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post #1 of 31 Old 04-04-2012 Thread Starter
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Wiring up electronics to a switch?

We have purchased all our electronics and are connecting them to the NEMA 2000 network.
They are all from the same manufacturer.
So our radar draws 4 kw. And I am not sure what that means yet. The dome is now maunted on the mast.
We are about to wire up our chart plotter and wind sensor and radar.

We will be cruising Mexico south Pacific side.

So my thinking is power is only an issue for us for sailing at night. We have lots of solar while sailing during the day, it may vary but still.

We have lots of power if motoring. We do have a wind generator but cannot count o that.

We have no experience with the instruments and I do not remember seeing on\off switches at the binnical for wind sensors and depth sensors etc. on any sail boats.
So what about Radar? It is probably the biggest draw (Garmin 18 HD).

We would probably not need them all on while the Auto pilot is on?

We will wire them all to a blad fuse block and to a switch.

I have not figured out all the amps for each sensor and radar yet.
My idea (here goes) is to have a three way push pull switch at the nav station for the instruments.
When ON the:
Wind sensor
Depth sensor
Auto pilot
Chart plotter
And Repeater will be powered. The chart plotter, repeater and Auto pilot have on\off buttons on the interface.


Then on the third position the radar comes on with all the rest. In our case the radar is connected directly to the char plotter.

The flawed part of this.
While on watch if you want to turn on\off the radar you would need to go to the nave station making it impractical. I have heard where people turn off\on the radar about every 20 min for a look see.

We do not really want a switch at the binical.

How do people on sail boats do this?

Could it be we just wire them to an on\off switch and they all run when on?
Thanks for the help,
Chip
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post #2 of 31 Old 04-05-2012
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Re: Wiring up electronics to a switch?

Just a few thoughts :

1) They like to quote peak power for radar and sonar because it sounds more impressive. The actual time-averaged power consumption is MUCH lower. The 24HD radar draws 34W. My 100W depth sensor uses about 5W.

2) A switch is OK inline but the power TO the switch must come from a breaker in the panel for the best overload protection.

3) My understanding is that the radar can be switched from standby to on via the chartplotter. Therefore this would be your solution for turning on the radar to "have a look" from the helm. I couldn't find much info on the Garmin site so I'd suggest checking with them a) if this is true and b) what the standby current is.

Bristol 31.1, San Francisco Bay
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post #3 of 31 Old 04-05-2012 Thread Starter
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Re: Wiring up electronics to a switch?

Hi,
I talked to Travis at Garmin support (they have always been real nice) and he said our Chart Plotter (Garmin 740) did have radar standby by mode. I was calling about the amps but they will email on that.
4 kw is power and does not convert to amps (current).
Ok I can wire a fuse block to a nav sation breaker toggle switch for power to the instruments.
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post #4 of 31 Old 04-05-2012
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Re: Wiring up electronics to a switch?

Chip

You have several options. Probably the most common is for there to be breakers on the main DC panel for radar, autopilot, depth, and wind instruments. These items (with the exception of wind instruments possibly) all have their own power switches so when the breaker is on you are able to turn each on individually.

Alternatively you could install a waterproof breaker panel outside but I wouldn't bother.

As Mark said, your radar maxes out at 4 kw output - its usage will be around 3-4 amps probably.

The breakers or fuses should be rated for the wire size. Often electronics have inline fuses of a smaller size for equipment protection.

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post #5 of 31 Old 04-06-2012 Thread Starter
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Re: Wiring up electronics to a switch?

Hi,
How about this.
I wire up all the instruments to a T fuse block and then have that block powered up by a switch at the nav station? The switch would conect to the T fuse bl;ock and then to a buss for power?
That way each instrument then has its own fuse and they are all powered when the switch is on.
Then if we want to turn say the autopilot we can by the on\off button or the chart plotter by its on\off button etc?
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Re: Wiring up electronics to a switch?

By the way here is what Garmin sent for the radr amps. They could not find the stand by mode amps.
Units
12v = 2.79 amps
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Re: Wiring up electronics to a switch?

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Originally Posted by SanDiegoChip View Post
Hi,
How about this.
I wire up all the instruments to a T fuse block and then have that block powered up by a switch at the nav station? The switch would conect to the T fuse bl;ock and then to a buss for power?
That way each instrument then has its own fuse and they are all powered when the switch is on.
Then if we want to turn say the autopilot we can by the on\off button or the chart plotter by its on\off button etc?
Chip

You mean power the fuse block from a breaker at the nav station? That works if you don't have enough breakers for everything, but the wire to the fuse block should be fuse/breaker protected.

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Re: Wiring up electronics to a switch?

You've been mislead.
"4 kw is power and does not convert to amps (current)."
Power, in watts, equals potential (volts) times current (amps).
4kW for the radar, which in this case is normally running at 12.6 to 14.4 volts (engine off or on) converts to 317-277 amps. Roughly, 300 amps consumed by the radar when it is actively emitting. Since it is not doing that on a simple continuous basis, the average current that it takes will show up as way less, even when it is on.
You might think there's a discrepancy between ~300 amps and the <3 amps that Garmin told you. Well, 300 amps for a couple of microseconds, could well average into 3 amps of continuous power. The magic is all in having ALL the numbers, and having them in context. If it averages 3 amps while opearting, that's all you'd have to be concerned with.
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post #9 of 31 Old 04-06-2012 Thread Starter
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Re: Wiring up electronics to a switch?

OK I am getting the fuse to the fuse block protection as we have done that on all our bus and fuse blocks. I am not getting why we need a breaker at the nave station instead of a switch? We are trying to avoid the breaker as you may see by now because there are not any open. I would need to allocate one from something. The old instruments came on when? Still not sure of that. We will know this weekend as we are still removing the old wiring.
If this is is a must then what is the formualr to tell me what size breaker?
Can I skip the breaker and not be at my own mercey?
The T fuse block is going to be wired to a positive\negative buss that has a fuse for catastrophic failure.
The buss we have is wired for 35 amps total and has an 85 amp fuse.
Almost nothing is currently wired to bus.
Thanks,
Chip
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Re: Wiring up electronics to a switch?

Chip

You fuse or use a breaker to protect the wire. The 85 amp fuse is there to protect the wire to the bus. I do not know how far the new fuse block is from the bus, but the wire to it will may well be smaller than the wire that feeds the bus. Every time you go to a smaller wire there should be a fuse to protect it. The fuse that protects a large wire will not protect a small wire if it is rated higher than the wire.

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