Adding a voltmeter for two batteries????

[mrcool]

I have decided to use two batteries this year after finding myself with a dead battery on the lake once last year. I think I will have engine ONLY on the main battery, and add a second battery to run all other acsesseries, fish finder, trolling motor, radio ect... and just use a home battery charger to keep the charge up on the second battery.
My question is, I just bought a Telex voltmeter and would like to use it on both batteries at different times. So can I use allagitor clips on the battery end of the wires and clip the positive end to the positive battery post and the negitive end to the negitive post, then switch alligator clips to the second battery to check its charge? or will this not work?
As far as wiring the gauge, it has a ground terminal (no brainer) and a (I) terminal I'm guessing that stands for ignition, I'm also guessing that lead would connect to my positive battery posts. It also has an (L) terminal (Light??) can I just connect that wire to Ignition terminal? or maybe put a switch on that wire so as not to have the light on and drain a bit of the battery during the day when the light is not needed?

One last thing the gauge needs a 2 1/8" hole in the dash board to install it, whats the best way to drill that hole? I'm not real big on drilling a whole that size into my dashboard thanks for the help!!

 

[Silvertip]

Re: Adding a voltmeter for two batteries????

If you want the gauge in the console you have no choice but to drill the hole and it's not that difficult. Buy a hole saw at Lowes, Home Depot, etc. Use masking tape to cover the area where the hole will be drilled and have at it. Your wiring scheme is a very poor technique and will be a source of confusion since you will not know which battery you are checking. Install a simple toggle switch so you can simply flip the switch to check either battery. Here is a diagram. The toggle switch is available at Radio Shack or even in the electrical department at Lowes/Home Depot. It must have three terminals on the back and be an On/Off/On type. The center terminal goes to the I (+12V) terminal on the gauge. The other two terminals connect to the POS terminal on the batteries. The NEG terminals on the batteries are connected togethr and then to the NEG (-) terminal on the gauge. The Light terminal connects to the light terminal on any other gauge or to the "A" accessory terminal on the ignition switch. Do not use alligator clips on the batteries. Add ring terminals for a secure connection.

 

[Expidia]

Re: Adding a voltmeter for two batteries????

I pondered this question last year when I was looking for a meter to give me the condition of how much charge is left in a battery, especially the deep cycle one when I'm trolling.

Someone correct me if I'm wrong but it sounds like this poster is thinking the way I originally thought and was looking for a volt meter.

The forum corrected me on this as to if a battery is 12 volts, it's still going to read 12 volts as it's exhausting it's charge.

I was corrected into looking for a battery condition meter.

I would think a voltage meter mostly tells you that the battery is correctly charging when the motor is running or the battery is putting out 12 volts when motor is off.

This was what I bought: http://www.boatersland.com/far-12823.html

This is the thread where it was discussed and I was set straight on what I actually needed to solve my issue was how much "juice" does my battery have remaining. I was running my battery down while hanging out in a bay for the day while some of the electronics were on like the stereo:

http://forums.iboats.com/showthread.php?t=269075

P.S. you wire it just like Slivertip showed you above with a momentary switch.

 

[mrcool]

Re: Adding a voltmeter for two batteries????

I pondered this question last year when I was looking for a meter to give me the condition of how much charge is left in a battery, especially the deep cycle one when I'm trolling.

Someone correct me if I'm wrong but it sounds like this poster is thinking the way I originally thought and was looking for a volt meter.

The forum corrected me on this as to if a battery is 12 volts, it's still going to read 12 volts as it's exhausting it's charge.

I was corrected into looking for a battery condition meter.

I would think a voltage meter mostly tells you that the battery is correctly charging when the motor is running or the battery is putting out 12 volts when motor is off.



This was what I bought: http://www.boatersland.com/far-12823.html

This is the thread where it was discussed and I was set straight on what I actually needed to solve my issue was how much "juice" does my battery have remaining. I was running my battery down while hanging out in a bay for the day while some of the electronics were on like the stereo:

http://forums.iboats.com/showthread.php?t=269075

Thanks so much Expidia!! This is exactly the info I was looking for! and Like you , I am corrected.. I did not buy a voltmeter, I bought a Telex Battery Condition indicator! and hopefully it will give me the "charged" condition of my batteries. it reads to a "low charge" of 8 volts to a "full charge" of 18 volts. Thanks for the info, you guys rock

 

[Silvertip]

Re: Adding a voltmeter for two batteries????

Sorry but you are misinformed on your purchase. Although it looks like an electrical gas guage, it is merely a voltmeter that has it's scale calibrated around 11.5 to about 13 volts. No 12 volt battery will read fully charged at 18 volts and it is stone dead at 8 volts which is what a normal voltmeter indicates. A 12 volt battery is nearly discharged when it gets into the 11 volt range and is fully charged in upper 12 volt range. If the batteries are connected to the engine charging system you will read in the 13.6 - 14.5 range with the engine running and in the 12.6 range with the engine off. You will never see 18 volts unless there is an electrical malfunction. You bought a charging system voltmeter. There are two ways to measure the state of charge of a battery -- 1) a hydrometer that measures the specific gravity of the electrolyte which is a manual process and tough to do on a sealed battery, and 2) a load test which requires placing a known load on the battery and measuring its ability to deliver the stated current while staying in the correct voltage range. The so called condition gauges that are marked "Discharged or Low, Fair, and Good" sometimes have voltage readings on them as well. Regardless what the scale says, they are still only voltmeters. Besides, if you have a fish finder, the voltmeter in that unit reads to at least 1/10 volt and would likely be more accurate than the condition meter.

 

[john from md]

Re: Adding a voltmeter for two batteries????

Well said Silvertip.

John

 

[Expidia]

Re: Adding a voltmeter for two batteries????

"1) a hydrometer that measures the specific gravity of the electrolyte which is a manual process and tough to do on a sealed battery, and 2) a load test which requires placing a known load on the battery and measuring its ability to deliver the stated current while staying in the correct voltage range. "

Expidia says: Gee wiz, aren't you throwing a little too much over the top info at this guy here ???

He just wants to know how much charge he has left in his batteries.

Last season's use of my battery "condition" gauge did exactly what I wanted it to do . . . that is to let me know how much juice I have left in either battery with the flip of a switch!

Anyone in my family can see that gauge and know exactly what it means (time to turn the stereo off or pull out the oars) without even knowing what a volt or a hydrometer is

Many gauge companies carry them so I guess there must be a demand. maybe it's like an idiot light on a cars dash vs a gauge. Actually, some of those condition gauges have the lights too.

Whatever floats yer boat I guess.

 

[Silvertip]

Re: Adding a voltmeter for two batteries????

The point of these forums is to clarify and educate people about what they are actually buying. Vendors play very funny games with terminology and in the process suck people into buying stuff that does not do what they say it does. This device is a voltmeter, not a battery condition gauge. A gas gauge is a voltmeter as well, as the sender in the tank merely provides a varying voltage to the gauge which just happens to be calibrated from E-F. My point here is that ANY voltmeter will do the same thing this "Condition Gauge" tells you. And the term "Condition Gauge" is still misleading. It is not a condition gauge at all. A battery in poor condition can still measure 12.6 volts but not have enough "capacity" to light a bulb. That condition gauge would show good in that case until you actually tried to power something at which time it would drop like a rock to bad.

One cannot have too much information. In society today people look for YES - NO answers and don't seem to want to be bothered with the WHY. As a result they continue to be sucked into bad situations and don't understand why. The answer is called "Education".

 

[waterinthefuel]

Re: Adding a voltmeter for two batteries????

ST has a very good point. No voltmeter will show you the condition of a battery. AFAIK, there is no gauge or meter that can accurately show you how much charge a battery currently has.

Volts are just one thing a battery puts out, they also put out amps. THIS is the power in a battery. Cold cranking amps are important, just like that amp/hour rating of a battery. You can make a machine that puts out 50,000 volts but 1/1000 of an amp. It wouldn't be able to power a toaster. (it would make your hair stand on end though) But a voltmeter would show, correctly, 50,000 volts. But those volts have no amps behind them to "push" them.

Again, like ST said, it's not as cut and dry as yes and no. It's not that simple. A true and deep understanding of electricity is important if one is going to be able to correctly interpret what a gauge is telling you.

Rather than just read volts with the engine running or not, why not check the battery and engine charging system together? It wouldn't be hard to do, and all you would need is a good accurate voltmeter with volts out to tenths of a volt. Just charge up the battery when new, and put everything in the boat on, all lights, all pumps, all fish finders, everything. Put a good heavy load on the battery. Observe the voltage drop. Now, start the engine and put no load on the battery. Observe voltage. It should be around 13 volts, or if on an unregulated charging system on a small outboard, rev it just a bit and it should go up to that. Put everything in the boat on and observe voltage drop. If it doesn't, the charging system not only can charge the battery, but can handle the entire load in your boat. Or, if you notice that it can handle SOME load but not everything in the boat, then you know how much you can run before you are pulling from your battery when your engine is running. None of this can show you the percentage a battery is charged, but if you know that from 100% charged (right off the charger) the voltage drop at the battery is down to, say, 11.5 volts with a full load, and out on the lake it eventually gets down to 11 volts, you know it is definitely not fully charged. With no load, the battery shouldn't be below 12.4 or so. 12.2 is a weak battery, so if it goes down to 10.5 with a load and only 12.1 or 12.2 without a load, the battery is almost dead. All of this can be done with just a voltmeter, but UNDERSTANDING of the concepts and what you're checking is a must because a voltmeter in and of itself doesn't tell you much. It's kind of a like a slide rule, just looking at it doesn't tell you anything, but if you know how to use it it can be a very valuable tool.

You can also use this method to compare different batteries to see how much the voltages drop when an equal load is placed on each. If, after 30 minutes, the voltage on one is several tenths of a volt higher than the other, than it can probably be safely assumed that that particular battery can handle a current drain better than the other.