Monitoring Battery Voltage While Using Equipment

[KJRitchie]

I have a 12v plug in battery meter that I have plugged into a 12v socket in my entertainment center. Yesterday I pulled the AS out of storage and took it home and plugged into shore power. I left it on shore for at least an hour then unplugged shore power. The battery voltage was 13.7 under shore and after unplugging observed the battery voltage. The only 12v appliances running was the fridge on LP and the LP leak detector.

I noticed the voltage slowly ramp down as the batteries settled down after being on shore power. It got to 12.8v put slowly headed south to 12.6. I turned on a few of my converted LED lights and overhead fluorescent lights that have been converted using two LED light strips in each fixture. I noticed the voltage take a hit so it was down to 12.5 and dipping to 12.4.

I also notice when turning on the Sony radio with an attached 10 disc player causes the voltage to dip. When the 10 disc player is running through its initialization procedure the voltage dips down to 12.4. If I unplug the 10 disc changer the voltage then rampped up to 12.6.

My question is given healthy batteries when you turn on some lights and run the radio with two batteries in parallel are these voltage dips normal or should the voltage remain constant and slowly ramp down not fluctuate when you turn things on and off.

I put a ammeter on the negative battery cable and the draw is less than 3 amps.

I would think with two batteries in parallel the voltage would remain at something higher than 12.6v even with a couple of lights on and the fridge on LP.

I'm wondering if I need to replace my 2 year old batteries which are 2 grp 27 Interstates. They may have been damaged since I had converter issues 2 years ago which wasn't charging the batteries and they may have been discharged to low a couple of times. I also had an issue where the tow vehicle wasn't charging the batteries while towing. I've fixed those two issues. This
winter I did have two low reading cells in one battery. Charging at 15v seemed to have recovered those cells but maybe the damage has been done.

[idroba]

You many be only reading the variations in the resistance of the coach wiring not the true battery voltage. The first thing I would do is to put a digital volt meter on the battery terminals and see what is going on there. If you have the voltage variations you see in the coach at the batteries, with the light load you mention of about 3 amps, you may have some battery issues. If you don't see the same voltage variations what you have been recording is coming from the coach wiring connections and voltage drops.

If you want to do a poor man's test of the batteries, disconnect one and put a constant load on it of about 5 or so amps. Watch the voltage (measured at the battery) over about 10 hours. It should hold pretty steady for most of that time, maybe drooping to 12.4 or so. A 5 amp load for 10 hours is 50 amp hours. The battery capacity of # 27 batteries is in the range of 100 amp hours, so it would discharge about half in that time period. If the battery was fully charged to begin with, this load test will not bring the battery down to where the voltage drop is really noticeable.

Then repeat it with the second battery. Your results should be the same or very similar. If not, one or both batteries may be on their last legs.

So, a bit more testing is in order to know what is going on for sure.

[leedav]

Lead acid batteries will get a surface charge on the plates, esp if they've been sitting and not fully charged. Everything I read says you need to give them a full charge and let them rest before you can do this kind of test

[KJRitchie]

After work I'll remove shore power, wait for the batteries to stabilize then turn on some lights and check the readings from the battery monitor and voltage directly from the batteries.

Unfortunately, I don't have anything that can test the batteries load as mentioned.

I would think if the voltage is dropping on the batteries themselves in a short time I might have to replace the batteries.

I'm leaving on a trip to Utah on Friday and will be staying at two national parks without hookups so I want to insure my batteries will be OK. I do have a portable solar panel but just incase it gets cloudy I don't want any battery problems.

Kelvin

[KJRitchie]

I had the trailer on shore while at work yesterday. I decided to pull the plug and turn on the two Fantastic fans on low speed and with a few LED lights on and one overhead (LED strip replaced fluorescent). The fridge is running on propane. Before I turned on the fans and lights I noticed the voltage with just the fridge on LP would slowly drop. I would expect the voltage to stabilize with two batteries. I turned on the fans and the lights and 2 1/2 hours later checked the voltage at the battery terminals and it was 12.4 volts, which according to a 12v chart is 80%. Does this sound right? Is battery discharge linear or do they fall off from 100% and then stay at 80% for a long time?
I plugged in shore power and went to bed.

Before leaving from work today I unhooked shore power, the fridge is on LP and I have the rear Fantastic fan set to turn on once the temperature rise today and a front window open. I want to simulate leaving the trailer for 8 hours while I go hiking. The fan should run most of the day. Its supposed to reach about 72F today.

Kelvin

[idroba]

The fan on low is about 1 amp. The refrigerator probably 0.6 amps on average. So, in 8 hours you are not putting a very big load on the batteries.

My actual measured fantastic fan current is: Low .93 amp Medium 1.23 amp and High 1.55 amp.

[KJRitchie]

Using my ammeter on the negative battery cable this morning I saw closer about 2 to 2 1/2 amps with just the fridge on LP, no fan running. The TV amplifier is turned on and the radio is off and the subwoofer unplugged. LP leak detector on. Can't think of anything else that is drawing power.

Kelvin

[Al and Missy]

I believe a fully charged battery should read 12.6 volts. You were reading 12.4 with a 2A load. That is telling us that the internal resistance of the battery is .2/2 = 0.01 ohms. I'm not a battery expert, but that seems reasonable.

You can do as idroba suggests. Disconnect one battery. Charge it for 12 hours or so. Let it rest for an hour or so with no load. Turn on enough stuff to get about 5A of load. Let it run that way for 10 hours. If you can't get up to 5A, run for 24 hours at 2A. Then measure the voltage. Record that number and repeat for the other battery.

Al

[KJRitchie]

I'm at work and I just had the wife check the voltage after 4 1/2 hours running just the fridge and one fantastic fan. Voltage is now 12.46v. To me that seems too low after charging the two batteries all night and now just running the fridge on one fan.

I don't have time to test each battery individually before my trip on Friday.

Should I replace the batteries? I don't want to get stuck one morning with the batteries down so the power jack won't work.

Kelvin

[dznf0g]

Kelvin, that sounds about right. I have watched mine on the trimetric and they will drop into the 12.4 range relatively quickly (several hours with 3 - 5 amps draw), then sit there for a long time before they start going south any further.

Also, note that the voltage reading with a load is not the true level of the battery (for 50% recharge limit, etc.) Resting voltage is the bogie. If in your above example you disconnected all loads on the 12.46V battery(s), you would see it rise over a bit of time to 12.5 - 12.55ish.

[KJRitchie]

I'll have my wife check the voltage again at 4pm. If its still around 14v then I guess I'll forego buying new batteries for my trip.

I'll be driving out to North Rim Grand Canyon and stopping at RV parks. Then its 3 nights at NR without hookups. I'll have my 200w portable panel. Then its a short hop to Zion where I'll be staying 4 nights at Watchman that has electrical hookups. Then a short drive to Bryce where I'll be staying 3 nights with no hookups but with my portable solar. Going back home I'll be staying at RV parks with hookups.

Kelvin

[KJRitchie]

Had wife check voltage again at 2pm. 12.42 down from 12.46 two hours ago.

Kelvin

[KJRitchie]

4pm and 12.42 with fan and fridge running on LP.

Kelvin

[dznf0g]

Holding in there....do yu have a meter that tells amp hours used, like a trimetric? Or do you know how many amps are being drawn for the time you're keeping?

[dznf0g]

What batts? Group 24?

[AtomicNo13]

[KJRitchie]

Originally Posted by dznf0g

Holding in there....do yu have a meter that tells amp hours used, like a trimetric? Or do you know how many amps are being drawn for the time you're keeping?

My batteries are two Interstate Grp 27 dated 3/13.

When I got home after work yesterday I check the battery voltage from the battery terminals. The wife was just checking the voltage from a 12v socket plug in meter. I found the voltage steady at 12.48.

I don't have a Trimetric. I'd like to have one but after looking at the installation instructions it scared me away. Also I'm not sure where to mount it in my 25fb. I guess I could mount it on the curb side pantry wall above the sink and try to fish wires from the slide out pantry area through the bathroom, under the bedside wardrobe to under the queen bed to where all the wires from the battery come up through the floor.

Placing my handheld clamp on ammeter on the negative battery cable it looks like the fridge on LP, one Fantastic Fan, TV amp on and LP detector was drawing about 2 1/2 amps. I started the test at 7:30am and plugged in shore power again at 5pm.

I'm at the conclusion my batteries are performing well enough not to replace at this time. I have today and tomorrow to change my mind before I take off on my trip.

Kelvin

[KJRitchie]

Originally Posted by AtomicNo13

Attachment 239852

I've seen these charts and sometimes they vary on what is 80% and 70%. I've also read articles stating those internet charts are not correct.

What I may decide as a future project to modify the battery box and convert to two 6v batteries. They can be deep cycled more than the hybrid Grp 24/27/31 batteries. They are about 10lbs heavier each to the Grp 27. Wish someone made a kit for this project.

Kelvin

[dznf0g]

Kelvin,

It appears you're OK...at least for the brief test run. FWIW, I use the chart posted above...some do vary on the exact voltages and their corresponding percentages. That looks like Interstate's chart to me.

[idroba]

Originally Posted by KJRitchie

I've seen these charts and sometimes they vary on what is 80% and 70%. I've also read articles stating those internet charts are not correct.

What I may decide as a future project to modify the battery box and convert to two 6v batteries. They can be deep cycled more than the hybrid Grp 24/27/31 batteries. They are about 10lbs heavier each to the Grp 27. Wish someone made a kit for this project.

Kelvin

It is a fairly easy modification to do. See my photos on post #18 of this thread:

http://www.airforums.com/forums/f449...-124829-2.html