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Old 09-10-2019, 02:45 PM
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Default Using car batteries on solar system?



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I have very little experience with solar systems but I have the ability right now to pick up 3 320 watt solar panels for $200. I am thinking of picking them up and a controller and connecting them to a couple large car batteries I have. For the most part I would use them to run lights and radio in my shack so would use it for very little load. Although if we have an extended power outage I would use it to run the freezer and a few lights in the house.

I realize repeatedly draining a car battery will kill it, but would light loads(like lights and radio) also kill them quickly? Is it the worst idea ever to use car batteries in a small solar set up? Or since I already have them and no other use(too large and wrong post set up for any of my vehicles) would it be a cheap system that will work until I can justify spending the money on proper batteries?
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Old 09-10-2019, 03:00 PM
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Since you have them already there is no reason not to use them. They are not going to last as long as Deep Cycle batteries and you'll want to avoid deep discharge cycles. Probably setup up your shutdown voltage a bit higher for any inverter so that you keep from dropping below 75% charge.

However they will serve to be a ballast during the times your solar panels are being used to supply loads. With 3-320 watt panels you would have a decent amount of power to work with. ~750 watts in full sun.
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Old 09-10-2019, 03:03 PM
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So it looks like I may have to pass on the solar panels. I just found out they are 36 volt. I have to look and see if charge controllers can convert 36v to 12v. I would assume with enough money it can be done but I'll have to do some research.
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Old 09-10-2019, 03:11 PM
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So it looks like I may have to pass on the solar panels. I just found out they are 36 volt. I have to look and see if charge controllers can convert 36v to 12v. I would assume with enough money it can be done but I'll have to do some research.
No problem at all with a MPPT controller. My Blue Sky Solar controller can take up to 80vDC and convert it to for 12vDC charging. It can go up to 105vDC for 24 volt battery charging and 160vDC for 36&48vDC battery charging.
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Old 09-10-2019, 03:26 PM
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No problem at all with a MPPT controller. My Blue Sky Solar controller can take up to 80vDC and convert it to for 12vDC charging. It can go up to 105vDC for 24 volt battery charging and 160vDC for 36&48vDC battery charging.
I will have to look into MPPT controllers, I just did a quick search for them and they look affordable but I'll have to do some more research to see what size I need.
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Old 09-10-2019, 03:32 PM
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As to size, 3-320w panels for a maximum of 960 watts. Divide watts by volts to get amps. 960/12 = 80 amps if you go that route. If you wire your batteries for 24vDC you would drop down to 40 amps.
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Old 09-10-2019, 03:35 PM
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I just did some searching and all the cheaper controllers(less than $200) that were 80 amps said 12v or 24v. The smaller 40 amp ones said 23/24/36v. Does that voltage refer to incoming or outgoing voltage or both?
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Old 09-10-2019, 03:56 PM
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https://makeskyblue.com/

If you click on the 40 amp unit you will see a spec sheet where the max PV input is mentioned. For a 24v battery charging system the max PV array is 960 watts. Price is $85
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Old 09-10-2019, 03:57 PM
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MPPT controllers will have two voltage ratings, one for the battery bank and another for the maximum input voltage. Make sure your solar panels Voc rating doesn't exceed the max input voltage. For example the controller I have can handle 100v input and 24v battery bank.
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Old 09-10-2019, 04:15 PM
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MPPT controllers will have two voltage ratings, one for the battery bank and another for the maximum input voltage. Make sure your solar panels Voc rating doesn't exceed the max input voltage. For example the controller I have can handle 100v input and 24v battery bank.

Just to make sure I understand. This controller https://cuttingedgepower.com/product...smart_campaign
should be able to handle 3 the panels I am interested in and charge 12 volt batteries? I have no idea if it is any good, it is just the first one I clicked on.
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Old 09-10-2019, 04:21 PM
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Just to make sure I understand. This controller https://cuttingedgepower.com/product...smart_campaign
should be able to handle 3 the panels I am interested in and charge 12 volt batteries? I have no idea if it is any good, it is just the first one I clicked on.
I doubt that is a MPPT controller. It's too cheap especially for a 100a controller.
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Old 09-10-2019, 04:38 PM
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Also, you don't have to find a single controller that can handle all your panels, you can just use multiple smaller controllers which will also build redundancy into your system. If you did a 12v system, you could use 2 of the 60a units or 1 30a and 1 60a from MattB4's link, or 3 of the controllers I linked to
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Old 09-10-2019, 04:39 PM
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I doubt that is a MPPT controller. It's too cheap especially for a 100a controller.
Any idea on how to tell the difference if they claim they are? There are lots of what claim to be MPPT controllers for as little as $13? But then there are the better ones in the $600-$800 range, which I am assuming are the real thing.
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Old 09-10-2019, 04:41 PM
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Any idea on how to tell the difference if they claim they are? There are lots of what claim to be MPPT controllers for as little as $13? But then there are the better ones in the $600-$800 range, which I am assuming are the real thing.
Best way to tell is to look at reviews of the controller you are intersted in. MPPT controllers are generally larger and require more cooling than PWM.
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Old 09-10-2019, 04:55 PM
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AP is very much correct. There are a LOT of cheapo Chinese PWM controllers that they slap a MPPT label on and try to sell you. You can find them on Ebay any day of the week. If they ship it internationally from China, and it's a fake, you don't get your money back, and you trash your batteries. The toroid coils in a real MPPT use a lot of copper, so the units are heavy. If a controller is marked "MPPT" and the shipping weight is 6oz, it is fake. If it weighs 6lb, it's more likely to be a real MPPT.
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Old 09-10-2019, 05:14 PM
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Google D8 batteries. I used two to run a slot car track, when charged they last a long time. They’re used in forklifts
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Old 09-10-2019, 06:44 PM
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The plates in car batteries are kinda thin, this reduces the number of discharge cycles your going to get.
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Old 09-11-2019, 01:54 PM
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Originally Posted by lasers View Post
I have very little experience with solar systems but I have the ability right now to pick up 3 320 watt solar panels for $200. I am thinking of picking them up and a controller and connecting them to a couple large car batteries I have. For the most part I would use them to run lights and radio in my shack so would use it for very little load. Although if we have an extended power outage I would use it to run the freezer and a few lights in the house.

I realize repeatedly draining a car battery will kill it, but would light loads(like lights and radio) also kill them quickly? Is it the worst idea ever to use car batteries in a small solar set up? Or since I already have them and no other use(too large and wrong post set up for any of my vehicles) would it be a cheap system that will work until I can justify spending the money on proper batteries?
Car batteries just won't last as long or take a deep discharge very well.

You will need to decide if you are going "all in" with the solar power thing. Or will the couple of car batteries and the three panels be it. One of those panels and a 30 amp MPPT charge controller will charge the car batteries you have. In order to run your lights and freezer you will also need an inverter of 500 watts or more. (compressor starting current is 4 times running current figure 100w freezer) Your couple of car batteries may not last the night. You will need more batteries. Which will require the other panels. Which will require a larger charge controller and a larger inverter. You can either do it once or start small and work up.

Just lights and ham shack? Easy, with one panel, two car batteries, a 30 amp charge controller, a 500 watt modified sine inverter. Ham radio runs off of 12vdc. (at least mine does)

For reference, I have 4 - 100 watt Renogy panels wired in series-parallel, a 40 amp 100 volt input MPPT charge controller, 4 - 6 volt golf cart batteries and a 1750 watt modified sine inverter in my ham shack/shed. I can also run a small microwave oven long enough to heat lunch.

It will run the lights and radio for as long as I like, but if I run the small window A/C unit I need full sun all day to keep it going. Actual measured output of the panels in full sun in the summer is about 300 watts.

===
P.S. jump on the panels at $200 if they are like new. That works out to be 20 cents per watt. You can decide what else you want to do later.
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Old 09-11-2019, 02:13 PM
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Car batteries just won't last as long or take a deep discharge very well.

You will need to decide if you are going "all in" with the solar power thing. Or will the couple of car batteries and the three panels be it. One of those panels and a 30 amp MPPT charge controller will charge the car batteries you have. In order to run your lights and freezer you will also need an inverter of 500 watts or more. (compressor starting current is 4 times running current figure 100w freezer) Your couple of car batteries may not last the night. You will need more batteries. Which will require the other panels. Which will require a larger charge controller and a larger inverter. You can either do it once or start small and work up.

Just lights and ham shack? Easy, with one panel, two car batteries, a 30 amp charge controller, a 500 watt modified sine inverter. Ham radio runs off of 12vdc. (at least mine does)

For reference, I have 4 - 100 watt Renogy panels wired in series-parallel, a 40 amp 100 volt input MPPT charge controller, 4 - 6 volt golf cart batteries and a 1750 watt modified sine inverter in my ham shack/shed. I can also run a small microwave oven long enough to heat lunch.

It will run the lights and radio for as long as I like, but if I run the small window A/C unit I need full sun all day to keep it going. Actual measured output of the panels in full sun in the summer is about 300 watts.

===
P.S. jump on the panels at $200 if they are like new. That works out to be 20 cents per watt. You can decide what else you want to do later.
First I have to clarify what I meant by shack. It isn't a ham shack. It's main use is an iceshack we drag out on the ice to fish from, it is also our syrup shack, honey house if we ever can afford some land our cabin. So we simply call it "the shack". When I refer to powering a radio I am referring to a am/fm radio. We currently power it with a single battery that we bring with us for the weekend then bring it back when we come home.

At the moment I just want to dip my toe into the "solar pool" as cheaply as I can. In the future I would like to build an entirely off grid cabin with a larger system and would view this as mostly a learning experience.

I realize for as little as I use power in the shack I could use a cheap panel intended for a fence charger to keep the battery charged.

It just feels like such a good deal on the panels that it would give me a chance to play with a useful amount of solar power on a low budget. But since my number one concern of being without power for more than a couple days is my freezer I would like to have a system that could keep that running as well. Even if it could only run when the sun shines that would be better than nothing.
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Old 09-11-2019, 02:57 PM
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First I have to clarify what I meant by shack. It isn't a ham shack. It's main use is an iceshack we drag out on the ice to fish from, it is also our syrup shack, honey house if we ever can afford some land our cabin. So we simply call it "the shack". When I refer to powering a radio I am referring to a am/fm radio. We currently power it with a single battery that we bring with us for the weekend then bring it back when we come home.

At the moment I just want to dip my toe into the "solar pool" as cheaply as I can. In the future I would like to build an entirely off grid cabin with a larger system and would view this as mostly a learning experience.

I realize for as little as I use power in the shack I could use a cheap panel intended for a fence charger to keep the battery charged.

It just feels like such a good deal on the panels that it would give me a chance to play with a useful amount of solar power on a low budget. But since my number one concern of being without power for more than a couple days is my freezer I would like to have a system that could keep that running as well. Even if it could only run when the sun shines that would be better than nothing.
Thanks! Yeah, get those CHEAP solar panels (before somebody else does) and an inexpensive 40 amp charge controller. Inverter too. You can decide on where you want to go later. Big inverters will run big loads but will run down batteries fast.

The charge controller at the link you posted said it was 100 amps, but if you look at the terminals size, there's no way they are rated at 100 amps.

Check out this actual 100 amp charge controller:



https://www.amazon.com/EPEVER-Charge...s%2C208&sr=8-3

If you wire your batteries in series for 24 volts, this charge controller will handle all three of your solar panels.

https://www.amazon.com/EPEVER-Charge...08&sr=8-3&th=1

Quote:
40amps solar charge controller, Max input power 520W(12V); 1040W(24V) solar pannel, Max. solar array Voc 100 V; And also fit for small load application, e.g. Fan, LED
You'll also need some 10 or 8 ga wire and MC4 connectors.

https://www.amazon.com/RENOGY-Female...K13PKGMVK60Q84
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