Hot SPST Switch

sdowney717 said:

I know in AC systems, If your not current limited in your power source, (relatively speaking to the load demands), the voltage going down means current will go up to keep the watts used about the same.

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How is the AC device able to control the watts? That makes absolutely no sense unless it's an electronic device with a switching power supply which might be able to control the duty cycle to draw more amps. For a simple AC device, lights, motors, etc. that is just not possible.

To add to my previous post, if the boat is wired with plain copper wires, not tinned wires, chances are the resistance is in the corroded crimped on lugs. had the same issue on our boat, solved it by cutting off the old lugs, stripped the wire back to get to some clean copper and crimped on new lugs.

psneeld said:

If you leave devices on till the battery fies, not all loads will trip the breakers....things like lights wont....depends on what the load is.

Corrosion in a switch is adding resistance just in the switch....even resisters have to dissipate heat.

You guys are arguing apples and oranges....thsts why the difference of opinion I think.

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Yes it is an apples (series circuit) to oranges (parallel circuit) argument.
Total current will go up in a parallel circuit as you add resistance. My example of seeing your amp meter go up as you turn stuff on.
But in a series circuit, current will go down when you add resistance.

I agree, just replace the switch.

Appreciate all of the info. Real life got in the way and I haven’t had the chance to get back to the boat to implement several of the good suggestions presented.

Al/Ski – no indicator lights.

DHeckrotte – may be size limited on the sealed switches – have 9-10 in a row, cheek by jowl – may not have space based on what I’ve looked at on line.

sdowney717 – never knew you could buy a sealing boot – or the name of that doomahitchee.

Toolbuddie – going to do that when I get back for my own education.

WesK, Parks, FOG – Remove and replace, that’s the plan. If there’s still a problem, I’ll investigate further downstream.

FOG said:

Yes it is an apples (series circuit) to oranges (parallel circuit) argument.
Total current will go up in a parallel circuit as you add resistance. My example of seeing your amp meter go up as you turn stuff on.
But in a series circuit, current will go down when you add resistance.

I agree, just replace the switch.

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Any resistance in the switches would increase the resistance in this series circuit and lower the current. Nobody would add "resistance" in parallel because that would not make sense. Someone might add another light, blower, etc. and the current would increase to supply these added loads.

Even with multiple appliances, this part of the circuit (the switch) is a series circuit. The switch is in series with the load(s).

sbu22 said:

Remove and replace, that’s the plan. If there’s still a problem, I’ll investigate further downstream.

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How about tearing into those switches with a cellphone camera handy to show us the condition inside? I've never seen the inside of a bad marine switch.

WesK said:

Any resistance in the switches would increase the resistance in this series circuit and lower the current. Nobody would add "resistance" in parallel because that would not make sense. Someone might add another light, blower, etc. and the current would increase to supply these added loads.

Even with multiple appliances, this part of the circuit (the switch) is a series circuit. The switch is in series with the load(s).

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Are you sure you want to make this statement?
It conflicts with your next sentence.
When someone adds another light, blower, etc. they are adding resistance in parallel. These added loads are resistance. As I have said before, turn stuff on and watch the amp meter go up. Each time you turn something on in your boat it adds another resistive parallel circuit.

Agree the switch is in series with the load. But disagree that the switch is in series with the loads (more than one load). Also, not sure what you mean by the first sentence. Maybe an example to help me understand.

A series circuit is not practical on a boat.

BobH said:

How is the AC device able to control the watts? That makes absolutely no sense unless it's an electronic device with a switching power supply which might be able to control the duty cycle to draw more amps. For a simple AC device, lights, motors, etc. that is just not possible.

To add to my previous post, if the boat is wired with plain copper wires, not tinned wires, chances are the resistance is in the corroded crimped on lugs. had the same issue on our boat, solved it by cutting off the old lugs, stripped the wire back to get to some clean copper and crimped on new lugs.

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Voltage drop, amperage increase? - electricity electrical engineering | Ask MetaFilter
Just a myth I suppose.

Motors (or compressors or whatever) also pull more current when the voltage drops as they still try to do the same amount of work.

Pretty much any computer, amplifier, or other electronic device with a modern power supply will draw more current when the line voltage drops. This is because the power needed by the device is constant (or at least not related to line conditions), and power = voltage x current. So if voltage goes down, current must go up to compensate.

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FOG said:

Are you sure you want to make this statement?
It conflicts with your next sentence.
When someone adds another light, blower, etc. they are adding resistance in parallel. These added loads are resistance. As I have said before, turn stuff on and watch the amp meter go up. Each time you turn something on in your boat it adds another resistive parallel circuit.

Agree the switch is in series with the load. But disagree that the switch is in series with the loads (more than one load). Also, not sure what you mean by the first sentence. Maybe an example to help me understand.

A series circuit is not practical on a boat.

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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.

Pretty much any computer, amplifier, or other electronic device with a modern power supply will draw more current when the line voltage drops. This is because the power needed by the device is constant (or at least not related to line conditions), and power = voltage x current. So if voltage goes down, current must go up to compensate.

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Let's try to have a little common sense here. We're not talking about a regulated computer power supply, we are talking about a common light bulb or blower motor.

WesK said:

Let's try to have a little common sense here. We're not talking about a regulated computer power supply, we are talking about a common light bulb or blower motor.

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This was just an example of how when voltage falls current rise to keep the total wattage the same.

I have a digital volt-amp gauge on my shore line.
When running the heat pump, I have seen when voltage drops the amps used do go up.

I have free 30 amp marina power, but it is shared to several boats along the pier, so when people use power available volts drop. So when I am running my AC, it is easy to see, plus if I run something else in the boat, I also see it happen. Worst it can get is down to 100 vac.

sdowney717 said:

This was just an example of how when voltage falls current rise to keep the total wattage the same..

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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.

WesK said:

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.

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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.

WesK said:

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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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.

tinped said:

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.

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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.

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.

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!!!

FOG said:

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.

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OK:

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.

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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.

tinped said:

Correct,because it is a shaded pole motor. Damn,you are good!!!

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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.

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.

Shaded pole motors are AC only.


thanks,didn't catch the op post that it was a dc fan.

BobH said:

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..

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Nope, there are many series circuits.

WesK said:

Nope, there are many series circuits.

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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!!

WesK said:

Nope, there are many series circuits.

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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.

My boss had a saying that he used over and over: "Engineers dream things up. Technicians make them work." I was a technician.

I like it, even though I was one of them engineers.

Electrical Engineer arguments are always the best at work too.

What ever became of the switch? SBU22

Toolbuddie said:

What ever became of the switch? SBU22

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We would hope the OP took it to West Marine and got a replacement and installed it.

Real life got in the way last week. Hope to get to it this coming weekend.

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.)

DHeckrotte said:

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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I like it...would fit Peggys reqmt to explain it 6 yr old