(Moved this from another thread to start a new subject)
I decided to do a little test to determine how much 12 volt power our coach consumes while parked, with everything turned off, except the things we always leave on. Does that make any sense? We have two 4-year old AGM8D coach batteries, and I wanted to see how they would hold up for a 24hr period. Our coach has been sitting for weeks in our driveway, plugged into 50 amp shore power. I went out yesterday, at exactly 12:00 noon, and turned off my solar panels and shore power. Batteries were at 100%. Our residential fridge is always on so the temps were completely stabilized in both compartments, and the compressor was not running. Our inverter kicked on immediately, but it initially showed zero amps out. My solar controller showed a immediate -5.8 amp draw from the coach battery bank. I have seen this number many times, and I consider it to be the baseline constant power draw for our coach. The following items were being powered:
1. Fridge
2. Microwave (clock is the only thing obviously drawing power)
3. 2 LED nite lights plugged into 110V outlets (I use these for a quick visual check that my 110V system is always being powered)
4. CO2 and propane detectors
5. LED TV (powered, but turned off, so only the power indicator is lighted)
6. DVR (powered, but turned off, so only the clock and panel lights are on)
7. Two hard-wired LED dash volt meters
8. LED engine compartment (cat and rat repeller) lights
9. Magnum inverter remote control panel (and of course the inverter itself)
10. Blue Sky solar controller remote panel (solar panels were disconnected, but control panel still monitors battery condition)
That's all I can think of that was running. This was a absolute best case scenario for battery power usage in our coach. I didn't open the fridge or freezer door. I didn't turn on any lights. For the 24 hours the coach sat as is, and at 12:00 noon today I recorded the result. I don't have all the fancy telemetry like Roger, but I can at least tell where the batteries ended up after 24 hours.
Chuck, how did you wire your solar controller to read amp draw from batteries?
(Sorry - I was off editing my original post so it made sense as a new thread)
To answer your question, I didn't wire the solar controller - AM Solar in Oregon did that installation. But I know from using the control panels that one of the things I can read on the Blue Sky panel is (coach) battery bank voltage and the sum of the amps going in and going out. I'll show some photos later.
You must have the ProRemote which is a solar controller/battery monitor, very nice.
OK, next few posts will be some data points I recorded during the 24hr period. I don't have any fancy equipment so it's pretty basic stuff.
Start of test:
Start battery bank voltage = 12.8
Coach battery bank voltage = 13.3
Coach battery bank at 100% SOC
As soon as I shut off the solar panels and the shore power, the inverter kicked on but showed zero output (fridge compressor off).
The Blue Sky panel showed -5.8 amp draw, which is my normal "baseline" 12V power load on our coach.
I have seen in the past that turning the inverter off drops that to about -2.0 amps, so our MS2812 inverter pulls about 4 amps in "standby".
Correct - Blue Sky Energy IPN-ProRemote
At 18:30 yesterday evening, 6.5 hours into the test, got these readings:
Start battery bank voltage = 12.8 (I'm also checking the isolator function as part of this test)
Coach battery bank voltage = 12.6
Coach battery bank at 87% SOC
Blue Sky panel was showing the same -5.8 amps
But as I was standing there the fridge compressor kicked on, and Blue Sky reading jumped up to -13.0 amps.
At 22:00 yesterday evening, 10.0 hours into the test, got these readings:
Start battery bank voltage = 12.8 (I'm also checking the isolator function as part of this test)
Coach battery bank voltage = 12.4
Coach battery bank at 77% SOC
Blue Sky panel was showing the "normal" -5.8 amps
At 07:00 this morning, 19.0 hours into the test, got these readings:
Start battery bank voltage = 12.8 (I'm also checking the isolator function as part of this test)
Coach battery bank voltage = 12.1
Coach battery bank at 57% SOC
Blue Sky panel was showing the "normal" -5.8 amps
I also thought to check the "Battery Amp Hours From Full" reading, and it showed -194
End Of Test
At 12:00 noon today, 24.0 hours into the test, these were my final readings:
Start battery bank voltage = 12.8 (Looks like our OEM factory installed isolator is still working fine!)
Coach battery bank voltage = 12.1
Coach battery bank at 50% SOC
Blue Sky panel was showing the -13.0 amps during this reading indicating that the fridge compressor was running.
The "Battery Amp Hours From Full" reading was -240
My next step was to turn the solar panels back on. High noon, clear blue sky, and clean panels (I swept them off this morning) equals best case scenario for solar production (parked in our driveway). As soon as they came on line, the Blue Sky panel showed a "Input" of 41.8 amps, and a "Output" (to the batteries) of 45.3 amps at a initial voltage of 12.9. Note: we have MPPT solar controllers.
The Blue Sky coach battery bank reading rose to 12.9 volts, and showed a +39.6 amps (which is the algebraic sum of amps in and amps out). The fridge compressor cut off right after I turned the solar panels on, so the inverter was in standby, and the only draw on the batteries was the "normal" baseline -5.8 amps)
So I guess my question is: What Did I Learn?
1. Our old isolator still works! :thumbsup:
2. 24 hours of the absolute lowest "normal" 12 volt power drain (for our coach) sucks 50% of our available coach battery bank power.
3. Our solar panels will put out 45+ amps of charging current under ideal conditions. (I actually saw it go over 47 amps for short periods)
4. What else? Looking for wisdom from the smart guys in this group. I'm thinking another 8D battery would be nice?
And the same test with a kill a watt on the refer plug. My digital volt meters seem to use more power than you would think. Enough to unplug them from the dash cigarette ligher holes
Chuck. with your set-up I personally don't see an advantage to another battery. It isn't dark for 24 hrs. at a time and unless your solar can top off the 2 batteries in a day, you would only be trading down time with generator time.
I'm not the smartest person on this power management, so this is just my opinion.
Think Craneman has it, if you cannot top off your 2 depleted batteries the next day by solar, adding extra batteries will just extend your non solar run time a little bit, if you are at 100% by say, 2 pm, then you could probably recharge an extra battery as well.
Good job Chuck. This is really the only way to know what is going on in your coach, measure it. I will do the same early next week and measure refrigerator use as a subset as well and report.
My experience is that our refrigerator power use is about equal to all other use in normal conditions, actually using the coach. If that is the case you may have about 12 hrs to 50% SOC before recharge is needed.
50% SOC is the maximum discharge you should go to which is equal to 12.2 volts. At this depth of discharge your life time cycle count is as low as it is going to get, the time to 100% recharge is very long (less likely to happen with everyday solar) and not getting to 100% recharge reduces capacity over time.
A third battery will help, more capacity means less depth of discharge, higher cycle count, maybe less time to 100% recharge.
I am sure there are other experiences out there as well.
Sounds right to me. Since I didn't cut the panels on until noon, this was not a good test of how well they would do recharging over a full day. 85 degrees here today, and it was getting hot in the coach after lunch, so the DW wanted the A/C turned on cuz we keep a lot of food loaded in the coach, and she doesn't want it to spoil. So I had to hook the shore power back up.
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... :facepalm:
Great write up Chuck! Thanks.
I noticed a interesting interaction between the solar charging function, and the MS2812 charger function. As I said above, after I turned the solar panels back on, they were putting around 45 amps into the batteries (at about 13.0 volts) in the BULK charge mode.
When I hooked the shore power up, the MS2812 went into "charge" mode. It sat there for a minute or so doing nothing, then the output jumped up to about 40 amps, but it went into FLOAT charge mode. I am used to seeing it put out a lot higher charging rate with low batteries, but I guess it was being "fooled" by the battery voltage reading coming from the solar charger.
With both chargers running, the Blue Sky battery monitor showed about +80 amps. (sum total of both chargers minus load)
No problem. As long as the batteries get charged, I let the solar charger, the inverter/charger, and the alternator work it out amongst themselves.
Great real world test, good information.
I hope to be in that boat soon, over 1/2 coach buck in mounting hardware for 4 panels came yesterday from AM Solar.
I think I noticed the same thing. The solar seems to get the charger to go to float charge. Although the std me-cr controller switches to float at 85%? I think the me-arc controller allows that fixed percentage to be adjusted. Have to do more research. I think the original heart freedom 2500 was 90z SOC before going to float. Or how smart is the sw? The power pro and the sw seem to say that the sw will adjust itself to match the batteries.
Or it's possible that the full engine batteries that are auto combined when any charge is present are getting the charger to cut back as the red top fully charged voltage combined with lower SOC house side AND some solar might be cloudy things.
The auto combiner is probably best for storage with full engine batteries and any SOC house. Over time the solar will bring up the house side.
May try manual disconnect of the engine side and monitor their SOC from the dash plug in gauge.
I may be wrong but my gut sense if we are splitting hairs is that once the engine and house batteries reach fully charged that the solars 13.6 continuous input basically turns off the alternators output. The VPMS seems to show a jump in mpg.
Or i'm Crazy. Which is possible.
Been thinking about an off/on for the solar to separate out the house side to see if the charge rates change. My old cheap discontinued controller does not seem to have a off switch on its small panel that I can see
Versus surf the web more or watch the tube this is somewhat more mental exercise. If you are into it
I think we can say no matter how big your battery bank, if your solar amp-hr input is less than you battery amp-hr output, you will never see 100% SOC. I have 4 8d's and lost about another 10% everyday even with solar. By the 4th day dry camping down to 60%, had to run generator a long time to refill them to 100% If you use 250 amp-hrs from your batteries, you have to return 250 amp-hrs, one way or another, to return to 100%
Excellent, easiest way to get close to the recommended procedure from Lifeline. See page 22, 5.7, Capacity Testing. Well done. I will follow this post, as my batteries are 5 years old, and it will be nice to know their capacity. For me the draw could be increased by adding various sized 120V light bulbs to get to the Lifeline recommended 25 amps draw for the test. Thank you for the post.
By adding the third 8D you will increase your total AH available, thus your % of discharge daily will be less. With this less deep discharge your batteries will last longer. You can research Lifelines online pdf information attached regarding this on page 18, discharging regarding this. I remember before reading Lifeline literature that ideally only discharging (almost impossible) to 20% would give you the longest life.
Your 960 watt solar is almost double my 560 watts (two 280 watt panels), very nice. My previous rvs only had 150 watt (three 50 watt panels) with 2 8Ds, my goal was to keep batteries topped off and extend battery life by keeping batteries fully charged with less augmentation by generator. That 150 watt system was perfect for my needs for over 10 years. My current newly installed system has the same goal. Now though, I have a mppt controler, 3 8Ds instead of 2, and almost 4 times the amount of solar.
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.
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.
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).
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!
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.
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 (https://marinehowto.com/programming-a-battery-monitor/)
Randy
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...
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...
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
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
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.
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.
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 (http://www.skoolie.net/forums/f51/vissani-9-9-cu-ft-fridge-13339.html)
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.
(https://s14.postimg.org/dvrqgy1vh/86_EDD711-0_C46-446_B-8_C1_A-6343_B879_A1_E1.jpg) (https://postimg.org/image/dvrqgy1vh/)
(https://s14.postimg.org/dj0carrbh/EE57_F110-0080-40_E8-9056-_A36590_A23_A04.jpg) (https://postimg.org/image/dj0carrbh/)
On our Samsung, The maximum 120v load is 6 amps during a warm start with the ice make on and eco settings off.
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
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.
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.
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 (https://www.pplmotorhomes.com/parts/rv-appliances/rv-refrigerators-freezers/rv-refrigerators-and-freezers/portable-fridge-frzr-cfx-95_CFX-95DZW)
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.truckcamperadventure.com/2016/02/the-danfoss-compessor-refrigerator-pros-cons-and-a-few-tips/)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
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.
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
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