Using a relay with a new Simrad autopilot

[JOHNMARDALL]

Please stop, before you burn out your autopilot. The reason that autopilot manufacturers recommend relays is to prevent the current required by the electro-hydraulic steering pump or electric drive and related devices from passing through the autopilot and burning it out. Most, but not all, autopilots are rated to handle no more than 10 amps (read the manuals) and electrical steering pumps or drives often use more. The relays allow the small currents that the autopilot can handle to control large currents required by the motors, etc of pump and drives. DC to DC relays are readily available in a range of capacities and are used extensively on cars, boats and many other machines.

I hope this helps

John Mardall
Vetus Maxwell Group

[DeepFrz]

JohnMardall, maybe if you reread the original post you would change your post? The OP has nothing to do with the drive requirement.

[Boston Blackie]

I use Crydom DC60S3 solid state relays all the time for PLC control of production pneumatic automation. These have a control input rating of 3.5-24VDC and switch outputs up to 60VDC.

[JOHNMARDALL]

Originally Posted by DeepFrz

JohnMardall, maybe if you reread the original post you would change your post? The OP has nothing to do with the drive requirement.

Perhaps you missed the "related devices". This is all about how much current can pass through the autopilot without damaging it. Relay are simple and cheap insurance against doing that and yes, I learned this the hard way.

[skipmac]

Originally Posted by JOHNMARDALL

Please stop, before you burn out your autopilot. The reason that autopilot manufacturers recommend relays is to prevent the current required by the electro-hydraulic steering pump or electric drive and related devices from passing through the autopilot and burning it out. Most, but not all, autopilots are rated to handle no more than 10 amps (read the manuals) and electrical steering pumps or drives often use more. The relays allow the small currents that the autopilot can handle to control large currents required by the motors, etc of pump and drives. DC to DC relays are readily available in a range of capacities and are used extensively on cars, boats and many other machines.

I hope this helps

John Mardall
Vetus Maxwell Group

Hi John,

As Deepfrz points out, I think you missed a piece of my question. I am very aware of the high current requirements for an AP drive. However I'm sure you are just as aware that almost all AP drives (the only exception I know of is the linear drive from Alpha that uses a mechanical linkage) require two power inputs; one high power to drive the motor but a second, low power supply to activate a solenoid driving either a clutch or a hydraulic valve to engage the AP drive.

I am looking at the second, low power part of the system, which typically draws in the tenths of amp range.

Even with this low power section Simrad recommends using an isolating diode to drive that circuit, probably as I speculate as a CYA since it would be virtually impossible for them to address the requirements for every possible drive other than their own. I am 90% certain that the output from the engage circuit (as it is called in the Simrad docs) of the Simrad AP would be more than adequate to power the electric clutch only on my Raymarine mechanical linear drive but I'm still investigating options and potential ways to reduce the continuous power draw of the clutch solenoid.

Perhaps with your background you could offer some insight into that issue as this is an area where my real world experience is lacking. Can a clutch solenoid use one of the devices (smart relays I guess) that initially supply full power to engage the clutch but then drop to a lower current to hold the clutch once engaged or would a clutch solenoid require full power continuously to maintain full connection?


Thanks
Skip

[skipmac]

Originally Posted by JOHNMARDALL

Perhaps you missed the "related devices". This is all about how much current can pass through the autopilot without damaging it. Relay are simple and cheap insurance against doing that and yes, I learned this the hard way.

Hi John,

I have a Simrad NAC3 autopilot computer that specs 3 amp max output for the engage circuit which is used to activate clutch or hydraulic valve solenoids. I do believe that 3 amps is more than sufficient to drive a clutch solenoid on a Raymarine drive. Since the clutch circuit is independent and separated from any other part of the AP system then I don't think related devices will come into play.

[JOHNMARDALL]

Hello Skip,

There may be other devices that could protect your autopilot from high in-rush current or operating current, but why bother when the autopilot manufacturer has already made a low cost, easily installed recommendation? On my own boat, that's what I'd do, rather than put the autopilot warranty at risk by not following the manufacturer's recommendations.

Good luck
John M

[dietervoegeli]

De nada!

Raymarine SPX series cluch output.

Drive clutch output X 10 X 30
X SOLENOID
• 2.0 A at 12 / 24 V selectable
(SPX-10, SPX-SOL)
• 3.0 A at 12 / 24 V selectable
(SPX-30)

[skipmac]

Originally Posted by dietervoegeli

De nada!

Raymarine SPX series cluch output.

Drive clutch output X 10 X 30
X SOLENOID
• 2.0 A at 12 / 24 V selectable
(SPX-10, SPX-SOL)
• 3.0 A at 12 / 24 V selectable
(SPX-30)

Why didn't I think of this? Instead of trying to find the specification for the drive itself look at the specification for the computer output used to control the drive.

[skipmac]

Originally Posted by JOHNMARDALL

Hello Skip,

There may be other devices that could protect your autopilot from high in-rush current or operating current, but why bother when the autopilot manufacturer has already made a low cost, easily installed recommendation? On my own boat, that's what I'd do, rather than put the autopilot warranty at risk by not following the manufacturer's recommendations.

Good luck
John M

Thanks John. I do agree that adding a relay is a simple, low cost solution. My original question was just what kind of relay would be the best to use for this application but the discussion morphed into related issues.

Since I do have an EE degree and am a curious type I like to ask and understand why instead of blindly following the instructions. I have to say more than once asking why has revealed bad information in manuals or helped me find a better solution. Not saying the recommendation or manual from Simrad is bad or wrong, in fact quite the contrary, but I still like to understand the whys and wherefores.

So my question now, the Simrad computer has a 3 amp engage output which is used to activate the solenoid operated valves on the Simrad hydraulic drives. It is the exact same setup on both brands, the engage/clutch output from the AP computer Raymarine or Simrad goes to a solenoid on the drive, Simrad or Raymarine. Why would Simrad solenoids be any different, have any lower inrush current than the solenoid used by Raymarine? Note this output is connected only to and isolated from the power that drives the AP motor so the spikes that might result from a motor kicking in/out don't contribute.

[skipmac]

Originally Posted by Boston Blackie

I use Crydom DC60S3 solid state relays all the time for PLC control of production pneumatic automation. These have a control input rating of 3.5-24VDC and switch outputs up to 60VDC.

Thanks BB. Checked out the spec sheet on this and looks very good. I'm assuming if you use these in a commercial application they have a pretty good track record for reliability.

So anyone in your family a detective?

[Saltyhog]

The L&S solenoid relay (Ecopilot) is really a good idea. The engagement current on most drives is at least 1 A. On a passage, that's 24 AH used just to keep the thing engaged. That's in addition to the current the drive itself uses to actually steer the boat. For the DIY crowd, here is a part to do exactly what the Ecopilot does. The Ecopilot is likely using this or something very similar. I think it would be pretty easy to build this up. http://www.ti.com/lit/ds/symlink/drv102.pdf

[skipmac]

Originally Posted by Saltyhog

The L&S solenoid relay (Ecopilot) is really a good idea. The engagement current on most drives is at least 1 A. On a I just called PYI, the US distributor and the resident Ecopilot expert was completely negative to this idea. The Ecopilot is built for the L&S drives and only plugs into the appropriate socket on the drive and it operates the L&S solenoid and, and, and ...........passage, that's 24 AH used just to keep the thing engaged. That's in addition to the current the drive itself uses to actually steer the boat. For the DIY crowd, here is a part to do exactly what the Ecopilot does. The Ecopilot is likely using this or something very similar. I think it would be pretty easy to build this up. http://www.ti.com/lit/ds/symlink/drv102.pdf

I am all for saving 20 amp hours or so per day. That adds up to a lot when added to the power required to drive the AP motor. BUT



Seems like PYI isn't into thinking outside the box.

The main piece of data I'm missing is what minimum current is required to keep the clutch on the Raymarine pilot firmly engaged. Signed up for the Raymarine tech forum where real Raymrine engineers hang to see if I can get something.

[Saltyhog]

Originally Posted by skipmac

I am all for saving 20 amp hours or so per day. That adds up to a lot when added to the power required to drive the AP motor. BUT



Seems like PYI isn't into thinking outside the box.

The main piece of data I'm missing is what minimum current is required to keep the clutch on the Raymarine pilot firmly engaged. Signed up for the Raymarine tech forum where real Raymrine engineers hang to see if I can get something.

I think you would need to do a bit of testing/experimenting here. If it were me, I'd experimentally determine the minimum hold on current needed, and then add a healthy margin. I'd do the testing at hot, as the hold on current will likely be higher when hot.

[skipmac]

Originally Posted by Saltyhog

I think you would need to do a bit of testing/experimenting here. If it were me, I'd experimentally determine the minimum hold on current needed, and then add a healthy margin. I'd do the testing at hot, as the hold on current will likely be higher when hot.

That's pretty much where I'm heading but don't have a fixed voltage, variable current power supply to test the minimum hold current. Wouldn't be too difficult to rig a variable voltage supply but that wouldn't be the ideal.