by "Iain Churches" <IainNG@[EMAIL PROTECTED]
>
Apr 22, 2008 at 02:58 PM
"Eeyore" <rabbitsfriendsandrelations@[EMAIL PROTECTED]
> wrote in message
news:480DCE41.51F03960@[EMAIL PROTECTED]
>
>
> Iain Churches wrote:
>
>> "Eeyore" <rabbitsfriendsandrelations@[EMAIL PROTECTED]
> wrote
>>
>> > What's the alleged advantage of limiting heater current ?
>>
>> Longevity
>
> The simplest method would be a series resistor that gets swiched out by
> a time-delayed relay. Any semiconductor based method will be complicated
> if it has to cope with ac heaters for sure.
Most people use DC heaters these days.
>
> There's also the problem of having to produce a different voltage to
> start with that's not compatible with existing transformer heater
> secondaries.
If the heater current regulator is to be part of the design, one can
specify
the heater winding to the appropriate voltage. This is not a problem.
If the regulation of the transformer is good, a properly specified
heater winding of 4.5V will give 6.3V DC with a 10 000µF
reservoir cap, and a lighter or heavier load will still fall within
the 5%.
The standard 6V3 winding would give 8.8V DC.
Iain
