shore power

I have spent the past 1,941 days off-grid; I plugged into 15A shore power on Monday the 4th.

the Big Picture

I designed the system to pull a max of 12A (1,440w) off a 15A outlet. The 12A limit keeps it under the 13A continuous rating of the shore power port, and ensures I don’t trip a 15A breaker that I might not have access to.

Power comes in from the port into a breaker box with a 12A breaker in it. The breaker box feeds both a normal household GFCI wall socket and a 24v power supply (see below).

I have the solar set up to charge and float slightly higher (13.4v / 13.2v) than the converter (13.3v / 13.1v). This allows solar to run loads and charge the bank when sunpower is available. Right now this setup seems to stay between 75%-90% SoC, though it’s hard to tell (see below).

DIY converter

When I started designing this campervan in ~2017

1. I had a FLA bank
2. I had no solar yet
3. and three-stage “smart” converter/chargers were hundreds of dollars.

Since my current requirements were quite low¹ I decided to buiild a DIY converter/charger like I’d seen on YT: 24v power supply -> MPPT solar charge controller. I picked up an EpEver 1210A 10A MPPT for $40 from mainland China (eBay) and a 24v 15A Switching Power Supply.²

My original testing of the setup was with a Genasun 5A controller which specified the max efficiency would be a PV voltage of 23.0v. So I set up the 24v supply to output that. When I put the 10A EpEver in place I kept that 23v voltage. EpEver did not publish a specfic voltage, but in a few places mentioned 1.5x-2x the bank voltage. Since I charge to 13.8v this would mean 20.7v to 27.6v. Both the controller and power supply stay cool at this setting.

The 10A cc does not have voltage sensing, and so tends to run at lower currents than one would expect.³ I’ve seen it outputting 9.5A, but ~125W (8.88A) is more common. 125w might not sound like much but it’s absolutely enough to run my loads on average. Plus solar is there.

When making full power the converter setup appears to pull 1.3A from 120vac shore power.

AC loads

appliances

Hotplate 7.76A, 928w, rated 1100w, measured 928w. This is the maximal load. Under the 8.29A + 1.3A draw total max current is 9.59A.

Instant Pot, rated 700w, measured ~620w.

Ratty old heater, rated 1500w, but only one ceramic element works. Measured 425w on HI, 210w on LO.

side effects of shore power charging at low amp rates

The BMS in the Rebel batt is a JBD and only measures current >0.5A. With such gentle charging matched to my loads a lot of it isn’t getting measured and SoC % varies widely. I don’t think it matters much as long as I stay in the mid-13s, voltage-wise.

1. I didn’t know the 220AH FLA bank actually required ≥22A charging minimum. ↩

2. 10A would have been sufficient; I forgot the supply was 24v and the charging would be at 12v and buck converted. ↩

3. without voltage sensing, the controller thinks the bank voltage is higher than it really is. ↩