Dual cranking batteries...a problem?

[Eric in NC]

After 50+ years of sailing, I recently bought a power boat...and I'm still trying to figure out how some of the systems work.

The boat is a Grady White 190 Tournament with a Evinrude 150, which has a 35 amp alternator.

Both batteries are Interstate Marine/RV Cranking Batteries. I was told to start the motor with the Battery Select on "Both" and to run with it on "Both."

The only electrical draw after starting is the VHF, the depth/fishfinder, and the use of the power trim. The depth finder has a voltage gauge and it reads 12.2 or 12.3 all the time. I run the boat about 1.5 hrs/wk.

However, I have been reading some articles that make me wonder if having two crankers is wrong...and if running in the "Both" setting is wrong. Frankly, some of the writers I am reading seem to contradict other writers. Then I read the FAQ post on this forum about dual batteries and that just about fried my brain

So I have a few questions maybe someone here can answer.

First, is it a bad thing to have two crankers instead of a cranker and a deep cycle? Am I gonna run into problems using two crankers?

And, is running with both batteries selected wrong? It seems like it would be the right thing to do.

Sure would appreciate getting some guidance about this.

Thanks.

 

[Silvertip]

Re: Dual cranking batteries...a problem?

The fact that you have two batteries and a battery switch does not make both batteries crankers. The can be but the switch detrmines that. The idea of the switch is to be able to operate fish finders, VHF radios, downriggers, and other stuff off one battery (say BAT 2) and leave the other battery for starting duty. So here's how it works. You can start the engine with the engine with the switch set to BAT 1, BOTH, or BAT 2 -- it really makes no difference. But typically you would start the engine on BAT 1 (the cranker) or BOTH. Once started, by all means leave the swtich set to BOTH as this charges both batteries. If however, you know that one of the batteries is discharged more than the other, switch to that battery only. Only the selected battery will charge. Why is that important? Well, in the BOTH position, the two batteries become one great big one so it takes longer to get both batteries fully charged. When you get to your fishing spot, switch to BAT 2 and run all the accessories. This prevents drawing down BAT 1 which is the cranker. When you get ready to go, switch back to BAT 1, start the engine, and select BOTH to charge both batteries, or BAT 2 to charge the accessory battery that you probably drew down. When you get to the dock, kill the engine and switch to OFF. NEVER SWITCH TO OFF BEFORE YOU SHUT OFF THE ENGINE! ALWAYS SWITCH THE ENGINE OFF FIRST. Finally, if you have AC power available at the dock, install a two-bank on-board charger. These connect directly to both batteries. You plug into shore power and the batteries will always be topped off. The charger is smart and can be left plugged in indefinitely. The reason for adding the on-board charger is that if you make relatively short trips, the engine alternator may not keep up with the electrical demand.

 

[Boatist]

Re: Dual cranking batteries...a problem?

The voltage for a charged battery should be 12.6 volts. So get a good volt meter and check voltage on both batteries. Meters are very cheap and good to have on board. A Battery that reads 12.2 or 12.3 volts is very near dead.

When the motor is running the battery or batteries being charged should read 13.8 to 14.8 volts. If it does not read at least 13.8 I would say you have a problem. Running in Both it could be one battery has a dead cell and is taking all the charge. This would prevent either battery from charging.

Never Switch the batteries thru off with the motor running. It will blow your alternator. also If your switch is not a make before break type then only switch with the key off.

If you have a meter then with the engine off turn the battery switch to off. Now measure from minus to postive post on both batteries. A charged battery should read 12.6 volts if the temperature is 70 to 80 degrees or higher.

If one reads low then try to charge with a Smart charger and see if it chrarges up. If batteries have caps make sure the acid level is at the proper height.

If one of the batteries reads 12.6 Volts then turn the switch to that battery and start the Engine. With the engine at about 1000 RPMs your should read 13.8 volts or more. At least you should read above 12.6 Volts and raising.
If you see no change with the motor running then you likely have a alternator problem.

Turn off motor switch to the other battery measure the battery voltage. Again start the motor and measure the battery you switched to. Voltage should be 13.8 volts or higher. At least it should be Higher than before you started and raising.

 

[Eric in NC]

Re: Dual cranking batteries...a problem?

Thanks for the replies.

Boatist...
I went down to the boat and did all the things you said and regardless of the motor running or not, and regardless of the switch setting, I get 13.8-14v on both batteries. It looks like the batteries are charging fine...but they do not read 12.6v when the motor is off...they continue to read 13.8-14v. Do you think I have a problem?

The depth/fishfinder still reads 12.2v. Now I'm thinking it is hooked up after a voltage regulator, so I am not actually reading battery voltage? The manual for this motor says it has a "35 amp, fully regulated" alternator...but I don't know what "fully regulated" means.

Again, thanks for your help.

 

[Silvertip]

Re: Dual cranking batteries...a problem?

Fully regulated means that charging system voltage is regulated within specific limits. Charging voltage is limited to at about 14.5 volts. An unregulated system would typically run 16 volts or higher and on a very long run at WOT a battery might actually boil off some water. It is highly doubtful the locator is wired ahead of the regulator. Are you reading battery voltage with the dash gauge? If so, it may be reading high and the locator reading low. After being charged, batteries have what's called a surface charge that dissipates somewhat after the charger is removed. So If you made measurements immediately after charging, wait about 15 minutes or so before measuring. A fully charged battery should not measure 12.2 nor should it measure 13.8. 12.6 - 12.8 is a closer number.

 

[Eric in NC]

Re: Dual cranking batteries...a problem?

Are you reading battery voltage with the dash gauge? If so, it may be reading high and the locator reading low. After being charged, batteries have what's called a surface charge that dissipates somewhat after the charger is removed. So If you made measurements immediately after charging, wait about 15 minutes or so before measuring. A fully charged battery should not measure 12.2 nor should it measure 13.8. 12.6 - 12.8 is a closer number.

I first read the voltage directly across the posts on the batteries individually with the switch in OFF with a handheld voltmeter. (All the readings I last posted were made with the voltmeter directly on the battery posts.) The boat has been sitting unused for the past 10 days and I have not used a charger on them. I took the initial readings prior to starting the motor and got 13.8. So what's the deal? I was worried about undercharged batteries when this all started...now it looks like they are overcharged? Yikes!

 

[Silvertip]

Re: Dual cranking batteries...a problem?

Are you using an analog meter? If so, lay it flat and see if the needle is on zero. If not, adjust it so it is. It is very easy to have a 1 volt error on an analog meter. If you are using a digital meter, I would question it's accuracy. The locator is apparently providing a more accurate, although still not correct reading. A 12V battery will not measure 13.8 volts after a 10 day rest. Use another meter.

 

[Eric in NC]

Re: Dual cranking batteries...a problem?

Yes, analog. It was zeroed prior to use and used flat.

BTW, after all this I measured a bunch of small batteries...they all came out correct. So I measured my car battery...it was 15v. Sheesh. So I got a friend with a digital meter and he confirmed the car battery charge.

I give up. I know y'all are correct that 12.6v or so is full charge. I have no idea why all my batteries are so much higher. Maybe I need to chase down someone with a third meter. Or maybe I just need to quit worrying about it since there are no symptoms or problems other than these bizzaro readings.

Anyhow, thanks for the help. If I ever figure out what is going on here I'll post it back to this thread.

 

[Eric in NC]

Re: Dual cranking batteries...a problem?

OK, never one to let sleeping dogs lie, I started in on all the batteries I'd measured earlier and suddenly the meter needle started pegging on the 15v scale. And I can no longer zero the resitance...it pegs too. Obviously the meter is shot. I did try the 150v scale and it is working but is too small to tell the exact reading but it looks like 12v+. Haven't a clue why the digital my friend used earlier on the car read so high, but at this point I don't care.

First order of business tomorrow is to go get a new meter...and a new carton of beer, as I ran out of that tonight, too. Been a rough day, I tell ya.

Silvertip, I would have bought a digital meter had you not said you question their accuracy. I would have thought the digitals would have been more accurate. Not so? Should I get another analog?

 

[Silvertip]

Re: Dual cranking batteries...a problem?

I didn't mean to imply ALL digital meters had questionable accuracy. I asked if you were using a digital meter and if so, I questioned IT's accuracy. Regardless of the technology, a measuring instrument can provide incorrect results if not properly calibrated. Sometimes things are just bad or inaccurate out of the box. Just so we are on the same page, when I said zero the meter, I didn't mean zero it on the ohms scale. With nothing connected and meter turned off, the meter needle should rest at zero (full left). Most meters have a slotted adjustment at the pivot point of the needle. I meant to adjust that to zero the needle.

 

[Eric in NC]

Re: Dual cranking batteries...a problem?

Yeah, we're on the same page. That's exactly what I did. I was just saying that now, the meter pegs when trying to measure anything on the 15v scale...and it pegs when trying to adjust the ohms...both of these are toast. It still measures on the 150v scale, but obviously I can't trust anything on it at this point.

Anyhow, the meter is fried. So tomorrow I go buy a new one.

Thanks again for your help.

 

[Eric in NC]

Re: Dual cranking batteries...a problem?

Just to put some closure on this, turns out there were TWO (count 'em, 2) faulty voltmeters involved.

The new voltmeter I got today gave results very close to what the finder was showing. And showed the batteries were not being charged. I put the charger on them, and they held the charge (or at least they did fine while I was out for two hours today.) So, something is amiss with the charging system...and the boat gets docked at the boatyard tomorrow for repairs.

So, thanks to Boatist and Silvertip for sticking with me on this thing. What with the faulty voltmeter, I'm not sure I'd have ever figured this out without your advice.

 

[Silvertip]

Re: Dual cranking batteries...a problem?

Just so you know, both meters were probably damaged by trying to read "voltage" with the meter set to the "ohms" scale.

 

[Boatist]

Re: Dual cranking batteries...a problem?

You might want to check the batteries in your volt meters. If batteries are too low can affect the accuracy. Also as Silvertip stated measuring volts with set to OHM can burn the thing up.
A standard Lead acid battery should read 2.1 volts per cell with 6 cell in a 12 volt battery so 12.6 volts at 70 to 80 degrees.

I belive the number one killer of alternators is battery switches.
If someone turns the battery switch thru off with the motor running then the alternator should be blown.
If the switch is not a make before break type and someone turns switch at all with the motor running then it will blow the alternator.
Any thing that disconnects the charging battery from the alternator will also blow the alternator. This could be a Loose battery cable, crroded battery cable, someone removing either the positive or negitive battery cable with the motor running.

All these is one of the reasons I like batteries isolator for charging batteries.
With a battery isolator and 2 battery both batteries would have to disconnected at the same time with the motor running to blow the alternator.
Wired correctly then even switching thur off will not blow the alternator.

Now that you have a meter you can trust will really help your troubleshooting.

 

[Eric in NC]

Re: Dual cranking batteries...a problem?

I just bought this boat two months ago and have no way of knowing what the PO did, but my understanding is the battery switch is a "make before break" type. Whatever the case, I never switch off unless the motor is off first.

Anyhow, the boat's back at the boatyard and the mechanic's first thought is a bad voltage regulator.