Topics

Power supply fuses

entilleser@...
 

The "Fix reverse polarity" section on ubitx.net suggests a 0.5A fuse for the "rig" and 2A fuse for the "finals," but does not specify which wire is which.  The schematic says that the brown wire is "PA-PWR," but I am too much of a newphyte to be certain if this means the same as "finals" or "rig."

ajparent1/KB1GMX
 

Finals, PA-PWR, output devices... the same.

The other is rest of rig.

PLEASE, put the fuses before the polarity protect diode.  Example Fuse, reverse polarity protection diode, radio.

Allison

Michael Hagen
 

Speaking of Fusing and Over-Current protection.

I am experimenting with an LT6108 for a Real Fast over current limiter.

The circuit show is my 2 PCB, the LT part is fussy about getting reset.

I have it Latch Up, so you power down to reset.

The ap note says less than 5uS to shut down.

I got new PCBs coming.  The first go around I could not get LT to reset, it needs a 10uS pulse to get out of over

current condition.  I have a tiny (SOT 23-6) Pic programmed to do that. 

The PCB is about 1 3/4" x 1 1/8".  Should fit on back inside panel somewhere where power comes in on most chassis?


So 5uS seems like a really fast fuse to me?

73's

Mike, WA6ISP


On 6/7/2018 12:14 PM, ajparent1/KB1GMX wrote:
Finals, PA-PWR, output devices... the same.

The other is rest of rig.

PLEASE, put the fuses before the polarity protect diode.  Example Fuse, reverse polarity protection diode, radio.

Allison

-- 
Mike Hagen, WA6ISP
10917 Bryant Street
Yucaipa, Ca. 92399
(909) 918-0058
PayPal ID  "MotDog@..."
Mike@...

Martin
 

I'm a newbie on here and just dipping my toe into the world of BITX's

If you're running the radio at 13.8v is there enough wriggle-room to cope with a 1.4v drop using a bridge rectifier?

Reverse polarity diodes are a blunt instrument when protecting equipment, you still have to find a replacement fuse if you're in the middle of nowhere.

I've used a bridge rectifier with the incoming 13.8v on the AC inputs and, whatever way round you connect it, you will always get the correct polarities on the +ve and -ve sides.

Martin

F1BFU - Fr - 79
 

Hello 

For my uBitx I use a Pacific Antenna kit named VoltTattler.
This montage has the following features:

- Simple through-hole construction
- Draws only around 1 mA in normal use. 
- Reverse polarity protection.
- Programmable Thresholds over a range of 4V to over 27V.
- Single button programming with audio feedback.
- Audible announces activation with power on and indicator with LED flashing green.
- Audibly announces by Morse code when input voltage exceeds user programmed thresholds.
- Flashing Red and Yellow LEDs indicate that a voltage limit has been exceeded.
- 3V digital status signals are available on a header
- Cheap protection for low voltage DC equipment.

interesting to avoid inversions of polarities and portable QRP, in battery operation to know the state of health of your batteries.

73 QRO from F1BFU

2018-06-07 21:10 GMT+02:00 entilleser via Groups.Io <entilleser@...>:

The "Fix reverse polarity" section on ubitx.net suggests a 0.5A fuse for the "rig" and 2A fuse for the "finals," but does not specify which wire is which.  The schematic says that the brown wire is "PA-PWR," but I am too much of a newphyte to be certain if this means the same as "finals" or "rig."


Jerry Gaffke
 

I think that bridge rectifier is a bad idea.
Leaves your rig antenna port ground a diode drop away from your power supply ground.
A single schottky power diode in series with the supply coming into the main ubitx 12v supply line
would be a better idea, fused at 1/2 Amp.  If you hook up the power supply wrong, it just won't work.
So hook it up right.
I would feed PA-PWR separately, without a diode, and fuse it separately at 3 Amps or so.


On Thu, Jun 7, 2018 at 12:53 pm, Martin / G4VZO wrote:
I'm a newbie on here and just dipping my toe into the world of BITX's

If you're running the radio at 13.8v is there enough wriggle-room to cope with a 1.4v drop using a bridge rectifier?

Reverse polarity diodes are a blunt instrument when protecting equipment, you still have to find a replacement fuse if you're in the middle of nowhere.

I've used a bridge rectifier with the incoming 13.8v on the AC inputs and, whatever way round you connect it, you will always get the correct polarities on the +ve and -ve sides.

Martin

Michael Hagen
 

Yes it should work fine,  might knock down the power a little. Would be better with 4 Schotky diodes.

They are going to HEAT!   Probably over a watt for each of the 2 conducting diodes.  On battery it would be quite a waste of power.

Another detail,  chassis radio ground and 12V - battery input are not common. but separated by a diode?

I put an extra fuse inside the cabinet and just a 1N4007 to ground.  Ty wrapped extra fuse to some wiring.  I have never blow it.


73's

Mike


On 6/7/2018 12:53 PM, martin@... wrote:
I'm a newbie on here and just dipping my toe into the world of BITX's

If you're running the radio at 13.8v is there enough wriggle-room to cope with a 1.4v drop using a bridge rectifier?

Reverse polarity diodes are a blunt instrument when protecting equipment, you still have to find a replacement fuse if you're in the middle of nowhere.

I've used a bridge rectifier with the incoming 13.8v on the AC inputs and, whatever way round you connect it, you will always get the correct polarities on the +ve and -ve sides.

Martin

-- 
Mike Hagen, WA6ISP
10917 Bryant Street
Yucaipa, Ca. 92399
(909) 918-0058
PayPal ID  "MotDog@..."
Mike@...

entilleser@...
 

Well, if you're going to use two fuses, don't you need two diodes?

Jerry Gaffke
 

All that PA-PWR goes to is the IRF510 drains.
There's an intrinsic diode from source to drain inside the IRF510 that will 
suck all the PA-PWR you care to give it if that supply line gets reversed.
Hopefully that will blow the 3A fuse.
If not, it will blow board traces and burn out the wire in the two RF chokes into the drains.
That damage is easily fixed, fixing a reverse voltage into the main 12v supply to the uBitx board is not.
Also, a  diode voltage drop into the main uBitx board is not an issue, even when running form a battery,
should do fine with 10 or 11 volts.

But a voltage drop feeding into the IRF510's will impact power out. 
So the fuse+shunt(intrinsic-irf510)diode scheme there is appropriate.

Jerry


On Thu, Jun 7, 2018 at 01:29 pm, <entilleser@...> wrote:
Well, if you're going to use two fuses, don't you need two diodes?

entilleser@...
 

In the event that the power supply voltage is reversed, the reverse polarity protection diode, as suggested by HFSignals, will short circuit the power supply.  If the power supply has a small enough fuse, the short circuit will cause that fuse to blow, which will disconnect the power supply, therefore protecting your uBitx.  However, if the fuse in the power supply is too large, the diode may burn out before the fuse does, resulting in the reversed polarity being applied to your radio, causing damage.  It seems to me the simplest solution is to put a 2A fuse in the ground line before the diode.  If the polarity is reversed, the diode will still short circuit the power supply, which will result in blowing the 2A fuse (and therefore disconnecting the power supply), rather than burning out the diode.  Then you don't have to rely on an unknown fuse in the power supply itself.

Jerry Gaffke
 

I'd put that fuse in the +12 line first. 
Easy to imagine supply ground having an alternate path through house wiring and RF ground rods,
vehicle sheet metal, etc.  I believe Allison once said she puts fuses on both +12v and ground,
which is more than I usually see.

Splitting it into two portions, fusing most of the rig at 0.5 Amps and the IRF510's at 3 Amps,
means you don't need a smoke inducing event within the main part of the uBitx to blow the 0.5A fuse.


On Thu, Jun 7, 2018 at 02:26 pm, <entilleser@...> wrote:
In the event that the power supply voltage is reversed, the reverse polarity protection diode, as suggested by HFSignals, will short circuit the power supply.  If the power supply has a small enough fuse, the short circuit will cause that fuse to blow, which will disconnect the power supply, therefore protecting your uBitx.  However, if the fuse in the power supply is too large, the diode may burn out before the fuse does, resulting in the reversed polarity being applied to your radio, causing damage.  It seems to me the simplest solution is to put a 2A fuse in the ground line before the diode.  If the polarity is reversed, the diode will still short circuit the power supply, which will result in blowing the 2A fuse (and therefore disconnecting the power supply), rather than burning out the diode.  Then you don't have to rely on an unknown fuse in the power supply itself.

K9HZ <bill@...>
 

Reversing diodes shorting/ blowing fuses and diodes in series with power leads, brute force, works but is quite unnecessary. See more far more elegant solutions at ubitx.net .

 

Dr. William J. Schmidt - K9HZ

Jerry Gaffke
 

I assume you were vaguely pointing in the direction of the relay trick, powering the coil through a diode.
That's a good solution, one I might use for a KW rig someday
Or even 100 Watts.
Though I'd still have a fuse.

For the uBitx, and me not being a mechanical engineer, diodes and fuses seem quite appropriate.
This rig has too many relays already.  ;-)


On Thu, Jun 7, 2018 at 03:07 pm, K9HZ wrote:
Reversing diodes shorting/ blowing fuses and diodes in series with power leads, brute force, works but is quite unnecessary. See more far more elegant solutions at ubitx.net .

Gary Anderson
 

Surprised someone has not mentioned using a P-channel power MOSFET for reverse polarity protection this low current application.
(I think someone has on an older thread that this is re-hashing)
You can find them with pretty low Rds these days.  ~ 0.06 Ohms.
That rivals the contact resistance of a relay, plus no power consumed by energizing coils.
(the power loss trade off is power consumed by the relay coils verses the difference between relay contact resistance and Rds)
We are talking < 500mA here. 

I quickly found an app note from TI.
http://www.ti.com/lit/an/slva139/slva139.pdf

Regards,
Gary
AG5TX

Jerry Gaffke
 

Be careful, how that PFET thing works is tricky.
Several "how I done its" are out on the web with the PFET in the schematic drawn backwards.
Here's some old threads on reverse polarity protection, everyone has an opinion, some have several.
These point to posts specific to the PFET, but there's plenty more in the threads.
    https://groups.io/g/BITX20/message/35632
    https://groups.io/g/BITX20/message/35434




On Thu, Jun 7, 2018 at 04:17 pm, Gary Anderson wrote:
Surprised someone has not mentioned using a P-channel power MOSFET for reverse polarity protection this low current application.
(I think someone has on an older thread that this is re-hashing)
You can find them with pretty low Rds these days.  ~ 0.06 Ohms.
That rivals the contact resistance of a relay, plus no power consumed by energizing coils.
(the power loss trade off is power consumed by the relay coils verses the difference between relay contact resistance and Rds)
We are talking < 500mA here. 

I quickly found an app note from TI.
http://www.ti.com/lit/an/slva139/slva139.pdf

Richard E Neese
 

on the 3 pin power plug on the ubitx the middle pin is the pa and the pin to the outside edge is the board power

Lee
 

From power jack to power switch.  From power switch through a 5 amp rectifier to 2 fuses, .5a and 3a.. From fuses to the board.  Reverse polarity protection and no blown fuses. The approximately .7 voltage drop of the 5 amp rectifier will not be noticed in your receive or your output to others.
--
Lee - N9LO  "I Void Warranties"

 

MVS Sarma
 

I humbly feel that the fuse should be for on the power input for the diode alone to ground and not on load side. I shall upload a sch soon.
regards
sarma
vu3zmv

Regards
MVS Sarma
 

On Fri, Jun 8, 2018 at 12:47 AM, Lee <mr.olson@...> wrote:
From power jack to power switch.  From power switch through a 5 amp rectifier to 2 fuses, .5a and 3a.. From fuses to the board.  Reverse polarity protection and no blown fuses. The approximately .7 voltage drop of the 5 amp rectifier will not be noticed in your receive or your output to others.
--
Lee - N9LO  "I Void Warranties"

 


MVS Sarma
 

apologies . The diode should be in reverse.


Regards
MVS Sarma
 

On Fri, Jun 8, 2018 at 5:46 AM, Mvs Sarma <mvssarma@...> wrote:
I humbly feel that the fuse should be for on the power input for the diode alone to ground and not on load side. I shall upload a sch soon.
regards
sarma
vu3zmv

Regards
MVS Sarma
 

On Fri, Jun 8, 2018 at 12:47 AM, Lee <mr.olson@...> wrote:
From power jack to power switch.  From power switch through a 5 amp rectifier to 2 fuses, .5a and 3a.. From fuses to the board.  Reverse polarity protection and no blown fuses. The approximately .7 voltage drop of the 5 amp rectifier will not be noticed in your receive or your output to others.
--
Lee - N9LO  "I Void Warranties"

 



MVS Sarma
 

The corrected diagram is here.