Frabill Minnow Bucket - 3V input

[BroomJM]

I have a Frabill insulated minnow bucket (cooler, really). It has a small electric pump that oxygenates the water in the insulated cooler that the minnows swim around in. I have attached a picture, below. This pump can be powered by 2 D-cell batteries, which provide 3V and a total of around 24 watt-hours. The pump also has an input for a 110v source, which uses a 5.5mm plug that provides 3V at 500ma. If I'm doing my math right, this means it uses about 1.5 watts, so the D-cell batteries last about 16 hours of continuous run-time. This might be 3 days of my normal fishing trips, if I remember to turn the unit off...and therein lays ONE of the problems!

The other problem is that replacing the batteries requires you to unscrew the pump from the top of the cooler, disassemble the case for the pump, replace the batteries, and then put it all back together. The nut that the screw goes into is inside the lid of the cooler, so this is not a fun job when you have water/minnows in the bucket. I don't have a 110 outlet on my boat, although I do have a small (Energizer) portable power station with a 150w inverter and LiFePO4 battery. It could run the minnow bucket for a hunnert years...or so. I'd rather not have to bring that on the boat to run the 110v plug, but that would "work", for sure. (I've tested it and it's not a horrible solution.)

In learning about various lithium batteries, it has become obvious to me that most of the cells used in lithium batteries are somewhere in the 3.0 to 3.65 volt range. You put four in series and you get a 12v battery...but my device actually uses just 3 volts. So, is there any reason I couldn't use one or more 18650 cells, wired in parallel, to provide the ~3V used by this little air pump? The output of an 18650 is 3.5v (nominal) and they can easily cover the 500 milliamps drawn by this little pump. I guess my main question is whether or not the pump could be damaged with a 3.5v power source, versus a regulated 3 volts?

Thanks in advance for any replies.

 

[MisterSandals]

I guess my main question is whether or not the pump could be damaged with a 3.5v power source, versus a regulated 3 volts?

DC motors will run faster at a higher voltage and will likely be just fine with .5v over the recommended nominal voltage.

 

[BroomJM]

DC motors will run faster at a higher voltage and will likely be just fine with .5v over the recommended nominal voltage.

I got to thinking about this a little bit, and it's not like the power coming from the D-cell batteries is a regulated 3v...it varies (drops) as the battery discharges. The 3.5v from a single 18650 cell, or similar, is going to stay constant.

With that said, I can also just cut the cigarette lighter end off the supplied 12v cable (which has an inline buck converter to 3v) and wire it to use the XT-30 connector on one of my trolling motor batteries. That way I have a virtually endless supply of power and no need to fuss with the individual cells.

 

[BroomJM]

This isn't exactly UL approved, but it does work quite well. The meter says this cell is around 3.9v, which surprised me, but it runs the little air pump just great. It doesn't sound any faster than it does with D-cells, so I think it'll work well enough. My plan is to put probably 5 of these in a parallel configuration, just for fun. It's still way easier to just use the 12v to 3v buck converter and wire it for the XT-30 plug.

 

[BroomJM]

I have another update on this project, which has kind of split into two directions:

1) I bought a 12v-3v sealed, water-proof buck converter. I wired one side with an XT-30 connector that plugs into one of my trolling motor batteries, where I would normally have the on-board lithium charger plugged in. On the other side, I wired roughly 3 feet of extension cable to a 5.5x21mm barrel plug that fits into the air pump, shown in the previous post. I tested this out yesterday and was able to confirm that you can run this all day on the regulated 3v output from a 100AH battery. No surprise there!

2) I'm building a 3-cell pack of 18650's, wired in parallel, which will connect directly with the 5.5x21mm barrel plug. I also purchased a power supply with a female input for that plug, so that I can recharge the entire pack, after using it. This results in 3.5v (nominal) into the air pump, which is a little too much voltage. My ear tells me that this higher voltage results in the "low" setting creating as much output as the "high" setting does, when fed the correct 3v input. I don't know what the long-term effect might be on the pump, but it's something I'm interested in testing.

Here is an Amazon link to the buck converter I am using for solution #1.

Amazon.com: SMAKN DC/DC Converter 12V Step Down to 3V/3A Power Supply Module : Electronics

Buy SMAKN DC/DC Converter 12V Step Down to 3V/3A Power Supply Module: Power Converters - Amazon.com ✓ FREE DELIVERY possible on eligible purchases

www.amazon.com

 

[JeepDaddy]

Thank you, you just gave me an idea of what to do with my single low capacity LFP cell that's being replaced. It tested low at 259AH, instead of 280+. That should run a bait tank for a while.

Also a new D cell battery is somewhere around 1.6 volts each so you should be good to at least 3.2 volts. 3.5 volts should be fine. Those things are not designed to maintain synchronous orbit, lol.

 

[BroomJM]

Thank you, you just gave me an idea of what to do with my single low capacity LFP cell that's being replaced. It tested low at 259AH, instead of 280+. That should run a bait tank for a while.

Also a new D cell battery is somewhere around 1.6 volts each so you should be good to at least 3.2 volts. 3.5 volts should be fine. Those things are not designed to maintain synchronous orbit, lol.

Yeah, I reckon you could run a 3v pump for a while one a 259AH cell. :D