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 <mailto: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: CnC-List [mailto:cnc-list-boun...@cnc-list.com <mailto:cnc-list-boun...@cnc-list.com> ] On Behalf Of Josh Muckley via CnC-List Sent: Tuesday, August 11, 2015 10:03 AM To: C&C List <cnc-list@cnc-list.com <mailto:cnc-list@cnc-list.com> > Cc: Josh Muckley <muckl...@gmail.com <mailto:muckl...@gmail.com> > Subject: Re: Stus-List Universal Engine panel wiring I don't have a universal or any experience with one but it sounds to me like the glow plugs are drawing down the starting voltage. I would suggest installing a solenoid for the glow plugs in addition to a solenoid for the starter. The 2 articles below talk about poorly wired universal panels and make similar suggestions. http://www.pbase.com/mainecruising/universal_wiring_harness_upgrade http://www.pbase.com/mainecruising/solder_trouble_shooting Josh Muckley S/V Sea Hawk 1989 C&C 37+ Solomons, MD On Aug 11, 2015 8:50 AM, "Neil Gallagher via CnC-List" <cnc-list@cnc-list.com <mailto:cnc-list@cnc-list.com> > wrote: The power to the starter button is supposed to come off the switched terminal of the glow plug button. You are supposed to to have to push the glow plug switch and the starter switch every time you start, as the glow plug switch also powers both the electric fuel pump until the oil pressure builds up, and silences the low oil pressure alarm. Once the oil pressure rises, its switch powers the fuel pump. I put an M30B in our club launch and it has the same setup. Neil Gallagher Weatherly, 35-1 Glen Cove, NY On 8/10/2015 11:15 PM, David Knecht via CnC-List wrote: Since I got my boat, I have been bothered by the fact that the engine will not start in the way it is described in the manual unless plugged into shore power. The manual says to hold the glow plug button for about 30 seconds and then while continuing to hold that button in, push the start button. When I do that, the starter does not turn over. If I release the glow plug button and push the start button the engine starts fine. My father (retired electrical engineer) and I (genetic engineer- useless in this case but sounds good) spent some time trying to diagnose the problem this weekend and found two interesting things: 1. The buttons both tested fine in terms of their switch function. We then tested power at the engine. There is a heavy red cable coming from the battery to the starter measured 12V. The red-yellow wire from the start button is attached to what I am presuming is the solenoid (the wiring diagram in the manual does not show a solenoid). We only measured 8 volts at the solenoid when the button is pushed, but 12 volts everywhere else. So that probably explains the fact that both the glow plugs and starter won’t work at the same time because we appear to be losing 4 volts in the solenoid. I will pull the starter next winter and have someone test it unless someone has an alternative suggestion. 2. The wiring diagram in the manual (Fig 2 on page 13) shows the power from the key switch coming into the glow plug button and then a wire from the other lead to the start button. The manual shows that wire running from the downstream side of the glow plug switch so that the start button should only be energized when the glow plug button is pushed (as the manual describes). If that were the case, the I would not be able to start the engine with only the start button. Nevertheless, it does start the engine. Tracing the wires, we found that the bridging wire actually came from the hot side of the glow plug switch, so that either button will work independently as both are always powered. What I don’t understand is why you would wire it the other way (as the manual shows) since that would remove the ability to start the engine without the glow plugs (as in an already warm engine). I don’t know if the PO or some yard mechanic made that change or if it is indicated wrong in the manual, so I am curious how other Universal panels are wired. The way it is actually wired makes more sense to me than what is in the manual unless I am missing something. Thanks- Dave Aries 1990 C&C 34+ New London, CT _______________________________________________ Email address: CnC-List@cnc-list.com <mailto: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 _______________________________________________ Email address: CnC-List@cnc-list.com <mailto: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 _______________________________________________ Email address: CnC-List@cnc-list.com <mailto: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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