Three 280 watt solar panels on Casita 13 - Page 2 - Fiberglass RV


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Old 05-14-2019, 01:16 PM   #21
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Originally Posted by Kai in Seattle View Post
We are arranging to have solar, wind, and hydroelectricity generated wherever we go before we get there, and wired in ready for us to use. We find 110/120V acceptable and will accept no substitutes except for our 12V car battery running our 12V/110V car ice chest and our trailer lights...


Hence, yes, shore power.


I know, I know.


I know.


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K
LOL. I have no problem with that! Different strokes for different folks.
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Old 05-14-2019, 05:00 PM   #22
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LOL, thanks Bill. YMMV! Your Mileage May Vary.

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Old 05-15-2019, 07:25 AM   #23
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So I have been doing dome more research on batteries and I think I'm going to change my plans a little.

As bmoores mentioned, LiFePo4 batteries have a ton of advantages. What I didn't know before is that they can be stored inside of the camper because they are completely sealed and don't off gas anything, and they are safe enough that I don't have to worry about them catching on fire. If I put them inside of the camper, I'm pretty sure I can find a way to keep them below the 140F Max temps.

The LifePo4 batteries will also give me more capacity, in a smaller and lighter footprint. The batteries I specd will weigh 92lbs (vs 320+ lbs for 4 Trojan 1275's) and give me 24v 240AH. That's 200AH of useable power @ 24V, which is a good amount of power. The footprint should be roughly H7" x W11" x L16"

Something else I found out while researching these batteries that I don't see many other people talking about is how efficiently they take a charge compared to a lead acid battery. Lead acid batteries have a pretty high resistance, which means a good portion of the energy (almost half) going from the solar panels and into the battery gets turned into heat, instead of stored energy. LifePo4 batteries are about 96% efficient. Because I'm trying to pull as much energy as I can from the panels, it makes sense not to turn that energy into heat. They can also discharge higher power loads more efficiently.

The downside to these batteries is they aren't cheap and you generally have to assemble them yourself. However, if you factor in how much more efficient they are and how much longer they last, they are actually cheaper long term.
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Old 05-15-2019, 11:01 AM   #24
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...The batteries I specd will weigh 92lbs (vs 320+ lbs for 4 Trojan 1275's) and give me 24v 240AH....

so all your DC electrics on board will need to be 24V rather than 12V? water pump, fan, fridge, water heater control, lighting ?
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Old 05-15-2019, 02:06 PM   #25
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so all your DC electrics on board will need to be 24V rather than 12V? water pump, fan, fridge, water heater control, lighting ?
No, I will be using a 24v to 12v step down by Victron. It is capable of producing 25 amps of power at 12V. The only 12V items I have in the camper are the refrigerator, lights, and water pump and a few other small electronics with minimal draw. However, the 24V system allows me to cut down the amperage draw in half of what is needed to power the inverter at 12V.

https://shop.pkys.com/Victron-Energy...ut_p_1697.html
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Old 05-19-2019, 04:39 PM   #26
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So I got the chance to work on the solar rack this weekend. I had to weld in a few cross bars to give the slides something to mount to. After that, I brought it inside because it is getting so hot outside. This was pretty straight forward....

I also bought 16 3.2v 120ah LiFePo4 batteries this weekend. I am waiting for the balancer I ordered to get here and I will post again when I put the battery together.

This thing is wide!


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Old 05-19-2019, 04:42 PM   #27
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Wow that looks like a great setup... Iím enjoying following your build
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Old 05-19-2019, 05:16 PM   #28
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Beautiful!
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Old 05-20-2019, 11:46 AM   #29
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Nice work, maybe you should put this into production?
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Old 05-20-2019, 11:52 AM   #30
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is that skinny black wire I see in the expanded picture the power connection to that panel? it seems kinda under-gauge for a 280W panel, even at 24V thats like 12 amps or something.
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Old 05-20-2019, 12:39 PM   #31
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if you don't mind sharing the info, i'm curious what the batteries set you back and where you got them?
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Old 05-20-2019, 05:44 PM   #32
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Nice work, maybe you should put this into production?
I don't think anyone would want to pay even what I am paying to do this. Not to mention... Who knows if it will work?! lol

Its quite ridiculous and impractical. Lets say you could make a kit, the person installing it would still need to weld brackets to the trailer, get rid of the fan in the roof, modify their existing awing possibly, put new holes in the roof, get rid of pretty much all the factory wiring and electrical components... Just nonsense lol

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Originally Posted by John in Santa Cruz View Post
is that skinny black wire I see in the expanded picture the power connection to that panel? it seems kinda under-gauge for a 280W panel, even at 24V thats like 12 amps or something.
The main wires from the panels to the mppt charge controller don't need to be super big. Since the panels will be hooked up in series, they will only be carrying a max of <9 Amps. I plugged all three panels in on Sunday just to see how they performed and I was getting 107-108V in bright sun.

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if you don't mind sharing the info, i'm curious what the batteries set you back and where you got them?
The batteries were $110/each with tax and I bought them from a guy that is local to me but also sells the batteries on eBay. His seller name is "sir-watson".

https://www.ebay.com/usr/sir-watson?_trksid=p2047675.l2559

The batteries aren't cheap, but once you do the math on how many lead acid batteries you would need to match the USABLE power of LiFePo4, combined with the 4x lifespan, more efficient charging and discharging, and that they are 25%-35% the weight of lead acid, its really a no brainer.
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Old 05-20-2019, 05:59 PM   #33
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Made a pretty cool little battery holder when I got home after work today.

I used some angle aluminum and some square 3m double sided sticky things. I used two of the little squares pushed together on all four corners, and then left the cover on the sticker so it wouldn't be sticky. This give the battery cells about an 1/8th inch of air gap between them so they have better heat dissipation.

The rack allows me to put two banks of 8 batteries in series which makes 24V@100AH. I then can combine the two banks of batteries in parallel to get 24V@200Ah.

The other benefit is that I will be able to get two 8S (eight cell) battery balancers and hook them up to each bank separate from each other. With a battery disconnect between the two banks of batteries, I will be able to test and balance all the individual cells and monitor them.

Because LiFePo4 batteries are easily damaged by over and under charging, you want all of the cells to be as close as possible. This way when the battery reaches its maximum charge, you don't have some individual cells being overcharged. The same goes with discharging. If a few of the individual cells are less charged than the others, and the battery is drained way down, some of those cells may go beyond their maximum discharge voltage. This is why they say you should never really FULLY charge or FULLY discharge the batteries for maximum longevity.

In all honesty, just watch the videos that were posted to this thread, because there is a ton of valuable information in it that would take me way to long to type out.

And now for what you really wanted to see.. Pictures!


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Old 05-20-2019, 11:20 PM   #34
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I would add a pretty serious insulation layer between the top of the lower batts and the metal brackets above them that hold the upper row, so that if a battery comes unstuck on a hard bump it doesn't short... maybe a rectangle of plexiglas or lexan. actually, I would be thinking of some sort of non-conductive battery clamp to secure the batts, and not rely on double-stick tape, even VHB. campers get hot, they get cold, and they can really shake a lot on a bad road..
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Old 05-21-2019, 05:54 AM   #35
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I would add a pretty serious insulation layer between the top of the lower batts and the metal brackets above them that hold the upper row, so that if a battery comes unstuck on a hard bump it doesn't short... maybe a rectangle of plexiglas or lexan. actually, I would be thinking of some sort of non-conductive battery clamp to secure the batts, and not rely on double-stick tape, even VHB. campers get hot, they get cold, and they can really shake a lot on a bad road..
I thought the same thing once I put it all together. I made the battery trays pretty tight fitting so the batteries really don't move in the tray, but still...I was thinking about using some heavy duty Velcro to make straps that I could fasten to the trays to hold the batteries in. The double sided tape isn't there to do anything but space the batteries apart.

I also want to put some sort of rubber/plastic around the posts that hold up the second tray to avoid any possible shorts from the battery connections touching the posts.

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Old 05-21-2019, 08:54 AM   #36
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The batteries were $110/each with tax and I bought them from a guy that is local to me but also sells the batteries on eBay. His seller name is "sir-watson".

https://www.ebay.com/usr/sir-watson?_trksid=p2047675.l2559

The batteries aren't cheap, but once you do the math on how many lead acid batteries you would need to match the USABLE power of LiFePo4, combined with the 4x lifespan, more efficient charging and discharging, and that they are 25%-35% the weight of lead acid, its really a no brainer.[/QUOTE]

that's a good price on those batteries and i totally agree that they are the way to go. i built a solar system and took our residence off grid in 2014 and my one regret is using lead acid. also used lead acid on the solar system on our trailer. the maintenance is a pain. the one caution i hear on the lifepo4 systems is to make sure they're balanced well and check that periodically. also, for building 3v Li into a 24v system, i think you take the opposite approach as you do with lead acid, where you want to minimize parallel hook ups. i am looking forward to the day the batteries on my home and trailer systems go down and i will replace all with lifepo4, if that's still the best option. i love your project; you're doing some beautiful and creative work!
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Old 05-21-2019, 12:01 PM   #37
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[/QUOTE]

I watched part of the second video and, unless i misheard him, he gave some info i totally disagree with. he said that you can use a standard lead acid charge controller with these because the charge profile for lead acid and lithium is identical. not true at all! lead acid are brought through an absorption phase well above target (float) voltage and then maintained at float for the duration of charging. lifepo4 are brought up to target voltage (which is typically around 13-13.5V i believe), held there for a set period of time and then the charging is removed altogether until the next charge cycle is entered. you need a charge controller with lithium specific profile or one that can be programmed to achieve it.
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Old 05-27-2019, 08:07 PM   #38
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I watched part of the second video and, unless i misheard him, he gave some info i totally disagree with. he said that you can use a standard lead acid charge controller with these because the charge profile for lead acid and lithium is identical. not true at all! lead acid are brought through an absorption phase well above target (float) voltage and then maintained at float for the duration of charging. lifepo4 are brought up to target voltage (which is typically around 13-13.5V i believe), held there for a set period of time and then the charging is removed altogether until the next charge cycle is entered. you need a charge controller with lithium specific profile or one that can be programmed to achieve it.
If you are using a basic lead acid battery charger, then you would be correct. However, most chargers these days have different charge profiles that you can choose from with different set voltages. Then it would be a matter of finding the correct voltage for your battery and finding a setting that is at or below that voltage. While it may not be perfect, people have been charging LifePo4 batteries with lead acid charges for quite some time now with success. As long as they aren't being over charged, it shouldn't affect the battery life or damage them. Hence a good BMS.
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Old 06-01-2019, 05:02 PM   #39
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So I have been working on the battery system the past couple days when I have time. I also have been working on getting the camper ready to put back together.

So here is how far I have gotten. It's not yet complete, but close. I still need to put another battery selector under the MPPT charger so I can cut power to the batteries and also have the ability the charge the battery banks separate from one another just in case I might have to for some reason. I also need to put a 40 amp fuse in between the MPPT charger and the battery switch just in case. The 24v to 12v isn't fastened to the panel because I accidently fried it somehow and have to get a new one. Apparently the wiring directions are wrong for the the thermostat (cheap Chinese junk) and when I put power to them, they shorted out the step down. It is still under warranty and I should be able to get it replaced, but major time bummer.

The MPPT charger has a fan connected to the back of it on a thermostat so once it gets hot, the fan will come on and cool it. It is only .1amp so I'm not worried about the consumption. I also have another themostat that will be hooked up to a 4" ducted computer fan that will vent from the electrical compartment to the outside of the camper. I'm really trying to avoid a build up too much heat in the storage area.

The green LED shows amps being used. I am also putting a volt meter above the ammeter and going to put both of them on switches so they can be turned off when I'm not looking at it.

The two boxes are the BMS for the two banks of batteries. Though I will not be charging the batteries through these, it allows me to monitor the individual cells of each battery and also balance them when needed.

The little blue rectangular box is a battery protect. It will cut outgoing power from the batteries at a selected low and high voltage level. It will also sound the little black buzzer above it, which will let me know why the power has stopped.

All the connections are heavily insulated on this battery and the aluminum frame is not grounded. This way if the a positive leed does somehow touch the frame or panels, there is no short. Maybe someone can correct me if I'm wrong, but I think this would be considered a floating ground.

This whole thing is about the size of two Trojan 1275's and weighs about 90lbs. Pretty cool IMO.

One of the things I quickly realized while working on these lithium batteries is that they have a TON of short circuit power. Mistakes can actually hurt you pretty bad, even at 24V. When combined like these batteries are, they are capable of 700 amps at 24V in a short circuit situation. If you are going to do something like this, pay attention, take your time check everything twice and use appropriate size fuses.

Probably going to make a plexiglass top that bolts on to cover all the terminals on the top as well.
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Old 06-07-2019, 02:36 PM   #40
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Just wanted to give anyone a heads up if you are considering these batteries. This is very important to know....

The cells are case positive. If you wear through the blue shrink wrap on the outside of the battery cell, you will get a full positive voltage from the battery. In my case, I left a little ball of splatter from welding on the aluminum frame. That little ball of metal wore it's way through the outter blue layer on the battery eventually after moving the battery around a bunch and was energizing the whole battery chassis. I was getting 26+ volts from the negative terminal to the frame. I found out when I went to move the battery and was touching the ground terminal and chassis at the same time. Luckily it wasn't a very strong connection and could only feel tingling in my fingers, but that was enough to let me know something was wrong.

I sanded down the frame once more to make sure I got all the burs and splatter off of it. I then insulated the frame with some rubber tape that is used to seal in windows. It's thick enough to give some cushion and sticky enough not to come off. The batteries are really snug in there now.
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