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KX3 charger failure?

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István Szabó

KX3 charger failure?

When I plug in the 13.8V PS the radio shows 13.8V for only 1 second and
drops to 10.4V. Eneloop batteries all OK 1.29V individually. Running a 4
hour charging cycle it turns off when voltage reached and shows the
dropped voltage. When batteries removed the voltage shown on display 13.8V.
Is it known failure, what can I do to fix it?
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Don Wilhelm

Re: KX3 charger failure?

Istvan,

There are protective diodes in series with both the internal batteries
and the external supply, so the fact that the KX3 shows 0.3 to 0.4 volts
lower than the external supply is normal.

73,
Don W3FPR

On 10/8/2020 2:53 AM, István Szabó wrote:
> When I plug in the 13.8V PS the radio shows 13.8V for only 1 second and
> drops to 10.4V. Eneloop batteries all OK 1.29V individually. Running a 4
> hour charging cycle it turns off when voltage reached and shows the
> dropped voltage. When batteries removed the voltage shown on display 13.8V.
> Is it known failure, what can I do to fix it?
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István Szabó

Re: KX3 charger failure?

Don,
This value is shown when the 13.8V PS is connected. It had shown the PS
value before, have I missed something?
73, István HA4ZD

On Thu, 8 Oct 2020 at 15:58, Don Wilhelm <[hidden email]> wrote:

> Istvan,
>
> There are protective diodes in series with both the internal batteries
> and the external supply, so the fact that the KX3 shows 0.3 to 0.4 volts
> lower than the external supply is normal.
>
> 73,
> Don W3FPR
>
> On 10/8/2020 2:53 AM, István Szabó wrote:
> > When I plug in the 13.8V PS the radio shows 13.8V for only 1 second and
> > drops to 10.4V. Eneloop batteries all OK 1.29V individually. Running a 4
> > hour charging cycle it turns off when voltage reached and shows the
> > dropped voltage. When batteries removed the voltage shown on display
> 13.8V.
> > Is it known failure, what can I do to fix it?
>

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Rich NE1EE

Re: KX3 charger failure?

I am missing a point:
Istvan said When I plug in the 13.8V PS the radio shows 13.8V for only 1 second and drops to 10.4V.
Don replied so the fact that the KX3 shows 0.3 to 0.4 volts lower than the external supply is normal.

Istvan said When batteries removed the voltage shown on display 13.8V.

I don't have a KX3, but I understand the diode issue..and it makes sense...but a drop from 13.8 to 10.4 doesn't seem right to me.

On 2020-10-08 18:56:+0200, István Szabó wrote:

>On Thu, 8 Oct 2020 at 15:58, Don Wilhelm <[hidden email]> wrote:
>
>> Istvan,
>
>> There are protective diodes in series with both the internal batteries
>> and the external supply, so the fact that the KX3 shows 0.3 to 0.4 volts
>> lower than the external supply is normal.
>
>> 73,
>> Don W3FPR
>
>> On 10/8/2020 2:53 AM, István Szabó wrote:
>> > When I plug in the 13.8V PS the radio shows 13.8V for only 1 second and
>> > drops to 10.4V. Eneloop batteries all OK 1.29V individually. Running a 4
>> > hour charging cycle it turns off when voltage reached and shows the
>> > dropped voltage. When batteries removed the voltage shown on display
>> 13.8V.
>> > Is it known failure, what can I do to fix it?

Rich NE1EE

Re: KX3 charger failure?

I just downloaded the schematic from the Elecraft site. I think this style of schematic, while space-saving, is difficult to read.
On p 9 @ B5, please find J1.
9-15VDC.
There you will see D6. I was expecting a different circuit, one that fed BAT+ and 15V+ each through a diode. That would provide a diode drop for each device, and provide reverse polarity protection.

If you are supplying 13.8V, the KX3 should report about 0.3-0.4V less. These are likely low forward drop diodes.

Even so, I am guessing that this is the correct place to look. Your problem suggests that if the voltage drops when good batteries are inserted, and pops back to 13.8Vdc when they are disconnected, then the problem might be in the charging logic. Some device may be making active choices for when to charge and when not to, and how much.

More than that is out of my league...

On 2020-10-09 00:23:+0200, István Szabó wrote:

>Rich, this is correct. I do not see diode on the charger board circuit diagram. I am lost.
>73, István
>
>On Thu, 8 Oct 2020 at 20:33, Rich NE1EE <<mailto:[hidden email]>[hidden email]> wrote:
>I am missing a point:
>Istvan said When I plug in the 13.8V PS the radio shows 13.8V for only 1 second and drops to 10.4V.
>Don replied so the fact that the KX3 shows 0.3 to 0.4 volts lower than the external supply is normal.
>
>Istvan said When batteries removed the voltage shown on display 13.8V.
>
>I don't have a KX3, but I understand the diode issue..and it makes sense...but a drop from 13.8 to 10.4 doesn't seem right to me.
>
>On 2020-10-08 18:56:+0200, István Szabó wrote:
>>On Thu, 8 Oct 2020 at 15:58, Don Wilhelm <<mailto:[hidden email]>[hidden email]> wrote:
>>
>>> Istvan,
>>
>>> There are protective diodes in series with both the internal batteries
>>> and the external supply, so the fact that the KX3 shows 0.3 to 0.4 volts
>>> lower than the external supply is normal.
>>
>>> 73,
>>> Don W3FPR
>>
>>> On 10/8/2020 2:53 AM, István Szabó wrote:
>>> > When I plug in the 13.8V PS the radio shows 13.8V for only 1 second and
>>> > drops to 10.4V. Eneloop batteries all OK 1.29V individually. Running a 4
>>> > hour charging cycle it turns off when voltage reached and shows the
>>> > dropped voltage. When batteries removed the voltage shown on display
>>> 13.8V.
>>> > Is it known failure, what can I do to fix it?

Steve Gray

Re: KX3 charger failure?

In reply to this post by István Szabó

I had exactly the same symptons as the OP just a couple of weeks ago and it puzzled me too. With my KX3, the "cure" for this behaviour was to change the display settings from external voltage to internal voltage. I think that the radio displays a default reading first and then changes during its boot up procedure dependent upon how you have it configured?

Apologies if I'm off target here- I've just endured an hour and a half trying to work out how to post a reply and I'm still not sure! My bad I guess?

Steve, G4VRR.

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