24hr Battery Drawdown Test

Topic: 24hr Battery Drawdown Test (Read 1533 times) previous topic - next topic

Re: 24hr Battery Drawdown Test

Reply #25 – March 10, 2018, 07:19:29 pm

The only part of the equation you can do anything about day to day is consumption. If your average daily solar input exceeds your average daily use and you start at 100% you should stay balanced. If not then residual capacity goes down over time. Most people significantly under estimate actual use. Without measurements in a real world situation preferably over many days you just won't know.

Your capacity to recharge (in any way available) has to be equal to or greater than your consumption.

For our use we are not trying to be indefinately off-grid, just extend the time between the need to run the generator. Four or five days are easy now.

Re: 24hr Battery Drawdown Test

Reply #26 – March 10, 2018, 07:48:35 pm

Quote from: Chuck & Jeannie – March 10, 2018, 05:47:01 pm

Roger pointed out (in a PM) that my 07:00 battery bank voltage reading (12.1) looked like a outlier. I may have wrote down the number incorrectly - not sure. No way to go back and check...

I'm not sure the 12.1 volts was an outlier, as there was a load on the coach batteries. If you turned off the fridge and the salesman switch, the batteries would "theoretically" be at rest, and perhaps show a bit higher voltage. I could be wrong, but using voltage to indicate battery charge level, there should be no draw, and batteries should be at rest.

Re: 24hr Battery Drawdown Test

Reply #27 – March 10, 2018, 07:53:48 pm

In real world boon docking, with solar turned on, and a one hour gen run before quiet hours, and a one hour gen run in the AM, the current batteries might meet your needs (even with more amp draw from living in the coach).

Re: 24hr Battery Drawdown Test

Reply #28 – March 10, 2018, 10:04:29 pm

Quote from: AC7880 – March 10, 2018, 07:48:35 pm

I'm not sure the 12.1 volts was an outlier, as there was a load on the coach batteries...I could be wrong, but using voltage to indicate battery charge level, there should be no draw, and batteries should be at rest.

No, you are right - voltage is a very poor indicator of actual condition, especially when there is any draw. But it's all I had to work with. I know this was a crude experiment, but I was hoping it would give me a little better idea on how to best manage my 12V system. The more you play with this stuff, the better you understand how it all interacts. Plus, it's fun!

Re: 24hr Battery Drawdown Test

Reply #29 – March 10, 2018, 10:35:54 pm

Quote from: AC7880 – March 10, 2018, 07:53:48 pm

In real world boon docking, with solar turned on, and a one hour gen run before quiet hours, and a one hour gen run in the AM, the current batteries might meet your needs (even with more amp draw from living in the coach).

And, in fact, this is pretty much what I found out at Q this year. It actually took a couple of hours of generator time in the evening plus at least an hour in the morning, to keep our batteries above 50% over 5 days of "average" use (without air conditioning). If adding a third battery would not totally eliminate running our generator, then I'll just stick with what we've got. Truth is, since we prefer to camp in warmer temperatures, we will usually end up running the generator anyway so we can use the roof A/C...or else we park where we can plug in.

Re: 24hr Battery Drawdown Test

Reply #30 – March 11, 2018, 08:06:50 am

Thanks to all for the thread and comments. As we get ready to pull out in May for 7 months I've been trying to learn the use/refill balance of our rig. This electrical stuff is all new to me so posts like this really help.

We use our Victron battery monitor as our primary source of info since our Outback solar charge controller is in the basement and does not have an external monitor or Bluetooth/WiFi reporting function. In researching how to use the battery monitor I ran across this article which I'm reading/re-reading to try and decipher what it has to offer.

Making Your Battery Monitor More Accurate – Marine How To

Randy

Re: 24hr Battery Drawdown Test

Reply #31 – March 11, 2018, 09:50:22 am

Quote from: floridarandy – March 11, 2018, 08:06:50 am

In researching how to use the battery monitor I ran across this article which I'm reading/re-reading to try and decipher what it has to offer.

That looks like a good article, but like you I will need several "reads" to figure out how to use the info. Playing with our electrical system makes me understand just how much I don't know about how batteries and charging systems work. But I'm trying to learn...

Re: 24hr Battery Drawdown Test

Reply #32 – March 11, 2018, 10:50:17 am

Randy, I commented to Chuck about minimum discharge voltages and the normal difference between rated capacity and real life capacity. Especially at lower temperatures. This is a good article and gives us a better understanding of battery systems. The more we know helps us make better decisions about how we use and modify what we have.

Roger

More good info...

Re: 24hr Battery Drawdown Test

Reply #33 – March 11, 2018, 11:15:14 am

Randy good info.

By random luck, maybe, in his tested marine battery bank list the closest by far in measured versus actual capacity was the Deka 8g8d's that Foretravel installed new as far as I know in every unicoach.

My guru buddy uses them exclusively. As far a AGM's go he thought the Lifelines were the best available

Re: 24hr Battery Drawdown Test

Reply #34 – March 12, 2018, 02:49:22 pm

My last two rvs had Lifeline AGM 8ds, now I have Deka-Penn AGM 8ds. I found these specifications from a Deka-Penn for Gel and AGM battery pdf

AGM 100% charge at least 12.8 not 12.6 and also why batteries last longer with discharge of only 10%, which is often possible with a combination of shore power and a solar system. I found these 3 paragraphs especially important for my 3 AGM 8Ds from Deka-Penn and a primary reason why I have solar. 12.6 is 25% discharge, 12.3 is 50%.

"Does depth of discharge affect cycle life? Yes! The harder any battery has to work, the sooner it will fail. * You may experience longer or shorter life based upon application, charging regimen, temperature, rest periods, type of equipment, age of battery, etc.
As you can see, the shallower the average discharge, the longer the life. This is why it's important to size a battery system to deliver at least twice the average power required, to assure shallow discharges."
Typical* VRLA Battery Cycling Ability vs. Depth of Discharge
Typical Life Cycles
Capacity Withdrawn Gel AGM
100% 450 150
80% 600 200
50% 1000 370
25% 2100 925
10% 5700 3100

Open Circuit Voltage vs. State of Charge Comparison*
% Open Circuit Voltage Charge Flooded Gel AGM
100 12.60 or higher 12.85 or higher 12.80 or higher
75 12.40 12.65 12.60
50 12.20 12.35 12.30
25 12.00 12.00 12.00
0 11.80 11.80 11.80
NOTE: Divide values in half for 6-volt batteries. * The "true" O.C.V. of a battery can only be determined after the battery has been removed from the load (charge or discharge) for 24 hours.

"The shallower the average discharge, the longer the life. It's important to size a battery system to deliver at least twice the energy required, to assure shallow discharges. Follow these tips for the longest life:
1) Avoid ultra-deep discharges. The definition of ultra-deep discharge may vary with application and battery type.
2) Don't leave a battery at a low stage of charge for an extended length of time. Charge a discharged battery as soon as possible.
3) Don't cycle a battery at a low state of charge without regularly recharging fully.
4) Use the highest initial charging current available (up to 30% of the 20-hour capacity per hour) while staying within the proper temperature-compensated voltage range."

In the Deka-Penn literature I once saw to set absorption charge at 14.6 for one or two hrs. There is diffenent info now in Renewable Energy charge pdf

Re: 24hr Battery Drawdown Test

Reply #35 – March 12, 2018, 03:22:30 pm

Being as lifeline is used in airplanes the extended low temp of the AGM design would seem to be superior to a gel.

Foretravel equipped our unicoaches with a high quality high current flow spiral wound for vibration absorbation AGM batteries that work well in low temps. And are mounted where air flow can cool them?

Same time the house side used east penn gels for the much longer cycle life and to not need equalizing and to match the then available inverters/chargers best. House batteries in a unicoach are in a compartment and may be in a more temp controlled area?

Both mk and lifeline state that a temp controller charger is required for best results.

You get what you pay for I guess. Especially in batteries.

Re: 24hr Battery Drawdown Test

Reply #36 – March 12, 2018, 07:05:26 pm

Being the smrtest persen in dis group, he he, I can say that the problem is that any SOC (State of Charge) measurement made by a simple voltage measurement must be made while the battery is under no load for at least one hour. This applies both to lead and lithium batteries.

The best system would be to have two battery banks. One is "on-line" while the other bank is under no load and being tested for SOC, then charged and readied to become the next "on-line" bank. A computer could manage the switching, but such a computer or techniques do not exist yet.

Question: Don't residential fridges use 800 to 1200 watts, which would be up to 100 amps from a 12 Volt battery? This is not what the original post reported.

Re: 24hr Battery Drawdown Test

Reply #37 – March 12, 2018, 07:13:15 pm

Quote from: Tim – March 12, 2018, 07:05:26 pm

Being the smrtest persen in dis group, he he, I can say that the problem is that any SOC (State of Charge) measurement made by a simple voltage measurement must be made while the battery is under no load for at least one hour. This applies both to lead and lithium batteries.

The best system would be to have two battery banks. One is "on-line" while the other bank is under no load and being tested for SOC, then charged and readied to become the next "on-line" bank. A computer could manage the switching, but such a computer or techniques do not exist yet.

Question: Don't residential fridges use 800 to 1200 watts, which would be up to 100 amps from a 12 Volt battery? This is not what the original post reported.

http://michaelbluejay.com/electricity/howmuch.html
My propane/electric fridge has two 400 watt electric heating elements.

Re: 24hr Battery Drawdown Test

Reply #38 – March 12, 2018, 09:31:57 pm

I have been planning on switching to a small residential refer (about 10 cft). I found a thread on a school bus conversion site with a photo of the spec sticker on a Vissani 9.9 cuft. It shows current draw only 1.4 Amps at 115 VAC, power input 120 Watts. (No, the math doesn't work.) The thread is at: Vissani 9.9

Re: 24hr Battery Drawdown Test

Reply #39 – March 12, 2018, 09:35:05 pm

Quote from: Tim – March 12, 2018, 07:05:26 pm

Being the smrtest persen in dis group...

Question: Don't residential fridges use 800 to 1200 watts, which would be up to 100 amps from a 12 Volt battery? This is not what the original post reported.

Every residential refrgerator uses 800 to 1200 watts, eventually Most will use tens of thousands of watts if not hundreds of thousands of watts. Millions of amps. But not all at once. 👍

My full sized Samsung idles at less that 30 watts and runs at about 135. During 24 hours it uses about 1500 watts or 62 watts on average. Plus 6 or 7 watts for the inverter gets me to about 70 watts and at 12.5 volts that is an average draw of less than 6 amps including the inverter.

Here is what my refrigerator power monitor is reporting over tha last couple hours. Running right now, under 30 at idle.

On our Samsung, The maximum 120v load is 6 amps during a warm start with the ice make on and eco settings off.

Re: 24hr Battery Drawdown Test

Reply #40 – March 12, 2018, 09:48:33 pm

The Vissani refrigerator has R600a (butane) which is about 20% more efficient than R134a plus lower operating pressure.
R600a is pretty common in Asia on small refrigerators.
Steve

Re: 24hr Battery Drawdown Test

Reply #41 – March 12, 2018, 10:15:31 pm

Look at the annual estimated power use sticker. It is a pretty good real world estimate. Divide by 365 then 24 to get hourly estimate. Mine was somewhere arround 480 KWHrs/yr as I recall. About 55 watts per hour on average over a year. About 1.4KW per day. About right.

Re: 24hr Battery Drawdown Test

Reply #42 – March 12, 2018, 11:40:26 pm

Hello Tim, I am so glad you are on this forum to keep us in line and bring up the possible. "Question: Don't residential fridges use 800 to 1200 watts, which would be up to 100 amps from a 12 Volt battery? This is not what the original post reported." I believe you are technically correct, except that the defrost cycle is seldom on. On the average I believe my customers told me their residential refrigerators draw no more than their rv refrigerators as the defrost cycle seldom ran, the compressor seldom ran, all of this because the residential refer was insulated multiple times what a rv refrigerator was.

Re: 24hr Battery Drawdown Test

Reply #43 – March 13, 2018, 12:27:07 am

Most new frostless refrigerators has a sensor that determines when it needs a defrost, it can go days before it needs one depending on use.
Also I'm going on the limb in that ammonia absorption refrigerator will be phase out in all new RV's within 10years. The European's such has Danfoss have been developing variable speed DC compressors for sometime. The trend is heading for a micro DC compressor in the 24 to 42 volt or 100 to 500 watts depending size of the refrigerator. One company is developing a household refrigerator that only needs couple solar panels and a battery to run year around for countries that don't have a reliable or no power grid.
Steve

Re: 24hr Battery Drawdown Test

Reply #44 – March 13, 2018, 10:03:14 am

Quote from: Willy White – March 13, 2018, 12:27:07 am

Most new frostless refrigerators has a sensor that determines when it needs a defrost, it can go days before it needs one depending on use.
Also I'm going on the limb in that ammonia absorption refrigerator will be phase out in all new RV's within 10years. The European's such has Danfoss have been developing variable speed DC compressors for sometime. The trend is heading for a micro DC compressor in the 24 to 42 volt or 100 to 500 watts depending size of the refrigerator. One company is developing a household refrigerator that only needs couple solar panels and a battery to run year around for countries that don't have a reliable or no power grid.
Steve

Danfoss compressors have been around a long time, especially in marine use. Many high end motorhomes in the early 2000's came with 12 volt bay refrigerator/freezers as an option. You can buy them now but the are not cheap. Portable Refrigerator/Freezer | CFX-95DZW | PPL Motor Homes
Lower end rv's that have no solar or generator and a small battery will always require propane for heat and cooking, and in this case a propane refrigerator will probably be the best route.
Pros and Cons of the DC Compressor Refrigerator – Truck Camper Adventure http://www.backwoodssolar.com/novakool-dc-refrigerator-model-4500
But on that note, as soon as they start making them in th 14+ cubic foot size, they will probably become standard on high end motorhomes

Re: 24hr Battery Drawdown Test

Reply #45 – March 13, 2018, 02:01:01 pm

Three years ago I replaced my original refrigerator (lost to fire) with a custom "marine" refrigerator that uses two Danfoss 12 volt compressors, one each for the refrigerator and the freezer. Each compressor draws 4A when running.

Re: 24hr Battery Drawdown Test

Reply #46 – March 13, 2018, 05:17:25 pm

The frost free part with timer, heated gaskets and defrost can be disabled or put on a switch for dry camping. The fridge schematic will show which wires are used.

Pierce

Re: 24hr Battery Drawdown Test

Reply #47 – March 13, 2018, 05:52:09 pm

Yes Danfoss 12 volt compressor been around a long time, I've repair many of them. Most of the time I just replace the boat refrigerator from Home Depot and install an inverter, much cheaper and work better. (I had a small side by side in my boat).
Anyway the new so call high voltage DC compressor I was referring too will operate with a newly developed high pressure (earth friendly) refrigerant for an efficiency much greater than today. Also within 10 years or so Battery technology and solar panels will have greater efficiently and at a lower cost, so I standby comment that absorption systems well fade away like the Fax machine, well at least IMHO

Steve

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