I'm in the process of rebuilding / refitting a 1968 cruising sailboat, which needs a total electrical refit as well. I was thinking of options for music, and decided to build a portable bluetooth speaker instead of hard wiring speakers and a typical marine stereo into the boat for a couple of reasons. Even when we're on the boat, we aren't always in the cabin where the stereo would sound best. I didn't want to mount speakers inside and out in the cockpit to keep it simple. But the best thing of a portable bluetooth speaker is that is can come to the beach, or be used around the shop when we aren't messing around on the boat. The is the prototype for a future (potential) refined version, which works amazingly well and sounds awesome.

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Step 1: Select Your Components

Of all places I started first with my components, it was the batteries. I found a closeout sale of 26650 LiIon batteries at my local Radio Shack, which let me get them for $4.99 for a two pack. I went to another Radio Shack in the area and got a total of 5 2-packs, and began to test them. For $25 total, it was a good price to experiment with them.

I also picked up the BMS, amp, marine speakers, dual USB / voltmeter combo, and 2.1mm female jacks from Amazon.

Step 2: 4S Lithium Battery System

I found one battery of the bunch that wasn't performing as well, so I paired 8 of them into a 4S battery pack, and used a DROK 4S LiIon BMS board to manage the charging and prevent me from over charging any one cell. I don't know that this is the best solution, but in my experimenting, I also wired in a typical balance cable that I can plug into my Tenergy balance charger to periodically double check that they are staying well balanced.

The 26650 batteries are rated at 3.5Ah each at 3.7v (4.2 charged). By pairing two together in each cell, we've got 7Ah in each cell. Then putting those 4 pairs into series produces 14.8v (16.8v charged) at 7Ah.

This setup is more complicated and expensive then just buying a 12v 7Ah SLA battery, but this was also my first project building my own pack, and I wanted to give it a try. This 4S lithium pack does carry more total watt hours, and is lighter too. Plus with the battery protection, I'm less likely to run the pack until the batteries go low enough to sustain damage, like a sealed lead acid system would do.

Not shown here, I wrapped the pack in gaff tape when it was done to prevent any potential shorts in the case later.

Step 3: Design an Enclosure

Since I'm designing for use on a classic sailboat, I wanted something that sounded good, and looked like it fit in. I was going to make an enclosure that was build from strips of teak wood built around a form, kind of like construction of a wood boat. But, teak isn't cheap, and I didn't know if the speakers would sound any good in an enclosure that small. So I opted for this prototype version that would be about the same volume, but out of 1/2" birch plywood.

After roughly measuring the location where the speakers needed to fit (using some tape and paper because I forgot my tape measure at home), I used the Makercase website to help me get started with a basic plan for a wood box.

Using Adobe Illustrator, I edited the bottom to change the box joint seams to a clean base with just a piece of plywood that would sit inset the bottom. I designed an internal frame with the same dimensions, but the whole center cut out, so it could be glued in place and leave a nice flat lip for the above shown screws to attach to, which wouldn't be visible from the outside when the speakers were sitting normally upright. This is where I go in the box to install everything, and can get access later as I make changes.

I cut all the pieces on a 130w CO2 laser cutter from 1/2" 5ply birch plywood. I chose to use the side of the plywood that has more grain variation to make it look more interesting.

Step 4: Design the Button Interface and Test the Speakers

This is the first I've used one of these simple and cheap little Bluetooth amps, so I attached it directly to a speaker just to get a sense of the sound quality before wiring it in for good. The speakers didn't have much fullness without an enclosure, so I was a little nervous at first if the amp was lousy.

You can see some photos as I was figuring out how to extend access to the 5 buttons on the face of the amp to the exterior of the housing. These photos are from before I used slightly longer bolts that reach the buttons better, but you get the idea. As you press on the tip of the bolt (which are covered with cap nuts in the final enclosure) the head of the bolt presses the button, and you compress some foam which pops the bolt back to the resting position when you release the button. The bolts and cap nuts are stainless steel.

Step 5: Assemble the Box

After I glued the box together and sanded it, I put on a coat of oil/poly finish and then later sprayed a few coats of gloss polyurethane finish. I screwed in the speakers, wired them to the amp, and mounted the amp to the inside so the bolts protruded through the 5 holes I previously had laser cut in the original design.

You can also see here the toggle switch that cuts power to the amp from the battery pack. At the bottom is a combination dual USB charge converter with digital voltage gauge in between the 2 USB ports. This takes 12-24v and outputs 5v DC, so it was perfect since my range with this pack is 14.8-16.8v. The voltage gauge will help me know how much juice is left so I don't unexpectedly lose my tunes. Having the USB charge ports right on the speakers assures the source of the music (my phone) isn't going to run out of juice unexpectedly either.

I also lined the interior of the box with some synthetic insulation scraps I had left from another project. Adding insulation improves acoustics, allowing the enclosure to perform like a larger enclosure. I decided not to port the enclosure in this initial prototype, since a closed design is easier to calculate (or ballpark) for good sound, where ported enclosures need to be just right for it to pay off with the best sound.

Step 6: Last Notes and Testing So Far

I'm already planning some changes in my next revision, but to start, I'm using a balance charger without the balance cable attached (since it's got the over charge protection inside the pack). I have a 2.1mm female power jack run to the exterior of the case from the internals, and I soldered together a cable to convert the XT60 connector on my balance charger to a 2.1mm power plug. This isn't the best solution, since it doesn't keep the cells balanced, but rather shuts the pack off if they get too far out of whack. I'll still open the case periodically to attach the XT60 connector and balance cable directly to my charger so I can see how quickly it loses balance. In initial tests, it didn't seem to get out of balance any noticeable amount, but that could drift over time.

In my next version, in addition to the external power input, I'll add a connection for the balance leads on the exterior. I haven't found a good BMS board for the internal pack that provides the protection like the current one does, AND balances during charging. I know they are out there, but I'm just new to building my own lithium packs, so feel free to suggest better options with URLs for buying for USA shipping. Once I have a board that does both inside, I could just use a DC to DC converter to supply 16.8v to the pack from my 12v boat battery.

So how does it work? AMAZING SOUND. This little amp is surprising clean and powerful with 50w output per channel, and the Polk Audio DB651 speakers are clean and bright at 60w RMS each, so no fear of blowing them out. A larger case would provide more low end bass, but there is good bass for all but the lowest range. The case fits perfectly in a little shelf in the main cabin of the boat, and is not too small a design for good sound.

In my next revision, I'm also going to wire a switch so I can also get power directly from the boat's 12v system or choose the internal battery. This way it doesn't use the internal lithium batteries at all when it's in the boat, and will prolong the life of the 4S pack. I'll also add a handle to the top, now that I confirmed there is sufficient clearance getting it in and out of the shelf space :)

If this project was useful, entertaining, or inspiring to you, please vote for it in the Wood contest (top right corner of your browser!) Thanks!!!

<p>I have a question regarding the Overcharge protection, I'm doing this for my major project for Year 12 Electronics. I was wondering about the functions of the VH, VM and VL pads on the board and where they go. It's very hard to follow without a schematic or block diagram.<br><br><br>Greatly appreciated if someone could please help me out!</p>
<p>Those three pads provide the connections needed for the individual battery monitoring. In my case, I also added a JST cable that is typical if I want to charge the pack with a multi-cell lithium battery charger, which essentially bypasses the balancing functions of the board installed in the speakers. I did that initially, because I have a tester that shows the voltage of each individual cell, letting me know if the circuit was working properly.</p><p>So to explain how to use those 3 pads (referring to my diagram), you can isolate each battery with the following connections, either to monitor the voltage individually, or in the case of a balancing circuit, draw a little power from the cells with more power until they match the cells with a lower charge.</p><p>Battery A can be monitored between B+ (pos) and VH (neg)</p><p>Battery B can be monitored between VH (pos) and VM (neg)</p><p>Battery C can be monitored between VM (pos) and VL (neg)</p><p>Battery D can be monitored between VL (pos) and B- (neg)</p><p>At each of those set of points, you should be able to read the voltage of that individual cell. If you read the voltage between B+ and B- you'll get the total series voltage of this 4S pack. </p><p>3.7 + 3.7 + 3.7 + 3.7 = 14.8v (Nominal)</p><p>4.2 + 4.2 + 4.2 + 4.2 = 16.8v (Fully charged)</p>
<p>And not to confuse things, but hopefully to clarify:</p><p>This is a 4S2P pack, meaning 4 cell groups in series, 2 cells in parallel in each of those groups. Hopefully, if you can read my scribbling, the following diagram will illustrate how the 8 22650 batteries were wired into this pack. It's a combination of both parallel and series wiring, very common in this kind of lithium pack.</p>
<p>Thank you so much!</p>
<p>Cool project</p>
<p>Great build! I've got a suggestion to upgrade your installation: Install a Raspberry Pi (3) based OpenPlotter system, and then install a slimserver and Squeezelite. It would probably already fit in the box you have. I've got a 250gb hard disk on the system on my boat, which stores my 34K song music collection, and stores charts for Openplotter. So, with a single $35 computer (plus a few add-ons), For not a lot of money, you can have:</p><p>A chart plotter (it displays on a tablet via VNC) with inputs for a cheap SDR-based AIS receiver and NMEA inputs from sounder, log, wind, GPS, etc.</p><p>A WIFI hot spot and repeater</p><p>A huge music library with integrated music player</p><p>Have a look at these links:</p><p>OpenPlotter: <a href="http://www.sailoog.com/en/openplotter" rel="nofollow">http://www.sailoog.com/en/openplotter</a></p><p>Squeezeserver and Squeezelite: <a href="https://www.instructables.com/id/Raspberry-Pi-Multi-Room-Audio-MobileTabletPC-Contr/" rel="nofollow">https://www.instructables.com/id/Raspberry-Pi-Multi...</a></p><p>Again, great build, and good luck on your boat project!</p>
<p>Wow, where have I been... I never heard of OpenPlotter until you shared this. I am going to rethink my electronics update. Up to this point, I've been using the Navionics app on my phone on a tablet. The yearly subscription to the sonarchat data is really worth it for the increased accuracy with 1ft contour lines in places. But recently I realized for about $150 I could get the Vexilar SP200 Sonar Phone: <a href="https://www.amazon.com/dp/B00CJJBMDO" rel="nofollow">https://www.amazon.com/dp/B00CJJBMDO </a> </p><p>This uses a dual sonar sensor to create a Wifi hot spot that send the data to your tablet or phone running navionics. So it's crowd sourcing the continual re-mapping of the bodies of water you travel, and you can download updates to the charts to get everyone else's contributions as well. It seems pretty cool in theory, although I have seen once where it has bad data (an apparent 500ft deep spot north of the Bay Bridge on the Chesapeake Bay). </p><p>But it doesn't connect to anything else. Now I'm going to look into how these two might work together potentially. Thanks for the suggestion. I might be more likely to wire the Pi in to the boat directly, since I'd have to tether cabling to my NEMA devices anyway, but I'm thinking about the pros and cons. Much appreciated!</p>
<p>Happy to help, and perhaps I'll do an instructable when I'm done with everything. I'm also a Navionics Boating HD user, and I'm also interested in potentially streaming depth and log data to the tablet. So, I'll be using OpenCPN and Navonics on the same tablet. I sail in Mexico, and the charts are not as good, or easy to obtain, as the great NOAA charts in the USA. Have fun and good sailing!</p>
<p>Nice!</p><p>How should it modify to operate it with AC power also?</p>
<p>I was thinking a simple method, a single throw double pole switch, so that as I switch the power from one to the other in one click. You could make it a 3-position switch instead if you wanted the middle to be OFF, and the two other positions to be ON with two different power sources.</p>
<p>You'd just use either a switch for power input source or a relay energized by the AC rectified source, then either as a separate power brick or built into the enclosure you'd put a suitably rated transformer, bridge rectifier, and some beefy filter capacitors, OR for arguably lower sound quality but higher efficiency you could wire up a suitably rated laptop power brick, which will be the easier and cheaper option for the average person, but wouldn't suit many audiophiles.</p>
<p>If you need to test a speaker setup before you have a housing, just use a cardboard box. .Also, you were right to not port the speaker.. Porting requires pretty complex math, and for a smaller box they'll sound great totally sealed, it just requires a bit more power to the speakers. I live in a trailer and never considered a bluetooth system for my computer audio out.. I was using a high quality home audio setup that I never reattached since moving into it, just listening with headphones. Thanks for the idea!</p>
<p>Just use a cardboard box? Little good that will do, the acoustics are quite different. The primary determining factor for pleasant sound will be the box density, with cardboard being about as low density as you can get and still have it holding the speakers.</p><p>Yes a sealed enclosure is easier to design, but there are existing designs for ported if the math is too much to tackle, and a seldom thought about aspect of ported is that you can situate an amp heatsink in the path of the port airflow to cool it pseudo-passively. Granted this is a relatively low power digital amp design that won't need as much heat removed, but if going to this much trouble I would build for higher output power capability, since you can always turn the volume down if you don't need it loud.</p><p>Plus, on a boat above deck or on a beach, lack of walls to reflect the sound means you need more watts for the same audible sound level especially in the lower midrange and bass.<br></p>
<p>You guys that build these things are talented. I would think there is a business opportunity in this. </p>
<p>Nice looking speaker housing.</p>
I've built something simular. the same amp as your setup. rear speakers from a surround sound system I got from a hard rubbish pickup. and I used the battery from my Ryobi drill.
<p>Wilkinsonaw, that looks like a nice compact setup. </p>

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