Low Engine voltage Help !!

[gradywhite248]

Came to the beach to find I left my battery switch on both batteries. Batteries completely dead for two weeks We jump started the boat And it started rather quickly. I left the marina trying to charge the batteries and the voltmeter on my Garmin and on the boat never got over 12 or 12.4. I replace the batteries with new and the voltage was the same? Boat started fine for two days since voltage issue. And still starts fine. Are there any ideas what happened an how to fix or what to replace? Boat worked great the weeks before I killed the batteries. Also boat engine has a miss in the engine can this be caused by low voltage.
thanks for any help. I don’t have access to the boat since it’s at the coast. Maybe I have Zimmermans Yamaha dealers at Southport look at if I can come up with a fix.

 

[Doc Stressor]

What was the voltage reading on your Garmin before you killed the old batteries? The voltage you read at the instrument is typically lower than that at the battery posts because of the small gauge wiring and the distance of the run. With a fully charged battery, it's not uncommon to read 12.4 - 12.5 V on the MFD and 12.8 V at posts when the engine is not running. You should see greater than 13 V with the engine running at over 1600 rpm. If you don't, you need to suspect the alternator or the voltage regulator.

You can have a miss when the battery voltage gets run down from a bad alternator/voltage regulator. Just before the engine quits entirely. Yamaha engines take current from the batteries rather than directly from the alternator. They won't run with dead batteries.

 

[DennisG01]

Adding on to what Doc said... get yourself an inexpensive volt meter and measure directly at the battery. Using readouts at the dash is not helpful without first knowing a TRUE baseline. Dirty connections are another "error" factor.

As noted above, you should be seeing 13 to 14 volts with the engine (what engine, by the way?) running. Even at idle, it would be higher than what you're seeing.

However, 2 weeks with the batteries swtich left ON shouldn't kill the batteries. Unless an accessory was also left on. So, IF no accessory was accidentally left on, tracing down a parasitic draw is possible. But wait on that till better info on V is attained. It may just have been the old batteries time to die.

 

[gradywhite248]

Thanks Doc & Dennis,
So yesterday I checked both battery voltages before starting the engines and both were at 12.6 & 12.5. These are new batteries just installed on Friday. So we started the engine and ran down the water way and I checked the voltage on both again while running @ 4500 RPM's they were the same voltage as before we started the engine. I'm pretty sure the Com radio was on over the two weeks and killed the batteries since I left the battery switch in the both position.
So I'm thinking the next step would be to change the voltage regulator? Just wondering how an why that would go bad?

 

[seasick]

Don't leave the switch in both when away from the boat. When in both, the batteries may feed each other, one charging the other and vice versa. That is especially true if the batteries are not the same model or not the same age.
The voltage reading at rest of 12.6 is fine. Note what the voltage gauge that you used earlier reads with the motor off. It will be less than 12.5
Now start the motors and run at about 1000 rom (in neutral). See if the voltage increases on that gauge. It should be 13 or more. If it is the same as the first reading (ignition on but motors not running) then your motor is not charging. That could be several things so get a hold of the service manual and go through the diagnostics. I wouldn't change the rectifier without the diagnostics first.

 

[DennisG01]

You should still really verify directly at the battery, but yes, it sounds like something in the charging system is kaput. There are a couple parts in the system - the stator is another one - so you really need to follow the diagnosing steps in the service manual to avoid throwing parts at it or drop it off at the shop.

 

[Hookup1]

As others have said get a inexpensive voltmeter (Harbor Freight). Measure voltage at the batteries.
Battery switches set to each engine.
Charger off. motors off. Check voltage. Should be 12.8 vdc.
Charger on. motors off. Check voltage. Should be 13.1 vdc.
Charger off. motors on. Check voltage. Should be 13.1 vdc.

You need to be careful using the Garmin unit to measure voltages. I have found the voltage on say the sounder display to read low (house battery). The engine gauges, if you are setup that way, Tend to read correctly.

House battery charging is a little different. Ideally you have a 3rd-bank charger and one motor wired properly to charge 3rd-bank.
Charger off. motors off. Check voltage. Should be 12.8 vdc.
Charger on. motors off. Check voltage. Should be 13.1 vdc.
Charger off. motors on. Check voltage. Should be 13.1 vdc. Assuming you have a charging shunt from one of the motors.

If the batteries are discharged it may take a while (overnight) to bring them to a full charge. There are usually fuses on the individual charger cables as well as on your engines. The voltmeter will tell you what's charging and what's not.