Adapting a marine autopilot for a continuous running pump to a reversing pump

Discussion in 'General Electronics Chat' started by GlenP, Jul 23, 2017.

  1. GlenP

    Thread Starter New Member

    Jul 23, 2017
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    Hi my 1st post on the forum, I'm looking for help on the feasibility or a fix for my problem, my knowledge is basic so please answer is simple language. My existing autopilot (Raymarine S3, too old to connect to new multi function chart plotter) drives a Raymarine Type 1 hydraulic pump powered by a 12v motor. It is connected to the pilot by 2 wires, the output here is protected by a 15a fuse. The pilot switches the polarity to reverse the pump to turn the rudder one way or the other, in normal use it operates for a max of say 10 to 20 secs, then nudges for a sec or 2 as required to maintain course.

    I have been given a much more modern autopilot (Raymarine XSol, that will connect to my chart plotter) but it is designed for a system with a constant running pump (non reversing), whereby the direction is controlled by opening 1 of 2 solenoid valves (the operation of these valves triggers the pump to run) to direct the flow of hydraulic fluid, the rated output is also 15a. It connects to the solenoids with 2 terminals for the negative cables and 2 terminals (marked A&B) for the positives.

    I'm after advice on how to connect this up to my existing system e.g.
    1. Use a simple connector block that connects both outputs of the Xsol to the pump motor reversing the polarity of A against B, my logic being that output form A would drive the pump one way and output from B the other way, my concern (you can see I have no electrical knowledge) is that in each case I will be connecting a + output to the - side and fear this may damage the pilot or send the lot up in flames. Could I protect the "opposite circuit" with something like a diode?
    2. Use something like a set of relays to make it all safer, perhaps solid state to prevent minute delays in running the pump? So that output A closes a relay that supplies a current from the main power supply in one polarity and output B does the opposite. If I can't do the 1st option can someone sketch out the layout and components for this one?

    Any solution that cost less than £100 would be economic for me.
     
  2. Tonyr1084

    Well-Known Member

    Sep 24, 2015
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    Recently someone has asked a VERY similar question. Here's a link to that conversation.

    https://forum.allaboutcircuits.com/...t-will-be-either-positive-or-negative.137863/

    Personally I don't like the idea of reversing a DC motor, though they can easily be made to run in either direction. My concern is that if it's running one direction then receives a command to change to the opposite direction, that's hard on the motor and the electrics that are controlling it. A running DC motor can act as a generator when slammed in the opposite direction. Doing so can increase the current drastically, blowing your 15 amp fuse.

    I'd recommend finding a different solution. If the new system depends on valves then attempting to circumvent the engineering of that system can easily lead to damage of something. Be careful.
     
  3. crutschow

    Expert

    Mar 14, 2008
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    Let's see if I understand. :confused:
    You are going from a system with a reversing pump, to one that uses a non-reversing pump with solenoids, but you do not have the solenoids, correct?
    Would it not be better to add the two solenoids and just use you pump as non-reversing?

    But if you want to convert the two solenoid signals to a reversing signal for your present motor you could use relays, however the reliability would be problematic.
    Likely better is to use a high-current MOSFET H-bridge to control the motor direction.
    You would want ≥50A MOSFETs with an ON resistance of ≤10mΩ.

    Here's an example H-bridge circuit:
    For your purposes inputs A and D would be operated from one solenoid signal and inputs B and C from the other solenoid signal.
    (The diodes and MOSFETs would need to be larger devices than shown.)
    [​IMG]
     
  4. GlenP

    Thread Starter New Member

    Jul 23, 2017
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    "Let's see if I understand. :confused:
    You are going from a system with a reversing pump, to one that uses a non-reversing pump with solenoids, but you do not have the solenoids, correct?"


    No the plan is to keep the reversing pump which is fairly new, I'd like to control it with the newer AP unit designed to operate solenoids, I have to confess I don't understand your diagram, but will be doing some surfing to see if i can. If not perhaps I could take it someone to make it for me are the components likely to be expensive?
     
  5. GlenP

    Thread Starter New Member

    Jul 23, 2017
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  6. crutschow

    Expert

    Mar 14, 2008
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    Yes.
    It would appear that circuit would work for you, (here's more info on it) but it would require some simple added control logic since it has a Direction and a PWM input, which needs to respond to your Solenoid commands.

    Below is an example of the needed control logic for the Pololu G2 consisting of three transistors and 8 resistors:
    It could be built on a small perf board.

    The Port and Starboard signals are the A and B solenoid outputs from the autopilot.

    upload_2017-7-23_12-50-59.png

    Here's a slightly simpler circuit using a single CD4047 OR gate logic package and 4 resistors.

    upload_2017-7-23_13-49-41.png

    Here are the Pololu connections:

    upload_2017-7-23_23-16-56.png
     
    Last edited: Jul 24, 2017
  7. tcmtech

    Distinguished Member

    Nov 4, 2013
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    The types of motors used on small hydraulic pumps that operate as the OP is describing are typically overbuilt well enough to handle such rapid reversing operation without problems. Extended use at load duty cycle is the only real concern.

    As for the OP I don't see any reason to over complicate a systems that obviously already does what he need it to do by making it run continuously when the stock design obviously works and has a simple two input control system. Plus when not being actively used does not have the motor and pump running for no reason.
     
  8. debe

    AAC Fanatic!

    Sep 21, 2010
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    Personaly I would be using a H bridge system to drive the original reversing hydraulic motor as its obviously worked well before. This should be the the new Autopilot SPX-SOL that he is going to use. A1.jpg A2.jpg
     
  9. GlenP

    Thread Starter New Member

    Jul 23, 2017
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    Thank you very much for taking the time to respond, but I confess that I lack the knowledge to build the logic board, can I buy something like that?
    There are many H bridge controllers on this site see:-
    http://www.robotshop.com/uk/brushed-motor-controllers.html
    Would another type be a simpler install for me?
    I have picked another board out, a Cryton MD30C http://www.robotshop.com/media/files/images3/md30cusersmanual_1_.pdf
    simply because it has more capacity and looks a more sensible size, could this offer a more sensible solution?
    Another is a Cryton Smart drive MDS40B which has even more capacity https://docs.google.com/document/d/1WtfqfUlUlLCjGR_q33lZQt5xLPtft4zG0jJk5PX1A8Y/view
    I'd really appreciate your guidance on helping me find a solution
    Glen
    I've attached a screen shot from the XSol's manual showing its connections Screen Shot 2017-07-24 at 08.06.45.png
     
  10. debe

    AAC Fanatic!

    Sep 21, 2010
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    If the boat is powered by an engine, you could run a Hydraulic pump of the engine to power the auto pilot. That's what a lot of fishing boats use.
     
  11. crutschow

    Expert

    Mar 14, 2008
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    I looked at the two Cryton ones you posted but neither seems exactly suited to what you need.

    You need to look for a bridge controller motor board that has a separate input for going one direction and another input for the other direction, not one with a single direction (DIR) input as most seem to have.
    That may be hard to find. :(

    Edit:
    Here's a simpler circuit to allow you to use the Pololu or most other H-bridge circuits with a PWM and DIR input.
    It only has two diodes and four resistors, and would be quite easy to build on a small perfboard.
    You just need to brush up a little on your soldering skills. ;)

    upload_2017-7-24_14-1-54.png
     
    Last edited: Jul 24, 2017
  12. debe

    AAC Fanatic!

    Sep 21, 2010
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    This is the H bridge & drive circuit for the Raymarine S3 hydraulic motor. A3.jpg
     
  13. GlenP

    Thread Starter New Member

    Jul 23, 2017
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    Crutschow, thank you very much for you time and knowledge, I'm going to have a go at making the board as you have described (I've never made anything like this before but believe I can solder ok) and connect it to the Cryton MDC30 as it has more than enough capacity. I've made a shopping list of the parts you describe (Maplin), only 1 choice on the Diode & 20k resistor (0.6w) but the 10k resistor comes in 0.6, 2 & 3w? will any of these be ok?
    Thanks again for all your help

    Screen Shot 2017-07-25 at 08.29.46.png
     
  14. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Not the Veroboard plain board. Get the Veroboard copper stripboard.
     
  15. GlenP

    Thread Starter New Member

    Jul 23, 2017
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    Alec thanks for that have changed it.
     
  16. crutschow

    Expert

    Mar 14, 2008
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    0.6W is fine as they will be dissipating only a few mW.

    Be sure and order a few extra diodes and resistors to take care of attrition. ;)

    Note that the direction logic for the Cryton unit is opposite of what I showed on my schematic in post #11:
    Output A to the motor is low when DIR is high (and PWM is high).
    upload_2017-7-28_9-6-34.png
     
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