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Old 08-14-2020, 06:38 PM   #1
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Sorry, another solar question

I'm finally boondocking with new trailer. My solar is in the sun all day and shows 100% charged, 13.4v. As soon as the sun moved off the panel controller now reads 85%!
Only thing running is small fan on fridge.

Was really not charged all the way? If it is charged how can it drop 15% that quick?

Thanks!!

I have 2 group 27 batteries and a 190w solar panel.
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Old 08-14-2020, 06:43 PM   #2
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Just like when plugged into shore power the reading will be higher while there is power going into the battery. It's reading the charging current not the battery level.
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Old 08-14-2020, 06:48 PM   #3
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Just like when plugged into shore power the reading will be higher while there is power going into the battery. It's reading the charging current not the battery level.
I'm confused then because it's showing a picture of the battery and the percentage.....see picture
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Old 08-14-2020, 07:22 PM   #4
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My multi meter is reading 11.95 at the batteries, can that be right??
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Old 08-14-2020, 07:24 PM   #5
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The battery, the charger, and the meter are all connected together. Your meter is reading all the current at the terminal. To get a reading of just the battery you have to disconnect the charging source.

I wish I had a better example but imagine checking how much gas is in your tank by a sensor at the fill neck while gas is being poured in.
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Old 08-14-2020, 07:29 PM   #6
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Ok makes sense, controller is showing batteries are at 12.5
I still don't understand though how it went from 100% down to 85% as soon as the sun moved off the panel
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Old 08-14-2020, 07:50 PM   #7
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The panel was generating 13.4 volts. Your meter was reading 13.4 volts. Your meter will read the greater of the panel or the battery. It can only read what's at the point your meter is connected.
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Old 08-14-2020, 09:10 PM   #8
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I am running a 600w inverter that is running the TV. The controller says the batteries are at 12.3v
The battery minder of the trailer reads full...
It is dark outside, solar is off
I guess I don't understand the controller, or it's not reading right? Or which reading i should believe?
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Old 08-15-2020, 04:57 AM   #9
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Couple of things to think about here.
Let's go back to the reading of 13.4. Let's say you first hooked up your meter to the panel. It shows 13.4 volts which is the current being produced by the panel. Then you added the battery, the meter will continue to read 13.4 volts. It's not smart enough to know which is the current coming from the panel and which is the current coming from the battery. It just knows there is 13.4 volts of current where it is measuring. Now you disconnect the solar panel or a cloud appears. The meter will just be reading the battery. That may be 12.3 volts. The cloud moves or you reconnect the panel and the reading jumps back to 13.4. The poor dumb meter only knows what current is flowing at that point, not how much stored energy is producing it.

Now onto the lights on your converter.
You presumably have a light for full, 3/4, 1/2, and 1/4. When each light turns off is up to the designer. If your full light turned off at 99% it would not be of much help. So instead four lights generally means somewhere between 12.7 or above and 12.35. Three lights between 12.34 and 12.06. Two lights 12.06 to 11.7, and one light below 11.7 and finally cut off around 10.5.

At 12.3 you should only have three lights so we could have a slight difference between the meters which isn't uncommon or it's actually 12.36 but the display only reads to tenths not hundreds of a volt. These are not scientifically precise devices.
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Old 08-15-2020, 07:44 AM   #10
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Would I get a more accurate read with an MPPT controller? Or does it matter?

My previous trailer I installed the solar myself, only had group 24 batteries and ran the same 600w inverter many hours at night and never saw it get to 12.3v.
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Old 08-15-2020, 08:09 AM   #11
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Try an experiment today. Check the voltage with your panel in full sun then put a blanket over the panel and check the reading. Let's see what the difference is.
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Old 08-15-2020, 10:23 AM   #12
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Try an experiment today. Check the voltage with your panel in full sun then put a blanket over the panel and check the reading. Let's see what the difference is.
Sounds like a good test.....I have to leave for a while but if not today will try it tomorrow! Thx!
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Old 08-15-2020, 06:56 PM   #13
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So been gone all day, only thing running was fan on fridge and just like yesterday it read 100%, as soon as sun moved of panel it went to 85% and 12.7v ��*♀️
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Old 08-15-2020, 07:37 PM   #14
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There’s another angle at play too. Your assuming your batteries aren’t damaged and they have the ability to take a full charge. 85% or 12.7 might be the best they can provide at their “full charge”. You need to forget the solar panel and it’s controller and first make sure your batteries are ok. You need a reading from the batteries using a multimeter with the solar disconnected from them or at night and see what that is at full charge, nothing drawing power while you take a reading if possible.
What is the total amp hours of your batteries? Rough estimate, the amps drawn by a device are doubled when the power is converted from DC to AC. As mentioned you are using a 600W inverter to run things. You need to total up all the amps from devices you are using during the day and see if that exceeds the amps your batteries can provide from full charge. Your available amps (amp hours) listed on the label on your batteries must be divided by 2. That keeps you from drawing your batteries down past 50% charge because past 50% charge your batteries are being damaged. You might be in a situation with inadequate or damaged batteries that can barely provide the amps you need and the solar is just barely keeping them from tanking in the daylight hours.

Make a list of everything you use for how many hours you use it in a 24 hour period and the amps they draw and total that up

See how many amp hours your batteries are and divide that x2 (this is your available amps before your batteries are depleted to critical)
Should be on the sticker on top of battery

Subtract the amps used by the devices you added up by the amp hours your batteries say they can provide and see where you stand. Did you exceed the amps available from your batteries?

Now look at the specs for your solar panel and charger. How many amp hours during peak time does the solar provide? This is what your solar can help to put back into the batteries when the sun is shining and it’s working great. Figure out how many good daylight hours your panels are getting and multiply the amps provided by that many hours (it’s usually 6 hours on a good day when the sun is overhead).

Do the amps put in by your solar equal enough to offset the drain on your batteries and keep them from getting depleted past 50 percent?

It’s a delicate balance of use and return and you need to know exactly what your system is capable of or you’ll just smoke batteries never knowing how much your using and putting back in.
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Old 08-15-2020, 08:33 PM   #15
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So as stated before, nothing but the fan on the fridge runs during the day, only thing that runs at night is the 600w inverter with TV and small (wally) satellite box for 3 or 4 hours, nothing else running.
The batteries are brand new, I hope there is nothing wrong with them.
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Old 08-15-2020, 08:50 PM   #16
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So as stated before, nothing but the fan on the fridge runs during the day, only thing that runs at night is the 600w inverter with TV and small (wally) satellite box for 3 or 4 hours, nothing else running.
The batteries are brand new, I hope there is nothing wrong with them.
Unfortunately there no way of knowing without testing them. Are they the cheap batteries they give you when you buy a camper? If so it’s possible they are as worthless as the ones I got with my 5th wheel.

I know my post was clunky and confusing so simply

1- you need to know if your batteries are good and how many amp hours you have to deal with

2- you need to know exactly how many amps you are drawing. You say you are boondocking so I’m assuming no shore power or generator. So, the amps using that inverter to run the t.v and satellite needs figured, the amps used by the fridge fan, the amps used by any lights you turn on (I’m assuming it’s dark, someone turns on a light), the amps you use for the water pump (I’m guessing you wash hands, do dishes, etc), the amps drawn by the CO2 detector (it’s always using power), the amps drawn by anything passive (fridge circuit board, radio memory, etc), anything you use at all In a 24 hr period needs added up. If you are boondocking and using anything that requires power then it needs accounted for. This is crucial

3- you need to know how many amps your solar is adding back into the batteries at peak time

Without this knowledge you are just assuming “I’ve got some batteries, and I’ve got some solar, the sun is shining so I must be just fine”. Nothing is further from the truth. You have to know what your system is doing and capable of or you’ll just be chasing your tail wondering why it’s not doing what you think it should do. That solar controller readout is just what the controller is reading at the battery terminals where the panels are putting in amps, not what the batteries actually are capable of providing if the solar was disconnected. I’d bet money, which you’ve already described above is that as soon as the panels aren’t providing voltage/amps to the battery that the voltage reading at the batteries with a multimeter or even at the generic display for the solar controller that the reading drops. This tells you that the reading you keep relying on at the charge controller is not an accurate depiction of the batteries capability and not intended to be so. It’s just a real time reading of the power being supplied by the panels to them.
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Old 08-15-2020, 08:58 PM   #17
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First thing I did was get rid of the one group 24 battery that came with the trailer. They are 2 group 27 interstate batteries now.
I will try to figure out all that you mention, not sure I can find all the info/answers.
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Old 08-15-2020, 09:41 PM   #18
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First thing I did was get rid of the one group 24 battery that came with the trailer. They are 2 group 27 interstate batteries now.
I will try to figure out all that you mention, not sure I can find all the info/answers.
I sat down with a piece of paper and thought in my head “what do I use in an average day” and wrote those things down in a list.

Then I figured out roughly how many hours I used each item in a day (just a rough estimate is ok) and wrote that down next to each item.

Then I googled or looked on the devices stickers (for T.V.s and other items) for their watts which you can convert to amps (google watts to amps calculator) and wrote the amps used next to each item.

Now take the hours you use each item in the day x the amps each item draws and write that next to each item. Now you have your total amps drawn each day written down next to each item

Add up all the amps used numbers that you wrote down next to each item on your list and you’ll have a pretty good idea of what you use in an average day as far as amps.

Now if your batteries don’t say the amp hours on the sticker that’s not a good sign, google the brand and size and find that number. Remember it’s divided by 2 because you can only use 50%. So a in reality a 75 amp hour battery would only have 37.5 amp hours you can use before your critical. You have two batteries add them together and you’ll have your total amp hours you have at your disposal at full charge.

Somewhere online, in the paperwork, on a sticker somewhere you should be able to find out how many amps your solar panel provides at peak. Multiply this by how many good hours of sunlight that panel sees in a 24 hour period. Like I said above it’s usually at best 6 hours, your always going to get less from it during sunrise and sunset (and overcast days and rainy days). Now you know how many amps (roughly) that your solar can put back into your batteries in a given day.

Example: You use 40 amp hours a day. Your batteries can provide you with 80 amp hours before they go critical. You’ve now used 40 amps from your 80 amp battery bank. You have 40 amps leftover to use at the end of the day. Your solar puts back in 40 or so amps in a given day (I have no idea what your solar does, this is just an example). You’ve fully recharged your batteries and start out 100% the next day.
Rock and roll, your off grid.

Example: This time you use 65 amp hours a day. Your batteries can provide 80 amp hours before they go critical. You’ve now used 65 amps from your 80 amp hour battery bank. You have 15 amps left to use at the end of the day. Your solar puts back in 40 or so amps in a given day. You start out the next day with 55 amp hours in your batteries. You again use 65 amp hours that next day. You’ve taken your batteries down below 50% because your solar cannot put back into the batteries enough amps to charge them back up fully and you cannot keep up with demand. Now it’s a downhill slide to damaged batteries and frustrated camping. You are not happy.

This is why you need to know what you are using and how much is going back in. It can’t be a guess.
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Old 08-16-2020, 07:28 AM   #19
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I'm finally boondocking with new trailer. My solar is in the sun all day and shows 100% charged, 13.4v. As soon as the sun moved off the panel controller now reads 85%!
Only thing running is small fan on fridge.

Was really not charged all the way? If it is charged how can it drop 15% that quick?

Thanks!!

I have 2 group 27 batteries and a 190w solar panel.
Measuring voltage is inherently unreliable for determining the state of charge of a battery. It only works when 1) there is no load on the battery, when 2) the battery has had no load for a while (resting state), and when 3) the voltage probe is very close to the battery terminals. If there is no load, 12.7 V measured at the battery is roughly 100% state of charge. In real life, measuring with no load is not practical.

The much better way to check battery state of charge is with a current meter. I bought a cheap one, like this:

https://www.amazon.com/bayite-6-5-10...584136&sr=8-15

This allows you to know exactly how many Ah go into or out of the battery. It only works in one direction, but you can install a reverse polarity switch, to know how many amps go in or out. If you want to spend more, these ones are recommended and are bidirectional:

https://www.amazon.com/AiLi-Battery-...7584263&sr=8-6

Knowing how many Ah the trailer consumes, and how much goes back to the battery through solar has changed the way how I approach my battery status. It has taken the guess work and worry out of the equation, because I know the exact numbers. Installing the amp meter is very easy, I can give tips if needed.
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Old 08-16-2020, 08:05 AM   #20
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Measuring voltage is inherently unreliable for determining the state of charge of a battery. It only works when 1) there is no load on the battery, when 2) the battery has had no load for a while (resting state), and when 3) the voltage probe is very close to the battery terminals. If there is no load, 12.7 V measured at the battery is roughly 100% state of charge. In real life, measuring with no load is not practical.

The much better way to check battery state of charge is with a current meter. I bought a cheap one, like this:

https://www.amazon.com/bayite-6-5-10...584136&sr=8-15

This allows you to know exactly how many Ah go into or out of the battery. It only works in one direction, but you can install a reverse polarity switch, to know how many amps go in or out. If you want to spend more, these ones are recommended and are bidirectional:

https://www.amazon.com/AiLi-Battery-...7584263&sr=8-6

Knowing how many Ah the trailer consumes, and how much goes back to the battery through solar has changed the way how I approach my battery status. It has taken the guess work and worry out of the equation, because I know the exact numbers. Installing the amp meter is very easy, I can give tips if needed.
100%
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