Wiring to plotter - voltage loss?

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Venus1

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My Vulcan 7 at the helm has a voltage display. It always shows about 0.9v less than the voltmeter in the cabin. I guessed that the wire is too small a gauge, or there is a bad connection somewhere. The plotter still works ok, but I am perplexed at the different voltage, and annoyed at the occasional low voltage alarm.
Today I disconnected the Vulcan connector, and checked the voltage there (at the helm), and it was the same as the cabin voltmeter (albeit with no load).
Can I conclude that the connections are ok, but the wiring is too small a gauge? The manual says the Vulcan only draws 1A. You will ask me what gauge the wiring is, and I should know that...How do I tell?
Thanks from an electric numpty
 
As well as the cable possibly being too thin, the main culprit of voltage drops can be connectors, especially in the damp environment of a boat. Pulling out and replugging can often clean up any bad joint that is introducing resistance and thus voltage drop.

You can check with a multimeter on a low DC voltage range across the connector to see where the drop might be.

If you need any new cable or connectors, I favour www.vehicle-wiring-products.eu who have a fantastic range of products.
 
My Multi and Graphic repeaters also show voltage and both show about +0.3v. It may just be a calibration problem that you have to live with.
 
If you used ridiculously thin wire and measured it at the plotter, with the plotter disconnected, it would read battery voltage. As soon as you apply a load the voltage would drop. How much would depend on the wire size and length, as well as the load. Similar results will result from bad connections though, a connection my be good enough to carry a small current, but not a larger one. Also, a bad connection may not carry a small current, but will carry a heavy current, which might seem counter intuitive.

So your test is inconclusive i'm afraid. Check all connections. You can measure the wire diameter with a vernier gauge, but you need to measure the conductor, as the insulation thickness varies with different types of wire. You might be lucky and find some writing on it to identify it.
 
Venus1 said:
My Vulcan 7 at the helm has a voltage display. It always shows about 0.9v less than the voltmeter in the cabin. I guessed that the wire is too small a gauge, or there is a bad connection somewhere. The plotter still works ok, but I am perplexed at the different voltage, and annoyed at the occasional low voltage alarm.
Today I disconnected the Vulcan connector, and checked the voltage there (at the helm), and it was the same as the cabin voltmeter (albeit with no load).
Can I conclude that the connections are ok, but the wiring is too small a gauge? The manual says the Vulcan only draws 1A. You will ask me what gauge the wiring is, and I should know that...How do I tell?
Thanks from an electric numpty
Click to expand...

No!

I guess you used a digital multimeter? They take so little current that they will give a normal reading even if there is a poor connection. as Paul Rainbow points out

If you want to compare the true battery volts, the cabin volt meter and the Vulcan's voltage display you should make all three measurements with your meter while the Vulcan is connected and operating. You may well find that either or both the cabin meter and the Vulcan display do not agree with your meter!

Regarding the wiring the very lightest I'd expect to see is 0.5 mm² but I'd think at least 1.0 mm² should be used for physical robustness. PR will probably suggest 1.5 mm²


0.5 mm² has resistance of 34 milliohms / metre therefore 10 m of wiring ( total negative plus positive) would cause a volts drop of 340 mV (0.34 V) at 1 amp .
1.0 mm² wiring will have half the resistance and cause half volts drop per metre.

3% (0.36 V) is generally the maximum acceptable figure for volts drop on a 12 V system however the "Tech spec" for the Vulcan indicates that that it will operate with a supply within the range 10 V to 17 V. Voltage drop due to unsuitable wire size is therefore unlikely to be an issue!

.
 
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Short of replacing the wire I would start off by simply cutting off the old ends and fit properly crimped 'bootlace' terminals, or similar, depending upon what connections you have.
I used to have contact problems with the socket for the tipper-pilot. Rubbing the contacts with fine wet&dry abrasive paper was a regular occurrence. Eventually I replaced it with one that was a proper water-proof type that has a screw-on cap. An aerosol can of 'Contact Cleaner' is useful to keep on board. (Costs around €5,00).
 
My Vulcan 7 gets remarkably warm after a few hours if it's really drawing under 1 amp as per the specs. I wonder if the spec sheet measures at a low brightness setting, not full brightness on a sunny day.

I had to rewire the power to the binnacle a couple of years ago after fitting it: the original instruments all drew 12v off a daisychain of Seatalk 1 connectors - that was how the boat was supplied new, probably OK for just four ST60s. Ran a new 29 amp rated cable to the binnacle from the switch panel to power the plotter and a St-StNG interface.
 
VicS said:
Regarding the wiring the very lightest I'd expect to see is 0.5 mm² but I'd think at least 1.0 mm² should be used for physical robustness. PR will probably suggest 1.5 mm²
Click to expand...


You know me too well Vic :)

Regarding 0.5mm cable, i usually only use that for short runs to LED lights.

the "Tech spec" for the Vulcan indicates that that it will operate with a supply within the range 10 V to 17 V. Voltage drop due to unsuitable wire size is therefore unlikely to be an issue!

.
Click to expand...

Although the lowest operating voltage is 10v, the alarm could be set higher. IMO, it should be set higher, so the alarm warns of low system voltage, rather than the impending doom of the plotter lowest working voltage having been reached and the plotter turning off seconds later.

Unfortunately, the manual gives no details of the alarm thresholds, perhaps the OP could confirm ?
 
When the Vulcan 7 was launched there was much trumpeting about the low 1a consumption, it was good at the time. The 1a figure is for the plotter only, no depth.

I have a Garmin 9" plotter that they claim a typical 1a consumption. If i turn the other N2K equipment off i get a 1.1a current draw, that's powering the N2K network with the plotter and a DST 800 giving depth and water temp (no STW as i'm not moving).
 
Talking of cable sizes.........

You could sit there and work out the voltage drop and current requirements for every bit of kit on the boat and wire them all up with the exact size of cable. If you did, you'd probably be a nut job or certifiably OCD :)

For general wiring very few sizes are needed. A huge amount of stuff can be wired using 1.5mm cable. It might be a bit overkill for some stuff, but it certainly does not hurt to be over spec. No worries about voltage drop and it's physically robust. When 1.5mm starts to get border line, step up to 2.5mm. There are few single pieces of equipment that would need wiring bigger than 2.5mm. Maybe your fridge or your heating will need some 4mm, or the battery charger or solar controller might need some 6mm, or even 10mm. Not many things will need these cables though.

In some installations i like to arrange things so you don't have to run a gazillion wires to one place. Maybe run some 10mm cable to a fuse/switch panel, which then steps the cables down to 1.5mm or 2.5mm etc. Or you have a switch for your nav electronics that feeds a fuse panel via 2.5mm, then smaller cabling to the N2K network, plotter, sounder etc. The single switch turns on all the equipment you need for navigation, whilst everything has it's own, correctly rated fuse.

Do away with all the oddball inline fuses and stick to blade fuses. Make sure that anytime you step down in cable size that you step down in fuse ratings too. So that 10mm cable from the isolator has a hefty fuse, much bigger than any single item it will supply, but lower rated than the cable (75amp). This ensures the cable is protected, but the fuse won't blow if a single piece of equipment fails. At the fuse panel the 10mm cable supplies, fit appropriately rated fuses for each piece of equipment.

Looks like 12v planet agree with my cable size selection :)

https://www.12voltplanet.co.uk/single-core-tinned-copper-thin-wall-cable.html
 
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Thanks all for replies - very helpful.
I will act on the advice :)
Regarding the alarm thresholds: I will check on the boat and report back.
 
[QUOTE Unfortunately, the manual gives no details of the alarm thresholds, perhaps the OP could confirm ?[/QUOTE]

I checked my Vulcan 7 today. There are 2 voltage alarms, 18v and 11v. In settings you can activate one or the other or both (or neither). I can testify that the 11v alarm works - but it will sound much less often when I re-wire as per this thread :)

simonfraser, good point but no, there are no other connections to that wire
 
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