voltage drop

[Pearson30]

I am noticing a large voltage drop when I try to start the engine, it drops slightly when I turn on the ignition and then drops to ~6 volts when I crank it. It only turns over for about 15 seconds.

Probably related: when the battery is on, I notice a slow voltage leak.

I redid the points this spring and just finished a Carb rebuild today. It still hasn't run right this year. I've got spark.

I love sailing into the slip, but I had grand singlehanding plans this summer, as well as taking a bunch of newbies sailing. Auxiliary power would be ideal.

Any assistance would be appreciated.

Thanks in advance

[Maurice]

It should drop when you crank it because you are putting a significant draw on the battery. A small drop when you pull on the ignition key...maybe a needle width. When the starter is drawing power the volt meter needle will drop then should return back to about 13 volts when running. It should be above 12 while replacing the power it just used then settle back around 12 or so as the battery is replenished...thats the short answer. Alot depends on how good your guage is; how good your starter is; how easily the engine starts; voltage regulator and the battery itself. Just remember, put a large draw on it and it will drop out.

Hope this helps you.
Mo

[hanleyclifford]

The A4 draws about 130 amps cranking. This is enough to lower system voltage to around 9 volts or even less. 6 volts is a bit low even for cranking. If the voltage recovers right away after starting to 12 volts and continues to build to 13 volts your charging system is OK. Do you have gauges to test volts and amps?

[rigspelt]

15 seconds is a long crank. Not starting well, I take it?

[ArtJ]

How old is your battery? Did you measure the voltage directly across the
battery. Sometime when batteries become old,they develop internal
resistance between the cells which would cause a voltage drop

Regards Art

[ndutton]

I agree with Rigs, 15 seconds of cranking is an eternity. Intake thru-hull closed during cranking?

It would be useful to determine if the battery is fully charged at the start of this episode. If not, then why not? If it is, then look at the wiring and connections between the battery and the starter and on a long shot, maybe the starter itself (I don't think it's the starter but at this stage it can't be overlooked yet).

As Art said, where are you measuring this low voltage?

What's the battery voltage before trying to start the engine? This simple chart gives an indication of battery condition based on open circuit voltage.

[Pearson30]

Thank you all for the quick reply: I was measuring voltage over the battery, that is where the drop occurred, Im glad to hear that this is normal. As for the drop to 6 volts, the battery was not entirely charged, so lower starting point voltage wise should mean lower end voltage??? Anyhow, after a while last night I decided to check spark - none off the coil, and I was reading resistance too! ((OH NO)) I thought. So I pulled the connections to the ignition coil and checked resistance again: 0 = continuity (phwew). I hooked it back up and then monkeyed over and took the cap off the distributer, all looked as it should be. Test for spark off the coil=good. I tightened it back down and just before I decided to pull the #1 plug to take into the store (replacement set), I decided to try a bit of starting fluid, nothing. So I put a cap of strait gas into the flame arrestor and low and behold it chugged!

Fiddling with the choke and throttle, I coaxed her to life, checked all my voltages, good, the amp meter on the instruments was reading ~+20 (good) and furthermore, she sounded like she was running very smoothly! I ran it for about half an our, let it cool and then (fingers crossed) started it again. It popped right to life! With good throttle response and a nice clean sound, Im going out to test her under load today.

Recent work I've done: Ignition system rebuild, fuel system clean out, carburetor rebuild. It was a somewhat long but necessary learning curve. Prior to this my engine experience was none.

Im so glad this forum exists, you all are the best!

[rigspelt]

Recent work I've done: Ignition system rebuild, fuel system clean out, carburetor rebuild. It was a somewhat long but necessary learning curve. Prior to this my engine experience was none. Im so glad this forum exists, you all are the best!
Well done. Nice to be able to work on one's own engine on a boat. Adds a significant layer of comfort to sailing.

Starting the engine is a kind of load test on the battery. If it really is dipping to 6V, I'd wonder about whether the battery is near end of life. Good question about whether a partially charged good battery would dip lower than the transient 10V I might during a start -- not sure.