How much voltage drop at Starter while cranking?

[JackConnick]

Still troubleshooting my low voltages while cranking.

I see like 12.4 at the starter to begin, but upon cranking it drops to 10.4 or less fairly quickly. Batteries are fairly new 2x Group 27 charged up.

What's the norm? I'm beginning to suspect the starter or solenoid...

Jack

[Dave Neptune]

Need more input

Jack, that's not really that bad at the starter when starting I assume(?) depending on battery condition and age.

Did you clean ALL of the big wire connections at the battery, switch and starter?

What is the voltage at the "starting" battery or batteries not the starter at rest and cranking?

Dave Neptune

[JackConnick]

Batteries same voltage at rest. Not sure while cranking, sort of hard to deal with by myself. Connections at battery cleaned. Not seeing any corrosion at starter, but will have another look at it.

Bigger issue is small spark from coil - about 1/4"+. Low voltage there while cranking - 12.4v "resting" - 9.4v cranking. So I'm seeing a 1 volt drop on ignition circuit. Even with the battery charger on and the banks at 13.5, I still am seeing a pretty big drop and weak spark.

Ignition switch is just a push button, shows continuity. Gauges at helm are in series with it. the only other things on the circuit are the fuel pump (newish MM electric) and an hour meter. Have older Ignitor magnetic ignition from MM.

I'm going to replace the primary wire from it to the coil as it is old, and has one splice in it. I assume 12 gauge is enough. Battery cables are in good shape, will double check ground, but have also tried second isolated battery bank with similar results, same when I change neg leads over to 1st bank.

Aargh.

Jack

[JOHN COOKSON]

Jack
If you want to fool around with it you could do this:
Disconnect the primary wire at the switch and coil +. Connect a jumper wire to one end and run the wire near the other end and lay an ohm meter on the other two ends. S\B zero ohms of course.
What size wire are you running switch to coil?
What's the voltage reading at the switch?


TRUE GRIT

[hanleyclifford]

Anything over 10 volts at the coil+ will start the engine; however, you need every bit of it. If you have other items like an electric fuel pump in parallel that is where you are losing voltage. You may be one of those rare cases where the use of the "R" terminal on the solenoid is warranted. The "R" terminal is energized only by the cranking (push button) switch. Run a #14 direct from "R" to coil+.

[JackConnick]

Yeah, some interesting ideas to try. The wire to the coil is about 14 gauge I'm guessing, but has one butt joint, due to an "issue" ;-). I will check the voltage at the switch.

However, this is a new issue. I've run the fuel pump etc and this configuration for years...

Hanley, so I leave the starter wired as is and run an extra lead from the "R" term to coil? What advantage does this give...?

Jack

[Dave Neptune]

Argh the R

Jack, the "R" wire hookup will do nothing for you unless you are using a resistor on the EI. The "R" terminal just runs full voltage to the coil by bypassing the resistor during cranking which is the only time it is activated. This supplies "full voltage" for starting while cranking only.

Dave Neptune

[JackConnick]

No, I'm using an internal resistor coil, a Flamethrower. Which although it seemed ok (3.5 ohm across the leads), I am having to replace as I broke off one of the terms. yesterday.

But full voltage to the coil while cranking sort of seems like it may help...

You leave both R & S connected?

[Dave Neptune]

No R

If your not using an external resistor it will make no difference, but it may supply a bit more than your switch but only during cranking.
Have you had your batteries "load tested" by any chance. If they're week which 12.4 at rest would indicate for a fully charged battery and it just may be your meter.

Did you check the connections at the battery switch and on the starter? Also take a good look at the ground from the engine back to the battery, if it is weak it will show up as a voltage drop too.

Dave Neptune

[JackConnick]

I haven't had them tested, they are maybe about 1.5 years old at most. But even with the charger on and everything at 13.5, I'm still only getting 9.4 at the coil. I went out and bought another meter yesterday, as I was getting some spurious readings with the old one.

Jack

[edwardc]

The problem of the drooping voltage during cranking all stems from the high current that the starter draws while cranking the engine. So even a tiny amount of resistance can produce a significant voltage drop.

<WARNING=MATH CONTENT>

Consider: Ohm's law says V = I x R (Voltage equals current times resistance).
So, for convenience, let's say your starter draws 25 Amps. Even 1/10th of an Ohm of resistance will produce a significant voltage drop:

25 Amps x 0.1 Ohms = 2.5 Volts !!

</WARNING>

So all of the (tiny) resistance of the heavy starter wire, and the battery lugs, and ring terminal, are going to be in series with the heavy terminal on the starter, and are going to be responsible for the voltage drop seen there.

And yet, for some unfathomable reason, almost every stock boat wiring I've ever seen seems to take the ignition + feed from that terminal!! It's a guarantee that you're going to see a lot of voltage drop on the ignition during cranking!

If, instead, that + feed to the ignition is moved to the other end of that big cable, directly on the battery, then you will avoid all of that voltage drop across the cable and its connectors! Any remaining droop will be a function of the condition of your battery.

[hanleyclifford]

Why not do a little test? Check voltage at the "R" terminal during cranking. See if you might like to have that delivered to coil+ (during cranking).

[JackConnick]

OK, more tests on Saturday... ;-)

And yet, for some unfathomable reason, almost every stock boat wiring I've ever seen seems to take the ignition + feed from that terminal!

Are you saying from the starter terminal? The other thing I have there is the wire from the battery I think.

Jack

[roadnsky]

Bigger issue is small spark from coil - about 1/4"+. Low voltage there while cranking - 12.4v "resting"

The voltage on a fully charged battery should be about 12.7-12.8 volts. If it's higher, the charger is on.
Batteries will usually fail to start an engine at 12 volts or less.
This is dependent on the age of the battery.
A new, but depleted battery may only fail to start at a voltage as low as 11.5 volts.
Be wary of electric panel meters; they are often very inaccurate. Use a multi meter to test the batteries and then reset the panel meters if they are adjustable.

[JackConnick]

Back to it...ignition battery volt problem

Well, I got to traveling and busy with life and haven't had too much time to work on the boat.

But I went down yesterday and finished rewiring a new coil in as the wiring to it was messy. In the process I broke off a terminal to the coil, so I have a new one.

Went to try to start it and same issue, crank and crank, no start. Tried a jumper per Don's instructions from the starter to the + of the coil. No difference.

Checked the batteries and they showed 13.75 with the charger on. So I filled them with water and decided to put the charger on an equalization high-volt charge. It takes them up over 15v to boil off the sulfates. They are about 3-4 years old at this point.

So I was looking at all that high voltage and tried to start the boat. Off she went very easily! No hesitation, very light crank.

So I'm thinking bad batteries, or some sort of serious voltage lose with the wiring, except hat none of that has really changed...

I'll see how it goes tomorrow, probably pull them out (2x Group 27HD on one circuit) 1 on another, isolated.

I am thinking to replace the primary ignition wire it has one splice in it, although it's run for years with it in place.

If anybody has a better ideas, let me know.

Jack