Prius House Battery Migration From Gel Cells to LiFePo4

                      
Above is my original house battery setup for my first year of Prius Travels.

In case you have not been following my Prius Travels since 2014 you may not know what I am talking about. 

Living in my Prius for 4 months out of the year brings power requirements that are not best suited for the Prius 12 Volt system even though the Prius is a generator that resupplies power to the 12 Volt system from the hybrid high voltage battery through a DC to DC converter. When the high voltage battery gets low the Prius engine starts and generates power to replace what was taken from the high voltage battery. To do this the Prius ignition must be left on or what is called "Ready Mode".

My biggest demand for power is my Engel compressor fridge that I recently posted about how well it operates and how little power it draws. 

My first year of Prius Travels I had two gel cells and found that although the two 12 volt 7 amp hour batteries got me though the night when March comes to the southwest it gets hot and the fridge runs more and I was stressing the 2 batteries.

Note that Gel Cells are lead-acid batteries and if they say 7 ah you can only use half of that number so my first year I had 14 ah and only 7 ah were usable without killing the batteries. 

Above is my Prius house battery setup for year 2 of my Prius Travels.

To solve this problem my 2nd year of Prius Travels I upgraded the gel cells to 8 amp hour batteries and added a third battery. (picture above)  This gave me 24 amp hours but remember to divide in half and I had 12 amp hours of usable power.  This was a large improvement in available power and solved my stressing the two batteries.

Here is my post of upgrading my Prius House batteries.
http://macaloney.blogspot.com/2015/06/prius-house-battery-upgrade.html

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All was good in the world of house batteries for my Prius Travels, but I still had a couple of issues. 

- Gel Cells should be replaced each year before the next to prevent problems on the road.  They cost about $20.00 each, which is not that bad.

- In the afternoon after hiking or parked for some adventure I sometimes found myself with my batteries needing charge before I parked for the evening.  Charging usually took 2-3 hours.  Stealth parking is most important as you don't want the Prius turning on and off to draw attention, but I was also having to run the Prius in Ready Mode more than I cared to.

- Lastly, I like to hike and when I hiked first thing in the morning before it gets too hot I may only have an hour or two at most to try to recharge the gel cell batteries and then run the fridge off of them while I am hiking.  Again I found I was stressing the batteries.

Above is the new LiFePo4 replacement battery for house batteries.

I knew that the solution was Lithium battery, but I wanted to properly investigate the technology and find the right product before I would install it. 

First thing to understand is that Lithium is the name for a variety of battery technology or chemistries.  The first lithium batteries that came out are Lithium Ion (Lion) and are the kind of battery in many devices and have the bad history with burning things up. 

The technology I looked at for my house battery replacement and decided on was LiFePo4 (Lithium Iron Phosphate).  It is much more stable and also has a lower operating temperature (down to 14 degrees), can be recharged many more times than Lion, and here is the big one, you can use up to 90% of the rated amp hours.  You heard that right.  With lead-acid technology you can only us 50% of the rated amp hours on the battery, but LiFePo4 can use up to 90%.  Also, Lithium batteries weigh much less per amp hour.  So many advantages.

BUT! Not all LiFePo4 batteries are made the same by all manufacturers.  I read a lot online and wrote technical questions to the companies and I selected to work with the Bioenno Power as they were the most responsive to my questions. 

I wanted my battery to be as high an amp hour battery that could reasonable fit in the space I have in the back of my Prius and be able to be fast charged. 

But wait! more choices.  Companies are putting in circuitry to protect the batteries.  PCM or Protection Circuit Module is encapsulated in the battery pack to protect the battery from over charging or under charging the battery as well as other things.  With a lead-acid battery if you go over the 50% mark of its capacity you risk damaging the battery.  The PCM will shut off the LiFePo4 battery to protect it from being overdrawn. 

You can also get your battery with BMS or Battery Management System.  BMS takes the individual cells that make up the battery and balances the individual cells after a charge to keep the cells from becoming a problem. 

I chose a battery that has the PCM and BMS for the most protection and longevity of usable life.  Getting the BMS means though that I have to wait 30- minutes after a recharge to let the BMS to balance the cells before applying a load on the battery.  I figured out I didn't mind this inconvenience.

I settled on the battery in the picture above (Bioenno Power BLF-1230LB) that is 30 amp hours so that is 27 amp hours of usable power for the same size as the 3 8 amp hour 12 volt batteries that I was currently using that gave me only 12 amp hours of usable power.

The spec for this battery listed that it could only be charged at 4 amp hours.  This wasn't acceptable as it could take 8 hours to charge a fully depleted battery.  No way!  One of my emails discussed this with the company and with some research it was found that the PCM had been recently updated to allow for 10 amp charge rate.  Yes!

The battery was $279.99.

Above is the new LiFePo4 battery charger for my new house battery.

I ordered their LiFePo4 10 amp charger (BPC-1510C) for $48.99.  You must use a LiFePo4 battery charger on this battery! You can use battery chargers that pulse to remove sulfur deposits on lead-acid batteries like you can use on Lion drop in replacement batteries for lead-acid.  We are dealing with a whole different technology.

 Above is my initial charge of the LiFePo4 battery and compatible charger.

The first thing I did when the battery and charger arrived was to charge the battery as they are usually shipped at 30% of their charge.

After fully charging the battery I plugged in my Engel fridge and let it run until the battery stopped as a test.  The fridge ran 52 hours before the battery shut off.  Excellent!  The battery measured 1.1 volts but as soon as I disconnected the load the battery went to 12.1 volts.


                             
Above is my test measurement that I was delivering 10 amps to my new battery.


After depleting my new battery I set out to fully charge it and it charged in 2 hours and 50 minutes.  Excellent Again!  Above you can see the charge rate of just under 10 amps.

With everything tested out great the next step is the install the new battery and charger in the Prius removing the current gel cell batteries and multi-chemistry lead-acid charger I have to charge them.

For those wondering about LiFePo4 and solar.  Stay tuned.  After my install blog on the new LiFePo4 battery I will be working on the solar connection to this system and will blog about that.

For those interested in moving to Lithium battery technology please keep in mind the differences I mentioned above.

Brent

macaloney@hotmail.com

My Compressor Fridge Review - Engel Model: MT17F-U1

When I planned my travels for the winter of 2014 I did not know what kind of vehicle I would have to travel in.  I had first thought of using my Toyota Tacoma pickup truck.  I thought I would put a cap on the back of the truck and live in it.  I started a design for the interior bed of the truck and went about looking for what cap I would want.  I had a list of things I wanted to bring with me and one was a fridge.  I had researched and before I had my design for how I was to travel I bought (invested in) a compressor fridge from online reviews.  My choice was the high-end Engel compressor fridge for its ability to use so little power. 

As it turned out I could not find a cap for my Tacoma that I truly liked due to the sloped sides. I was also running out of time to get a vehicle for January and I was lucky to find a 1994 Class B Coachman in nearby New Hampshire that was to be my first year's vehicle to travel in.  My Class B had a 3-way fridge but I knew how much work they involve and how much 12 volt power they use so  I ended up using the Class B fridge for dry storage and my Engel fridge for cold storage.

Here is the tag on the side of my Engel Fridge.  My model operates on both 12 Volts DC and 120 Volts AC.  I bought this with dual power so I can use it at home as well as on the road.  The price tag online from Engel was $800 and $60 for shipping to MA.  This was an expense purchase and more than what I wanted to pay, but I saw it as an investment. 

When not on travel I use my Engel fridge for short and long trips and even for going to the grocery store to put items in that you don't want to spoil or thaw.

It is well known that compressor fridges are great for vehicle dwelling and they use little power.  For me this was my goal, but when I came back from my first year of travel I knew I couldn't sustain the cost of fuel for my Class B and travel the way I want.  I could not have been more pleased in planning for my second year of travel and switching to a Prius that my small Engel fridge was just the right size to allow me to continue to have a fridge and have room to sleep along side of it. It fits great under the privacy cover too!

From my other blog postings you know that I have done a lot of designing with the Prius including a house battery to power the fridge at night so the Prius doesn't have to run at night.  My first year I ran the fridge overnight on 2 12V gel cells at 7 ah each for a total of 14 amp hours.  Since you only have use of half the amp hours in a lead acid battery such as these, my Engel fridge got by on 7 amp hours a night!

My house battery had limitations the first year in that when I wanted to hike in the morning I hadn't sufficient time to recharge the gel cells before going out, and I stressed the two batteries.  My second year of travels in the Prius I upgraded the gel cells to 3 12V 8 ah batteries for a total of 24 amp hours and half of that was 12, and this provided me a much better buffer for my house battery usage.  I am currently planning my third year of travels in the Prius and I am working on a whole new house battery design that I will be posting in this blog about soon.

I like to cook and eat fresh food.  To say I like my Engel fridge is an understatement.  It just does what it should.  It is not a fridge with lots of gages.  It has a knob for setting the temp and there is no temp indicator.  I fixed this my first year by using a remote outdoor wireless thermometer from Walmart for $10.00  Other than that it just runs and runs and does it efficiently.

How efficient?   I didn't know and I decided to perform some tests 3 years after buying it so I could  pass the information on to all of you considering a compressor fridge. 

The tag on the Engel fridge says 2.5 amps running at 12 volts.  The high I measued is 2.65 amps when it first starts and then it drifts down to 2.14 before cycling off.

In standby mode between turning on and off the Engel fridge uses from .184 to .125 amps.  This powers the circuits and the LED in the 12 volt plug end so you know there is power to the fridge wire, and another LED on the fridge itself to let you know the fridge has power.

What does all this mean.  Well, I did some duty cycle testing.

I put the fridge in the house where it is a constant 70 degrees F
I let the fridge come down to 35 degrees F

The fridge has a 11 minute 45 second total on/off cycle under these conditions.
The fridge runs 2 minutes 10 seconds on during this 11 minute 45 second cycle
So the fridge is off 9 minutes 35 seconds during the cycle.

This is a constant on/off that the fridge goes though.

This results in a duty cycle of 22.7%

If we use the tag on the fridge for amperage draw of 2.5 amps we would have 2.5 amp hours usage if the fridge ran and never shut off.  Since the fridge cycles on and off at 22.7% from my measurements the actual usage under these fixed conditions is .57 amp hours.

This explains how my fridge ran overnight my first year on the usable 7 amp hour of gel cell battery power (half of the 14 amp hour rating)  If I parked at 6 pm and started charging again at 6 am I would have used all the available 7 amps, thus leaving me nothing if I went to hike.

I solved this problem of needing more power by unplugging the fridge and not running it during my morning hikes.  I always kept a 1/2 gallon of my drink of choice in it and this acted as a good mass to withstand the time during the hike, but then I need to spend time charging in the pm and getting the temp in the fridge back to 35 before night so I could run the fridge at night.  All this worrying about battery power and the fridge was distracting and why I added a third battery my second year of travels.

This gets me to my new house battery design I am working on to allow more flexibility of power at night.  I would like to run other items at night off my house battery such as a USB fan, and with my current design, with only enough power to support the fridge, I can't do this.

Of course I have a Prius with all kinds of power since Ready Mode supplies power from the high voltage drive battery to the 12 Volt Prius system allows me to have the Prius run only when it needs to charge the high voltage battery, but I also like to stealth park and running the Prius even in Ready Mode would cause attention. 

I hope this post explains how well my Engel compressor fridge works and how little power it consumes. I need to add that in January, even in the southwest it is cold at night and mild during the day and there are times that the fridge can be unplugged at night.  On the other hand, by mid-March it is getting very hot in the southwest and in the car even hotter. Even with my windows cracked for air circulation, it is hot in the car and the fridge is subject to using a lot more power to keep cool and also because it can't dissipate the heat from the condenser.  On these hot days with no shade for hours I may leave my Prius in Ready Mode and leave the air conditioning on (set to a higher temp) to help the fridge through that situation.  I do put Reflectix around my fridge leaving the fridge vents open to repel the heat and this works well.  I don 't have room for foam insulation around the fridge in my Prius design, but you still have the issue of the dissipating the heat from the condenser.

Brent

macaloney@hotmail.com

Prius Rear Hatch Split Storage Cover Design

Above is my redesigned Prius Split Rear Hatch floor compartment door.

This solution allows my compressor fridge to sit on the 40% split-side while still being able to access storage under the cover on the 60% side where my bed is.

Before this change, I was required to move the fridge every time I wished to access the storage space when on my travels.

Since space in my Prius Campervan is limited, I usually access this space daily, making moving the fridge aggravating. I know, I traveled doing this for the 2015 and 2016 Travels.

You can see the marks on the original Prius cover, where the compressor fridge sits on the 40% side of the back. Marks are exacerbated by the daily movement.

Above is the original Prius cover with the single storage door open.

The  original Prius cover is plastic and makes for a great template to make my split cover design.

Note that sides of the original Prius cover are not square, so I had to cut the outside edges of my design to match the taper of the original cover.

The 60/40 center cut was a straight cut.  I used 1/2" plywood, which is the same material i used for the bed platform to replace the rear seat.  See separate post on my rear seat bed design that I did the first year I traveled in the Prius.

If you look at the underside of the Prius Cover you will see it has indents where it sits on the rim of the tray below the cover.  What this means is that I needed to add shims to the bottom edge of the plywood to fill the voids to have it sit flat around the edges.  

Problem! You can see (above) the sag where the two sides sit next to each otehr.  Since the Prius cover is made with full side to side support there is no sag in the center.  This split design is not supported full length side to side so there is a sag in the middle that I needed to address.

I use 1/2" plastic board in some of my designs so I made a box that covers all four corners of the new split cover design. This plastic box stores some cables for me and sits on the plastic Prius pan directly below this cover.

In testing out my design (above), you can see the white box I made to support the split cover design.  The box is usable space and provides the support all in one.  

After validating my design I chose to spray paint the plywood with gray paint to protect the wood and match the Prius interior. In addition to the pain on both top and bottom I added felt to the top on either side of the piano hinge and rolled over the sides.  Then I drilled holes and put pull straps up from underneath to make for easy lifting of the new access panels.

I protected the area where the hinge was with masking tape and sprayed contact cement on the service and laid the felt on top.

With this change I am ready for my 2017 Prius Travels without having to move the fridge each day.

Brent

macaloney@hotmail.com