Hello-
Possibly it is just my own peculiarities but I have struggled with understanding the current ratings on the HV secondaries of the Hammond 290 series power transformers. Nearly all secondaries are center tapped and used with full wave rectifiers whereby the center tap is grounded. An example is the 290-DX that shows a HV secondary 650 VCT at 230 mA. Since in nearly all cases the center tap is grounded the secondary will supply 1/2 the voltage. In my feeble mind, since this is the common usage, I felt like the secondary power rating was for only half the voltage. But a conversation today with a Hammond engineer gave me a surprise. I was told, in no uncertain terms, that in all 290 series transformers the HV secondary current rating is at the full winding voltage. In other words, the 290-DX HV secondary is rated for 650 volts at 230 mA (leaving center tap unused/floating such as with a bridge rectifier). I was originally thinking the secondary winding current rating of 230 mA was for only using a full wave rectifier with the center tap grounded (thus yielding 1/2 the voltage).
What brought this to light with me was the use of the 290-HX which is the replacement for the Marshall JCM800 100 watt series. Attached is the 290-HX datasheet. It shows a 350 VCT HV secondary rated at 420 mA. In the Marshall power supply the center tap is unused and left floating; a bridge rectifier is used. Thus the full voltage of secondary is used in this case, very much out of the norm for most designs.
One of the things that helped confuse me was the maximum primary current rating shown on data sheet. This specification is not the loaded primary current. It is the primary excitation current. I was looking at this current figure thinking it was related to maximum current allowed in the primary during use, thus yielding power capability.
I was surprised that the 290 series HV secondary current rating is for the full secondary voltage. But after learning this let me ask - - in the case of the 290-DX with the 650 VCT at 230 mA HV secondary. This represents 149.5 watts of power. Is is correct to say that if using this secondary with a full wave rectifier/center tap grounded, at 1/2 the voltage, that the current draw could be increased in order to yield the same power? I am suspicious that the current rating would probably still be near the 230 mA rating even at 1/2 the voltage due to wire size in transformer or principles of operation in the transformer.
I asked Hammond if they could clarify this in their 290-series product info description, and give VA ratings on these transformers.
Just looking for a little help clearing these clouds out of my head!
Thanks all.
Topic: Hammond 290 Series Ratings (Read 2997 times)