When a load is rated at 12 volts and hooked up to a 12 volt battery, does it consume all 12 volts?

This may seem like a very dumb question but I took electronics two years ago as a high schooler and cannot seem to remember much about it. So I have a circuit that has a bilge pump hooked up in series with a 12 volt battery. The bilge pump says 12 volts, I know that that means it must have a 12 volt supply, but if I hooked it up with a 12 volt battery, would there be any left over volts to say, power a small light?

Here are links to the battery and bilge pump I purchased from Amazon:

All responses are greatly appreciated!

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iceng2 years ago

A water anology just for you

iceng iceng2 years ago

Then if you want a pressure ie voltage regulator...

Have fun plumbing ;)


+1 Nice one!

A 12 volt battery can supply power to a plurality of 12 volt loads. As an example, imagine a 12 volt battery in your car, supplying power to three separate loads: interior lights, a radio, a blower fan. All these loads are "on" and drawing current from the battery. To make this fantastic picture complete, the car's engine is turned off, so all the power dissipated by these loads is coming from energy stored in the 12 volt battery.

Typically, almost always, these loads are connected in parallel.

Loads connected in parallel share the same voltage.

Therefore, all three loads, the lights, the radio, the battery, have the same voltage across them, which is the battery voltage, nominally 12 volts.

You should wire your boat the same way. The lights, the bilge pump, the radio, the GPS, etc, all these loads get wired in parallel.

Switches to turn these loads on, or off, go in series with each load.

If you want, I'll draw you a picture, or rather a wiring diagram, of this, and I'll label it with little symbols to represent the real voltages and currents my mind's eye imagines are there in these imaginary wires that symbolize real wires.

Well actually, drawing such a diagram should be your homework, but you said you couldn't remember how electricity works, so I'd willing to help you out. The only caveat is that my drawings look like circuit diagrams, like,


So if that kind of drawing is meaningless to you, then me drawing you a picture won't help.

Wired_Mist2 years ago

Just wire the pump and light in Parellel, after your float switch :)

The Pump Operates at 12v, but Consumes 1.9Amps

Think of it like a highway....

If your car (the pump) is going at 50 mph and the speed limit (Operating voltage) is 80 mph you have some problems. if you are driving the same speed at everyone else all is good.

Then think of Amps as space on the road. Even though you are going the speed limit, there is space of the road for other vehicles. Some may consume more space like say a semi vs a car

**Sarcasim. And when you go faster then the speed limit, Someone pulls you over, and you stop operating :P**

It sounds like you are looking for a indicator light to show the pump is working ?

You will need to wire your light just after the float switch but before the pump it'sself like this


Btw how often will this pump turn on? with a 2Amp draw your 7Ah battery will only last 3.5H at best

-max-2 years ago

Volts are like water pressure, amps is like flow rate, and resistance, or impedance is like the diameter of a pipe, or a blockage.

Another great way to remember what the big 3 are is Volts push Amps though Ohms.

A decent battery or constant voltage power supply, the voltage will not change much across it So when you hook up a load like that pump, the voltage across that battery should stay close to what it was before hooking anything up to it. However, due to internal resistance (which causes a voltage drop when current flows),the voltage will probably sag a small amount. You should be able to connect a few more things in parrelel as long as you do not exceed the rated wattage of the battery or power supply.

-max-2 years ago

Yeah, basically. If you have things in series, then the voltage is divided amongst those things. THe classic example would be a resistor divider.

Here are some short videos I made awhile back, they will probably catch you back up to speed and jog your memory some.

It takes 12V. There will be 12 V across its terminals which can feed your light.