Re: reverse polarity protection (

MVS Sarma

Here is a more meaningful diagram

On Wed, Aug 8, 2018 at 4:17 PM Mvs Sarma <mvssarma@...> wrote:
I got your point Mike
 I shall upload a suitable diagram with jack more understandable.

On Wed, Aug 8, 2018 at 1:17 PM Mike Woods <mhwoods@...> wrote:
MVS Sarma

It is the drawing of the jack that people are referring to, not the positioning of the fuse!
The vertical bar would normally represent the sleeve - and you have this connected to the fuse and on to +12v?   Shouldn't the sleeve and the tip be reversed in the diagram?  Or do you normally have the sleeve positive and the tip negative (some people do - but most don't) in which case the diode is shown incorrectly!


On 8/08/18 12:34 AM, Mvs Sarma wrote:
Sarma surely responds.
 The reverse protection diode has been shown in the ubitx sch , both v3 and v4 perhaps.
 I would only suggest that let us have a fuse in series to dc of say 5 amps. the reverse diode would sit after the fuse to ground.
 Any accidental reverse connection , the fuse would blow and reverse voltage would not continue to the actual circuit, once fuse blows.

MVS Sarma

On Tue, Aug 7, 2018 at 1:56 PM, Mike Woods <mhwoods@...> wrote:

I will add PH2LB's reverse voltage protection solution to that page at your suggestion.  I hadn't noticed that idea previously, but did recognise the distinctive build so I guess it is on somewhere.

I am not sure about the diagram from MVS Sarma.  Let's wait and see whether he responds?   He may care to redraw the diagram if he agrees!  Everybody seems to draw those sockets differently ...



On 7/08/18 2:58 AM, Jonathan Washington wrote:
Hi there,

In wiring my µBITX based on the guides and notes available at,, this group's wiki, and the like, I noticed a discrepancy related to reverse polarity protection.

I believe the diagram with included fuse by MVS Sarma at has the jack wired in reverse (- tip, + sleeve) of the standard (+ tip, - sleeve).  I suppose wiring it this way could be a good way to test if the fuse will do its job!

I should note that this solution seems preferable to the solution(s) provided in W4RJP's wire-up diagram (v1.9) posted at , where it looks like the fuse and the diode would both blow in the case of reverse voltage, and the reverse voltage would still flow through the µBITX.  In MVS Sarma's solution, my understanding is that only the fuse would blow, and the µBITX wouldn't be exposed to any reverse voltage.

Also, I wonder if Mike might consider adding to the reverse polarity page PH2LB's reverse polarity protection solution from here:

I haven't tried it yet, but it seems ridiculously simple, and reasonably effective.  I'd probably still want to add a fuse with that solution, though, to protect against accidental shorts.

Jonathan, KD5CFX

Mike Woods

Mike Woods

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