Electrical usage

[Al and Missy]

Originally Posted by Kellycanoe

Correction: I got a battery reading of 12.0 when the batteries had rested overnight but not yet been recharged. So that would be 25% charge remaining if it were a single battery. Is the actual drainage each battery experienced more than that since I'm reading the number for two batteries? And, I'm using the display provided in the AS. I gather from other posts this might not be accurate. Do you advise against relying on it? Thanks!

If you have two 12V batteries in parallel (+ to +, - to -) then the two batteries have the same voltage and are at the same level of discharge, at least according to the table. In an ideal world (I don't know where that might be) you would have double the capacity of one battery, but still be at a percentage of charge as depicted in the table. When two batteries are in parallel, a poor battery will drag down a good one, so you may not get twice the capacity of one battery. It is best to replace both batteries when replacement is needed.

If you have two 6V batteries in series they must deliver the same current so one may discharge faster than the other. In that case it is better to monitor the voltage of the two batteries separately and divide the numbers in the table by 2. The table is specific to the battery technology, i.e. lead-acid will have different characteristics from Lithium chemistry.

Al

[idroba]

Originally Posted by KYAirstream

If damage to batteries begins occurring once 50% discharged, is there any sort of device that will automatically disconnect the batteries at that point?

Flooded cell lead acid batteries have a lot of seemingly mysterious properties. First and foremost is that they are not linear in many of their characteristics.

As an example, if you discharge them slowly, they will have more capacity than if you discharge them fast. So the same battery discharged at say 3 amps per hour will give you much more energy prior to total capacity loss than it would if discharged at 30 amps per hour.

Similarly, a battery which is only used down to 80% of it’s capacity and then recharged will have many more cycles possible than the same battery used down to 20% of it’s capacity and then promptly recharged. A battery never fully recharged will have a far lower cycle life than one which is brought back to 100% of capacity. So, a discharge to 20% and recharge only to 60% over and over will shorten the life of the battery significantly.

The question of “damage” is hard to pin down as we are really talking about cycle life. Do you want a battery to last a long time? Don’t work it hard and recharge it promptly. If you are not as concerned about long life, you can discharge it deeper, and not recharge it as thoroughly or as soon. The “damage” is what you will accept. It is common to say that a battery should not be discharged below 40 to 50% of capacity but what is really meant is that the battery cycle life will be shortened a fair amount if it is done often. Is this “damage”? Only you can say.

A couple of things will shorten cycle life very severely, and should be avoided or never allowed to happen at all. These things would probably fall under the category of damage, if not abuse.

1. Total discharge of a battery to 0% and no recharge for days, weeks or months. You will most likely never recover a battery which has sat discharged for any length of time. So, if you for some reason run your batteries down to nothing get them charged up ASAP or you will probably be purchasing new ones. Even doing this a few times will greatly reduce the total cycle life of a flooded cell battery.

2. Letting a battery sit for weeks or months partly charged. Chemically this allows the plates to become unable to accept a full charge and total battery capacity is then reduced. They may seem to “work” but not to their original capacity. They charge up fast, but discharge equally fast as their capacity has been changed.

3. Letting the tops of the plates show before you add water. It is battery murder. The tops dry out, expand, and even when covered again with distilled water will have become essentially useless. They may even short plate to plate which is instant cell death.

On the question of a device to limit depth of discharge to any specific amount, then automatic shutdown, yes, such things exist but can be annoying or even dangerous in an emergency situation. And if you have a slow battery drain which causes discharge to say 50% and then the device shuts off the power, your battery sits half charged until someone does something about it, and by that time the battery has been “abused” and may not recover anyway. Sitting half charged for long time periods is not good for batteries. See 2 above.

So, considering the cost of batteries, and the desire to use them as fully as possible with out abusing them, in general don’t use them below 40 to 50% of capacity and then promptly recharge them. You can use them harder, just expect a shorter life from them. You can use them easier, and they will generally last considerably longer.

I recommend a well set up battery monitor such as a Tri Metric (and others) to allow you to see just how far down you are drawing your batteries, and when they are fully charged. Only with a device like that will you actually be able to see what is happening to your batteries. Most everything else is guessing.

In my own case, I use a pair of 6 volt golf cart type batteries in series for a capacity of about 220 amp hours at a 5 amp discharge rate. I have a 200 watt solar system which, when out camping, replaces some or all charge into them daily. I tend to find spots in the shade, so my solar does not bring my batteries back fully quite often, but they are totally recharged when I return home with my PD 4645 converter/charger. Even in late fall weather with furnace use and more lighting and inside occupation, I have never seen my Tri Metric meter show them at less than 40%. In the summer, like now, they seldom go below 80%. My last battery set lasted over 10 years in the Argosy. I am only on my second year in the Airstream’s set as it is new.

So, ask a simple question, get a load of too much information. But there are few simple battery question answers in truth. They all are filled with if’s and’s and but’s.

I hope this helps some.

[KYAirstream]

Thanks for the well written explanation, idroba. I appreciate you explaining the many factors that affect battery life. Let me run this scenario by you... There are times when I leave my trailer in one place and may return days or a week later. In such cases I'll leave the fridge stocked and the shore power on to my 12v/120v fridge. While this doesn't happen often, there have been times when the power has cut due to a storm and I imagine my batteries may have been depleted. Any solution to such a case so I can have my cake and eat it too.

Maybe switching to a propane fridge would be the answer.

[idroba]

When the power comes back on your converter/charger will recharge the batteries and I really don't think you would have any serious problem with reducing cycle life. It is not the ideal situation but as long as the recharge is reasonably soon (like most power outages, the power does not stay off that long) I would not worry about it.

I hope you have already replaced the old Univolt converter/charger with a more modern 3 stage one such as a Progressive Dynamics 6245 or 6255. If you have not done that yet, I would put it on the budget to do list.

[KYAirstream]

Thanks. I am using a PD converter--I'll have to check, but I believe the one I have is the 9200 series.

[idroba]

Originally Posted by KYAirstream

Thanks. I am using a PD converter--I'll have to check, but I believe the one I have is the 9200 series.

My error, I meant the 9200 series but somehow it came out 6200.

[cwbiii]

If you have an airstream with an inverter/charger in it instead of a converter then the multistage charger is usually normal for an inverter/charger. Inverter/charger is an option in most airstreams and many of the lot models will have them.

Chuck

[KYAirstream]

Does the Trimetric also show the status of the batteries while plugged in? For example, I have an analog meter that reads 12+ volts for my batteries when I'm plugged in. However, my batteries where shot and as soon as I would get off shore power the meter would drop to nothing. Would the Trimetric give an accurate read regardless of shore power status?

[dznf0g]

Originally Posted by KYAirstream

Does the Trimetric also show the status of the batteries while plugged in? For example, I have an analog meter that reads 12+ volts for my batteries when I'm plugged in. However, my batteries where shot and as soon as I would get off shore power the meter would drop to nothing. Would the Trimetric give an accurate read regardless of shore power status?

No, as long as batteries are connected and charging, the system voltage is whatever the converter is putting out. No meter can read the battery state unless it is not being charged.

[idroba]

The Tri Metric and other use meters which are similar work like this:

When you set them up, you put the Amp hour capacity of your batteries into the set up process. In my case with two 6 volt golf cart batteries in series I used 220 amp hours as my original battery capacity. The batteries are fully charged, and then you are set to go.

As you use battery power, the meter counts down in either % of original capacity or Amp hours (your choice, I use %). So, if you are not plugged in, or your system is not charging it counts down the amount of power you have used. So, say you have the 220 amp hours of capacity I have. With it set in % display, it will slowly decrease the reading on the meter, 99%, 98%, 97 ... 55, 54, 53%. So that tells you the % of power remaining in your batteries. If you have solar, as I do, it adds the amount of charge input, so if you are using less than your solar is putting out, the meter will show an increase in % capacity. If you tow, and a charge is put into your batteries, that will also show as a % increase. If you stop and plug in, the converter/charger will put power into the system, and it will go (over the time needed to charge) to 100%. If you remain plugged into line power, the meter will stay at 100% as the converter/charger is supplying all the power, not the batteries.

Once it gets to 100%, it will reset itself (saying the batteries are fully charged, determined by their reaching float voltage) and only decrease if you start taking power from the batteries.

As an example, I am out camping right now (wildfires have driven me from my home) and have been in a Forest Service campground for 8 days. My Tri Metric shows that my batteries are at 87% of capacity. This is because I have solar recharge. It is a poor slow recharge, because of all the smoke, but still I have used only 13% of my battery capacity which has not been recharged by the solar panels. This morning it was 82% of capacity, so I have recharged 5% today, so far. No sun, only smoke, or it would be up to 100% I am sure. BTW, the meter adds a "fudge factor" for partial recharge, of about 10 to 15% as you must put more power into a battery to recharge it than you can take out. That is compensated for.

Now, if your batteries are shot, the original capacity number you put in when you program it is no longer accurate, and the Tri Metric cannot determine that. So, it would assume all is well and NOT produce an accurate number. So, once your batteries lose capacity due to end of life aging, the meter will no longer be accurate. However it does have a voltage function on it, and an amp readout, so if you find the voltage is rapidly decreasing with a moderate current drain, you could safely assume your batteries have reached the end of their life and replace them. I like to start with a fresh set of batteries when setting up a Tri Metric, but if your batteries are in reasonably good condition, it is not necessary to replace them.

You can think of the Tri Metric as similar to your checking account. You put money into it, you take money out of it, the meter watches the in and out and tells you the % of what you have at any specific time point. The difference between the meter and your checking account is that you program a ceiling into the meter, with a checking account there is no ceiling so no % of money can be determined.

But the meter also is great to tell you when your batteries are fully charged after driving, or when they are only partly charged when you come back home and thus need to be recharged so they don't sit discharged which will cause damage over time.

You can watch the meter and see if you are running less than 50% charge and how often it happens, which will give you a clue as to your degree of battery "abuse". You can look at the meter on a cold evening and see if you may have a problem getting through the night if you run your furnace (with some experience that is). If it says you only are running 30% capacity, and you know it is going to be 35 F and the furnace will run a lot, you may wake up to a cold trailer.

Battery use meters such as the Tri Metric are one of the only ways to really know what is going on in your 12 volt electrical/battery/solar/tow vehicle charge system. I recommend them highly.

[dznf0g]

idroba has it right. The short version is: by voltage you cannot tell the state of charge of the batteries while charging, by whatever source....but by the programmed amp rating plugged into the TriMetric, one can tell the state of charge by %, as idroba says, or by the amp/hour reading of rate of charge, or by watts.

After you have a good monitoring system for awhile, you learn what is a normal charge progression and can note a suspect battery(ies) by a deviation from a normal charge sequence.

Of course, then pulling a batt and performing proper diagnostics is in order.

[KYAirstream]

Thank you both for the replies. The Trimetric is something I'm definitely adding to my list. It really does sound like a great way to monitor with a good deal of precision. Solar someday too, but that will have to wait for now. With your setups you guys can really be self sufficient and camp just about anywhere you want. I guess the only limiting factor may be water...

[KYAirstream]

The overhead compartment above the kitchen that houses the control panel in my 1979 seems like a logical place to put the meter. When installing the Trimetric and the shunt, would there be any issue with using the positive and negative leads that feed into the control panel, or do I need to go directly to the batteries?

[KYAirstream]

After looking at some pics online, it appears the shunt is typically installed close to the battery with a pretty heavy gauge wire. Looks like I have to figure out a way to fish the wires if I want to put the meter in the overhead compartment above the kitchen counter.

[rmkrum]

The wire from the shunt to the meter is much smaller and fairly easy to fish.


Sent from my pocket Internet using Airstream Forums

[KYAirstream]

Difficult to fish from one side of the ceiling to the other? I'm assuming ribs are in the way.

Another thought I have is running alongside the bottom of the opposite wall and tapping into the wires for the blank tank sensors, which are unused and lead back to the control panel.

[idroba]

Look at the bottom photo in post #18 of this thread:

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


If you look at the very most bottom part of the bottom photo you will see the shunt for my Tri Metric meter. It must be in the negative line and at the batteries. All the power from the negative side of the batteries must go through the shunt.

The wire to the Tri Metric meter itself is a very small three wire set starting at the shunt and running to the meter itself.

[KYAirstream]

Thanks for the pic. That's a nice looking battery box as well. I like how it's outside on the tongue.