Chinook Power System Upgrades Part 2 – Lithium Batteries

When we bought Harmony in 2014, the dealer had replaced the batteries with a new set of Interstate lead-acid deep cell batteries. After upgrading the shore power charger and solar charger and adding a couple of 50-watt solar panels to the original 50-watt panel, the batteries stayed charged up pretty much full-time. The only times our low voltage disconnect ever tripped, was when we were running the refrigerator on DC while driving and forgot to switch over to propane when we parked for lunch. One day I forgot to set the refrigerator to DC and at the end of our driving, I found the fridge temperature to be about the same as when we left it in DC mode. So, it turned out that DC operation was not any better than an icebox, even though it drains the batteries in about an hour! After that we just turned off the fridge while driving and leave a bunch of drinking water bottles in the freezer to help work in “icebox” mode.

Finally, after over six years of operation, the batteries started to act up. I leave the 12V on all the time in the driveway, and the solar would keep up with our occasional 12V usage. But I started coming outside in the morning and find the RV coach radio playing! I would turn it off, the batteries seemed to be fine, and the next morning the radio would be on again! I finally realized the low voltage disconnect (LVD) was coming on in the night when the batteries had consumed their puny solar charge for the day. What I didn’t realize was that the LVD would reconnect automatically when the battery voltage came back! The radio however recognized the power outage, and when the power came back after the sun came up it defaulted to “ON” after power up and started playing on its own. This radio (JVC) did not have an option to stay off after a power cycle.

The bottom line is that the lead acid batteries reached their end of life after a remarkable 6 or 7 years and needed to be replaced. It was tempting to buy a new set of inexpensive lead-acid batteries and continue for another 6 or 7 years. However, the prices of 100AH lithium batteries had dropped from over $1000 to under $400, and can be found for about $300 now, which is not much more than the lead-acid batteries. I decided to make the change in order to get the huge advantages offered by the lithium batteries, rather than regretting the opportunity to upgrade when I needed to replace the batteries anyway.

Why Lithium

Lead cell batteries have been around without much change for more than 100 years and have been a remarkably resilient technology. They are a proven solution and are relatively inexpensive, but they are also incredibly heavy, not particularly environmentally friendly, and are not very efficient and require a fairly complex charging scheme to avoid overcharging or life-shortening damage. Their operation is straightforward: once fully charged to a little over 13 volts, voltage drops during use in a linear fashion until they are too low to operate the attached devices. In general, “too low” is a value less than 12 volts. The LVD is set to disconnect the batteries when they drop to 10.8 volts but draining to this level may already do some damage. The big problem is that the lead acid batteries drop to an unusable level when they are only 50% discharged. So, your 100 Amp Hour battery only provides a usable 50 Amp hour before it needs recharging.

Lithium batteries, or the more-specific modern LiFePO4 (safer lithium chemistry) have a completely different discharge cycle. They maintain a high voltage until they are nearly discharged, and then the voltage decreases dramatically. The voltage is usable (over 12V) until they are nearly discharged, so the 100AH lithium battery gives you 80 or 90 usable amp hours, instead of 50 for the lead acid.

The bottom line is each lithium battery provides almost the same useable electricity as two lead acid batteries, so you can effectively double your capacity in the same space and with considerably less weight. Two lithium batteries give you the `same capacity as three or four lead acid batteries, or equivalent to nearly twice as long of a boondocking period.

What needs to change?

Lithium batteries (the RV kind) generally have a computer inside (battery management system or BMS) that takes much of the complexity out of charging. The BMS just wants a constant high charging voltage (like 14.6 Volts) and the BMS will take whatever it needs from that and will protect the battery cells from overcharging or severe depletion.

Lithium as a Drop in Replacement (Pretty Good!)

The Chinook provides three different battery charging methods: shore power (via a converter/charger), solar power (via a solar controller), and engine power (via the alternator) while driving. It turns out that the lithium batteries can work reasonably well as a plug-in replacement to the lead acid batteries, but the chargers will not work at the optimal efficiency. In particular the lithium batteries may charge with the existing chargers, but they may never charge to 100%, for example, as they would with a lithium-specific battery charger. That is because the higher voltage from the lithium batteries looks like a full charged lead acid battery to the charger, so they stop charging before the lithium batteries are full. This is not a terrible thing. A lithium battery at 80% charge still outperforms a conventional battery and keeping the battery at less than full charge can extend its life. Hybrid cars, for example, generally try to keep the battery between 20% and 80% full charge in order to maximize battery life.

Lithium Optimized (Great!)

It takes a different charging scheme to charge lithium batteries to full capacity. It’s actually a much simpler scheme, because the BMS handles all of the internal details. Basically, you provide a steady 14.6 V supply, and the BMS takes it from there. The batteries will suck up all the current you can supply until they are full, and then they stop. This also means that the lithium batteries will charge faster than the old lead-acid batteries. In my case, I initially upgraded the shore power charger and the engine charging circuit but left the solar controller as is. Harmony spends most of her time parked in the driveway with year-round solar, and the lithium’s have kept charged just fine using the old 3-stage PWM solar controller. Even though they aren’t charging to 100%, if they charge to 80%, they are still better than lead acid batteries fully charged. Following is a discussion of each of the charging methods, as regard to lead-acid vs lithium.

Shore Power Charging

As noted in my original power upgrade post, the factory converter/charger (Magnatek 7345 in my case) was a single stage charger and could actually damage the lead-acid batteries if left plugged in continuously. I upgraded that to a Progressive Dynamics 4645 which includes a 3-stage charger which fixed the overcharging situation and worked well for the lead acid batteries. I am now thinking I could have stuck with the PD4645 and had satisfactory (but not optimal) results, but I went ahead and installed the lithium-specific (no going back) PD4645LIV charger/converter. (These upgrades are kits that install in the existing Magnatek box, so you don’t need to re-wire the whole system to use them).

The PD4645LIV still does the converter function of converting shore power 120V AC to 12V DC for the coach. The charging function changes from the 3-stage charging scheme to a fixed 14.6 V output, that is compatible to the lithium battery management system (BMS) for charging the lithium batteries. Installation of the PD4645LIV is pretty much exactly the same as the installation of the PD4645 upgrade I previously did and described in my original post.

Engine Alternator Charging

The alternator charging circuit is the most confusing part of the lithium conversion. Ironically, the alternator already puts out the 14-plus volts needed to charge the lithium batteries, but there are complications. The lead-acid batteries generally do not use a high number of Amps when charging. The shore power charger is limited to 45-amp output but is usually providing less. The solar charger is limited to 30 amps or less. The engine alternator on the other hand can put out over 100 amps, typically 130 or more in our RVs. Lead acid batteries will not demand that much current, but the lithium BMS will take it happily and charge the battery cells as rapidly as possible. You need to make sure you have big wires to handle that much current, but more importantly, it may burn up your alternator or diminish its lifespan if you pull that much current for long periods.

A further complication in the engine charging circuit is the existence of the battery separator (Sure-Power 1314 or 1315) used in our Chinooks. The separator is designed to prevent the engine battery from draining when using coach devices. Basically, if either side of the battery separator has a charging voltage the separator connects them. If neither side has a charging voltage, the separator disconnects them. Since the lithium batteries spend a lot of their time over 13 volts, it looks like they are charging even when they are not, so the separator would keep the engine and coach batteries connected just about all the time. I’m not sure if this is a problem or not, but it is not the configuration the separator was designed for.

One approach to the lithium upgrade is to stick with the factory (lead-acid) charging circuit and let the chips fall where they may. At worst it seems the batteries would always be connected, and the alternator would pump a lot of amps to the coach batteries if they were in need of charging. The alternator is rated for that and might work fine.

The more careful approach most people (and I) are taking is to add a smart device between the alternator and the coach lithium batteries. A specialized DC to DC converter will regulate the voltage so that whatever voltage is put out by the alternator is converted to the desired BMS charging voltage (14.6 Volts) AND to limit the charging current to the batteries at 30 amps or 15 amps, depending on the device chosen. This guarantees optimal charging voltage and protects the alternator from overheating by limiting the current. This might actually slow down the charging process due to the reduced amps, but 30 amps is pretty hefty, and will likely charge the batteries with a good drive. (2 100AH batteries could take as long as 6+ hours at 30 amps if they are completely empty, but they are rarely completely empty, so they are usually just getting topped off.

A fairly important (to me) disadvantage of the DC to DC converter is that the batteries only connect when the engine is running, so the truck battery does not get charged by the solar panels as it does in the original configuration. I fixed this by upgrading to a dual-output solar charger as described below.

Solar Charging

As I stated, I initially left the solar controller alone. I was still using my faithful Coleman (Sunforce) 30 Amp PWM controller, and it was working great. I know the lithium BMS’s were not getting 14.6 Volts from the solar controller, but they were definitely staying mostly charged with the 13.3 Volts from the solar controller.

Unfortunately, my new engine charging circuit (described above) left the coach batteries disconnected from the engine battery when the engine is not running. I had to splice the solar charging wire to both batteries, so the solar controller would keep the engine battery charged when parked for long periods. It is not common to try to charge two disconnected batteries with a single solar controller, but it appeared to be working for me for some time. However, after a few months of operation, I went out and found the LVD tripped, and the lithium batteries were discharged. It turned out the fuse on the solar wire to the battery had blown, so the solar controller was only charging the truck battery. I’m not sure why the fuse blew, but I was nervous about having the solar attached to both batteries at once and creating a “backdoor” connection between the coach and truck battery, so I decided to revisit the solar controller.

What I needed was a solar controller that was designed to charge two sets of batteries with different characteristics, so I did a Google search for a “dual battery solar charge controller” and came up with the perfect solution. An upgraded product from Go Power was designed exactly for my situation. The “Go Power 30-Amp Dual Bank Bluetooth-Enabled Digital Solar Controller” is the perfect solution, and it is the same size and shape as the original Chinook controller. The model is GP-PWM-30 UL Solar Controller, available here at Amazon: Amazon.com: Go Power! By Valterra GP-PWM-30-UL Solar Controller – 30A, Digital , Black : Patio, Lawn & Garden

The controller supports lithium charging for the coach and has a second battery charging output that allows charging of the lead-acid truck battery. When the first battery is fully charged, the controller will charge the second battery (generally a trickle charge), so the solar will keep both sets of batteries charged in a safe way.

I needed to find or connect a new wire from the solar controller to the truck battery for the second battery output. By happy coincidence, Trail Wagons had originally wired a hot wire (always on) to the coach radio in the cabinet next to the solar controller. I didn’t like having the coach radio powered by both the truck battery and the coach battery at the same time (two different power wires in the radio connector), so when I installed the lithium batteries, I re-wired the radio to use the coach power only. The disconnected radio power wire was a perfect connection to the truck battery circuit to use for the solar charging. I got the idea from commercial “booster packs” that use the cigarette lighter port to add power for emergency starting. I realized that any wire connected to an “always on” circuit could be used as a charging port for a low power charger, as ultimately the power gets back to the battery.

After replacing the Coleman (Sunforce) solar controller with the Go Power controller, and configuring the two battery outputs, both the coach batteries and the truck battery were topped off and fully charged by the second day!

More Solar!

During the long Covid break, our roof air conditioner stopped working. Unfortunately, we didn’t realize it until we were stuck on the side of the highway in 100 degree weather, and found out the AC did not blow cold (or even cool) air. We changed out the air conditioner with the equivalent current Penguin model, which came with a new shroud. Since I had a 50 watt flat solar panel attached to the old shroud, I went shopping for a new panel to place on top of the new AC shroud. I found a perfect fit 55 watt solar panel at Amazon, here; Amazon.com : ATEM POWER Monocrystalline 55W Flexible Solar Panel 245° Bendable 12V Portable Solar Charger with Uneven Surfaces Lightweight for RV Tent Roof Boat Cabin Marine Camping : Patio, Lawn & Garden This panel is more rugged and more efficient than the old flat panel I was replacing. The size also was a perfect fit for the flat section of the roof behind the air conditioner, so I added a second panel and fastened it to the roof. This gives me a total of 4 55-watt panels or 220 watts! As before all 4 panels are wired in parallel, and wired to the 30 amp solar controller inside the coach.