Appropriate Relay for (Raymarine) autopilot installation

[antaris]

Hello to all,

I will be installing a (new-to-me) RaymarineS3G+ST6002 with a Type 1 Linear Drive. What type of Relay can I use, so that I do not deploy long, heavy cables everywhere? System is 12V.

What I understand is that I need a relay:
4-pin
20 Amp, rating for said system is 15A Max
Typical automotive type (electro-mechanical).

Is this correct? Will they handle continuous duty? Are solid-state appropriate for this use?

Thank you!

 

[Rappey]

20 A is not a huge amount. I would just use cables as one less thing to go wrong and far less complicated

 

[Graham376]

20 A is not a huge amount. I would just use cables as one less thing to go wrong and far less complicated

Agreed no need for relay and it may have negative effect on reliability with constant clicking in and out, linear drives don't move every few seconds, they can be twitching almost constantly at times.

P.S. Just looked up the spec as mine doesn't have any heavy duty cables, states 18w - 36w which is only 3 amps.

 

[Hoolie]

I think it depends on the wiring configuration. I have an SPX30 controller driving a Type 2 linear drive with 40 amp max current. The AP is connected directly to the house batteries via a circuit breaker in the aft locker but can't be switched on/off by the electrical panel instrument breaker. I have an automotive relay to fit that will allow the main instrument breaker switch to also control the autopilot. No need for additional heavy cabling - even 20amp cables would be OTT assuming the electrical panel could handle such a load; mine can't!

 

[Hoolie]

Agreed no need for relay and it may have negative effect on reliability with constant clicking in and out, linear drives don't move every few seconds, they can be twitching almost constantly at times.

I don't think the OP was thinking of a relay controlled by the autopilot - he'd need more than one if he was (port,stbd and clutch). An overall on/off relay was my interpretation of his requirement.

 

[Graham376]

I don't think the OP was thinking of a relay controlled by the autopilot - he'd need more than one if he was (port,stbd and clutch). An overall on/off relay was my interpretation of his requirement.

But why a relay for on and off? Our Autohelm on/off switch is a push/pull circuit breaker in the instrument panel but can't remember the rating. Relays are obviously needed in some circuits but to add them where not necessary is just another potential point of failure. Where does your 40 amp draw come from? Type 2 linear drive's specification quotes 72 watts max = 6 amps. Raymarine Type 2 12 Volt Autopilot Short Shaft Linear Drive, Up to 15,000kg Displacement - M81131 - Hudson Marine Electronics.

From thousands of miles with type 1 on two boats, I've found the power draw pretty frugal when sails properly balanced.

 

[Rappey]

Where does your 40 amp draw come from?

I bought a used autohelm 300. What worried me was a connector with a 40 or 45 amp fuse..
Rang up raymarine who were really helpfull and explained it was for a linear drive but since I was driving a hydraulic drive I didn't need the 40 amp connector as would only draw around 3 amps.

 

[PaulRainbow]

You need to get power from the supply to the ACU and from the ACU to the linear drive. Fitting a relay between the ACU and the drive would be a bad idea, it would be opening and closing too often. Fitting a relay between the supply and the ACU might save a little bit of higher rated cable, depending where the supply is in relation to the ACU. If it means running several metres of relatively heavy cable from the swith panel (or to the panel and back to the drive) it might be worth fitting a relay. It's worth noting that a typical automotive relay will need power to keep it closed, so be sure to fit a latching relay.

 

[LadyInBed]

A relay is an unneeded extra point of failure

 

[PaulRainbow]

A relay is an unneeded extra point of failure

Not necessarily.

For instance, a Moody 376 has the batteries under the aft cabin berth, very close to the rudder stock where the linear drive would be fitted. So, fit the ACU in the same area and the cables from the ACU to the drive will be very short. The switch panel is almost midships on the Stb side, so about 8m of cable, rated for the drive, taking into account current inrush and voltage drop. You could use some relatively heavy cable, or use a relay and a length of 1.5mm positive cable.

 

[Graham376]

For instance, a Moody 376 has the batteries under the aft cabin berth, very close to the rudder stock where the linear drive would be fitted. So, fit the ACU in the same area and the cables from the ACU to the drive will be very short.

Mine has the drive where you suggest but no separate computer, all's contained in the ST5000 plus (now superseded) display head mounted on coaming adjacent to helm, with hand head remote under sprayhood. The display/controller only draws 1.5amps and the linear drive 3 amps so I didn't need heavy cables, IIRC correctly around 4mm sq. Obviously don't know what controllers/computers the two posters above have but I wouldn't want anything with their stated current draw, batteries would be flat pretty quickly.

 

[Talulah]

Not necessarily.

For instance, a Moody 376 has the batteries under the aft cabin berth, very close to the rudder stock where the linear drive would be fitted. So, fit the ACU in the same area and the cables from the ACU to the drive will be very short. The switch panel is almost midships on the Stb side, so about 8m of cable, rated for the drive, taking into account current inrush and voltage drop. You could use some relatively heavy cable, or use a relay and a length of 1.5mm positive cable.

I have a relay for this very reason. Without a relay the supply to and from the switch panel would have to be significantly bigger. Without heavier cabling you might think it is working fine until sea conditions require higher power draw.
The relay has been fine but should it fail it’s easy enough to join the supply to the out.

 

[tjbrace]

I have used an automotive relay for my Garmin AP kit as the installation instructions recommend that the the power is taken directly from the batteries , via a suitable circuit breaker, but I wanted switching control from the distribution panel. Has been ok for more than 10 years now.

 

[antaris]

thank you everyone for taking time to discuss!

Here is a schematic of my options (me thinks):


Indeed, I just want to switch the whole Autopilot "system" on/off - which will sit near the batteries.

Two reasons for relay:
1. Uncertain if my panel cabling is sound and able to take 10-15 Amps (supposed max in Raymarine's manual)
2. I usually over-spec cabling, so running long, heavy and parallel cabling will be... tricky!

 

[antaris]

Not necessarily.

For instance, a Moody 376 has the batteries under the aft cabin berth, very close to the rudder stock where the linear drive would be fitted. So, fit the ACU in the same area and the cables from the ACU to the drive will be very short. The switch panel is almost midships on the Stb side, so about 8m of cable, rated for the drive, taking into account current inrush and voltage drop. You could use some relatively heavy cable, or use a relay and a length of 1.5mm positive cable.

Yes, exactly. Similar case here. (and panel is on port side, too)

 

[antaris]

Here is the Raymarine forum response, stating a max 15 Amps (therefore the 20 Amp Relay I mention)

 

[PaulRainbow]

Yes, exactly. Similar case here. (and panel is on port side, too)

If i was fitting it, i would, in this case, fit the relay as you show in "C" above. I would take the relay switching coil negative from the battery and the positive from the switch panel.

Fit a latching relay, which has no current overhead when closed and operate it from a momentary switch or button at the panel. Press for on, press again for off. A LED to show the AP status might be useful ?