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Old 10-05-2016, 10:46 AM   #41
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Originally Posted by sdowney717 View Post
This was just an example of how when voltage falls current rise to keep the total wattage the same..
It's not relevant to this discussion and it confuses the issue.

BTW: Your marina has an inadequate electrical system and it should be upgraded before boats (including yours) are damaged.
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Old 10-05-2016, 11:20 AM   #42
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Originally Posted by WesK View Post
1) A wire from the battery, through a circuit breaker, through a switch, through a light bulb or blower and back to the battery is a series circuit.

2) Extra lights, blowers, etc. are wired in parallel and do increase the current flow in the circuit but if the switch controls them all, the switch is in series with the load (the lights and blowers). Any resistance in the switch lowers the voltage available to the load and lowers the total current.
A wire from the battery, through a circuit breaker, through a switch, through a light bulb only and back to the battery is a series circuit.
Another wire from the same battery, through a circuit breaker, through a switch, through blower and back to the battery is a parallel circuit not a series circuit.
So in practice there are no series circuits on a boat.
If you wanted to have series circuits on a boat you would have to have a battery for each series circuit. One battery for the light bulb and a different battery for the blower. Not practical!

The OP does not have a series circuit. He has a switch for the lights and another switch for the blower. This is a parallel circuit.

The only switch that controls all, is the battery switch and that is not always the case as many people wire a bilge pump prior to the battery switch.

You're not going to have this condition.

Putting the switch in series with the load (the lights and blowers) is not practical. You don't want the blowers to come on every time you turn on the light. You would have a different switch for each, a parallel circuit.
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Old 10-05-2016, 11:50 AM   #43
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Originally Posted by WesK View Post
It's not relevant to this discussion and it confuses the issue.

BTW: Your marina has an inadequate electrical system and it should be upgraded before boats (including yours) are damaged.
I was responding to another poster's response to me.

This marina was originally built in 1945!
And has never had an electrical fire.
Of course the wiring was redone, decades ago. The wiring is simply 12 gauge wire runs off a 30 amp breaker in a distribution panel. Yes, likely wholly inadequate, but it works ok anyway. Some people paid to have their own meters installed, simply because they were hogging so much free power, Ehrlin the owner said he would cut them off. Not sure, but there maybe 5 or 6 slips on my shared line. All the power is underground. Wires run to a wood post with a 15 amp socket to which I plug in my Marinco 15 to 30 amp adapter.
A few years ago, I slipped for a year at another old place, Thomas Marina in Seaford, VA. The lines ran overhead on posts as you walked the dock. More free power but also looked ratty to me.

I get by fine. Sometimes I do turn on the gen and use my own power.
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Old 10-05-2016, 01:32 PM   #44
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Technically, you are both correct, but in the context of the op question, Wes K is more correct. Lightbulbs are a pure resistive load, and will NOT increase the amperage to compensate for lower voltage, the bulb will not be as bright. Motors are inductive loads,and will increase the amperage ,due to low voltage.
A motor and a generator are very similar. So similar that the motor in electric vehicles can be used to generate electricity to recharge the batteries when braking.

When an electric motor is turning (powered by electricity), it is actually generating current that is opposing the power that is turning it (counter EMF). This is what limits the power consumption. As the motor slows down (because of too little available voltage or because of an increased load), there is less counter EMF generated and yes, the consumption may go up. The limit is reached when the motor stops. At this point it is no longer generating any counter EMF and is essentially a resistor. The current passing through the circuit would then be as if it was a purely resistive load. This would be referred to as the "locked rotor current". Depending on the design of the motor, it will probably overheat and burn up if left in this condition for very long if the circuit protection device doesn't interrupt the circuit. Many small motors have an internal thermal fuse that will blow if the motor gets hot enough to be a fire hazard.

A light bulb or group of light bulbs will not do this and a typical boat blower motor will not increase the current significantly with lower input voltage, it will simply slow down. A windlass or bow thruster is a different story.
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Old 10-05-2016, 03:12 PM   #45
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Qoute : A motor and a generator are very similar. So similar that the motor in electric vehicles can be used to generate electricity to recharge the batteries when braking.


Correct,it is called dynamic braking,used in trains.
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Old 10-05-2016, 03:14 PM   #46
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Qoute: A light bulb or group of light bulbs will not do this and a typical boat blower motor will not increase the current significantly with lower input voltage, it will simply slow down. A windlass or bow thruster is a different story.


Correct,because it is a shaded pole motor. Damn,you are good!!!
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Old 10-06-2016, 10:52 AM   #47
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One of the reasons I post on this site is to help others understand what I was fortunate enough to learn by receiving a Bachelor of Science Degree in Electrical Engineering and developing many systems throughout my career.

Since you feel that I do not know what I am talking about and clearly have very little understanding of electric circuits, and you went to school and did this stuff for a living, a good living, you should have no problem pointing out the specific errors that I have made in my posts, so others on this forum may learn from my mistakes.
OK:

Quote:
A wire from the battery, through a circuit breaker, through a switch, through a light bulb only and back to the battery is a series circuit.
Another wire from the same battery, through a circuit breaker, through a switch, through blower and back to the battery is a parallel circuit not a series circuit.
So in practice there are no series circuits on a boat.
Each circuit is a "circuit". That's why there are "circuit breakers" (or fuses) for each circuit. The circuit to the light bulb is a series circuit. The circuit to the blower is another series circuit. The circuit to the refrigerator is another series circuit.

A circuit to several light fixtures could be considered a series/parallel circuit but for troubleshooting purposes, it would be considered a series circuit up to the point of the first fixture.


There are several individual series circuits on a boat, connected to the same battery.
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Old 10-06-2016, 11:51 AM   #48
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Correct,because it is a shaded pole motor. Damn,you are good!!!
Shaded pole motors are AC only. A circuit from the battery to a switch to a load back to the battery is a series circuit. Taking in the whole boat there are multiple series circuits so in effect there are many parallel circuits.

All this theory is totally irrelevant to the OP's original problem, the switch gets hot, bad switch or bad connections on the switch. Really doesn't take a EE to figure that out, although I am one, having majored in vacuum tubes when I got my degree.
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Old 10-06-2016, 12:33 PM   #49
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Shaded pole motors are AC only.


thanks,didn't catch the op post that it was a dc fan.
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Old 10-06-2016, 02:48 PM   #50
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Shaded pole motors are AC only. A circuit from the battery to a switch to a load back to the battery is a series circuit. Taking in the whole boat there are multiple series circuits so in effect there are many parallel circuits..
Nope, there are many series circuits.
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Old 10-06-2016, 02:53 PM   #51
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Nope, there are many series circuits.
How about many series circuits in parallel..
Enough already...whats the difference re sw or contacts being bad???

Take a deep breath...have a beer...and lets get back to boating!!
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Old 10-06-2016, 04:31 PM   #52
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Nope, there are many series circuits.
But all of those series circuits are in parallel if they feed off the same source. Silly argument, has nothing to do with the original problem. Over and OUT.
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Old 10-10-2016, 10:10 AM   #53
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My boss had a saying that he used over and over: "Engineers dream things up. Technicians make them work." I was a technician.
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Old 10-10-2016, 11:26 AM   #54
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I like it, even though I was one of them engineers.
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Old 10-10-2016, 05:44 PM   #55
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Electrical Engineer arguments are always the best at work too.
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Old 10-10-2016, 06:56 PM   #56
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What ever became of the switch? SBU22
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Old 10-10-2016, 06:57 PM   #57
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What ever became of the switch? SBU22
We would hope the OP took it to West Marine and got a replacement and installed it.
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Old 10-10-2016, 07:38 PM   #58
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Real life got in the way last week. Hope to get to it this coming weekend.
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Old 10-15-2016, 11:08 AM   #59
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C'mon. Perhaps it's just not that tough. (This appeared in my Facebook feed this morning, posted from Italy by one of my Flying Dutchman sailing friends.)
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Old 10-15-2016, 02:11 PM   #60
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C'mon. Perhaps it's just not that tough. (This appeared in my Facebook feed this morning, posted from Italy by one of my Flying Dutchman sailing friends.)
I like it...would fit Peggys reqmt to explain it 6 yr old
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