We are at the farm this weekend. Turned into bed at 9am, it’s a brisk 4am now. Coffee is brewing, it’s Indiana Winter trademark’d pitch black outside. Soon, birds will be chirping to greet the Sun.
My body has forgotten how the bed feels in the RV. Or is it a placebo, considering I associate the first night’s sleep in the RV with my sore body from hitching and loading it?
I discovered yesterday that my Raspberry Pi Venus GX install had crashed. Research into why my Buck Converter didn’t work to power the wireless generator fob led me to learn that the buck converter I’ve deployed has a 100Hz pulsed output, NOT a stable DC supply voltage. The Arduino prevailed, speaking to the reliability of the ATmega.
As part of our preparations, I installed some DC voltage stable 2.1A USB ports in the Solar Box and an OpenWRT 802.11AC router that I modified, installed external antenna ports. I now have a use for my giant Hawking 15dbi outdoor antenna. Can you say Solar Truck Wardriving?
I’m actually really pleased with the router I used. It has a MicroSD card slot, two radios, non-removable antennas (but the connections inside are UFL/ipx, easy to mod)
I have proper wiring and mounting to do. I’ve been lazy when it’s come to taking photos of my work to share. I’m hoping to get some good drone footage of the truck and trailer in the country before we leave. If trends continue, I’ll be in bed by 7pm this evening 🙈
Ah, yes. The generator auto start/stop system. This is the first time we’ve tested it out! So far, it kicked on at 6pm and around 4am. I have the Venus programmed to kick on the gen at 70% SoC during the day, 60% during the night. Both will run the generator until the batteries charge to 95% (we have a 400Ah AGM bank).
It takes about an hour and thirty minutes to charge from 75% SoC (No Solar/Night) to 95%, and about one hour fifty minutes from 60% SoC to 95% (No Solar/Night). Solar (with good sun) should be able to handle daytime loads and provide battery charge with no problems.
Summertime A/C draw (1,000W-1,500W — 13,500BTU) will require generator usage. I’m debating if I should install an AC power monitor and always trigger the generator on high AC draw, or just keep it DoD. I’ll be able to get about an hour and a half to an hour draw from A/C on the bank before I hit generator DoD, which it’ll run for an hour to two hours to recharge (while powering the A/C at the same time).
We have been running the fridge on AC power all night, it kicks in at about 300W more often than you’d think. The furnace (200W or so), house battery charger float, lights, water pump. Since the truck only outputs AC which I plug the RV into via the TT-30R 30A shore power plug, there’s about ~50W of inefficiency from the inverter sitting idle off the top.
I think that if we switched over the fridge to propane, we’d make it through the night without a generator event.
One topic I’ve finally listened to Reddit on, 400Ah isn’t that much capacity, especially for 800W of solar. Any additional batteries I add will be Lithium. The thing is, I can’t afford to just dump in the money for xxxAh of lithium up front.
I should expect 1,500 cycles out of my AGM batteries at 30% DoD. Let’s try to calculate worst case 24/7 A/C usage cycle count. So, 24 hours. We can power the A/C for one hour before needing to kick on the generator for an hour and a half. That’s 9.6 cycles per 24 hour period of each 1 hour battery cycle, 1.5 hour generator cycle.
We could expect to run the A/C constantly before wearing out the AGM batteries for 156.25 days. Not bad. That’s 14.4 hours on the generator per day. That’s 7 days between oil changes though and 17 days between “Cleaning the combustion chamber”.
Of course, this doesn’t account for the A/C kicking off/on as needed to maintain temperature. This is 24/7 runtime.
I’ll need to do some more thinking, but it seems that sacrificing some battery cycle count to run the generator less is going to be more economical.
I think what I’ll do is spend a little per paycheck and build one or two 12V 18650 packs per month. I’ll be able to take advantage (or get screwed by) Lithium prices over time and treat it more like a monthly subscription.
I can buy 100Ah of 18650 for ~$156, plus the cost of BMS, terminal welder, etc. I think that most of the 100Ah packs are like a grand or something stupid. Ah, some are $600. I’m sure there’s hidden cost there. LiFePO4 batteries seem more expensive, and I think these are what I should use.
Either way, additional battery bank capacity should be my first priority, past enjoying what we already have. We don’t live in the RV full-time, so we could have gotten away with just the generator. I’ll need to keep this is mind to stop me from splitting hair on the most “ultimate, bestest, perfect” solar setup. But I’m a perfectionist.
To be continued..