How much voltage drop at Starter while cranking?

[hanleyclifford]

Once again, if you have anything on that ignition circuit (like an electric fuel pump, for example), it is robbing you of voltage to coil+. Run the direct #14 wire from "R" on the starter to coil+ and watch her start easily.

[ndutton]

The 'R' terminal

I'm so against this it's hard to find the words. Here goes.

Using the 'R' terminal in this instance only masks the problem, does nothing to solve it. Jack, as you've discovered you have a massive voltage drop to the coil input during starting and we haven't really found the root cause yet. As discussed it could be the batteries aren't cuttin' the mustard any more, maybe the ignition wire with splice has developed a high resistance for one reason or another, could be the battery cables or their terminations, any number of things but installing an ignition system bypass and calling it good will only delay the inevitable. Whatever is really wrong ain't gonna get better on its own.

The idea that an electric fuel pump is contributing to the problem doesn't fly for me for at least two reasons:

1. It should not be drawing any power in the early phase of starting because of the OPSS.
2. Nobody elses electric fuel pump is drawing down the system. If it did, that's a comment on the system, not the pump.

I have an electric fuel pump connected through an OPSS per USCG requirements, an electric coolant pump and a ballast resistor ahead of my coil input (identical Flamethrower) yet mine starts instantly without the 'R' terminal bypass. How can this be??

Back to the 'R' terminal
I suggest that our engines don't need it period. If your ignition wiring and components impart such a voltage drop that the engine can't start without the 'R' terminal bypass, there's a problem or several that need to be addressed. The bypass is not a solution, it's a band-aid.

Before you say it, for those (not Jack) who need to bypass a ballast resistor during starting to get her to fire, your resistor is way too aggressive, simple as that (assumes the rest of the ignition system is in good repair).

[hanleyclifford]

I'm so against this it's hard to find the words. Here goes.

Using the 'R' terminal in this instance only masks the problem, does nothing to solve it. Jack, as you've discovered you have a massive voltage drop to the coil input during starting and we haven't really found the root cause yet. As discussed it could be the batteries aren't cuttin' the mustard any more, maybe the ignition wire with splice has developed a high resistance for one reason or another, could be the battery cables or their terminations, any number of things but installing an ignition system bypass and calling it good will only delay the inevitable. Whatever is really wrong ain't gonna get better on its own.


The idea that an electric fuel pump is contributing to the problem doesn't fly for me for at least two reasons:

1. It should not be drawing any power in the early phase of starting because of the OPSS.
2. Nobody elses electric fuel pump is drawing down the system. If it did, that's a comment on the system, not the pump.

I have an electric fuel pump connected through an OPSS per USCG requirements, an electric coolant pump and a ballast resistor ahead of my coil input (identical Flamethrower) yet mine starts instantly without the 'R' terminal bypass. How can this be??

Back to the 'R' terminal
I suggest that our engines don't need it period. If your ignition wiring and components impart such a voltage drop that the engine can't start without the 'R' terminal bypass, there's a problem or several that need to be addressed. The bypass is not a solution, it's a band-aid.

Before you say it, for those (not Jack) who need to bypass a ballast resistor during starting to get her to fire, your resistor is way too aggressive, simple as that (assumes the rest of the ignition system is in good repair).

Well there you have it, Jack; forget the "R" bypass - just.....

[marthur]

As discussed it could be the batteries aren't cuttin' the mustard any more, maybe the ignition wire with splice has developed a high resistance for one reason or another, could be the battery cables or their terminations

I will share my experience: I had poor charging voltages at the batteries. When I replaced the wire that ran from alternator to the ammeter I saw a BIG increase in charging voltage. That wire looked perfect, but it was no longer up to the job. Now it's replacement is seriously over-sized and much shorter.

Oh, BTW I also bypassed the ammeter entirely. I am using a voltmeter in it's place.

[hanleyclifford]

There are many ways voltage can be hijacked in a system before coil+ can be fed; that's the beauty of the "R" terminal - ever so briefly it gives coil+ all the system can deliver.

[marthur]

I recommend that you check the resistance of some of the wires/components in you ignition circuits.

The easiest way is to use a decent mulit-meter or ohm-meter. You should see essentially zero resistance. Remember to zero the meter!

If you do not have a decent (read high quality) meter be careful measuring resistances. My experience with inexpensive multi-meters is that they often do not do a fantastic job measuring small resistances even if they are pretty good at higher resistances. But many of these meters are better at reading small voltages. YMMV, so the first commandment is "Know thy meter." I am basing this on the 30 meters from 5 different manufacturers in my HS physics lab and the 4 meters I have at home. NOTE: If anyone from the FLUKE company reads this, I have a couple of your meters and I am ready with my testimonial!!.

SO if I am using the cheap meter I leave in my tool box and I suspect a wire has too much resistance due to size or age or damage what I do is to measure the voltage drop across the wire. Specifically, measure from one end to the other when current is flowing. In this case, your meter should read zero volts when you have the leads on each end of the wire and current is flowing through the wire.

Somewhere you have a series of little voltage losses or one big loss that is robbing your coil of the energy it wants to make spark. Find those and you will solve your problem!

[marthur]

There are many ways voltage can be hijacked in a system before coil+ can be fed; that's the beauty of the "R" terminal - ever so briefly it gives coil+ all the system can deliver.

I agree with Hanley AND Neil on this. Hanley is right that the R terminal can be a helpful thing, but Neil suspects that there is too much voltage being lost suggesting a repair is in order.

I would consider the R terminal. But I would not rest well until I tested the components the ignition and starting circuits. A corroded terminal or broken wire can fail unexpectedly or get hot due to the increased resistance and cause real trouble. Better safe than sorry.

[hanleyclifford]

+1 on FLUKE, and digital is best.

[hanleyclifford]

I agree with Hanley AND Neil on this. Hanley is right that the R terminal can be a helpful thing, but Neil suspects that there is too much voltage being lost suggesting a repair is in order.

I would consider the R terminal. But I would not rest well until I tested the components the ignition and starting circuits. A corroded terminal or broken wire can fail unexpectedly or get hot due to the increased resistance and cause real trouble. Better safe than sorry.

Good thinking, but even with perfect new wiring you cannot get around the resistor(s) you have put in front of coil+ except thru "R"; electronic ignition has resurrected the value of the "R" terminal.

[Dave Neptune]

Battery bet

Jack, volts and power(amps) are not the same. Seeing 13+ on the charger and seeing 12.something at rest is just volts not power. As you increase the load the voltage will begin to drop and the worse off the batteries the more the voltage drop. You added water and with the charger she'd spin well enough to start that's adding "POWER" or amps to start!
Take the batteries out and get them load tested!!! I'll bet a liquid bread that is your problem. Weak batteries especially a load of them tied together not being able to spin the engine fast enough but with the charger all is bliss. That's batteries in a weak state.
I have the need for new house batteries at the present. The house side in my set-up are a pair of 6v235's for the house and an isolated grp27 for the engine. I usually start on the both and when out I use only the house for starting and power at anchor, to save the start battery if needed. The 2 big 235's will run the lights tv and stereo for days and all is well to start on them. At the present the "charged voltage" at rest is down a bit and they will barely start the engine when cold. The voltage drops considerably upon cranking and they will be replaced before the summer cruising starts!

The "R" terminal was a necessary part on the original wiring and ignition set-up on the A-4's equipped with the "old style ceramic ballast resistors". The ignition was reduced to 8v for the stock 8v coil and full voltage was tendered for the cranking circuit to boost the available spark!

Dave Neptune

[ndutton]

Ballast resistor discussions have nothing to do with Jack's (the OP) starting problems. He doesn't have one.

if you have anything on that ignition circuit (like an electric fuel pump, for example), it is robbing you of voltage to coil+. . . . . but even with perfect new wiring you cannot get around the resistor(s) you have put in front of coil+ except thru "R"; electronic ignition has resurrected the value of the "R" terminal.

Then please explain how my engine (and others) - - with multiple loads on the ignition circuit - - even starts. I have:

• 0.885Ω ceramic ballast resistor ahead of the coil
• Johnson CM30-7 electric coolant pump running directly off the ignition circuit
• Facet electric fuel pump but we've already explained the OPSS factor
• Single G24 start battery, as small or smaller than most
• #4 battery cables throughout
• And most important to this discussion, no R terminal bypass.

[Dave Neptune]

Power and delivery

Neil, good wire sizing and load carrying capability go a long way~that's why it works! You may notice a bit of an issue if the batteries get weak but that would be the batteries and not the wiring.

All loads do come from the battery so where they are hooked up only has to do with load capability of the activated circuits in combination with battery condition.

Dave Neptune

[ndutton]

You make my point Dave.

I have other loads going at the same time but they are on the house bank rather than the isolated engine starting battery, that's why I left them off the list.

[JackConnick]

Take the batteries out and get them load tested!!! I'll bet a liquid bread that is your problem. Weak batteries especially a load of them tied together not being able to spin the engine fast enough but with the charger all is bliss. That's batteries in a weak state.
Dave Neptune

Dave et al; Thanks for the discussion. As I said, I jumped the starter to the coil with no difference in starting. "R" term isn't going to make a difference.

The rest of wiring was replaced a while ago, but looks to be in pretty good shape. I'm going down there and see if there's any difference after putting a hard charge on the batteries. But all in all, I think they are the culprit for the most part. As stated earlier, she's always started easily with the same curcuits in place.

I will for sure look at some of the rest of the wiring, my volt/amp hour meter isn't working for some reason and needs to be sorted out, as well as that primary ignition wire.

I'll report in later...

TIA, Jack

[Dave Neptune]

Hmmm ?

Neil, very interesting. Why did you isolate the battery to such an extent. Good idea maybe. I did see another done that way and thought it odd too. Most boats are wired so that all circuits go the battery switch so all is hot in any switched position. IE if I needed light to start because the house failed at night, I would not want to work or stress in darkness.

Yours is not shall we say conventional and perhaps you could elaborate as to your reasoning in this. I do understand looking at the purity of a "start battery" but not to that extent.

Dave Neptune