battery monitor upgrade

5.10.2014 – Saturday

Through a bit of luck I somehow managed to acquire a Victron BMV-702 this Spring (big thanks to Matthijs & John). The current BMV-600s has served the cabin since July 2011 and performed like a champ. For a technical overview/run-down on the BMV-702, check out John’s post: BMV-702 insights | Victron Energy. I’ll share some photos and impressions from my specific application.


The packing is compact and tidy and the box includes everything necessary for installation (clockwise from bottom):

  • Quick installation guide (featuring tidy diagrams)
  • User Manual
  • 500A/50mV shunt
  • 2 meter battery cable with fuse (red)
  • Faceplate for front mounting
  • Meter (with rear mounting ring, in anti-static packaging)
  • 10 meter RJ 12 UTP data cable


Upon close examination the shunt is different from the BMV-600s shunt that it replaces. The BMV-702 features two quick connect PCB on the current shunt where the BMV-600s featured only one. So… what to do with an extra quick connect PCB? After a leisurely read through the user manual I uncovered a few different uses. The one that peaked my interest involves an optional battery temperature sensor that can automatically adjust battery capacity as temperature decreases. Once the sensor becomes available in the United States I’ll be installing it in short order (hopefully before October concludes and winter begins again). Due to our battery placement in an unheated garage, this alone is reason enough for the upgrade at the cabin.

Fore reference, the BMV-600s was programmed as follows:

  • 85% CEF (charge efficiency factor)
  • 1.20A Ith (current threshold)
  • 1.25 PC (Peukert exponent)
  • 13.5V Vc (charged voltage)
  • 1500Ah Cb (battery capacity) — use 850Ah for winter
  • 50% DF (discharge floor)
  • 0.8% It (tail current)
  • 4 min Tcd (charged detection time)
  • 1 Tdt (time to go)

Having to not reprogram for winter (<50°F) would simplify and increase the accuracy of the readings. I’m happy to pass this adjustment off to a computer. For now I carried over all the settings from the 600s to the 702. To install the shunt I simply cut power to the system and swapped in the new shunt. After install I replaced the bus bar shield and headed in to the cabin to swap out meters.

IMG_0944 IMG_0950 IMG_0952

The 702 retains identical physical dimensions to the 600s, making for a seamless upgrade. I spent more time taking photos than installing this time around. The “+” and “-” buttons toggle through the following displays:

  • Amp hours
  • State of charge (percentage)
  • Time to go (hours)
  • Battery temperature*
  • Voltage
  • Current (Amps)
  • Power (Watts)*
  • State of charge icon (lower right of display)*

*Added feature

IMG_0969 IMG_0970 IMG_0971 IMG_0972 IMG_0973 IMG_0974 IMG_0980

The added features to this meter (temperature, watts, fuel gauge style state of charge icon) only add to the utility of the meter in our application. Programming is straight forward and the text scrolls across the screen on the 702. You no longer need to program with the user manual in one hand like on the 600s, where a displayed abbreviation corresponds to a definition in the manual. I recommend setting the scroll speed just a bit faster than factory preset on the 702 for faster programming.

In everyday use I usually leave the display on the percent readout and toggle between the amp hours and watts displays. An easily missed convenience on the 702 is the backlight. It can be set to “always on” or programed to turn on for several seconds once a button is clicked. When set to turn on after a button click the first click does not toggle through screens – it only turns the backlight on. I really like this small touch (ie, not having to toggle back to the screen I was on before turning the backlight on).

UPDATE: 5.28.2014

Just the same as on the BMV-600s, the 702 produces an error in its readout under a very specific condition. When multiple large (>300 watt) loads are applied the meter will get stuck reading out 85 watts / 6.5 amps. The voltage will remain accurate however. Observed loads at time of error:

  • Kurig K10 MINI Plus Brewing System running
  • Oven on (300 watts)
  • LED lights (100 watts)
  • Well pump turned on (water running)

Once the error was in effect, several different approaches were attempted to reset the meter and remedy the situation. This took some time to perform since after several of the attempts the meter had to be reprogramed to the desired settings.

  • synchronisation
  • meter reset to default settings
  • cut power to meter 5 seconds
  • cut power to meter 30 minutes
  • cut power to shunt 5 seconds
  • cut power to shunt 30 minutes
  • disconnect Solar input (zero input)
  • disconnect Inverter and all loads (zero output)
  • disconnect solar and all loads (zero current at shunt)

All failed. I reprogrammed to desired settings and then waited… After about 12-16 hours it resumed normal operation. I’m still attempting to figure out what is happening. Again, this is a very specific situation and though it has been reproduced reliably, it only happens when there are multiple large loads and at a frequency of about 4 or 5 times a year. The glitch first occurred when we ran an air conditioning unit off battery power. Now it appears that the well pump and the Kurig can do the same. The exact cause is unknown and under investigation. I would really like to be able to hit a button and reboot the meter instead of waiting 12-24 hours for the meter to fix itself.

Bottom Line: I would buy this meter again. The feature set and build quality are second to none. And while the glitch is nuisance, it occurs infrequently. I’m confidant that a solution will eventually be uncovered (I’ll review my wiring, it could very well be my fault). Also, look for a new post this winter once a battery temperature sensor is added.



Michigan Maple Syrup

4.9.2014 – Wednesday

A warm spring night, a wood fire, and the sweet smell of hot sap 100 yards off…


With my mid-week break I packed up the family and we trucked to camp in the Pilot… well, most of the way. The Honda has some neat AWD tricks but when the Ol’ man decides to park his Z71 Silverado 4×4 at the end of the road and walk the rest of the way, I wasn’t about to bury the Pilot and risk damage to a vehicle without proper skid plates. Quite handily, the Ol’ man was kind enough to provide us with transportation via the Pioneer. Once the family was dropped off at the cabin, Dad and I made a gear trip and hauled the rest of our supplies to camp. This also gave me a chance to document the mud. There are a handful of photos in this post that are HDR (high dynamic range). Each HDR photo is a composite of 3 photos taken at different exposures. I processed my HDR photos to achieve realism (versus the over-processed artsy stuff you find elsewhere on the internet).

IMG_9622 HDRThe loggers chewed up the half-mile of road it took to get from our forest parking spot to the gate. While the ride was rough, the heavy machinery drove the frost down so the real mud didn’t start until our little two-rut road.

IMG_9638 HDRThe frost had kept the water on top of the road and created some spectacular mud. It’s thick and slimy, resisting remodeling just enough to force the Pioneer’s tires in to the ruts. The 11″ of ground clearance was used up in a number of spots. After our trip we regrouped and ate supper. During supper, the Ol’ man mentioned there was a spectacular view to be had from some recent logging a few miles down the road. The night was young, and that was all the push I needed to take an evening side-by-side ride with the kiddo. Meanwhile, Sarah and the little one decided to tend the fire and see how far they could sink into the big comfy couch.

IMG_9690 HDR We soon found ourselves on a beaver dam the loggers used as a road. The water was beginning to eat away at the frozen embankment. After the crossing we scaled a steep hill that the Spring melt had turned into a 200 foot mud-run. The Pioneer made it about 100′ before coming to a stop. It appeared that the spectacular view was in jeopardy, and additionally that I had the entirely wrong footwear for trekking through a foot of mud. Quite amazingly, 4-wheel differential lock got us moving again. Sorry, no photos of the hill. Dad wasn’t stopping once we started moving again.

IMG_9681 HDR A view from the beaver pond.

IMG_9658 HDRIt was worth the trip. In the right 3rd of the above photo the clear cut can be seen.

IMG_9696 HDRLooking back at the ridge we just traveled. The previous photo was taken from the ridge in the center of this photo. Tomorrow we would start boiling.

The equipment has been in storage since Spring 2013 – when we originally planned to do the inaugural run. Going back to 2010 I can remember the slow acquisition of parts and supplies. Bags and holders were one of the first supplies bought. I think some of the bag-holders were acquired in the 1970’s. The pan was the next big purchase. It was custom made from stainless steel. After the pan a steel stove was produced by a high-school shop class to match – for the price of metal and a pizza party upon completion. Later acquisitions included ball valves, garbage cans, buckets, skimmers, hydrometers, a turkey deep-frier, bottles, and so on.

The stove, sketched out by high school shop teacher Derek is revision 2. Revision 1 had a tapered fire box that ended at the pipe. Revision 2, what we have, has a square firebox with a flat exhaust to the pipe. Ultimately, we achieved a very controlled boil with no foam. Revision 1 has historically produced a lot of foam and a very strong boil. It’s a mystery why we did not get foam from boiling, but we noted a few differences between last year’s boil from Revision 1 and this year’s boil at our camp from Revision 2:

  • We used bags to collect instead of buckets
  • Our stove produces a consistent boil, but the smaller fire-box means the boil is not as vigorous as the boil produced from Revision 1
  • Our trees are 30 miles North and about 30 years younger

IMG_9734 HDR

Nonetheless, the reason for little to no foam from our boil eludes us. To achieve “ideal boil” we established the following settings:

  • 3 – 4″ of sap in the boiler pan (24″ x 48″ x 7″) and the top dripper pan (12″ x 24″ x 6″)  slowly adds sap at about the same rate as the boil removes moisture from the sap.
  • Bottom ash tray was opened about 2″ for increased airflow to the fire
  • Maple and birch was burned in the firebox, criss-crossed to form a latticed stack three pieces high by 3-4 pieces wide
  • As soon as the wood burned down we raked the coals and made a new stack of wood (about 25-30 minutes)

IMG_9745 HDR IMG_9759Unlike a wood burner in a house we did not want coals. A complete combustion is preferred with lots of flame. A hot fire gives a good boil and clears out the coals, making room for more wood. Too many coals kills the boil.

IMG_9765We tested our boil rate to give an estimate to how many hours would be required to boil down the 200 gallons of sap we collected. Once we had a stable boil and the depth of the boiler pan was consistent at 3.5″ we measured the drip-rate at 2 cups in 1:16.00 minutes. That came out to about 6.25 gallons per hour.

IMG_9774 HDRWhile the boil was underway we collected sap from the 80 taps placed a few weeks earlier. The sap flowed hesitantly this year, so today’s collection was 3 days worth of sap. The plastic tailgate on the Pioneer needs some reinforcing when there is over 500 pounds of sap sloshing around. It may be hard to see, but there is a strainer cloth (flour sack dish towel) bungee-corded to the top tank inlet. We filter the sap at collection.

IMG_9784 IMG_9797 HDRToday’s collection didn’t even average a gallon per tap over three days. The bags pour better than the pails and we had very little spill when transferring to the collection tank.

IMG_9801 HDRThe collected sap is then drained into a sterile 5 gallon bucket and transferred to some 35 gallon garbage cans buried in the snow bank or a larger snow-covered tank just barely peaking into the photo below. From there, sap is added 5 gallons at a time to the dripper pan.

IMG_9804 IMG_9812Tools of the trade: folding chairs, card table with foam skimmers, the 5 gallon bucket, and some iron tools for raking and shoveling coals.

The last bit of the process was not documented. My break ended a day earlier than required to see the process completed. We ended up boiling about 200 gallons of sap and getting 5.75 gallons of syrup (after spills). Once the sap reached the correct moisture content (59 brix at boil) to become syrup the fire was quenched and the hot syrup was transferred and strained through a flower sack dish towel into a 6 gallon turkey deep frier. The frier is stainless steel and allows us to strain the finished syrup and reduce the surface area to volume ratio of the boiler pan, keeping temperature and specific gravity stable, allowing more time to fill bottles with hot syrup. The bottles are filled, capped, and set on their side for at least 20 seconds before being stored upright. Due to my absence during the final steps I don’t have photos or much in the way of commentary. For more information on how to make maple syrup, check out this helpful document from the University of Maine Extension: Bulletin #7038, Maple Syrup Quality Control Manual

Cabin :: specifications

4.5.2014 – Saturday (revised 4/16)

What size is the cabin? That is the #1 question I’ve been getting the past few months. Looks like a good time go over some details on the design and dimensions of the cabin. The Ol’ man dug up the last remaining set of prints for the cabin allowing me a good look at them. The prints are roughly 90% accurate. However, there are a few notable changes.

  • The front (large) porch roof is integrated into the main trusses; if the supports were taken away, the porch roof is engineered to be self supported even under heavy snow load. As a result there is a flat ceiling on the porch instead of the pitched ceiling in the plans.
  • The stairs are not as steep as depicted. Either because of a building code or the unreasonably steep angle, it was modified during construction. The landing at the bottom is also only one step, not two. As a result, the closets intruded too far into the stair way and the floor of the closet was reduced for more clearance when walking down the stairs.
  • The bathroom has a full tub/shower insert and the toilet is positioned next to the sink. Insulation was placed between the shower insert and the log wall to keep the tub warmer in winter.
  • The small porch off the main entry way was added by the head carpenter and is not shown in the plan. The recessed light in this small porch and the shelter offered by the porch roof really add convenience in snow and rain.
  • The two footings in the basement floor may be slightly left or right of drawn to accommodate our plans for finishing the basement as a game room.

_MG_4922 Front porch roof is integrated into the main house truss.

_MG_5028Center of photo: the closet floor has been reduced.

_MG_6343 The tub and toilet differ from the original plans

_MG_6547 HDRThe back porch was conceived in its entirety by the head carpenter.






Click each photo to enlarge. Having enjoyed the cabin for about 4 years now there is a surprisingly short list of design features that either I or the Ol’ man would dare change. An extra log in the wall would have moved the bedroom ceiling fans up just a little bit more and not added much to the overall cost of the cabin. A loft and two more solar panels on the pole make the design wish-list but were ruled out due to cost. Another wish list item ruled out due to cost is engineered basement floor trusses (would eliminate the two supports and keep all plumbing and gas lines concealed within the trusses – a benefit when we decide to finish the ceiling in the basement). The bathroom may have benefitted from an insulated toilet (it sweats from time to time) and a vent fan to evacuate the humidity from the shower – though there is a window above the shower). The cabin was constructed on a remarkably efficient budget due in part to the downturn in the economy. If constructed today, I doubt my blog would feature a log cabin, log sided garage, and a nearly finished basement. One choice the Ol’ man regrets is going with a oak veneer floor in the upstairs. It’s real wood with a factory finish over an engineered wood material. It looks nice, but we’re starting to notice some small deteriorations that would not occur with a solid wood floor.  On the garage we should have put 8′ garage doors instead of 7′ doors for more clearance, specifically to better accommodate the side-by-side and full size truck. If we redid the garage it would have an extra row of block (2nd row), span a few more feet in width, and have a 9′ wide, 8′ tall main garage doors and a 7′ by 8′ high secondary door.

f2056960The garage has a 8′ x 7′ main door and 7′ x 7′ auxiliary door Some details about the garage:

  • The four large 57 watt CFLS in the garage (~3,500 lumen) are placed so that when both garage doors are open the lights are set back just enough not to be covered by the door.
  • A hand winch is mounted to the wall with two pulleys to create an overhead hoist good for about 600 pounds lift. The crank style winch has proven faster and easier to use than a more expensive electric overhead winch.
  • Ceiling height is 9′ 2″ overall.
  • The wall LP heater can raise the temperature in the garage fairly quickly in winter (for skinning and quartering deer)
  • There is a spare mini-fridge set up for freezing meat during the warmer months of deer hunting season
  • Old kitchen cabinets have been salvaged and repurposed for shop storage
  • Concrete slab is 5-bag mix with re-rod outside edges with wire reinforcements through slab and is 4 inches thick.

Knowing what we know now about concrete slabs, the Ol’ man would have built up an even sand base under the garage slab, used 1/2″ re-rod spaced every 2′ throughout the slab (instead of just wire), and used a 6-bag mix. Our soil is mostly clay and rock with a 12-18″ covering of black dirt and detritus. We removed the dirt and have an adequate sand base under the garage, but because the garage is not heated in winter and frost sets in, a carefully constructed sand base that has a uniform thickness would have increased our chances having a slab that won’t crack after a few seasons. The slab needs to float – that’s where a stronger slab with a thick, uniform base to float on is important. Currently we have a nice long crack in the slab. The cabin gets lots of airflow on top of the ridge, if we were in a hollow where condensation is common the slab would benefit from a vapor barrier and insulation underneath.

An interesting question we get up in snow-country is why did we choose shingles over a metal roof. The shingles are rated for 30-something years (we’d be happy with 25). Aside from the cost premium for metal, we did not want snow build up. Metal roofs are well-known and advertised to shed snow. That’s a good trait if there is concern over the roof holding up under a snow load. Take a closer look at the plans and note the roof has a load rating of 50 pounds per square foot (psf). With some simple unit conversion, 50 psf is equal to 9.1″ of water, 9.9″ of ice, 118″ of fresh snow, or 30″ of compressed snow. At this point a snowbank sitting right next to the cabin or garage is more of an inconvenience than some snow on the roof. With snow butted against a structure we would have to worry about water intrusion when the spring thaw begins. We already get a small amount of water coming in through the row of block around the garage in the generator corner (we’ll be sealing this over summer). Additionally, the only metal roof that I’ve liked the look of imitates the physical shape of shake shingles. It is quite expensive.

I hold the main carpenter and cabinet maker in high regard because they utilized a style I would call “legacy construction”. They take advantage of historical principles of design that utilize strength and longevity, but whose construction is achieved through modern techniques. One example is the edge trim outlining the entrance to the hallway. The trim is a solid pine 2×2 that has been sculpted into an “L” shape. The trim sleeves the edges and is impervious to tear out. Using a single piece of trim where two separate pieces adjoining along an edge would be adequate, but forgoes the simplicity and durability of a single piece. The cabinet maker placed solid wood panels (3/4″ thickness) on the end of the counter and I still find things to admire about his joinery when I visit the cabin. He also constructed the L-shaped counter top in his shop, making it a single solid peace. Simple and durable.


There are plenty of posts going over details that I like about the cabin as well as some of the projects undertaken. To balance things out here is a list of what the Ol’ man and I really like about the design and construction of the cabin:

  • Glass block windows in basement
  • Vaulted ceiling in living room
  • Carpeted bedrooms
  • Tiled bathroom and entryway
  • Free-standing wood burner
  • Large windows in every room
  • Window grids really dress up exterior
  • Roman shades on windows
  • Covered porches on both sides
  • Tall ceiling in basement
  • Egress window for basement (allows for sleeping quarters in downstairs)
  • Half wall by kitchen opens up main room
  • Minimal space wasted as hallways
  • Garage set back so living room has view of maple ridge
  • Cork flooring in basement is reasonably warm
  • 8″ pine D-logs
  • Placement of Inverter control panel and battery monitor in cabin
  • 12V DC and 110V AC power supplies
  • The gate! and the location

The utilities of the cabin were all added during construction. Because we cleared forest for the cabin we had the burden of drilling a well and adding a septic. Michigan building codes are great fun in this regard and now we have a septic that has the capacity for a 3-bed, 2-bath house for our 2-bed, 1-bath cabin that is occupied 120 days per year with an average occupancy of about 2 people. The septic is overbuilt (1000 gallon tank) so it can safely be considered low-maintenance. Our biggest concern is making sure that the drain field is kept tree-free and that tree-roots don’t cause problems several decades down the road. The well is 110-115 feet deep and utilizes an off-grid friendly 110V Grundfos soft start submersible pump. The pressure tank is a bit oversized additional water use when the power system is turned off and set to 30/50 psi to accommodate the 110V pump/well depth . This fall (2013) a water softener was added per Mother’s request. We manually recharge the softener since the power is not consistently on and our water use is relatively low. The propane tank is owned (not rented) and we shop around and pre-buy propane. The tank is 500 gallons and as far as use is concerned, it was filled mid-October 2013, and as of April 1, 2014 was at 40%. This will vary depending on how many nights the cabin is occupied in winter, but keep in mind that winter 2013-2014 was a record cold winter. The thermostat is set at 42-45°F for the winter months. When we stay we rely solely on wood heat. The new propane heater in the basement is also set at 42-45°F as a back up. Even though the plumbing is PEX material and the water is manually shut off when we leave, a cracked toilet from a freeze would still be a pain to deal with and neither the Ol’ man or I would like to test the freeze-resistance of PEX or risk freezing and exploding beer bottles and soda cans in the pantry.

There were a lot of choices to make when building the cabin. As in the plans, we have 3″ of pink foam on the basement walls, and blown cellulose insulation in the roof (with vapor barrier). The garage is insulated with R19 fiberglass insulation in the walls and ceiling. We chose logs for looks. What we are finding is that the logs are relatively low-maintenance on the interior of the cabin (finished with a UV-protector) but the outside will require periodic maintenance with Sikkens. The logs also provide a thermal mass which is convenient in winter and summer. In summary, when the logs are warm they tend to stay warm, and when cool, tend to stay cool. We chose slider windows (instead of double hung) due to cost. Adding covered porches instead of a deck added cost but the shade in summer and the weather protection for the decking are two benefits we are currently enjoying. Most of our gas appliances are electronic ignition to avoid a pilot light. Since the cabin is not a permanent residence, we like to minimize the number of pilot lights on when we are not around. It also gives us control over the water heater so we can selectively recharge our hot water supply once a day. The stove is also electronic ignition but with a big downside. The stove has a glow-plug that stays on whenever the oven is in use. Power consumption for the glow-plug is on the order of 400 watts! Without power the stove will not work. Here is a previous post with more information on our appliance power use. Appliances that have pilot lights are the two gas heaters and the fridge. The fridge is made by Dometic and offers up 8 cu ft of space with a 1.6 cu ft freezer. Fuel use is around 2 gal/wk. We have a sump-pump pit but after 4 years have never had so much as a drop of water in it. The pit is drained out the side of the hill with a PVC pipe with a screened end. In winter we cover the pipe with foam insulation and cover it with a board and a brick. The 12V DC system is one of our favorite decisions. I’ve covered it before on the blog and it will be covered again. It’s’ that awesome. We presently have six 12V accessories:

The 12V LEDs offer virtually no downsides. They run cool, use little power, and have roughly a 30 watt incandescent-equivalent output per fixture. The timed light in the kitchen is a great night light while the garage service door and bench light make arriving to camp after dark a bit more convenient. 12V LED was a gateway to replacing our existing CFLs with LEDs cabin-wide. The post off-grid system :: diagrams has been updated with the AC LED conversion. The upgrade was done in 2012 and we haven’t looked back since that time. The biggest advantage of LEDs (other than power consumption) is the instant-on nature. CFLs take far too long to warm up when used in exterior applications – especially in winter. The lighting quality and choice offered by LEDs is another advantage. See the post 12V LED lights :: observations for more on lighting spectrum.

Lastly, some thoughts on how to deter or prevent theft. Our previous camp was broken into and a number of curious things were stolen (frozen pizza, firewood sling, and some tasteful magazines from the 1970’s renowned for witty and intelligent commentaries on social and political matters). The break-in demonstrated the value of not keeping valuables at a non-permanent residence (guns, jewelry, hunting gear, electronics, etc…) I’m not going to discuss exactly what we do for security, but I have some suggestions. The number one way to deter theft is to always be at the cabin… or make it look like you are home. Motion lights can help, but if the locals are going to rob you they’ll know when you are home or away. In addition to lights, a garage where a car can be parked makes it harder to tell when you are home or away. Speaking specifically about a camp I’m not convinced strong locks make much difference. Any lock can be overcome with the appropriate amount of time or force. If on the end of a dead end or gated road, don’t advertise that there is a nice cabin at the end of it. I prefer a rusty gate and a weather worn Do Not Trespass sign. Also do not post the location of your camp on the internet and especially do not post GPS tagged photos (pretty much any photo taken with a smart phone at present). There is software for adding or removing GPS data from photos. I am very diligent about stripping location data from my photos before posting – I have been Geotagging since 2005. Trail cameras are another good security option. They are nearly impossible to find (especially if you have more than one!) and there is a good offering that allows cellular data connections at a reasonable price for remote surveillance. With our current state of technology, even the would-be-thief not burdened with an abundance of brains is likely to take a “Video Surveillance in Use” sign into consideration. A handful of companies make trail cameras specifically for catching license plates and now with true infrared flash it’s getting harder to get away with unsavory activities, even at night.


This post took a bit more research and time to assemble than most of my previous entries. It’s been in the works in some form or the other for over a month now. I’ve searched through old e-mails, my notes, and had at a least a dozen conversations with the Ol’ man on the technical details of the cabin and garage. As always, questions welcomed :-)

Revised for accuracy on 4/16/2014

off-grid system :: diagrams




  • off-grid inventory 5: (ADDED 4/12/2014) – I’m 18 months behind on this but I finally updated the inventory to include our conversion from CFL to LED lighting in the cabin. The update cost $486.10 for just 22 LED emitters. Wow how the price has changed. Non-the-less, we remain happy with the upgrade. LEDs in my observation offer much better lighting characteristics than CFLs and a wider choice of spectrum choices than incandescent.



  • Cabin DC wiring 2 (ADDED 8/26/2011) – updated; now includes battery monitor
  • Cabin Power System Schematic 2 (ADDED 8/26/2011) – Completely reworked and updated! This is a huge improvement over the old schematic. And that big blank spot on the LED diagram – that is reserved for the technical drawings of the 12V LED install planned for the cabin. The wire has been run from the garage and the bulbs have been ordered. We’re going to use standard E26 screw in bulbs specifically designed for 12V DC with a wide 180° coverage with 400 lumen output at 5.6W – in other words: we can use a standard light fixture and wire it for 12V DC instead of 120V AC.



Throughout the research and design phases of the project I created and updated this schematic: Cabin Power System Schematic (UPDATED 1/27/2011). Please note that the DC switches used in the LED light diagram are standard 110V AC light switches and not the toggle switches in the diagram.

  • Each item purchased in the construction of the system was also briefly catalogued in order to keep track of expenses: off-grid inventory 3 (UPDATED 7/31/2011). In this new inventory I’ve added pie graphs and itemized expenses by project.
  • I also created a DC wiring diagram (ADDED 3/7/2011) to better show how the panels, inverter, fuses, and breakers are connected.

I will continually update this post to reflect the current set up of the off-grid system.

Previews of the most recent documents (open PDFs above for easier viewing):

Overview Inventory

Ice Climbing

4.6.2014 – Sunday

Brian and Paul made the trip up from Milwaukee after Friday classes. When not in med-school they trade a place to stay and home-made breakfast for access to their ice climbing expertise and gear. We climbed the Good, the Bad, and the Ugly on March 29th… on roughly 5 hours of sleep.


8:30am – start out on foot across lake
9:45am – reached destination of hike (2 miles later)
10:45am – reached the easy ascent route
11:30am – ascended easy route
12:45pm – reached final climb
2:30pm – repelled final climb
3:15pm – began climbing
5:30pm – concluded climb
6:00pm – began trek back to car
7:30pm – reached car
8:00pm – departed for home

batteries :: cold weather

3.24.2014 – Monday

IMG_0869 HDR

There has been little doubt that these past few months have been Winter. Little chance of mistaking it for any other season. Records are adding up and it’s reasonable to say that it has been consistently cold. The silver lining has been the lake ice of Lake Superior. More ice means the liquid water is locked away and we have more sun and fewer lake-effect snow showers.

2014 data from NWS Marquette:

  • February averaged 5.6°F
  • 78 consecutive days were below freezing
  • 5 days this winter the high was below zero
  • 20 days in February had a low below 0°F
  • -28°F was recorded on 2/28/2014

The off-grid tech we have in the un-heated garage faired quite well this winter. As a result, I think we can endure future winters without much worry. Despite the cold, the lowest recorded temperature at the battery terminal (where the sensor is bolted on) was still in the twenties. The garage is fairly well insulated and the generator exhaust vent gets closed off when we depart – sealing up the garage quite well. An interesting observation the Ol’man and I noted was that the exhaust fans for the generator (two 100 cubic-feet per minute 110V muffin fans) were not working as efficiently as hoped. The solution was to crack the service door just a bit to let fresh air in to displace the air vented by the fans. The garage is very tight with doors shut and windows latched.

Before departing we like to make sure the batteries have a charge somewhere between 85-100% in the winter months. After some data mining I assembled the table and drew up the graph in this document: Freezing Point Depression. Below is the graph.

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The document was my effort to determine what it would take to damage our battery bank. The short answer is that it is almost impossible to freeze-damage our batteries given the lowest observed temperature in the garage.

We charge up to 85% or more before departure because of the lake-effect skies. It may take 10 days for our panels to collect 100 Ah in winter. The 12V LED lighting requires about 30 Ah (at 12V DC) to operate each day. In 10 days without sun (not an uncommon event) we’d find our battery bank down 300 Ah! The battery bank is rated at 1540Ah at 80°F. Ever wonder why batteries get ratings at specific temperatures? I recorded some data from our battery bank (via amp-meter and specific gravity) and found that at 30°F the batteries are down to roughly 50% of the 80°F rated capacity! The reaction required to transform chemical energy to electrical energy gets inefficient as the temperature drops. In deep winter, 300 Ah becomes 40% or more of the battery bank capacity.

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My data set only has three samples and it would be nice to get another point below freezing. However, given how well this graph has aligned with casual observation, I’m not too enthusiastic about drawing up below-freezing electrolyte in a glass bulb for an additional dot on a graph.

While cold batteries may last longer, warm ones sure work better. If you happen to be in the process of deciding where to place batteries in an off-grid system, hopefully I’ve given you some useful information. To finish up, here are a few parting shots of winter. Despite the cold I enjoyed winter this year and the lake ice made for some fun family outings. None-the-less, I’m happy to move on to maple tapping.


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12V :: fan box

2.27.2014 – Thursday

Sure was nice out today… except for the temperature. The sun was warm and bright but the wind dulled my sense of touch to the point that taking off my gloves to gain more dexterity for strapping a car seat into the Honda Pioneer was a foolish decision.

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But inside the cabin the weather was much the better. Wood heat. Wonderful, radiant, wood heat. A rolling flame softly rising against the glass pane. As much as I could while away the day sinking into the couch next to the fire, the latest cabin project required my attendance in the basement. The Ol’man had already run a surrogate wire up the wall behind the gas stove from the floor to the ceiling – which we would use to pull the lamp cord through and up the wall. In the two weeks previous I was able to acquire some things:

  • $17.62  – KingWin Four Channel Turn Knob Multi-Fan Cooling Controller FPX-001 (LED Indicator for Power On/Off, Control 4 Sets of Fans, 3 Pin Fan Connections)
  • $5.00    – 2x Neodymium Magnets 1/2 x 1/2 inch Cylinder N48 (26 lbs pull force each)
  • $1.51    – 2x Neodymium Magnets 1/4 x 1/4 inch Cylinder N48 (6.3 lbs pull force each)
  • $27.80  – 4x Evercool 60 x 25mm High speed 3 pin fan EC6025H12CA (Dimension (mm): 60 X 60 X 25, Bearing Type: 1Ball Bearing, Speed (RPM): 5000, Rating Voltage (VDC): 12, Power Current (AMP): 0.24, Air Flow (CFM): 26.5, Noise (dBA): 30, Pin Type: 3 Pin Type / 3 wire)
  • $0.85   – 5 amp blade fuse
  • $6.20   – 4x male &  female insulated connectors
  • $0.35   – 1x butt connector
  • $9.00   – 50 feet of lamp cord (18-2 copper stranded, $45/250 feet roll)

I had some extra parts as well – that’s just what was used in the final installation. The actual construction took about 5 hours start to finish with some additional time invested in gathering measurements from the stove. The total for this project was $68.33 and 5 hours.

 The fan box is an alternative to a $260 factory accessory. The factory accessory plugs into exiting connections on the stove and requires access to a 110V outlet for power. The objectives that had to be met by the fan box were 12V DC power, easy installation, ability to use existing wiring on stove, and to force enough air between the fire-box and firewall to increase heat distribution throughout the basement. 12V DC power means that we can heat up the basement without wasting power idling an inverter. The magnets allow for easy installation and adjustments. I purchased wire connectors that mated with the existing wiring on the stove for installation. And lastly, the fan controller allows for each fan to be individually adjusted for output (which is nice for fine-tuning the airflow to noise ratio).

Design wise, the fan box is glued together with a few plugged wood screws. The fans slide in from the open end and all the wiring connections are enclosed.IMG_1786

Sliding everything into the box allows for easy maintenance and fewer screws. The fit is snug so there is no rattling. IMG_1783

Once the cord cover panels and controller plate is slid in the end cap is magnetically held in place by small 1/4″ x 1/4″ cylinder magnets that mate up with screws counter sunk and adjusted for a perfect fit. IMG_0254

The two large magnets are quite powerful. As a test I was able to easily support two hammers over the fan area without failure of the magnetic  bond. IMG_0259

I had thought that a rheostat was pre-installed on the stove, but when I started the install I discovered that there was a space for a rheostat and not actually a rheostat. The stove has an aesthetically pleasing ON/OFF rocker switch for the front flame. The flame turns ON and OFF with the switch, but also turns ON when the stove fires up and starts to produce it’s 20,000 BTU output. I suppose in a house it would be nice to see a constant flame without having the stove run at 100% in order to see the flame. For the time being the switch has been repurposed as the ON/OFF switch for the fans (instead of the rheostat switch like originally planned). The install went reasonably smooth, making this the 3rd 12V accessory added to the cabin after the LED lights in the kitchen and the charging station automotive outlets. Three of the six slots on the 12V cabin fuse block are now in use.


The blue LEDs are visual indicators that the fans are on. They do make sound as well, but if we decide to slot in quitter fans in the future it may be nice to have a visual indicator that something is running. IMG_0300

Two additional accomplishments for today were the replacement of the energy hungry 42″ plasma TV with a much more conservative 42″ LED TV, and the discovery of a battery charger that does not make LEDs on the 12V system pulse. The unofficial drop in power for plasma to LED is from 15 amps to 2.5 amps (multiply by 12V for watts). The charger we now use at the cabin is better designed for utilizing 12V power and uses a constant current to charge batteries instead of a pulse wave. The result is no more voltage fluctuation on our 12V system. The charger appeared in the previous post and is the Nitecore IntelliCharger i4. The charger is able to charge our AA, AAA, CR123a, and 18650 flashlight batteries. A $5 car cable makes it ideal for our charging station. At about $20 street price, it replaces the Lacrosse BC-700 Alpha that we’ve been using with a 12V to 3V automative transformer and charges the batteries in about 1/3 the time – still acceptable to promote longevity of the battery, yet quick enough to provide a useful upgrade to the current charger.


Now at night we can charge our flashlight batteries, have only the 12V kitchen lights on, and watch shows on a 42″ LED TV and only use a total of 6.5 to 7 amps! (or about 80 watts). Add just 0.5 more amps and the basement can be warmed up using the fan box to push hot air out of the gas stove. IMG_0298


Remember how I mentioned it was cold? It reached 0.0°F at the cabin in the sun. Right now, at midnight EST it is -21°F and dropping (without windchill). This is a winter for the record books. I’m glad I’m not a yearling deer this winter.