Monday, January 30, 2012

Project ST5000: Report #3

My testing workbench
I have made some progress.
  • The MOV's have arrived (part no. V33ZA70)
  • I have determined that feeding the control inputs to a SSR with reverse voltage results in a 76 mA current flow - probably unacceptable for long-term use.  I got a couple of diodes (Radio Shack, $1.19) which will prevent back-feeding the inputs.
  • The MOV's are temporarily installed - they're the two red disks attached to the terminal strip in the drive... one for the clutch relay, and one for the motor.
  • I have successfully actuated the clutch in the drive unit, using the ST5000+
  • I have successfully activated the drive motor from the ST5000+, using the one SSR that I have. 
  • Irony: reviewing the schematic shows that the output circuit of the ST5000+ is actually an H-bridge.  Which I will be using to feed another H-bridge (albeit one that can handle a lot more current).
Now some thoughts about specifying solid state relays (SSR's) for the H-bridge... One of the figures of merit for solid state relays is its resistance in the "on" state - indirectly, this is used to rate the current carrying capacity of the units.  Using a SSR from Crydom as an example, the D1D40 (40 amps capacity) has an internal resistance of 0.05 ohms.  Using Ohm's law, the D1D40 will be generating heat at a rate of 80 watts (that's a lot - think about how hot a 75 watt light bulb gets) when carrying full load.  Obviously, this would require a heat sink.  The Benmar drive unit has a 10-amp rated motor in it - that's what it says on the motor.  Actual tests with my installed Benmar show that when the motor is stalled (I'm holding the wheel and preventing it from turning), the load is 15 amps.  But under normal operations, the load is something like 5 amps.  So with the D1D40, I could expect to see heat production at something like 1.25 watts under normal operation, and 11 watts in worst-case, locked rotor conditions. 

A Crydom D1D20 (20 amps rated capacity; 0.10 ohms internal resistance) would produce twice the heat.  Both Crydom units far exceed the needed current rating, but considering heat output, I am leaning toward the 40-amp unit.  My plan is to bolt the SSR's to the inside of the cast aluminum drive case cover, using it as a heat sink.  If I stick with 40-amp units, and given the intermittent nature of the motor's duty cycle when the autopilot is in use, heat should not be a problem.

There are a large number of Chinese SSR's on eBay with suitable advertised current carrying capacity.  However, none of these units show internal resistance in their specifications (on purpose?), and many of the ads show the SSR's bolted to large exotic heat sinks.  Tho they are more expensive, I am strongly tempted by the Crydom units.


    Sunday, January 29, 2012

    The Boat Show, the Big Seattle Boat show...

    If you live in Seattle, you probably recall that jingle that endlessly appears on TV this time of year...  "The boat show, the boat show, the big Seattle boat show...".  And then there are the billboard ads, and the ads on the sides of the buses...   Wait... No?  No jingle this year?  No ads this year?

    This year it's almost as if the show producers plan was to depend on word-of-mouth from prior boat show attendees to produce the crowd.  And the "free parking with on-line ticket purchase" thing?  Gone this year too.  Luckily tho we found free (it was Sunday, and we were early) on-street parking.

    So I have to say that, using the Seattle Boat Show as some kind of indicator of the health of the marine industries, I must admit I was apprehensive going in.  It just didn't look good.

    And after attending, I can't say it looked good either.  Attendance at the show was light.  I can't even say it was anywhere near as large as the last time we went, when the crowds were so heavy that it was hard to walk, and there were long lines for boarding the large boats.

    For a sailor, the show at the Expo center was a huge disappointment.  There was one forlorn sailboat - a Little Harbor 28, waay over in the far corner.  That's it.  And the wake boats and aluminum river sleds, which have in the past been relegated to the tunnel by the pressure of the large boat manufactures like SeaRay, Bayliner, et. al. for main floor space?  Well they had bled out into the main floor, occupying perhaps 25% of the space.  Apparently the big boat manufacturers did not want to pony up the bucks for floorspace this year.  And I can't say I blame them, with the price for a 25 foot boat now approaching $100,000, sales must be slim.

    And here's the final insult.  I took the exit survey at the Expo show when we were leaving.  One of the questions asked what kind of boat we had.

    "Sail" was not one of the choices.

    It's become the Seattle Power Boat Show.

    In the credit-where-credit-is-due department, I must say that the gear and accessories in the side halls seemed to be about the same as always - and they were seeing lots of business (and I contributed - I bought a pair of scuba gloves).  And despite the rain, we enjoyed touring the new and previously owned sailboats at the Lake Union in-the-water show.  There more used boats this year, a pleasant surprise.

    Thursday, January 26, 2012

    Now here's an idea whose time has come...

    How to get that first line ashore when you are approaching a dock? Here's a simple idea, available from DockWand, that we all, every one of us, need to have on one of our spring lines:

    Giving credit where credit is due, this was seen first at The World Encompassed.
    I'll be looking for this item at the Seattle Boat Show this coming weekend.

    Monday, January 23, 2012

    What a difference!

    What a difference a few hours makes!

    Here we are, literally less than 75 hours after the end of this year's "Seattle Snomageddon", and there is beautiful bright sunshine outside, temps in the mid to upper forties, and there is not a trace of snow in sight. 

    After living decades on the Western slope of the Rockies and having to shovel my roof at least once a year, I just cant say enough praise for Seattle's "self-shoveling" snow!

    Hello sunshine!

    Thursday, January 19, 2012

    Project ST5000: Early findings

    Findings so far:
    • The Benmar clutch relay draws 100 mA.  Plenty of headroom within the ST5000's spec of 2 amps.
    • Yes, PWM* is used for the output in all operating modes.   When set up to drive a hydraulic pump, the duty cycle is higher, but still uses PWM
    • When you press the +1 button (adjust the course 1°), the PWM duty cycle is about 10%.  There is no chance this will operate a relay coil.  The mechanical relays in the Benmar drive will need to be replaced.
    • The PWM frequency is 48 Hz - well within the operating range (multiple kHz) of almost any solid state relay
    • An H-bridge of 4 solid state DC relays can operate a reversing DC motor and will pass thru the PWM.
    • Having soft start and low speed runs for small rudder movements will be a huge boon.  I welcome the PWM overlords. 
    • Update:  I have ordered Allied Electronics part No. 70184710 as the MOV - it will shunt 20 amps at 58V, and cost a thundering $0.67.
    There are no barriers to proceeding.   Next step:  get 4 suitable solid state relays and a big MOV (to quench the magnetic field collapse back currents - the motor is a very inductive load).

    * PWM: an acronym standing for Pulse Width Modulation.  The DC power to the motor is not continuous, but rather is rapidly switched off and on.  The duty cycle is the fraction of the time that the power is on, and can vary from 0% (no power at all) to 100% (full power).  For a familiar example, your microwave uses PWM when you select anything less than full cook power.  When cooking at 80%, it will run the magnetron at full power for 8 seconds, and then turn it off for 2 seconds, repeating (you would measure a frequency of roughly 0.1 Hz).


      Wednesday, January 18, 2012

      Murphy was a Liveaboard

      It never fails, does it?

      In the middle of the biggest storm of the year, your water tanks run low.  So you have to go out and face 20+ kt out of the North, filled with stinging blowing snow (it doesn't show in the picture, does it?). 

      You have to hook up the very stiff hose to the dock hose bib. 

      You have to de-ice the hose - its full of ice, but not quite frozen solid (thank heavens!).  For a while, it blows chunks like a little ice cannon.

      And then finally you have to fill your tanks.

      Your gloves are soaking wet.  The wind chill on your hands is unbelievable.

      And you know what?  Even in this, it is still worth it.

      I love living on a boat!


      Monday, January 16, 2012

      Project ST5000: And so it begins - thinking out loud

      The old Benmar 14B
      (Remember when schematics came with electronics?)
      You may remember that a long, long time ago I posted a picture showing the bench testing of a Raymarine ST5000+ autopilot (sadly, that post seems to be gone...).

      Well today I start in earnest the process to graft the ST5000+ onto the old Benmar drive.  I am thinking out loud here, while I write this up, so bear with me...

      Why am I keeping the old Benmar drive, you might ask?  Well, for three reasons:
      • It is built like a brick sh%*#house
      • I have a spare
      • It is already installed - no small task by any means

      Basically, to interface with the drive unit, I need to supply +12V on either of two leads to get the drive to steer to port or starboard and a -12V common, and +/-12V to engage the clutch.

      That's it.

      Well, there is one slightly tricky part...  As I just mentioned, the Benmar drive unit has two wires for direction control - basically a port and a starboard wire - and a common -12V connection, while the ST5000+ has  just two terminals, which reverse polarity for port/starboard.  Since relay coils don't care which way the current is flowing thru them, a pair of diodes will take care of interfacing this, presuming that the -12V directional control common on the drive unit is isolated.

      As far as current requirements that need to be met by the ST5000+, everything in the drive unit is driven by relays, so the ST5000+ (which was designed to feed small hydraulic or linear drive motors directly) won't be taxed at all.  For example, the ST5000+ can supply 1-2 amps on the clutch line, but the clutch relay in the Benmar only needs 100 mA.  So the ST5000+ will be coasting.

      The larger issues are these:
      • I want to make the initial installation a "trial" install.  Just in case something doesn't work out.
      • I need to find a place near the roll/yaw/pitch center of the boat to mount the compass.  But unfortunately, that is very close to the engine.  And guess what - you're not supposed to mount the compass near any large masses of iron.  I guess I'll be trying compass locations out...
      • Running the wires will not be easy at all.  Especially considering that I will want to keep the old wiring in place, at least for a while, so I can't use the old wiring as messengers to pull in the new.
      • Mounting the rudder reference transducer will not be fun, hanging headfirst into the compartment beneath the aft berth.  Neither will be stringing wire to it.
      So today, I started by making current measurements.  Well I tried to make current measurements.  Sadly, it seems that my multimeter no longer has a functioning current circuit (no, its not the fuse).  The numbers I quoted above are based on the component values I found on the schematic.

      So stick with me here while I try to figure out my next moves...
      • Get a new multimeter and measure current flows for real.  Check to see if the -12V common lead for directional control is isolated.
      • Trial install #1:
        • Temporarily hook up the ST5000 to the drive unit, with the compass but without the rudder reference.
        • First, ensure that engaging the autopilot causes the clutch to engage.
        • Next, have the autopilot request a course correction - the drive should operate.
        • This trial can be done in the slip, with short wires.
      • Trial install #2:
        • Basically a parallel install with the existing Benmar controller.  This will require a lot more wire to get the ST5000 into the cockpit, where I can actually use it on the water.  At this point, I will also have to have the rudder reference installed.
      • Final install:  
        • Remove the Benmar controller.  
        • Make a proper mount for the ST5000 in the cockpit.
        • Locate the optimum compass location
        • Clean up the wiring.
      At least that's the way it looks from here, right now.

      {Time passes}

      I just went over the schematic yet again...  Unfortunately, I have now convinced myself that the Benmar drive unit has the common -12V lead on the directional control tied to the negative buss inside the drive.  I can easily lift this, but it will require opening up the drive.  Maybe Trial #1 should take advantage of that spare drive...  That would have the further advantage of the trial being completely a bench test, with no alteration whatsoever to the existing autopilot setup.

      Previous post in series


      Thursday, January 12, 2012

      Breathing easier

      It is probably a coincidence that the marina posted this notice at the head of our dock Tuesday, just a week after this blog posting.

      And kudos and thanks go to Deborah and Marty of Three Sheets Northwest, for giving that original post prominence on their site, putting it just under the article about the two boats that recently burned in Edmonds.

      Monday, January 9, 2012

      Let there be light! And heat!

      You may have one of these fairly ubiquitous Dickenson Newport heaters aboard.  I hope you are familiar with the process for lighting it, but if you are not or you struggle to get it lit, here is the process we have developed on Eolian over the years:

      This is a "pot burner" type of heater.  That is, the diesel is admitted into the bottom of a "pot", where the heat of previously burned fuel vaporizes it.  Once going, it is diesel fuel vapor which is burning, not liquid.  But to get it going, it is liquid diesel which much be ignited.

      Go to the head and get 4 squares of toilet paper.  Roll up three of them into a loose roll, leaving the fourth as a tail.

      Open the door on the Dickenson, and use the rolled up toilet paper to wipe off the soot from the last use from the inside of the glass

      Drop the paper into the heater.  You will note that there is an internal baffle device in the burner - this serves as a heat reflector which, when hot, will provide the heat to evaporate the incoming liquid diesel.  But now it is just in the way.  Using a poker, try to get the rolled up portion to go at least partially beneath the disk at the bottom of the baffle, leaving the tail accessible for lighting.  Do the best you can - usually you can't get more than one end under the disk.

      Turn the oil valve all the way on (to number "5").  Note that there may be a couple of stops that prevent you from turning the knob this far in normal operation.  But if you pull up on the knob, you can turn past the stops.

      Do something else for 2 minutes.  Do not lose track of the time!

      Using a BBQ lighter, light the protruding tail of the toilet paper.  Close the door.  You will need to turn on the combustion air fan all the way to get enough air down to the paper to keep it lit.  When the burning paper ignites the oil, it will be obvious - the flame is a rich bright yellow-orange instead of the pale yellow and blue of the burning paper.

      As soon as the oil lights, turn the oil valve back to number "1.5".

      If the burning paper fails to ignite the oil, turn off the oil valve.  There is very likely enough diesel in the pot, it's just that the flame from the paper didn't reach it, or the diesel did not yet wet out the ash in the bottom of the pot far enough to reach the paper.  Roll up some more toilet paper and try again, leaving the oil valve closed.

      When the oil ignites, turn the combustion air fan down one notch.  When it is all the way up, it will force smoke and fumes into the cabin.

      How much combustion air the heater requires once it is settled in is a variable depending on the stack length.  Ours (stack is approximately 36") requires none.  If the flame is burning cleanly (no trailing soot tendrils off the tips of the flames, yellow in color - not orange), then adding more air just means you are pushing valuable heat up the stack.
      Some notes:
      1. Before lighting the heater, be sure that there is nothing combustible near or above the Charlie Noble outside.
      2. In the unhappy event that you get too much oil in the burner before getting it lit, your first clue will be that the flame grows much more quickly than normal, and to a much higher level.  Should this happen, turn off the oil!  If you suspect it might be happening, turn off the oil!  In our heater, the oil burns off harmlessly when this happens, tho with a frightening pulsing roaring sound, and the heater does get very hot.  Standing by with a fire extinguisher would be prudent if this happens.
      3. The oil valve is very non-linear in controlling the heat output.  Normal operation will be only be between the "1" and "2" marks.
      4. The oil feed and combustion air should always be adjusted so that the flame remains above the top ring of the baffle.  This is the way the burner is designed to operate.
      5. If you should ever be moved to clean the heater, be advised that the collection of ash and crud in the bottom of the burner is an important part of the combustion process - it serves as a high surface area diffusion plate/evaporator, much like a candle wick.  If all the material on the bottom of the burner is removed, the heater will be difficult to light until this layer gets re-established.


      Friday, January 6, 2012

      How to: Make ricotta

      Recently (and earlier) I've referred to making ricotta onboard - that wonderful sweet creamy cheese.  Bonny, the Italian lady that taught us to do this, told us that making cheese which would be used in cooking dinner was just another part of making the dinner itself in her family.

      I have been asked how we do it - it is simplicity itself:
      • In a pan which is large enough, put 1/2 gallon of whole milk and 1 pint of buttermilk.  Mix well.
      • As slowly as possible, heat the mixture to 175°-185°.  DO NOT BOIL!  
      • By the time you get to 160°, curds will probably be starting to form.  This will impede the heat flow by thickening the mixture.  Occasional gentle stirring is in order.  But I repeat, GENTLE.  You don't want to break up the forming curds.  When curd formation begins in earnest at say 170°, cease stirring.
      • Once the mixture reaches 175° to 185° and the curds are beginning to separate from the whey, turn off the heat.  Be careful not to overheat.  Measure the temperature of the mixture in multiple locations - the thickening mixture will trap heat near the source.
      • Let the mixture stand for 10 minutes.  
      • Drape a double layer of cheese cloth over a colander or strainer.  In a pinch you can use another pot, but you'll have to lift out the cheese cloth and dump off the whey as it drains.
      • Using a slotted spoon, carefully and gently scoop out the curds from the whey and place them into the waiting cheese cloth.  Every inch or so of depth, sprinkle on a little salt.
      • The more you drain the cheese, the firmer it will be.  For a nice spreadable cheese, do not over drain
      160° - curds starting to form
      180° - curds separating from whey
      Into the cheese cloth with you!
      Drip, drip, drip
      Some notes:
      • Don't bother doing this if you feel you must use anything less than whole milk.  Abominations: 2%, 1%, skim milk.
      • If you don't have buttermilk, any source of (edible) acid will do - vinegar, lime juice, lemon juice.  But the character of the resulting cheese will be subtly different.  Try starting with a tablespoon or perhaps two of vinegar or citrus juice.
      • Real cheese cloth works best - not that filmy stuff that you could push your finger thru.  Use a double layer.
      • An oriental noodle spoon - the round flat one with all the tiny holes - works really well for scooping up the curds
      • Don't just discard the whey - it is a wonderful cooking resource.  For example, if you are making pasta, boil it in the (already hot) whey instead of plain water for a wonderfully creamy taste.  You were making pasta, weren't you?


      Wednesday, January 4, 2012

      Cheese night

      It's a kind of music. 

      The wind is howling, rain is blowing against the deck and windows, the fenders are squeaking, and the boat is rocking back and forth, keeping time in the slip. 

      And down below we are cozy.  The heat pump is keeping us warm, and I am making cheese (ricotta).

      Life is good.
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