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Old 18-06-2010, 04:47   #1
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Could this Get any More Confusing ? Wiring Alarm Buzzer to Plotter...

Hello all,

I could use a little guidance on this. I am trying to wire an optional alarm up to my new Garmin 3206 Plotter. I want it to wake me up when I set the anchor drag alarm. Right now it just makes some soothingly soft beeps. I bought a 65ma piezo alarm buzzer that makes 85 decibals of buzzing noise.

The instructions say that I need a relay between the battery and the buzzer, that the maximum current is 100ma for the buzzer, and that the unit switches to low voltage when the alarm sounds. The installation instructions are here:

On another site I found a very clear but conflicting explanation of what to do: BoatUS Club House Messageboards: Using the GPS alarm circuit The poster (Frank C) says I don't need a relay as long as my alarm doesn't draw more than 100ma of current. He sounds like he knows what he's talking about, but what he says conflicts with the manual.

I called Garmin tech support, and they were just as confused as I am. I called twice to double check. The first guy said I didn't need a relay. Then he changed his mind and said I need a "coil current" where the relay is on the diagram. he didn't sound convincing, and I don't know what a coil current is. The second guy said that I need a relay since the manual says I do. That's fine, but unfortunately nobody seems to make relays that small for 12v circuits. He had no suggestions on where to this, although he did wish me good luck in figuring it out.

Can anybody straighten this out for me? Can I hook up an in-line fuse on the buzzer and just wire it to the GPS without a relay? If I need a relay or something else to limit the current, where can I find such a thing? I'm guessing other people have had this issue but I can't find any clear answers...

Thanks a lot!

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Old 18-06-2010, 05:00   #2
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Id use the relay.
Relay, 8 Pins, Dpdt - Relays - Relays - Electrical : Grainger Industrial Supply
this one has a coil rating of 75m milliamps you need the base as well

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Old 18-06-2010, 05:42   #3
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That diagram indicates an ordinary single throw relay, energized to close with 100ma from the unit. These are used in automotive constantly, you should be able to pick one up at any auto parts store.
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Old 18-06-2010, 06:04   #4
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No. The plotter controls the relay, and the relay controls the alarm. The plotter output will go to the relay's coil. The other side of the relay coil will either go to +12v or gorund depending on wetaher the plotter alarm output goes low(gnd) or high(+12v) when an alarm condition exists. The relay output contacts go to +12v and the alarm. Now when the plotter gets an alarm condition the output signal closes the realy and the relay contacts close and route +12v to the buzzer. This assumes that the other side of the buzzer is wired to gnd.

IF the buzzer pulls more than 100ma (probably does)then a relay is required.

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Old 18-06-2010, 06:34   #5
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Since a typical 12V piezo alarm draws between 10 & 35 mA, it will not require a Relay.

Notwithstanding, if a relay is used, ensure that the Relay Coil Current is less than 100mA (they typically run 30 - 50 mA for small 12V relays).
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Old 18-06-2010, 06:57   #6
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I'm still not really getting it. The diagram shows 4 connection points on the relay. What do I do with an 8 pin relay? Even if I get a 4 pin relay, the diagram is confusing to me. It looks like two of the pins are basically wired to each other and then to the positive battery terminal (with no fuse?) . Another pin goes to the yellow wire and another goes to positive lead on the alarm. The negative alarm wire gets connected to the negative battery lead. Is this correct? If so, can anybody tell me how to connect that 8 point pin or point me towards another relay that might work? Will the relay come with a wiring diagram? How do I know which pins are which?

Gordmay, my buzzer draws 65ma. How confident are you that I can get by without the relay? I have an inline 100ma fuse that I can wire up to it, but I am not sure where the fuse would go on the diagram. In place of the relay?

Forgive my ignorance but this stuff is a bit over my head.

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Old 18-06-2010, 07:18   #7
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What is confusing you is the fact that nearly all relays have the capability to make up in different circuits so most will offer a couple of switches that can be wired either normally open (connection not made when de-energized) or normally closed (connection made when coil energized).

You need to wire the relay as follows: The energizing coil is wired from the plotter output. We are working with 12 volts so polarity sensitive. One set of normally open contacts will be wired to the alarm. So Plotter outputs 12 volts at low amp capability; this signal energizes the relay coil allowing higher amperage current to flow in the alarm circuit.

Select a relay that has a coil current lower than the plotter maximum output current and a contact rating that is of a higher current rating that the alarm rating.
Do NOT use an octal base as they can shake out of the base on a boat and can corrode the pins over time. Use a relay that is sealed and has integral base with good tinned connections on the terminals, or has pigtail leads that can be connected to a terminal strip.

Make sure you have a 12 V DC relay, as there are 12-volt AC coils available as well.

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Old 18-06-2010, 10:34   #8
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Muito obrigado, um saudade. Do you have a relay in mind that would work? I am looking but I really can't tell which ones are appropriate.
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Old 18-06-2010, 12:12   #9
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I love to hear your solution when this is all said and done !
I wired a 65 ma. piezo buzzer in line with no success, per the Garmin wiring diagram.
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Old 18-06-2010, 12:28   #10
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Well, for starters, that wiring diagram is crap. The relay connections are not correctly identified. As is, the diagram is unusable, but there is something about the coil that this circuit needs.

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Old 18-06-2010, 16:15   #11
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Your buzzer draws less than 100ma, you don't need a relay. Connect it direct. Yellow wire to the negative terminal of the buzzer, +12v to the positive side assuming the buzzer is polarity sensitive, some are not.

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Old 18-06-2010, 18:30   #12
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Go sailing. This is far too complicated to be worth the effort. It's the problem with getting too focused on all the gizmos. Of course, if you really like the process, well, better you than me.....
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Old 18-06-2010, 18:38   #13
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restart. test your alarm across the battery if ok then the end which is connected to the neg is the one to put onto the yellow. the other is wired to the pos. no relay needed.
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Old 18-06-2010, 18:48   #14
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You should be able to wire the piezo buzzer directly to the Garmin. Connect the "-" (negative) buzzer terminal to the Garmin alarm output, and the "+" (positive) buzzer terminal to +12V, through a 100mA fuse if you like.

The Garmin wiring diagram leaves a lot to be desired, but it shows the Garmin alarm output connecting the relay coil to ground, with the other end of the relay coil tied to +12V. The normally open relay contacts are connected to +12V and to the alarm buzzer. The other buzzer connection is grounded. This will work as well, but with the buzzer you have it is simpler to use the direct connection method.

[I just saw bill good's reply. He's got it right.]
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Old 18-06-2010, 18:59   #15
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The wiring (yellow) and current limit look the same as the GPSMAP 545 unit I have. I just finished wiring two piezo buzzers to my GPS. The plus terminal goes to +12V and the negative terminal goes to the yellow wire. It works fine. My buzzers draw about 10 ma.

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