#### Hedges

##### I See Electromagnetic Fields!

The idea is to determine if fuses and BMS need to be oversized to account for extra I^2 x R power dissipation due to ripple current.

My system has four Sunny Island SI-6048US wired 2s2p. I considered reconfiguring as 2s for half as much capacitance, but didn't do that.

Using the oscilloscope and current transformers described in another thread, I instrumented it by putting one CT on the negative battery cable of one Sunny Island, an one around the AC output wires of two Sunny Islands on a single phase:

### Power Factor and Startup Amps

Because I have suitable equipment I'm going to put up measurements I've taken, might help someone with planning a system or general education. Motors draw a startup surge of considerably more amps than they draw while running. With grid power you may see the lights dim briefly, but if you have...

diysolarforum.com

I don't have a DC clamp ammeter, so I relied on Sunny Island to report watts and battery voltage, and calculated average current. The current transformer measured just the AC ripple component. It is rated for 100A rms, and used on just one inverter's cable kept DC + AC component within that limit.

PV charging battery, 7.2A rms at 240V for 1728W (probably aborption.)

The two channels have 300:1 scale factor entered, an what it shows as "V" is amps.

Battery powering A/C (PV offline), 11.4A rms for 2736A delivered.

Strange triangular waveform of AC current, wasn't expecting that.

CT on battery shows 2.85A rms ripple in draw from battery.

Battery powering Pool pump. This is a VFD driving 2hp 3-phase motor. VFD has diode/capacitor front end, so current draw from AC just clips tops of sine wave (poor PF).

Note 5.08A rms ripple in battery current, a spike each time AC draws current.

Hmm, Guess I should have oriented CT the other way so more current would be up not down.

On grid, with PV producing and pool pump running.

Note how the sine wave current from PV has notches taken out of the sine wave peaks by VFD's diode/capacitor front end.

I didn't run this pair together off-grid because the transformerless Sunny Boy don't like that. But tied to the bottomless grid, no problem.

Battery powers 10kW electric heater. Now we're talking!

Inverter reported 10.2kW output, 47V battery which means 217A average draw from battery (just over 0.5C for 48V, 405 Ah battery)

CT measures 41.9V rms on AC line, x 240V = 10,056W

CT on battery cable shows 16.24A rms. Note that is for a single inverter; for all four, 65A rms.

Instead of a steady 217A, superimposed on that is a sine wave +/- sqrt(2) x 65A. (125A minimum to 309A maximum)

Rather than 217A rms, by numerical methods I came up with 227.6A rms, about 5% more heating of fuses and wires.

This doesn't seem like enough to be a big deal. Would probably be higher if only a pair of inverters was used (half as much capacitance available), or if load was near 100% of inverter capability rather than about 40%.

If an inverter had less capacitance than these, ripple would be higher. Although,

With LiFePO4 rather than AGM, lower internal resistance (possibly 1/5th as much) would mean capacitor voltage wouldn't draw down as much and more current would come from battery.

I'd like to see battery ripple current waveforms or clamp AC ammeter readings for other inverters.