What size inverter?

[Suzzz]

I'm in the process of buying everything I need for a solar set up on my van and I'm wondering what size of inverter I should be getting.

So far I've bought 4 x 100w panels and a 30 amp charge controller. Most of my power needs will be to run my 12v fridge. I cook and heat the van with propane and use rechargeable batteries for my lighting. I plan to use the inverter to charge my non 12v electronics (phone, laptop, and camera gear) and to watch a small tv and possibly run a DVD/Blue Ray console occasionally. 

How small is too small and is there such a thing as too big of an inverter?  Can an inverter drain the batteries if it's too big? I understand that Pure sine wave is better than modified but if you can only afford a modified sine wave inverter, do you need a bigger one or is it the same thing (in term of size: Pure vs Modified)?

I heard that solar power is addictive and that it's better to have more than less so I'm trying to do things the right way. Once I've got the inverter thing figured out, I'll concentrate on the batteries. I've also ordered a book on solar power from my local bookstore and can't wait for it to arrive!


Thanks for all your advice!

 

[Mrcap]

I'm in the process of buying everything I need for a solar set up on my van and I'm wondering what size of inverter I should be getting.

So far I've bought 4 x 100w panels and a 30 amp charge controller. Most of my power needs will be to run my 12v fridge. I cook and heat the van with propane and use rechargeable batteries for my lighting. I plan to use the inverter to charge my non 12v electronics (phone, laptop, and camera gear) and to watch a small tv and possibly run a DVD/Blue Ray console occasionally. 

How small is too small and is there such a thing as too big of an inverter?  Can an inverter drain the batteries if it's too big? I understand that Pure sine wave is better than modified but if you can only afford a modified sine wave inverter, do you need a bigger one or is it the same thing (in term of size: Pure vs Modified)?

I heard that solar power is addictive and that it's better to have more than less so I'm trying to do things the right way. Once I've got the inverter thing figured out, I'll concentrate on the batteries. I've also ordered a book on solar power from my local bookstore and can't wait for it to arrive!


Thanks for all your advice!

I have 300w on the roof and 200 in batteries. I use a 500w pure sine inverter to run my Mac mini and a 28” monitor and other electronics camera GoPro etc. It came with a remote control that has been super convenient. Some draw power while idle do watch for that. Got mine from Renogy. It is also very quiet. Some have noisier fans.


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[John61CT]

The majority of your list, and possibly every item, can be powered directly from DC, just converting voltage.

The manufacturer may well sell a 'car adapter' specific for their device, which is ideal.

Otherwise it isn't hard to find adapters, just need besides voltage to ensure enough watts, and to get the tip size and polarity right.

This will be much more energy efficient and cheaper. Start with the "universal" type that comes with switchable voltage and a huge collection of tips, and the DC5521 style as a "standard hub" makes for good interoperability between different ones, making built-in ports etc.

If you end up with one or two devices that you figure are not worth the hassle, at least needing a much smaller inverter size makes a higher quality one much more affordable.

Make sure you turn them off when not actively in use.

 

[MrAlvinDude]

Inverter: How small is too small

Well, a 100W device needs a minimum of a 100W inverter (also see note 1).  All of the devices you have so far mentioned, are typically less than 100W each.  So if you can add up the watt of the things you need to run simultaneous, then you have your lowest rating for your inverter.
I would say that it is highly likely that any 300W inverter would be able to run what you have mentioned so far.

and is there such a thing as too big of an inverter? 

Not really.
However... all electronics will have a minimum idling power usage (or stand-by power usage), so even when they do nothing, they will still use power. And for inverters this idling power usage can often to be a small percentage of its max power capability.
So for a 3000W inverter 10-30W might be wasted as idling power usage. Where the number could be 1-3W wasted by a 300W inverter.

So for this reason it can be energy wise to use as small an inverter as possible, to run your 110V devices.

Can an inverter drain the batteries if it's too big?

All inverters should be turned off, when they are not actively being used to power a 110V device. As they all have an idling/stand-by power usage.

I understand that Pure sine wave is better than modified

Yes.  
It can sort of be compared to running a car down a smooth road or a bumpy road. Both roads will get you to your destination, but your smooth (pure) road is often the preferred choice.

but if you can only afford a modified sine wave inverter, do you need a bigger one or is it the same thing (in term of size: Pure vs Modified)?

300W is basically 300W for both modified and pure sine wave inverters.

---


Note 1:
(a little more technical details)
Watt numbers of devices and inverters can be directly compared for "simple" power usage devices. Battery chargers and power bricks for laptops are typically such "simple" power usage devices.
So a 100W power brick for a computer can typically be powered from a 100W inverter.


Once a device includes a motor, then things may be a little different, as motors typically draw more power (for a short time) when they are first turned on. Inverters are however typically designed so they can offer a higher start up watt (peek watt) than the continuous watt number. So a 300W inverter can typically handle 500-600W peek - for a short time - so the inverter can still be used to both start and continuously run a motor.  
There is however no guarantee that a 300W moter can be started by a 300W inverter, so for a 300W motor it might be necessary to have a bigger inverter, just to be able to handle the startup power needs.

For complex devices that include several motors as well as other electronics and/or heater elements (for example a laser printer)  it may be necessary to have an inverter that is 3 to 10 times more powerful than the watt number on the label of the device.

 

[Suzzz]

Mr Alvin Dude...  WOW !!!  

Thank you so much for your answer.  It was very clear and precise.  I haven't added up the wattage requirements of all my gadgets yet, I'll have to get to it.  I don't plan on having EVERYTHING plugged in all at the same time but one never knows, right?  It could happen and most likely will.  I'll also look into buying some 12v adapters but I think I'll still get an inverter for those situations when I have something new to plug in or if a family member/friend visits me and wants to recharge something.

I find this all very facinating!

 

[Trebor English]

I bought a Harbor Freight 400/800 inverter for $20 with a coupon.  Regular price is $25.  I have used it for all of my 120 volt needs.  I used it with a variable speed electric drill and jig saw to cut the 14 inch hole in the roof for the vent fan.  I have used it with an electric shaver, charged a laptop and recently started using it to run a 120 volt fridge.  

My plan is to avoid 120 volts when possible and use a cheap inverter when necessary.  My plan is to replace the this inverter when I get a device this inverter won't work.  So far this one has been fine with everything I have plugged in to it.  I don't expect to replace it.

 

[jimindenver]

One thing to add is that modified sine wave and pure sine wave are very broad descriptions with no standards. There are MSW inverters that provide dirty power and higher end units that provide power almost at a PSW level. There are PSW inverters that when you see them on a scope you wonder how it got a PSW rating the wave is so jagged. So in both cases a quality unit is best.

 

[frater secessus]

Mr Alvin Dude...  WOW !!!  
Thank you so much for your answer.  It was very clear and precise.

Alvin is becoming one of my favorite posters.  Lots of helpful and clear information.

 

[deadwood]

The first question I think to ask is if you even need an inverter. I realize that some people need it to run either a microwave, coffee maker, toaster, hair dryer, etc.....
But when I was initially figuring out my electrical needs I realized that I had none of these items in my van. So I opted for no inverter. I bought a 12v plug to charge my Macbook Air. And everything else I have is 12v as well.

It really comes down to how elaborate your system is and what you need to run. And you could always install one later if you find you need one.

 

[BigT]

Everything I've read, both here and on various websites, including Apple's, suggests that it's not a good idea to charge sensitive electronics, like a Mac, with one of those inexpensive Acc / cigarette outlet-powered chargers.  Something to do with potentially screwing up the power brick and damaging your expensive laptop.  And while I realize that many people run the less expensive chargers with no issues, I didn't / don't want to chance damaging my obscenely expensive Mac.

Choosing to run a 400W inverter was also a matter of simplicity.  Sure I could buy one of those $30, 12V chargers you find on Amazon or eBay for my Mac, but what about the other stuff I'd like to charge from the van?  I'm not sure I can find a 12V charger for my Remington beard trimmer, and I know I can't find one for the charger to my cordless drill, my CREE bike light, or my DSLR.

Even if I could find 12V chargers for each and every one of the various items I want to charge, why should I when all those items already have their own 110V cords, ready to be plugged into a wall outlet??  Also, buying separate 12V chargers for each item will likely end up costing you more than a single inverter.   

That's just my opinion, it's not intended as advice.  Heck, a few days ago I didn't know squat about inverters!  Now I sound like I sell the darn things! 

 

[Suzzz]

The first question I think to ask is if you even need an inverter. I realize that some people need it to run either a microwave, coffee maker, toaster, hair dryer, etc.....
But when I was initially figuring out my electrical needs I realized that I had none of these items in my van. So I opted for no inverter. I bought a 12v plug to charge my Macbook Air. And everything else I have is 12v as well.

It really comes down to how elaborate your system is and what you need to run. And you could always install one later if you find you need one.

All excellent points, Deadwood. I do own a hair dryer and I don't think I can live without it! For now anyway but all that may change once I've been on the road for a few months. I think I'll get an inverter anyway since right now I'm working and I can afford it. If I decide that I don't need it, I'll sell it. Also, the van I have now is a practice van. I plan to buy my forever/long term van in about 4-5 years when I retire. I'm hoping to have all this figured out by the time I'm ready to drop some serious cash into a new-ish van because once I'm retired most of that disposable income will disappear and I won't be able to afford expensive experiments.

 

[John61CT]

what about the other stuff I'd like to charge from the van?  I'm not sure I can find a 12V charger for my Remington beard trimmer, and I know I can't find one for the charger to my cordless drill, my CREE bike light, or my DSLR.

Even if I could find 12V chargers for each and every one of the various items I want to charge, why should I when all those items already have their own 110V cords, ready to be plugged into a wall outlet??  Also, buying separate 12V chargers for each item will likely end up costing you more than a single inverter.

Do what you like of course, but the "why" is being more energy efficient, in some scenarios that can be very important.

And you don't need to "find" a purpose built adapter for each, the voltage adjustable type with an assortment of tips works for multiple devices.

Cobbling one together from $3-5 parts is also not difficult.

But your rig your call

 

[Trebor English]

I do own a hair dryer and I don't think I can live without it!

A 2000 watt inverter for an 1800 watt hair dryer is easy to get.  A battery to power that load is big, heavy, and expensive.

 

[B and C]

I think RoadPro makes a 12V hairdryer. Haven't used one though as my hair is fine and short. It dries really quick after a towel dry. Maybe a way to save on battery power. YMMV

 

[BigT]

I think RoadPro makes a 12V hairdryer. 

There are also low Watt hairdryers (1000W instead of 1800W).  Amazon sells a few.   Low Watt hairdryers for animals can use as little as 650 Watts.  
I'm not sure how well they work.  They get mixed reviews on Amazon.

https://www.amazon.com/Andis-Gentle...1516219194&sr=8-2&keywords=low+watt+hairdryer

 

[Knit]

What are your current thoughts on the battery type and sizes you will be using?

The fact is that one cannot wait to figure out the batteries separately from the inverter, solar and intended use as they all work together. The best way to do this is to figure out how much battery storage is needed to run your refrigerator and how much for the other devices.

For the low wattage electronics mentioned in the original post (phone, laptop, etc.) I’d recommend spending $50 or so on a cigarette lighter plug in pure sine wave inverter. Maybe a 300 watt one so you could run tv and dvd at the same time. Plug it in when charging something and unplug it otherwise.

If you want to permanently install an inverter and add home like 110v plugs, then the choice of batteries and wattage of the inverter become critical design issues in addition to the wattages of the devices you want to plug in.


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[Suzzz]

What are your current thoughts on the battery type and sizes you will be using?

The fact is that one cannot wait to figure out the batteries separately from the inverter, solar and intended use as they all work together. The best way to do this is to figure out how much battery storage is needed to run your refrigerator and how much for the other devices.

For the low wattage electronics mentioned in the original post (phone, laptop, etc.) I’d recommend spending $50 or so on a cigarette lighter plug in pure sine wave inverter. Maybe a 300 watt one so you could run tv and dvd at the same time. Plug it in when charging something and unplug it otherwise.

If you want to permanently install an inverter and add home like 110v plugs, then the choice of batteries and wattage of the inverter become critical design issues in addition to the wattages of the devices you want to plug in.


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I'm not sure I understand what you are saying. Sorry, but this is all very complicated to me as I have absolutely no expertise in this field. I just received the book on solar power I had ordered and I'm hoping that it helps me make sense of all this.  I plan to hire someone to install my system, but I also want to understand how all this works.


So... You say that I need to know how much I need in batteries before I can figure out the size of the inverter?  From what I've been reading so far and some of the answers I got here, I thought there was no such thing as too big of an inverter, so I figured I'd just buy the biggest one I could afford and go with that.  Am I understanding this wrong?  As for the batteries, I'll get everything out this coming weekend and I'll add it all up... and read my book.

 

[John61CT]

Go back and see if my post #3 makes any more sense to you.

Yes too big an inverter is a waste of money and wasteful of your precious stored energy.

You may not need one at all.

Make your list of devices, how many minutes / hours per day and start figuring a ballpark AH per day energy budget.