Building a Portable Solar Battery Pack

GeoRoss

 
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I've been searching and reading a great deal on this, learning on-the-fly. I am likely clueless about many things too. I purchased an 80 qt Edgestar Scratch-N-Dent last year and took it on its first camping trip over Memorial Day. I am now sold on fridges by the way. I borrowed a friend's GoalZero Yeti 400 and 45W of panels to run it. I knew this wasn't ideal, but should suffice for 3 days and two nights in a single camp site. It did, but it was close. No way am I shelling out the money for a Yeti 1250 though. Time to build my own.

This is a work in progress and I've already asked some questions in other threads and thought I'd consolidate them here. The goal is to build an 80-100 Ah system that will run the fridge, LED lights and charge small devices while camping. We often set up camp some distance from the Land Cruiser so it need to be portable. I also want to be able to swap this between multiple vehicles, take to swim meets, etc. I'd like to just set it up and keep the fridge running constantly in the garage.

Soooo, here is what I have purchased so far based on CruiserDrew, george-tlc and others.

Renogy 100W suitcase

Morningstar Sun Saver 10

GT 130A Power Analyzer


The idea is to put it all in a single box using a sealed AGM deep cycle battery. I picked this up the other day as a maybe. It is a MTM Dry Box Spud 7



I'm considering some Dewalt/Rigid resin tool boxes as well.

I found these other watt meter/battery minders. I ordered two of them. I bought the 100A and I think that was a mistake. It has a rather large current shunt. They have a 20A version that contains an internal shunt. I don't think my system will ever go over 10A of current. I wish the voltmeter when down lower for analyzing the solar efficiency.

Bayite DC 6.5-100V, 0-100A Digital Current-Voltage-Power Multimeter



I'll use SB50 connector for the fridge, a cig lighter and dual USB port. That should cover all my needs and can be upgraded. Mount the plugs, switches and monitors in the little top compartment. I'll add some sort of plastic/resin shelf to isolate the battery from the main wiring. I'm hoping to avoid too many holes in the box itself. The rest I'm trying to figure out. I'm OK on wire size and connectors. I do have some questions.

1. How much ventilation will I need for the charge controller? Mount it at the top of the box and prop the lid open while charging? Have a separate small box like CruiserDrew?



2. Should I run the load through the charge controller? Does running loads directly off the battery while solar charging do hinky things to the charging algorithm?

3. Can I set up an AC trickle charger that runs through the Morningstar charge controller? Say a DC 12V-6A power supply?

4. System isolation switch. Do I need to use some big old battery isolated switch rated to a brazzillion amps? Since this is such a low amp set up I was thinking a simple SPST 10-20A switch with a 10-20A breaker would suffice.

5. What is acceptable voltage drop in the wiring from the panels to the charge controller? I was hoping to have one length of cables 40ft long. 8awg will have about 2.5% drop at 12V.

I'm sure I'll have many more questions.
 
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Cruiserdrew

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GT 130A Power Analyzer






1. How much ventilation will I need for the charge controller? Mount it at the top of the box and prop the lid open while charging? Have a separate small box like CruiserDrew?


2. Should I run the load through the charge controller? Does running loads directly off the battery while solar charging do hinky things to the charging algorithm?

3. Can I set up an AC trickle charger that runs through the Morningstar charge controller? Say a DC 12V-6A power supply?

4. System isolation switch. Do I need to use some big old battery isolated switch rated to a brazzillion amps? Since this is such a low amp set up I was thinking a simple SPST 10-20A switch with a 10-20A breaker would suffice.

5. What is acceptable voltage drop in the wiring from the panels to the charge controller? I was hoping to have one length of cables 40ft long. 8awg will have about 2.5% drop at 12V.

I'm sure I'll have many more questions.
1-A PWM charge controller doesn't generate much heat. It needs some ambient air circulation but it doesn't get hot like an MPPT controller. The Morningstar is a very good controller for small $$.

2-No. Run off your battery and let the controller do it's thing. If you take the voltage down below whatever, it will drop back into bulk charge and you're getting the maximum it can do. THe "Load" terminals on your charge controller are for powering stuff like street lights and signs. You can ignore it.

3-No, don't do this. Go direct to the battery. It won't mess with the charge controller.

4-No. Keep the batteries separate or combined, however you like. I think the best way is with a voltage sensing relay, and the Blue Sea ACRs are great voltage sensing relays.

5-10 gauge will be ok, and 8 even better. You won't really have any voltage drop-all your resistance losses will be manifested as current loss which you won't really notice. Remember voltage drop is dependent on current flow. So no current (ie full batteries) no voltage drop. Your batteries will still come up to full charge, just marginally slower with smaller wire. But 12 ga can easily handle the 5 amps of a 100 watt panel. Don't sweat this, it's an overblown problem. Do mount your charge controller near your battery.


Assuming you're only going with a 100 watt system (which is enough 99% of the time), even 12 ga wiring will be sufficient. I've used inexpensive low voltage cord, speaker wire, extension cords, and Marine duplex. The low voltage wire from Home depot is good and it's cheap. That would be my first recommendation. It's helpful to have a bunch of cord lengths and ways to hook it all together on the fly.

The first time you use it in the real world, it's immediately clear. Free, quiet, battery charging with no running of the motor. Cold beer all the time. Full batteries every day at dark. What's not to like?
 

GeoRoss

 
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1-A PWM charge controller doesn't generate much heat. It needs some ambient air circulation but it doesn't get hot like an MPPT controller. The Morningstar is a very good controller for small $$.

2-No. Run off your battery and let the controller do it's thing. If you take the voltage down below whatever, it will drop back into bulk charge and you're getting the maximum it can do. THe "Load" terminals on your charge controller are for powering stuff like street lights and signs. You can ignore it.

3-No, don't do this. Go direct to the battery. It won't mess with the charge controller.

4-No. Keep the batteries separate or combined, however you like. I think the best way is with a voltage sensing relay, and the Blue Sea ACRs are great voltage sensing relays.

5-10 gauge will be ok, and 8 even better. You won't really have any voltage drop-all your resistance losses will be manifested as current loss which you won't really notice. Remember voltage drop is dependent on current flow. So no current (ie full batteries) no voltage drop. Your batteries will still come up to full charge, just marginally slower with smaller wire. But 12 ga can easily handle the 5 amps of a 100 watt panel. Don't sweat this, it's an overblown problem. Do mount your charge controller near your battery.


Assuming you're only going with a 100 watt system (which is enough 99% of the time), even 12 ga wiring will be sufficient. I've used inexpensive low voltage cord, speaker wire, extension cords, and Marine duplex. The low voltage wire from Home depot is good and it's cheap. That would be my first recommendation. It's helpful to have a bunch of cord lengths and ways to hook it all together on the fly.

The first time you use it in the real world, it's immediately clear. Free, quiet, battery charging with no running of the motor. Cold beer all the time. Full batteries every day at dark. What's not to like?

Thank you for the reply! I will probably stay at 100W. I'm really just down to picking out a battery, a few breakers/fuses and the outlets. One thing I'm trying to decide about is a power distribution/fuse box vs just in-line fuses wired from the battery. The fuse box is cleaner, but I'll only have 3 or 4 outputs. I'll probably go with a fuse box.
 

GeoRoss

 
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I built version 1.0 yesterday. I finished late so didn't get to check it until today. I needed to get something quick as I'm going to be working at an off grid work site for the next couple of weeks. It is only wired to run the fridge right now.

I went with 12 AWG outdoor landscape wire with SAE connectors for the solar to controller, 25'. I fused it close to the panel. I don't have any 20A fuses, so I put in a 15A for testing.

I can't find a box to make a completely integrated battery/controller box that doesn't have a lot of wasted space. I have found that a 30mm ammo can that could work, but it is heavy. I may just use this marine battery box and have a separate box for the charge controller and outputs. It will make packing a little easier.

I only wired in one of the Bayite power analyzers to monitor the solar. It seems to be working. I have a GT Power Analyzer that I can through in to check out the numbers. So far no fires or explosions!

The complete unit with a 100Ah deep cycle battery.


When it was cloudy.


With the sun out. I do prop the tool tray up for ventilation.


I made some rookie mistakes, like not offsetting butt connectors that I will fix on version 2.0. I could have wired it so the all the fuses are in their respective boxes too. I used Anderson PowerPole connectors to connect the final legs of the solar and the battery to the charger. I have a nice ratcheting crimper, but I had to massage the crimps to click into the housings. I hate to invest in a power pole crimper, but I may do it.

I have a second Bayite power analyzer. I haven't decided if I will use it monitor battery charging or the load. I'm thinking a simple volt meter will suffice for the battery. I do have the GT power analyzer that I can use for that too. Version 2.0 will get the fuse box and the multiple outputs. It will be neat to see how it works out over the next two weeks.


R
 

Jakes40

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I am looking to do a similar thing for me 45qt Edgestar fridge but mine will be more of a perminant install. And looking at 80watt solar panel with 2 65Ahr batteries. I have the setup now in my tow rig without the solar panel and it works ok but have to start the tow rig in the morning and at night when I get off the trail.
 

GeoRoss

 
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I am looking to do a similar thing for me 45qt Edgestar fridge but mine will be more of a perminant install. And looking at 80watt solar panel with 2 65Ahr batteries. I have the setup now in my tow rig without the solar panel and it works ok but have to start the tow rig in the morning and at night when I get off the trail.
It is pretty simple to do. Good luck!
 

GeoRoss

 
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Well, the 7 day test was a tremendous success. Day time temps where in the 90's and lows int eh 60's. I was only getting good sun for about 2/3's of the day and my overnight voltage never dipped below 13.3V. I know that this isn't a super accurate way to asses a battery that is under charge/load, but I am very happy. The power analyzer I put in the box did a great job that I could confirm its accuracy with the GT power analyzer. I will use my second Bayite to monitor battery loads. I will also incorporate a dedicated voltmeter to the battery box with a momentary switch. I do need to build a more versatile power distribution box. Charging devices proved challenging when you forget to bring any AC chargers. I wish I could integrate everything into a single box for the sole reason of one less thing to move around. I was working at an off-grid job site and had to move the fridge multiple times a day to keep the fridge out of the rain or out of the way of the only sheltered spot where I was working. Not really a big deal just a convenience thing. I do need to fashion a "transit" bag. Taking the tarp off every time I wanted something is an unnecessary step.

The reason I was up there was to trouble shoot a 1.2 kW solar system (4 285W PVs) with a 440Ah battery bank. I am pretty unqualified to do this, but hey I thought I might learn something. I sure did. I also ended up having to rewiring all the AC circuits. This was really fun. I had to rewire the panels and to bring down the cold temp V. The designer sent 10 A breakers for the the 4 285W solar panels. Needless to say the breakers would trip in full sun. I called them and they said it was a mistake and they have 15 A breakers for me. I asked why not just use 30 A breakers as it is all 10 AWG wiring and the inverter/charge controller can handle 60 A. No answer on that yet. I had one "scare" while I was rewiring the panels. A big gust blew all the cardboard I had used to cover the panels while wiring them. I'm glad I was wearing leather gloves. Lesson learned, use more tape.

The manufacture sent two nearly identical energizing instructions. At a glance they didn't look different. I had a 50-50 chance to choose the right one. I chose poorly. It took a few phone calls to clear up the instructions, but I got the system working. It was much nicer using the solar rather than the generator. I think I learned enough that I feel comfortable to do the solar installation in my house. Even hooking up to the grid would not be a problem, though I'll let my licensed electrician friend do it and the permits. I can't tell you how exciting it was to get this thing working.

I head back up on Friday to do the plumbing for a pressure tank, solar water heater, shower and sink. I will not miss the solar shower bags. This is turning into some of my funnest vacation time ever.
 

Jakes40

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It is pretty simple to do. Good luck!
I'm waiting for a watt meter to size my solar panel. I would like to make the panel as well so I can make it to fit in my tow rig for travel. Found a couple of kits on eBay for80- 100w kits.
 

Cruiserdrew

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Well, the 7 day test was a tremendous success. Day time temps where in the 90's and lows int eh 60's. I was only getting good sun for about 2/3's of the day and my overnight voltage never dipped below 13.3V. I know that this isn't a super accurate way to asses a battery that is under charge/load, but I am very happy. .

I'm thinking you meant to say 12.3 volts? If it was really 13.3 volts, I want your batteries!

It sounds like you had some nice success with your system.
 

GeoRoss

 
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I'm thinking you meant to say 12.3 volts? If it was really 13.3 volts, I want your batteries!

It sounds like you had some nice success with your system.
:lol:

I was checking the battery voltage by plugging in the GT Power Analyzer. When I get back up there later this week I'll put a meter on the battery. I can't say enough positive things about this system, which is based largely on your advice. :cheers:
 

Cruiserdrew

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Got it. Those GT power analyzers are optimistic in a lot of ways. My voltage always reads high. I installed volt meters inside the truck and on the charge controller to keep it grounded (sic) in reality.

I think the watt meters are great for measuring loads and monitoring charging status, just don't put too much faith in the absolute numbers.

Even a small solar "system" adds a lot to your camping experience and capability if you have a refrigerator. It totally solves the "can I sit here for 3 days" question.
 

GeoRoss

 
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I started putting a voltmeter on the battery in the morning. It ranged between 12.65 and 12.7 every morning. The GT power analyzers are handy, but inaccurate. I'll be wiring in a voltmeter into the battery box with a momentary switch. The Bayite power analyzer is much more accurate. It usually just over reads the volts by about 0.3V instead of the 1.0V of the GT unit. I have to say I love this set up.
 

GeoRoss

 
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Time for an update.

I've done nothing but get a new box for the battery, another 20ft panel extension cord and some better wiring for the fridge. ;)

I have done some more testing. I have a huge 80qt Edgestar. I decided to test the system with the fridge in the Land Cruiser here during a Tucson summer. Land Cruiser under a shade cloth, daily highs >100˚ and overnight lows in the low 80˚s, interior of the Land Cruiser doors and windows shut was often around 120˚ inside and the fridge empty. The 100A AGM battery, 100W Renology folding panel and 20A Morningstar PWM controller could not keep up even with the panels pushing almost 6 amps most of the day. Every morning I'd find the battery at around 12.1V or lower. I could barely get the battery back to float every day. I'm not really surprised as it is hot and the Edgestar is not very efficient. So I think desert summer camping will need a little more work.

I finally went on a mountain camping trip where we moved fairly often. I've been worried about this sort of trip from the beginning as my aux battery is only charged by my folding panels and so is not charging while driving. I can run the fridge from my starting battery while driving, but I was a bit curious about how it would fair when moving camp every few days. Camped at over 9000ft for about 10 days with highs in the 70's and lows in the 50's. Most mornings the aux battery would be at about 12.4-12.5V.I found that if I can catch the early morning sun the battery will go to float charge in about an hour. It didn't even need to be direct sunlight, maybe putting in 1A. Days of rain and overcast conditions and it never failed. The aux battery would go to float faster than I thought possible. This is more than enough time as breakfast and packing takes us more than hour. Catch a couple of hours of solar in the afternoon at the next camp site was just icing on the cake.

I am really impressed with this Morningstar and 100W folding Renology panel. Although it works, I will integrate some way to charge the aux battery while driving for peace of mind.
 

e9999

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some criticism of the "GT Power" wattmeters up there... Well, mine (one actual GT power, one clone) both read only 20 mV low around 13.3V and are only 30mA low at around 1A and better above that (and worse below). In comparison with good Flukes. So, not that bad for the price actually.
 

Cruiserdrew

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I agree with @GeoRoss that an integrated system is the way. That way, not only is your Aux charged, but even your main starting battery gets topped a bit every day the system is on. Charging while driving is good too, for instance what if it rains or you park in the shade?

I'm just back from Rubithon, I'd say the majority of trucks I saw are doing some sort of solar, and I'd say that with a fridge, and a stay overy 1 day, it's basically mandatory. Now I want to see good panels get lighter, and not give up the robust strength of a traditional panel.
 
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