How do UPS trigger circuits work?

Partly depends on the topology of the inverter/charger or UPS. Not sure about the one on Amazon.

An inverter/charger like the one you referenced could use either a separate charger circuit not shared with the inverter OR it could use the same circuitry for charging than it does for inverting.

If it is a separate charger, then all it has to do is wait for the AC input to go away and turn off its AC input relay but keep inverting off the battery storage.

If combined inverter/charger, it can be more difficult to know when the grid AC is gone so that the inverter does not try to drive the AC input line since the AC load output would be connected directly to the grid or shorepower input. That is more or less how a grid tie inverter works that can sell power back to the grid or AC input. That is called anti-islanding and has strict regulations the company must follow but I don't think this inverter/charger does this function. So that inverter/charger might take a couple of seconds to find that the AC input went away and invert properly.

Usually, when the AC grid goes away, there will be a short time where there is NO AC output until things stabilize. If it uses a completely separate charger and inverter, the it can be truly UPS or uninterruptabe power when the grid goes away.

One or two AC cycles is typical for a good/fast inverter/charger to transfer. Relays take a couple milliseconds to switch.

Lettuce know if you happen to take it apart. The inverter company support or sales people probably won't know how it works. The manual won't say either.

boB

That's the core of my question. How is the decision made? Is there a dedicated power management IC for the purpose?

away and turn off its AC input relay but keep inverting

I did take a few photos of the insides, but to me they weren't very informative:

Rumor has it that most inexpensive inverters are clones or outright copies of commonplace designs. If anybody recognizes this one it would be helpful.

Thanks for reading,

bob prohaska

That's what I'm dealing with.

But how is the expetation generated and tested, in a timely fashion?

Thanks for writing,

bob prohaska

The AC-OK sensor circuit of an old UPS design is found on Sheet 1, in the upper right corner (D8 - C5):

AC's apparently applied to a transformer, rectified, and compared against a zener diode reference. It's relatively simple circuit.

Danke,

The AC-OK sensor circuit of an old UPS design is found on Sheet 1, in the upper LEFT corner (D8 - C5):

AC's apparently applied to a transformer, rectified, and compared against a zener diode reference. It's relatively simple circuit.

Danke,

An inverter/charger will work instead of a "UPS"... But might or might not have a lot of transfer time.

The only question is, does this have a built in charger as well as an inverter ?

Batteries not included of course as a real UPS would have.

boB

Yes, your analysis makes sense. Thank you.

T1 functions as a fairly foolproof sensor. Its PHAS-REF and IN-RECT outputs signal AC availability.

IC21 is technically a Precision Programmable Reference. The circuit's topology utilizes it as a temperature compensated, 2.5 VDC reference.

D20 and D21 function as an "or power gate," so to speak. To enable energy to flow from either the battery or AC. Why? Because if the battery's been drained it's unable to provide 24V and AC must be used instead. Open question, does: 1. the fully-charged battery or 2. T1, provide the requisite energy for 24 VDC, during normal use?

The 87C51 inputs PHAS-REF on pin 14. It probably serves as an interrupt.

The IN-RECT passes through an ADC0831 Multiplexer on its way to pin 28. From where the 87C51 decides whether the AC failed.

Danke,

This largely answers my question. I'd been trying to think of a way to detect mains loss without a local replica. Evidently that's not how it's done.

Thanks for writing!

bob prohaska

Time to update my analysis. :)

Q41 acts as a switch to more-or-less "square up" PHAS-REF. It's off time is skewed slightly due to the 0.7 VDC required to turn it on. So it stays off a little longer than ideal. When Q41's off the 87C51 pulls P3.4 up to 5 VDC. If the UPS is supposedly powered-on but P3.4 stays stuck on one (5 VDC), the software knows there's no AC present at T1. Otherwise the frequency of P3.4 indicates one component of AC health.

Danke,

No real need, merely curiosity. Especially how mains loss might be detected without recourse to a microprocessor. I started out thinking in terms of using comparators and RC filters. Clearly I'm out of date!

Thanks for writing,

bob prohaska