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reverse polarity protection (ubitx.net)
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Jonathan Washington
Hi there, In wiring my µBITX based on the guides and notes available at hfsignals.com, ubitx.net, 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 https://ubitx.net/ubitx-fix-reverse-polarity-protection/ 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 https://groups.io/g/BITX20/wiki/UBITX-Assembly , 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
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ajparent1/KB1GMX <kb1gmx@...>
A while ago (months?) I stated that fuse first then diode is the preferred way.
You want the diode to block reverse voltage and the fuse to blow to keep from burning the diode open and destroying the radio. That needs to be get out to everyone. Allison
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Jonathan Washington
Thanks, Allison. Yes, I believe fuse-first, then diode is what MVS Sarma's solution does, once the reverse polarity of the jack is accounted for. The wiring diagram on this group's assembly page, however, seems to have no particular dependency. I guess the fuse would probably go first, assuming it reacts faster than the diode, but the µBITX would be exposed to the reverse voltage before the fuse blew, and the diode would blow too. But my understanding of this sort of stuff isn't terribly extensive, so someone probably needs to verify my assessment. Any suggestions? Jonathan, KD5CFX
On Mon, Aug 6, 2018 at 11:01 AM, ajparent1/KB1GMX <kb1gmx@...> wrote: A while ago (months?) I stated that fuse first then diode is the preferred way.
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Ralph Mowery
Around 1970 I repaired the CB radios for extra spending money. Many of the mobile 12 volt rigs had a fuse in line before the radio and a diode across the line inside the radio across the line. I repaired about a dozen or more where the diode had shorted and blew the fuse, but the radio was ok. The thing is that you use a fuse that is as low in amp ratings as you can. Many of the fuses were around 3 to 5 amps and the diode was rated for 1 amp. I did see one or two where someone had put a 20 amp fuse in it and the diode burnt open and the rig was beyond reasonable repair. de ku4pt
On Mon, Aug 6, 2018 at 11:07 AM, Jonathan Washington <kd5cfx@...> wrote:
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Mike Woods
Jonathan 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 ubitx.net 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 ... 73 Mike ZL1AXG ubitx.net
On 7/08/18 2:58 AM, Jonathan Washington wrote:
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w4rjp
Unfortunately, I did not make it clear about the DC power source fusing on the early wire-up version I gave Patrick for his stock Wiki. My assumption was that DC power source fusing would be ahead of the uBitx power jack and the reverse polarity protector.
The fast blow fuses shown on the wire-up diagram were me being overly cautious about the possibility of excessive current draw, mostly from the PA and had nothing to do with reverse polarity. In addition to the DC power source fusing I use Anderson Power Poles to insure the correct DC polarity. MVS Sarma fusing/reverse polarity is a better approach than what is recommended by HF Signals. Keep in mind a silicon diode is just a starting point for reverse polarity protection. Anyone acquiring, wiring, and using one of Farhan's great low cost radios should realize they are meant for experimenters and tinkers.
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MVS Sarma
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. Regards MVS Sarma
On Tue, Aug 7, 2018 at 1:56 PM, Mike Woods <mhwoods@...> wrote:
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MVS Sarma
the diode could be 1N540x a 3 amp device , as it is feared that diode might blow faster than fuse (rule of MURPHY !!)
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Bill Cromwell
Hi,
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I have been in and repaired radios (and other electronics) where that reverse diode has blown. The failure mode was dead short to ground so the rest of the gear was still protected. When one of my daughters married Dr. Murphy I thought I would get a break from Murphy's Law. But instead I get extra! 73, Bill KU8H
On 08/07/2018 09:34 AM, Mvs Sarma wrote:
the diode could be 1N540x a 3 amp device , as it is feared that diode --
bark less - wag more
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Jerry Gaffke
My preferred solution:
https://groups.io/g/BITX20/message/52904 The instructions for reverse polarity protecton on the uBitx WireUp page would be acceptable if they also showed a 3 Amp fuse in line with the +12v lead from the power supply. A large Schottky would be preferable to a 1n4007 if using a shunt diode like that, a 1n4007 at significant currents might have a forward voltage of a volt or more. The drawing at the top of the polarity protection page on ubitx.net is wrong and best ignored: https://ubitx.net/ubitx-fix-reverse-polarity-protection/ I see two issues with that drawing: 1) Jack has +12v going through the barrel of the connector, that's not typical. 2) If black is truly ground (as it should be on the provided wiring harness) then the shunt diode is reversed in the drawing For a shunt diode scheme like that, be sure to have a fuse in the +12v lead. A few people recommend a fuse in the ground lead too, but equipment grounding (3 wire plugs, RF ground rods, etc) can give a path around that ground lead fuse. I never bother. Jerry
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Jerry Gaffke
The hfsignals WireUp instructions for power into the rig at the top of http://www.hfsignals.com/index.php/ubitx-wire-up/
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have a symbol that looks like headphones. Some have mistaken it for a fuse, that's definitely the wrong position for a fuse. The label on that symbol says "On/Off", so we can assume it's a power switch. Here's an old post showing how I wired mine up: https://groups.io/g/BITX20/message/53016
On Tue, Aug 7, 2018 at 07:31 AM, Jerry Gaffke wrote:
My preferred solution:
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K5ESS
I agree with Jerry and that’s how I wired my uBitx up except I added a separate switch for the PA. Mike K5ESS
From: BITX20@groups.io [mailto:BITX20@groups.io] On Behalf Of Jerry Gaffke via Groups.Io
The hfsignals WireUp instructions for power into the rig at the top of http://www.hfsignals.com/index.php/ubitx-wire-up/ My preferred solution:
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Jerry Gaffke
Actually, I did the same.
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I'm mostly playing with it on the bench rather than using it. When poking at the first 95% of the transmitter, it's very handy to just shut down power to the IRF510's so you don't have to worry about them heating up. Jerry
On Tue, Aug 7, 2018 at 10:17 AM, K5ESS wrote: I agree with Jerry and that’s how I wired my uBitx up except I added a separate switch for the PA.
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The K9HZ solution on https://ubitx.net/ubitx-fix-reverse-polarity-protection/ is better. Nothing shorting out, blowing fuses, etc. Radio just doesn’t turn on until you get the polarity right.
From: BITX20@groups.io [mailto:BITX20@groups.io] On Behalf Of Jerry Gaffke via Groups.Io
My preferred solution: -- …_. _._
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Mike Woods
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! 73 Mike
On 8/08/18 12:34 AM, Mvs Sarma wrote:
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MVS Sarma
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:
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MVS Sarma
Here is a more meaningful diagram
On Wed, Aug 8, 2018 at 4:17 PM Mvs Sarma <mvssarma@...> wrote:
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Mike Yancey
I usually prefer the P-FET solution - prices have come down for these, around a buck per P-FET. No fuse to replace (if you're 'wrong') and nearly no voltage drop (when correctly connected). Also: consider Power Poles. Using Power Poles makes it *very* hard to mal-connect. Mike Yancey, KM5Z
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MVS Sarma
Very Nice concept to use a pFET, mike Yancey. I suppose, most power fets would have a reverse diode across Drain and Source. what happens of some one connects DC input in reverse, The diode takes on and sends the reverse voltage to the load not caring "gate control" . Please analyse and let us find a way.
On Wed, Aug 8, 2018 at 8:15 PM Mike Yancey <mikeyancey@...> wrote:
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Jerry Gaffke
Here's an old discussion about using a PFET for reverse polarity protection.
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https://groups.io/g/BITX20/message/35434 Useful, but how it works is confusing enough that it is often implemented incorrectly. Which makes it dangerous, especially for the hobbyist. For the uBitx, I prefer the solution of post 56141 Jerry, KE7ER
On Wed, Aug 8, 2018 at 10:20 AM, Mvs Sarma wrote:
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