NECO motor failing

GWSwan

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My Swan 441's autopilot system consists of a Simrad AP16 / AC40 head and computer controlling the 12VDC motor from the boats original NECO system using the computers solenoid outputs. This has worked well for years but on this trip the port direction drive started failing after several minutes of use then will not work again at all until is has had a few minutes to "cool off". After which it will only work for several seconds before failing again. The starboard drive is fine.

The problem appears to be the motor or very close to it. I pulled the cover to the motor electronics and the port drive relay contacts continue to operate after the failure happens, but the motor no longer responds. Any thoughts on what these symptoms point to?

Thank you,
GW
 

GWSwan

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Very likely it is the relays that are going. Does anyone know where to source the Potter Brumfield PR5DY relay from? Or if there is a cross reference part from another manufacturer that will work?

Thank you!
 

TQA

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While it is possible that you have a relay problem [ easy to diagnose just bridge it ] I would say that the brushes on the main drive motor are the most likely culprit.

This is the goto guy for old Neco stuff https://www.facebook.com/DfMarineElectronics

But at a push a larger brush can be filed down and fitted. When my 592 failed in the out islands I got one in the Turks and Caicos from a monster dynamo and was soon back in autopilot heaven.
 

ribrage

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TQA I want your babies - my old neco died years ago all the "engineers" wanted to replace it with Micky mouse Rams and electronics. I found a used kit on eBay several years ago and bought it as a punt

Just messaged This neco guy and seems pretty good chance we can restore the system from why I have.

Thanks
Ian
 

danielefua

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Very likely it is the relays that are going. Does anyone know where to source the Potter Brumfield PR5DY relay from? Or if there is a cross reference part from another manufacturer that will work?

Thank you!
This appears to be indeed the most likely problem. The brushes of the Neco never fail, just consider how many turns an autopilot motor is required to do with respect to any other ordinary motor where the brushes last many, many hours of continuous running.
On the contrary, the relays are required to open/close a high current inductive circuit an enormous number of times and after 20-30 years, their contacts burn even if they are industrially rated.
The original relays can be substituted by the type PRD-5DY0-12 and if you perform a google search you will find several retailers who stock them. They are just slightly different mechanically but can be easily fitted; other people and myself alredy did it succesfully and if you need advice I will be very glad to help.

Daniel
Swan 411/008
 

GWSwan

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The relays were indeed the issue and my system is now repaired and working properly again.

Although only one relay was failing I replaced both as they were of similar age and use. The PRD-5DYO-12 relays Daniel suggested cost $32 each online, are made by TE Connectivity and seem near identical to my original Potter Brumfield units. The entire swap over took less than half an hour and that included creating a wiring diagram sketch to ensure I reconnected them properly.

The only surprise that may be unique to my system was a small custom looking shunt between two connection points that was on only one of my old relays. It was easily moved to the new relay.

Thank you for the help!

This appears to be indeed the most likely problem. The brushes of the Neco never fail, just consider how many turns an autopilot motor is required to do with respect to any other ordinary motor where the brushes last many, many hours of continuous running.
On the contrary, the relays are required to open/close a high current inductive circuit an enormous number of times and after 20-30 years, their contacts burn even if they are industrially rated.
The original relays can be substituted by the type PRD-5DY0-12 and if you perform a google search you will find several retailers who stock them. They are just slightly different mechanically but can be easily fitted; other people and myself alredy did it succesfully and if you need advice I will be very glad to help.

Daniel
Swan 411/008
 

danielefua

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The relays were indeed the issue and my system is now repaired and working properly again.

Although only one relay was failing I replaced both as they were of similar age and use. The PRD-5DYO-12 relays Daniel suggested cost $32 each online, are made by TE Connectivity and seem near identical to my original Potter Brumfield units. The entire swap over took less than half an hour and that included creating a wiring diagram sketch to ensure I reconnected them properly.

The only surprise that may be unique to my system was a small custom looking shunt between two connection points that was on only one of my old relays. It was easily moved to the new relay.

Thank you for the help!
As a Neco "amateur", I would be very interested in knowing more about the misterious shunt. Can you pinpoint where it was connected exactly?
Did you restore the "clamping diodes" in parallel with the coils of the relays? Their presence can be quite important depending on the electrical characteristics of the driving circuit, a Simrad in your case.
According to my experience, the tails of the diodes must be extended in order to fit the new relays.

Daniel
 

geem

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I have a Neco rotary drive unit on my boat driven by a raymarine course computer. I don't have any relays as the Raymarine unit sorts all that out. I don't know how it does it but I just have a two wire supply from the raymarine course computer to the motor and a two wire supply to the clutch
 

danielefua

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I have a Neco rotary drive unit on my boat driven by a raymarine course computer. I don't have any relays as the Raymarine unit sorts all that out. I don't know how it does it but I just have a two wire supply from the raymarine course computer to the motor and a two wire supply to the clutch
As far as I know the only Neco motors that can be driven without relays by modern autopilots are the DU20 and DU80, i.e. permanent magnet DC motors. Yours is probably one of them.
The OP was dealing with a different kind of Neco motor, i.e. a compound series-shunt DC motor. A totally different beast!

Daniel
 

geem

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As far as I know the only Neco motors that can be driven without relays by modern autopilots are the DU20 and DU80, i.e. permanent magnet DC motors. Yours is probably one of them.
The OP was dealing with a different kind of Neco motor, i.e. a compound series-shunt DC motor. A totally different beast!

Daniel

Daniel, do you know what autopilot these DU20 and DU80 motors were fitted to?
 

danielefua

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Daniel, do you know what autopilot these DU20 and DU80 motors were fitted to?
I am sorry that my reply may not be exhaustive but, as far as I know, they were originally fitted to Neco 8401 systems.

Derek Coventry, a former technician at Neco, will be able to supply much more information.

Daniel
 

danielefua

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Daniel, my drive unit is a 17DR8 24v driven straight from the Raymarine S3G
I am afraid but without relays your unit cannot be driven as originally intended. I insist: it CAN be driven but incorrectly, i.e. without exploiting all its possibilities.
Namely its "series coil" cannot be used making it a simply "shunt field" DC motor; nothing really terrible but you loose some torque especially at start.

Daniel
 

geem

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I am afraid but without relays your unit cannot be driven as originally intended. I insist: it CAN be driven but incorrectly, i.e. without exploiting all its possibilities.
Namely its "series coil" cannot be used making it a simply "shunt field" DC motor; nothing really terrible but you loose some torque especially at start.
That's interesting. It has taken me across the Atlantic and coped with all sorts of heavy weather and steered beautifully. I can't fault its performance. I suspect it is so over sized the loss of torque has little or no effect. It is more than capable of moving my huge rudder regardless of the weather conditions
Daniel
 

charles_reed

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While it is possible that you have a relay problem [ easy to diagnose just bridge it ] I would say that the brushes on the main drive motor are the most likely culprit.

This is the goto guy for old Neco stuff https://www.facebook.com/DfMarineElectronics

But at a push a larger brush can be filed down and fitted. When my 592 failed in the out islands I got one in the Turks and Caicos from a monster dynamo and was soon back in autopilot heaven.

I'd second this diagnosis - my Autohelm actuators occasionally mimic this behavior (having two I just change over) and take the other back to UK for service.
Invariably it has proved to be worn brushes causing overheating.
 

danielefua

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This discussion is becoming quite interesting and useful for understanding more about the Neco's; at least for me...

I like to share some thoughts.

The oldest Neco drive units (35DR8 and 17DR8) are compund shunt-series DC motors which means that they have two "stator" windings that produce the static magnetic field (one in series to the armature and one in parallel) and one "rotor" winding (armature) fed through the brushes. There are different units that run at 12V, at 24V and at 32V but, as far as I know, they are very similar from a mechanical point of view. The only differences are in the impedance of the series and armature windings. In particular I think that they all have the same kind of brushes.

Neglecting small differences, they all produce a similar mechanical power and this implies that the higher voltage units deal with lower currents; i.e. the current passing through a 24V unit is roughly half the current passing through a 12V unit and so on. My guess is also that as the brushes are safely rated for the 12V units, they are overrated for the other units.

Now the "non relay" possibility.
Driving the motor without relays is possible only if the series winding is not used and the armature is fed directly at full voltage. Apparently the mechanical power produced is still enough (at least for the 24V units) but one very important consequence must be considered: without the additional impedance of the series winding, a larger current than designed passes through the brushes and the armature. This issue may be negligible for the higher voltage units, but may be very critical for the 12V units., i.e. it may overheat the rotor and burn the brushes.

I would appreciate very much comments.

Daniel
 

geem

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This discussion is becoming quite interesting and useful for understanding more about the Neco's; at least for me...

I like to share some thoughts.

The oldest Neco drive units (35DR8 and 17DR8) are compund shunt-series DC motors which means that they have two "stator" windings that produce the static magnetic field (one in series to the armature and one in parallel) and one "rotor" winding (armature) fed through the brushes. There are different units that run at 12V, at 24V and at 32V but, as far as I know, they are very similar from a mechanical point of view. The only differences are in the impedance of the series and armature windings. In particular I think that they all have the same kind of brushes.

Neglecting small differences, they all produce a similar mechanical power and this implies that the higher voltage units deal with lower currents; i.e. the current passing through a 24V unit is roughly half the current passing through a 12V unit and so on. My guess is also that as the brushes are safely rated for the 12V units, they are overrated for the other units.

Now the "non relay" possibility.
Driving the motor without relays is possible only if the series winding is not used and the armature is fed directly at full voltage. Apparently the mechanical power produced is still enough (at least for the 24V units) but one very important consequence must be considered: without the additional impedance of the series winding, a larger current than designed passes through the brushes and the armature. This issue may be negligible for the higher voltage units, but may be very critical for the 12V units., i.e. it may overheat the rotor and burn the brushes.

I would appreciate very much comments.

Daniel

Daniel,
My 24v set up works fine as already mentioned. Crossing the Atlantic last winter we had a period of very light wind. We ran the engine for several days and with the high engine room temperatures everything in there got pretty hot. The engine room extract fan failed. I replaced the engine room extract fan with a larger one and added a computer fan to cool the casing on the autopilot motor. This dramatically brought the temperature of the motor down.
I am going to fit a larger cooling fan to the autopilot motor when I get back out to the boat as I believe the cooler I can keep it the better. Your thoughts would be appreciated
 

danielefua

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Daniel,
My 24v set up works fine as already mentioned. Crossing the Atlantic last winter we had a period of very light wind. We ran the engine for several days and with the high engine room temperatures everything in there got pretty hot. The engine room extract fan failed. I replaced the engine room extract fan with a larger one and added a computer fan to cool the casing on the autopilot motor. This dramatically brought the temperature of the motor down.
I am going to fit a larger cooling fan to the autopilot motor when I get back out to the boat as I believe the cooler I can keep it the better. Your thoughts would be appreciated
You should be more precise on the meaning of "pretty hot". Were you able to touch the motor?
Overall your actions sound sensible but, I am sorry, although my scientific knowledge is pretty good they would be better commented by an electrical engineer. In fact I would appreciate comments by an expert also on my previous post.


Daniel
 

geem

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You should be more precise on the meaning of "pretty hot". Were you able to touch the motor?
Overall your actions sound sensible but, I am sorry, although my scientific knowledge is pretty good they would be better commented by an electrical engineer. In fact I would appreciate comments by an expert also on my previous post.

From very hot to touch without fan to quite cool with fan. It's not really a big issue when sailing it's just the temperature of the engine room when the engine is running.
Daniel
 
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