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Onan Magniciter Theory FAQ


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  #1  
Old 03-07-2008, 01:51:17 PM
Ted_Cool Ted_Cool is offline
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Default Onan Magniciter Theory FAQ

Thanks to several members for sending the Magneciter diagrams and schematics to me. Very Helpful!

After pondering the information on saturable core reactors here, and carefully looking over the schematic, I think I have the basic idea: ( 04SX and 06SX Magneciters )

1: The gate reactors limit the current supplied to the field. There are two, one for each half of the AC cycle. Each one only receives current in one direction. The magnetic flux in each reactor is always in the same direction.

2: The control windings of the gate reactors are wound to oppose the flux of the gate windings. Increased DC voltage on the control windings reduces the current flow through the gate windings by de-saturating the core.

3: The control windings are powered by the generator output. As the generator voltage increases, the control voltage increases.

4: The control reactor seems only to reduce the voltage/limit the current to the control rectifier. It is not magnetically coupled to the gate reactors. Just a big inductor.

5: The compound winding seems to be for core flux bias. It saturates the cores to move the saturation into the 'knee' of the saturation curve, where they will be most sensitive to control inputs. These are also wound to oppose the gate flux.

6: The calibrated shunt ( hand noted on my drawing as being for 06SX only ) seems to be used to set the current in the bias winding very low. The cores only need a little bias , not full field voltage.

Magneciters are pretty cool. Hard to break them, simple to trouble shoot.

Has anyone experimented with changing the values of the damping resistor to try and tighten it up? I'm thinking of replacing it with a 500 ohm rheostat and moving it around a little to see what happens. It's in parallel with the field, so it seems like there's little risk.

It seems like the optional voltage regulator filter would be a large capacitor placed at the output of the control rectifier to smooth out the control voltage. It must be pretty choppy there. Has anyone seen anything like that? The other alternative is to have the big cap right at the feed to the field. Maybe both places could use a little smoothing. Yes, I know about bleeder resistors. I don't want to weld screwdrivers or take a farad across my heart...
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  #2  
Old 03-07-2008, 07:35:29 PM
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BTPost BTPost is offline
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Talking Re: Magneciter Theory...

Ted, does this mean you are now going to be the "GO TO GUY" on Magniciter questions?
I am sure Jim and Gunny would like to have someone else field the Magniciter questions.
We could even get Harry to make a "Magniciter FAQ" just for you. The rest of us think
Magniciters, are just MAGIC.
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Bruce in alaska
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  #3  
Old 03-07-2008, 08:16:34 PM
Ted_Cool Ted_Cool is offline
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Default Re: Magneciter Theory...

Hmmm. There's not much that can go wrong with a magneciter, other than letting the very expensive blue smoke out of the reactor coils, or the much cheaper smoke out of the diodes. I'm always glad to help out!

Along that note - upon seeing the prices that Onan wants to replace the magneciter, I've decided that I will be adding fuses in line to both sides of the magneciter AC input. 10 amps should be about right. That should help to keep the magic smoke in where it belongs...
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Old 03-07-2008, 11:05:21 PM
Donald Randall Donald Randall is offline
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Default Re: Magneciter Theory...

Ted,
Wouldn't the field windings act as a choke and provide adequate filtering for the DC pulses, or is its inductance, (inductive reactance actually), too small to have much influence? If you have an operating unit, would it be a good idea to take, and make notes of, the voltages and currents of the: field windings, control windings, and each reactor winding separately, while the generator is running, unloaded or with a specific load,for future troubleshooting reference? Or does Onan supply some baseline values? I find very few specifics on voltage, current, and component values, or their functioning, in any of their manuals in my posession. If you figured out the operation of this unit only by studying the schematics, I am impressed. Don
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Old 03-08-2008, 12:09:50 AM
Donald Randall Donald Randall is offline
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Default Re: Magneciter Theory...

Did you notice that the reactor coils are phased oppositely? (Note the dots). I understand that they induce some voltage into the control windings, and being out of phase with each other, cancel out the effects of the induced voltage on the control voltage. Which I believe, is also why they each use only their particular half of the ac cycle. One half of the ac cycle has more influence than the other, so they use the one with the least influence on each coil. Don
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Old 03-08-2008, 02:52:56 PM
Ted_Cool Ted_Cool is offline
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Default Re: Magneciter Theory...

I haven't gone through and measured things yet, except the field voltage, around 40 volts at 30% load ( 10 KW single phase gen end ).

The reactor coils are phased oppositely, and the control windings are arranged so the control flux is always opposite the main ( gate ) flux - this provides the negative feedback mechanism.

I have reconsidered the purpose of the compound winding that loops through each of the reactor coils. I don't think it's a bias winding - those are only used when the control windings are fed AC. The magneciter control is DC. I also couldn't see anything like a calibrated shunt on my set, even though I have an 06SX magneciter. If I can't find it, I'll add it in to see if it provides tighter regulation. The current it would provide would be fairly miniscule. The name Onan gives it must be meaningful, but I haven't yet figured it out. as one reactor coil's field collapses, a current is induced, and transfers to the other reactor as it is building it's field. I haven't figured out yet whether it increases or lowers the flux of the opposite reactor coil, or what purpose it serves.
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Old 05-09-2009, 03:23:28 PM
bmilbourn bmilbourn is offline
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Default Re: Magneciter Theory...

Well put Ted!
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Old 11-17-2009, 12:32:48 PM
Ted_Cool Ted_Cool is offline
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Default Magneciter differences -06SX

Does anyone know when/where/why the different 06SX magneciters were used? I have a 10.0 JC spec 'H' with the 06SX1N1B. Is the 06SX1N3B used in a later spec? The Onan Service Bulletin dated 3-73 says 'Some newer units have an automatic field flashing circuit...'

06SX1N1A - No field flash.

06SX1N1B Field flash push button switch.

06SX1N3B 'Automatic' field flash via extra diodes. Two in series, same part numbers as the regular field diodes.

Why two in series? <To Increase the PIV Rating Of the Diodes>

150 ohm stabilizing resistor listed as 50 watt in specs, but appears to be a Dale G series 10 watt.

'Compound Winding' 14 gauge ( Rev A ) or 13 gauge ( Rev C ) wire 27.5 inches

'Calibrated shunt' 16 gauge wire 27.5 inches long in parallel with 'Compound Winding'

Same gate and control reactors.
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Old 12-17-2009, 10:14:13 PM
Jim Rankin Jim Rankin is offline
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Default Re: Magniciter Theory FAQ

I figured there was enough demand for these Onan Magneciter pages that I would just put them here instead of everyone having to request them from someone who has them.

I won't duplicate what has already been posted in this thread, so if you don't see the one you need, check the rest of this Magneciter threead.
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Old 05-08-2011, 03:47:40 PM
Leon N. Leon N. is offline
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Default Re: Magneciter differences -06SX

Hello Ted:

Just happened to review the Magneciter FAQs. Very interesting. Re your question: Does anyone know when/where/why the different 06SX magneciters were used? I think I found the answer in the Onan JB Operators manual, # 967-320. See page 23 for the appropriate the parts key number. And on page 44, the note indicates the 06SX series was used on the 50 cycle plants.


Leon
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