General > General Technical Chat
Can anything be done about AC load "ripple"?
paulca:
... and any attempt to store even more (on the DC side) will come with it's own worse problems.
paulca:
On load response... it's rather amusing what happens when it's running the 250-300W office and I hit it with the 300W garden strimmer.
Basically, I hit that button and the inverter goes "Nope, no f'ing way dude" and drops snaps the transfer switch closed pass-through'ing the grid.
However, very quickly after that it comes back up, transfers out the grid again. It's just that huge VA spike from the cold static motor start up that freaks it out. Thanksfully it does "accept AC" at that point instead of tripping out. Through out the on/off, on/off cycle of the strimmer the inverter dropped in and out of grid a few dozen times, just using the grid to take the load spikes when the strimmer went from stop to run. Impressively it did not need to accept grid to dump the -VA coming back on spin down. That appears to have gone to the battery.
The only "miss performance" comes when you monitor the AC voltage live and introduce a 250W load suddenly. That load is probably more like 600W for a quarter of a second. The neon indicators almost blink out and a multimeter is even fast enough to show the voltage ramping from 180V to 230V over about 2-3 seconds.
I suppose that is expected. Unlike the grid it doesn't have that "near ideal voltage source" property, it will take time to respond. The fact the voltage bounces very rapidly and nothing crashes or reboots is a testament to it. Also the slow ramping from 180 up is most likely deliberate to prevent overshoot, especially if it's a short transient spike from an inductive load that will disappear just as quickly. Undervoltage drops are usually far less damaging than transient over-voltages.
The only times I have plunged myself into darkness has been my own fault.
1. Testing how low the battery would go. Couldn't get the remote config re-uploaded fast enough to stop a low voltage disconnect while "Ignore AC-In" was active. BANG- blackness.... oops. That one I had to get dressed and go out in the rain to the garage to turn the battery back on and bring the system back up. The cons of being your own micro-grid operator... you get the call at 3am to fix it in the rain.
2. Top balancing a battery using the inverters build in charger (reversing the inverter). The unit is apparently not able to cope with the battery terminating charge input sudden while it's feeding it with 16 Amps AND running a 350W inverted load. I imagine those 16 amps current in the transformer coil has suddently nowhere to go and instead of letting it spike the ACOut well over voltage it has no choice but to trip out completely. BANG darkness. This one did self recover though, the power came back on 1 minute later automatically.
Siwastaja:
--- Quote from: paulca on July 07, 2023, 11:23:54 am ---... and any attempt to store even more (on the DC side) will come with it's own worse problems.
--- End quote ---
Well, I think you could quite safely increase the capacitance of the 400V (PFC) electrolytic capacitor in PC PSU, to make that tens of milliseconds into... maybe just a hundred. (This is the best place because it's the only one where voltage ripple is acceptable and normal, and capacitor energy capacity is directly proportional to delta V, so can't store a lot if you just parallel capacitors on some 12V bus which is always regulated to 12V.)
But the big question is, why? Everything's working just as expected. Power changing is natural and causes no issues whatsoever. If the inverter is too small to handle those say 500ms peaks, then by far the easiest is to get a bigger inverter. Or if the battery can't handle them, get a bigger battery.
Best place to store energy is that battery DC side of the inverter; batteries are like 1000 times more energy dense than capacitors.
paulca:
Bigger inverter. Indeed. I downsized due to inavailable stock on a 1600VA inverter from another brand. 800VA from Victron will do 800VA until it overheats and then it will drop the voltage ... if the load responds by increasing current, it trips. The cheap 1600VA, reviews see trips outs frequently for half of that. Victron 800VA is thermal, but "realistic temps" and smooth derate. cheap brands, a 1600VA will probably not even run 800W for longer than 5 minutes before it overheats and trips. (Small/multi transformers, dozens of mosfets and parallel inverter sections).
So I got the right brand, or rather I spent the right amount. Half the VA, same price, thus better quality.
i 'should' have put the purchase off a month and bought the bigger victron 1600VA Only £250 more..
the most annoying thing ... I cannot run the coffee machine on it! In fact, outside of the office and the multitude of small consumers ... all my loads are momentary, short term and 1.5-3kW.
I am weighing between, going self "project funded/managed" and source my own parts and labour to extend this system onto the main roof for solar panels ~3kW and into 10kWh+ of DIY lithium + 4kW hybrid inverter.... then try to get that "notified" by an expensive spark (Like andy's off grid garage)... or... put a normal "package deal with finnace" grid tie system up there with 0% finance (hopefully) and ... keep the two separate... although ican run the battery charger on the "off grid" system when there is "house solar" available. An anti export cross feed if you will.
Siwastaja:
Wire two identical coffeemakers in series, so that coffeemaking power is reduced to half (quarter per coffeemaker), which your inverter could handle, making double the amount of coffee in 4x the time. Then drink all that coffee and come up with more interesting threads here.
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