Feedback for My DIY Solar Generator Project

KurtA81

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Hello DIY Solar Forum Members,

Thank you for starting to read my post! I’ve begun designing my first system which is meant to be a small(ish) solar generator for camping. I’ve been reading (Will’s book included), reviewing forum information, planning my build and sourcing parts. This post is meant to publish my design in hopes of receiving honest feedback on any potential design flaws and best practices. Although I have no electrical background and I am a victim of the Arizona education system, I did stay at a Holiday Inn Express last night and feel that I’ve prepared myself for this endeavor.

First, a listing of the capabilities sought with rationale for specific component selection:
  • -Price. Guess this is an obvious one, I didn’t want to buy a unit (Jackery, GoalZero) which I thought would have a higher cost, provide less longevity and lack modular features for maintenance and future improvement.
  • -Weight. I wanted to keep total weight below 50lbs while maintaining high durability which led me towards 60ah LiFePo4 prismatic batteries.
  • -12v DC. Based on the devices we use, a marine-style 12v accessory 4 slot panel should answer the mail. I want to run a 12v fridge which led me to add the voltage regular to the schematic.
  • -AC Power. Right now we don’t have a regular need for AC power but I wanted to over build this set up. I feel a 700w inverter is sized right for this battery set (4s, 12v 60ah LiFePo4)
  • -AC Charging. While in storage I would like to have the batteries maintained by a small (3-5a) charger specific for LiFePo4 chemistries.
  • -Solar Charging. My calculations indicate a 100w 12v array feeding a 20a MPPT charger will be sufficient for the battery capacity previously indicted. I may cheap out and get a PWM charger but welcome feedback about any future pitfalls from such a decision. The unit will not be under constant load and 5-8a of current would be sufficient under most conceivable circumstances.
  • -Self Cooling. I want to build in a small fan with temperature switch.
  • -Internal light. Guess that speaks for itself….
  • -Battery monitor (shunt). I feel this provides the best bang for the buck without having to shell out for something like a Victron unit.
Ok, so hear is the schematic….

1591854126023.png



Lastly, the stages to my plan.

1) Source and build battery. The battery back will have at least a basic BMS (Daly). I do not anticipate using the generator in temperatures below 0C and for now won't include low temperature disconnect.
2)Assemble components. Amazon and Aliexpress will be my primary sources. The cells from Spirit Energy have my eye as you can get the 4s 12v 60ah cells without BMS for $250 and 5yr warranty (I’m not affiliated with Spirit).
3) Assemble generator.
4)Test.

Wow, if you are still reading at this point then I say a big THANKS! For those who took the time to provide feedback know that it is most appreciated. I intend to buy the batteries this weekend. I was going to include all my source links for feedback but based on forum rules relating to affiliate links, I thought it best leave them out.

I look forward to hearing from anyone who will respond. Have a great day!
 

Bob142

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Welcome to the forum and the DIY solar generator club! Here are my initial thoughts on your plan:

Overall I like the idea and it looks like you've done a bunch of homework and planning. Nice job on the diagram, it really helps these discussions.

Some specific points:
I did stay at a Holiday Inn Express last night
Always a good start.

AC Charging. While in storage I would like to have the batteries maintained by a small (3-5a) charger specific for LiFePo4 chemistries.
LiFePO4 has a very slow self-discharge rate so you don’t need to maintain with a trickle or float charge like lead acid batteries. When not in use you can just leave it disconnected and ignore it. If you are going to store it for a long time it’s recommended that you do not store it at 100% state of charge (SoC).

That said, having an AC charger is always a good idea if you've got access to the grid or a generator.

Solar Charging. My calculations indicate a 100w 12v array feeding a 20a MPPT charger will be sufficient for the battery capacity previously indicted.
You may want to budget for 200W of panels if you want to be able to recharge your power station in a single day. For example, if you use a bunch of the capacity overnight and are using it while charging during the day 100W may not cut it. Although if you’re in Arizona and you manually track the sun during the day maybe you’re good with 100W. I wouldn’t be able to pull that off in Rhode Island. This one is easy though: you try it with a single panel and if it doesn’t do what you need, you buy a second panel down the road.

I may cheap out and get a PWM charger but welcome feedback about any future pitfalls from such a decision.
I suspect you’ve done the research and understand that you’d leave some power on the table by going PWM vs MPPT. If that’s what your budget supports, there are no real future pitfalls in that decision. You can swap it for MPPT later if you find the PWM is insufficient. Just make sure your enclosure is big enough to support that upgrade! You’d also need to run panels in parallel rather than series if you stick with PWM and go with more than a single panel. Not a big deal or budget buster to get MC4 branch connectors.

Battery monitor (shunt). I feel this provides the best bang for the buck without having to shell out for something like a Victron unit.
Good plan. I use the budget monitors and they work well for me.

Ok, so hear is the schematic….
1) I have some concerns about your wire gauges and fusing.
  • I prefer each wire to be individually fused. (You have two wires coming out of a single fuse in the top left.) There’s a good presentation on fusing in the Resources section that another member put together. You may find it helpful: Fuse and Breaker Sizing and Placement.

  • 10 AWG is too small for a 700W 12V inverter. Even if it’s 90% efficient you’d pull about 65A at full load. Check ampacity charts for appropriate wire sizes for your build and consult all of the product manuals to see what they recommend for wire size and fusing. The Resources section also has several good references in the Planning and Sizing Tools category for determining appropriate wire sizes.

    When you sort out the proper wire size, I suggest buying welding cable. It's super flexible so it makes wiring easier in the tight spaces of a portable system.

  • Don’t forget to fuse the tiny power wire to the shunt monitor. I didn’t on one build, and it came loose and shorted on the shunt. Pretty good way to melt the tiny wire and see some smoke. Fusing that wire protects you from faults, including self-inflicted bad connections…
2) You may want to consider a master on/off switch, or individual switches to turn things like the solar charge controller (SCC) off for when the unit is in storage so you don't deplete the battery.

I was going to include all my source links for feedback but based on forum rules relating to affiliate links, I thought it best leave them out.
It would be helpful if you listed out your components so people can weigh in with feedback on them. We can look them up on our own if you give us manufacturer and models etc.

Wow, if you are still reading at this point then I say a big THANKS!
Right back at ya.

I hope this is helpful and I look forward to seeing your progress on this.
 

KurtA81

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Jun 10, 2020
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Hello Bob,

Thanks for the feedback. Below I have some responses and my list of components. If you or other have more time, I'd welcome continued comments to help me get closer to the mark.

-AC-DC Charger: I think I'll add external posts to make this a possibility. I understand there would be a variety of uses for external posts, aside from connecting a wall charger.
-Panneling: 200w array sounds like a good idea. But space is at a premium so maybe I'll set-up the system to allow for such expansion. 200w at 12v would still be within the limits of a 20a solar charger. But, at that wattage it would make most sense to install an MPPT unit to maximize my production. Which leads me to the following point....
-Solar Charger: from a cost standpoint, I'd be served better buy getting an extra panel vice spending more on an MPPT charger. But, as you have said, I will leave a lot of power on the table. I'll also need to buy a larger box which will already contain bulky items like an inverter and battery pack. Why not spend more? I'll probably get the MPPT.
-Wiring and fusing. Thank you for these comments. I will increase 12ga wires to 10ga and 10ga to 8ga. Do you believe it best to individually fuse wires vice use a fuse block? I didn't think I needed to have an inline fuse going to my fuse block which led me to run the fuse block and solar charge controller off the single 30a fuse. I'll take a look at those resources mentioned to better educate myself. I will also add a master switch to my schematic and post below. I will also fuse the "tiny" positive wire to the shunt.

Here are my parts candidates:
Battery
Spirit Energy 12v 60ah LiFePo4 4s battery. Seems to be my best cost-effective option with warranty (5yrs). Not UL listed. Will need me to add a BMS. Not a well known supplier.

Seller with good history on Ebay. More expensive than the above but still cost effective and would include a simple BMS. Warranty is shorter (1yr). Would require wiring in parallel and may necessitate some changes to fusing and wires selected.

Inverter

I feel this is one of many good options. Its an Amazon preferred seller which would provide me some protection if there were an issue. Ad claims 18mo warranty. I don't see a need for more than 700w AC.

Solar Panel

I've seen the reviews and it seems Rich Solar glass poly panels are the best bang for the buck. I want something durable, will be deploying the array (panel) from the ground and didn't want the limited life of a flexible panel.

Solar Charge Controller

I know there are a lot of opinions but I feel you can't go wrong with Renogy. This unit allows for low temperature disconnect, Bluetooth monitoring an 30a charging (I know I have discussed a 20a charger previously🤷‍♂️). I would prefer a unit with a simple display as I don't feel I need Bluetooth or to monitor charging via my phone.

This unit would be almost too much but allows for future expansion. I know their computer interface is...difficult. But the remote screen is reviewed to be quite useful. If I components to the Renogy 30a PWM unit (temp sensor, Bluetooth module) then the cost is nearly the same as this listing. But, it will certainly eat up some space. This may be the best move if I go with the two 35ah batteries in parallel.

BMS

I've seen a lot mentioned about DALY units and gravitated this direction. Looking at the parts list again, I seem to have overlooked the need to build the balance leads. Am I missing something? I don't know if I am up for that which may lead me to choose a battery pack with built in BMS.

Battery Monitory with Shunt

This one appears to provide all I would ever want. Seems to be a little learning curve in programming but I feel I could make it work.

12v Marine Accessory Panel

I believe these products to be a dime a dozen but if some one knows of a better option, I'm all ears. I will wire in the voltage regulator to the 12v outlet on this panel.

Voltage Regulator

I selected this item as I read that a regulated 12v outlet is best for a 12v fridge.

AC Outlets

These options seem a dime a dozen. I wanted something that would be easy to secure to my box with external access as well as a device meant for outdoor use. I would plug directly to the inverter.

DC Cooling Fan

Another item with a myriad of options. I would want to mount this to an opening cut in to my box. I will also mount vents on the opposite of the box to maximize airflow

Vents

These seem simple and appropriate.

Temperature Switch


Both options seem to have similar functionality. I don't know if I could go wrong with one or the other.

Fuse Block

One of many options.

Negative Buss Bar

One of many options

Master Switch

https://www.amazon.com/UTSAUTO-Batt...-Disconnect-Vehicles/dp/B071D55VM3/ref=sr_1_9
Second link seems to be most simple and comes with a key!

ACtoDC LiFePo4 Charger

https://www.amazon.com/gp/product/B07VL7N3SX/ref=ox_sc_mini_detail
This seems like a sensible option.

Here is my updated schematic.
1591940088828.png
 
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KurtA81

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forgot to mention, I am not affiliated with or receive any incentives from any of the above-mentioned suppliers.
 

Bob142

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-AC-DC Charger: I think I'll add external posts to make this a possibility. I understand there would be a variety of uses for external posts, aside from connecting a wall charger.
Maybe take a look at the various Anderson Powerpole or SB connectors for providing higher amp DC connections to the battery. I find them very useful.

-Solar Charger: from a cost standpoint, I'd be served better buy getting an extra panel vice spending more on an MPPT charger. But, as you have said, I will leave a lot of power on the table. I'll also need to buy a larger box which will already contain bulky items like an inverter and battery pack. Why not spend more? I'll probably get the MPPT.
Two panels in parallel and the PWM will definitely deliver more charging power than a single panel and an MPPT for about the same money. So I agree with you that you get more bang for the buck going that way. But if you can swing the MPPT and two panels, maybe have a look at the smaller Victron SCCs. For example the Victron SmartSolar 75/15 is not that much more expensive than the Epever you listed. It's higher quality, smaller, has built-in Bluetooth, and will handle the 200W of solar. Maybe gives you the best of both worlds: MPPT in a small package.

-Wiring and fusing. Thank you for these comments. I will increase 12ga wires to 10ga and 10ga to 8ga. Do you believe it best to individually fuse wires vice use a fuse block? I didn't think I needed to have an inline fuse going to my fuse block which led me to run the fuse block and solar charge controller off the single 30a fuse. I'll take a look at those resources mentioned to better educate myself.
You're still too small on the inverter wire, so definitely take a look at the wire sizing resources before hooking that up.

The fuse block is a great way to have an individual fuse for each wire.

Here are my parts candidates:
Your parts choices look reasonable as far as I can tell.

The Giandel inverter seems like a good choice. I just picked up a couple of the 300W models and they appear well-built. Will rates them highly and has been running his solar shed AC off of one non-stop for a while.

Many of the Daly BMS listings I've seen look like they come with the balance leads. So you should be able to get one without having to build them yourself.
 

KurtA81

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Thank you sir. That really helps. My last decision seems to center around using shunts with a solar charge controller that has similar battery monitoring functions. As I’ve done my research It seems redundant to have both. I’m gonna call avivaron and Epever to get their feedback. Thanks again for all your time
 

Dzl

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Thank you sir. That really helps. My last decision seems to center around using shunts with a solar charge controller that has similar battery monitoring functions. As I’ve done my research It seems redundant to have both. I’m gonna call avivaron and Epever to get their feedback. Thanks again for all your time

What charge controllers have similar monitoring capabilities to a shunt based monitor?

I've never looked into it, but my assumption is that most charge controllers monitor voltage, but cannot measure SOC accurately (at least with lifepo4 batteries) because they do not have the capability to measure current or energy in/out of the battery.
 

deckeda

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My first post ... I’m drawn to several of the ideas here for a small, high performance system to run a few things.

Kurt, did you wind up building this?
 

rin67630

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IMHO considering you have a 12V 100W panel, that would probably never deliver more than 7 A, I consider the rest to be overkill.
The 100A shunt is ways too large.
Most of the 20A and above solar regulators do not really care about their own consumption.
You will end up having more energy wasted in the standby of the regulation electronics, then what you will really use operatively.

If I where you, if you already have purchased all the stuff, go for at least for two additional 100W panels and a second battery, so your components are half way balanced. Do not forget: a 100W solar panel pretty never delivers 100W and deliver its maximum only for a few hours under ideal conditions. On a cloudy/rainy day you can found your self being lucky if you get 5W out of it.

I would not connect directly the load to the battery.
Most serious solar regulators have a load output and will disconnect the load just before deep discharging the battery, which is frequently a dead sentence for the battery.
 

KurtA81

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Rin67630,

that’s good feedback. The 100a shunt had been a recommendation based on what the700w inverter would draw including losses for efficiency. Others have said it’s better the shiny be a bit large than a bit small.

deckeda,

I did not build the system, unfortunately. a fatal flaw my plan was to design the system before evaluating the costs. Based on my own research, I would not have been able to build the system for under $600. I then compared my current needs and went with a Bluetti unit because it’s size fit what we require camping. I tables the project but want to come back to it. I’ll continue to keep track of feedback from others
 

deckeda

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"I then compared my current needs and went with ..."

I get it, I really do. I did a rough evaluation of what few things I know we want to power and what that would require power-wise. Trouble is, the # of days estimate, which instantly doubles (or more) the battery bank requirement automatically dictates you have experience with what you "truly" need. And we don't camp or whatever enough to really know. We're not yet ready to build a system of over-capacity, which is kinda how I see solar in general unless you like disappointments.

I'm super tempted to just buy a small solar generator and learn where the nexus actually is between need vs. would-never-probably-use. Not enough power and/or reserve? It'll have a handle to let you repurpose it elsewhere, or sell it. That's not something a suitcase or hand-truck system will really let you do.
 
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