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Topic: 24hr Battery Drawdown Test (Read 1717 times) previous topic - next topic

Re: 24hr Battery Drawdown Test

Reply #20 –
Great real world test, good information.

Re: 24hr Battery Drawdown Test

Reply #21 –
Quote from: Chuck & Jeannie –

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.
I hope to be in that boat soon, over 1/2 coach buck in mounting hardware for 4 panels came yesterday from AM Solar.

Re: 24hr Battery Drawdown Test

Reply #22 –
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

Re: 24hr Battery Drawdown Test

Reply #23 –
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%

Re: 24hr Battery Drawdown Test

Reply #24 –
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.

Re: 24hr Battery Drawdown Test

Reply #25 –
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 –
Quote from: Chuck & Jeannie –
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:


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 –
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 –
Quote from: AC7880 –

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 –
Quote from: AC7880 –
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 –
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 –
Quote from: floridarandy –
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 –
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 –
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 –
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 –
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 –
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 –
Quote from: Tim –
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 –
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 –
Quote from: Tim –
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.