Replacing Markon SL105 AVR with SX460

[Tasemu]

Hi all, a few might remember my old post a while ago regarding my diesel generator outputting around 270v @ 50hz and how I was going to replace the AVR. Long story short I still haven't had the guts to tear the generator open again but am finally getting ready to take the dive. I was looking online and a lot of people appear to be recommending the SX460 as a decent and cheap AVR for generators. I'm wondering if it would be a like for like replacement for my old AVR that is very difficult to find nowadays... The mounting holes seems different but... Zip tie magic?

Cheers for any advice!

[Tonka]

4 minutes ago, Tasemu said:

Hi all, a few might remember my old post a while ago regarding my diesel generator outputting around 270v @ 50hz and how I was going to replace the AVR. Long story short I still haven't had the guts to tear the generator open again but am finally getting ready to take the dive. I was looking online and a lot of people appear to be recommending the SX460 as a decent and cheap AVR for generators. I'm wondering if it would be a like for like replacement for my old AVR that is very difficult to find nowadays... The mounting holes seems different but... Zip tie magic?

Cheers for any advice!

Do you have a manual for Markon. I can send you a softcover of one if you have not.

I have recently replaced a Markon SL105 with a Mecallte Es16f-150 on a Beta BD3

[Tasemu]

Just now, Tonka said:

Do you have a manual for Markon. I can send you a softcover of one if you have not.

I have recently replaced a Markon SL105 with a Mecallte Es16f-150 on a Beta BD3

 

Cheers, i do have digital copies so should be fine but thanks for the offer.

I'm hoping replacing the the AVR will sort the issue rather than the alternator side of the genny. Mostly for money and the pain of the job in a confined space on the boat. Hence why this SX460 avr looks tempting at only ~£20.

[Tonka]

@Biggles may know your answer

[Tasemu]

Potentially stupid question, but if i replace the MD1C markon avr with the SC460, could i use some wire extensions to mount the avr outside the generator for easier access in the future? Pulling the whole damn thing apart is a nightmare.

[Tonka]

3 minutes ago, Tasemu said:

Potentially stupid question, but if i replace the MD1C markon avr with the SC460, could i use some wire extensions to mount the avr outside the generator for easier access in the future? Pulling the whole damn thing apart is a nightmare.

has yours got the box on it with the connections in it ? cant see why that box couldnt be replaced with a bigger box with the AVR in

[Tasemu]

On 16/12/2023 at 11:44, Tonka said:

has yours got the box on it with the connections in it ? cant see why that box couldnt be replaced with a bigger box with the AVR in

Yeah mine has a box on top of the alternator part of the genset, its quite large and only contains the brakers for it... perhaps i could mount in there 🤔

[Tasemu]

So i'm totally stumped... I set the generator to 50hz and it was outputting 280v with the old AVR. I then installed the SX460 and its still outputting 280v with the voltage trimmer down to minimum. Then i even disconnected the wires to the brushes.. which as far as i know should be powering the rotor windings through the slip rings and its still outputting 280v! Its almost like the generator is totally ignoring the AVR's and getting power to the slip rings from somewhere else... I'm so confused. For now i've set the Hz back to 42 and its dropped the voltage back to 230v. Can anyone offer any advice on what might be going on here?

I managed to find this online... i'm guessing that this kind of AVR reduces the power to the rotors, but it will work without an avr but at a higher voltage... So i'm guessing that the SX460 wont work with it... I'm honestly not sure.

 

Info:

The SL105 The SL 105 range have two stator windings. The main winding is used to provide the alternator’s output power and therefore, will be connected to the load. It typically consists of two 120V windings, brought out to terminals by four leads identified as U1 – U2 and U5 – U6. Connecting these windings in series [link U2 to U5] will provide the most commonly required 240V output between terminals U1 and U6. The output leads of the auxiliary winding are marked Z1 and Z2 and this winding provides power for the excitation system. The output of this winding is connected, via a series connected choke, to the ac input terminals of a single phase full wave bridge rectifier, which is the 4-terminal solid state device mounted near the choke. The dc output of the bridge rectifier is connected to the rotor windings via the slip-rings. The positive (+ve) lead is identified by the marking F1 [X on old alternators] and this is connected to the slip-ring closest to the alternator bearing. The negative (-ve) lead being marked F2 [XX on old alternators]. AGN 102 ISSUE B/13/21 This excitation system is designed to generate slightly more excitation than is really needed for any condition between No-load and Full-load. Excess excitation is diverted away from the rotor [field] windings by a solid state Automatic Voltage Regulator [AVR]. The AVR is designed to momentarily short-out the excitation voltage being supplied to the slip-rings and by so doing, it reduces the effective level of excitation available to ‘flow’ through the rotor winding. The alternator’s output voltage is controlled by the level of excitation current flowing through the rotor winding. The AVR senses the voltage of the main winding and compares this voltage level with the ‘set’ voltage level and maintains a constant output voltage under load conditions by constantly adjusting the level of the excitation being applied to rotor winding. As explained above, the alternator actually generates more than required excitation and this is reduced by the action of the diverter type AVR. This means that the alternator will operate without an AVR, but will generate higher than nominal output voltage. Without the AVR being connected, the output voltage will be some 300V under a No-Load condition. If load is applied to the alternator, then this 300V will reduce in proportion to the level of load applied such that at rated load the output voltage will be some 250V. In emergency conditions, where the alternator must be operated without an AVR, the output voltage can be reduced to acceptable levels if the engine speed is reduced.

[Tonka]

Does the attached help

markon application guidance note.pdf

[BEngo]

There are two stator windings.  One is the output.  The other provides the field current, and this à is permanently connected to the field winding.  The rotor  is designed to produce too much field current.  If  there is no load and no AVR  there should  be enough field for the  output to reach 300V.  The basics of the generator thus seems to be working as designed.

 

The AVR is supposed to divert some of the field current elsewhere when the voltage is  higher than the  set point.  I guess this will be by switching  a resistor in and out of parallel with the field windings.  The (new) AVR either does not work like this or is not working.

 

N

[Tasemu]

15 minutes ago, Tonka said:

Does the attached help

markon application guidance note.pdf 671.98 kB · 2 downloads

 

Cheers, i think it does explain why i'm getting voltage after disconnecting the old AVR.. Though i'm still puzzled how i'm supposed to install this SX460 if the slip rings are getting power directly from the full bridge rectifier...

Just now, BEngo said:

There are two stator windings.  One is the output.  The other provides the field current, and this à is permanently connected to the field winding.  The rotor  is designed to produce too much field current.  If  there is no load and no AVR  there should  be enough field for the  output to reach 300V.  The basics of the generator thus seems to be working as designed.

 

The AVR is supposed to divert some of the field current elsewhere when the voltage is  higher than the  set point.  I guess this will be by switching  a resistor in and out of parallel with the field windings.  The (new) AVR either does not work like this or is not working.

 

N

 

Yeah it looks like the SX460 actually supplies a voltage to the slip rings rather than siphons it off from there. So i'm guessing its incompatible

[Tonka]

I used to mine serviced by Cox's at Atherstone. They may be able to help

[Tasemu]

This might be crazy, but if i disconnected the rectifier from the slip rings... could i not use the sx460? As it connects to the slip rings through the brushes? In my mind it would work as the field winding would no longer be powered from the auxillery coil, but instead powered from the sx460 through the brushes?

[Tonka]

I honestly do not know but @Tony Brooks may be able to help. You may need to send him a copy of the manual so as he could look at the schematic drawing

[Tasemu]

Yeah i have a link to a digital copy if needed. Any help would be appreciated highly, I have a new victron multiplus sitting there collecting dust for months now as i can't use it with the current avr so I need to sort something out 😅

[Tonka]

SL105 Alternator
The SL105 alternator is of self-exciting, automatic voltage regulator (AVR) controlled,
rotating field design. It is designed to operate with close regulation when supplying single
phase loads. Primarily designed for loads at or near unity power factor, it has a capability of
operation at 0.8 power factor.
The principle of operation is schematically represented in the diagram below. The auxiliary
winding provides excitation power through a choke and rectifier into the rotating field via
sliprings.
The AVR diverts excess excitation at low loads to maintain the main stator winding output
voltage within close limits.
The main stator winding is designed for series/parallel connection to give a dual voltage
output with voltage adjustment.
The SL105 alternator may be supplied without a divertor AVR for specific applications. For
these alternators the instructions given in this manual for the SL105 alternator apply, but
references to the AVR or its control should be ignored.
A046V047 (Issue 1) 11
-
4.

[Tony Brooks]

41 minutes ago, Tonka said:

I honestly do not know but @Tony Brooks may be able to help. You may need to send him a copy of the manual so as he could look at the schematic drawing

 

Sorry, I would love to, but mains stuff is well outside my competence. I think a similar form of regulation was done of one make of permanent magnet 12V DC alternators back n the late 60s, but I had nothing to do with them.

 

Tonka's diagram suggest to me that the AVR pulse shorts out the supply to the rotor windings, probably at high frequency, but why that does not burn the AVR out I have no idea unless the "short out" pulse is of very short duration.

Edited December 22, 2023 by Tony Brooks

[Tasemu]

I think i may have a shot at disconnecting the rectifier completely from the rotor windings, as the SX460 takes the 230v output from the generator and uses that to supply a dc regulated field winding voltage. I feel in my gut that it would work... I am terrified about damaging my generator though

[Tony Brooks]

5 minutes ago, Tasemu said:

I think i may have a shot at disconnecting the rectifier completely from the rotor windings, as the SX460 takes the 230v output from the generator and uses that to supply a dc regulated field winding voltage. I feel in my gut that it would work... I am terrified about damaging my generator though

 

Be careful, I have a suspicion that a perm ant magnet rotor may be involved to make it self-exiting, and if so I doubt that what you propose will work.

 

In fact, the actual rotor winding MIGHT be acting in opposition to such permanent magnets, so if you regulate them you might get an even higher voltage.

Edited December 22, 2023 by Tony Brooks

[Tasemu]

5 minutes ago, Tony Brooks said:

 

Be careful, I have a suspicion that a perm ant magnet rotor may be involved to make it self-exiting, and if so I doubt that what you propose will work.

 

In fact, the actual rotor winding MIGHT be acting in opposition to such permanent magnets, so if you regulate them you might get an even higher voltage.

 

If the rotor magnets were permanent, then wouldn't it not require a field winding voltage at all? I'm still new to a lot of the theory of all this.

[Tony Brooks]

Just now, Tasemu said:

 

If the rotor magnets were permanent, then wouldn't it not require a field winding voltage at all? I'm still new to a lot of the theory of all this.

 

Be aware I am spouting assumptions based on theory.  

 

Think of the rotor permanent magnet having north at one and south at the other. Now put a winding around the rotor with the winding north and south the opposite way round. If you now put sufficient currant through the rotor so it produces the same strength of magnet as the permanent magnet and the two field cancel each other out. This is how RCDs work. No effective magnetic field, so no output. In this scenario, the rotor winding is used to reduce the effect of the permanent magnet.

[Tasemu]

12 minutes ago, Tony Brooks said:

 

Be aware I am spouting assumptions based on theory.  

 

Think of the rotor permanent magnet having north at one and south at the other. Now put a winding around the rotor with the winding north and south the opposite way round. If you now put sufficient currant through the rotor so it produces the same strength of magnet as the permanent magnet and the two field cancel each other out. This is how RCDs work. No effective magnetic field, so no output. In this scenario, the rotor winding is used to reduce the effect of the permanent magnet.

 

I think i understand yeah, assuming i have no loads connected to the generator. Do you think this would be something worth testing? Or would you say there would be a significant risk of damaging my generator?

[Tony Brooks]

10 minutes ago, Tasemu said:

 

I think i understand yeah, assuming i have no loads connected to the generator. Do you think this would be something worth testing? Or would you say there would be a significant risk of damaging my generator?

 

Sorry, I don't know enough about the circuits and construction to give an opinion.  If there is no load connected then there is no load to destroy by over voltage, but you might damage internal components like the rectifier, or in extreme cases produce enough voltage to "punch through" winding insulation.

 

basic answer is that I decline to give an opinion.

[GUMPY]

Obtuse thought:

Set it to 50hz/280v and use a transformer to drop it to 230v.

You will have to mess around with the exact voltage to get the regulation right at full load.

Or even a Variac 🤔

[Tasemu]

So after looking at this video, i think it might be possible. He's putting a sx460 on a Markon SC21G (mine is a Markon SL105), and he seems to have a bridge rectifier like mine and a choke like mine, only difference being the resistor method over my old avr. He's disconnected all that stuff and the sx460 seems to be working. As it looks like i have no option but to suck it and see.. I guess i'll come back with the results once i work up the courage? Cheers!