Valley People Dynamite hum

[saint gillis]

https://groupdiy.com/index.php?action=dlattach;topic=44848.0;attach=11248

Hello just to share my experience repairing a dual 19" rack of these. I realized there was a hum at the output, but only when booth compressors were powered. Like if the power transformer was undersized. And in fact it is a 2x12VAC (120mA IIRC) instead of 2x18VAC 340mA  on the schematic.

The crazy thing is that it really looks like original design !

 

[JohnRoberts]

just guessing but back when these were sold, was your mains voltage 240V?  Is it now 230V? (Actually Belgium was probably 220V back then, should be better now).

Not a huge difference but perhaps enough to make the smaller transformer work, at the time, but not now.

JR

 

[saint gillis]

I'm not sure, I tried slightly more powerful transformers and it looks like we need too times the power to avoid voltage collapse...

 

[saint gillis]

BTW the datasheet says 220VAC, now Belgium is 230VAC, I don't now how much is was before.

 

[JohnRoberts]

BTW the datasheet says 220VAC, now Belgium is 230VAC, I don't now how much is was before.

Continental europe went from 220V to 230V, UK went from 240V to 230V.
======
If you need two times the PS current something seems wrong. Is it possible PS was for one unit, but now powering two?

JR

 

[Newmarket]

Continental europe went from 220V to 230V, UK went from 240V to 230V.

Yes but not really. The tolerance on the voltage  +10% -6% IIRC means that actual voltages didn't actually need to change to be in spec. In UK I typically measure a few volts over 240 at the wall outlet.

 

[JohnRoberts]

Yes but not really. The tolerance on the voltage  +10% -6% IIRC means that actual voltages didn't actually need to change to be in spec. In UK I typically measure a few volts over 240 at the wall outlet.

Yes, but as a manufacturer selling product into both markets, we were able to sell one 230V unit to both regions.

Before that many units had 220V/240V selector switches on the rear panel. I even had customers blowing up units from over voltage by plugging into 240V mains, with unit set for 220V. Since the customer is always right (even when wrong), we upgraded the breakdown voltage of the diodes that failed. Easier than explaining to the customer that they blew up their units.

JR

 

[Newmarket]

Yes, but as a manufacturer selling product into both markets, we were able to sell one 230V unit to both regions.

Yes. Standardisation has benefits. When is North America going to join in ?
Now wondering what they typically actually now get in mainland EU.

 

[JohnRoberts]

The US already has 240VAC in most homes for high current appliances.

JR

 

[Newmarket]

The US already has 240VAC in most homes for high current appliances.

Oh yes - that rings a bell now.
We are so used to thinking USA mains is always 110/120 V.
And most stuff I've worked on for a few years has had Universal Input spec 85 - 264 Vac.

I guess the text below that I just found on the interweb basically explains it ?

North American Voltage Ranges

In the United States and Canada, the electrical power supplied to most homes is from a split-phase system. That power enters your home at about 240 volts, that voltage is split at the main circuit breaker panel into two 120 volt halves. Those 120 volt halves are routed through the home to outlets.This 120 volt level is commonly referred to as 110, 115, 120, or 125 volts. Similarly, 220, 230, 240, and 250 volts are used to describe the higher voltage range. This higher voltage range is used to supply power to large appliances, such as washing machines, dryers, and large air conditioners. Buy why all the different numbers? And how should they be used when discussing voltage ranges?...

 

[JohnRoberts]

Oh yes - that rings a bell now.
We are so used to thinking USA mains is always 110/120 V.
And most stuff I've worked on for a few years has had Universal Input spec 85 - 264 Vac.

I guess the text below that I just found on the interweb basically explains it ?

North American Voltage Ranges

In the United States and Canada, the electrical power supplied to most homes is from a split-phase system. That power enters your home at about 240 volts, that voltage is split at the main circuit breaker panel into two 120 volt halves. Those 120 volt halves are routed through the home to outlets.This 120 volt level is commonly referred to as 110, 115, 120, or 125 volts. Similarly, 220, 230, 240, and 250 volts are used to describe the higher voltage range. This higher voltage range is used to supply power to large appliances, such as washing machines, dryers, and large air conditioners. Buy why all the different numbers? And how should they be used when discussing voltage ranges?...

Actually the power drop to most residences is 240VAC from a center tapped transformer winding (stepping down the higher voltage distribution from power lines).  Center tap to one leg is nominal 120V, center tap to other leg is also 120V with opposite polarity.

JR

 

[Walrus]

  Center tap to one leg is nominal 120V, center tap to other leg is also 120V with opposite polarity.

JR

Is the centre tap earthed or floating??

 

[JohnRoberts]

Is the centre tap earthed or floating??

The center tap is bonded to neutral in the service panel, and earthed via a ground rod.

JR

 

[PRR]

> Is the centre tap earthed or floating??

JR is correct what (should be) wiring in the fusebox.

The CT of the transformer, typically on the street, is bonded to the "neutral" of the 13KV line, which (should be) earthed every so-many poles. This to divert lightning from damaging the 13KV line, but incidentally keeping all customers "near earth". (Street-wire "neutral" is never a true neutral, there's always some potential on it.) If you run a transmitter, or keep cows, you need to provide your own dirt-rods in excess of the minimum required at each building service.

 

[saint gillis]

Here are the pics of the original transformer :

Here's the one I've painfully put instead :

  No more hum !

 

[JohnRoberts]

Good job... small US companies (like Valley People) selling SKUs into foreign markets often have to source specialized power transformers in small quantity. Even if the small company tests their transformers with 240 VAC, 60Hz is easier on power supplies than 50 Hz.

JR

PS At Peavey we rigged up 50 Hz 220-240 VAC mains bench supplies for testing modest power skus but testing high power amps at 50 Hz was more involved. 

 

[pvision]

Quite a lot of the US-made stuff I see hums (mechanically) like fury when powered up in the UK. The awful undersized transformers in some kit just makes it worse

I looked for a replacement for the same model of Dynamite and came up dry. I just couldn't find anything which would fit the cutout in the PCB and stay within the height of a 1U high case. Non-toroidal transformers with flying leads seem unavailable in Europe

Nick Froome

 

[saint gillis]

This one I got from TME is ok, 14VA, it should not be bigger than it, 24mm height and 57x68mm. Lots of mecanical vibrations though... but with a piece of foam between it and the top cover it is acceptable.