Changing to daylight

This week I started working daylight, 4x10 hour days. This is a big change after nearly 5 years of night shift. Instead of getting off work and going directly to bed, I'm getting off work and having hours to kill before sleep. Then I get up shortly before going into work.

How does this affect a van dweller like me? First off, I'm getting off work as the sun is preparing to set. I still have the heat  from the day in the van, but hopefully on the downward slope. I might have to run the generator and air conditioner a bit in the beginning to get things cooled down. Then it should continue to cool during the night. I won't have to sleep through the daylight seeping into the van. Ultimately, it will definitely help during spring and summer. During the winter.. hopefully it won't get too cold at night. I guess we'll see how that plays out.

My first night, Monday, I went to flip on a light and it didn't work. I have two lights in the van. One is mounted "permanently" over the desk. The other is a fluorescent drop light plugged into a cigarette lighter. The power for both of these is provided from my solar/battery system. That system is 24V and I have a 24V to 12V converter. I tried both lights and neither worked. I also tried my exhaust fan that is connected to the same system. No dice. At this point, it was already getting dark in the van and I have hours till bed - no lights. 

I use my cell phone to dig out a multimeter and connect it. I get a nice 12V. I test my appliances again, still no luck. I disconnect all of them, then try each one at a time with still no luck. Finally, I give up and watch some shows on Hulu until it's time for bed. 

Today I did some more troubleshooting. Even with a load attached, I was still getting 12V. Eventually I discovered a loose ground. I have two grounding bars - one stand alone that the batteries and 12V downverter connect to, and another that sits on top of my fuse block.  The two are tied together with a wire. My devices use the grounding bock on the fuse block. Measuring the voltage between positive and that ground only gave me +5V. Tightening the ground returned me to 12V and allowed me to power all my devices at once. 

This means that tomorrow, I will be able to do something I didn't do Monday or Tuesday - run the exhaust fan all day. There should be plenty of sunlight to power the fan without touching the batteries. That will help keep the van from cooking up into the 90s like it did today. I  may still need to run the air conditioner off of the generator for a while, but hopefully not for long.

Charger Replaced

I gave Xantrex a call and they walked me through some troubleshooting steps. One interesting thing was to unplug it for 10 minutes and then connect the batter first. "Sometimes if you connect the PV first, the micro-controller locks up." was an interesting factoid. However, they eventually concurred with my theory, which is that the controller is no longer working.

Today, I received the replacement controller and put it in place. Right away, it started charging the batteries back up. With the old controller -or- no load on the PV connections, I get around 40V.  However, once I connect those wires to the charge controller and it starts charging, that voltage drops to 24.2V, which is a good sign. Now, I just need to send the old controller back.

I also brought the generator down and hooked that back up. So I will be able to run the generator and air conditioner over the summer. I still plan on further insulating the van, covering the windows and separating the cab from the the living area. But I'm not going to try to get the A/C working off of batteries and solar.

A major change for me this summer will be me moving to a daylight position. So I will not really be in the van much during daylight hours, just for sleeping at night. This should be an advantage to me during the summer months as I will not have to contend with direct sunlight. Obviously, there will be some disadvantage during the winter, but I think I can deal with that.

Back into Spring

March 2012 makes 31 months of camping at work. Over the winter, I haven't had to run electricity, and my only purchase was $7 (actually $5.98 + tax, but I round up) for two propane bottles. For most of the winter, I used one left over from last year, and I'm currently on the first one of my purchase. Since we're getting back into 60F+ weather, I suspect I won't need the second bottle.

Here is a quick snapshot of my savings, and as always, the spreadsheet is available.

31 Months Van
Equipment: $5500
Operating: $1380
Total: $6,879
Equipment Average: $178
Operating Average: $45
E+O Average: $222

31 Months Apartment
Rent + Utils: $600/month
Total: $18,600

Savings: $11,720

Over the winter, I haven't needed any electricity, but I've been observing that my batteries haven't been charging properly. I assumed that this was a problem with the batteries themselves. However, today I went ahead and disconnected all the wires and measured the voltage of each battery. They are all reading 12.5 and when combined, 24.8, so they seem fine. After disconnectng and reconnecting the inverter, I was able to power it on, and I can power the light and fan from the batteries. I then measured voltage from the solar panels. The PV array is putting out around 40V, which is pretty good. My Xantrex C35 can handle up to 55V, so we are well within limits. The problem is when I measure the voltage on the Load/Battery terminal from the C35. The C35 is putting out only 0.1V, which is bad.

I checked my history, the the C35 arrived at my house on 3/12/2010 with a 2-year warranty. I am very glad I decided to fully troubleshoot the system today, as it allowed me to put in a warranty request and get an RMA number before the 12th. I will find out this week if it will still fall under warranty (the warranty language only requires notification within the warranty period). Hopefully they don't attempt to finagle their way out. The device hasn't been working for at least a month, if not more.

Not at all awkward

Here we are in the middle of November. I haven't been posting as much, so I figured it was time for an update.

The summer months of July and August were unreasonably warm and I was running the generator a lot more than I remember in previous years. The big difference to me was that things warmed up MUCH sooner than before. It got to the point where I would start the generator at 6 in the morning so I wouldn't have to get up at 9 to turn it on. However, as we went into October, I was able to get by with just running the fan off of the batteries.

In September, I had to take the van in for some shock and strut work, as well as new tires on the front. I also got the van's air conditioner fixed for the first time since I purchased the van. I paid over $500 for the repair work and over $200 for the tires, so my expenses did jump up a bit.

Now that we are firmly into Fall, there are some days I don't even have to turn on the fan. The only power I use is to charge any portable devices and run my drop light. It's rather pleasant this time of year.

Either this week or next, I need to take my van up for inspection, but since I did those repairs in September, I shouldn't have much issue. I also plan to drop off the generator at home so we have it available during the winter months.

I have updated my spreadsheet, and posted my current summary below. I am rather pleased to report that my "savings" is well over what I have spent on the van including investment and operating costs. Over the course of two years, I saved over $9k in post-tax dollars! Or for those of you familiar with living costs around DC and NOVA, I have maintained an "apartment" for 2 years for just under $7000.


Totals as of November 15th, 2011:
Equipment: $5,500
Operating: $1,380
Total: $6,879

My comparison is a $500/mo apartment + $100 utilities.
From 8/1/2009 to 11/1/2011, the cost would be $16,000.
Which means I have currently saved $9,120 or 43%.

When you can't wait 2 years

This would probably be better as a 2/year 24-month post, but I just updated my expense spreadsheet and wanted to share my findings.

Here we are at the "22-month" status. My operating expenses come to $50month and if you factor in the original equipment costs ($4,750) divided over 22 months ($215), it comes to $265/month expenses. In other words, I spent $5,860 over the last 22 months vs $13,200 on an apartment ($500/month rent + $100/month utilities) for 44% savings!

Another fact I like to keep in mind is that all this equipment I've purchased (the van, the solar panels, the generator, etc) is all still in working order and should continue to remain so. So if my situation changed tomorrow (say I got to work from home)I would still have a working camper van and equipment to either use or sell.

Spring Cleaning

Today I did some spring cleaning in the van.  I also re-arranged the furniture somewhat, placing the bed at the back of the van.   This works for me, but for taller people, it would be rather cramped.  It's almost too small for me at 5'7.  The width is 66", so I sleep at an angle or with my knees slightly bent.  The one window does give a few more inches for my feet to hang out.

Winter wrap up, oncoming Spring

Since I replaced the battery, my power situation seems to be stable.  However, with some of the warm days, I tried running the air conditioner off of batteries (this is the 9500 BTU air conditioner) and it only runs a few hours.  My watt meter's screen doesn't appear to be turning on, so I'm not sure how much it is drawing.  I also tried running it on "fan only", and that seems to draw the batteries down just as well.    More on this further down.

Some tidbits from Winter:  I bought a heated blanket from Target.  It worked wonderful... for about 3 hours.  I woke up freezing.   Now, these blankets have an auto-shut off for 8 hours that can be reset by turning it off and on again.  That was not the issue.  So I exchanged it for another blanket and that one never turned on in the first place.  This was very frustrating.   I returned that one for cash.

I ordered a Sunbeam heated blanket from Amazon.  This works "ok".  It takes about 20 minutes to heat up, but does remain heated.  However, the blanket seems to only be useful if I foldit up around me (which the instructions warn me against doing).  Otherwise, you don't really feel any warmth from it.  I would say my sleeping bag remains more useful.

What would probably work better would be a mattress pad.  These are designed to be placed under blankets and radiate warmth.  I would love to have one of these setup with a remote control/timer.  Say at 5:50am it turns on and starts heating up.  I would get out there by 6:20 and just climb right in to heated goodness.


Finally, today marked a grand entrance into Spring for me with temperatures outside bordering around 90F.  I had brought the generator back down yesterday, topped it off, and had it ready for today.  It got to 84F by 11am, so I went out, started up the generator, and fired up the air conditioner.  The temperature started dropping nicely and I actually got cold enough to put a blanket on.  Sweet, sweet, air conditioned bliss.

Battery replaced

Battery D has been completely replaced now.  I ended up spending $49.77 for the replacement.  The warranty is 24-months, but the warranty is really just a pro-rating.  I will have to add that cost to my spreadsheet.

The battery pack held 24 volts overnight.  This morning, I ran the electric heater for a bit, which took it down to 23 volts.  I was expecting it to recharge that almost completely during the day while I slept.  It did not.  The reason is rather simple though -- the panel was covered in snow. 

I also managed to clean out the front and back of the van today.  I never let it get very messy, but there was some stuff strewn about under the bed and in one of the baskets.  Some bread I've been meaning to throw out for several months, things like that.  Since it's nice and cold, nothing was creating a stink, just going bad.

I also finished off another propane tank today.  I have been using the heater a lot more this winter than last.  I usually like to get it up to 50F before turning it off.  That takes about 30 minutes from 25F.  However, I realized that I could avoid that by purchasing a heated blanket.  Last winter, I didn't really have the power (except via generator) to run an electric blanket, but this year I can just plug one in and sleep under it.  It would also be nice just to heat up the sleeping bag before I crawl in.  So that's on my list for this weekend.

Nice weather

Today had some amazingly nice winter weather.  The temperature was at least 45 all day and I did not need to run the heat for anything.  I also managed to sleep till 4pm, which was sweet.

I dropped my battery off on Thursday, and they were supposed to call me either that day or Friday, but as of today, there is still no return call.  They were going to attempt to recondition it, so I hope that takes.  If that, hopefully they can pro-rate me the cost of a new battery.

Battery D is dead, probably.

I gained access to a decent battery charger last night and let the battery.  I let it charge at 10A and when I checked on it a few hours later, it dislayed F01.  I looked this up and it means "F01 Internal Shorted Cell Battery - Cannot be charged. Have battery checked by certified auto service center."  

So this week, I'm going to drop that battery off at the vendor and see if they can get it working.  Apparently, this is one of the first two batteries I got in Oct of 2009.  It's been going bad all summer, so hopefully I can get them to replace it if need be. 

On another note, I finally finished up the leftover tank of propanee from last year.  Yesterday and today I've been running the propane heater quite a bit.  Yesterday I ran it for over an hour during the day, and this morning I let it run for 30 minutes as it warmed the van from 25F to 50F.  So a new canister is in and I have 3 remaining.

Battery Saga continues

In my previous post, I commented on battery C dragging down the system. Since then, I recharged battery C and put it back into the array. For the first day or two, things were fine. However, when I returned the next week, the entire array was again reading 19V. I ran the battery equalizer function on the charge controller and this failed to resolve the issue.

I didn't do anything else with it right away, and then I went on vacation. Today however, I went ahead and investigated the batteries again. A&B had 12V while C&D had 7V. As a test, I decided to rotate the batteries, moving battery C to A's spot and battery A to C's spot. B & C paired together nicely, but when I went to pair A & D together, I got sparkage. A little sparkage isn't an issue, so I held the wire on. The contact area maintained an electric glow and after a few seconds, battery D began bubbling.

Now, I then tested each battery individually and found D holding at 7V while C had 11V. I also checked the specific gravity and D shows as being "fair" with some wells being "good". I don't like the sound of bubbling battery acid in my van, so I am going to take D home and charge it with the trickle charger. Alternatively, I might just take it to the store I got it from and ask them to check it out.

In the mean time, I connected two of my good batteries in series. At least this way, I have enough power to run the inverter because it will shut off if the voltage dips below 19V and 19V is about the maximum I can get out my system with the bad battery in.

Wiring Diagram

Above is the current wiring diagram I have in the van.  I recently had issues where battery C died, dragging down the system.  I used a battery checker - a little clear plastic device with a floater in it.  Battery C showed as weak while battery D showed as good (despite only measuring 7 volts when isolated from the system).  So battery C appears to have died and dragged down battery D's charge with it.  I took battery C home, replaced the fluid with fresh distilled water, and it charged up properly to 12V.  Hopefully that means the battery is now good.

Part of me wonders though, could my wiring be to blame.  Perhaps the right side is not charging like the left side and caused battery C to fail.

More battery findings

So today had more sun and the meter was reading around 25V. I dug around and was able to pull the "quick disconnect" apart. They don't always want to disconnect, and certainly not quickly. The disconnect was the positive lead between the charge controller and the battery bank.

Immediately, the meter dropped to 22.58, which just verified that they had been getting power from the panel. I then left and came back 3 hours later. The voltage had dropped to ~20V. This confirms that at least one of the batteries is bad.

So next week, I'll bring down my battery tester (the one that measures specific gravity) and hopefully a nice funnel or water bulb (like you sue for ears) to refill the water in them.

If a battery is fully bad, they should have a multi-year warranty that I need to check out.

Gotta go, my battery is low.

So I've been noticing for a long time that my batteries seem to drain down at night. This was a minor annoyance previously, but now that there are only around 10 hours of sunlight in the day (sunrise ~7AM / sunset ~5PM), it has become a real issue as the batteries are now hovering around 20V and barely get above 22 after a full day's charge.

Now, the charge controller is supposed to have a night disconnect that prevents nighttime discharging through the solar panel. I had assumed that this was controlled by one of the potentiometers on the inside. So last week, I broke out the manual and went over all the details and found that they really only control how high it takes the voltage before it stops charging. They do not impact the low voltage disconnect. I did make a few adjustments to have it try to give more charge to the batteries. This seemed to have no affect.

So I emailed the Xantrex support people. They gave me a few troubleshooting tips, one of which is to determine if the batteries themselves are holding a charge. To test this, I would charge the batteries to full capacity (which at this point may involve taking them home), disconnecting the load and charge controller, and see if the voltage drops over a 12 hour period. If I had one, I could also try a DC clamp on ammeter to see if current is flowing to the solar panels.

I currently have no easy way to disconnect the solar panels. I have ordered two DC circuit breakers - 1 50A one for between the solar panels and the charge controller and one 100A for between the batteries and the load. Each breaker is around $25 so I will be adding $50 once I set these up.

Weather and Life

Traveling

Last week, I took my van back home to get it's yearly inspection.  Unfortunately, the garage itself was out of stickers.  They could have scheduled me again for Monday, but I of course had to work Monday.  So we have one scheduled for Thursday, which means I'll be taking the van up a second time.

Remodeling

While I did have the van at home, I took the time to do some remodeling again. I cut the bed to be shorter (my length), made the desk a bit shorter (lengthwise, not height wise), and secured the sink to the side of the desk.  All in all, this gives me much more room to move about inside the van.

I also have brought down a microwave to heat soup up with.  I am not sure how well it works.  Transporting it the first time, it fell over, hit some junk I was transporting and dented.  I put my soup in on Monday to heat it up.  It ran, but made a whiny noise.  The soup came out tepid instead of hot, like I would hope.  I'll try it again next week (I only had the one can) for a longer period.

Weather

Things have been a bit chilly this week, with freezing/frost conditions in the morning.  I was supposed to bring my heater down with the van, but left it at home.  Despite this freezing weather, my sleeping bag still remains a viable source of protection from the elements.  Also, the temperature does warm up inside the van into the high 60s by mid-day.  On Monday, i even had to open a window and roof vent to let the cooler outdoor air in.

 

Oops and soup

Things are starting to cool down, but I still find myself needing ac for a portion of the day. Today around 11, I fired up the generator and the ac.  Then, around 3:30, I was up and noticed my inverter was only reading 20 volts. Turns out I had been running off of the inverter all day. That would be fine, except I was also running the generator with no load.

At work, I have been primarily eating soup, while eating fast food during the day. So this week I purchased a thermos.  It seems to work pretty good. The soup I made at 6am is still hot and it has its own cup to pour the soup into.  My plan is to take the thermos back into work each day for cleaning and refill.

One Year Anniversary: One year of camping.

As of August 17th, I have weathered summer, fall, winter, spring, and summer again in the van. It wasn't always easy, but it wasn't that bad either. Over time I have improved the interior of the van to the point where I now have reliable power, a bed, a desk, a chair, and storage. In short, it has become an adequate mobile apartment (minus a shower/sink). From the world's perspective -- I am roughing it in a van. From my perspective, I have a comfortable place to sleep.

One thing that has really helped is the presence of a local library. I can go to the air conditioned library with my laptop, get online, and stay there for as long as I like. I recently been utilizing the library to study for an Oracle certification. In fact, the library is tied in with Safari Bookshelf, so I have access to large number of study materials beyond what the library has.

Money-wise, I have continued to keep up with tracking my expenses. This spring, I had some major expenditures in solar panels, batteries, charge controllers, and wiring of the same. The end result of this is a 24V solar-charged battery system that provides 12/24V DC and 120V AC power to anything I need. I spent around $1700 on this system, so that brought my equipment costs to $4,698, or $391.50/month. My operating costs include things like generator fuel, propane, inspection, insurance, and gym membership. The total in operating costs for the year was $581, or $48.44/month. The combined total was $5,279, or $439.40/month.

For comparison, a cheap 1-bedroom apartment (in a shared house) in this area is $500/month and utilities would easily add $100 on top of that. So over the course of a year, I would have spent $7600 on such an apartment. This means that over the course of 1 year, I saved $2,321 in rent/utilities by camping at work.  What makes this more exciting is that the bulk of my cost was purchasing equipment.  Barring any issues with my equipment and assuming $50/month operating cost, my second year will only cost me $600.

Where I Went Wrong

Looking back, there are a few things I would have liked to do differently. 

1. The mattress.  I started off with the van's mattress, which was an ok way to get started, but then I went to an air mattress.  If I had done my research, I would have learned that air mattresses and cold weather don't mix.  I replaced it with a foam mattress from Ikea, but I would have been $50 richer going with the foam mattress from the start.
2. Solar panels.  I should have gone a full summer of measuring my air conditioner's load before building my battery/solar panel array.  I was basing it off of my usage from the end of August.  Also, I didn't get a chance to measure wattage pull until winter.  To do this, I cranked up the furnace at home and then turned on the air conditioner.  I came up with a pull of 500-600 Watts.  However, during this hot summer, I really pull 1000-1200W, about double what I built for.  In order to handle that, I will need 2-3 times the batteries I currently have, plus the copper wiring to tie it all together.  Once I increase my batteries to handle the load, I would then need to add another solar panel to recharge the system in time for each week.  If I had waited and got a full summer's worth of readings from the watt meter, I could have purchased and built with more confidence.  On the other hand, researching setting up the system was a desired learning experience that I suspect will prove useful in the future.
3. Generator choice.  Granted, I probably couldn't have known this, but the generator I got often requires moving the choke in order to start it.  So while I was able to rig up a remote start, most of the time I still had to go to the generator and operate the choke.  I may be able to work around this using a cable and spring setup, but I suspect the result will be flaky.  Some of the more expensive generators from Honda come with remote starts (and are quieter).  The downside is that they usually only hold 2 gallons of gas.

 Camping at work has been a dual-purpose endeavor.  On one side, it has a very practical application of saving me money.  The other purpose is that of learning.  When you go "off-grid" you no longer can rely on cookie-cutter solutions.  You have to come up with your own solutions for each issue and experiment until you find what works. 

84 sq foot house

During half the week, I live in a 60ft square foot home, but I don't cook and shower inside it. This lady has essentially built a house on a trailer and has 84 square feet.  I like it.

   http://www.ebaumsworld.com/video/watch/81014570/

Low Voltage Beep

I ran the air conditioner for a short while yesterday, along with most of today.  Around 3:30pm, I got a low voltage warning from the inverter.  The voltage reading on the inverter was at 20V (vs 25V where it starts at).

For 5/24, I ran the air conditioner for 46minutes and pulled 0.41Kwh.  For today, I ran it 5hrs, 40 minutes and pulled 1.74Kwh before I got the beep.  That totals to 6hrs, 26minutes of run time and 2.15KWhrs.  In my last post, I had estimated my battery bank of being capable of 8.4Kwhrs (Each battery being a 2.1KWhr battery, times 4 batteries).  So I seem to be getting about the run time of one battery instead of 4 (or even 2).  

Now, to be 100% fair.. once I turned off the air conditioner, I continued to run the fan for another 1.5 hours.  Granted, the power usage of the fan is less than the output of the solar panel, so it could potentially run indefinitely.

Given the current setup, I definitely will not be able to use the air conditioner for 3 days on one charge.  At this point, I'm not exactly sure why I'm only getting 25% of my capacity out of the  system.  Perhaps I need to redo the wiring inside the battery box to more evenly draw across all 4 batteries.

As a stopgag, I can try a few other options.  The easiest would be to bring the generator back down and only run it once the batteries have ran out.  I also have a 24V charger, so I could be charging the batteries off the generator at the same time.  I could also upgrade my battery array to 6 or 8 batteries.

Another option I've been considering is one of the evaporative/swamp coolers.  Generally, these are a fan that blows over water.  They work on two concepts: 1) water has thermal mass and stays cooler longer, and 2) small drops of water will cool you down and then evaporate away.  They have a few downsides: 1) they don't actually cool the air, just make you feel cooler, and 2) they increase the humidity.  If you let them run long enough in an enclosed space, the humidity increases and the cooling effect stops.  Also, if the humidity is too high, sweat stops evaporating and you warm up either further.  Another disadvantage is that you have to refill the water from time to time.

Back to the drawing board..

Electrical setup details.

Today I thought I'd take some time and explain my electronics setup in greater detail.  A lot of this system is all about crunching numbers.  The math isn't complicated - it's all multiplication and division, elementary school type word problems.

A friend of mine likes to claim that I should be able to calculate all of this out before purchasing the first battery.  And you sort of can.  You can determine how big your system will be and how long it will operate under different loads.  But what he doesn't seem to get is that you can't always determine your load.  The bulk of my setup is in place in order to operate an air conditioner.  How much I use this air conditioner and how hard the air conditioner works changes like the weather. The compressor kicks on and off as needed and this is a variable you can only learn by testing over a period of time.  Manufacturers may have this data, but rarely is it published.  Plus, a number of variables such as humidity and thermal change make this data unreliable.  More on this later.

First, we have the battery pack.  These are 4x 12V deep-cycle batteries with a reserve capacity of 175Amp-hours each.  What is an amp-hour?  Simply put, it measures the amount of Amps a battery can produce for 1 hour before it is discharged.  So a 175Ah 12V battery can (theoretically) produce 175 Amps for 1 hour before becoming depleted.  For our purposes, we really wan the "watt-hours" of the battery.  This of course is how many Watts of power a battery can produce for one hour.  To caclulate power, we multiply Amperage times Voltage: 175A * 12V = 2100Wh (or 2.1KWh).   So each battery can run a 2000 Watt appliance for 1 hour, or a 1000 Watt appliance for 2 hours. 

 We have 4 of these batteries, divided into 2 sets of 2.  Within each set, the batteries are connected in parallel using #2 AWG wire, which increases the amperage capability from 175Ah to 350Ah, but not the voltage.  The power rating for 350Ah set is 4.2Kw.   The two sets are then connected in series, which leaves the amperage the same, but increases the voltage to 24V.  So we now have a 350Ah system at 24V, or more importantly an 8.4KWh battery system.

At this point, you may be wondering why I am going from 12V to 24V.  If all 4 were hooked up in parallel, I would still have gotten an 8.4KWh system.  The reason has to do with wiring and efficiency.  DC voltage can drop quite easily over short distances.  So if you're going to work with DC voltages, you want to get your voltage up as high as possible before transmitting it.  In practice, most people have to choose between 12V, 24V, and 48V systems.  You usually only see 48V in grid-tie systems and industrial applications.

Connected to this battery pack, I have 3 devices:

1. A 24V 1500W A/C Inverter  - this will convert my 24 volt DC electricity into 120V house current and can power 1500W devices (with a peak of 3000W).  This is connected via #4 AWG wire.
2. A 12 volt converter.  This little box regulates the 24V voltage down to 12 volts, which is quite useful since a large number of devices are designed to operate at 12 volts.  The box claims to be rated at 30A, but I have it fused at 25A.
3. A Xantrex C35 - 24-volt DC charge controller.  This charge controller is capable of 35A @ 24V or 840W.  This is then connected to the solar panel.  Due to the higher voltage/lower wattage, this is connected with #10 AWG wire -- technically called MC4 Interconnect wire, which is standard on most solar panels these days.

The Inverter powers my air conditioner.  I also have another power strip connected to it that I use on occasion for small devices, such as the fan or my netbook.

The solar panel is an HQRP  24V, 180W solar panel  (7.5A).  Most guides on designing solar systems recommend that you get a solar panel array capable of producing 30% of your system's capacity.  This guideline is for a daily use system. When the guides discuss this, they typically refer to your battery bank's capacity (and the battery capacity should always be 2-3 times your load). Apparently 30% has been determined as the optimal amount for recharging batteries.  If you recharge with too much power, you could damage the batteries.  If you recharge too slowly, you could end up never recharging the batteries.

My solor panel is way below this recommendation.  At the 8.4KWh rating, the 180W panel is around 2% capacity.  If I built my array out to the full 840W that the charge controller can handle, I would still only be at 10% capacity.  However, I do not use this system on a daily basis.  During last August's super hot weeks, I ran the air conditioner 4-5 hours each day.  So on a peak long week, I will use the air conditioner for 3 x 5-hour stretches, for a total of 15hours each week.

My current air conditioner peaks around 1000W while the compressor is running.  The compressor will run for 1-2 minutes, and then run the fan for 4-6 minutes. During the one measurement I recorded (1hr, 20 minutes), the air conditioner averaged 0.31KW/hour.  A 15-hour week should pull 4.62KW, or just over half of my battery bank's capacity.   I do want to take more measurements of this load to get better figures.  This air conditioner is a 5200 BTU with an EER of 11 - see it on my equipment page.

To be fair, the inverter and wiring do loose some power, just as any system does.  Also, I will from time to time run some 12V appliances off of the system.  All of these impact my calculation.  Also, during the morning and evenings when I am not utilizing my air conditioner, the solar panel is hard at work recharging the system.  I have only run the air conditioner on a few occasions, and only 2 days in a row so far (cooler weather outside).  But on day 2, the battery pack is recharged before I start the air conditioner.  On day three, the battery pack is recharged again even though I haven't started the air conditioner.


I don't know if that will remain true when the weather heats up and the air conditioner has to work harder.   At 8.4KWh, the battery pack can sustain around 0.5KW/hour for 15 hours, then it would need completely recharged. If hotter weather begins taking me beyond 0.5KW/hour, my best solution is to increase the size of the battery bank to match.  If I increase the size of the battery bank and find that the batteries are not getting recharged in suitable time, I will have to increase the size of the solar array to shorten the recharge time.  Neither is exactly cheap.  The batteries run around $85, plus the expensive wiring (call it $100/battery).  I also need to find room for the batteries (somewhere where I can tie them into the existing set).  The solar panel itself can run $500-$600, but can be easily mounted on the roof with the other one.


The 12V converter was purchased on ebay for around $30 and comes from Hong Kong. It is rated at 30A, but I have it fused at 25A (the fuse goes between the converter and the 24V battery pack) for added safety.  The converter has two accessory wires which I have no use for (but come in handy for a radio setup).  The 12V output goes into a fuse block.  I paid way too much for this on ebay for $48 shipped.  If you are smart, you'll go with my original idea and pull one off a junkyard car for much less, perhaps free.  This fuse block has two independent positive buses, a negative bus, and 14 fuse slots.  I could technically run separate 12V and 24V devices off of this, but I have no 24V devices, so the two positive buses are linked together.

Currently, I have 3 x 5A circuits coming off of the fuse bus.  One goes to the fan vent in the ceiling.  Another goes to a set of lights over the desk (which I pulled out of the van originally).  The final one goes to a 3-port power socket (cigarette lighter socket).  This lets me plug in common 12V car accessories such as cell phone chargers.