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diy solar

Low battery automatic transfer inverter (PROBLEM SOLVED)

fblevins1

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Aug 14, 2021
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Howdy folks, I am a beginning Solar Power harvester with two 100 watt panels to charge my Vmax 100 Amp/Hour AGM battery which is then used via an inverter to power a 100 watt twin mattress heating pad. I have unplugged my central heating system and this has produced huge savings in my utility bill. The problem is on some nights, especially when the wife goes to sleep early, by the time the morning comes the battery has fallen well below the 50 percent (12.3 Volt) level and sometimes so low that the inverter beeps a warning. This is bad ju ju for my battery lifespan. I know that buying another battery would help but my current solar harvesting ability will only support charging one 100 Amp/Hour Battery on a good day, and I also know that increasing the number of panels will also help. But what I really want is an inverter that plugs into the AC outlet and the battery and when the batteries drop below a predetermined voltage threshold, the inverter will automatically switch to AC power and save my poor batteries. I have found transfer switch inverters but those are designed by default to switch over to AC when it senses the presence of AC and that is great for emergency back up when you lose power. But I want to use the batteries even when there is AC available and only use the AC when the batteries fall below a certain voltage level. I have relied on my ability to check on the system when I wake up at night to use the bathroom and if I see the battery has dropped to near 12.3 volts, I manually move the plug over to an outlet.

Do any of you folks know of an inverter that will do this for me?
 
I have similar use and found this works well.
Moes Auto Transfer Switch

Cheaper than upgrading to an all in one inverter too.
My system was intended to supply power to my maple sugar shack, use included lights, an induction hot plate and occasional power tools.
It irked me using the power for only a month, so I ran a line to the house and now power my aquariums for half the day. A few hours after sundown the ATS flips to grid and in the morning it only takes a couple hours of sun to switch back to battery.
 
I have similar use and found this works well.
Moes Auto Transfer Switch

Cheaper than upgrading to an all in one inverter too.
My system was intended to supply power to my maple sugar shack, use included lights, an induction hot plate and occasional power tools.
It irked me using the power for only a month, so I ran a line to the house and now power my aquariums for half the day. A few hours after sundown the ATS flips to grid and in the morning it only takes a couple hours of sun to switch back to battery.
I will take a peek and see what that thing can do. And Will put that video up so I know it is from a trusted mind. Thank you. Edit: I think that is exactly what I want and most importantly, I can program the cutoff threshold for the specific battery I am using. If I understand right, I won't need an inverter if I buy that box, although that probably won't matter because I have inverters, so for that price, I am going to buy one because I have everything else I need to make a working system no matter what. Wow...thanks man.
 
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Yea, this is the cat's pajamas for our use.
I don't think you can skip the inverter, the ATS is looking for AC from the inverter and not DC from a battery, if I caught your drift correctly.
But since you already have an inverter you're all set to go.

The only downside is catching the bug to upgrade my solar array and battery capacity.
 
Yea, this is the cat's pajamas for our use.
I don't think you can skip the inverter, the ATS is looking for AC from the inverter and not DC from a battery, if I caught your drift correctly.
But since you already have an inverter you're all set to go.

The only downside is catching the bug to upgrade my solar array and battery capacity.
Yep, that is my thoughts exactly. I already have most of what I need so when the unit arrives I will check the manual and figure it out. I will be upgrading my panels and battery capacity over time as well. This is an inexpensive band-aid to keep me from killing my batteries early until I finally get my set up more permanent. I can't buy more batteries because my old ass can barely wheel the 136 Amp/Hour battery in and out of the house. I will eventually figure out how to run the charge controller from outside to the inside so I don't have to move the batteries. I rent so I can't go gung ho with my solar setup. All I know is my portable set up has reduced my PGE bill by at least 200 dollars a month because I only keep the wife warm at night vs heating the entire house. Can you believe she wants to use the central heating at night...in August....in Monterey California? I know it gets cold here at night in the summer but I just use blankets as needed. There were times she would set the thermostat to 85 degrees at night and I would have a window open to fight the heat. She accepted my solar solution and uses a 100 watt heating pad at night. But my single AGM battery just could not power it for 8 hours a night without dropping below 12.3 volts (loaded) and that significantly shortens the battery life. Upgrade wisely my friend.
 
I can't buy more batteries because my old ass can barely wheel the 136 Amp/Hour battery in and out of the house.
I'm nearly there myself., and to think I used to be able to more 1 ton boulders by "hand". LiFePo4 batteries are all the rage here and I can understand why. Deeper DoD, lighter weight and longer life. More expensive up front but not so much that a good prebuilt is out of the question.

Our problem is we can not just add new batteries to our lead/acid battery bank. That's another plus to LiFePo4 batteries, they can be added to at a later date. Going to LiFePo4 give you more usable power too since you can discharge to a lower rate.

I'm looking at a number of of options ranging from $1200 to $1500 which I'd have to save up some cash for. I have a 24v system
With a 12v system like yours you could buy something like this and really up your battery capacity
https://www.amazon.com/dp/B088RM4W4...colid=2XNVZP9L8O0JD&ref_=lv_ov_lig_dp_it&th=1
It might not meet the standards of most forum members but I think they're good enough for someone like us. There are cheaper ones out there but these seem to be a better buy.

My problem is I have to buy 2 batteries which doubles the price of any 12v choice I make. This is why I'm looking at a 24v prebuilt with a a bit more quality. https://shop.signaturesolar.us/products/24v-200ah-lifepower4-battery-by-eg4
 
I'm nearly there myself., and to think I used to be able to more 1 ton boulders by "hand". LiFePo4 batteries are all the rage here and I can understand why. Deeper DoD, lighter weight and longer life. More expensive up front but not so much that a good prebuilt is out of the question.

Our problem is we can not just add new batteries to our lead/acid battery bank. That's another plus to LiFePo4 batteries, they can be added to at a later date. Going to LiFePo4 give you more usable power too since you can discharge to a lower rate.

I'm looking at a number of of options ranging from $1200 to $1500 which I'd have to save up some cash for. I have a 24v system
With a 12v system like yours you could buy something like this and really up your battery capacity
https://www.amazon.com/dp/B088RM4W4...colid=2XNVZP9L8O0JD&ref_=lv_ov_lig_dp_it&th=1
It might not meet the standards of most forum members but I think they're good enough for someone like us. There are cheaper ones out there but these seem to be a better buy.

My problem is I have to buy 2 batteries which doubles the price of any 12v choice I make. This is why I'm looking at a 24v prebuilt with a a bit more quality. https://shop.signaturesolar.us/products/24v-200ah-lifepower4-battery-by-eg4
That is something we need to discuss and work out the cost vs benefits. 12 V vs 24 V But I gotta walk the dog and get some chores down. I will get back to this later. Thanks for the information. Edit: Something else I want to explore on these forums is amp/hour rating definitions. For example is my AGM 100 Amp/Hour spec based on an assumed 50 percent discharge or what. Does the Lithium Iron 100 Amp/Hour assume complete discharge or what. The only thing I am good at is measuring shit because that is my occupation, but when it comes to batteries...forget it, I am the noobiest of noobs.
 
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So tomorrow I am purchasing that transfer switch and a new Vmax 100 Amp Hour battery. In the mean time though I am setting myself up a battery test bench using either one 1000 Watt Electronic Load or two in parallel to give me a 2000 watt electronic load, probably the latter because at 100 Amps, it will pull too much for just one. For my set up testing I will be just using one to validate my set up using a small 36 Amp Hour Battery. I will be using a cheap 300 Amp Hall effect sensor that displays volts, amps, amp hours, watt hours and watts. Should be sufficient for baseline testing. I want to test my new Vmax battery compared to my older Vmax Battery (both same model number) to test how well the older battery has been holding up. I have broken a few rules along the way so I would like to see just how much of a difference over the 6 months that my brutalizing that poor thing has. Should be fun. I think I need to get an insulated wrench or socket to make connecting less hazardous.

I appreciate you folks helping this noobie out Here are the electronic loads I intend to use. Mine is the upper right hand corner of the page (two of them) https://www.kepcopower.com/el.htm While I know squat about solar and batteries, I have 41 years in the measurement science field. I remember when I first dove into this mess, the first thing I realized was wow, batteries are the worst dc power supplies I have ever seen. I am used to dealing with power supplies with load regulation specs of .01% good luck getting that out of a battery. Good times. Edit: Note to self, learn how to test a battery amp hour rating BEFORE hooking it up to the electronic load. I am going to charge the battery and try again tomorrow, turns out a 36 amp hour battery means does not mean you can kick it to the curb with 36 amps and expect it to last an hour. I will give it a much smaller load and simply observe how long it takes to discharge to a depth of 50 percent. I am such a tool. I am going to wind up being like that Indian guy we see on YouTube that is always blowing shit up and shocking the shit out himself. Fortunately I had the hands on the interrupt and bailed on the test early enough to avoid a Chernobyl. Damn.....
 
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Yea, this is the cat's pajamas for our use.
I don't think you can skip the inverter, the ATS is looking for AC from the inverter and not DC from a battery, if I caught your drift correctly.
But since you already have an inverter you're all set to go.

The only downside is catching the bug to upgrade my solar array and battery capacity.
After taking a look at the transfer switch set up diagram and watching the video, I understand the set up now. Yes, I do need the inverter as the switch box looks at the system DC voltage and decides, based on my threshold setting whether to use grid or solar/battery power. This box solves all my problems. I will have an active Solar/Battery/Grid power set up that I can just walk away from and never really worry too much about problems. I will also keep a fire extinguisher near the set up so if shit goes sideways I can always whack myself in the head with the extinguisher body. Thanks wiseacre.
 
Yesterday I ordered the transfer switch, another Vmax 100 Amp Hour battery, another 100 watt solar panel and a couple of splitters. In theory that should keep the wife happy while allowing me to keep that circa 1958 central heating unit unplugged saving me a butt load of cash. Watt for watt, solar system usually take a while to pay for themselves but not when you are replacing a heating system that I am sure once existed during the Jurassic period.
 
So the transfer switch arrived quickly and the set up was really easy and programing the unit, even easier. I just hit the menu button and it asked me for my low voltage switch point and then the high voltage switch point and poof, I was off and running. I am still waiting for the other battery and panels so I can get the semi-permanent set up going but....I did notice that while the unit switched over to grid power during the night as it was supposed to do, because the inverter was still powered up, it continued to eat battery power and when I woke up in the morning the battery voltage was at 12.0 volts (the transfer threshold was set for 12.3 volts). I turned the inverter off and it eased up to 12.1 Volts. The battery was not fully charged for this test so I expected an early switch. However without the switch the heater (100 watt) would have continued to eat my battery until the inverter beeped and shut off so the transfer switch will save my batteries from an early death. And once I get the rest of the parts in, I will have twice the battery power and 4 panels backing them up. So I will rarely if ever need to worry about doing anything. Just let the system run.
 
The main reason we can't really switch off the inverter is because its primary usage is at night, while we sleep. I woke up this morning saw the battery was sitting at 12 volts and turned off the inverter. Still, with the transfer switch in place it keeps the battery from being sucked dry to the point that the inverter beeps and shuts itself off, that is bad ju ju for the battery. I think once I double my capacity this week, that will probably take care of the problem and once the sun comes up it will start charging the battery again. I suppose until the new stuff arrives I can simply set the trip point to 12.6 volts to allow for inverter draw. Or just not worry about it until the new stuff arrives, chances are that as many times as I have drawn my AGM well below the recommended depth of discharge, it is not going to live to be an old man anyway. I am working on some kind of grid sensor to automatically shut off the inverter in another thread. I will see where that goes. Thanks wiseacre.
 
Well, looks like this transfer switch is defective. It worked when I first installed the unit, but I noticed that whenever I went to verify it's transfer set points they were always at the default settings of 11 volts low and 13.5 volts high. Initially I just assumed that it went default whenever you entered the menu, but that is not the case. I calibrated the set points using a DC power supply and confirmed that even though I can enter the desired set points as soon as I enter the last setting (hi set) it defaults back to 11 - 13.5 volts. I confirmed this several times and came to the conclusion that the control board is defective and does not retain the memory of your selection. I have a new one on the way now and can drop my unit off at the UPS store at no cost. But unfortunately that makes this weekend's project a bust. It is probably good that I had decided to wait for the new battery and panel to arrive because had I continued to use it, it would have waited until 11 volts to switch over to grid. I did an initial test and it worked great but somewhere along the way the control board ate itself. Oh well, nothing last forever. I will wait for a response just in case one of you folks know what I did wrong, but the unit is so simple to operate it hard to imagine I could have mucked up the settings. still, nobody is perfect. Edit: Well maybe this weekend's project is not a bust. I can still set up the third panel and second battery just like I was going to do but I just won't have the transfer switch in place. It is really easy to set up so once I get the replacement unit it, I will simply insert it into the set up. The extra panel and the second battery will likely extend the amount of time during the night to operate the appliance so when I wake up in the morning I can just monitor the battery voltage and move the plug over to grid myself. One battery was being depleted dangerously low during the night but doubling the battery power should buy me time.
 
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the unit is so simple to operate it hard to imagine I could have mucked up the settings. still, nobody is perfect.
Well I just freaked out. My setting was at 24v default when I looked. Can't remember if I reset it to that or not after a power outage or if it reset because of the power outage.

Adjusted it to 24.4, hit the select (middle button) and looked again to find it at 24. Tried again and held the select button for a "long" time and it took.
 
Well I just freaked out. My setting was at 24v default when I looked. Can't remember if I reset it to that or not after a power outage or if it reset because of the power outage.

Adjusted it to 24.4, hit the select (middle button) and looked again to find it at 24. Tried again and held the select button for a "long" time and it took.
I am going to try that and see if it takes. I have already processed the return, but if that trick works then I can use my transfer switch until I receive the replacement and then ship this unit back. Well, you just solved my problem for me. When you hit the middle button and set the low voltage you have press and hold the middle button and after a couple of seconds it changes to the hi set point and after you set the hi setting you hold the middle button down and after a couple of seconds it engages the unit. From there you can verify the settings and they are there. Thank you good sir I think we just helped each other. I am going to look at the manual again. but it looks like we have solved the problem. So to summarize and I just confirmed with the manual. When you are trying to change the default value you have to hold the middle button down for 3 seconds to force the change and you have to do that both the low and high set points. And, you can actually calibrate the voltmeter on the display. If you notice there is an error between what the display voltage indicates and your reference meter you hold both the plus and minus buttons for 3 seconds and then you will get a flashing display you simply hit the plus or minus keys to offset the display in .1 volt increments until the reference meter and the display meter agrees. Note that the when you enter the calibration mode what is displayed is the current correction factor in my case it was set to 0.2 volts and I changed it to 0.3 volts to make it agree with my meter. Then you hold the plus and minus buttons again for 3 seconds and it takes the correction and your display is calibrated. Now when my precision supply reads 12.500 volts my display reads 12.5 volts. Mr. Wiseacre you are a genius. Thank you.
 
LOL, Amazon is trying to refund my money via chat and I am trying to tell them that the unit works fine and I just want to cancel the return/replacement.
 
And just a further note, once you commit the hi and low set points even if you remove the unit from battery power it will still remember the settings once you put it back on the battery. Whether or not it remember the settings when removed from the battery for a long time, I don't know.
 
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