Guru
Joined: 13/10/2014
Location: AustraliaPosts: 2165
| Posted: 11:35pm 11 May 2026 |
Some interesting observations with regard to Load switching and currents.
With fast transfer, in this case < 20ms. Mains AC to Inverter AC switching under any load is basically the load current, with no abnormal phase difference spikes, even 40ms seems to make little difference.
It's interesting that we have have discussed the possible need for syncing when switching between Mains and Inverter under load, but in my real world testing, the real problem is when switching cold loads, either to Mains or Inverter.
This became even more apparent when I reverted back to a Manual Mains - Generator switch. There are a few reasons I did this, but that's for another post if anyone is interested, the Auto switch is great, but without Street power it won't be needed, and the Auto switch needs a separate housing as they are about 5mm deeper than standard DIN rail RCBOs and AC breakers etc, the manual switch is a perfect fit, and looks almost like 4 AC breakers, same size, unobtrusive and very neat in the din rail cover housing.
These Manual switches usually have a centre off position, the one recommended and supplied by the Sparky is the a HAGER SF263, apparently this seems to be the favourite when installing an Emergency Generator backup facility, which I'm informed, is happening quite a lot lately.
The SF263 is rated at 63A, Sparky had the data sheet and it's very good, especially the build quality when compared to the lower cost unit he had, and the cost itself is quite reasonable. The Fuse box Main AC breaker/disconnect is a 100A unit, so the SF263 as per the data, should have a 63A-C breaker between Mains and the SF263, and the same for the GEN Input, or lower depending on the Gen output and wiring. The easiest generator input is an isolated output type, which the Inverter Toroid transformer is, that means everything back from the GEN AC output is also isolated from the House AC Supply.
The SF263 data sheet and typical install labels for changeover switches indicate that the loads should be removed before switching. Loads then switched back on, usually via the circuit breakers in the Fuse box for the loads required, since this is obviously where the changeover switch is located, it only takes a few seconds.
I monitored the loads as the circuits were switched, and there are up to 400A peak DC inputs on the Inverter when switching circuits that have Inverter supplies, like Fridge and Freezers, SMPT devices like Computer and screen Plug packs, TV and other device standby loads, I would imagine a large number of incandescent lights and older fluros would also present high initial cold surge currents.
So dumping the lot at one go can see a peak DC input of around 580A, in my case that's less than half of the Inverters capability. But why stress it when it's easy to just switch the load circuits one at a time, worst case is then around 300A, which happens to be what two LCD monitors and a NUC-PC plug pack can draw on cold power on.
BTW a 2.7kW restive load powered first can reduces these SMPT cold start currents by around 30% to 50%.
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Edited 2026-05-14 10:42 by KeepIS