Do you really need an AC inverter?

#31
Lol ! Define "portable device". Hitachi Magic Wand ? Dyson Hairdryer ??
Maybe thats a buzzword of mouseclicker culture, No doubts will be outmoded late next week...
As this topic is AC, DC, inverters, etc. "Device" is defined as other than a conductor (wire) an electrical item what carries or controls electric current.
You understood the intent, and I'm guessing your a forum Troll.
 
Last edited:
#32
Other then previously stated, here are my thoughts.

High powered inverters often have substantial shore power chargers build in (100A+) So space/weight cost savings can sometimes be actualized if you need a decent sized inverter for loads like Aircon starting, water heating, cooktop etc.

12v power adapters are available for most items. As mentioned some battery chargers are not offered. If there is no need for a beefy inverter, a 300W or smaller unit can easily power these loads. Morningstar makes an excellent 300W continuous pure sine inverter with high efficiency and low standby usage.

It depends on the inverter, but many have a (zero load) power consumption in the 10-40W range. The Morningstar suresine uses less than 1 watt in standby, but has a 6W (~450ma) zero load consumption. Which means a 10W load such as a phone charger will use 16W minimum (not counting losses at the inverter or the wall charger). Many inverters have a search function, which pulses power every few seconds/minutes and only stays on if a load is present.

I have seen a few suggestions on other forums that DC appliances (such as fridges) are too expensive. Instead a "dorm" fridge and inverter should be used. Long story short this about doubles the power consumption compared to a DC native fridge. :ROFLMAO:

For big rigs that have substantial solar (over 700W) and/or normal generation runtime schedules. A always on inverter and 120VAC based system makes some sense. This would allow you to run a 24 or 48 volt system for better inverter efficiency, and smaller wiring (it also lets you avoid having lots of batteries in parallel). A 95% efficient DC-DC converter can handle any DC items that need a lower voltage than the main bus. Of course DC appliances are often more efficient than their AC counterparts, so there are lots of variables.


In our vehicle we use an induction cooktop. This is the main reason for a large inverter. As a bonus it also is a fantastic shore power charger, rapidly topping off a depleted bank. I have been tossing around the idea of cutting apart a 5kbtu window Aircon unit and turning it into a compact minisplit for cooling my sleeping area. The inverter would power that as well.
 
#33
Other then previously stated, here are my thoughts.

High powered inverters often have substantial shore power chargers build in (100A+) So space/weight cost savings can sometimes be actualized if you need a decent sized inverter for loads like Aircon starting, water heating, cooktop etc.

12v power adapters are available for most items. As mentioned some battery chargers are not offered. If there is no need for a beefy inverter, a 300W or smaller unit can easily power these loads. Morningstar makes an excellent 300W continuous pure sine inverter with high efficiency and low standby usage.

It depends on the inverter, but many have a (zero load) power consumption in the 10-40W range. The Morningstar suresine uses less than 1 watt in standby, but has a 6W (~450ma) zero load consumption. Which means a 10W load such as a phone charger will use 16W minimum (not counting losses at the inverter or the wall charger). Many inverters have a search function, which pulses power every few seconds/minutes and only stays on if a load is present.

I have seen a few suggestions on other forums that DC appliances (such as fridges) are too expensive. Instead a "dorm" fridge and inverter should be used. Long story short this about doubles the power consumption compared to a DC native fridge. :ROFLMAO:

For big rigs that have substantial solar (over 700W) and/or normal generation runtime schedules. A always on inverter and 120VAC based system makes some sense. This would allow you to run a 24 or 48 volt system for better inverter efficiency, and smaller wiring (it also lets you avoid having lots of batteries in parallel). A 95% efficient DC-DC converter can handle any DC items that need a lower voltage than the main bus. Of course DC appliances are often more efficient than their AC counterparts, so there are lots of variables.


In our vehicle we use an induction cooktop. This is the main reason for a large inverter. As a bonus it also is a fantastic shore power charger, rapidly topping off a depleted bank. I have been tossing around the idea of cutting apart a 5kbtu window Aircon unit and turning it into a compact minisplit for cooling my sleeping area. The inverter would power that as well.

Nice write up, and, yes, inverters have greatly improved over the years.

Now for the but.

Now matter how good an inverter is, it still will be a power load / loss, and with smaller systems (or space/weight restricted to the number of batteries you can bring), every watt can make a big difference in your storage batteries ability to recover (solar in my case) without being attached to the grid or using fuel.

Since the proliferation of Lithium based batteries, the impacts have been huge, but some cultures have remained steady. What I'm really getting at, is a culture of thinking we "need" an inverter, when, in reality, many DC products already exist, the market is growing, and, as consumers, we can help drive that market. For example, over the past 5-7 years, look at how far solar panels have come, portable wind turbines almost didn't exist 7 years ago, and battery storage has increased while loosing weight. So the opportunities to be truly of the grid are growing, and it is very exciting.
 

DaveInDenver

Expedition Leader
#34
Now matter how good an inverter is, it still will be a power load / loss
You've changed the criteria. The original question was about the need for an inverter and anyone would reasonably say no. You can often find a 12 VDC appliance and doing no conversion is the best option. That is a good thing to point out, but you had a conclusion to support in your posit.

Several people pointed out that sometimes there are things that can't run on 12 VDC or doing so would lock you into niche product or custom solution. You acknowledged that battery chargers and laptop adapters are common reasons to need something other than 12 VDC.

You'll need a conversion and whether you select a DC boost converter or an inverter isn't going to matter much. The primary loss of efficiency is due to the large switch on the primary source and that's going to be present in both cases. Once you've chopped the 12 VDC with a large FET and stored energy in a big inductor you've lost the majority of the energy you're going to lose, so the additional loss from choosing to rectify back into a higher voltage DC or create an AC output is marginal (and the current bleeding edge transformer-less inverters are essentially exactly the same as an equivalently sized DC converter).

So *if* you can't find a 12 VDC solution for a given power requirement what drives your losses is the quality of the converter and sizing it right. Selecting a poor quality modified square wave inverter running at 10 KHz that is lightly loaded will result in a lot of lost power. Selecting a true sine 400 KHz PWM inverter that you run at 80% of load rating won't. The same is true of a DC boost, though. If you size it right and it's running completely in continuous mode at the peak load it will be good while putting 10% of the rated load, forcing the switcher to go discontinuous and shunt power to remain in regulation might reduce it's efficiency to 1/3rd of its peak efficiency.
 
Last edited:
#35
I knew I screwed up when I started out with Makita. Been using them since the days of red plastic housings and a free Japanese Millwrights cap included in every metal tool case...
Had I only known Dewalt would make servicable screwed case NiCads...

I started with Makita cordless back when the best thing they had was the 7.2V black stick batteries. I still like Makita tools and have a bunch of them, but I started switching over to Dewalt cordless about ten or more years ago, because they seemed to be a better value when I factored in battery cost and availability. My battery guy will replace cells in glued Makita post batteries, with the caveat that if the case breaks while he's working on it, it's all on you. So not worth the risk. Aside from screwed cases on the Dewalt nicads, their backwards compatibility allows me to run 12V batteries on my 9.6V tools and 14.4V batteries on my 12V tools, with no damage to the tools and improved tool performance. I think I can run 14.4V batteries on my 18V tools in a pinch, but it's been a while since I tried that because I have so many 18V batteries.

FWIW, my old Craftsman 12V and 14.4V drills also have screwed and rebuildable batteries, probably made by Black & Decker.
 
#36
I would say we don't "need" 90% of the crap we drag with us , don't need a rtt, don't need a camp kitchen , don't need a fridge , don't need tablets and cameras and ect ect . but if it's something you feel to be useful to your situation and style of traveling then by all means use it . I keep a small inverter in the tahoe and it's come in handy a few times when a car charger has been forgotten or I needed to use a corded power tool in a pinch . yes I could buy some other tools that are cordless but that's money that could go to getting out and exploring .
 

Happy Joe

Apprentice Geezer
#39
This thread has sparked the contrarian in me...
After much careful consideration (30++ years ago) I decided to go with 12 volts (sealed lead acid) and an inverter; primarily because it allowed me to use a compact Edison base fluorescent light, and not worry about wire length.
Fast forward a quarter+ century and I have stayed with the system (past several inverters destroyed by near miss lightning hits)... Don't camp under/near trees with scorch marks down their sides...
Honestly; no one that I know cares anything about inverter loses or efficiency; if it works first time, every time and is easy to get the right color temperature LED bulbs and is easy to recharge devices from(one USB fits most); folks are happy.
If it can be used to power equipment at home during power outages its even better (I use the same bulbs camping and in the living room so living room lighting just means plugging any table lamp or computer into the tent supply's inverter and switching both on).

I have been waiting for lithium tech (especially inverters) to come down in price enough to make it relatively affordable but until then; sealed lead acid (with or without) inverters is fine.

Enjoy!
 
Last edited:
#40
Yes many people - and/or their use cases - do not care about optimizing energy efficiency.

This discussion is really only relevant for those who do have that need.

Otherwise it's just a question of preference.

PS the type of bank you carry has little bearing on that topic
 
#41
You've changed the criteria. The original question was about the need for an inverter and anyone would reasonably say no. You can often find a 12 VDC appliance and doing no conversion is the best option. That is a good thing to point out, but you had a conclusion to support in your posit.

Several people pointed out that sometimes there are things that can't run on 12 VDC or doing so would lock you into niche product or custom solution. You acknowledged that battery chargers and laptop adapters are common reasons to need something other than 12 VDC.

You'll need a conversion and whether you select a DC boost converter or an inverter isn't going to matter much. The primary loss of efficiency is due to the large switch on the primary source and that's going to be present in both cases. Once you've chopped the 12 VDC with a large FET and stored energy in a big inductor you've lost the majority of the energy you're going to lose, so the additional loss from choosing to rectify back into a higher voltage DC or create an AC output is marginal (and the current bleeding edge transformer-less inverters are essentially exactly the same as an equivalently sized DC converter).

So *if* you can't find a 12 VDC solution for a given power requirement what drives your losses is the quality of the converter and sizing it right. Selecting a poor quality modified square wave inverter running at 10 KHz that is lightly loaded will result in a lot of lost power. Selecting a true sine 400 KHz PWM inverter that you run at 80% of load rating won't. The same is true of a DC boost, though. If you size it right and it's running completely in continuous mode at the peak load it will be good while putting 10% of the rated load, forcing the switcher to go discontinuous and shunt power to remain in regulation might reduce it's efficiency to 1/3rd of its peak efficiency.
Great discussion can easily change criteria of the original intent, but that is assuming I had intent, of which, I didn't. Just stirring thought, in a giant think tank to hear different views.

In an ideal world, we could have uniform power, without conversion, but as you mentioned, some are and/or aren't better than others.
 
Last edited:
#42
I would say we don't "need" 90% of the crap we drag with us , don't need a rtt, don't need a camp kitchen , don't need a fridge , don't need tablets and cameras and ect ect . but if it's something you feel to be useful to your situation and style of traveling then by all means use it . I keep a small inverter in the tahoe and it's come in handy a few times when a car charger has been forgotten or I needed to use a corded power tool in a pinch . yes I could buy some other tools that are cordless but that's money that could go to getting out and exploring .
Working from a base, you need less, but if you are on a true expedition, you will be very far from a base, and you needs will change accordingly.
 
#43
FWIW, the Milwaukee guy told me this morning that they will intro 12ah batteries for their M18 system in Q3. Dewalt has a new power bank that uses four 60V Flexvolt batteries to provide portable 110V power, and it also works with a mix of 20V Max batteries.
 
#44
One thing that I haven't seen discussed here is: what if someone else on the trip has a device that has a unique AC battery charger and you want to charge it? I carry one or two very small 150W inverters for computer, cam batteries, etc. They travel in a bag buried behind the driver's seat and I haven't had to use them in 5 or 10 years, but they're there if needed.
 
Top