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Generators & Electric Motors General Discussion Antique Generators and Old Electric Motors: Questions and answers about restoring and showing old power generation systems.

Generators & Electric Motors General Discussion

Automatic Voltage Regulators


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  #21  
Old 05-09-2018, 06:33:42 AM
Kevin K Kevin K is offline
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Default Re: Automatic Voltage Regulators

It's early in the morning, and I would need to study the circuit for a while, but the thing that stands out from a quick look is the lack of a stability adjustment to match the response time of the regulator to the generator.
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  #22  
Old 05-09-2018, 08:55:48 AM
Thaumaturge Thaumaturge is offline
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Default Re: Automatic Voltage Regulators

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Originally Posted by Kevin K View Post
It's early in the morning, and I would need to study the circuit for a while, but the thing that stands out from a quick look is the lack of a stability adjustment to match the response time of the regulator to the generator.
Thank you. I wasn't aware any such was needed. Circuit is pretty much real time. As to opperation it is pretty simple.

LM10 is an old National Semiconductor dual op-amps, but with one of the op-amps devoted to a scalable internal voltage reference of 0.2 volts. This is scalable by feedback ratio to any desired voltage within the power supply limits. This voltage is then fed into input of second op-amp, wher it is compared with sample voltage from RMS converter. In this case the reference voltage is set for one volt, which is what the voltage sample from transformer is scaled to output as DC from RMS converter.

Op-amp tries to make voltage on negative input the same as that on positive input. Doing so it turns on LM395 Ultra Reliable transistor, which incorporates internal current limiting and thermal protection. (Thus no current limiting resistor feeding LM395.). This turns on main output 2SC5200 which pulls down low side of exciter field. Existing aux supply feeds positive to top side of exciter field.

Thus the entire generator head becomes one big feedback loop feeding into comparitor op-amp. If generator output feeding sample transformer is below desired level (120 or 240) secondary voltage will reduce proportionally, resulting in lower output from RMS converter, dropping below reference voltage, causing output to turn on LM395 driver transistor, turning on 2SC5200, increasing drive to exciter field. All fully linear and proportional.
Increased exciter field increases generator output until sample voltage equals reference voltage. The bigger the discrepancy the greater the drive. The smaller the error the proportionally smaller the drive response. Under no load condition system should settle into equalibrium of desired output voltage.

Under voltage drop from increased load, proportional response is roughly real time.

Probably not how others would do it, just how I came up with. Same basic circuit will work for many applications from temperature control to automotive charge controller. Just depends on what you feed into comparitor op-amp and how you scale reference for comparison.
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  #23  
Old 05-09-2018, 11:27:18 AM
Fred M. Fred M. is offline
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Default Re: Automatic Voltage Regulators

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Originally Posted by Thaumaturge View Post
My entry for a bullit proof AVR design. Assumes ground referenced aux supply rectified and positive fed to other side of field. Transformer primary is wired to select 120 or 240 input. Trimmers set 1 VAC into RMS converter and internal reference to set output. Transistors are thermally linked on heatsink. If output overheats LM395 automatically shuts down. Only assembly difficulty is RMS converter ONLY available in tiny little surface mount dip package.
Doc
D5 is backwards.

Fred
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  #24  
Old 05-09-2018, 12:16:46 PM
Vanman Vanman is offline
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Default Re: Automatic Voltage Regulators

I believe that it may oscillate, due to the large inductance of the field, and the resulting delay between a regulator correction and the response of the generator output. I believe that is the reason for the stability adjustment.

Also, since my electronics knowledge is rather weak, is this circuit ON with no voltage present? It needs to be to allow the machine to build up.
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  #25  
Old 05-09-2018, 04:33:55 PM
Thaumaturge Thaumaturge is offline
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Default Re: Automatic Voltage Regulators

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Originally Posted by Fred M. View Post
D5 is backwards.

Fred
Good catch, it is. That would have clamped minus supply to under a volt.
Odd thing is upon thought it might still work. Minus supply only needed for RMS converter to swing full volt.... input is internally diode clamped for over drive protection. Hmmm.

Anyway. D5 IS BACKWARDS as drawn
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Quote:
Originally Posted by Vanman View Post
I believe that it may oscillate, due to the large inductance of the field, and the resulting delay between a regulator correction and the response of the generator output. I believe that is the reason for the stability adjustment.
Have to think about that... was thinking only one inductive phase shift, but there are 3, or even 4! (Exciter, Stator, Primary & Secondary.) But that would be full 360 degree phase shift... minus hysteresis. Will have to bench test with two transformers back to back and see how it acts.

Quote:
Also, since my electronics knowledge is rather weak, is this circuit ON with no voltage present? It needs to be to allow the machine to build up.
Yes. Should come up linear. Internal reference would come up first causing output to swing on. (I think.) Will know more once I bench test it.
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  #26  
Old 05-09-2018, 05:03:34 PM
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Default Re: Automatic Voltage Regulators

Corrected schematic showing D5 Zener in proper orientation.
(Should anyone be curious, schematic drawn using "Quick Copper" on Android tablet. The ONLY such app that seems to actually work!)
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  #27  
Old 05-09-2018, 05:08:07 PM
Rich Mc Rich Mc is offline
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Default Re: Automatic Voltage Regulators

Some expected waveforms at the signals I/O would be helpful.
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  #28  
Old 05-09-2018, 07:43:37 PM
Thaumaturge Thaumaturge is offline
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Default Re: Automatic Voltage Regulators

Pretty much just DC levels.
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  #29  
Old 05-09-2018, 09:47:19 PM
Rich Mc Rich Mc is offline
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Default Re: Automatic Voltage Regulators

The rated Vceo on the LM395 is 36 volts, isn't that a problem?
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  #30  
Old 05-10-2018, 12:14:45 AM
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Default Re: Automatic Voltage Regulators

No. Most aux supplies run under 25, I think. But even so Q1 is fed off bottom side of exciter field just atop Q2. Once Q2 begins turning on the bottomside voltage will drop considerably. Q1 only fed from bottom side to insure sufficient drive to fully turn on Q2 if needed. If however someone had an aux supply with greater than 30 volts they could just use a beefier sample transformer and feed collector of LM395 from +5 supply.
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