daft question about inverter

[Tennentslager]

Bought a 120W inverter from Aldi for 20 squid last night.

Wasn't going to have a TV at the hut at all but the boy with autism isn't coping without one so...

I have an old telly that I can cut off the transformer and connect directly to my 12v leisure battery.

Or plug in the inverter and run it with a three pin standard plug.

Is the second way more inefficient?

Guess it means converting the voltage up then down? The telly I have is 12v input.

The inverter seems handy to have for other things such as a Bluetooth speaker. 

Means we just use music from a phone when we're having a party?

[Jeremy Harris]

If the TV with the separate power supply really runs on 12V DC from that power supply, then it's far better to run it direct from the battery.  Using the inverter to boost 12V DC to 240 VAC will waste around 10 to 15% and then using the power supply unit that comes with the TV to convert 240 VAC back to 12 V DC will waste another 10 to 15%, so you could be wasting 20 to 30% of you battery energy by using the 240 V inverter.

Before running the TV from 12 V, best check that the power supply does put out 12 V DC.  Some seem to run on laptop supplies, and they are often around 18 to 19 V DC.

[ProDave]

Another caution about "12V" stuff is a battery on charge can easily be close to 14V.  One example of this was Sky once made a mini sky box that ran from 12V but they would have a habit of blowing up if connected to a battery on charge at close to 14V.  Motorhomes were the big problem and anyone using one in a motorhome was advised to unplug it when driving the vehicle which was when the charging voltage would be highest.

[Crofter]

It might be worth using one of those adapters designed for running laptops etc from a car- DC-DC should be more efficient. Generally designed to output 19v but multi-voltage ones are available.

 

Having said that, on the boat I use an inverter all the time since my 50w solar panel produces far more power than I need so 'waste' isn't an issue, whereas destroying something by trying to run it straight from the battery certainly would be!

[Tennentslager]

Plan would be to connect it to the 12v output from the charge controller, this has 3 pairs of terminals.

PV in, battery out and 12v out.?

[Crofter]

Measure that 12v out, both under load and without any load, and maybe see how it behaves when the system is charging as well. But I would expect it to be much more stable than trying to get 12v direct from the battery.

[Jeremy Harris]

The TV may well have a voltage range marked on it.  My (limited) experience is that "12V" TV sets, that have an external power supply to allow them to run from mains, will work over a pretty wide range and are often designed to be used in boats and caravans where the battery voltage can vary a fair bit (although quite why on earth anyone would ever want one in either is beyond me!).

As above, definitely a better bet to connect it to the charge controller output, as even the cheap ones often have some forum of voltage limiting.  I have a cheap Ebay one here that was falsely labelled as an "MPPT" charge controller, (as many are) and when it arrived I took it apart, as it seemed suspiciously lightweight for a real MPPT controller.  Sure enough, all it had inside was a voltage regulator, but it does regulate on the output side as well as the battery side, albeit with the output side limited to the battery float charge voltage of 13.2 V.

If you get stuck, there are some very good and efficient boost/buck regulators on Ebay that can supply a constant 12V from around 7V to 30V input, but I'm pretty sure you should be OK with a direct connection to the charge controller output.