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Old 21-11-2018, 15:51   #1
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High power autopilot relays

I have a recent Raymarine wheelpilot and am interested in connecting the unit to a Type 2 linear drive.

I can put in a separate circuit and switch for the clutch.

Wondering if there is a commercial unit available to deliver the higher power to the linear drive, using the wheelpilot output as a switching signal, or if someone has access to a circuit that would do the job.
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Old 21-11-2018, 16:39   #2
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Re: High power autopilot relays

You can get a continuous duty reversing relay by Cole herse.
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Old 21-11-2018, 17:10   #3
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Re: High power autopilot relays

Why would you need to do such a thing?

If the wheel pilot is in fact "recent" sell the computer and buy the proper one. The rest of the parts will work with it.
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Old 21-11-2018, 17:22   #4
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Re: High power autopilot relays

I would start out with horn relays, they handle 20 amps. They also use that same relay for extra lighting on cars and trucks etc.
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Old 21-11-2018, 17:28   #5
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Re: High power autopilot relays

High power is not the only requirement. The course computer likely uses pulse width modulation to control the speed of the motor, so you need a relay that will also operate very fast and tolerate fast and short pulses.
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Old 21-11-2018, 17:33   #6
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Re: High power autopilot relays

https://www.amazon.com/Intermittent-...B8K2P8H3AS1FRW


If the output is not PWM, this will do it.
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Old 21-11-2018, 17:33   #7
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Re: High power autopilot relays

H-Bridge relay for robotics is what you want.

Matt
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Old 21-11-2018, 22:11   #8
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Re: High power autopilot relays

PWM indeed. Relays will not work you would need SCR or IGBT and the hardware associated with driving them. Good luck with that. Save yourself the stress and buy a proper course computer.
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Old 21-11-2018, 22:45   #9
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Re: High power autopilot relays

Few years ago, I worked on getting a old neco Autopilot, was on a 65 ft Swan. It had a compound wound motor in it. Couldn't use a modern controller dirctly on the motor didn't work, need a drawing to remember why. But any way fed the AP power control to the neco relays. They were absolutely huge relays, contacts were maybe 8mm dia, can imagine the sparking that would occur due to inductive coils and back emf.
I agree you probably need bloody big relays if its a compound wound motor. the coils of the relays by the way had diodes to protect them.
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Old 22-11-2018, 09:35   #10
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Re: High power autopilot relays

Actually, the diodes across the coils are there to protect the driving circuitry from the voltage spikes generated by the disconnect of the coils.
They act like an ignition coil in a car.
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Old 22-11-2018, 11:02   #11
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Re: High power autopilot relays

In days of old when men were bold, mercury relays were used for high current switching. My Wood-Freeman autopilot uses them to switch a 1/2 hp hydraulic pump motor. Today, with the known risks of mercury and concurrent disposal issues, solid state relays are used. Here's an example that can handle 40 amps at 3 to 32 v DC:
https://www.sparkfun.com/products/13015
Lots of information available via a Google search using "solid state relay".
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Old 22-11-2018, 11:26   #12
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Re: High power autopilot relays

Quote:
Originally Posted by mvmojo View Post
In days of old when men were bold, mercury relays were used for high current switching. My Wood-Freeman autopilot uses them to switch a 1/2 hp hydraulic pump motor. Today, with the known risks of mercury and concurrent disposal issues, solid state relays are used. Here's an example that can handle 40 amps at 3 to 32 v DC:
https://www.sparkfun.com/products/13015
Lots of information available via a Google search using "solid state relay".
WARNING: The above is a solid state switch that's only intended for switching AC. It switches at the load current AC voltage zero-crossing. DC has no zero-crossing. It won't switch DC currents (well, it'll turn on, but never turn off). Internally, it uses a silicon controlled rectifier (SCR) that latches on until the voltage drops to zero. This happens twice per cycle with AC, and never with DC.

Assuming you actually need a relay (there are posts here that dispute that need)....

If 30 amp contacts are sufficient (you didn't specify), and the coil voltage is 12 volts (you didn't specify this either), then these will do (you didn't specify single or double pole):

SPST: https://www.digikey.com/products/en?...N1X-DC12&v=236
DPDT: https://www.digikey.com/products/en?...N2C-DC12&v=236

I personally buy the double-pole versions when only a single-pole is needed, and then connect the relay contact terminals in parallel. It doesn't cost much more, and the relay will last much longer (about twice as long). CAUTION: Don't use this type of open-frame relay if any explosive atmosphere could ever be present. (i.e., gas fumes). In explosive environments, never use any relay that isn't hermetically sealed and certified for use around explosive gasses (I don't trust potted relay's - the potting can crack).

Be sure to install a snubber diode connected in reverse polarity across the coil (just Google "snubber diode" for an explanation).
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Old 22-11-2018, 11:30   #13
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Re: High power autopilot relays

Oops, you're right. I picked the wrong link. Good catch, thanks.
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Old 22-11-2018, 12:07   #14
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Re: High power autopilot relays

You're asking an important question - most autopilots cannot handle more than ten amps. If the motor on your electro-hydraulic pump (may be a combined pump and cylinder) pulls more current than the autopilot can handle, you must install appropriately sized relays between the pump controls (valves) and the autopilot or you'll burn out the autopilot control circuits. DC relays are readily available and an earlier post has already named a good supplier.
Good luck
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Old 22-11-2018, 14:22   #15
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Re: High power autopilot relays

We recently discussed this here: AC12 autopilot running higher output linear drive


So yes, chuck the relay idea and get an h-bridge.


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