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Go Back   SailNet Community > On Board > Gear & Maintenance
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  #21  
Old 04-15-2008
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Quote:
Originally Posted by sapadeni View Post
1. Try reversing the polarity of the buzzer in parallel with the panel light. (I originally wired it with the buzzer positive to the low oil switch, neg to the black leading to the bulb).
This is the problem right here. When you attached the neg lead for the buzzer to the black (I'm assuming neg lead) of the light, you did the same thing as hooking it directly to the oil sending switch. OK so far. When you hooked the positive up to the oil sending switch, it has the same effect as if you hooked both the positive and negative wires to the neg post on the light. When the switch grounds, the entire wire from the switch to the bulb becomes ground. You had both wires attached to ground. Put the pos lead of the buzzer to ignition power, and you should be good.
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  #22  
Old 04-15-2008
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Scott, if your buzzer is a real buzzer (basically a relay) they are not polarized and will run regardless of which wire goes to which. If it is a piezo "buzzer", etc. it will be polarized.

If you do use something like a car horn, they can draw a lot of power and normally are driven by horn relays in cars. You would need to check the power draw and perhaps use a common Bosch 30A-rated relay to make sure the relay points don't get burned from the load, a typical cheap relay from Radio Shack might only be rated for 2 amps. Enough for a piezo alarm but not a car horn.
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I'll try the "pos to ignition power" technique first since it appears to be the easier route. I'll try the relay if it still doesn't work. I don't have the buzzer with me so I'm not sure if it's a piezio. I do know that it's a pulsating buzzer (similar to a truck backup warning), and it does have a red and black lead.
Good thing I'm a much better mechanic than electrician.
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I have a related question. I'm looking to add an audible alarm for my alternator so I'm alerted if the belt breaks. There is a lug on the alternator for an idiot light. The lug puts out +12v during normal operation and goes to ground if the alternator quits. Can I simply put a buzzer between that lug and a +12v source to create an alarm?
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Quickstep-
In theory you could. In practice, you would be creating a path between two different "12" volt sources, one being perhaps a real 12V at the idiot connection, the other being 12-14.4V at the battery positive. that can set up a voltage loop which wastes power and screws up other things, like the brains in the regulator. Whether it works well or not will depend on the details of your setup.
So, you could try setting it up that way, and using a voltmeter and ammeter to check and see if it is behaving nicely. Or, use the idiot connection to power a relay. Idiot on, relay on, and if you use a "double throw" relay there will be a set of contacts that are OFF when the relay is on. When the relay turns off (because the alternator is off) another set of contacts comes ON, so the buzzer only comes ON when the alternator and relay are OFF.
(And of course that relay takes no power unless the alternator is ON.)

Your choice, spend $5 on a relay that isolates things and be sure are isolated, or take the multimeter to see the details. Or, just take a chance that the simple thing works. (I'm often not that lucky.[g])
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Quote:
Originally Posted by Quickstep192 View Post
I have a related question. I'm looking to add an audible alarm for my alternator so I'm alerted if the belt breaks. There is a lug on the alternator for an idiot light. The lug puts out +12v during normal operation and goes to ground if the alternator quits. Can I simply put a buzzer between that lug and a +12v source to create an alarm?
Yes you can. In fact that's exactly how the warning light works. You have to be a bit careful though, as many alternators need that 12 volts fed through the bulb to turn the alternator on. You may need to leave the bulb in place and add an alarm. Then make sure the alternator is still working properly with a meter.

edit: I just read hello's post and he's got a great point. Make sure you use a 12 volt source that is only on with the key on and you should be in good shape.

edit again: You really should use a relay if you use a buzzer that pulls any kind of amps. That's why I like those pezio alarms that only pull 0.015 amps.
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I have not tried that one. I just look at the ammeter every now and again.

How often does a belt break? It is not a terminal failure, unlike oil pressure failure.
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Old 04-15-2008
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I had a alternator belt break last year running between the dock and the pump out. The same belt runs the FWC pump in the block, so I basically had cold lake water going through the heat exchanger, but very little heat exchanging going on. This was basically "at idle" for 20 minutes or so, as I didn't switch off while decrapping the holding tank.

The coolant got to 240 F before I noticed it. No harm done, apparently (except to my nerves), but for the funny smell and baking heat when I opened the deck hatch! The oil pressure stayed at its customary 55 PSI the whole time.

Now I carry two spare belts, including a Gates Green Line, supposedly the best in show.
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Old 04-16-2008
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In my case, there's no light installed now. I do have a temp gauge, but I don't stare at it all the time. I am also trying to avoid the circumstance where the belt breaks and I'm overheating without realizing it.
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Before we go cruising, loud low-oil pressure and coolant temp alarms will be in full effect. It's cheap insurance.
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