|Topic Review (Newest First)|
|02-10-2014 07:33 PM|
Thanks for asking a question I can actually answer Up until Paul wrote up his excellent explanation of the elegant regulator circuit he designed for the FrankenBebi, I was a little unclear on how the circuit functioned as well.
Anyway on to your question... Generally speaking you would be correct for a couple of reasons.
First, a single (or even a group) of resistors for current control is not advisable in a situation where the input voltage may vary. Onboard, we could have from less than 12Vdc (batteries at less than 25% SOC) to over 18Vdc (battery equalization cycle). With a fixed resistance acting as current control, LEDs would dim at low voltages, and at higher than "nominal" voltage excess current would be dissipated as heat.
Second issue is parallel/series arrays are a problem in and of themselves. If we loose one LED in a series "leg" the current (say 100mA) that was divided among 5 legs is now supplying only 4 legs with a resultant 25% increase in forward current. If this exceeds the max forward current of the installed LEDs the magic smoke will escape, and we have a dead FrankenBebi
The latest design deals with these issues in the following manner.
Second issue first... The regulator circuit as designed is only driving the Cree C530D LEDs at about 60-70 percent of their rated max forward current. If we should lose one leg of the array, we are still below the rated max forward current for the balance of the array, hence no magic smoke.. Of course this situation would entitle you to a warranty replacement, but the FrankenBebi would continue to function until it arrives. The earlier change in board design
staggers the LEDs in any given leg around the radius preventing an entire 45 degree sector from going dark, as no LEDs in the same Leg adjoin each other.
As to the first issue (current control)... While the circuit contains a number of resistors, none of them actually provide current control as such. The current control circuit (which is on the low-side of the array) Uses a combination of 2 resistors (R3, R4) an N-channel MOSFET (Q3) and a general-purpose NPN transistor (Q2) Paul's explanation is as clear as it gets so here is a quote from his document
Here is a local copy of the schematic for reference.
Hope that answers the question... Nice exercise for me to prove to myself I understand the new circuit. My previous background is in the mechanical end of things (ME not EE) so this whole project has been a real learning curve on the electronics end. I will be posting the latest (and last?) revision of Paul's circuit discussion paper (doc revision 1.2) which includes another section on testing, expected vs real test values, and troubleshooting. It will be accessible via the same links in the above post in an hour or so...
Good opportunity for me to thank you for your earlier suggestion about the "icecube" case. We are well on our way to solving the issues on that one, and it should be "ready for prime time" about the time our new batch of PCB's arrive in a few weeks.
(aka Cap' Couillon)
|02-10-2014 04:31 PM|
Cap, I have no certain memory just a big fuzzy thought that large series-parallel arrays of LEDs with only the one resistor feeding them were frowned upon in this type of design? Wrong fuzzy memory, or is there something to that? No drawback?
|02-10-2014 02:52 PM|
FrankenBebi Circuit Description
We have posted an in-depth description of the latest FrankenBebi circuit design, including theory of operation, component selection, and some test results. It can be viewed online or downloaded as a PDF File (150KB)
The FrankenBebi Project
|02-07-2014 11:17 PM|
Re: FrankenBebi new news....
New News at The FrankenBebi Project
Latest schematics and board designs posted. Future options and more... Please take the time to fill out our survey if you haven't done so already.
As always, your comments and suggestions are encouraged, either via this thread, or via the project site.
|01-30-2014 02:41 AM|
New Case Preview
Here is a preview of the new "Ice-Cube" case design
Igor's latest Newsletter will be sent out this weekend....
|01-12-2014 08:26 PM|
New FrankenBebi Project News
New News at the FrankenBebi Project.
New project team members
New circuit design with better performance and reliablilty.
New monolithic case design (Thanks "HelloSailor")
Effects of new designs on release dates.
For all the latest news visit the FrankenBebi Project website
While you are there, you can subscribe to Igor's Newsletter to get the latest delivered to your inbox in a semi-regular fashion.
If you haven't done so yet, please take a minute to fill out our short (6 question) survey in order to help us tailor the FrankenBebi to the cruising community's needs.
As always, thanks for your interest and support.
|12-27-2013 06:29 PM|
Re: FrankenBebi new news....
New news at The FrankenBebi Project..
First up, we now have our own domain, FrankenBebiProject.org and new email addresses to match. Shiny new toys for the holidays. If you have our older pages bookmarked, you will be forwarded to the corresponding page on the new site. All the old email addresses are still usable, but as always, it is best to update your bookmarks.
Along with the new domain, we have made a few changes to the web pages, mostly just housekeeping issues. We have however added a quick-mail form to our contact page so you can contact us directly without having to copy and paste our email address.
We have also added a short (5 question) survey to the home and news pages on the site. If you have the time, please stop by and fill it out so we have a better idea of what the community at large wants from the FrankenBebi anchor light. No personal information requested, just the facts ma'am.
Meanwhile, testing of existing designs continues along with some new experiments by our latest team members.
Igor will have the full newsletter for late December mailed out sometime this weekend. See the website for how to subscribe if you want "the rest of the story"....
Thanks again for your interest and support.
|12-10-2013 01:24 PM|
New FrankenBebi Project News
New news at the FrankenBebi Project
Cheops' Law: Nothing ever gets built on schedule or within budget
We have had some changes in our release dates. For the full story, follow the above link.
Documentation: Now available online
Documentation pages are now online at the website. This area contains zip archives of each posted version of the FrankenBebi up to and including the latest untested v0.11.03. Each file includes the native Eagle Lite sch and brd files, standard image files of the schematics and board traces and layouts, and additional files concerning licensing and appropriate use.
Download and enjoy.
As always, if you have questions or comments, please contact us via this thread, a PM, or via the Email address listed on the website.
|11-30-2013 09:57 PM|
Crowbar would eliminate the voltage drop but too large a fuse (over the rated current of the crowbar diode) could cause the crowbar to fail open, cooking the innards anyway. Everything is a compromise, and from the performance of our prototypes at low battery voltages (less than 11Vdc) it was decided that the .5V drop across the Schotky diode we have decided to try will have a negligible impact on performance.
We would have preferred to eliminate reverse voltage protection all together (a can of worms indeed) but as it only takes a millisecond mistake to let the magic smoke out, we might be replacing a lot of units under warranty that were ok other than installation error.
As far as a strobe/sos generator, it should be fairly trivial to design if one does not already exist as an IC. Problem would be where to put it (see comments on board density above) and how to trigger it. It might however, make another kind of neat project as a stand alone device wired into the supply side circuit? If properly sized, it could be used on existing anchor/tri-light circuits or any other resistive load.
Hmmm.. add that one to the list of future Franken-Projects for the community to kick around.
|11-30-2013 09:19 PM|
Cap, as an alternative to a blocking diode, what about installing a crowbar diode across the power leads? If power is hooked up in reverse, it goes through the crowbar and that appears to be a dead short, blowing the fuse in the power line to the light. Rashly assuming a proper fuse has been installed, of course. But it gets the voltage drop from a blocking diode out of the circuit. Or opens the whole can of worms on "protections".
I'd still suggest adding a chip (there must be cheap ones out there, because they are being used in really cheap flashlights) that would allow the light to strobe and SOS. Seen in LED flashlights shipping from China to the US for $5 each, including ground post shipping, so the chip can't cost more than what, one cheap LED does?
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