Reduce Current on a 12V Pump

[ryanturner]

Hello,
As you can see this is my first post, so ill try and be brief.
Basically i have a kayak with a 12V 7A battery fitted, also fitted a fishfinder that draws 0.15A an hour. This gives me plenty of time when at sea.

I have just fitted a live bait well with a water pump that draws 2.5A an hour. As you can see this wont last long on my battery so i was wondering if i can put a circuit in to reduce the Current, saving my battery, or better still design a logic circuit to lets say, turn it on for 2 mins, every 10 mins.

I have actually just started an electric/tronic apprentiship so have a bit of knowledge in logic etc.

If any one could provide me with a starting block that would be amazing! thanks i advance for any replies.

 

[mister_rf]

You may use a ‘555’ timer to control a relay, read this topic:
https://www.edaboard.com/threads/237875/

 

[ryanturner]

ahh yes, of course, thanks for that. Ive built these before for other small apps such as flashing led's. I will get at building it now then... you may hear from me again yet though, thanks for your help.

 

[mister_rf]

More details about timers using 555 circuit here:
**broken link removed**

Meanwhile, look at this diagram:

 

[mister_rf]

:lol:
Let's try to modify the first diagram in order to achieve correct duty cycle...

 

[ryanturner]

Thank you for that diagram, i guess youve done the hard work for me there, thanks. so thats what i need to make the circuit go on for about 2 mins and off for 8-10 mins? This should save alot of battery power, thanks.

I did start to try get my head round things and built this with a motor as an output. Would this not work? seems rather basic but i worked out tm=0.7x200kx1mF=140s ON and ts=0.7x1Mx1mF=700s OFF. Also like the idea of being able to give it a 'boost' by pressing the push to make switch, resetting the cycle, starting from on for another 140s

 

[mister_rf]

Yes, in theory that’s correct but in practice the 555 circuit output can’t give you too much current to drive directly the motor. Also there’s a need to use some protection diode (when power is cut the diode is supposed to re-route the voltage/current from the coil/motor back onto itself, so the magnetic field energy is dissipated from the coils own electrical resistance).

 

[ryanturner]

Sorry to bother you again, I cant seem to get the circuit you gave me going on croc tech, maybe im connecting the relay wrong.

On that circuit i drew, can i not connect a MOSFET from the output of the 555 into the gate, the motor inbetween drain and power then source to ground. I dont know much about this component so will this get me enough current... what value should i aim for?

thanks for your patience with idiots like me!

 

[mister_rf]

Yes, that's the same diagram for using a bipolar transistor.