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Old 04-04-2015, 06:17 PM   #15
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@ rmkrum
You may have expected too much from your panel. What's the panel capacity in watts?

What is the battery capacity in amp-hours. To me, it sounds like you tried to pull too much off the battery and the panel did not have enough capacity to put it all back.

I'm not sure where to find the battery capacity in amp-hours? The top of the battery has the following designations: SRM-24 550 CCA 690 MCA. I also don't see any information on the Solar Charge Controller referencing wattage; only amperage. Is there another place to look on either the solar panel, or the batteries for the information you requested?
Those sound like standard Interstate wet cell group 24s, which are 80 amp/hours each.
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Old 04-04-2015, 06:52 PM   #16
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@rmkrum
What's the panel capacity in watts?
Digging through the sales material, I found a reference to the solar panel capacity: it's 95 watts.
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Old 04-04-2015, 07:01 PM   #17
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@ lewster
Those sound like standard Interstate wet cell group 24s, which are 80 amp/hours each.
Thanks for that information. Unfortunately, my ignorance is about to be exposed: do you think we overtaxed the batteries' capacity, pulling too much power using the inverter, perhaps?
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Old 04-04-2015, 07:25 PM   #18
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This is my first post on the Airstream Forum, so forgive me if I inadvertently breach Forum etiquette in this very long reply/question. We live in Los Angeles, and store our 19' Flying Cloud in an open facility in Marina Del Rey. My niece and her family keep their 16' Bambi in another open storage facility near Pasadena. We both just spent a week dry camping in Death Valley. Prior to leaving for DV our coach had been idle for six plus months; however, the solar panel had kept the batteries charged. (The batteries are flooded Interstate Deep Cycle, installed Jan, 2013.) The drive to DV took 5-6 hours, and the batteries were fully charged upon arrival. There was no shortage of sunshine throughout our stay. The first full day there, we ran both fans all day while we were out hiking, thinking the solar panel (12 volts - 10 amps, producing 12.8-13.0 volts consistently) would replenish the batteries. That evening there was enough charge in the batteries to run the lights into the evening , and the fans all night. We didn't use the fans the next day, but did use the 1,000 watt inverter to boil water/blend smoothies, had the lights on that evening, and ran the fans all night. By the third night, we could only run one fan, and some lights because the solar panel had not completely recharged the batteries (the monitor never showed the batteries as 'charged'). The fourth, fifth and sixth nights were progressively worse - we used camp lights, no fans, and the batteries still discharged so much with minimum water pump usage that by morning, no charge was left. Have we found a new way to ruin RV batteries, or did we expect too much from our solar panel?

Ps - We've been back a couple of days now. I washed the solar panel and its output is 13.8-14.0 volts. The output monitor keeps alternating between 'charging' (yellow light), and 'charged' (green light). The batteries appear to be retaining their charge.
It is hard to estimate your actual use from afar and your description, but, although the fans don't take a lot of power on low, on high they use much more and you have two of them. On high they take about 1.5 amps each or 3 amps total. Running them for 24 hours would take 75 amp hours which is the total capacity of one battery.

Your refrigerator electronics and fan take more power. Along with the pump and the water heater electronics, I would estimate another 1 amp per hour or 24 amp hours in a day's time.

The inverter should be shut off when not being actually used, as it takes 1.7 to 1.9 amps per hour not doing anything. If you left it on, it can take 40 to 45 amp hours a day.

Then you said you were using the inverter to "boil water". That can really really take your batteries down. Use propane and the stove to boil water, not your batteries. Run the blender to make smoothies, that is a short use and not too bad, but not to heat water.

If you have a factory solar system, it probably does not put out much more than 50 to 100 watts (4 to 8 amps) maximum for a few hours a day, but you are using power 24 hours a day.

Sounds like you have simply overloaded your system. learn to conserve power. You have a pretty limited amount to begin with.

Be sure to totally recharge your batteries before you put your rig(s) away too, otherwise you will ruin your new batteries.
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Old 04-04-2015, 07:48 PM   #19
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@idroba, rmkrum, and lewster
Thank you for all of your input regarding my battery question, especially for the original post and the detailed reply by idropa. This is such a valuable forum for those, like myself, who are not as mechanically savy as so many of you appear to be. I appreciate your taking your time to walk me through this issue.
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Old 04-04-2015, 08:05 PM   #20
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General comments: Using your batteries to heat water can really suck your batteries down. If you use a 1000 watt microwave running off an inverter, you are discharging your 12 volt batteries at the rate of 1.4 AH (ampere-hours) per minute, or 84 AH per hour. I believe the fans draw about 3 amps each when running, so the two of them add another 72 AH discharge, per 12 hours (if they are running constantly and not cycling on and off via thermostats) (142 AH per 24hours). I believe the batteries you referenced have a capacity of approximately 84 AH each (when new) (total 168 AH) and I think the guidelines are to not let your batteries go below 40% of capacity (if so that means you only have 100 AH per day available for use, excluding solar generation).

You state the solar was putting out 10 amps at 12 volts. That may be the max, with less in the morning and tapering off in the evening, going to nothing at night. Lets say that effectively you produce 10 amps for 10 hours per day, or 100 AH per day from your solar (more in summer, less in winter).

If you have incandescent lights, they draw about 5 times the power of LED lights, so depending on how much lighting you are using they can suck the batteries down too. To heat a quart of water from 60 degrees up to boiling (without boiling) takes 7.4 AH (continuing to heat it with 1000 watt inverter would be adding another1.4 AH per minute).

All that said and done, Iím a believer in using the propane stove to heat water, and run the fans and lighting judiciously. A heavy overcast day can mess up your anticipated solar generation. Donít let the batteries get too far discharged. Make sure they have the plates in the batteries complete covered (by adding distilled water if necessary). You can play around with the numbers, but still see that without additional power being supplied you still have to be conscious of your rate of consumption.

Sorry for being so verboseÖ
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Old 04-05-2015, 02:20 AM   #21
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Thanks WindyJim for another really helpful post. Don't mind you're being verbose at all.
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Old 04-05-2015, 08:05 AM   #22
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Mind if I chime in??

Quote:
Originally Posted by WindyJim View Post
General comments: Using your batteries to heat water can really suck your batteries down. If you use a 1000 watt microwave running off an inverter, you are discharging your 12 volt batteries at the rate of 1.4 AH (ampere-hours) per minute, or 84 AH per hour. Battery discharge is measured in amp/hours (A/H). If you wish to obtain amp/minutes, divided A/H by 60. You then have amp/minutes.There is no measurement for battery discharge called amp/hours per minute I believe the fans draw about 3 amps each when running, so the two of them add another 72 AH discharge, per 12 hours (if they are running constantly and not cycling on and off via thermostats) (142 AH per 24hours). I believe the batteries you referenced have a capacity of approximately 84 AH each (when new) (total 168 AH) and I think the guidelines are to not let your batteries go below 40% of capacity (if so that means you only have 100 AH per day available for use, excluding solar generation).The generally accepted rule of battery discharge is a 50% depth of discharge, which for Interstate Group 24 liquid cells would be 80 amp/hours of usable capacity.

You state the solar was putting out 10 amps at 12 volts. That may be the max, with less in the morning and tapering off in the evening, going to nothing at night. Lets say that effectively you produce 10 amps for 10 hours per day, or 100 AH per day from your solar (more in summer, less in winter). No solar charging system puts out a consistent, continual amount of power during a sunny day. There is minimal charging from dawn that increases with the sun's azimuth, and hence the solar radiance that the solar array receives and increases to 'solar noon' which is generally 2 hours before and after peak sun angle. If one assumes a 10 amp maximum solar output during solar noon, then the projected output of this system would be approximately 70-80 amps including 10 amps/hour during solar noon and a tapering of this amount for the remainder of the day. Let's call it 80 amp/hours of solar charge per day. This is assuming a summer sun pattern.

If you have incandescent lights, they draw about 5 times the power of LED lights, so depending on how much lighting you are using they can suck the batteries down too. To heat a quart of water from 60 degrees up to boiling (without boiling) takes 7.4 AH (continuing to heat it with 1000 watt inverter would be adding another1.4 AH per minute). Don't know where you got these figures from, but there are few electric kettles that will run from a 1000 watt inverter, as many have 1200 or 1500 watt heating elements. And remember, there is an increase in the load by a factor of 10 going from AC to DC, so a 1000 watt heating element appliance (8.3 amps) would draw 83 amps plus 15% for inverter inefficiency or a total of almost 100 amps from the batteries for each hour of use, That translates to 1.7 amps for each minute of use that will be coming out of the battery bank.

All that said and done, Iím a believer in using the propane stove to heat water, and run the fans and lighting judiciously. A heavy overcast day can mess up your anticipated solar generation. Donít let the batteries get too far discharged. Make sure they have the plates in the batteries complete covered (by adding distilled water if necessary). You can play around with the numbers, but still see that without additional power being supplied you still have to be conscious of your rate of consumption. This is good advice for any system.

Sorry for being so verboseÖ
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Old 04-05-2015, 08:25 AM   #23
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I have also made the mistake of over-estimating the solar output. For me it was just running the fans. We were in Taos, NW with no-hookups. I ran both fans on high for 6 hours. The figures I remember is each fan uses 1.5 amps on low, 2 on medium, and 2.5 on high. so I used 30 amps just to run the fans, which was my total solar input for the day. So I got exactly zero charge put back into the batteries that day. Actually less than zero. But I learned that I needed to think in terms of "the total amount you take out of the batteries has to equal the total you're putting back in" or else you finish each day with less power than you started. What a revelation.

I also learned that running 2 fans on high is kind of pointless with the factory setup. They both blow out. A couple of days later on the same trip, and we were courtesy parking at my in-laws on a street with lots of traffic. Could not open any of the windows, and it was August and hot. We opened the fan above the bed, but turned it off. We set the front fan on low, and had nice circulation of air throughout the AS as air was sucked into the opening above the bed, and discharged out through the front fan. Two revelations on the same trip!
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Old 04-05-2015, 09:41 AM   #24
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@lewster
Thanks for the clarification on WindyJim's post. I'm getting the itch to go out again just so I can put all this new found knowledge to work!

@RAH
I appreciate those refinements on amp usage for the various fan settings. We also discovered how to circulate the air more effectively by using just one fan.
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Old 04-05-2015, 11:20 AM   #25
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Like most threads, this one has drifted, but if it helps people understand batteries and their use, that is OK.

One thing that many RVers have little concept of is just how little energy they have stored in their batteries. Let me try to put that into perspective.

Most Airstreams come with two group 24 batteries, with a storage capacity of about 75 amp hours each. An amp hour is what it sounds like. These batteries will supply a one amp load for 75 hours. They would supply a 5 amp load for 15 hours. Not to try to confuse things, but the more load you put on them, the lower the amp hour capacity would be. So, loading them hard, like running a 1000 watt inverter with a coffee pot would reduce their capacity considerably. But most RV loads are relatively small these days with LED lights and so on, so lets say that the 75 amp hour capacity is a good number.

With two batteries, you then have a total capacity of 150 amp hours, in theory, assuming they are fully charged and you can run them down to no charge.

But, that is a very bad idea, running down to no charge. With the charge varying between 40 to 100% you might get 300 to 400 cycles if promptly recharged to 100%. If you left them sitting at 40 to 50 % charge, never bringing them back to 100%, they soon will have a permanent capacity of 40 to 50%. In other words, damaged.



If you discharged them to 0% you might get 10 to 20 cycles before failure. If you ran them down to 0% and left them un recharged for a few days to a week or two, I doubt you would get 5 cycles from them. Flooded cell batteries hate to be left discharged. AGM batteries are somewhat better, but not much. This is battery abuse for any lead acid battery.

So, the common recommendation is to not discharge a lead acid battery to less than 40 to 50% of it’s capacity, and then promptly recharge it to 100%. Prompt is a day or two, less than a week.

So, you have two 75 amp hour batteries in your Airstream. You don’t discharge them lower than 40%. (you use 60%) Thus you have a capacity of 75 x 2 x .6 = 90 amp hours.

Lets put this into household perspective. We all get electric bills. The energy you pay for is listed in kWh (kilowatt hours, 1000 watt hours). Most households use 400 to 1400 kWh a month.

Your RV batteries were rated in amp hours, so how to convert? A watt is a volt x an amp. We had 90 amp hours of capacity and a 12 volt system. So the battery capacity of our two RV batteries, not used lower than 40% is 90 amp hours x 12 volts = 1080 watt hours, or a bit more than 1 kWh.

So, in your home you probably use 400 to 1400 times that amount of energy in a month. Think of 400 to 1400 pairs of 2 batteries sitting around your yard.

RV batteries have VERY limited capacity. That is one reason they are so often abused and fail regularly, and are replaced often. But if not abused, they can hold up quite well. You simply must not ask more from them than they can deliver, and replace it quickly. (recharge).

I hope that helps in your understanding of RV battery capacity.
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Old 04-05-2015, 05:49 PM   #26
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Like most threads, this one has drifted, but if it helps people understand batteries and their use, that is OK.

Sorry to have been the one to pull the thread in a different direction. (I was afraid from the outset that I might violate proper Forum protocol.) That said, this has been extremely informative to me, and I've appreciated the contributions of all who have take the time to post to my question on your thread. I've learned a lot. Your latest post provides great perspective on how to think about the limited power we have available to us in our coach, and the need to conserve all the energy we can.

If I may, I have one final question pertaining to this topic. We have LED lights throughout the coach. Can you/anyone quantify how much power they tend to pull from the batteries? Should they be the least of our concerns?

Thanks in advance, and Happy Easter/Passover to all.
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Old 04-05-2015, 06:27 PM   #27
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You have not violated anything, rest easy. Threads drift. When they go too far off, they either self limit, or there is a slight possibility that a moderator will say something.

I am posting a chart I have posted in the past, but don't know just where it is now. It may help answer your question about LED lighting and some other loads. My 2014 20' FC has only LED lighting.

Amp draw for things in a 2014 20' Flying Cloud "Bambi"

Measured with a Tri-Metric meter and 100 amp shunt.

Water heater, when flame on: .74 amp

Refrigerator, flame on: .32

Refrigerator fan only: .55

Bed lights, reading, each: .17

Bed lights, overhead, 3: dimmest .1
brightest .52

Main overhead lights, 6 dimmest .23
brightest 1.18

Step light: .06
Scare light (floodlight) .13

Table light: High .62
Low .31

Kitchen lights (either, there are 2) High .38
low .19

Bath lights (2, each with high and low) All .72
one high .38
one low .19
Every LED light inside on at the same time: 3.9 amps


Fantastic fan, each: High 1.55
Medium 1.22
Low .93

Bath fan (little, 4" round) 1.5

Kitchen range fan: 2.4

Kitchen range fan lights (halogen) 3.5

Furnace, 18,000 btuh, direct vent burner on: 3.65
fan only: 2.9

Radio, all off, no lights showing: no measure
Radio, disco lights on, no volume: .7
Radio, lights on, medium volume: .9 to 1

Propane detector: .06
(note: mis measured and posted an error recently on the forum, I was off by a factor of 10)

Pump: (variable speed) 2-4

1000 watt sine wave inverter, on, no load 1.76
with TV and DVD plugged in, but not on: 1.76

TV on and DVD playing: 3.6

TV on DVD playing, + radio on for sound: 4.9-5.3

Very small microwave, supplied by inverter: 89

Toaster, supplied by inverter: 75

Apple Mac Book Pro, charged running from
inverter: 3.1 to 3.3
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Old 04-05-2015, 06:48 PM   #28
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Not that it makes a whole lot of difference but the group 24 Interstates in the trailers are aprox 84ah each, not 80 and 75 as has been quoted in this thread.
I know ,picky, picky!


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