# DC Circuits: Watts/Volts/Amps - Exploring Advantages of Negative Switching

• arimike
In summary: The pump is higher at 15.5A and the switch is lower at 5.8A.In summary, the conversation discusses a basic circuit with a 12vdc battery, a level switch, and a water pump. The switch is rated for 1/4 HP @ 32 vdc and the pump is 12vdc rated at 15.5A. There is confusion about the switch's capacity to handle the motor load of 15.5A and the advantage of placing the switch on the negative side of a DC circuit. The conversation also touches upon the rating of the switch and pump and the need for a 12vdc rating. Overall, it seems that the switch may not be suitable for
arimike
Basic question here: I have a simple circuit consisting of a 12 vdc battery, a level switch and a water pump. The switch is rated for 1/4 HP @ 32 vdc, and the pump is 12 vdc rated at 15.5A.

If 1/4 HP = 185 watts, I assume that equals 5.8A @ 32 vdc, and is not capable of handling the motor load of 15.5A. Is this right?

I keep wondering if I am looking at this wrong because I see this exact motor/switch combination in use in various places...with the switch used to make/break the NEGATIVE line. What is the advantage of placing the switching mechanism on the negative side of a DC circuit?

Any insight would very appreciated!

Your analysis seems correct to me: Typically, switches are rated for a certain amperage. It is odd to see a switch rated at 1/4 hp @ 32 vdc (strange voltage too!). But 185/32=5.8A

Location of the switch in the circuit really doesn't matter much in a dc circuit.

Is this switch is electromechanical or purely electronic? In purely electronic switches, negative side aka "low-side" switches can be simpler to implement usually. One reason might be that they don't need any voltage to be in the "off-state" but they need a positive control voltage to turn on. That is usually a desirable characteristic. I agree that rating a switch in terms of hp is not intuitive.

I am working with a mechanical switch.

Some further thinking about these ratings are confusing me even more. The switch is rated 1/4 HP (185 watts) @ 32vdc which equals 5.8A. Does this mean at 12vdc and 185 watts it is good to 15.4A?

Another way to look at it is the pump is rated 15.5A @12vdc which I believe equals 186 watts. In this analysis it looks as if the switch is ok to use with this pump.

I am just not sure what the important part of the spec is...1/4 hp @ 32vdc. Is it the calculated watts (185) or the amperage (5.8 @ 32vdc) that should be used as a limit??

arimike said:
Basic question here: I have a simple circuit consisting of a 12 vdc battery, a level switch and a water pump. The switch is rated for 1/4 HP @ 32 vdc, and the pump is 12 vdc rated at 15.5A.
Yes, that's an interesting rating. It's all very fine if you have a 32 volt supply, but you are not given a rating at 12 VDC, right?

I would go with Russ on the current rating. Don't use it for over a 6 amp inductive load.

No 12vdc rating listed in spec sheet. I wish I could get the manufacturer to give me a spec...I guess I don't present enough buying potential to get them to do that though...

Thanks for all the comments and help!

arimike said:
No 12vdc rating listed in spec sheet. I wish I could get the manufacturer to give me a spec...I guess I don't present enough buying potential to get them to do that though...

Thanks for all the comments and help!

The points being made are that common relays are governed nominally by two independent parameters: current rating and maximum voltage across the points. You normally shouldn't exceed either.

You should draft shortly 12vdc battery rating.

## 1. What is the difference between watts, volts, and amps in DC circuits?

Watts, volts, and amps are all units of measurement used in DC circuits to describe different aspects of the flow of electricity. Watts measure the amount of power being used, volts measure the electrical potential difference between two points, and amps measure the rate of flow of electricity.

## 2. How do negative switching circuits work?

Negative switching circuits use a negative voltage source to control the flow of current. This means that the voltage source is connected to the ground or negative terminal of the circuit, and the switch is used to break or complete the circuit. When the switch is closed, the negative voltage is applied and current flows, and when the switch is open, the negative voltage is removed and current stops flowing.

## 3. What are the advantages of using negative switching in DC circuits?

There are several advantages to using negative switching in DC circuits. One advantage is that it can reduce the amount of power loss in the circuit, as the negative voltage source can help to regulate the flow of current. Negative switching can also help to protect sensitive components in the circuit, as the negative voltage can act as a buffer against any fluctuations in the power supply.

## 4. Can negative switching be used in all types of DC circuits?

Negative switching can be used in most types of DC circuits, but it is most commonly used in circuits that require precise control of the flow of current. This includes circuits used in electronics, telecommunications, and power supply systems.

## 5. Are there any safety concerns when working with negative switching circuits?

As with any type of electrical circuit, there are some safety concerns when working with negative switching circuits. It is important to ensure that all components are properly insulated and grounded, and to follow proper safety protocols when handling electricity. It is also important to use caution when working with high voltages, as the negative voltage source can still pose a risk of electric shock.

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