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Registered Member #55205
Joined: Mon Jun 08 2015, 06:06AM
Location:
Posts: 15
I was just given a 1000w HID ballast, I was wondering If it would be any good to use as a power supply for a small to medium SSTC? I believe the output is around 400-485v ...
Obviously I am talking about just the transformer, minus cap and igniter.
Aside from that I just got my first SSTC working using a PLL driver :D
Registered Member #55205
Joined: Mon Jun 08 2015, 06:06AM
Location:
Posts: 15
Here is the beast next to my 1400va MOT.
Once rectified, I calc'd output to be approx 635vdc. Should I be looking for transistors with a min 1200v rating? or is that not important so long as max V is not exceeded? Output current seems to max out around 8a in short circuit according to the label. So I think(?) it should be plenty powerful enough? I have 2 900v 10 MFets left I'd like to not destroy, but willing to test with.. Should I just go for it?
Or could I provide 120v-in on the 240v pri. tap, increasing the primary winding ratio and get a lower output voltage? I am going to be using 120v input, so Thought that may help bring the voltage down to a happier medium.?.
Registered Member #46007
Joined: Wed Apr 30 2014, 08:02PM
Location: Walsall, UK
Posts: 36
Hi there, I believe that this wont work quite as you expect it to. These transformers provide a higher voltage open circuit but this is easily pulled down once the transformer is loaded at the specified 6.4A - 7.8A current
The lamps these run generally settle around the 120-130V mark once ignited and pull the current region specified. If you multiply these figures V * I you'll get the wattage indicated on the label. I don't know the exact design of these transformers but doubt they'd like running over 1Kw if they will indeed do so at all. I think they have a high leakage reactance which causes the secondary voltage to fall and current to limit which is desirable for running HID lamps.
Registered Member #4074
Joined: Mon Aug 29 2011, 06:58AM
Location: Australia
Posts: 335
As Chris has said, the autotransformer has a high open circuit voltage, but will rapidly drop as the load increases because its a shunted ballast. It might be possible to remove any iron shunts between the coils, which would increase the short circuit current and provide a slightly higher voltage for a given load. But that may well lead to overheating issues.
A lightweight alternative would be a voltage doubler, using only two capacitors and two diodes. That's what I'm using to provide a 650VDC bus from 230V mains. I like to use 600V rated devices for up to 325V input and 1200V devices for 650V, as is usually seen in commercial designs. You can push the voltage ratings much much further if reliability isn't a key goal :)
Registered Member #55219
Joined: Tue Jun 09 2015, 11:21PM
Location:
Posts: 80
Awesome guys, thanks for the replies .. As I said a buddy came by the other day and said I could have it for my projects.. I was hoping due to it's shear mass (32lbs) that it would be a good lower current hv supply.
Still trying to wrap my head around how the ballasting works.. So I do see the shunts, approx : 1/2" * 3/4" * depth : between the primary and secondary, one top one bottom. These are what limit the current?
This says Auto-Xfmr, so I assume the Cap and second neutral wire from primary side is what makes it into that config.?. I read up a little, and the Cap is for PFC as current starts to shift phase.
I do see what you are talking about with voltage drop now .. P = 1000w, Secondary short current = 8.9a ( on the high side ) So then P / I = V = 112v
My thoughts were to separate the 2 sides completely, Pri: Nothing to do.. Sec: 1) Cap wire is the low side of L2. This would become ground for L2 2) DO NOT use COM wire from Pri side..
Aside from the Shunts, this "should" bring it back into a standard xfmr Without the internal ballasting..?
I'd just hate to tear it apart to make a welder, but that's still an option too. Maybe even a Carbon Arc Furnace
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HID AutoTransformer Ballast
