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New KX3 reverse voltage smoke

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G4JQT

New KX3 reverse voltage smoke

Well I did it. Inadvertently got the +ve and -ve reversed. Loud buzz from PSU and smoke from KX3.

Surely D6 in the volts input should just stop everything from working if the polarity is reversed? So I don't understand what has happened.

I didn't actually switch it on so hopefully it isn't terminal and just enquires a new diode. If it is terminal, I'm really surprised it hasn't any protection.

Ian, G4JQT😒😭
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David Haines

Re: New KX3 reverse voltage smoke

Don't feel bad Ian. I reversed the polarity from the power supply, too.
After the smoke cleared and the smell went away, I called Elecraft
and after a few questions, service said send in my KX3. They called in a
couple days to thank me for sending the melted wire, but why did I send
the KX3, which was fine? They apologized, checked out the KX3, and
gave me a free replacement wire. Great company!

david, KC1DNY

On 9/5/2020 10:06 AM, Ian Liston-Smith wrote:

> Well I did it. Inadvertently got the +ve and -ve reversed. Loud buzz from PSU and smoke from KX3.
>
> Surely D6 in the volts input should just stop everything from working if the polarity is reversed? So I don't understand what has happened.
>
> I didn't actually switch it on so hopefully it isn't terminal and just enquires a new diode. If it is terminal, I'm really surprised it hasn't any protection.
>
> Ian, G4JQT😒😭
> ______________________________________________________________
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Mike Morrow-3

Re: New KX3 reverse voltage smoke

In reply to this post by G4JQT

The failure reported by G4JQT and the response of KC1DNY do not reflect what should happen when reverse polarity DC is applied to the KX3 or any other Elecraft rig. All have that series blocking diode (D6/CMS04 in KX3) that should prevent any significant reverse current flow and certainly should have prevented "smoke" and "melted wire" from developing. If indeed that is an accurate report, then an explanation from Elecraft should have been requested.

Something else aside from reverse polarity DC is being hidden in the picture being presented so far.

Mike / KK5F

-----Original Message-----

>From: David Haines <[hidden email]>
>Sent: Sep 5, 2020 9:17 AM
>
>Don't feel bad Ian. I reversed the polarity from the power supply, too.
> After the smoke cleared and the smell went away, I called Elecraft
>and after a few questions, service said send in my KX3. They called in a
>couple days to thank me for sending the melted wire, but why did I send
>the KX3, which was fine? They apologized, checked out the KX3, and
>gave me a free replacement wire. Great company!
>
>david, KC1DNY
>
>On 9/5/2020 10:06 AM, Ian Liston-Smith wrote:
>> Well I did it. Inadvertently got the +ve and -ve reversed. Loud buzz from PSU and smoke from KX3.
>>
>> Surely D6 in the volts input should just stop everything from working if the polarity is reversed? So I don't understand what has happened.
>>
>> I didn't actually switch it on so hopefully it isn't terminal and just enquires a new diode. If it is terminal, I'm really surprised it hasn't any protection.
>>
>> Ian, G4JQT
>> ______________________________________________________________

David Haines

Re: New KX3 reverse voltage smoke

I'm using the PowerWerx Power supply sold by Elecraft. I mixed up the
connections from the binding posts on the back of the power supply then
plugged the other end into the KX3. The KX3 was off. Next I turned on
the power supply. The wire melted, but I think I was able to disconnect
the KX3 right away, so it's possible nothing got into the KX3. Or maybe
the melting wire broke the connection -- I forgot to do a continuity
check on the wire. The KX3 seemed OK, but service said to return it anyway.

David KC1DNY

On 9/5/2020 11:26 AM, Mike Morrow wrote:

> The failure reported by G4JQT and the response of KC1DNY do not reflect what should happen when reverse polarity DC is applied to the KX3 or any other Elecraft rig. All have that series blocking diode (D6/CMS04 in KX3) that should prevent any significant reverse current flow and certainly should have prevented "smoke" and "melted wire" from developing. If indeed that is an accurate report, then an explanation from Elecraft should have been requested.
>
> Something else aside from reverse polarity DC is being hidden in the picture being presented so far.
>
> Mike / KK5F
>
> -----Original Message-----
>> From: David Haines <[hidden email]>
>> Sent: Sep 5, 2020 9:17 AM
>>
>> Don't feel bad Ian. I reversed the polarity from the power supply, too.
>> After the smoke cleared and the smell went away, I called Elecraft
>> and after a few questions, service said send in my KX3. They called in a
>> couple days to thank me for sending the melted wire, but why did I send
>> the KX3, which was fine? They apologized, checked out the KX3, and
>> gave me a free replacement wire. Great company!
>>
>> david, KC1DNY
>>
>> On 9/5/2020 10:06 AM, Ian Liston-Smith wrote:
>>> Well I did it. Inadvertently got the +ve and -ve reversed. Loud buzz from PSU and smoke from KX3.
>>>
>>> Surely D6 in the volts input should just stop everything from working if the polarity is reversed? So I don't understand what has happened.
>>>
>>> I didn't actually switch it on so hopefully it isn't terminal and just enquires a new diode. If it is terminal, I'm really surprised it hasn't any protection.
>>>
>>> Ian, G4JQT
>>> ______________________________________________________________
> ______________________________________________________________
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G4JQT

Re: New KX3 reverse voltage smoke

In reply to this post by Mike Morrow-3

In my haste to disconnect everything I didn't notice that the antenna was connected, and thus the chassis had a good earth. On close inspection there is a tiny burnt patch around the power supply plug and presumably that's what created the smoke. So I guess the reverse current went through the plug mountings on the board to earth and the reverse diode did its job.

There doesn't seem to be any serious damage to the board at the solder point to the plug, just a black spot that joint took the full force of the shorted current! I gently reheated that spot. Just hope there's not any overheated damage to any internal tracks.

Anyway, seems no obvious harm was done. This KX3 still received and transmits.

I have now replaced most of the original lead with a proper, clearly coloured red/black lead.

73,

Ian, G4JQT

________________________________
From: [hidden email] <[hidden email]> on behalf of Mike Morrow <[hidden email]>
Sent: 05 September 2020 16:26
To: [hidden email] <[hidden email]>
Subject: Re: [Elecraft] New KX3 reverse voltage smoke

The failure reported by G4JQT and the response of KC1DNY do not reflect what should happen when reverse polarity DC is applied to the KX3 or any other Elecraft rig. All have that series blocking diode (D6/CMS04 in KX3) that should prevent any significant reverse current flow and certainly should have prevented "smoke" and "melted wire" from developing. If indeed that is an accurate report, then an explanation from Elecraft should have been requested.

Something else aside from reverse polarity DC is being hidden in the picture being presented so far.

Mike / KK5F

-----Original Message-----

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k6dgw

Re: New KX3 reverse voltage smoke

K2/100, not KX3, and not a reverse polarity problem but just a
reminder: There are two 2-conductor cables in a KPA100 that reach down
and connect to the main K2 board. The connectors are identical and the
cables are long enough that either will reach to either RF board
connector. If you cross them, you will short the 12V bus on the RF board
and will likely burn through a trace.

Reporting for a friend, [:=)

73,

Fred ["Skip"] K6DGW
Sparks NV DM09dn
Washoe County

On 9/5/2020 10:20 AM, Ian Liston-Smith wrote:

Alan - G4GNX

Re: New KX3 reverse voltage smoke

In reply to this post by G4JQT

I don't understand why the antenna being connected provided a path to
ground for the supply.

If that really is the case, there would seem to be a fault with your
power supply. The secondary (low voltage) side of a PSU should never be
connected to ground. Both poles should always 'float'.

I'd be very surprised if Elecraft had connected the negative supply to
chassis ground inside the KX3 either.

73,

Alan. G4GNX

------ Original Message ------
From: "Ian Liston-Smith" <[hidden email]>
To: "[hidden email]" <[hidden email]>; "Mike Morrow"
<[hidden email]>
Sent: 05/09/2020 18:20:44
Subject: Re: [Elecraft] New KX3 reverse voltage smoke

>In my haste to disconnect everything I didn't notice that the antenna was connected, and thus the chassis had a good earth. On close inspection there is a tiny burnt patch around the power supply plug and presumably that's what created the smoke. So I guess the reverse current went through the plug mountings on the board to earth and the reverse diode did its job.
>
>There doesn't seem to be any serious damage to the board at the solder point to the plug, just a black spot that joint took the full force of the shorted current! I gently reheated that spot. Just hope there's not any overheated damage to any internal tracks.
>
>Anyway, seems no obvious harm was done. This KX3 still received and transmits.
>
>I have now replaced most of the original lead with a proper, clearly coloured red/black lead.
>
>73,
>
>Ian, G4JQT
>
>________________________________
>From: [hidden email] <[hidden email]> on behalf of Mike Morrow <[hidden email]>
>Sent: 05 September 2020 16:26
>To: [hidden email] <[hidden email]>
>Subject: Re: [Elecraft] New KX3 reverse voltage smoke
>
>The failure reported by G4JQT and the response of KC1DNY do not reflect what should happen when reverse polarity DC is applied to the KX3 or any other Elecraft rig. All have that series blocking diode (D6/CMS04 in KX3) that should prevent any significant reverse current flow and certainly should have prevented "smoke" and "melted wire" from developing. If indeed that is an accurate report, then an explanation from Elecraft should have been requested.
>
>Something else aside from reverse polarity DC is being hidden in the picture being presented so far.
>
>Mike / KK5F
>

ANDY DURBIN

New KX3 reverse voltage smoke

In reply to this post by G4JQT

"If that really is the case, there would seem to be a fault with your power supply. The secondary (low voltage) side of a PSU should never be connected to ground. Both poles should always 'float'."

Many of the currently marketed small switching supplies have the same internals and only differ in branding, rear connectors, and metering. I own two Jetstream switching supplies and there quite a few "badge engineered" power supplies that use the same internals.

These power supplies most certainly do have the negative output terminal connected to chassis and mains supply ground. No, you can't isolate the output terminal.

I was remined that the negative terminal is not isolated when I used one of these power supplies to drive the reversible DC motor that tunes my magnetic loop. One direction works ok, the other direction lets smoke out of the wires. If you want to feed reversible polarity DC up the coax using a pair of bias T then the PSU better be isolated!

Opinions on whether PSU output terminals should float seem to be quite stong so I expect a protracted debate.

73,
Andy, k3wyc
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Alan - G4GNX

Re: New KX3 reverse voltage smoke

In which case I maintain my original point that the PSU is faulty, but
it would seem to be by bad design rather than a developed fault.

Whilst the mains ground is there for safety, if there was a ground
fault, it's quite possible that high voltage/current could be applied to
the PSU low voltage side and cause untold damage, a fire or even death.
If I had bought a PSU connected like that, I would return it if
possible, otherwise it would be in the trash!

Apart from the perceived PSU fault, have Elecraft really connected the
-ve input terminal to chassis? That would kinda negate the use of the
reverse polarity diode. The KX3 circuit diagram is not entirely clear.

73,

Alan. G4GNX

------ Original Message ------
From: "Andy Durbin" <[hidden email]>
To: "[hidden email]" <[hidden email]>
Sent: 05/09/2020 19:59:14
Subject: [Elecraft] New KX3 reverse voltage smoke

>"If that really is the case, there would seem to be a fault with your power supply. The secondary (low voltage) side of a PSU should never be connected to ground. Both poles should always 'float'."
>
>Many of the currently marketed small switching supplies have the same internals and only differ in branding, rear connectors, and metering. I own two Jetstream switching supplies and there quite a few "badge engineered" power supplies that use the same internals.
>
>These power supplies most certainly do have the negative output terminal connected to chassis and mains supply ground. No, you can't isolate the output terminal.
>
>I was remined that the negative terminal is not isolated when I used one of these power supplies to drive the reversible DC motor that tunes my magnetic loop. One direction works ok, the other direction lets smoke out of the wires. If you want to feed reversible polarity DC up the coax using a pair of bias T then the PSU better be isolated!
>
>Opinions on whether PSU output terminals should float seem to be quite stong so I expect a protracted debate.
>
>73,
>Andy, k3wyc
>

David Woolley (E.L)

Re: New KX3 reverse voltage smoke

In reply to this post by Alan - G4GNX

I'd definitely expect the chassis ground to have a low impedance
connection to the negative power supply rail, and normally that would be
a DC connection. Without it the screening of internal circuitry would
be less effective.

The K2 definitely has a DC path from supply negative to the case.

I'd also expect any power supply large enough to require a ground
connection, and eventually have exposed voltage output rails, to have
ground connected to one. Without that, capacitive leakage can generate
a significant electric shock hazard, or even cause damage when the
powered equipment is being interconnected with equipment on another
power supply.

If the safety earth rises significantly above that of other conducting
items during a fault, there is a defect in earth bonding in the
installation as a whole, that needs urgent rectification.

--
David Woolley
Owner K2 06123.

On 05/09/2020 19:32, Alan - G4GNX wrote:
> I don't understand why the antenna being connected provided a path to
> ground for the supply.
>
> If that really is the case, there would seem to be a fault with your
> power supply. The secondary (low voltage) side of a PSU should never be
> connected to ground. Both poles should always 'float'.
>
> I'd be very surprised if Elecraft had connected the negative supply to
> chassis ground inside the KX3 either.

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David Woolley (E.L)

Re: New KX3 reverse voltage smoke

In reply to this post by Alan - G4GNX

See page 3 of
<https://ftp.elecraft.com/KX3/Manuals%20Downloads/KX3SchematicDiagramDec2012.pdf>
for confirmation that the KX3 chassis is connected to the the same
network as the negative supply to the internal components.

On 05/09/2020 19:32, Alan - G4GNX wrote:
> I'd be very surprised if Elecraft had connected the negative supply to
> chassis ground inside the KX3 either.

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Dave Johnson

Re: New KX3 reverse voltage smoke

In reply to this post by G4JQT

Many items of radio equipment are supplied with a fuse in both the +ve and
-ve leads to avoid damage from missing return connections in vehicle
installations, as well as providing a fuse if the -ve rail is accidentally
connected to a +ve power supply point, where -ve at the supply connects to
ground.

Some mobile radios had a “fuse” from their power socket -ve point to
chassis inside the radio, this was a short length of tinned copper wire to
protect the wiring in case of reversed connections. I replaced a lot of
those fused links when I worked for a mobile radio manufacturer.

73 Dave G4AON
--
Sent from my iPhone SE
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Mike Morrow-3

Re: New KX3 reverse voltage smoke

In reply to this post by G4JQT

Yes, it's "surprising" how much surprise there seems to be that the KX3 (and almost any other ham rig) DC power connector's negative terminal connects ultimately to the case.

Let me "flog a dead horse". This whole affair amounts simply to this:

1. The KX3 case and the power supply's negative output were tied together through an owner-established conduction path that was independent of the KX3 power cable.
2. The KX3 power cable was carelessly installed such that power supply positive output was on the KX3 power connector's negative terminal.
3. When the KX3 power connector was applied to the KX3, the power supply's positive terminal was shorted to its negative side through the power cable and KX3 case and whatever external conduction path the owner had established between the KX3 case and power supply negative.

The KX3's D6 polarity protection diode did not come into play in any manner.

It is common good practice for DC power cables to have fuses in BOTH the positive AND the negative leads. That would have prevented power cable damage here.

Mike / KK5F

-----Original Message-----

>From: David Woolley <[hidden email]>
>Sent: Sep 6, 2020 7:14 AM
>
>See page 3 of
><https://ftp.elecraft.com/KX3/Manuals%20Downloads/KX3SchematicDiagramDec2012.pdf>
>for confirmation that the KX3 chassis is connected to the the same
>network as the negative supply to the internal components.
>
>On 05/09/2020 19:32, Alan - G4GNX wrote:
>> I'd be very surprised if Elecraft had connected the negative supply to
>> chassis ground inside the KX3 either.

Rich NE1EE

Re: New KX3 reverse voltage smoke

On 2020-09-06 09:26:-0400, Mike Morrow wrote:
>Yes, it's "surprising" how much surprise there seems to be that the KX3 (and almost any other ham rig) DC power connector's negative terminal connects ultimately to the case.

So I don't routinely get into this level of ham gear assembly...but I find that I am increasingly going there.
When I read "DC power connector's negative terminal", I immediately think of + and - rails, and a neutral ground. I do understand that when I look at barrel connector, the icon usually shows a + and - terminal. But it seems to me that the - terminal is really ground...not a negative rail.
I can see how, even with my terminology, swapping leads on a power connector can lead to shorting + to ground.
So are we really saying that the case is connected to ground, when we say negative terminal?

>Let me "flog a dead horse". This whole affair amounts simply to this:

I understand the SOE that led to this event....I am only addressing nomenclature. But thanks for succinctly summarizing...

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