Voltmeter install in Roo 19

[Kansas Camper]

At 11.2 that means you should have started it already.

[palmetto rogue]

Thanks Kansas, I knew that. I was trying to understand why camaraderie says it tells you nothing. I boondock frequently and watch my battery voltage religiously.

[Kansas Camper]

Oh, I agree. We leave tomorrow to go to the mountains and will be doing the same thing. My wife gets made at me as I check with my volt meter multiple times a day. How low do you allow your deep cycle to go before charging? I have always heard not to let it drop below 50% which is around 12.1 or it could damage the battery.

[RJHuser]

ALWAYS disconnect the negative cable first! That is the safe way on negative ground systems. If you try to disconnect the positive cable first you risk blowing the battery up if you slip and your wrench goes to ground. Personally, I never bother disconnecting the battery, 12VDC won't hurt you.

Rick

[camaraderie]

Well as I said...it will indicate a flat battery....so it would indicate that you have already done damage to your battery life and it is way past time to recharge...it cannot reliably tell you when it is REALLY 12.1 OR 12.2 AND TIME TO RECHARGE without cycle loss OR WHEN THEY ARE 100% TO AVOID the same fate. If you boondock a lot you need a true battery monitor like the trimetric or victron...in the $150 range. Alternative is buying batteries much more often.

[oldtool2]

Originally Posted by jeff64

:
Sounds like a lot of trouble to go through. You will get the information you need out of a 120v plug in voltmeter in one of your outlets and for about $15

I just added one in my 5er to monitor the battery. Converter is trickle charging the batteries right now, meter reads 13.68 VDC right now. I wired in a vom meter I don't use any more so it has a switch I can use to turn it off and on when I want. I sits in the switch panel just inside the door. This will allow me to watch the batteries voltage when I am boondocking, so I will know when I need to charge them. Much more accurate than the idiot lights! Herk7769 supplied this chart to use to watch your batteries charge.



Jim

[rsdata]

Harbor Freight sells a great tool to tell you if your battery capacity is up to snuff.

It measures the battery voltage condition under a load and will give you the best information you can get in an inexpensive package.

100 Amp 6/12V Battery Load Tester

You don't need to use it all the time, but after a season is over or at the beginning of a new season. I have used one for years and works great.

[Jim Schings]

Originally Posted by camaraderie

A voltmeter tells you nothing useful about the state of your batteries IN USE except if they are flat dead or presently charging. if it reads 12.4 or such then you have no idea what the ACTUAL state of charge is unless it is reading after the batt has been disconnected from everything for 24 hours..

Incorrect. Yes, you don't want to have a significant load on it to make the evaluation, but a few lights, etc. won't make any difference at all. I have been testing batteries for 20 years.

.even more importantly is cannot tell you when you have charged to100% ....

Incorrect. During charging, of course not. But after charging is stopped, and a slight draw is used to remove the float (a few lights for a couple minutes) the indicated voltage will tell you exactly what state of charge the batter is at.

I have tested Lead Acid, AGM, and Gel Cells very accurate load and time instruments. With proper reading the DVM method is very accurate. There are other devices that can do a slightly better job, but installation and price are not worth the effort in normal RV boondocking application.

[Jim Schings]

Originally Posted by RJHuser

Personally, I never bother disconnecting the battery, 12VDC won't hurt you.

Wanna see a watch or a ring get welded to the frame ? Wanna see a red hot wire leave a neat scar on the arm? Did you know you can arc weld with a car battery pretty well.

[Jim Schings]

Originally Posted by rsdata

Harbor Freight sells a great tool to tell you if your battery capacity is up to snuff.

It measures the battery voltage condition under a load and will give you the best information you can get in an inexpensive package.

Yes a good tool, to have. (to indicate how well the battery will charge and to some degree, it's available energy. ) However, by the time you notice that the battery is getting a bit old (sulfated), you probably already knew this from use.

[oldtool2]

Originally Posted by RJHuser

Personally, I never bother disconnecting the battery, 12VDC won't hurt you.

Rick

That is one of the stupidest comments I have seen here so far !! You are half right I guess. 12 volts won't, neither will 500 volts. The current from a car battery across your heart though can make you a dead man!

Grab a terminal of a well charged battery, one in each hand, and when you get out of the hospital let me know how it felt. Oh, have the rescue squad sitting close by when you do it. I am sure we can wait till you get out of the hospital for your reply.

On second thought, PLEASE DON'T TRY IT!

Jim

[Jim Schings]

Originally Posted by oldtool2

That is one of the stupidest comments I have seen here so far !!

If I told you once, I told you a million times, "Don't exaggerate"..

Yes there is plenty of current in a car battery to kill you. There is plenty enough current in a flashlight battery to kill you. Even a good hearing aid battery COULD deliver enough. However below 20 or 30 volts of EMF (voltage) the risk is almost nil. To get enough current across the heart to cause death of even contractions you would have to be in the bath tub and both probes into the epidermis. (Even then it would have to be across the chest area.

(BTW, I just grabbed both leads from a charger set to 24V. Couldn't even feel it.)

BY far the only risk with a 12V system with lots of current is burns. THAT is why you should disconnect.

[camaraderie]

Originally Posted by Jim Schings

Yes a good tool, to have. (to indicate how well the battery will charge and to some degree, it's available energy. ) However, by the time you notice that the battery is getting a bit old (sulfated), you probably already knew this from use.

It is also useful with a new, top condition battery to wipe out the surface charge after several hours of charging and get a true voltage and SOC rating without waiting 24 hours for the surface charge to dissipate. Those without a REAL battery monitor might be surprised how long it takes ton get to "full" at 12.6-12.7 V... and realize how long they've been undercharging their batts and killing off life cycles.
Note that my comments on this thread apply to those who boondock on batteries alone...and need know when to charge them and how long they need to be charged. If you plug in everywhere,,, you just need to use the idiot lights or a volt reading to insure you are getting a charge (13.2-14.5 volts) and don't have dead batts.

[camaraderie]

Originally Posted by Jim Schings

Incorrect. Yes, you don't want to have a significant load on it to make the evaluation, but a few lights, etc. won't make any difference at all. I have been testing batteries for 20 years.

That's nice...I was an auto battery buyer for a major company AND I lived on an 1100 amp hour bank of wet cells then AGM's exclusively for 6 years t sea supplemented by wind, solar and an 8kw generator driving a 130 amp smart charger and YES a real battery monitor which told me things that you can't report accurately.
You need more than a few lights to fully wipe out the charge...see harbor freight bove...and you don't know WHEN you have HIT the 100% mark...so you either have to keep charging and turn the genny back on...OR you waste gas. A battery monitor will tell you exactly when you hit 100% full. It will also tell you exacrtly how much charge you nhave left at any moment and how long you have left AT present input/output before you need to charge again using Peukerts constant rather than some guestimate.
I repeat...IF you boondock relying on deep cycle batteries... your cheap voltmeter will COST you way more in GAS, TIME and NEW REPLACEMENT BATTERIES than proper battery monitor and shunt for around $150.

[oldtool2]

Originally Posted by Jim Schings

If I told you once, I told you a million times, "Don't exaggerate"..

LOL!! Not trying to exaggerate at all, but couldn't leave such a foolish remark go unanswered either. I don't want to see anyone get hurt, or killed, because or a bad statement like that!

Originally Posted by Jim Schings

Yes there is plenty of current in a car battery to kill you. There is plenty enough current in a flashlight battery to kill you. Even a good hearing aid battery COULD deliver enough. However below 20 or 30 volts of EMF (voltage) the risk is almost nil. To get enough current across the heart to cause death of even contractions you would have to be in the bath tub and both probes into the epidermis. (Even then it would have to be across the chest area.

(BTW, I just grabbed both leads from a charger set to 24V. Couldn't even feel it.)

BY far the only risk with a 12V system with lots of current is burns. THAT is why you should disconnect.

Granted conditions need to be right but why take chances to save two minutes work? I learned my trade from a retired Navy instructor and he is the one that taught me about DC voltage and currant.

Here is something to think about. A defibulater does nothing but shock your heart with mili-amps to restart it. Why don't they use higher amperage? Because it would kill the heart muscle.

Burns are a very real possibility. A friend of mine shorted the two terminals once with a wrench and spent two days in a hospital because the battery blew up. That was twenty some years ago and he still has scars from the acid burns. Because of that I now place a rag over the terminal I am not working on so I don't hit it with a wrench.

Take the time and disconnect the battery, it only takes a minute or two.

As for your charger, was it for a cell phone or such? Probably very low current output.

Jim


BTW, love your mentioning a bath tub! When you drop the hair dryer, or such, into the tub filled with water you will be ok. It is when you grab it with ONE HAND to toss it out you will die. That is when the current will go thru your heart and stop it. If you are lucky the breaker will trip right away!

[Jim Schings]

Originally Posted by oldtool2

Here is something to think about. A defibulater does nothing but shock your heart with mili-amps to restart it. Why don't they use higher amperage? Because it would kill the heart muscle.

They also use several hundred volts (200-1000) to overcome the resistance of the epidermis. 12V or 50V would do nothing at all.

BTW the actual current used is limited to MICROamps anywhere near the heart. OH, AND, a defrib is not used to START the heart. It is used to regulate the heart after fibrillations have started. It does not RE-START the heart.

Burns are a very real possibility.

No argument there.

Take the time and disconnect the battery, it only takes a minute or two.

As I directed him to.

As for your charger, was it for a cell phone or such? Probably very low current output.

A 80 ampere battery charger. AND the open DC output voltage was actually closer to 30 volts. Felt nothing. Do this same thing with AC at that voltage and you will typically feel some tingling.

BTW, love your mentioning a bath tub! When you drop the hair dryer, or such, into the tub filled with water you will be ok.

Almost always. Actually clean water is a poor conductor of current. In most cases won't blow a normal fuse or circuit breaker. However a GFI will open very quickly since it trips in the milliamp range.

It is when you grab it with ONE HAND to toss it out you will die. That is when the current will go thru your heart and stop it. If you are lucky the breaker will trip right away

I don't understand this statement a bit. Since the hair dryer has both L1 and N attached to it and in the water, it makes no difference whether you grab it with one, two, or 3 hands. This would make SOME sense if the hair dryer only had L1 connected to it. Then, the potential current flow would be from the hairdryer to the tub or your hand. In actuality the path would be from L1 right to N internal in the hairdryer. That is why death or even shock is unlikely. Maybe you could explain your logic?

[Jim Schings]

BTW. Actual "Electrocution" is almost always a voltage above the 120 V ("low voltage") with current that gets to the heart muscle at an amount that causes fibrillations. (uncontrolled heart beat) In this condition the heart does not pump blood properly. (sorta like a cavetating water pump.) Without immediate treatment the heart may continue like this until death. A defib device is used to "shock" the heart back into regulation.


Note that with VERY high voltages enough current could be forced through the heart muscles(s) (or brain) to actually burn it. Then defibrillations don't help much.

[Jim Schings]

Originally Posted by camaraderie

A battery monitor will tell you exactly when you hit 100% full. It will also tell you exacrtly how much charge you nhave left at any moment and how long you have left AT present input/output before you need to charge again using Peukerts constant rather than some guestimate.

Sorry, but Peukerts constant ONLY works in theory with a NEW battery. After ANY sulfating all bets are off. Using a voltage monitor is simple and cheap. As I said, it is not quite as good as a full monitor. However after a few charge and discharge cycles any reasonable boon docker has a very good idea on his battery cycle life. I am not aware of anyone that cuts the battery life so close as to have a full monitor. If you have one, that is great. IMO it is overkill for the typical RV'er.

We have used (simple voltage monitors on Data acquisition systems) on Formula race cars with zero loss systems. (no on board charging). With AGM or even standard L/A batteries we NEVER had a battery failure before it's time. These units were in far more harsher environments. A failure was far more catastrophic than no coffee.

[oldtool2]

Originally Posted by Jim Schings

A failure was far more catastrophic than no coffee.

Sorry Jim, but nothing is more catastrophic than running out of coffee !

Jim

[Jim Schings]

Yes, I probably should have used a better comparison....