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# Need input on a prototype I am working on

#### jonohoff

##### New Member
I am working on finding parts for a wacky prototype idea, and I could really use some help from you folks. I need to run a DC water pump off a bank of D batteries. I know the pump in the link is not exactly meant to run off such a power source, but I literally need it to run for about 2 seconds, 3 times a day. Do you guys think I would be better off using 4 D batteries with a step-up transformer to get the 12 volts, or would I need to use 8 cells?

https://tinyurl.com/yc39xe8u

I looked for some step-up transformers, but could not find any that will pump out the needed 70 watts. At least not ones that are in the price range i would like to find.
If someone would be willing to chat with me and help find the best solution it would be awesome

Thanks so much,
Jono

Do you guys think I would be better off using 4 D batteries with a step-up transformer
That sounds like a really bad idea.

The pump appears to be rated at 6 amps.
I guess that will be the running current when fully loaded.
During start up, the pump will take more than the full load current, maybe 1.5 to 2 times than full load current during start up.

What you describe as a step-up transformer will have some kind of transistor oscillator/amplifier to drive the transformer to make a voltage converter.
Transformers do not work on DC.

or would I need to use 8 cells?
A much better idea.

JimB

The pump appears to be rated at 6 amps.
I guess that will be the running current when fully loaded.
During start up, the pump will take more than the full load current, maybe 1.5 to 2 times than full load current during start up.
I would say that 1.5 to 2 times is a significant underestimate. My best guess if that were connected straight to a 12 V car battery is that it would take 5 - 10 times the normal current of 6 A.

Depending on what pressure the pump has to run against, it is likely that it will start at a much lower voltage than 12 V. A supply with a current limit of 10 A might get it to start. However, it's very difficult to be sure without trying.

I recently worked on a 12 V air compressor. It took about 12 A when running. If the current supply was limited to 50 A, it would often not start unless the air pressure was reduced.

You picked a huge motor that needs to run for a couple seconds and want to run it off of D-cell batteries that don't like to deliver more than an amp or two.
How about picking a smaller 12-volt motor pump that runs for a few seconds or minutes. Some small (indoor) fountain pumps deliver a gallon or two gallons per minute and need about 150 to 250-milliamps. Much better design and less chance of fire. If you don't think it can work, please describe your need a bit better.

Dump the D cell idea, use a 12V lead acid gel battery!.

You have many variables to work with here. Volume, battery density/chemistry,
battery lifetime.....Compute the # Joules you need for the pump and back into
the solution looking at battery density/chemistry, from alkaline to Lithium,
choose size and current ratings.....

You could do a super capacitor type solution and a boost SMPS module to charge
the super caps.

Even off the shelf, something like this (hundreds of amps, this is overkill, but you
get the idea) :

Regards, Dana.

Thankyou very much for the feed back guys! I'm so happy I posted this. What I am trying to do is make a water gun alarm clock (shoots water in ur face, then gives you 30 ish seconds to get ur butt out of bed and walk across the room to run to turn it off before it shoots you again lol). I want a pump that's strong enough to shoot 12 to 14 feat so you can't just roll over and turn it off. You have to physically walk across the room. Should I consider making this a 120 AC plug in setup instead? I wanted to do the battery thing so people don't have to have access to a plug in and have the ugly aspect of cords runnin around, but if that is a bad idea, I am 100% ready to listen to suggestions. I am stoked that I got all this feed back in a couple hours.

I am planning to find a nozzle that has a lot of range as far as going from a straight shot to a wider spray depending on if your someone who rolls around in bed and need it to hit you even if you roll 2 feet over.

Thank you again for the help you guys probably saved me from creating a serious fire hazard!

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The little pump I posted should be enough, those fountain pumps can shoot a 1/4" stream of water about 6-feet high so a small nozzle should do it for you.

I don't recommend 120v AC with a wet floor and wet hands. Dangerous.

The 8 pack of D-cells is perfect for a gag gadget. No need to go lead acid, rechargable, optimized, ... try the little fountain pump with a proper nozzle and you can have some fun. All you need for those pumps is a bucket of water to set the pump in and then a hose from the pump to your nozzle.

The little pumps are sealed with a magnetic clutch to the impeller so you don't have to worry about straining the pump too much if you want to start the pump before you open a valve or what ever combination you have.

Dump the D cell idea, use a 12V lead acid gel battery!.
Yes, use a 12 volt SLA. You will have the power and you only need to charge it (no math involved) every other month.

While I don't think this prototype is such a good idea I have one that doesn't need a pump. Instead of a pump, in use that would also put water on the floor as it shuts down and pressure is lost, why not a water in a bottle? Have the bottle hanging above your pillow filled with water and a solenoid valve wired to the alarm clock. When the clock goes off the solenoid valve would open and water would drip directly on you.

The only way either of these things would work is if you aren't someone who moves in your sleep. I for one, never wake up in the same position I go to sleep in.