Correct Voltage?

[RBBailey]

What should be the correct voltage while the engine is running?

I suppose the Alternator should be producing more than 12v, or it wouldn't be charging the battery would it? But it should also be controlled right?

I've got a dual battery set up, the previous owner had them set up in parallel, but he had a power drain problem because he had the 4 cig lighters and a 10 speaker 4 amp stereo with a DVD player.... it was a show car. Anyway, he installed an isolator that kept the batteries in parallel, but allowed one battery to be cut off from the system with the flick of a switch. So, if I don't have that switch closed, the radio, voltage display, and the power sockets do not work.

When I am running I am getting 14.3 volts, and it only goes up and down by one tenth of a volt or so, when I turn on the AC it drops to 14.0 -- sort of expected, but is that supposed to happen?

I'm wondering because since I connected the batteries to a charger I have not had the cold start problem that I was experiencing right after I bought it. I think it will take another few days of driving and then cold starts to see if it is a real pattern. I'm wondering if the Odyssey batteries, when they get low, may be able to act as if they want to start the engine, but just don't have the power to start it. So they turn it over, but not fast enough, then just die completely after 3-5 tries.

Thanks.

 

[sean]

you have to have a charger specifically for the optimas or you will kill them. sounds like you already have, voltage drop is one of the first signs.

 

[ptschram]

The voltages you are seeing are acceptable to me. Unless you add more load and that voltage goes down, I'd not worry about it.

I'm almost embarrassed at the great success I've had with Wal-Mart and Napa deep-cycle batteries. Nothing wrong with a good Marelli alternator. The key is finding a good one.

 

[garrett]

you have to have a charger specifically for the optimas or you will kill them. sounds like you already have, voltage drop is one of the first signs.

i'm not sure i understand. a voltage drop with the a/c turned on is completely normal. at least to me. 14 volts is a very solid reading. a drop to the 13.5 range is normal too with lights, radio, etc on.
what is so bad with a voltage drop when accessories are turned on?

and what kind of charger are you talking about?

i like the Johnson Controls at Advance. Optimas suck in my experience.

 

[ptschram]

i like the Johnson Controls at Advance. Optimas suck in my experience.

You do know who makes Optimas, don't you?

 

[garrett]

yes. JC. but for whatever reason the two Optimas i have gone through have not laster more than 2 years. one swelled up like Lohans liver. i had a talk with the the manager at the local Advance in PA and he said they had more returns on Optimas than anything else.
i like my Napa Spiral. thing holds a charge over extended times of non-use far better than a Red Top.

 

[antichrist]

I'm not real clear on exactly what your current setup is.
If you're using an isolator and it's not a schottky diode one, you'll get at minimum 1 volt of volt drop, maybe more, between the alt and battery. A schotty diode isolator will only cause about 0.3-0.6 volt drop. At least that's for the Surepower isolators.
With either a schottky diode or "regular" isolater you'll get additonal volt drop if your charging cable isn't sized properly. Cable size can also impact the charging if you're going through a separator (relay). Also, if the duty cycle of the relays in the separator aren't 100% for your charging current you'll start to get volt drop.

 

[apg]

Back to the original question: my Disco 'runs' right at 14 volts. That's enough to charge the batteries, but not enough to boil 'em. 14.3 should be OK...above 15 and certainly 16 volts, you are going to cook the batteries.

The Oddessey is a pretty good battery, but even a good one can be defeated by teaming it up with a bad one. One the boat, I always replaced both batteries together, as the bad one can and will drag down the good one, though the isolator is supposed to prevent this. Maybe that bit of kit is hosed....

Over charging can also lead to sulfation (lead sulfate "sponge" forming on the plates) which interferes with the transfer of electrons between the electrolyte solution and the electrode plates. Batteries then develop what I call a 'surface charge'. A meter across the terminals will read 12 volts, but it is analogous to a measuring a puddle rather than a pond or lake: there is no 'depth' to the charge and a spin or three of the engine drains it.

 

[RBBailey]

Let me take some pictures of the set up and get back to you.

I do not have Optima, I have Odyssey, two of them. And I'm only going on owning the truck for two weeks now, so I'm taking the previous owners word when he says they were in parallel, then separated with a Phoenix Gold isolator and a manual relay.

 

[garrett]

the way i see two batteries working the most efficiently is by isolating them and using a deep cycling ONLY for the accessories. that's how they (deep cycles) work the best and most efficiently. they are not intended as a starting battery, but rather for low amp over long periods. they don't do well with lots of high draws over and over. that will kill them. this is how i understand it.
as Sandy said keeping them parallel will only draw down a weak battery faster and start the process of the strong one shortly after.

 

[apg]

I might add that a load test should be the next step. Instead of a multimeter across the terminals which draws micro-milliamps, the load tester (any of the big, chain auto parts stores will have one to use for the test) has an attached resistance coil that *really* exercises those electrons.

Now if the battery(s) is sulfated, I used a JC Whitless product that *really* worked - it wasn't snake-oil. Years ago, the battery in the '72 88" was dying. Added this product called VX-6 to each cell. (It's some kind of cadmium compound, so it's *very* toxic...probably carcinogenic, too.)

Hand-cranked the engine to start the vehicle get to work and then drove the three or so miles to the office. One-half block from work, I ran out of gas in the middle of a major intersection. (Doh!) Put it in first and hit the starter. In just the three mile drive, the "dead" battery had been given enough life to haul the vehicle through the intersection on electrical power only.

YMMV....

 

[RBBailey]

OK, here is the situation. I can't quite figure out the wiring. I would appreciate it if you could read the captions with the photos here: Batteries

I'm betting that I need a new battery or two, since just over night with the switch left "ON" caused me to show 10.3 volts this morning -- not enough to start the car.

I will do a little more investigation on where the cables are running, but basically, the only thing I really know is that one battery can be turned off and that the stereo system does not have power when you turn that battery off.

I'm getting the feeling that I have a super sweet set up that was wired wrong.

 

[apg]

How is the alternator working? Disconnect the alternator overnight and see if the same voltage drop occurs. The alternator contains a diode pack that functions like a one-way valve: it keeps the battery from draining down back through the alternator. There are three diodes in the Lucas 16-ACR in a series Rover. I have no idea how many are in the Magnetti-Marelli (sp??) alternator. It could still 'work' with one or more blown - but then drain the battery when not running.

Now here is a quick (and cheap) way to determine where this drain is. Disconnect the battery ground lead, and connect a low-wattage bulb between the battery post and the cable. The brighter the bulb, the bigger the drain. (Mind you, there will always be some drain, from things like the clock, alarm system, etc.) Now start disconnecting circuits, like unplug the alternator. When the light dims appreciably, you've found the culprit.

 

[antichrist]

When I am running I am getting 14.3 volts

From where are you taking that reading?

...then separated with a Phoenix Gold isolator and a manual relay.

FWIW I did a search of Phoenix's web site for Schottky and came up empty. So I'm guessing you're getting a lot of volt drop though the isolator.
Mind you that's just a guess.
You can test that. Just see what the charging voltage is to the isolater input, then what it is to the isolator output. I'd set your meter to something like 24v scale so you can get an accurate reading.
Ignore this if you're getting your 14.3 volt reading at the POS terminal of the battery.

 

[ptschram]

the way i see two batteries working the most efficiently is by isolating them and using a deep cycling ONLY for the accessories. that's how they (deep cycles) work the best and most efficiently. they are not intended as a starting battery, but rather for low amp over long periods. they don't do well with lots of high draws over and over. that will kill them. this is how i understand it.
as Sandy said keeping them parallel will only draw down a weak battery faster and start the process of the strong one shortly after.

I'm going on ten years of using deep-cycle batteries as starting batteries with no problems. They seem to last as long or longer than regular batteries.

Works for me.

 

[RBBailey]

I think that the small wire coming from the isolator to the firewall is the voltage meter that I have in the cabin. So I am getting my voltage reading from the isolator... strange thing is, the isolator is not connected (directly) to the battery where the isolator switch is located -- ??

I'm looking at the batteries, one is the 1200, it is connected to the switch and seems to be the one that drives the accessories (the lights work with or without the switch ON) The other is a different type of Odyssey, but the same size.

It also appears that while the lights get their power from the battery that is wired into the truck "stock", that they are grounded through the extra battery.

 

[antichrist]

I think that the small wire coming from the isolator to the firewall is the voltage meter that I have in the cabin. So I am getting my voltage reading from the isolator...

On the input or output terminal?
If it's from the input, you need to check it on the output.

 

[RBBailey]

On the input or output terminal?
If it's from the input, you need to check it on the output.

Ha! You know as much about this isolator as I do by looking at this picture:
It's the middle stud

 

[apg]

Looking at the photos, I only see *one* brown wire - going directly to the passenger side battery. The brown wire is the output from the alternator, so it appears that only the passenger side battery is getting charged...and there may be enough voltage drop through the isolator so that the driver's side ain't getting enough juice. And one bad battery can bring down the entire system....

You got a "good deal" on the truck, right?

 

[antichrist]

Ha! You know as much about this isolator as I do by looking at this picture:
It's the middle stud

You mean the smaller of the studs, second from left?
If I'm not mistaken, not knowing the layout of the isolator, that stud is for exiciting the alternator so it will start charging. The isolator looks suspiciously like a sure power or delco, in which case that's what the stud is for. The voltmeter should really be connected to the battery, or at the least, to the output terminal (that goes to a battery) of the isolator.
If it is a surepower isolater rebadged as Phoenix, then it's not a schottky diode model as they don't have 4 posts, only 3.

Actually, looking at that picture again, I have to ask, "WTF?"
It looks like all the cables are connected to just one stud, with the exception of the voltmeter wire. So I wonder why the heck the person even has an isolator? It appears to be doing nothing but serving as a "post" to bond multiple cables.
Right now I'm thinking that whole setup is a SPOT.