need to reduce current in a 12v dc system

[13Adam]

I'm looking for the most efficient way to knock down wattage from a 12v battery, putting out 425-340 amps. I need to run a pump that needs 50 watts, and a waste gate valve that only needs 4.8w. I picked up a small potentiometer, that claims output of 4.8w. Was this the right move?

 

[kanewolf]

A battery isn't PUSHING amps. It is a resovoir that can be drawn from. The pump will pull slightly less than 4A. Only as much current as is needed will be used. The internal resistance in the pump motor will limit it.

 

[13Adam]

A battery isn't PUSHING amps. It is a resovoir that can be drawn from. The pump will pull slightly less than 4A. Only as much current as is needed will be used. The internal resistance in the pump motor will limit it.

Apologies, I'm a novice, and didn't phrase my initial question very well. I have 2 devices on the same 12v circut. Both powered by a battery labeled 425a, cold crank 325a. The first device is a pump labeled at 50w, which runs fine on direct connection to the battery. The second is a small switch, labeled at 4.8w. I purchased a potentiometer, as I was afraid of connecting too much power to the smaller device. Is this necessary? Or will it last if I connect it directly to the battery?

 

[kanewolf]

Is your question "Can I control a 50W pump with a switch rated at 4.8W?" Normally a switch will be rated in amps (A) rather than watts (W). Are you sure your switch isn't rated at 4.8A ???

 

[13Adam]

Is your question "Can I control a 50W pump with a switch rated at 4.8W?" Normally a switch will be rated in amps (A) rather than watts (W). Are you sure your switch isn't rated at 4.8A ???

The pump is operated directly from the battery. The "switch" is an electronic waste gate valve. It needs to open to allow the pump to get water. There isn't an issue with the pump, as they are 2 seperate devices on the same circut. I'm only wondering if I can run a device rated for 4.8w off of a battery, which puts out higher power, without limiting the power. If it does need to be limited, is a potentiometer the proper way to achieve this?

 

[VincentP]

Is your question "Can I control a 50W pump with a switch rated at 4.8W?" Normally a switch will be rated in amps (A) rather than watts (W). Are you sure your switch isn't rated at 4.8A ???

The pump is operated directly from the battery. The "switch" is an electronic waste gate valve. It needs to open to allow the pump to get water. There isn't an issue with the pump, as they are 2 seperate devices on the same circut. I'm only wondering if I can run a device rated for 4.8w off of a battery, which puts out higher power, without limiting the power. If it does need to be limited, is a potentiometer the proper way to achieve this?

You connect the pump and the switch in parallel to the battery, so positive from the battery goes to postive on both, and negative from the battery goes to negative on both.
The current passing through each device is limited by the resistance. If these are rated at 12V, they will draw the correct current.
Your potentiometer is not required. If you put it in series with a device it will lower the voltage across that device.

 

[13Adam]

Is your question "Can I control a 50W pump with a switch rated at 4.8W?" Normally a switch will be rated in amps (A) rather than watts (W). Are you sure your switch isn't rated at 4.8A ???

The pump is operated directly from the battery. The "switch" is an electronic waste gate valve. It needs to open to allow the pump to get water. There isn't an issue with the pump, as they are 2 seperate devices on the same circut. I'm only wondering if I can run a device rated for 4.8w off of a battery, which puts out higher power, without limiting the power. If it does need to be limited, is a potentiometer the proper way to achieve this?

You connect the pump and the switch in parallel to the battery, so positive from the battery goes to postive on both, and negative from the battery goes to negative on both.
The current passing through each device is limited by the resistance. If these are rated at 12V, they will draw the correct current.
Your potentiometer is not required. If you put it in series with a device it will lower the voltage across that device.

Perfect. Thank you for the advice. I only had one, and was afraid I might fry it. Hooked it up, works great. Saved me days waiting for Hong Kong to ship.