volts on the multimeter - this is the same as is showing on the battery charger unit. Why are they the same if there is voltage drop - I know no load is being applied at the moment but the voltage is there to be used ?

That is because you have no load connected, with no current flow you get no volt drop. The circuit wire are effectively just an extension of your volt meter cables when there is no current flow  I find this useful for cable voltdrop Cable sizing and selection | 12 volt planet