[Elecraft] KBT2 charging question

[Douglas Todd]

Take a look at the charging specifications from the datasheet:

http://www.powerfactorinc.com/Batteries/ps-1229.htm

It appears that the 100 - 200 mv drop across the shockey diode is 
acceptable. This lowers the 13.8 volt output from the power supply to 13.6 
to 13.7 volts. The float voltage can go as low as 13.5 volts across the 
battery terminals.



Doug (KE7GYQ)



----- Original Message ----- 
From: "Tom McCulloch" <thom2 at att.net>
To: <N2EY at aol.com>; <elecraft at mailman.qth.net>
Sent: Thursday, November 02, 2006 8:26 PM
Subject: Re: [Elecraft] KBT2 charging question


>I want to make sure I'm following this.  I
>
> need to see 13.8 volts immediately after the protective diode.  Is that 
> correct?
>
> Thanks
> Tom
> WB2QDG
> K2 1103
>
>
>
> ----- Original Message ----- 
> From: <N2EY at aol.com>
> To: <ncsailors at yahoo.com>; <elecraft at mailman.qth.net>
> Sent: Thursday, November 02, 2006 10:22 PM
> Subject: Re: [Elecraft] KBT2 charging question
>
>
>> In a message dated 11/2/06 11:50:28 AM Eastern Standard Time,
>> ncsailors at yahoo.com writes:
>>
>>
>>> Sounds like an Elecraft design glitch!
>>
>> It's not. It's actually a very good design.
>>
>>  Why would
>>>
>>> one want to adjust their DC 13.8VDC Astron, to make
>>> up for it?
>>
>> Because it's what is needed.
>>
>> Circuit needs a mod.
>>>
>>>
>> No!
>>
>> Elecraft rigs are, above all else, QRP CW rigs. They are meant to be as
>> portable as possible, which is why the small size and provision for 
>> internal
>> battery.
>>
>> The battery needs a certain voltage for charging. That's determined by 
>> the
>> type of battery used, and the power supply/charger must be adjusted to 
>> deal with
>> it, because the battery is not adjustable.
>>
>> The blocking diode is a special low-drop part, to waste the minimum of 
>> power.
>> It serves two purposes:
>>
>> 1) to protect the rig from reverse-polarity applied to the power input 
>> jack,
>>
>> 2) To prevent discharging the internal battery into an external load.
>>
>> In portable operation, and even at home, the diode prevents a lot of 
>> possible
>> problems. The design is very well thought out and needs no changes.
>>
>> There's nothing magic about 13.8 volts, btw,
>>
>> 73 de Jim, N2EY
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