Lithium Battery Update and Magnum Magna Hybrid Sine Inverter / Charger

Hi Folks,

It has almost been a year since my last update.  I stare at a computer all day at work, so I can go weeks before I even turn on my Home PC.  As a results, this poor blog hasn't been updated, since I have other things I want to do.  

I started freeze drying back in September 2017 (kind of a hobby), so I would start eating more fruits and vegetables instead of other things for snacks.  It takes a fair amount of work to keep it going, but I hope to have a bunch of food freeze dried before we hit the road.  The nice thing about making freeze dried food, is it doesn't require refrigeration (can be stored for 25 years), is light weight (10 lbs of potatoes weighs only 14 ounces freeze dried), and it retains 97% of the nutrition.  Maybe someday I will do a blog on that. 

At any rate I retire in December of 2018 and we plan to hit the road until we get tired of it.  So maybe I will do a better job keeping up on my blog then.

Chevy Volt Lithium Batteries Reconfigured

This was done in February 2017.  After one year of use, several things were learned.  First, the batteries never really got hot from use or charging,  so liquid cooling is not needed for this type of application, but heaters are needed when RV sits in the cold in storage.  This is why I used a star configuration in the first place, was to allow for liquid cooling.  This configuration is not best keeping the four batteries balanced or maximizing space.  

Old Battery Box (Star configuration).

New Battery Box.  I added 1/2 foam insulation on inside.

Batteries are now lined up in parallel.  Each battery has a battery balancer which keeps all the cells at the same level (very import with Lithium batteries).

The second item I learned is the BMS hooked up to the battery port didn't truly keep all cells balanced.  I found the first cell in the first group to be way out of balance after one year of use.

The batteries were converted from 48 volts to 12 volts, so each battery has four 12 volt (of 3 cells each) inside each battery.  Here I am balancing the first of four batteries (inside the physical battery).  Only the first one was way out of balance.  BTW, this is the hobby battery balancer I have used for last two years and works great.  The nice thing about this battery balancer is it keeps monitoring and balancing after the cells are balanced.  Most hobby balancers marketed today quit balancing when cells are balanced.  The blue balancer in the previous picture to this one is that type, and is hooked up to the Boostcaps.  I can't use the black one above, because the cell voltage of the Boostcaps are too low.

So once all the batteries were re-balanced, I connected all same voltage cells together, and wired my battery balancer directly to the battery.  Here the before and after modifications.

Here is the 48 volt battery as converted to 12 volts by eBay seller.  Basically they cut the series plates after every three cells and then connect the four pluses and four minuses together in parallel.  The cells at 4 volts and 8 volts are not connected together.

I connected all the 4 volts and 8 volts cells together, and then I wired my battery balancers directly to the cells, which are now wired in parallel at the cell level.  After a year, I have had no more problems with one battery cell within the battery getting out of balance.

The third thing I learned in the first year was that it was easier to buy Arduino UNO Shields and sensors than to build my own custom circuits.  Also I don't need to worry about cell level monitoring, since the battery balancer will keep all the cells balanced.  This made the Arduino much simpler, as well as the programming simpler.  The Arduino now monitors battery voltage, boostcaps voltage, and temperature.  I also went to a solid state battery relay which connects or disconnects the battery as need.  Using a relay shield, I have four relays to control devices on and off.  Currently I use 3 of the 4, (1) battery connect relay, (2) fan control, and (3) heater control.

New Battery Monitor System (BMS).  Much simpler, using a Arduino UNO (bottom), Relay Shield (next up), Ethernet Shield (above Relay Shield), and finally Custom Circuit Board (on top).  There are also two voltage sensors attached to top custom circuit board.  These are used for monitoring battery and boostcap voltages.

Another view of the four boards.

I added some buttons on to fine tune battery, boostcaps, and temperature, because when the PC is connected to Arduino it effects the accuracy of the measurements.

The new web page also includes raw data, so you can see what adjustments need to be done with the buttons on top of the custom circuit board.

The last change for the batteries was upgrading the battery cables from #2/O AWG to #4/O AWG to handle the 3000 Watt Hybrid Sine Inverter.

This winter we have been in the single digits and did not get above freezing for a week.  The RV sits in a storage lot right now, but I have alarm system, with a temperature sensor in the battery box so I can monitor the battery box temperature remotely.  The BMS turns the heater on at 38 degrees, and I have not seen it go below that, even with outside temp in the single digits.  If the box temperature gets to 32 degrees, the alarm system will text me, and notify the alarm center who will also call me.  This happened a couple of time last year, before I hooked up the heaters.  The heaters have been using about 16 AH overnight with current temps in the low teens.

Magnum Magna Hybrid Sine Inverter / Charger

Also done in February 2017, this was a big upgrade over the Xantrex PROWatt 2000 Inverter, which really didn't like running at the lower voltage of my lithium batteries, and could not handle high startup current of things like the vacuum cleaner.  

The Magna also has a charger function which I have tested on a 100 foot 14 GA extension cord and a standard 110 Volt 15 amp circuit.  Lithium batteries will take all the amps it can get while charging, and this will blow blow a 15 amp circuit in just a few seconds using the factory converter charger.  My factory converter will pull 34 amps, which will many times blow a 30 amp RV service when batteries are below target voltage. The Magna will let me set shore power to 12 amps, and will charge the batteries without blowing the 15 amp house breaker, since it will never pull any more that 12 amps from shore power regardless of load.

Before the Magna Inverter, I was only able to charge my batteries with solar when hooked up to 30 amp service, since the factory converter will pull 34 amps to change the batteries.

The other big advantage of hybrid inverters is to supplement shore power (or generator) using the batteries.  Example: if connected to someone's house, you can set the Magna to use 12 amps.  If you turn on the A/C or microwave, the Magna will make up the difference using the batteries.

Once the load drops back down, the Magna will then use the excess of the 12 amps to recharge the batteries, but at no time will it draw more than the 12 amps I set for it to take for shore power (or generator).   Since many places still only have 30 amp service, you can set the Magna to take 30 amps from shore, and can boost that to 60 amps (using the batteries).  When the load drops to less than 30 amps, the Magna will use those extra amps to recharge the batteries.


I also installed Micro-Air Easy Start With the Easy Start you can run the A/C on one Honda 2000, or just off the Magna Inverter itself. With the Magna Hybrid Inverter set to take 14 amps from the generator, I am able to run the A/C and the microwave at the same time. 

Magnum Magna Hybrid Sine Inverter / Charger.  It can take up to 30 amps shore (or generator) power and boost it 60 amps.  Just keep in mind, if pulling 30 amps from the batteries, will be around 300+ amps being drawn from the batteries.  That will drain your batteries pretty quick.  When load reduces below the 30 amps, the Magna will start recharging your batteries with the excess power from shore power.

This is the remote control unit for all of Magnum's products.  This is where you also set how much power to pull from shore power or generator.  I am also looking at replacing my Morning Star TRI-STAR MPPT 60 with Magnum PT-100 MPPT Solar Controller since it can handle 100 amps output.  The PT-100 will also use the same remote control unit I already have.  This will allow me to use my four panel in summer time.  Currently the three panels on the roof can produce more than 60 Amps, and the Morning Star will throttle the panels so output doesn't exceed the 60 amps the controller is designed for.

There are many other modifications I've done, and trips we have taken, I will try to put something together on those in the next day.

Spring projects for this year, are to replace the theater seating with higher quality seats, and upgrading the solar control Magnum PT-100 MPPT Solar Control.  

Not sure I can find space on the roof to mount the forth panel, so I will probably keep it as a standalone panel can place on the ground to catch morning and evening sun.  Also gives me options when camped under trees.