I disagree with your point about 8V at the starter solenoid. In a brand new system with good wiring the only load is the solenoid. When 12V is applied to it, the voltage drop across it is 12V. If it is not then there is some other load in series between the source and the solenoid. On the other side if there was a poor ground you would have 12V on the input side and some other voltage on the ground side. It is just basic electricity 101.
When two loads are in series the voltage drop across each will be in proportion to the ratio of the two resistances. An example would be a solenoid with 2 ohms resistance and a feed circuit with 1 ohm of resistance. In this case the drop across 2 ohms is 8V and across the 1 ohm is 4V. V/R = I, total resistance is 3 ohms 12/3 = 4 amps. In this example 1 x 4 + 2 x 4 = 12 Looking at it another way, if you can get 12V across the solenoid it will draw 6 amps. In the example 4 amps may not be enough to draw the solenoid contacts together to energize the starter. ---------- Forwarded message ---------- > From: Rick Brass <[email protected]> > To: <[email protected]> > Cc: > Date: Tue, 11 Aug 2015 11:17:02 -0400 > Subject: Re: Stus-List Universal Engine panel wiring > > David; > > > > Previous owners, shade tree mechanics, and inexperienced/inexpensive > mechanics often make repairs or modifications that are ill advised or less > than optimal. For example, I recently helped one of the boaters on our City > Docks diagnose why his recently replaced fuel gauge did not seem to work > reliably. Turned out the guy who replaced the gauge had gotten power from > the glow plug button – the downstream side of the glow plug button – so the > fuel gauge was only powered up when the glow plug button was pushed. > > > > Universals and Westerbekes are designed to be wired and started in the > manner described in the owner’s manual. I would restore the wiring to what > is shown in the wiring diagram, for a couple of reasons. > > > > Regarding the 8V at the starter solenoid terminal: You saw battery voltage > (about 12.6v) on the hot side of the starter button with the button not > pushed, 0v on the output side of the starter button with the start button > not pushed, and then 8v at the solenoid terminal when the button was > pushed. When you push the button you are energizing the coil of the > solenoid and creating what is almost a dead short across the solenoid. What > you were measuring between the solenoid terminal and ground is the voltage > drop that results from resistance in the coil, resistance in the metal of > the starter, resistance across the bolts holding the starter in place, and > resistance in the metal of the block as the current travels from the > solenoid terminal to the ground wire. 8v is a bit lower than I would > expect, but I see nothing unusual in such a reading. Your starter and > solenoid are fine. > > > > As Neil pointed out, pressing the glow plug button does a lot of things. > > > > Of course it powers the glow plugs, which are in essence a high resistance > short in the wiring, and the voltage at the output side of the glow plug > button will drop into the 11.5v to 12.0 v range. Powering the glow plugs > heats the air flowing into the combustion chambers, which is needed for a > cold start and improves starting during hot starts. In indirect injection > diesels (where fuel is injected into the airflow before the intake valve > instead of directly into the hot compressed air just before the conclusion > of the compression stroke) the glow plugs are needed to get good initial > combustion. Hot air makes the starting easier and faster, reduces the load > and cranking time on your starter, and ultimately how much current you draw > from the battery to start the engine. > > > > The glow plug button also powers the electric lift pump that supplies fuel > at 4 or 5 PSI (it might be as high as 7 PSI, but I don’t recall exactly) > through the engine fuel filter to the inlet of the high pressure injection > pump. That lift pump coming up to pressure is the rapid clicking sound you > hear for the first few seconds after you push the glow plug button. After > the engine starts, the pump is powered off the oil pressure switch as Neil > described. In a hot start situation without power to the lift pump, the > high pressure pump will supply fuel to the injectors for a few engine > rotations. But if the engine does not start the pump will be starved for > fuel and the engine will not start. Fuel starvation becomes more likely as > your fuel filters get plugged over time. > > > > As I said, I’d put the wiring back to what it was supposed to be according > to the manual and the wiring diagram. > > > > > > Rick Brass > > Washington, NC > > > > _______________________________________________ > CnC-List mailing list > [email protected] > http://cnc-list.com/mailman/listinfo/cnc-list_cnc-list.com > >
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