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Old 09-24-2020, 12:38 AM   #1
Mini-Skoolie
 
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Electrical System Run-down

So I have finally pinned down the major components of my bus' solar/electrical system and want to run it by the board to poke holes and make sure I havn't overlooked anything big. I'm also specifically wondering how compatible the AC charge function of the inverter/charger is with my particular battery set-up.

I plan to mount 8, 380w (3,040w) panels all wired in parallel. These panels have an IMPP of 9.4A (75.2A) and a VOC of 49v. They'll run through an Epever 80A MPPT controller into 2, 24v BYD Lifepo batteries rated at 3.5kwh/170ah wired in parallel as well. The batteries have a max charge/discharge rate of 130A. The battery bank will power an AIMS 3000w 24v-120v inverter/charger that has a charge rate of 40A. Is all my sizing correct and compatible? My specific question on the inverter/charger is whether or not the 40A will be sufficient for my batteries? I'm not sure why it wouldn't but it's nearly half the current that would be coming from the MPPT.

This system will be installed into a full skoolie conversion that I plan to mostly boondock in, with the occasional shore power hook up and with plans to potentially install a generator down the road. I do plan to include all the necessary safety components, to pull 12v through a converter, as well as wiring in an isolator switch. I'm not exactly sure on what my usage will require but it will be as much as I can get away with. Here are links to the components' datasheets:
https://s3.amazonaws.com/ecodirect_d...0W-72+Cell.pdf
https://www.epsolarpv.com/upload/fil...A%EF%BC%89.pdf
https://www.aimscorp.net/documents/P...w%20071618.pdf

Thanks for taking the time to read and any input is much appreciated.

Thanks
TJ
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Old 09-24-2020, 02:52 AM   #2
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Your numbers seem workable. Without knowing your load requirements, it is hard to say if you have sufficient battery storage. An energy audit would be most helpful.

Note: At FULL inverter output, you will have about 2 hours of runtime ... neglecting any current provided by the solar panels. So, figure this number as a full output nighttime worst case scenario. At full output from your solar panels (72A) and full load on the inverter (125A), you will use 53A from your batteries per hour. If you use the batteries down to 10% SOC, you have 333 Ah or 6.28 hours of runtime before your batteries are used up. I suppose the moral of this story is do not run the inverter at full load for that long. At 50% inverter load (1500 W), your solar should be able to supply the current needed without discharge of the batteries .... and have a little left over for charging the batteries.
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Old 09-24-2020, 04:12 PM   #3
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Solar:
  1. You are aware you will be overpaneled by 1.5x (~120A max solar input, 80A MPPT output). This is not an issue if your controller can handle it (the Epever manual will tell you, there is a table for it), and in some situations its desirable, but just be aware you will be leaving upto a kilowatt on the table during peak conditions. A 100, to 120A controller or 2 x 60A controllers would be a better fit.
  2. If you wire more than 2 panels in parallel, make sure each panel is individually fused.
  3. Consider wiring your panels in 4 sets of series pairs (2S4P) if you look in your manual I believe this is what is recommended for optimum performance.
Inverter / Charger:

  1. Does your aims inverter charger have a LiFePO4 charge profile? and a low voltage disconnect that works with LFP (11V or higher ideally)
  2. The 40A charge rate is fine.
"Isolator Switch":
  1. If I understand what you are referring to here: You can't/shouldn't use a simple isolator switch designed for lead acid batteries between your LFP house bank and your starting battery/alternator. This could kill your alternator and potentially damage your batteries. You need a "dc-dc charger" (also called battery to battery charger). Victron, Sterling Power, and Renogy make them.
  2. edit: Its possible I'm misunderstanding what you mean by isolator switch, and you are just referring to a manual disconnect switch.
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Old 09-24-2020, 04:12 PM   #4
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Thanks for the insight. I worked the process backwards a bit, I started with trying to get the most power out of the most I can spend comfortably. I have three or four must haves for usage: lights, device charging, cold food storage, and A/C. The two big consumers and the rest that I hope to include I'm pretty flexible with and havn't purchased yet. The A/C I'm leaning towards claims a continuous input of 660w. A small refrigerator I'd expect to be in the same ballpark.
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Old 09-24-2020, 05:41 PM   #5
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Quote:
Originally Posted by Tjurgensen View Post
Thanks for the insight. I worked the process backwards a bit, I started with trying to get the most power out of the most I can spend comfortably. I have three or four must haves for usage: lights, device charging, cold food storage, and A/C. The two big consumers and the rest that I hope to include I'm pretty flexible with and havn't purchased yet. The A/C I'm leaning towards claims a continuous input of 660w. A small refrigerator I'd expect to be in the same ballpark.

Your fridge should use much less than this hopefully.


Also FYI I edited my previous comment.
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Old 10-12-2020, 04:01 PM   #6
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Quote:
Originally Posted by dzl_ View Post
Also FYI I edited my previous comment.
Solar: I was aware that I was over paneling but didn't understand it fully when I originally posted. The 2S4P configuration does make more sense. If I went that route I would only need to fuse each pair in parallel and not necessarily the series connections correct?

"Isolator Switch": Oh no, you understood me correctly. Thanks for the correction. The DC-DC charger will likely be something I add down the road.

Oh and my Inverter is indeed suited for charging LiFePO4, I just hadn't read completely through the manual
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Old 10-12-2020, 06:28 PM   #7
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Quote:
Originally Posted by Tjurgensen View Post
Solar: I was aware that I was over paneling but didn't understand it fully when I originally posted. The 2S4P configuration does make more sense. If I went that route I would only need to fuse each pair in parallel and not necessarily the series connections correct?

Correct I think. From the POV of fusing, series connected panels can be viewed as a single entity, one fuse per string


Quote:
Originally Posted by Tjurgensen View Post
"Isolator Switch": Oh no, you understood me correctly. Thanks for the correction. The DC-DC charger will likely be something I add down the road.

I am not an expert here, but based on my research, if you charge from the alternator without a DC-DC charger or external regulator (more expensive but a good option), you risk damage to the alternator and possibly also the batteries, but more likely the alternator. So based on my limited knowledge, I wouldn't recommend charging from the alternator and adding dc-dc charger later. I would say don't charge lithium from the alternator at all before you have a safe way to do so.



Quote:
Originally Posted by Tjurgensen View Post
Oh and my Inverter is indeed suited for charging LiFePO4, I just hadn't read completely through the manual

Good news! That will simplify some things.
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