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Old 05-29-2018, 01:57 AM   #1
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Default Inverters or 12v native adapters?

From the time we got our Roadtrek a decade ago, we had always gone for as much native 12v powered things as possible, so had almost no 110v stuff that needed an inverter to run off the batteries.

Our first real deviation from that came at the last TV and DVD change we just did. We went from 12v native TV and DVD that had the wall bricks removed, but then run though a voltage stabilizer on the 12v line, to 110v TV and DVD player. It was getting more obvious that many of the things with wall bricks were moving up to 15 or 19 volts DC, so they would need adapters for that. To open up more options, we decided to use a small 120 watt PSW inverter with low idle amps and 110v TV and DVD units.

I measured power use both for TV only and TV with DVD running before and after the switch, and was surprised they were essentially the same amount of power use. The TV and DVD specs showed nearly identical power ratings, but I thought the inverter setup would add some power which it didn't. I wrote it off to the 12v stabilizer must have been using some power in the old system.

We just had to get a new laptop to carry with us, and of course it is at 19v instead of the 15 of the old one, so another new adapter needed. The new laptop has a 180 watt charger for 110v, and the biggest I could find was 120 watt for DC, but it appears the extra 60 watts would only be needed if the batteries were dead and you were gaming, so lots of power to the big video card. In normal charging and use, it never uses more than about 75 watts, off of the 110v charger.

I went out and did a similar power test off the 12v adapter and found it using about 20% more power than it did on AC power. To compare, I ran the test again with 110v charger running off the 2000 watt Magnum PSW inverter that has nearly 1.5 amps of idle current. Big surprise was that the DC power use was essentially identical to what we got with the 12v native adapter, so another big surprise. Even with a relatively high idle current inverter, the 12v native was not any better, so no need to have it. Put the 110 charger on a 300 watt inverter with .3-.5 amps idle current and save most of that missing 20% the 12v adapter lost.

It is starting to look like as the devices start to get away from being true native 12v, they also lose their advantage over low idle loss small inverters running 110v to the devices.

I can see sometime in the not too distant future, our "charging" area which has 12v outlets for adapters will probably turn into an outlet strip of 110 off a 300 watt PSW inverter as it will get rid of all the extra adapters and make any new devices instantly compatible.

Kind of looks like a changing of the rules, at least for us.

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Old 05-29-2018, 02:38 AM   #2
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Booster, the data you collect is very interesting. The circuits I see used for stabilizers (SEPIC) will have similar inefficiencies to any other buck-boost dc-dc converter IMO, so that aligns with some of your data. And the varying supply voltages for electronic gear, along with higher IR drop in a lower voltage distribution network, made me inclined to standardize at a higher voltage than the 12vdc common in US RV's. The Volta setup made me interested in seeing if you could source LED lighting, furnace blowers, water pumps, etc at 48v, and maybe you can in the marine world, but unless I'm missing something RVs appear to use 48-12v dc-dc converters with 12v appliances which just seems like a bad idea to me. So maybe you are right, maybe distributing 120vac is the way to go for TV's etc, leaving 12vdc for lighting and some of the appliances.

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Old 06-03-2018, 12:31 PM   #3
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I have argued this before. Thanks for posting the data you collected. I could not see how any voltage change would not have inefficiency. So why purchase a bunch of DC to DC converters, and try to keep them sorted, when I already had the power bricks for each device. I use a 300 watt sine wave inverter for all the electronics. I can't live without my microwave, so I also have a 2000W inverter.
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Old 06-06-2018, 03:24 PM   #4
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DC-DC conversion can be more efficient than DC-AC-DC, but it depends on the devices in play. A larger inverter (1KW or 2KW) can be designed with better components than a $30 inverter that handles just your laptop.

I have a new MacBookPro that uses USB-C to charge. USB-C PD (power delivery) includes negotiation between the device needing power and the power adapter. The Mac I use negotiates to 20V, 3A. I found an excellent 12v to USB-C adapter that will output this 60 watt power, cleanly and silently. Prior to that I was using small inverters (our rig doesn't have a large inverter built in) and all of these had fans of various sizes with one common theme, an annoying, high-pitched whine.

My wife uses an older MacBookPro for her work. We found a 12V to MagSafe II adapter for that.

We have a newer Travato on order that includes a 1KW inverter. We may well switch to using 110v to power the laptops (and almost certainly initially until I install extra 12v outlets). But there are inefficiencies here too. Those wall adapters from Apple do get hot when charging the laptops. That heat is energy that didn't get converted for use in the laptop. In other words, energy loss.
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Old 06-06-2018, 10:13 PM   #5
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Have you done a watts in to watts out comparison for the 12v to USB charger to see what the actual in use efficiency is?
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