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15

I have used external batteries on several old, out-of-warranty UPS models over 15 years, ranging from 500VA to 1500VA (about 400 watts to 1000 watts). I prefer sine wave UPSs for their universality with small transformers and solenoid valves, but most computers and peripheral equipment use switching power supplies that work fine with modified sine wave (a ...


13

Good quality (APC) UPS can be used like that. I have two units running at the moment. I use them for different purpose, they trickle charge my motorcycle battery and the battery I have left from the previous car. APC UPSes are very good storage chargers for Lead acid batteries (after all, that's one of their primary purposes) and I have a shop nearby giving ...


9

Well, sort of, but not really. The power supply would need to be adjusted to put out about 13.7 volts. This is the nominal float voltage for lead-acids, and is the point you should aim for. There would need to be some sort of isolation between the battery and the supply when power is off, or the battery may back-feed the power supply, and may well damage it....


8

Too small Your inverter and your UPS are too "small". You have too much electrical load attached for the power ratings of those devices. Why is there a UPS in there? A UPS (to the first-order) is just a battery + an inverter... which you, obviously, already have in your system. Too inefficient Also this is NUTS inefficient... Approximately: Battery (DC)...


8

No. The UPS includes that connection when required internally. That's why there is a "UPS Neutral Out" UPS --> SPS Most consumer products labeled "UPS" are actually SPS systems. UPS (Uninterruptable Power Supply) means that the nominal power path includes the battery output. That way power comes from the UPS battery power path regardless of whether there ...


7

I'm going to make a semi-educated guess at a suitable ferrite material (and core shape) to see how it pans out. I have no idea if I'll stumble upon a core that is suitable for the OP's requirements but, the process is going to be the same whether it is a ferrite, iron or powder core. I'm going down the ferrite route because I know the losses at the switching ...


6

I don't think you need any special kind of UPS, unless you have particularly power sensitive equipment. Nearly any modern switching power supply will handle the transition from mains power to battery of a typical line interactive UPS. This type of UPS will protect you from both power surges and power sags, switching to battery when the mains voltage is out ...


6

Jesus wept. Moderators - please close this question. Poster is asking for help in building equipment which is likely to get people killed. Worse, folks are helping him. That said, let me expand. I'm assuming that when you say "critical medical equipment" you mean exactly that. If you are exaggerating, then I'm overreacting. If you're not, then you really ...


6

There are many advantages. First, an MCU can replace quite a bit of discrete logic and monitoring circuitry for less than the cost of discrete parts or an ASIC. UPS units need to monitor several different parameters (line voltage, battery charge, load current, etc). Many MCUs have built-in ADCs, so using a microcontroller means that most of the necessary ...


6

Most high-power installations require an isolation transformer. Every variable frequency drive manual I've ever seen requires the same thing. So it's not a UPS-specific requirement. In general, the isolation transformer limits your available fault current, and keeps electrical disturbances generated by your load from propagating quite so easily through your ...


6

No. Capacitors are for DC. Wall power is AC.


6

simulate this circuit – Schematic created using CircuitLab Figure 1. Parallel PSUs with power indicators. V+ will be about 0.7 V below the power supply output voltage due to diode drop. Both PSUs on all the time and, if similar type, will probably share the load 50/50. simulate this circuit Figure 2. Relay switched PSU. Both PSUs on all the time but ...


6

You should re-think your topology if reliability is really so important. Your most likely point of failure is the switchover relay, not the 12 V power supply. I would set up the system to always run from the 12 V battery, just that the power supply charges the battery when line power is available. This is exactly how the 12 V system in your car works. It ...


6

This problem is an indication of resistance near or on the battery contact. When there is resistance present, any current through the connection will be converted to heat. As you described, when you put a load on the UPS, it starts to melt. The load is the increased current that flows through the connection. Try cleaning the connections, making sure any ...


6

You are using IRFP9240. This is not suitable MOSFET for this task. This MOSFET requires higher Vgs than you are providing. You are going to have Vgs around 3.6-4.2V. IRFP9240 requires around 10V to fully open (or at least 5V to be usably open). Try different MOSFET with much lower Vgs(th). For example something like PMV48XP (I just randomly googled, you can ...


6

Figure 1. Source: etchnog.com. A UPS converts mains AC to DC to charge the battery. The battery, when required powers the inverter and feeds the load. I wonder what stops this current from going to the rest of the household circuit ... The rectifier diodes are electrical one-way valves. They block current from flowing in the reverse direction. The LED ->...


5

The simplest approach is to get a SPDT relay whose coil matches your primary power source (220 VAC), and whose contacts are rated for your secondary power source (12VDC at whatever amps). Use the normally-closed contact to switch the secondary power to the secondary pump. Whenever the primary power is available, the relay will pull in and prevent the ...


5

You didn't say which Arduino you are using, these instructions are based on an Arduino Uno, but should work for most if not all Arduinos. Connect a 9v battery to the Vin pin of the Arduino through two 1N4001 diodes or similar. The PWRIN jack is already connected to VIN via a diode, so the two diodes will provide isolation between the two, and the 9v ...


5

The obvious thing that you are missing is that many devices will be destroyed if you apply a DC power supply to them. Most older electronic devices use a power transformer to convert the incoming voltage to the levels required by the device. Applying DC to such a device will damage or destroy it. Most consumers don't know if their devices can accept a DC ...


5

Calculating the needed capacitance is easy for a simple parallel cap: 1 microfarad will supply 1A of current for 1 microsecond while dropping the voltage by 1 volt. 1A is a typical steady-state current for a wireless routers, and I suppose most of these can survive an input voltage of 11V, so you roughly need as many farads as the seconds you want your ...


5

You could do this, but will it work? The charging circuit will be confused as it is built to charge/discharge at certain voltages. Because lithium ion batteries are considered dead below a certain threshold (like 3.0V) the UPS charging circuit may not switch on at all because a supercapacitor will have no voltage initially. As far as the capacitor goes, it ...


5

Note: I am not trained in electrical safety. Do not rely on this post for safety advice. I know you are asking theoretically, but I feel like I should put this disclaimer here anyway. Is it because the waves may not be synchronized and could then cancel out each other? Or something else? That is the main reason, but the consequences are worse than just ...


5

Car Starter motors on large cars do draw a lot of current even at no load .Old pre internet figure is 70 Amps at 12 VDC revving at 7800 rpm .This is from Joseph LUCAS Prince of darkness .The more modern permanant magnet motors will draw less and rev less under no load .Delco units like the lucas units are series wound and behave pretty much the same .Your ...


5

You can't switch your battery under load, that would lead to an inevitable voltage drop on the generated voltage keeping your devices working, and thus negate the idea of a UPS. So, give your old battery into recycling, and only use the new one – even using both in parallel (if that was possible, which is not really the case) would be giving you but 25% ...


4

It depends (but most likely yes.) Active PFC controllers will shape the input current to whatever input voltage waveform is sensed. The current will be as non-sinusoidal as the voltage, but will be in phase with it. The closer your UPS output is to a proper sine wave, the more likely your active PFC will work just fine. That being said, there's a strong ...


4

As Mrs Beeton would say - first catch your battery. The sealed lead acid type used in a myriad of long term applications such as UPS and alarms. Generally this battery is designed for exactly this type of application and will maintain its charge losing something in the region of 40% over a period of 1 year. (Some do better, some do worse - check manufacturer'...


4

There is no practical solution in your case. Some big changes must be done in the inverter circuit to make it give sinusoidal output. And it is not an easy and cheap work for an end user to do. There must have been a warning message on the box of the product, giving information about flaws of the product, which is understandable by any non-technical ...


4

Instead of a diode, use a relay. Connect the coil across the capacitor, the normally open contact to the + side of the capacitor, the + side of the load to the common contact, and the battery + to the normally closed contact. That way, with the mains hot the relay will be made and the capacitor + will be connected to the load through the relay's NO and COM ...


4

A linear voltage regulator converts excess power to heat. So dropping 7V to get 5V is worse than 50% efficiency. At 0.7A and 7V drop, that would be almost 5W of heat. So you'll need a decent size heat sink. Look at DC-DC converters instead if you care about that energy waste. Edit: to incorporate ACD's comment: "lead-acid batteries are usually ...


4

Assuming the UPS uses a common 12V SLA battery, you can replace it with a 12V lead-acid car or deep-discharge battery. All are common lead-acid batteries and should work identically. That said, it's a bad idea for several reasons: The UPS electronics, as the link you provide mentions, are not designed for operating for long periods of time. Typical home/...


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