Pilothouse window defroster

As the owner of a newly-acquired Pacific Trawler 40, I am confronted by the usual assortment of "warts". One of which is the propensity of my pilothouse window defroster to continuously trip the breaker that controls its operation. Upon opening the overhead cabinet that houses the defroster, I am confronted with a cramped installation (its a boat! what do I expect?), and absolutely no information regarding the make or model for the defroster. And, as it's constrained by the wiring, it is difficult to remove in order to gain full view of the unit.

My clamp meter confirms that is does, indeed, draw 24A at 12VDC, which is more than enough to trip the 20A circuit breaker it is connected to. Inspection of the defroster confirms the location of the 12VDC wiring. However, there appears to be an additional 110VAC 3-wire connection as well. That connection is inaccessible without removing the defroster, which will require cutting all the wires to get at the beast.

So... here's one question. Does any Pacific Trawler owner of around the 2000 year vintage have any documentation regarding the defroster unit I might have? I've searched the WWW, and found several that "look" like mine, but as I can't see a manufacturers data plate on mine, I can't confirm much. Nor is a telephone call to the various manufacturers particularly productive, as I can't confirm it's actually one of theirs!

Second, my defroster has both a centrifugal ("squirrel cage") fan providing the air flow, and a down-stream heating element. I can't tell if the heating element is getting hot, as the breaker trips after only a few seconds of operation. And I have no idea if the element is heated with 12VDC or 110VAC.

Third, if (as I suspect) the fan is the only power draw on the 12VDC circuit, why would the fan draw 24A? Heck, that's almost 1/3 hp, which seems excessive for this application.

And lastly, if both the fan AND the heater use 12VDC, whatineck is the 110VAC circuit for???

I be confusticated, and any insight would be appreciated before I perform surgery on the defroster to yank it out and sit it on my bench for R&R.

Regards,

Pete

Peter we just use a fan stuck on the "dash". Works amazingly well for what it is. I'd rather have a windshield washer than a built in defroster.

Holy cow .. (as if this was a farmers forum) ... you now have a Pacific Trawler 40 and presumably are selling the Canoe Cove? Seems you've had the CC forever and must be suffering from loosing your old friend.

I love the PT 40 but at times having the pilot house that far fwd could make for an exciting ride. What a roomy and stable boat w such a low CG (presumeably) and low windage. Where's the engine or engines? Suspect it may be a V drive to carry that "roomy" bit to the highest level. A new boat is always a great high.

Pete, it sounds like you have a good grasp on your trouble shooting approach, but just need to be able to get the unit out for further inspection. I know on our boat we run two Jabsco 35400-0000 blowers on a 20 amp DC breaker with no problem. It seems to me the heating element would be a huge draw-
How does the 110 AC connect to it?


1983 Present 42 Sundeck
Twin Lehman 135's

Eric-yeah, the CC has moved on. Hard to do, but the right call for many reasons. And while Linda and I are pleased with the performance of SPIRIT BEAR, I reminded Linda she might be less enamored when big water comes over the foredeck. It's a little boat, at least compared to the CC! But then, you know more than most about little boats.

Forklift-looks like I'll have to perform boat surgery and jerk the defroster from its hidey-hole to figure this thing out. No way to determine 110VAC connectivity, or R&R motor in place. That 24A is going somewhere, but obviously not to its proper home. Ditto the AC.

Standby for news at 11. I'll post progress.

Pete

I look forward to it. Post pictures if you can. Al (FlyWright) would really like to see some ?️


1983 Present 42 Sundeck
Twin Lehman 135's

Hi Pete.

Sorry to hear of your defroster challenges.

Please send me your contact information so I can send you the owners list, you might be able to contact owners of 2000 vintage boats directly.

Good luck. Jay N - cjnmaritime@gmail.com

Forkliftt said:

I look forward to it. Post pictures if you can. Al (FlyWright) would really like to see some ?️

Click to expand...

Well, I'm finally back at it. I have removed my heater/defroster unit from the overhead in my pilothouse, and am continuing my efforts to troubleshoot this bad boy. This thing is really tucked up in there tight, so in-place R&R is simply not possible.

After removal, I found the only markings on the blower/heater unit (I've attached a picture) are as follows:

SPAL Type 008-A37/C-42D 12V.

Attached to the left side of the black centrifugal SPAL blower is a grey box, housing a set of heating coils. Input to the heater/blower is via the 12VDC red leads with yellow connectors on the bottom left of the heater box.

What I originally thought was 110VAC input to the blower (it was inaccessible until I removed the thing) via the four tangs just to the left of the SPAL label are, in fact, connections to a 3-speed control for the fan, which I haven't found yet. My guess is these are common to the "bus heater" speed controls located to the right of the steering wheel.

The heating coil resistance measures 0.6 ohm. As the delivered voltage underway is approximately 13.5VDC, this results in a current draw to the heater alone of 22.5A. In addition, the blower draws another 4.5A at full speed. No wonder the 20A breaker at the helm station trips!

SPAL disavows any knowledge of the heating coils. They simply supplied the blowers to Pacific Trawler as OEM. So, now the quest for the heating coil manufacturer! Removal of the heater unit (it's simply a set of 15 series-parallel nichrome wire coils, housed within the grey aluminum box) reveals the following manufacturer's name:

FARNAM CUSTOM PRODUCTS
25012
2899

No evidence of shorting of the coils withing the coil assembly can be seen. All the coils appear intact, and are not inadvertently touching each other, which would lead to a short circuit within the coils. All appears well-they simply have too little resistance to function properly in the circuit as I understand it.

Contact with Farnam Custom Products to date has been unsuccessful. They haven't returned email, and I simply get voice mail on the phone.

Sorry for my rambling. I REALLY need a pilothouse window defroster here in the PNW, and don't want to butch up this install, so I'd like to fix what I've got. To do so, I need to figure out two things:

a. Where is the speed controller for the blower motor? It certainly isn't marked as such anywhere within my pilothouse. The only 3-speed controller I've found controls the blowers on the OEM "bus heaters" that provide heat underway. Could they be common with the defroster? And only control the defroster when the instrument panel breaker marked "DEFROSTER" is in the ON position?
b. What is the correct resistance for the heating coil portion of the heater/defroster?
c. Any guesses on who supplied the grey box with the coils inside? I'm guessing Farnam, but they're not responding.

This is one of the sweet mysteries of life, and troubleshooting this unit is making me nuts. With Pacific Trawler out of business, finding information on OEM installations is not trivial. If anyone's got some insight, I'd appreciate some guidance. Otherwise I may lose the rest of my hair. Sigh....
Regards,

Pete

OK, how 'bout the picture, as promised????

Put 12v to the heating coils and see what they do. Measure current draw. Be prepared to disconnect in quick order if they get too hot.

Note you cannot really use Ohm's law on heating elements. Special alloys are used so resistance varies with temp. This helps limit temp if air flow is interrupted.

Thing might work fine if you use a 30A breaker, just make sure the wires are up for that current.

Ski in NC-Thanks for your reply. Since my previous post, I have heard back from FARNAM CUSTOM PRODUCTS, who confirmed that they did, indeed manufacture the coils, they are no longer in production, they supplied them as OEM to Pacific Trawler, and said they should measure between 0.55-0.6 ohms at room temperature, which they do.

And yeah, I get it that nichrome wire changes resistance with temperature. But since the designed operating temperature of the heater is probably less than 300 deg F (that's my guess), the change is insignificant.

There are several nichrome wire heating element calculators on the WWW. The one I use confirms that, for the existing 0.32 dia wire diameter, ~300 deg F max temp, 13.4VDC input, the necessary resistance should be about 3.5 ohm at room temp, and the coils should draw about 3.5A. The calculator also confirms that, with my existing 0.6 ohm resistive coil, the coil temp will reach over 2000 deg F, and draw 22.5A while doing so.

I have confined that the current draw when connected directly to 12VDC, is ~22A, but not the temp-I won't let the coils get THAT hot!

So...I clearly still don't have a clue how the blower and the heating coils are integrated. My best guess at this point is my problem has something to do with the speed controller, which I have not yet located. And no, simply upping the circuit breaker to 30A is a bad idea. Ain't gonna take that chance.

I was hoping some Pacific Trawler owner would chime in here and educate me on how their unit works (where's the controller, for instance), but no joy to date.

Pete

Math seems a bit off. At 3.5A, the whole coil is going to make no more that 47W, which is not going to heat an airstream much at all. I use a hair dryer for my defroster and on low, it draws about 5A at 120V, for 600W. Even then, it is pretty lame.

22A at 13V is 286W, half of my rig on low. It's watts that give the heat, not the amps.

Try running it on the bench, see how warm the air discharge is.

Ski is right on. Exactly my thoughts. What is the wire size of the feed? I am guessing it is sized for 30 amps. The breaker may have held at one point and became tired after being overloaded. In the calculating of the heater wire values you have to calculate how the coils are connected to each other. Big difference if they are in series or parallel or a combination of both.

The saga continues. To summarize so far:

a. The blower (mfg by SPAL) functions correctly, drawing 4A at 12.5VDC. With the OEM wiring, it functions on the high-speed setting only. There is no speed control for the defroster; other wires in the wiring loom to control the speed are non-connect. The current draw is within specifications as confirmed by SPAL.
b. The heater element (mfg by Farnam Custom Products) has a coil resistance of 0.6 Ohm, which was confirmed by Farnam as correct. When connected to 12.5VDC, it draws 22A, and reaches red heat (~950 F). As the nichrome coils slowly heat to that temperature, the current draw reduces to 19.5A. And believe me-this is SMOKING hot! And FYI, that's a 250W power consumption.
c. The blower and heater are connected in parallel, controlled by a M&I Systems switch/breaker, rated at 20A. As I have previously related, this breaker functions as designed, opening when a current >20A passes through it.

Given the total circuit draw is 22+4=26A, there is no way this defroster EVER functioned as installed. I believe it was a flawed installation from the factory, and no previous owner bothered to track it down. And no, neither I nor my surveyor caught it at survey.

So, how to fix! The proper way is to replace the heater coil with one with a higher resistance. Given that Farnam no longer makes this particular coil package, this would be a custom part, and a non-starter for me.

Adding additional resistance to the heater coil via a coil-wound power resistor in series with the heater coil is a possibility, although we're talking about fractions of ohms (~0.2ohm) here, and tricky to get it right. Such power resistors are ~$60 each. This will also result in dropping the heater temperature about 400 deg F. Dunno if that's too cool or not.

Upping the breaker to a 30A rating is possible, given that M&I can come up with a direct replacement for the panel. All wiring in this circuit is >14ga, so (haven't confirmed yet) I think this is sufficient to carry this load.

Have any other Pacific Trawler owners of similar-vintage boats had this problem? As I said, I believe this is a legacy of a flawed OEM design. I can find no evidence of repairs, or previous owner's tinkering. All appears just like it came from the factory. Am I the only one that's run into this?

Regards,

Pete

At 300W, why do you want to add a resistor and reduce heat? When you need defog, you want as much heat as you can get. If supply bkr and wiring is undersized, size them up for the job.

Fogged pilothouse windows suck, so you want that system as powerful as you can get. And with a 12v source, it will be pretty weak by nature.

What kind of heating do you have? Can you put extra ducts to blow on the window? If you have water heating, can you put a bus heater there?

OK, I'm done now. Here's the final fix:

a. Replaced existing M&M breaker/switch in the pilothouse dash panel with an M&M breaker rated at 30A. And yes, I did verify the wiring to/from the defroster could handle this current draw without excess voltage drop and concurrent overheating.
b. Abandoned the separate blower feed (common from this breaker) to the fan. As the fan only operates at high speed, there is no need for a separate feed. FYI, the blower was wired OEM as if there were a 3-speed controller on the fan speed, but only the high-speed feed was active. The mid- and slow-speed feeds were N/C. If you look at my original post, you'll see where I thought this was a 110VAC feed to the heater. Tain't so. It's simply the 12VDC fan speed control.
c. Paralleled the fan and the heating element feeds direct from the breaker.

Final current draw in the circuit: 24A at 13.4VDC as with the OEM install. Heater draws 20A, blower 4A. Heater dissipates ~300W, and reaches a temperature of 950 deg F without the blower running. This temperature reduces to something like 150 deg F at the elements with the blower on, so obviously, one operates with the blower at full chat!

Not sure of the final air temperature that is achieved downstream from the heater, as I don't have a way to reliably measure the temp of the air being exhausted across the pilothouse windshields. Haven't had a chance to test at sea yet, but like I said, should work good, last long time.

Off to the next task....

Regards,

Pete

950 deg F ?

For folks with out a defogger that wish they had one , large trucks have plug in 12v heaters that could be used.

Replace the 12v cigar lighter with a 240V 15A plug and socket from a box store as it will carry good amperage for hours , and 120V plugs wont fit.

On our 2002 PT the defroster fan speed control is on the left side of the fold-out panel that holds the wheel and instruments. The heat comes from the diesel heater, not electricity. It is possible that your defroster may be effective by simply blowing ambient air on the wind screen. That is, just disconnect the electric heater. A poster mentioned that he just used an external fan blowing on th wind screen. Truckers do this effectively.