That does look good.....Kind of the same effect as painted numerals on classic tuner dials, but this time it isn't paint.
Laser etching is ultra cool. I purchased some custom made dog tags. You buy the tag (tiny things as it were) and insert it into this machine. You then get to watch as the machine takes this piece of coated metal as the laser "writes" the text onto the part. Ultra fine text can be done. The tags I bought had 4 lines of text of approximately 20 characters per line, all in a tag about 3/4" x 1-1/4".
I know I'm stating the obvious here buy I can personally vouch for SLA batteries. You want a simple and reliable 24v power source? - 2 X 12v SLA batteries and a 24v automatic charger - just plug in and forget. SLA batteries love continual top ups which should suit this size box that will spend most of its time indoors.
With the various D class amps I've tested, SLA batteries provide a nice,safe & clean power source. Whilst on charge, no noise is feed to the amp. SLA batteries are heavy but lighter than 20 D cells!!
So no internal transformer needed, just a simple 2.5mm charge jack on the box and you're done.
As I said in my long post, lead acid batteries like to be constantly charged but I was thinking more NiMH instead of lead acid.
James, a couple questions:
a. how much does 2 SLA batteries weigh? About 5 or 6 pounds each? Since SLA batteries are chunky as opposed to D cells which can all be spread flat in rows, SLA option mean a beefier chassis to handle the more concentrated weight. Also, that means they are better suited for semi permanent installation and probably aren't designed for regular removal as they are probably connected with 1/4" tabs?
b. How many volts is the charger? I'm thinking that they are 12 volts? If 12 volts, then it can't be used to charge the system and run at the same time since it poses some issues. Firstly, the dual batteries would ideally be run in series (24 volts) for the amp, and center tapped for everything else. A 12v charger would need the batteries to be connected in parallel during charge. Now, if the charger is 24 volts, then that can charge the batteries in series but the circuitry probably should not be operated in this manner without further testing since I'm not sure what will happen with the circuits tapped from center of the batteries during a charge. Additionally, the amps I have in mind are close to their max rating with the batteries at 24v. To charge a 24v system, the charge voltage would have to be higher than 24v. Not knowing anything about the chargers themselves, I would not trust the electronics to be run in this configuration. When SLA batteries reach near full charge, the charging voltages goes very very high. In fact, 12v lead acid batteries I've seen can reach charging voltages of up to 18volts when fully charged. I'm sure that a 24v charger will go much higher than 24v's when the batteries start to resist the charge. That the charger is automatic also means that it pulses.
Lastly, going back to one original goal which is to be able to make all the boomboxes the same. There is good reason for this. First is practicality. If we got 5 or 10 or 15 participants wanting boxes, and each wants different things, in other words, build to suit, then we are instead of building 15 of one design, we are building 15 separate boxes, each individualized and each with a new separate set of challenges. Each will have to have unique tweaks worked out and trust me there will always be issues that need resolving. In the end, some will get finished, some will be a never ending source of issues, some owners will be unhappy, etc. etc. Like I said, I think any customization to suit should be done by the individual owner of their own example and any participants should be familiar enough with how the thing is setup to be able to modify to their hearts content. I know I would like the ability to install standard readily available batteries without having to have them permently inside the boombox for a couple reasons. #1, it would be lighter, #2, I personally would likely never use that feature, and #3, there is less risk that I forget the batteries are in there and they eventually leak. Now there's no reason why anyone who gets one of these couldn't simply rig up some SLA batteries internally and connect to an external jack for a charger. But there's no reason to make them all like that unless that's what every participant wants. Anyhow, that's my feeling.
I know SLA they are a cheaper option than getting NiMH but NiMH does have it's advantages. First lead acid batteries do not like to be deep cycled. They lose life very quickly when run like this (how much depends upon the exact battery). Also once discharged, they better be recharged like RIGHT NOW or they might go dead forever. Lead acid batteries begin sulfating the moment charge is level is low. Then there is capacity. A 7ah SLA battery is a common size but it's still fairly large. NiMH batteries with 10,000mAH is common (10AH). They have no memory effect and can be charge hundreds of times, deep cycle is no problem at all so run em until they are dead, not an issue. Then there is weight. I have 7ah batteries in all my computer UPS's. They are not light and I'm not sure at all that they are lighter than 10 D cells. While I wouldn't bet my life on it, I'm pretty sure that certainly, a 10ah-12V SLA option has got to be heavier than 10 D cells.
On a side note, has anyone actually tried out the NiMH D cells commonly available on eBay? I wonder how well they do in boomboxes. Standard power tool battery packs are constructed using only sub-C cells and they last a very long time and have tremendous power. If the D cells are proportionally higher in capacity, then they should work out very very well. But in truth, I'm only going by advertised numbers and not via any personal experience.