RE: [CAD_CAM_EDM_DRO] Transformer and voltage drop

When you buy quality transformers you get a load regulation figure or graph,
sadly most normal transformers don’t provide this data, and the cheaper the
transformers the worse it gets.

At one time because of the special machines used to wind toroids their
quality and load regulation were quite good but that has been changing over
the last few years.



As an example, I have a transformer used for valve heaters in an RF
amplifier, it is 7.1V at 150Amp. Off load it is a snitch over 7.1 volt, at
full load it is 7.1 volt, I don’t remember the regulation figure but the
percentage has many 9’s in it. I actually bough it many years ago thinking
off load there would be loads of voltage and I could use it as a cheap arc
welder. Then there is the other end of the market where it is not uncommon
to see output voltage half from off load to on load.



In the DIY CNC field, money is an important issue which sadly means some of
us are going to get thrown junk transformers.

Ask your supplier for load regulation details.



On my mill I need a 160V supply so I use a simple mains 240V to 110V 3.3KV
isolation power tool transformer, £33. It is centre tapped with the taps
hooked to earth, but if you use a two diode full wave rectifier circuit with
the centre tap it gives a nice 80V DC supply which is ideal for servo cards
like Gecko’s, and has very good load regulation.



Hope this helps Regs Mark



Dr. Mark Vaughan Ph'D. B.Eng. M0VAU

Managing Director

Vaughan Industries Ltd, reg in UK no 2561068

Water Care Technology Ltd, reg in UK no 4129351

Addr Unit3, Sydney House, Blackwater, Truro, Cornwall, TR4 8HH, UK.
Phone/Fax 44 1872 561288

RSGB DRM111(Cornwall)

_____

From: CAD_CAM_EDM_DRO@yahoogroups.com
[mailto:CAD_CAM_EDM_DRO@yahoogroups.com] On Behalf Of Anders Wallin
Sent: 02 July 2007 16:33
To: CAD_CAM_EDM_DRO@yahoogroups.com
Subject: [CAD_CAM_EDM_DRO] Transformer and voltage drop



Hi All,

I'm assembling a PSU for my servo setup.

It's a simple design:
- AC input, fuse, 2-pole switch, inrush-current limiter
- 1.8 kVA toroidal transformer w. 2x30 V secondaries
- rectifier bridge
- four 10 000uF caps

I'm testing it with various loads, and the DC voltage drop I'm seeing
looks surprisingly big. This is all explained in my blog at
http://www.anderswa
<http://www.anderswallin.net/2007/06/1800-w-80-v-psu-for-servos/>
llin.net/2007/06/1800-w-80-v-psu-for-servos/
(scroll down, there are pics in the comments too!)

Testing only the AC side (no rectifier and no caps) gives me a voltage
drop of around 0,7 V for every amp of current. But with the rectifier
and the caps connected I see 1.9 V of drop, which sounds quite big!

any ideas on what is going on here? Should I be worried, or is this
typical for large toroidal transformers?

thanks,

Anders





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