If the contacts on the glow plug button are fouled with carbon, it may not be able to pass the needed current. Try shorting across the terminals on the back of the switch so you bypass the internal contacts.
Dennis C. Sent from my iPhone > On Aug 11, 2015, at 9:34 PM, David Knecht via CnC-List > <cnc-list@cnc-list.com> wrote: > > This has been a great learning experience and I think I understand most of > what has been said. One thing I don’t get is why Rick thinks I should change > the wiring back to the original design. With that setup, if you have a > problem in the circuit (as I apparently do) you would not be able to start > the engine. The way mine is wired seems to have no obvious disadvantage if > all is OK, but gives you the ability to start the engine with a poor > connection somewhere. If it were wired as original in the manual, I would > not be able to start at all. I don’t see a disadvantage to my panel’s wiring > design. Rick- are you suggesting that the start problem might be caused by > the wiring change? I can’t see that. > > One further clue if it helps, with the start button and glow plug button > pushed, you can hear the fuel pump slow way down and I hear a noise from the > solenoid but I don’t know if that noise is the solenoid actually closing. > > One clarification- I have no solenoid on the glow plug circuit either from > the manual circuit diagram or as far as I have found in the wiring, so I > presume that is just a difference in my engine and others. > > I should also note that when I first got the boat, I had problems starting it > at all unless plugged into shore power. I thought it was the batteries so > got new ones, but that made no difference. When I cleaned the ground wire > connections to the engine block, it started as I do it now. I can’t remember > if I ever tried pushing both at the same time back then. I was new to glow > plugs and had not found the manual yet and its description of the start > sequence, so I doubt it. > > Tomorrow my Dad and I are going to take apart the harnesses and fuse holders > and clean all the contacts and see if that makes a difference. Dave > >> On Aug 11, 2015, at 10:01 PM, Rick Brass via CnC-List >> <cnc-list@cnc-list.com> wrote: >> >> Your math is correct, and the high current through the glow plugs (and the >> fuel lift pump) accounts for the fact that the system voltage drops to >> 11.5-12.0v when the glow plug button is pressed. >> >> But I just looked at the manual for my M35B and the glow plug button does >> not provide current for the glow plugs or the fuel pump. It provides current >> to close a solenoid that connects the glow plugs and the fuel pump to the >> battery. So the high current flow is ultimately from B+, and the current >> flow through the glow plug button only needs to be a faction of an amp. >> >> I don’t recall David saying that the engine did not start or the starter did >> not engage. Rather he indicated that the engine panel was wired differently >> than the manufacturer’s wiring diagram and the starting procedure was >> different than the procedure spelled out in the owner’s manual for the >> engine. >> >> If the starter engages when the button is pushed, then there is demonstrably >> enough voltage and resulting current flow to close the solenoid (which >> should take well under an amp). >> >> When the starter solenoid is closed, that creates an almost dead short on >> the high current side from the battery (via the big red battery cable >> connected to the starter) to ground through the starter coil, and there will >> be 175 to 250 amps of current flowing through the starter. The resulting >> magnetic field creates enough torque and rotation speed to start the engine. >> On my boat, with a 4 cylinder M35B, the system voltage drops below 10.5 >> volts when the starter is engaged. As a matter of fact, if I restart the >> engine after the chart plotter has been turned on, the chart plotter will >> shut down due to the low voltage and will need to be restarted. (I swear >> every time that happens.) >> >> It occurs to me that the fact that the system voltage drops to around 10v >> when the starter is turning could be a contributing reason that David only >> measured 8v from the solenoid connection to ground when he pushed the >> starter button. If the starter does engage, then I stand by my diagnosis >> that there is nothing amiss with solenoid or starter, and that it would be >> best to restore the panel wiring to the way it left the factory. >> >> BTW, Mainecruising is right is saying the panel is the choke point for >> current supply. All of the current to power the solenoid that connects the >> battery to the glow plugs and fuel pump, the starter solenoid, and the >> instruments comes through the key switch. Of course the panel and wiring is >> designed for the current flow expected. And, of course, the panel on a >> Yanmar is also the choke point for current to the idiot lights, alarms, and >> the starter solenoid as well. >> >> >> From: CnC-List [mailto:cnc-list-boun...@cnc-list.com] On Behalf Of Josh >> Muckley via CnC-List >> Sent: Tuesday, August 11, 2015 12:27 PM >> To: C&C List <cnc-list@cnc-list.com> >> Cc: Josh Muckley <muckl...@gmail.com> >> Subject: Re: Stus-List Universal Engine panel wiring >> >> I checked the specs of the universal glo-plugs and they average 2 ohms. >> This equates to ~6amps times 4 cylinders equals ~24amps. That's a pretty >> good amount of current draw. The way Maine Sailor makes it sound the panel >> is the choke point and all the current for the glo-plugs AND starter >> solenoid has to come from the panel and through various plug connectors and >> relatively small gauge wire. Each adding it's own amount of additional >> resistance. Not to mention poor connections, burnt contacts, and corrosion. >> I'm not surprised at all to see the voltage dragged down enough to prevent >> the starter solenoid from being able to close. >> >> Josh Muckley >> S/V Sea Hawk >> 1989 C&C 37+ >> Solomons, MD >> >> On Aug 11, 2015 11:41 AM, "Rick Brass via CnC-List" <cnc-list@cnc-list.com> >> wrote: >> In about 20 years of working on boats, mine and others’, the photo is the >> first Universal panel I have seen with an ammeter instead of a voltmeter on >> the panel. >> >> Of course the glow plugs will draw down the starting voltage. When you power >> the glow plugs you are running ten amps or so across a couple thousand ohms >> of resistance to create heat. If your battery is OK, and of normal capacity, >> the voltage loss to the system will be negligible – maybe 0.1v or less. But >> that happens any time you put a load on the system. Doesn’t the voltage >> shown on your battery monitor drop from around 12.6 to 12.4 or 12.5 when you >> turn on the lights in the cabin? Same thing. >> >> The only way that the glow plugs will cause a significant drop in the >> starting voltage is if you have a direct short in the wiring or a defective >> glow plug that is shorted to the engine block. Then you get a direct short >> from battery to ground through the engine panel wiring harness, and you let >> all the smoke out of the engine wiring harness. (Sorry, old electrical >> engineering joke coming back to haunt me.) Which is why there is a typically >> a 20 amp fuse in the power wire that supplies the engine panel. >> >> Putting a solenoid into the system so the button engages the solenoid and >> the solenoid powers the glow plugs really doesn’t accomplish anything. >> Unless you have the unlikely confluence of a short in the solenoid and a >> short in a glow plug, in which case you get a short direct from battery to >> ground and you let the smoke out of the whole boat. >> >> >> Rick Brass >> Washington, NC >> >> >> >> From: > _______________________________________________ > > Email address: > CnC-List@cnc-list.com > To change your list preferences, including unsubscribing -- go to the bottom > of page at: > http://cnc-list.com/mailman/listinfo/cnc-list_cnc-list.com >
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