- Sep 20, 2013
How do you figure 14 3.9 ohm resistors in parallel would give you 2.66 ohms? :thinking:
Yea I have a bunch of videos somewhere of the testing I was going over with angelos basically using a driver with many starts via sessions of hot connect 9V or from zero the best way, fast loading and unloading hot and runs for longer durations up to thermal shut off then turning my supply to 12V and hot connecting with about a 20% kill rate. Best was I did get a pic of the input cap exploding on one. up. by hot connecting with 9VI can see the utility in having a jig to set drivers on, but I would never run them through on a hot supply as that is the best way I know to kill one. I know it is a PITA, but setting your supply every time when I am setting up a driver has saved me countless times from really stupid errors because you can't be aware of everything going on all the time. It also works quite well when driving LDs to check the wavelengths when you have twenty or more to do.
I think a linear driver is a bad idea for running that much current. There has to be a buck that would work for this. Far less waste heat to worry about.
That was my first thought for this build. A High voltage linear and run them like they are in the projector if you can stack enough cells with the way you configure the unit. Also if thee is anyway possible I would always choose a 2 Li-Ion in series config over a 3 Li-ion in series config with the common buck drivers we use. You get full battery cycle with two and you are asking the drivers to work harder and make more heat while edging ever closer to the max input voltage of the driver plus if you go with some high drain cells like IMR's or something are we not working more toward the extremely low resistance we are thinking might be an issue with the 3S packs or even the variable power supplies that don't do enough to suppress these events and in most every build I have seen batteries are not variable so it is always hot loding them.If a bunch of diodes in series, compared to using individual drivers, the loss or heat is divided by the number of diodes being driven, it isn't that much.
What I meant by the heat divided by the number of drivers might not have been fully understood by some, now that I'm reading what I wrote I'm not sure. I meant, for example, lets say you have 10 diodes with 10 drivers, and the heat loss is, for example, 5% in the driver, add the heat being lost per driver together and you get a sum of heat, now compare how much heat you are getting from a single LM338 driver, or two of them etc. which has a far lower efficiency, how much difference between them? I think the cost savings is worth it to use two or three less efficient drivers than 10 more efficient ones.
Of course, much depends upon how close the output voltage is to the supply voltage, if the two differ too much, now the heat being produced is huge. I.E. 30 volts input, 12 out... Nope! Don't do that. Sure, for the LM338, if enough heat sinking, it works, but the proper way to design it is to have your supply voltage closer to the output voltage needed so there is less power loss regulating the output. As long as you keep the dropout voltage consumed in mind along with other ohmic losses, should work great.
I was thinking at least two strands like the old A's had 4 strands of 6 in series. On these if you did say two strands of 5 diodes then say the 24V forward range. Add a volt for the dropout and you would want to do two strands of cells in series instead of all cells in one chain. To be near 25V when near full discharge needing to be recharged to get the most runtime. One factor to bear in mind the more you put in series then the larger the fully charged voltage to fully discharged voltage becomes and if you are able to get it near perfect then you are dropping near no waste heat at the very end of that cycle. So regardless of the number you end up with to make that math work right two parallel strands of cells in series would reduce the amount of waste heat at the fully charged voltage you get the doubled capacity so hopefully it will be about the same runtime compared to all cells in series where it would be twice the waste heat at the start.I figured with 12 18650 cells in series the LM338 will hardly have to dissipate anything, actually with the sag 12 may not be enough.
I don't know why you are not getting that x-ray'd asap!