You are correct, Garry, it is electricity 101. And the calculations are in line with the principals taught in electricity 101.
As a matter of practicality, it does not matter what the current associated with the 8 volt reading is. The engine starts when you push the start button. Any good solenoid will pull in with somewhere near 1 amp. No I have not tried to look up the spec for pull in voltage for the particular solenoid on a Universal diesel. If you put six amps across the solenoid, that is 5 more than you should need. No harm, no foul, unless the current flow is high enough to overheat and burn out the coil in the solenoid. I presume whoever engineered the starter put in some internal resistance to limit the current to a safe level. And that the person who selected the starter for this engine at Westerbeke/Universal took the current flow into account when designing the panel and wiring harness. Also as a matter of practicality it is not possible to measure the voltage drop across the solenoid alone, since it is an integral part of the starter. Measuring the voltage drop between the solenoid connection on the starter and ground includes the voltage losses associated with the rest of the structure that were listed in my earlier post. Also see the comments I made about the system voltage (between B+ and ground) dropping below 10.5v when the starter is engaged and there are 200 amps (+ or -) flowing from the start battery through the starter. Sort of makes the calculations at 12v with only a theoretical resistance of the solenoid coil moot. Remember the original question was not “Why does my engine not start?”. It was “Why is my panel wiring different from what is shown in the wiring diagram and the starting procedure different than that shown in the owner’s manual?” From: CnC-List [mailto:cnc-list-boun...@cnc-list.com] On Behalf Of Garry Cross via CnC-List Sent: Tuesday, August 11, 2015 12:33 PM To: cnc-list@cnc-list.com Cc: Garry Cross <garr...@gmail.com> Subject: Re: Stus-List CnC-List Digest, Vol 115, Issue 36 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 <rickbr...@earthlink.net <mailto:rickbr...@earthlink.net> > To: <cnc-list@cnc-list.com <mailto:cnc-list@cnc-list.com> > 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 CnC-List@cnc-list.com <mailto:CnC-List@cnc-list.com> http://cnc-list.com/mailman/listinfo/cnc-list_cnc-list.com
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