Which inverter for minimal energy consumption

[antobag]

I am currently in the process of setting up a small solar system that will consist of:
- 2 x 100W polycrystalline panels (200W total)
- A 20A MPPT charge controller
- A 12V 100Ah AGM battery

It will be set up at an off-grid hut in Wales in February, where I can expect to have an hour or so of daily sunlight (this is a conservative figure). I estimate that I will be using energy at a rate of no more than 40 watts for 5 hours daily, which means that each day I will have used a total energy of under 200 watt-hours. I will be using a laptop, an LED light, some audio equipment (microphone, keyboard, amp, etc) and I will be charging a mobile phone from time to time.

I would like to know what would be my best option in terms of choosing an inverter. One of my main criteria is that it uses as little energy as possible, and in this respect I have heard mixed things about PSW vs MSW inverters. Is it feasible to use an inverter with such a small system and still be left with enough power for it to be worthwhile?

I have also considered doing a straight DC to DC step-up conversion for my laptop (according to the adapter, it runs at 19V). This would obviously combat the inefficiency of going from DC to AC and back to DC again. My only problem with this method is that I would only be able to power my laptop and none of my other devices (eg. my light, my keyboard, etc). Using an inverter and AC power would let me install a multi-tap plug socket in which I could power multiple devices simultaneously. Is there any way around this problem (eg. a multi-tap DC converter with a range of different output voltages)?

[sro]

A couple things:

• I'd highly recommend a DC-DC charger for the laptop, you loose a lot of efficiency converting back to AC to then convert to DC to charge
• Use the smallest inverter possible for your power needs. For example, I have a 150W inverter for small miscallenous loads that I rarely use
• Only run the inverter when you're using it - it draws enegery even when nothing is plugged into it.
• I've heard Modified Sine Wave (MSW) inverters are less efficient than Pure Sine Wave inverters (PSW)

[antobag]

A couple things:

• I'd highly recommend a DC-DC charger for the laptop, you loose a lot of efficiency converting back to AC to then convert to DC to charge
• Use the smallest inverter possible for your power needs. For example, I have a 150W inverter for small miscallenous loads that I rarely use
• Only run the inverter when you're using it - it draws enegery even when nothing is plugged into it.
• I've heard Modified Sine Wave (MSW) inverters are less efficient than Pure Sine Wave inverters (PSW)

Thanks sro. So I guess I could run it purely through the DC-DC charger when using only the laptop and nothing else, but then connect the inverter when I have to use more than one device at the same time (for instance, when I need to use the laptop and light together). I'm guessing there's no way to have multiple DC-DC chargers coming out of one battery? My midi keyboard, for example, is powered by DC 9-12V while my laptop is DC 19V. In order to use both at the same time, would I have to buy a second battery?

[Mike90250]

Automotive laptop DC-DC adapters still have a 10 - 20% loss, as it converts the 12VDC to AC, through a step-up (boost) coil to get 19V, then rectifies it back to DC.

Pure sine vs Mod sine inverters. Pure sine are less efficient at the 12V end, because of losses creating a nice sine wave. All gear works great on pure sine.

Mod sine is a bit more efficient on the 12V end because it's a much simpler circuit, BUT powering loads with mod sine can cause problems with some (portable tool rechargers are sometimes very picky about their power) devices, problems with motors - motors buzz, get hotter from the harmonics and draw MORE power when on mod sine. Incandescent lights, and heating appliances are about the only thing that don't care about mod OR pure power. Small device wall wart power supplies can overheat on mod sine, and you have to replace them, or put the smoke back inside the parts.

My advice, a small 150w pure sine inverter, and only power it up when needed. Fine tune the size to be about 30% over your expected loads.

[antobag]

Thanks for the knowledge and advice Mike, I'm very grateful. Is there any other method I could use to avoid the 10-20% DC to DC step-up loss?

I've replied on the other thread that you posted on, but I'll quote it here as well just in case:

In terms of using a DC-DC adapter, I can't seem to find anything that goes directly from the battery (ie. crocodile clips) to a laptop charger. Could/should I use the following?:
[My 12V Battery connected to:]
1) A battery to car charger adapter: http://www.amazon.co.uk/TRIXES-Batte.../dp/B005G39HLY
[connected to:]
2) An in-car laptop charger: http://www.amazon.co.uk/In-Car-Charg...laptop+charger
[connected to my laptop.]

If this is okay, would it also be possible to place a car charger splitter between the two (eg. http://www.amazon.co.uk/Ring-volt-In...cessory+socket) so that I can use multiple DC appliances on one battery? I know that the splitter is rated at 10A maximum (so 120W on 12V), but this should be enough for my needs. However, I'm just a bit concerned that adding so many different car-charger connections could end up causing some adverse effects.

Any more of your fantastic advice would be much appreciated!

[Mike90250]

Only way to get a 12V car battery to charge a 19v laptop battery, is with a DC-DC step up converter. Most will be about 80% efficient, better ones will flaunt their efficiency. (Hey, it's in a car, just run the engine - who cares)

If you don't want to attach gator clips to the converter, then your only choice is the "clip-on-socket adapter" and then plug the converter into it. Be warned, hook the clips up backwards once, and you fry the converter.

[antobag]

Only way to get a 12V car battery to charge a 19v laptop battery, is with a DC-DC step up converter. Most will be about 80% efficient, better ones will flaunt their efficiency. (Hey, it's in a car, just run the engine - who cares)

If you don't want to attach gator clips to the converter, then your only choice is the "clip-on-socket adapter" and then plug the converter into it. Be warned, hook the clips up backwards once, and you fry the converter.

Cheers Mike, and thanks for the warning - I didn't know the consequences of backwards wiring were so big. I'll make sure to check and double-check my wiring before connecting anything.