Re: Remote Power Supply Connection

Trevor Wilson wrote:
> "Ian Thompson-Bell" <ruffrecords@[EMAIL PROTECTED]
> wrote in message 
> news:g0rmo0$27co$1@[EMAIL PROTECTED]
>>
>>
>> I agree when the rectifiers are close to the transformer supplying them

>> but not when they are separated from it my a couple of metres of cable.
> 
> **And again, it is not difficult, nor expensive to deal with such
issues. A 
> handful of capacitors will effectively deal with any problems.
> 
> 

Definitely not. The point is that the caps normally used to suppress 
reverse spikes in semiconductor diodes do just that. The have no effect 
on the forward current spikes which are significant. With remote ac 
supplies these current spikes must pass through the cable and they will 
cause serioes radiation. Any attempt to stop them happening will simply 
stop the rectifiers from rectifying. That is why is is essential to have 
the rectifiers close to the transformer.
>>>>>>>> http://www.arcadvisor.com/faq/dc_direct_current_arc.html
>>>>>>>>
>>>> This clearly shows that at low currents (e.g HT currents) and high
>>>> voltages (e.g.HT voltages) dc arcing is very unlikely to occur.
>> **Remind me: How much energy is able to be stored by large (unstated 
>> values)
>> capacitors?
>>
>> 0.5*C*V^2
>>
>> In a 100uF capacitor at 300V that's a mere 4.5 joules. Not worth
worrying 
>> about.
> 
> **Points:
> 
> * 4.5 joules is a substantial amount of energy. 

No it isn't. it is 4.5 watts for one second.

My small rotary hammer drill
> is rated at 2.5 joules per strike and can pulverise bricks.

And there you have hit the nail on the head. It is not the *amount* of 
energy but the *rate* at which it is consumed that matters. 4.5 joules 
in one mS is 4500 watts. And that is the key to making dc connections
safe.

Cheers

Ian