So, I’d been wanting a decent foam sprayer for a while. You know, the kind that actually makes good foam, not just bubbly water. My old manual pump one was a real pain in the arm, especially when doing the whole car. I kept thinking, there has to be a better way.

Getting The Idea and Parts

Then it hit me – why not try to make a battery powered one? Seemed like a fun little project. First thing I did was look around for what I already had. Found an old garden sprayer bottle, about 2 liters, which was perfect for the main container. That saved me a few quid right there.

Next, I needed a pump. I went online and found a small 12V diaphragm pump. Nothing fancy, just something that looked like it could handle a bit of soapy water. For power, I remembered I had a spare 12V lithium-ion battery pack from an old RC car project. Already had a charger for it too, so that was sorted.

The other bits I figured I'd need were:

• Some tubing to connect everything up.
• A simple on/off switch.
• A proper foaming nozzle – this was important for getting that thick foam.
• Wires, connectors, and some sealant.

Gathered all that stuff on my workbench. Looked like a promising pile of bits.

Putting It All Together

Alright, so the first challenge was getting the pump to work with the bottle. I decided to mount the pump externally, just to keep things simpler and avoid getting it too submerged in soap if things went wrong. I drilled a couple of holes in the original sprayer lid: one for the pickup tube going into the bottle, and one for the wire to the pump if I had decided to mount it inside (which I didn't, but I considered it). In the end, I just ran the pickup tube through a sealed hole in the cap to the pump intake.

I took the original hand pump mechanism out of the bottle's cap. Then, I cut a piece of plastic to fit over the large opening of the cap and drilled a hole in it for the suction tube. I used a hot glue gun and then some silicone sealant to make sure the suction tube going into the bottle was airtight where it passed through my makeshift cap cover. Had to be careful to make it a good seal, otherwise, it wouldn't suck properly.

Wiring was pretty straightforward. Battery to the switch, switch to the pump. I used some spade connectors so I could easily disconnect things if I needed to troubleshoot or charge the battery. I mounted the switch on a little plastic project box I had lying around, and then stuck that box to the side of the bottle with some strong double-sided tape. Made it look a bit more tidy.

The output of the pump then went to the new foaming nozzle via a short piece of flexible tubing. I had to play around a bit to get a good connection here, used a couple of small hose clamps.

First Test and Some Problems

Okay, moment of truth. I mixed up some car wash soap and water in the bottle. Not too scientific, just poured some soap in and topped it up with water. Connected the battery, took a deep breath, and flipped the switch.

The pump whirred to life! And… I got a sort of weak, bubbly stream. Definitely not the thick, shaving-cream foam I was hoping for. A bit disappointing, I won't lie. The pressure seemed okay, but the foam quality was just meh.

Tweaking and Getting It Right

I figured a few things could be wrong. Maybe the soap solution was too thin? Or the nozzle wasn't getting enough air mixed in. Or perhaps the pump wasn't quite up to the job with that specific nozzle.

First, I tried a richer soap mixture. Added a good glug more soap. That definitely helped a bit. The foam was a little thicker.

Then I looked at the foaming nozzle itself. These often have tiny air intake holes or a mesh screen that helps create the foam. I made sure it was clean and clear. I also experimented with slightly restricting the water flow before the nozzle just a tiny bit, thinking it might help the aeration. It’s a bit like tuning a carburetor, you just fiddle until it feels right.

I also checked all my connections for air leaks, especially on the suction side. An air leak there would definitely reduce performance.

Success!

After a bit more fiddling with the soap concentration and making sure everything was sealed up tight, I tried again. Flipped the switch and YES! This time, it produced some pretty decent foam! It was clinging to the surface I sprayed it on, nice and thick. Not quite like those professional foam cannons you see at car washes, but for a homemade job, I was super happy.

I’ve used it a few times now to wash my car, and it's a game changer. No more frantic pumping. Just point and spray a lovely layer of foam. It makes the whole process much quicker and, dare I say, more fun. The battery lasts long enough for a couple of washes too, which is great.

So yeah, that was my little adventure into building a battery powered foam sprayer. Took a bit of trial and error, but totally worth it in the end. If you’re thinking of a similar project, I’d say go for it. It’s satisfying to make something yourself that actually works well!