Battery/Multitester 101...

[crazylev]

Hello.

I am going to pick an analog-type multi-tester from Home Depot. I plan on using it to check the battery levels when I boondock, so I know when to hook up the Honda 2000 that I am the proud owner of at this time. The 2000 is very quiet, and I think it will work out great for our needs. If we find that we just can't live with out the air conditioner, we will consider another 2000 to run in parallel.

Here is my question: I have two coach batteries in the 19' CCD. The batteries are wired to one another (I think this is called series, or is it parallel?) Anyway, when I take a reading from one of the two batteries, what readings should I be looking to get? Do I need to read each battery individually, which means I'd have to disconnect one bat. from the other.

At what voltage do I then start charging with the Honda? I think RKMoe said that going to 10.5V was commiting battery homicide, I don't want this to happen.

FYI, I also have a BatteryMinder that I will use during the winter months, when the batteries are in storage in my basement.

If you could not tell from the above, I am quite green about batteries, multi-meters, anything electric, and any info, like, say how to even use a multi-meter would be most appreciated.

Blushingly yours.

Jonathan

[raebaker06]

You have not said what voltage the batteries are.
Are they connected Plus to plus and negative to negative. if so it is a PARLLEL connection.

If the wires go from one battery through the other it is SERIES and the voltages would be number one plus number two.

You can measure the voltage across each battery seperately, and across both batteries together.

I would seriously suggest that you go to a dealer or a garage and have a person explain the system to you. There is sulfuric acid in the batteries and if you do the wrong thing you might incure dire results in an explosion.

DO NOT FOOL WITH WHAT YOU APPARANTLEY KNOW LITTLE IF ANYTHING ABOUT.
I chide you not be careful.

Rae
Electronics Service Lab Burlington Ontario.

[Pick]

Your batteries should be connected in parallel. 12.6 Volts is considered fully charged, although will probably get a reading higher than that. You should start to charge them around 12.0 volts. No need to disconnect them. I am assuming that you are using the Bambi's built in charging system.

[nickcrowhurst]

Johnathon, you will be a lot happier with a digital voltmeter, even though it may cost twice as much as an analogue meter. You will be checking for small differences in voltage, and this can be much more difficult to measure with an analogue meter. There are couple of good books on RV electrics. Harold Barre has written a good one, entitled "Managing 12volts" . A little reading will increase your confidence. Nick.

[crazylev]

Thank you all for your replies. I am about to return to Home Depot my analog $13.00 tester that I used to test on aa 9volt battery before it died.

Rae: I am not at my trailer, but I believe they are hooked up in series, plus to plus, minus to minus. Sorry I was not clear on that in my first post. I've done a bit of electrical stuff around the house so I'm not TOTALLY clueless. Just confused.

Nick: I will look into the digital meter for sure.

Pick: 1st ? For now let's call my batteries #1 and #2. If I have the black(-) probe from the meter on the minus (-) of battery #1 and the red (+) probe on the plus of the battery #1, will the reading be only from battery #1, or will it also reading power off Battery#2? I guess what I'm asking is if there is a way to find out if each battery is in good shape individually, without having to undo the leads that go from battery 1 to battery 2.

Let me put it another way. Say my reading is 12.6 volts with batteries 1 and 2 hooked up in series and the reading is done as written above. If I disconnect all the cables to each battery (again for sake of discussion), should the reading of both batteries individually still be 12.6 volts?

Thanks again.

Jonathan

[raebaker06]

I still think that your batteries are 12VDC units and are in series. I have not seen most campers with 24 volts. Most are 12VDC units. Your vehicle charges 13.8 VDC, and would not charge a series circuit.


+ =======(+ B1 -)=(+ B2 -)======= - This is series
<--------- 12VDC-><12VDC>--------->
<----------------24VDC-------------->

<-----------12VDC---------->

+=====I==(+ B1 -)==I
: :
I==(+ B2 -)==I===== - This is parallel

I still think you had best get some authorative advice.

My advice is good. Take it.
You could be sorry.

Rae

[74Argosy24MH]

Got filler caps on the batteries? If there are 6 they are 12 volts, 3 is 6 volts.

If both positives and both negatives are hooked together or to a common terminal they are in parallel. If the positive of one battery is hooked to the negative of another and the other positive and negative are hooked to the charger/load they are in series.

John

[Tom Nugler]

Are the batteries deep cycle? You can draw them down farther.
Go digital DVOM. So much more easily read when you're eyes are going.

[Pick]

Crazy, your batteries are connected in parallel. With that in mind you are reading the combined voltage of both batteries. The only way to read an individual battery is to disconnect the - (Ground or Black wire) of the other battery in parallel. I would not do this on a trip. Just be satisfied with the combined reading. Every 3 months or so, you may want to check an individual battery, if you suspect there is a problem, or when checking water level and see one battery's level different from the other.

[Sav'h Steve]

Most everybody has 12 volt batteries. A few have opted for 6 volt golf cart batts that are true deep cycle-as noted they will have 3 cells (filler caps) on top.

When two batteries have been connected together for a while, the weaker battery WILL bring down the better one. So it is always best to have matched batts of the same age.

The biggest killer of batts is overcharging and boiling water off. Next is leaving a discharged batt set too long. Very inportant to check water level and add DISTILLED water only to the bottom of the caps.

Charging one will charge the other at the same time. That's OK.

Putting a timer on the Univolt is what I have done to keep from having to plug and unplug coach to 110volt. Set timer to come on 1 - 2 hours a day max.

Digital Multimeter is a must. Here is a great site: http://bart.ccis.com/home/mnemeth/12volt/12volt.htm

Keep asking questions...

Steve in Sav'h

[john hd]

hey lev,

don't chuck the analog unit just yet. i actually prefer them to digital units.

what you are looking for is overall trends with your voltmeter battery relationship. even the best voltmeters can be inaccurate by large margins! i use a wavetech meterman meter at work every day at the power company, i'm on my third one since we switched to digital meters about 6 years ago. they are fragile, don't work especially well in cold weather, and go out of adjustment without notice.

i have my original simpson meter that was issued to me back in the 80's and it still works perfectly! and it was probably 20 years old when i got it!

we have this test at the power company for delicate instruments, we call it the "drop test" my simpson has survived a couple of them and lived. my prior two digital meters have failed this test!

keep in mind, what ever meter you get. take a reading when you first get it and write it down. weather it is 12.4 12.7 etc, it doesn not matter much. what you need to look for is a general trend in the condition of your batteries. steady is good, a general downward trend is bad.

your batterys are most certainly connected in parallel.

john

[raebaker06]

John HD Gave you good advise. I too have a Simpson 260 analog meter. They are dependable and take a beating. Not so for digital meters. I have owned them as well.

Your Parallel connection needs to have one battery terminal removed to measure. When hooked together you are reading both batteries similtaniously.

Do not worry about very small differences. eg 12.6 or 12.5. Your meter lead resistance can make that difference.

Be sure to top up your battery cells with only distilled water. the chemicals in tap water will ruin you battery in time.

Batteries self discharge and need to be float charged to keep them working.

Starting batteries have the plates made of a lead paste and deep cycle have solid lead plates. and will last for years if you look after them.

Rae

[crazylev]

Thanks guys.

I bought the Ideal 360 digital meter from HD $60.00. My AS is a 2004 CCD, and the batteries are deep cycle. At this point I just wanted to keep an eye on the battery level when boondocking.

One of the things I learned is that in order to get an acurate reading, there should be no load on the battery for six hours.

Steve: great reading from the suggested site.

I'll be leaving Wednesday for a five night camp-out and will check to see how the batteries held up in storage for the past weeks. The only draw on the bat. should be the LP detector. The camp ground we are going to has hook-ups, so the 2000 won't get it's work out until October when we go to Sand Ridge State Forest in Ill.

Anyone else been there?

Jonathan

[norbert]

jonathan,
i also have a simpson 260, but i rely on the old style tester...a hydrometer...its only about 5 bucks at the auto store, and specific gravity readings give you a good way to monitor battery level although not as convenient...
norby

[dtbw]

BTW, YES, your batteries are in PARALLEL which doubles the current capacity (assumes identical batteries) and this means longer boondocking between recharges. Relying on a voltage reading (digital or analog) to determine battery condition is almost worthless, especially if you want the batteries to last (btw, if you insist on using voltage, then you really need a high accuracy digital multimeter as analog meters lack adequate resolution). By the time a lead acid battery falls below 12 volts you are already almost at zero charge left. The difference between a fully charged, resting battery under no load and 50% charged under no load is roughly .4 volts (12.64 vs 12.24). All voltage readings have to be taken under NO LOAD and after the battery has rested from either charge or discharge at least 15 minutes. You also have to know the temperature of the battery electrolyte as it has a direct impact on the voltage you will read. You should not discharge a deep cycle battery below 50% unless you want to replace them routinely. A deep charge battery drained to almost zero routinely has a life of around 350 charge cycles. That same battery recharged when it gets to 40%-50% has a life over over 3000 charge cycles. Here are some charts, note the the chart is based on battery temps of 80degrees...see following chart to get the offset for other temps. THIS IS TEMP of the ELECTROLYTE not the air.

see the attached jpg chart images


As you can see, trying to use voltage as an absolute indicator requires an extremely accurate, high resolution digital voltmeter and a knowledge of the electrolyte temperature.

Specific gravity as well as actual amp-hour consumption/charge tracking are the other ways monitoring batteries.

Using a professional, temperature compensated hydrometer (ie not one of the cheapo plastic ball things that you see in the auto stores), you can accurately determine the charge condition, but this means letting the batteries rest under no load for 15 minutes, then removing the caps and taking readings in each cell. You then compare the reading to the chart or use the relative charge scale on the hydrometer to determine the battery condition. The good thing about using a hydrometer is that it measures EACH cell and therefore, if you have a bad or weak cell, it will detect it. ALL other means of monitoring battery condition see the batteries as a single entity and therefore have no knowledge of individual cell issues.

The other way to determine charge state is to install a amp-hour monitoring system such as the Tri-Metric 2020. These devices works by tracking and recording the actual current going and coming from the batteries. When installed, you enter the total amp-hour number that you wish to be used as the monitored capacity. As 50% discharge is always the goal, you simple enter the total amp-hour capacity of the two batterys divided by 2. The monitor will then provide you with a "gas gauge" percentage reading that gives you an pretty accurate charge state of the batteries. Once the monitor reads zero, you need to recharge, and also by using the 50% rule, if the situation should arise where you can't recharge immediately, you do have a good reserve in that the batteries are actually only half discharged. This type of monitor also provides voltage, the present amps being pulled OR pushed (ie charging) to the batteries as well as the cumulative amp-hours pulled from the batteries since the monitor was connected along with some other techy data. The flaw in amp-hour monitoring is that a battery that has a small amperage, slow discharge will produce MORE amps-hours than one that is discharged rapidly (ie high amperage). The difference between the two discharge rates is dependent on the overall condition of the battery and amp-hour monitoring systems don't attempt to compensate for this effect. But if you are monitoring for 50% actual discharge, an amp-hour monitor will still be pretty darn close regardless of the rate of discharge. Installing one of these is fairly simple in that a shunt is placed in the negative line that goes to the batteries. As current flows, the shunt develops a small voltage drop relative to the current passing thru it and that is recorded by the monitor.

If you don't want to spend the $150buck or so for a Tri-Metric or something similar, then get a good professional grade battery hydrometer and learn to use it. The hydrometer is somewhat messy and if you get any battery acid on your clothing, it will eat a hole even if you immediately flush it with water. You can use a voltmeter but it is about like wanting to know the position of the sun but the day is totally overcast and you have no idea of the time. You know the sun is shining, but that is about it.

BTW, I went the amp-hour monitoring route as I wanted to see at a glance without fuss or muss the battery condition. As I also have solar, this gave me much better visibility of the actual usage so as to ensure that the solar panels had a running chance of keeping up.


david

[crazylev]

David.

Thanks for the post and attachments. I'll print these out for reference. This stuff is not real simple, is it?

Jonathan

[dtbw]

Jonathan,
Glad the info helped. One other thing that I should mention is the the discharge chart is NOT applicable for gel cell lead acid batteries (some owners have replaced original wetcell factory batteries with gelcell technology...A/S also now offers a gelcell technology battery as part of its solar upgrade package). Gel cell lead acid batteries have a resting, no load, fully charged voltage of 12.8v @ 80degrees and every .2volts below that represents an approximate 25% discharge. For most of us, we are running wetcell technology so the already posted info is applicable.

david