We are new campers and recently purchased a CL16DBS. It came with a standard Group24 battery. Before running to the store to
replace it with 2 Golf Cart batteries, we would like to know more about the battery we have and how it is discharging while we
monitor what we use etc.
Do most of you own a Digital Volt meter or a Multimeter and could you recommend one that you foud worked most accurately?
We are not techies and prefer something that is very accurate and reasonably simple. We now have an INNOVA Digital Multimeter
Model 3300 and it is not that clear how to set the dial for 12V. The first reading of our battery was also not encouraging.
After fully charging the coach battery and then letting the CL sit unused for two days, the battery had only 75% left. I realize
the radio, tv antenna etc continuously use power, but should it drain that much in such a short time? The Model 3300 was very
el-cheapo, but our small town does not carry any other.
It is an investment and we would like to purchase the right one next time we head to the Big Smoke.
We appreciate your suggestions and feedback!
Karen and Doug
"Sheep Creek", BC
[font size="3"]Karen and Doug,
Your Innova meter should be quite adequate for measuring your battery. Set the switch to 20 in the upper left quadrant which is labeled DCV in black. A fully charged battery should read about 12.6V. You should not let the battery get below 12.0V as this is about the 50% discharge point. Anything lower than this will begin to adversely affect the battery life. These readings should be taken after the battery has been "resting" for an hour, neither being charged or significantly discharged, and the readings should be taken directly on the battery terminals.
There is a small residual load on the battery when everything is "off", primarily the propane/CO detector. This will discharge the battery in 2-3 weeks so you must disconnect the battery or put it on a trickle charger if you can't leave the camper plugged in. When the battery is being charged it should read well above 13V. DO NOT pay any attention to the 4 light status indicator you may have in the camper. They are essentially worthless. Search this forum for charts and further advice on battery care or come back with more questions. Lots of help and expertise reside here.
When you get more comfortable with the meter you may want to invest in a better one that is also a clamp on ammeter, but that's down the line a bit.
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Thank you charliem, that is very helpful feedback!
The battery is now fully charged and after letting it sit for approx 4 hours, it reads 13.08. Will let it sit overnight and retest in the morning.
Thanks again
It was fun playing with the volt meter.
Our plan is to do some boondocking and I wanted to know how much the cpap machine would drain the battery,
so at night I first tested the battery "at rest" (reading: 12.95), then plugged the machine (without the humidifier) into the coach 12V socket and tested the battery 8 hours later.
Reading: 12.59. Not too bad, I thought, however we were not in it (using the radio, lights, fans, water pump, heater fan etc)
In many of the forum topics dealing with testing the coach battery, it is said to test when the battery is 'resting' (battery neither charging or under any significant draw?).
What is the most accurate method:
Should I test the battery when there is only minimal draw from the propane gas detector, radio ...
OR
should I test the battery when there is no draw at all? My husband has installed an on/off switch on the battery.
Example:
On September 1, at 8 am, with the battery 'at rest' (it had been at rest all night with minimal draw, as above), reading: 12.33
Then I turned the battery switch to 'off' and let it sit all day and all night.
On September 2, at 8 am, with switch turned to 'off' and no draw at all, reading: 12.71
I am confused; why is the battery charge higher than the morning before?
There are many posts and threads on the forum about batteries and testing but I can't seem to get a clear picture
as to what defines a 'resting battery' (No draw at all or just insignificant draw. Maybe there should be some draw to get a proper reading?)
And installing a battery monitor is definately above my techie skills, but I should be able to figure out how
to properly test this battery.
Once again, I appreciate your feedback on this
Karen
[font size="3"]The battery will tend to recover when not being charged or discharged. The best reading will be with the battery totally disconnected. The test under "minimal load" such as the propane monitor is not as accurate, but it is more convenient if you don't have a switch. Another variable is the battery temperature, but the difference is small.
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Trying to figure out state of charge (the percentage of the battery's capacity left) is very difficult to do using voltage. Even if you leave a battery with absolutely no load on it at all for several hours, the voltage will only tell you if it is 1/4 full, 1/2 full, etc. If you have even a small load (or charge) it will distort your results.
For flooded cell batteries with cell caps, a hygrometer is a much better tool. Unfortunately for AGM batteries, there is no good way to tell SOC. That is one reason why I like golf cart batteries.
David
To briefly return to the original question, I agree your Innova 3300 is fine. However, it is a bit easier to use an auto-ranging meter, so I have an Innova 3320 in both of my vehicles. They are very useful for quick checks of voltage and continuity. Carrying a multi-meter is an old habit from having owned a '46 Jeep that had spectacularly unreliable wiring. In the camper when at home, I use my Klein MM200 for general purposes. I also have a SeeLeveL monitor that reads out voltage. Since it always reads battery voltage under some load, the number requires interpretation. However, after some experience, you can get at least a warm and fuzzy feeling for how your battery(s) is doing and that's all you normally need. Voltage is all I have to work with since I've purchased only sealed AGM batteries for all uses for the past 11 years. Anyway, either of the meters above are fine.
We have been using a Craftsman multimeter and it has been working well (and they're not that expensive, especially if you get it on sale). Anyways, I have been using it to track the state of charge (SOC) of our batteries and I have a few questions...... First, we have two 6-volt golf cart batteries wired together in series. When fully charged, I found that the voltage reading was 13.13 (fully rested for a few hours after charging). Does that sound correct? Looks a little high to me, but maybe they are super batteries! Secondly, after dry camping recently for 3 days and using the batteries quite a bit (even ran the furnace on low during 2 of the nights due to cool temps), the lowest voltage reading that I got was 12.3 volts (as we were leaving). What was our SOC at that 12.3 level? Lastly, would a 12.0 reading be 50% SOC for our set-up?
[p]Batteries develop a "surface charge" when fully charged that can read well above the 12.7 that Trojan says (see below) is 100% charged. But it only takes an amp or so of load for an hour to bleed it off, then a couple of hours of rest to get a reasonably accurate voltage reading. The opposite is also true. When you pull say 10 amps like while the furnace is on, that drops the voltage below its resting state and you have to wait several hours to get a reliable reading.[/p][p]
[/p][p]I have a geeky boater friend who did a fairly rigorous analysis of measured open circuit voltage vs time vs specific gravity. He said that it took 12 hours of total resting before the voltage matched the specific gravity indicated voltage within 0.1 V. After a couple of hours of resting it was several tenths off.
Trojan published this voltage vs state of charge table (about midway down) and it is as good as anything: http://www.trojanbattery.com/tech-support/battery-maintenance/
But the true indicator of SOC is specific gravity.
David[/p]
Quote from: @swilky" source="/post/24414/thread" timestamp="1473277126Roughly: @80 degrees
12.66v-----100%
12.45v-----75%
12.24v-----50%
12.06v-----25%
11.89v-----0%
I thought I read somewhere above that a reading of 12.0 representated approximately 50% SOC.
[quote source="/post/24418/thread" timestamp="1473281062" author="@gbpack"][quote source="/post/24414/thread" timestamp="1473277126" author="@swilky"]Roughly: @80 degrees
12.66v-----100%
12.45v-----75%
12.24v-----50%
12.06v-----25%
11.89v-----0%
[/quote] I thought I read somewhere above that a reading of 12.0 representated approximately 50% SOC.[/quote][font size="3"]The above values seem extremely conservative (low) compared to other published data. I'd go with Trojan's numbers as cited by David. As a general rule of thumb I don't get concerned until I see 12.0 under no load. [/font]
One data point:
[img style="max-width:100%;" src="https://c4.staticflickr.com/2/1688/26349787411_ae362169cd_z.jpg"]
That's the back of my plug-in digital voltmeter.
Seems to roughly coincide with swilky's.
[quote timestamp="1473273924" author="@david" source="/post/24412/thread"][p]Batteries develop a "surface charge" when fully charged that can read well above the 12.7 that Trojan says (see below) is 100% charged. But it only takes an amp or so of load for an hour to bleed it off, then a couple of hours of rest to get a reasonably accurate voltage reading. The opposite is also true. When you pull say 10 amps like while the furnace is on, that drops the voltage below its resting state and you have to wait several hours to get a reliable reading.[/p][p]
[/p][p]I have a geeky boater friend who did a fairly rigorous analysis of measured open circuit voltage vs time vs specific gravity. He said that it took 12 hours of total resting before the voltage matched the specific gravity indicated voltage within 0.1 V. After a couple of hours of resting it was several tenths off.
Trojan published this voltage vs state of charge table (about midway down) and it is as good as anything: http://www.trojanbattery.com/tech-support/battery-maintenance/
But the true indicator of SOC is specific gravity.
David[/p][/quote][font size="3"]As an experiment I shut off the CL converter and measured the battery voltage over a day. Starting at 13.2V with the converter in its maintenance mode and only the 100+ mA residual load, the battery measured 12.8 at hour 7. It then remained at 12.8 through the last measurement at 24 hours. This supports David's surface charge discussion and I agree that voltage measurement is useful, but not perfect. But then so am I[/font] [attachment id="1697" thumbnail="1"]
I personally own one of these it works great for everyday use it is inexpensive and it defaults to DC for everything.
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