Re: Remote Power Supply Connection

"Ian Thompson-Bell" <ruffrecords@[EMAIL PROTECTED]
> wrote in message 
news:g0up1a$1ap1$1@[EMAIL PROTECTED]
> 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.

**No.

 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.

**No.

>>>>>>>>> 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.

**Yes, it is. It depends on how long it takes to charge/discharge whatever

capacitance is on the other side of the connector. In 0.1 Sec, that is 45 
Watts. In 0.01 sec, that is 450 watts. Certainly plenty of energy to
damage 
surface treatment of most connectors. And, as I stated earlier, lots of 
builders use considerably more capacitance than 100uF and more than 300 
Volts for their power amps. 1,000uF and 700 Volts is not unheard of. And 
THAT is a considerable amount of energy.

>
> 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.

**EXACTLY my point. 4.5 joules consumed in 10msec is a *lot* of energy for

thinly plated connector to cope with.

 4.5 joules
> in one mS is 4500 watts. And that is the key to making dc connections 
> safe.

**Exactly. Which is why AC makes a good deal more sense.

Trevor Wilson