Straight off, I have to disclose that the title of this post isn’t strictly accurate. I don’t really do “woodworking.” It’s more like “woodabusing,” in which I end up forcing, splitting, cutting, re-cutting and usually abandoning what seemed like such a good idea at the time. So I may buy the wood, measure the wood, and cut the wood. But the odds of my producing anything that looks more professional than a kid’s fort in the woods built from scrap wood and corrugated metal are pretty low. Wood isn’t one of my strengths.
I’m also not an electronics guy. I do electricity quite well and can integrate electronic systems, but my experience with making circuit boards, or assembling gadgets that work from scratch out of piles of resistors, capacitors, and MOSFETs (go ahead and Google it, I had to the first time saw it dropped casually into a technical solution) is very, very limited. That I am middle aged and have had typical near vision degradation like many in our fifties, learning to solder tiny little components to the back of circuit boards is somewhat problematic. Though with two pairs of reading glasses and a really bright headlamp I finally did it.
Meanwhile, back at the Battery Balancing…
When we finished the last post I’d started the balancing. This gave me several days of slack time to work on other aspects of the project while the charge level of each cell slowly crept closer to 3.5 volts. Other than checking the cells periodically, there was little to do with the balancing process. The way we’d set up the batteries – in the empty battery compartment under our bed in the master cabin – it was easiest for us to move from our bed to the V-berth for a couple of days while this happened. Just a small increase the pandemonium on a boat filled with boxes, brackets, and wiring.
Battery Framing
Setting up a couple of the battery frames had convinced me that they just weren’t going to work. Which was unfortunate, as the vendor who provided them had charged us a lot of money for “cutting and assembling” even though they arrived completely unassembled. They didn’t look much like the pictures I’d seen when I decided on this solution, either. But my plan to have the BMS and all its switches and components installed all neatly in a single location lay in ruins.
I began to toy with the idea of building a wooden box within the battery box to contain them. I drew sketches, made measurements, and bought wood. I started cutting the wood.
Bad idea.
Not just the cutting, the whole lot of it. After cutting and fitting and playing with various options, it became clear that there was no way we were going to secure the batteries well enough to stop all vibration and movement.
Part of the trouble is the batteries themselves need to be secured into non-moving blocks. Some do this with steel bands. It was one of the design functions of our almost abandoned metal framing. You also need compression on the ends of the cell groups, to prevent swelling and distortion in the battery cases in the event of a Bad Thing happening to them (overheating, overcharging, etc.).
On the advice of one of our vendors, we tried banding the batteries with really strong nylon packing bands. Steel bands require extra special tools and expense. So we spent a day driving off to an industrial packaging supply shop to get some banding tape, and made these nice little bundles of cells.
Those weren’t, ultimately, going to work. Two bands made nice tight groups and the straps had several hundred pounds of breaking strength and were plenty strong. But the metal connector made it impossible to keep the cell groups installed flush to the wall of the battery box. There would be wiggle room, even if the sides and bottom of the battery box were completely flat and smooth, which they were not.
When I inserted the cell groups into my “nice, compact block”, what ended up wasn’t tight or compact. As I put the boards of the box-within-a-box against the cells, it became clear that I’d need to do a lot of shims and wedges to make things tight. After collecting some wood for this and trying it, the futility of the whole exercise finally struck me. No amount of shims and braces would ever get me what I wanted – firmly mounted, immovable batteries.
When the balancing was near complete, we were back to square one on how to secure the batteries.
My First Circuit Board
Abusing wood and flailing at battery boxes wasn’t the only thing I’d done during the three-day hiatus while the batteries balanced. I also opened up the BMS box and started trying to make sense of the installation.
The BMS is a tiny little black box about two inches by three, with two multi-pin connectors in the back. It comes with the connectors, the “optical isolators” for inter cell communication, and some wiring. Everything else is pretty much a la carte. I’d worked with the vendor that sold the Emus BMS to provide all of the equipment I’d need. This included the power supplies, the relays, the contactors, switches, fuses, and the “cell monitors” that are also made by Emus. He’d also recommended “active balancers”, which are devices outside the BMS that help maintain cell balance.
I opened my boxes and started my inventory of parts and bits, trying to match them to the wiring diagram and invoice manifest provided by the vendor. Most of them lined up, but a few puzzled me. One of the more vexing, which wasted a couple of days time, was the DC-DC power converters.
On a 24V boat like Evenstar, dealing with 24V to 12V DC converters is nothing new. Many boat bits just aren’t made at 24V, so I’ve had to deal with converters with systems from the refrigeration to the NMEA 2000 instruments. You get a little box with four wires on it…two for 24V in, two for 12V out. You wire it in and forget it. That we needed a 24V-12V converter is a subject of another rant; suffice to say that what we got was I suspect what was in inventory, and I believe a 24V based system (which would have made sense for us) was a special order item.
What I didn’t expect was something that looked like this:
There were “board ready” DC-DC power converters. What they were NOT was “user ready” as a power supply. To top it off, I’d been charged $120 AUD each for these tiny 30W power supplies. Discussions with the vendor were fruitless…we needed “isolated” power supplies, and these were special orders and couldn’t be returned.
For about $103 AUD I could have gotten something like this, which would have been adequate to run the whole show and has 100W of power, not 30W.
Little holes for wires, no soldering. 3X the power.
Needless to say, when I found out what I could have ordered a “board ready” power supply for myself (a lot less than $120) and that I would need to find a way to mount, wire and rig these things the whole process made me a little hot under the collar. There may have even been a discrete bit of foul language dropped.
But I owned the stupid things, and I needed two power supplies to make it work. One supply dedicated to the BMS and its functions, and one to run the relays and larger contactors.
It took too many trips to Jaycar (a store that is what Radio shack used to be before it turned into a retailer for RC toys and modular connectors) to sort this, but I finally did. Initially, I purchased some of the wrong things, like a breadboard (useful for prototyping electronics, but not for permanent installation) instead of “Vero Board” for the circuit, and a box that didn’t fit everything.
Vero boards are quite handy things. You can cut them to size, and the provide a number of continuous bus strips you can use to electrically connect your project.
Eventually, after the second or third trip to Jaycar, one broken vero board, and several false starts, I learned how to solder circuitry to a board and built this:
It looks cheesy and I don’t trust it, but it works. There’s even a cover…
This was the sort of thing that would have taken an experienced electronics hobbyist a couple of hours to do, and this person could have gotten everything sent mail order and right on the first try. For me, it wasted a couple of days.
I still may buy that pretty blue box for $103 AUD, because I don’t really have much faith that this thing will survive in the marine environment in the long haul.
Installation Inspiration
About the time the batteries were nearing balancing, I’d reached the hair-pulling frustration level about how to install both the batteries and the BMS in an acceptable fashion. When the balancing finished, it was time to fish or cut bait and I had to move.
Kathy hit the solution. There is a settee next to the bed with some space under it. She suggested that I could fit the BMS components in there if I could get the wires to reach. There is also a space at the corner of the bed, next to the battery compartment, where the main power bus and the negative shunts for the boat wiring all meet. This is between the settee and the batteries and was a perfect place to install the master switches and contactors. So the decision was made – we’d go back to the frames we’d ordered, and we’d install all the components in these two spots. Perfect!
With the batteries balanced, my kluged up power supply complete, and a spot for the equipment located, we were ready to rock and roll on the installation!
But wait…there’s more!
Really, I can milk this for a few more posts; it was a pretty major undertaking.
