Made 'slide chocke ballast' - what im doing wrong here? / High Voltage / Forums

Forums

4hv.org :: Forums :: High Voltage

« Previous topic | Next topic »

Made 'slide chocke ballast' - what im doing wrong here?

1 2 next

Move Thread

LAN_403

Kizmo

Fri Aug 17 2007, 07:43PM

Registered Member #599 Joined: Thu Mar 22 2007, 07:40PM
Location: Northern Finland, Rovaniemi
Posts: 624

I made slide choke ballast to calm down my MOT 8-pack which not surprisingly wants to draw over 100 amps @ load. But here i'm limited to around 23amps RMS so i thought to made adjustable ballast.

I made coil like this:
- wound on 50mm (2") PVC pipe
- coil height is 280mm (11")
- two AWG12 wires in parallel (i didn't want my inductive ballast to be heater element as well)
- 37 turns per layer, 6 layers -> 222turns total

I did few tests with just steel axle (tight fit) inside the PVC pipe but results weren't that impressive. Load current dropped only to 45amps (insane arcs though) but it popped 16amp breaker in seconds. I think my problem has something to do with the core im using?

Zum Beispiel

Fri Aug 17 2007, 08:17PM

Registered Member #514 Joined: Sun Feb 11 2007, 12:27AM
Location: Somewhere in Pirkanmaa, Finland
Posts: 295

I presume you are using a solid core? It is just probably saturating. Ideally you should use a laminated core made of transformer grade iron in there, but things like welding rods seem to work well too.

Kizmo

Fri Aug 17 2007, 08:20PM

Registered Member #599 Joined: Thu Mar 22 2007, 07:40PM
Location: Northern Finland, Rovaniemi
Posts: 624

Yep, that steel axle was quite solid :D

I need to go looking for welding rods next week

Sulaiman

Fri Aug 17 2007, 08:57PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

Not quite correct,
if a solid steel core saturates then probably a laminated one will too.
Transformer steel does saturate at a higher flux density than 'normal' steel,
but not much higher.
The reason laminated steel is used is to reduce eddy-current losses/heating in the core,
which are surprisingly large.

I haven't calculated it but 7220 amp.turns (222turns x 23Arms x SQRT(2))
does seem too high for a (guess) 1.5" diameter steel core.

If you post the diameter and length of the core I can give you an estimate of amp.turns for saturation.

Kizmo

Fri Aug 17 2007, 09:37PM

Registered Member #599 Joined: Thu Mar 22 2007, 07:40PM
Location: Northern Finland, Rovaniemi
Posts: 624

That core i tested was 290mm x 45mm

Sulaiman

Fri Aug 17 2007, 10:05PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

I haven't got my notes to hand at the moment - I'll have a look tomorrow.

Meanwhile;
I estimate that the core will saturate with about 60 Vrms at 60 Hz
So if you measure the voltage across the inductor with the MOTs connected
and it's less than 60 Vrms then it's probably not saturating.

The core will get hot due to eddy-current losses though, even if it's not saturating.

I'll try to give a fuller answer tomorrow.

Kizmo

Fri Aug 17 2007, 10:10PM

Registered Member #599 Joined: Thu Mar 22 2007, 07:40PM
Location: Northern Finland, Rovaniemi
Posts: 624

I just found this, here is about same size slide choke ballast as mine is, and it has 22A minimum setting. Does core material (or appereance) really effect that much?

EDIT:

Another thing came in my mind also, what if i just unwound that slide choke and wind that wire on quite large UI transformer core so that current is adjustable by airgap. I think that it would work much better.

Core is like this (i have 6 of these, one disassembled):

But how many turns? 200? 500? As many as fits?

Dr. Slack

Sat Aug 18 2007, 06:47AM

Registered Member #72 Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659

If you want to delay the popping of your breaker, while still drawing the high current through your choke and MOTs, then you could try power factor correcting the load. Motor run capacitors are fairly inexpensive, and available in much bigger capacity than MO caps.

Initially without the load connected, monitor the current as you add more and more capacitors in parallel across your supply. Keep adding caps until they draw nearly 16A, when your breaker should still be intact. They are actually drawing a current that leads the voltage waveform by 90 degrees, in contrast to your inductive load, which draws lagging current. As such, the current through the power factor caps increases the available load current and reduces the supply current. So if your load takes 45A, and the PFCs run 15A, that leaves only 30A, not 45A being supplied through the breaker, delaying its pop.

If you can add more ballast to get your load current down to 30A, then 15A PFC should allow 15A supply to run continuously.

Steve Conner

Sat Aug 18 2007, 10:39AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

With a solid steel core, it will be more of a resistive ballast due to the eddy current losses. I'd suggest looking for welding rods or fence wire to cut up, and rewiring your two parallel windings in series.

Kizmo

Sat Aug 18 2007, 12:04PM

Registered Member #599 Joined: Thu Mar 22 2007, 07:40PM
Location: Northern Finland, Rovaniemi
Posts: 624

If i make ballast using laminated UI transformer core, how big core i should use? I have 6 laminated UI cores @ 29.4cm^2 core area Im thinking to put 2 of those together to prevent saturation @ higher power. That would make UI core with 58.8cm^2 core area.

1 2 next

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob