Mad Scientist Posted July 23, 2015 Author Report Share Posted July 23, 2015 High current low Rds(on) FETs are apparently now cheap enough to use as reverse battery protection. Here's a simple circuit that at first glance looks like it will do the job: http://www.ti.com/lit/an/slva139/slva139.pdf I haven't yet selected an appropriate FET for this application so if anyone has suggestions, that will save us all a lot of time. It has been a while so I'm not up to date on what all is out there anymore. Cheers. Link to comment Share on other sites More sharing options...
Mad Scientist Posted July 23, 2015 Author Report Share Posted July 23, 2015 Oh, I guess the charger won't work if we do this. Sorry about that. Link to comment Share on other sites More sharing options...
John Posted July 23, 2015 Report Share Posted July 23, 2015 That will charge (and is more or less how we did it on the 40) the problem is the simplistic approach doesn't prevent charging in the battery reversed case (conducts through the body diode), doesn't protect in the one cell reversed case (pack voltage 4v) and doesn't protect the balancer taps. I have our solution down to 5 Fets but I am still not 100% happy with it. Link to comment Share on other sites More sharing options...
Mad Scientist Posted July 23, 2015 Author Report Share Posted July 23, 2015 John said:That will charge (and is more or less how we did it on the 40) the problem is the simplistic approach doesn't prevent charging in the battery reversed case (conducts through the body diode), doesn't protect in the one cell reversed case (pack voltage 4v) and doesn't protect the balancer taps. I have our solution down to 5 Fets but I am still not 100% happy with it. You're way ahead of me. Let us know when you've got it perfected. Sounds great! In the mean time, maybe just a diode & easily replaceable fuse to crowbar the pack. I guess the cell taps would still be an issue? Link to comment Share on other sites More sharing options...
Mad Scientist Posted July 23, 2015 Author Report Share Posted July 23, 2015 Well, I think I solved my own problem another way. I plan to make 3S packs using 18650s with a balance connector and polarized output connector on each pack. No user error really possible.. The 18650s are supposed to be kept together for life anyway. Might as well make it a marriage without possibility of divorce lol. Link to comment Share on other sites More sharing options...
tonyisballin Posted October 11, 2015 Report Share Posted October 11, 2015 Would it harm the board by having a battery backwards through the balance taps? I am making a dna, and I have no intention of using the usb charging. I do want RPP, would 3 n channels work? with the gates wired to the positives. Link to comment Share on other sites More sharing options...
vapealone Posted October 26, 2015 Report Share Posted October 26, 2015 John said:That will charge (and is more or less how we did it on the 40) the problem is the simplistic approach doesn't prevent charging in the battery reversed case (conducts through the body diode), doesn't protect in the one cell reversed case (pack voltage 4v) and doesn't protect the balancer taps. I have our solution down to 5 Fets but I am still not 100% happy with it. I hope that in the meantime you have found the ideal solution.BTW, I was thinking a simple n channel fet solution with gate attached to the last (first? anyway the one is connected to B-) battery only. Source would be the (-) of this battery and drain would be B- on the board.If I read it right VGS would be + only (and circuit closed there) if the polarity is right and the dV is 3* V bat or there is no dv at all between B- and B+.It sounded promising but I was a bit worried about the extra load attached to 1 cell only and any unbalance it might result. Besides, it would cut off only the main circuit and I don't know if any unwanted potential difference on the charging tab would do any harm even with main ground cut or not.Not to mention that I didn't bother to look into the charging at allTherefore I went for a simple external quick blow fuse and hope for the best Link to comment Share on other sites More sharing options...
Tpat591 Posted January 2, 2016 Report Share Posted January 2, 2016 Wondering if that ideal solution has been found for 3s series 18650 reverse battery protection. Wismec Rx200s will be failing in ever greater numbers due to various issues and their owners will be seeking to convert them to DNA200 when Wismec/Joyetech support lets them down on warranty repairs due to purchase from unapproved vendors. Might not be a bad idea to have a guide set up for them to include proper protection into the battery sled when they do since the RX200 sled did not incorporate the raised protection rings that the DNA200 sled did. Here is one recent example. Any help toward this goal would be appreciated by those soon to be affected. Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now