Need a plan troubleshooting engine, overcharge surges?

[DDO]

Today while my Atomic-4 was happily cruising along I saw the engine batt S-W voltmeter in the yellow, near 10V or so... (A 2 battery sytem: the alternator output goes to house deep-cycle positive, a West Marine combiner 50 connects charging to the engine starter battery. (No 1-2-both switch, I use a separate switch for each: 1, 2, both.) Also there is in place a 2-lead A/C charger on these batteries.) So I switch on the house circuit that illuminates a house batt digital voltmeter -- the numbers going all over the place wild, then starting to drift down, finally 14.2V. Look back up at SW engine batt voltmeter and it is going through green and right into red overcharging near 16V.
For a bit, the engine surges like it is getting throttle, then back down. A few more short surges, and finally engine and electrical settled down, with the 14.2 green volts showing as batteries being charged, engine happy without surges.
Is this alternator, instruments, coil, (five year old) batteries, charging, tune-up,??? Too many thoughts to get a troubleshooting plan, especially since I haven't gotten this to happen again at the dock. I hate to think all of these systems are bad!

[Mo]

First, I'm not an electrical guru but here's what I think.

-check all connections, clean any that need it.
-take batteries and get them tested....load test the batteries. Some outfits charge them and then do a cell test and I don't think it's near as good. Ensure the batteries are load tested.

Batteries 5 yrs old may be a big part of it.
- ? low on water
- ? dead cells

[David Pugh]

over charging problem

Good Morning DDO;
I agree with MO, 5 year old batteries could be a big part of the problem. The fact that this is intermittent and voltage going wild also tells me there may be an issue with the alternator.

I would remove the batteries first and have them checked this would be the cheapest and easiest thing to do. Then I would contact a professional, and have the alternator checked. Could be a bad diode or something else that can be replaced.

Call Don @ Moyer, I'm sure he can help you better than myself.

Good luck, Dragonfly Dave.

[hanleyclifford]

It would be helpful if we knew what model/brand of AC charger you are using.

[Al Schober]

DDO,
The way this is intermittent, I doubt it's the batteries. I'm thinking 'bad connection' - probably a ground lead, as these ground connections tend to get neglected. One that's given me fits in the past is the ground connection to the alternator - the bolt through the alternator foot is not a good ground. I ended up running a separate ground lead from the alternator case to a common ground.

[hanleyclifford]

Sounds like you are relying on the combiner to switch in the starting battery when needed but it didn't do it because you are sensing somewhere else.

[JOHN COOKSON]

+1 +1 +1

DDO,
The way this is intermittent, I doubt it's the batteries. I'm thinking 'bad connection' - probably a ground lead, as these ground connections tend to get neglected.

I'll raise and take it one step further.
The overcharging and surges almost scream "bad ground connection".
IMO that is.

TRUE GRIT

[BunnyPlanet169]

I'm not sure that the variable nature of your description fits bad batteries....

I'd go through the electrical connections as mentioned, especially the ground wires from both batteries and the engine, and the positive lead from the alternator. Then I'd confirm my alternator belt tension, AND my alternator pulley nut.... The floating at 10 volts, then bouncing around, drifting to 16 and then back down to 14.2 (with engine surge) sounds like an alternator/voltage regulator problem to me.

[JOHN COOKSON]

especially since I haven't gotten this to happen again at the dock.!

Try shaking the relevent wiring while the engine is running.

TRUE GRIT

[DDO]

Thanks all for these suggestions. Together you really organized this investigation. I will start looking at grounds, wiggling wires, check all connections.
I am thinking to replace the batteries any way as they seem to be up next on the list and this time adding a fuse/switch so I can use it as a "service switch" for engine work.

Thanks very much!
MrsDDO'

[Borrowed Time]

My two cents, the opinions above regarding grounds are correct. I have been searching for an answer to this very problem for several months now and just found my solution last weekend. I have the original 35A Motorola, and my boat was showing the exact same symptoms, voltage spiking to 16+ volts but only for a moment or two, then it would drop a bit and settle at a more normal 13 to 14. This surge would drag down the engine 100 or 200 RPM at any RPM over 1200 below which it did not surge ever.

I followed advice (Edwardc) and installed a new ground lead, 12" of #8, on the alternator's ground terminal, its not marked but I assumed it to be where the black wire from the voltage regulator grounds to the alternator. This new ground ensures a solid connection for the voltage regulator to ground and has worked like a charm. Surging voltage problem solved on my boat.

Thanks to all the helpful advice guys!

[DDO]

Here's something to think about....

Sounds like you are relying on the combiner to switch in the starting battery when needed but it didn't do it because you are sensing somewhere else.

Hmmm... this started me thinking...
alternator out goes to House Batt, alt. sense is from coil+ via Ignition and Engine Batt positive bus. There are separate "use" not "charge" switches, on/off, for each battery and a on/off for BOTH (used rarely for startups). I leave engine switch on when running, but switched House may or may not be on. With the Combiner-50 silently working on the charging, I now wonder how it has worked so well for so many years.

[BunnyPlanet169]

Hmmm... this started me thinking...
alternator out goes to House Batt, alt. sense is from coil+ via Ignition and Engine Batt positive bus. There are separate "use" not "charge" switches, on/off, for each battery and a on/off for BOTH (used rarely for startups). I leave engine switch on when running, but switched House may or may not be on. With the Combiner-50 silently working on the charging, I now wonder how it has worked so well for so many years.

Time for a schematic....

[hanleyclifford]

Hmmm... this started me thinking...
alternator out goes to House Batt, alt. sense is from coil+ via Ignition and Engine Batt positive bus. There are separate "use" not "charge" switches, on/off, for each battery and a on/off for BOTH (used rarely for startups). I leave engine switch on when running, but switched House may or may not be on. With the Combiner-50 silently working on the charging, I now wonder how it has worked so well for so many years.

Your system relies on the combiner to "sense" that the starting battery needs juice and cut it into the circuit where the house battery is already enjoying the charge from the alternator which is being commanded from coil+ or so it would seem. The combiner may have become defective after so many years. It, in effect, is a second voltage regulator in the system. Let's look at a schematic.

[DDO]

In Conclusion....

If you see this, you might want to know...
I never found a wiring problem, although I jiggled and wiggled (the wires, that is...) The batteries tested just short of "bad" and the alternator tested "bad". New alternator, which has the more modern regulator on it, and since I had 'em out and they are old, new batteries. All seems good now, real good; engine ran smooth and strong during the cruising season.