...Anyway, what I was thinking about trying is putting a an axial power diode between the positive and negative battery terminals, after the resettable fuse, but polarity reversed on the diode so no current flows through it when the battery is inserted correctly. But if the battery is put in backwards, the diode shorts the battery and trips the resettable fuse. Anyway, just thought about it last night and can't seem to find any proper diodes in my stash, so will have to try it when I get some in. Just curious if anyone had tried it or if this will even work. I do electrical work, but no electronics designer by any means. So could fry everything. Figured this would be a good place to ask.
Did you get around to testing this?
I am doing the Arlo mod but saw this thread too. Can you post a link to fuses to use with the DNA 30 chip that will provide the needed protection? Also, right after the fuses on the original post you have red LED's. Is that something that would be good to have on the Arlo mod? If so, there are small transistors going from the battery's positive connector to the LED. Any chance you could provide some info on them (if they are needed).
Thanks for posting all this info on here!
Is there any way someone can put up something similar to this:
http://mamumods.com/pics/arlo-wiring.png
Using the SI4477DY?
The fuses I used with the DNA 30 are listed in the Arlo tutorial. Also, the Littelfuse 7A smd fuses will work for both overcurrent and reverse polarity if using 1x on each batt for dual parallel batts (I believe bapgood tested this), but do not if using 2x in parallel on 1 batt (this I tested in this thread).
If you want to use fuses other than what I or bapgood have tested, then you will need to test yourself. Breadboard the works, then put the batts in backwards. Be prepared to
immediately yank the batts if they or the DNA start to get hot.
For dual parallel batts, you have to have a P-FET for each batt to protect each batt from reverse polarity. A common P-FET will not work for parallel batts to protect from reverse polarity.
P-FET #1:
Source Pins 1,2,3 wired to DNA + input (solder a wire across all 3 pins then solder the wire to DNA +)
Gate Pin 4 wired to Batt -
Drain Pins 5,6,7,8 wired directly to #1 Batt + (solder a wire across all 4 pins then solder the wire to Batt +)
P-FET #2:
Source Pins 1,2,3 wired to DNA + input (solder a wire across all 3 pins then solder the wire to DNA +)
Gate Pin 4 wired to Batt -
Drain Pins 5,6,7,8 wired directly to #2 Batt + (solder a wire across all 4 pins then solder the wire to Batt +)
Because the P-FET is tiny, I mount it on a host board (a small piece of veroboard), then do the wire soldering to the pins, then use heat shrink tubing over the FET and wiring.
To make it easier to wire to the DNA + input, you can connect the Source pin wiring from each P-FET together with a common wire, then wire the DNA + input with the other end of the common wire.
