Does such an inverter exist?

StickyIcky

I'm looking for an inverter than can provide about 200 watts of power maximum.

It needs to be able to charge (car) batteries and be able to automatically transfer from AC to DC in the event of a power outage.

I've looked at UPS systems as they basically do this, except they are expensive for the battery life they provide. I figured I could make something myself out of a couple of car batteries and an inverter for around the same price with much longer battery life.

Alternatively if anyone knows any sources online or in bricks and mortar shops which may specialise in inverters I'll be very happy to give them all and ask. The only inverter places I've found so far are in the states.

StickyIcky

I know flip all about electricity etc but I think I found one.

http://www.ebay.co.uk/itm/1500W-3000W-peak-12v-220v-Power-Inverter-Charger-UPS-Quiet-Fast-Charge-C7-/141170667230

Now I just need to learn how to safely hook up a couple of car batteries too it

I'll figure it out

Irish Steve

How often are you expecting to run off the DC power, and how long for?

The reason for asking is that if you want to run on DC on a regular basis, and for any significant time, you will be very unhappy with the life and capacity of car batteries, they are not designed for deep discharge on a regular basis, and will end up costing you a lot of money in replacements if they are used regularly.

If you only need short duration cover, then a used UPS from somewhere like E-bay may be a more reliable option, as they have all the charging, checking and control systems inbuilt.

It all depends on what you want it for, what you are running, and the time you need it to run for,

StickyIcky

I'm expecting to run off the DC power if we're away from the house and the power trips and everything goes off, as tends to happen a couple of times a year. I would ideally want approx 100 watt device to run for as long as possible, a few days would be awesome.

UPS are over prices and over featured and have a pretty short battery life. They can only keep computers going for a few minutes, even time to save your stuff and log off.

I saw that you can hack UPS and add a car battery or two... but I feel a little bit dodgy about doing that, it could get dangerous

Or you can skip the UPS and get a inverter charger (auto switching) and a couple of big car batteries and they will last way longer.

Say a €300+ UPS would be about 800 Watt hours which would last around 6-8 hours of backup time. An inverter with a couple of car batteries would last much longer.

whizbang

There's really no issue with connecting batteries to a UPS, provided you understand the currents involved, and the connections for these currents.

But in the house, there are compressors for fridge/freezer, and lots of other inductive loads, that a lot of inverters cannot handle these power requirements.

The biggest issue is safely wiring the changeover switching, so this is where a UPS wins over cheapo inverter.

Irish Steve

StickyIcky wrote: »

I'm expecting to run off the DC power if we're away from the house and the power trips and everything goes off, as tends to happen a couple of times a year. I would ideally want approx 100 watt device to run for as long as possible, a few days would be awesome.

UPS are over prices and over featured and have a pretty short battery life. They can only keep computers going for a few minutes, even time to save your stuff and log off.

I saw that you can hack UPS and add a car battery or two... but I feel a little bit dodgy about doing that, it could get dangerous

Or you can skip the UPS and get a inverter charger (auto switching) and a couple of big car batteries and they will last way longer.

Say a €300+ UPS would be about 800 Watt hours which would last around 6-8 hours of backup time. An inverter with a couple of car batteries would last much longer.

100 W at 12 volts will need 9 amps or more, so a 100 amp hour battery is going to last less than half a day on continuous load. and that's why I made the comments I did, short term is no hassle, longer term is a major hassle, it needs massive batteries, or higher voltages, or both, and the batteries have to be deep cycle in order to not be destroyed within a few cycles, normal car batteries are not designed for long term delivery of high currents, or for being discharged to a low level.

Pre owned UPS's are dirt cheap on E-bay, the expensive ones have been fitted with new batteries, and that's the real cost, a new battery for things like a fork lift will cost in excess of €4000, and that's mainly down to the price of lead.

I have a UPS here at home, it went in when I needed to cover computer operations, it will happily run 16Kva, so I can run the entire house on it if I need to, but we're talking a device that's larger than a fridge, needs 3 phase power to charge the batteries, and needs batteries that live in a cabinet that's larger than an american fridge, and are VERY expensive, in order to provide the power levels that it does, the DC voltage is over 300 V DC, so this thing has to be treated with considerable respect. I could run for a number of days off it if I had to, on normal usage. It was originally running a server site, so way larger than normal computer UPS systems.

A few years ago, I picked up another one that runs on 48 V dc, it was capable of putting out 8 KVa, so enough to run a house with care, but not things like showers, or other heavy electrical loads, but it too was the size of a filing cabinet, and still needed significant capacity batteries to run it if the load was close to capacity.

The other factor to take into consideration is that something like a fridge may only use 100w when it's running, but the start current will be much higher, and if the backup device can't provide that surge power, there is the possibility of damage to the fridge, or the inverter, or both, depending on what happens, if the fridge stalls and doesn't start running, the motor can overheat, and so can the inverter.

Running the entire house off a UPS is not an easy situation to deal with,as there are a lot of complications in terms of connections, and management circuits, and ensuring safety of the ESB side of things in the event of a power failure. You certainly can't install a whole house system without using some specialised changeover or isolation circuits, as it will have to go in before the main breaker panel, so a second control panel will be needed to control that device, with appropriate protection and isolation devices.