[time-nuts] HP 5370B dropping mains voltage

[Robert Atkinson]

My reply did not go to the group  due to finger trouble,

Out of phase drops (bucks) the voltage, in phase boosts it. If you want variable 
boost/buck use a center tapped variac across the mains and connect the 
primary (rated at half supply voltage, easy in 240V countries) of the fixed 
transformer between the center tap and winding. 
With a 
resistive load as the voltage is reduced, the load current 
reduces so you can do the sums easily. The units I've used it on are 
constant power so the current increases with reducing voltage. However 
it does not matter as we are not generating power. The POWER is the same
 either side of the transformer (ignoring the small transformer losses),
 only the voltage and current change. The transformer is just supplying 
current, it does not matter if it bucks or boosts the voltage. With 
constant load power and transformer, a buck will have have higher 
current at the supply side, a boost will have lower. With a fixed 
resistance load the situation reverses because the power changes with 
the square of the voltage. The maximum load current is set by the 
current rating of the transformer secondary. This is why you can boost 
say 220V to 230V with a 100VA transformer and drive a 2300VA load 
(10Ax10V =100VA, 10Ax230V=2300VA) Some companies actually market "power 
savers"
 that are just a buck transformer. These things
 only work with resistive loads, or to a small extent, induction motors.
 
For modern equipment with switch mode power supplies they just increase 
the losses.

On insulation, As others have pointed out, a quality transformer will have adequate insulation ratings. and there is less differential than normal between primary and secondary. The main issue on conventional transformers would be a short secondary to frame. Making sure the frame is grounded an input fused caters for this. I used Toroids which were tape wrapped. The metal plate they were mounted on is grounded.  At least one machine was subject to an individual UL inspection (we were a UK company selling world wide) at MIT (no, not the audiophools:-) That I attended. The UL inspector had no problem with the boost arrangement which was specifically discussed. We did have an intersting discussion on shortwave UV light exposure though. Never ground the top of the bolt holding down a toroid, It forms a shorted turn.

Robert G8RPI.



________________________________
 From: Mark C. Stephens <marks at non-stop.com.au>
To: Robert Atkinson <robert8rpi at yahoo.co.uk>; Discussion of precise time and frequency measurement <time-nuts at febo.com> 
Sent: Saturday, 6 July 2013, 22:39
Subject: RE: [time-nuts] HP 5370B dropping mains voltage
 

How Does that Work Robert?
I mean why out of phase?

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On Behalf Of Robert Atkinson
Sent: Sunday, 7 July 2013 12:57 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] HP 5370B dropping mains voltage

Hi Marki, 

Dropping the mains voltage is easy. Get a mains to low voltage transformer. Connect the primary across the mains and the secondary in series opposition (out of phase) with the mains supply. Foar example a 100VA 12V transformer will drop your mains to just under 238V with a maximum load of 8A (the current rating of the secondary). 


HTH,
Robert G8RPI.



________________________________
From: Mark C. Stephens <marks at non-stop.com.au>
To: Discussion of precise time and frequency measurement <time-nuts at febo.com> 
Sent: Saturday, 6 July 2013, 13:25
Subject: Re: [time-nuts] HP 5370B Leds pulsing slowly, buttons selecting normally, PB ...


Hi Nigel, 


The only screw type electro can find is 29000uf at 10V. it's the same dimensions.
Should I risk the strain on the rectifiers (another 10Kuf is rather a lot)?
Without this timer I am dead in the water so I need to do the right thing here...

That's why I posted on the Agilent group too, I need to be sure that I do the right thing!

By the way, the failed electro measures 39uf :)

I reckon, the line voltage here is 250v and the equipment is set for 240V, that extra 10V on the mains is why I am having so much equipment failure.
Also the Heat sink on the 5370B got so hot I mounted a 5" fan across it to keep it at a respectable temperature.

How can I drop the Mains to 240V, I have a boat load of gear that needs to be powered concurrently.
(8566A, 8568B, 3585A, 5335A, 5370B, 8901A, etc, powered on together) we are starting to talk some serious current there.


-marki


-----Original Message-----
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