inverter

[Hart_family]

Thinking of getting an inverter. Everyone seems to have one for dry camping in case they want to watch TV or make a smoothie in their blender. I have an inverter/generator, but sometimes it might be nice just to draw off of 12 V DC power for something. Inverters seem to connect directly to batteries or to a 12 V outlet. I am reading that the pure sine wave types are more "clean" and similar to your household power, but that the modified sine wave ones may work just fine for many things. Inverter capacity seems to be rated by watts, both continuous and surge.

QUESTION #1: In order to now how "big" of an inverter to get, what is the best way for me to know how many watts certain appliances take? Is it labeled somewhere on each device? Honda says that 32" flat screen TV takes 125 watts, but other sources say 10 watts. Honda says a DVD player take 350 watts, so with the TV, that is 475....requiring me to get a 500 watt inverter or more.

QUESTION #2: Are there certain brands or features I should be considering? (or some brands to stay away from?)

[persistent]

Originally Posted by Hart_family

Thinking of getting an inverter. Everyone seems to have one for dry camping in case they want to watch TV or make a smoothie in their blender. I have an inverter/generator, but sometimes it might be nice just to draw off of 12 V DC power for something. Inverters seem to connect directly to batteries or to a 12 V outlet. I am reading that the pure sine wave types are more "clean" and similar to your household power, but that the modified sine wave ones may work just fine for many things. Inverter capacity seems to be rated by watts, both continuous and surge.

QUESTION #1: In order to now how "big" of an inverter to get, what is the best way for me to know how many watts certain appliances take? Is it labeled somewhere on each device? Honda says that 32" flat screen TV takes 125 watts, but other sources say 10 watts. Honda says a DVD player take 350 watts, so with the TV, that is 475....requiring me to get a 500 watt inverter or more.

QUESTION #2: Are there certain brands or features I should be considering? (or some brands to stay away from?)

A sine wave inverter insures you will not destroy your electronics. Computers, cell phone chargers, and entertainment devices like TV are likely to suffer from Modified Sine Wave inverters (MSW). However, many devices contain sensitive control circuits. Devices designed for TT's and RV's probably have warnings in the manuals. 115 volt home devices don't usually bother to specify. How lucky do you feel?

The best way to size your new inverter is to read the wattage on the label of every 115 volt AC device. Wattage, and or current (amps, A) are required on almost all such devices. Lists of estimated wattage are available, actual devices vary.
watts = voltage X amps

Peak or surge wattage is for starting things usually that have AC motors 1/4 horse or larger. Use the sustained wattage for most things. Running at peak longer than a few seconds will trip the inverter overload.

Usually inverters up to 400 watts can be plugged into a cigarette lighter socket. You may be able to run an LED TV and a DVD, but it depends on the actual devices.

1000 watt inverters will run multiple small electronic devices and appliances. They will not run heating devices like Microwaves and most electric coffee pots. These need to be wired directly to the batteries with short heavy cables.
My 1000 watt sine wave is mounted with 6 gage wire within two feet of my 200 amp hour battery bank. It draws 2 amps (24 watts) when idling. It draws about 85 amps (1020 watts) running at full capacity. It would drain my batteries in about two hours at the high rate.

2000 watt inverters will run your microwave. It will also run one air conditioner or one heating device as well as multiple small devices. It is equivalent to a 115 volt home outlet. It would draw about 170 amps and drain my batteries in about 1 hour. The microwave usually runs for less than 5 minutes, the others would kill your batteries to soon to be useful.

Consider a 12 volt LED TV plugged directly into a 12 volt cigarette lighter socket. (From Amazon and many other sources.) You also may be able to find a 12 volt DVD as well as other small appliances.

[wahoonc]

All appliances have labels on them, usually in watts. Add them up.

I use both modified and pure sign wave inverters depending on the planned use. For electronics you really should use pure sign wave, yes they cost more.

BestConverter.com is a good source of information as well as a good place to buy things. Not necessarily the cheapest, but Randy will answer questions and point you in the right direction. There are several good brands out there. A couple of my preferred ones are Samilex and Xantrex. WFCO makes them too, however based on my track record with their converters I would not recommend them.

Battery bank size will play into the size of inverter you want, can run and for how long. I use a 2000 watt Prowatt SW2000 by Xantrex. It was a quick and dirty option for what I needed at the time. I also use an automatic transfer switch. The only thing we power off of it are two TV's and the coffee pot plug. I have a pretty small battery bank at the moment, it is roughly 90 ah usable. I will be upgrading to a LiPo eventually, probably aiming for 300 ah.


Aaron

[ewarnerusa]

For the most part, don't even think about something larger than a 1000 watt inverter unless you have a large battery bank (like 4 or more batteries). The amp draw is just too high on the DC side to run something larger than that and it becomes dangerous. If you have just one battery, then stick to a 400 watt unit and just run little things like a charger or 2 or a TV. Forget about anything with a heating element, those require a lot of power and are best left to your generator.

[donzinger]

As far as brand, I have a complete Magnum system and am very happy with it and it's features. Mine may be much bigger than you are looking for, but the brand and features are worth looking into. Battery monitor kit and automatic generator start are tops of the list for me.

[Hart_family]

Originally Posted by ewarnerusa

For the most part, don't even think about something larger than a 1000 watt inverter unless you have a large battery bank (like 4 or more batteries). The amp draw is just too high on the DC side to run something larger than that and it becomes dangerous. If you have just one battery, then stick to a 400 watt unit and just run little things like a charger or 2 or a TV. Forget about anything with a heating element, those require a lot of power and are best left to your generator.

Thanks ewarnerusa - one comment about the heating element. One potential use of an inverter for me is to wrap my lithium battery in a heating blanket made for those purposes. They usually are labeled 80 watts (6.7 amps at 12 volts, I think?), which seems very reasonable if I was not using this continuously.

[persistent]

Originally Posted by Hart_family

Thanks ewarnerusa - one comment about the heating element. One potential use of an inverter for me is to wrap my lithium battery in a heating blanket made for those purposes. They usually are labeled 80 watts (6.7 amps at 12 volts, I think?), which seems very reasonable if I was not using this continuously.

Most Li battery instructions say not to charge them when battery temp is below 32 degrees. Instructions say they may be discharged in temperatures much lower, maybe 0 degrees F.

So if you install the batteries inside the cabin, the cabin will be warm when occupied. You can both charge and discharge without wasting amp hours heating the batteries.

If you mount them where temp might drop below 32, you only need to heat them when you charge them and it is below 32.
You only need to heat them to 0 degrees when you are discharging them. If you are charging using a generator or shore power, you can use cheap 115 volt heaters.

li batteries do not emit explosive gas nor do they spray acid mist. They do not require servicing so access to them is not necessary. Install them in an insulated place like under a seat or a pass through compartment. Any place out of the way and inside the cabin walls works well. You only need to tie them down so they don't bounce around.

My propane furnace with electric fan draws only 2.5 amps. Some RV furnaces draw a little more than 7 amps. Like your proposed battery heater, they are not expected to run continuously. 7 amps even on intermittently is a lot if you are drawing from your batteries.

[Hart_family]

Originally Posted by persistent

Most Li battery instructions say not to charge them when battery temp is below 32 degrees. Instructions say they may be discharged in temperatures much lower, maybe 0 degrees F.

So if you install the batteries inside the cabin, the cabin will be warm when occupied. You can both charge and discharge without wasting amp hours heating the batteries.

If you mount them where temp might drop below 32, you only need to heat them when you charge them and it is below 32.
You only need to heat them to 0 degrees when you are discharging them. If you are charging using a generator or shore power, you can use cheap 115 volt heaters.

li batteries do not emit explosive gas nor do they spray acid mist. They do not require servicing so access to them is not necessary. Install them in an insulated place like under a seat or a pass through compartment. Any place out of the way and inside the cabin walls works well. You only need to tie them down so they don't bounce around.

My propane furnace with electric fan draws only 2.5 amps. Some RV furnaces draw a little more than 7 amps. Like your proposed battery heater, they are not expected to run continuously. 7 amps even on intermittently is a lot if you are drawing from your batteries.

Thanks Paul. Yes, LFP batteries can discharge without any problem down to -4 F if not more. But charging is another matter. The BMS will not even ALLOW charging when too cold, and some batteries prevent it at 40 F or colder. This is the one "bugaboo" with LFP batteries, at least for those that may camp in these temperatures.

In our case, this is for a modest travel trailer with the plastic battery boxes on the tongue. There is really not other easy place to put them "inside", except perhaps some rewiring I could do it in the insulated but unheated pass-through storage area (?).

My plan was to just have a batter warming blanket on hand for the situation when the battery is too cold to charge, and I need to warm them up a tad before charging.

[Hart_family]

Persistent -

Our little travel trailer does not have any 12 volt "cigarette" style ports. Also, I am learning that most of these 12 volt connections like in cars and such can only pass 180 watts maximum through them (even if connected to a larger inverter, say 400 watts).

I had no idea that there were TVs made for 12 VDC power. So cool.

The TV in our trailer is an 32" HD (720p) LED flat screen, and apparently only consumes 28 watts. Who knew. That seems so little for such a large bright thing. With the batteries outside of the unit, still trying to figure out how I would watch TV using the battery/inverter only (not the generator). Hmmm...

[persistent]

Originally Posted by Hart_family

Persistent -

Our little travel trailer does not have any 12 volt "cigarette" style ports. Also, I am learning that most of these 12 volt connections like in cars and such can only pass 180 watts maximum through them (even if connected to a larger inverter, say 400 watts).

I had no idea that there were TVs made for 12 VDC power. So cool.

The TV in our trailer is an 32" HD (720p) LED flat screen, and apparently only consumes 28 watts. Who knew. That seems so little for such a large bright thing. With the batteries outside of the unit, still trying to figure out how I would watch TV using the battery/inverter only (not the generator). Hmmm...

You have a choice of paying more and installing large inverter or installing a 12 volt outlet for more general use like a TV or a fan. An outlet can go anywhere it is convenient. Wire would be fished back to the 12 volt service panel or directly to the battery with a fuse in the wire.

A small 250 watt inverter can also be wired directly to the 12 volt service panel or battery. It would draw about 20 amps. You would need smaller wire than for a 1000 watt inverter. 12 gage wire can be run longer distances.

12 volt outlets can be easily added. If you have even rudimentary wiring skills you can do it. Otherwise lots of service shops can do it. I paid $25 to have one added to my Kodiak Cub. The shop added it next to a USB phone charger port and tapped into the USB 12 volt supply wires. My wife uses it to run her CPAP machine and plug in a small inverter to run a vibrator.

Any 12 volt light or USB port can be a source.
Turn the light on. Pull the fuse so the light goes off.
Unscrew the fixture and gently pull the wire out.
There should be crimped connectors joining the light wires to the house wires. Mark the wires using masking tape and pen so you know which is which.
Use crimp connectors to connect a new length of wire and the light all together. Make sure the wires you marked before go back to the same connectors.
If you are lucky, the house wire will be red and black. Usually the red is the positive wire. To be sure measure voltage with a DC voltmeter $10 at a hardware store. Buy a digital one so you can use it to monitor your batteries.
Cut a mounting hole the size of the cigarette lighter fixture you bought at automotive store or "tractor" hardware store.
Fish the new wire through the new hole.
Connect the positive house wire to the center pin in the cigarette lighter socket. The negative goes to the socket side connector.
Mount the new socket.
Put the fuse back in and test. You are good to go!

Note, it is not as good to use twist on wire connectors in a TT because the road vibration can cause them to untwist.

[ewarnerusa]

Originally Posted by Hart_family

Thanks ewarnerusa - one comment about the heating element. One potential use of an inverter for me is to wrap my lithium battery in a heating blanket made for those purposes. They usually are labeled 80 watts (6.7 amps at 12 volts, I think?), which seems very reasonable if I was not using this continuously.

80 watt load isn't too large, but will run down a single battery in a handful of hours.
Regarding some of your other posts about power available to a 12V outlet, you're right that most OEM installs can only handle a small amp draw. This is mainly due to wiring, small power feed wires have higher resistance and when the inverter calls for more amps than the wiring can allow to flow the inverter will fault out and shut down. Any inverter will perform better if wired directly to the batteries using as short of wire length as possible and of at least the minimum gauge. Small inverters can work OK when plugged into 12V outlets because you're typically not requiring them to draw a lot of amps from the DC side. But once you're calling for say 500 watts, that translates into roughly 50 amps from the DC side and you need the wiring to be able to accommodate that. If it can't, the inverter can't provide the AC power it is trying to and will fault out and shut down.

[leisuresolar@gmail.com]

There are some misconceptions about modified sine inverters. They work just fine on almost all modern electronics with no problems, and are 1/3 the cost of pure sine. The issue with modified sine inverters is with inductive motors like compressors. The harmonics can cause the motor to run hot. Most motor driven appliances, like a blender, don’t run long enough to have a problem (plus they often have ice...margarita anyone?). In the old days, some TVs would have a problem, but modern TVs don’t.

Some of the Cummins generators actually produce a modified sine, not a pure sine. Look for the sine harmonic spec in the manual, if it doesn’t have one, it is likely a modified sine. Not the same modified sine as an inverter, but not a pure sine either. I used to build equipment that measures harmonics and we have measured hundreds of generators. And they work just fine with RVs.

All that being said, I mostly use expensive, American made pure sine inverters. Magnum’s and Outback’s are great, will last forever, and you never have to think about them again. Victron’s are great also, Dutch made, mostly.

A 400 watt inverter will blow the fuse on a cigarette lighter plug. It also will overload most wiring/fuses already installed in your camper. Don’t use anything over 150W inverter with existing wiring/fuses. Most inverters are best case about 85% efficient, which means a 150W inverter needs about 15A to run.

It is becoming more popular to use a “gas-less” generator for powering small loads in an RV. A good gas-less generator is built with a lithium battery in a box, along with an inverter and a charge controller. The boxes weigh less than 50# and is easily transported. This allows you to use your “generator” not only in your RV, but also for other outdoor activities like tailgating or fishing or picnics or beach days. They can even be used as backup power in your home.

[Hart_family]

Originally Posted by leisuresolar@gmail.com

There are some misconceptions about modified sine inverters. They work just fine on almost all modern electronics with no problems, and are 1/3 the cost of pure sine. The issue with modified sine inverters is with inductive motors like compressors. The harmonics can cause the motor to run hot. Most motor driven appliances, like a blender, don’t run long enough to have a problem (plus they often have ice...margarita anyone?). In the old days, some TVs would have a problem, but modern TVs don’t.

Some of the Cummins generators actually produce a modified sine, not a pure sine. Look for the sine harmonic spec in the manual, if it doesn’t have one, it is likely a modified sine. Not the same modified sine as an inverter, but not a pure sine either. I used to build equipment that measures harmonics and we have measured hundreds of generators. And they work just fine with RVs.

All that being said, I mostly use expensive, American made pure sine inverters. Magnum’s and Outback’s are great, will last forever, and you never have to think about them again. Victron’s are great also, Dutch made, mostly.

A 400 watt inverter will blow the fuse on a cigarette lighter plug. It also will overload most wiring/fuses already installed in your camper. Don’t use anything over 150W inverter with existing wiring/fuses. Most inverters are best case about 85% efficient, which means a 150W inverter needs about 15A to run.

It is becoming more popular to use a “gas-less” generator for powering small loads in an RV. A good gas-less generator is built with a lithium battery in a box, along with an inverter and a charge controller. The boxes weigh less than 50# and is easily transported. This allows you to use your “generator” not only in your RV, but also for other outdoor activities like tailgating or fishing or picnics or beach days. They can even be used as backup power in your home.

Thanks for the clarifications! A few questions:

1. I am imagining that an inverter rated for a 400 watt capacity can still run only 80 watts through it if that is all you are using, correct?

2. You mention the 150 watt limitation due to camper wiring. That seems so low in contrast to the 400, 750, and 1000 watt inverters so many are buying. Hmmm... What would one do if they needed to run 350 watts of stuff inside their camper?

3. So not owning a dedicated inverter yet, I was imagining connecting it directly to the battery (which I believe is an option). But it sounds like there is a way to connect the inverter inside the camper to the wiring??

4. You mentioned "gas-less" generators. I presume the Goal Zero Power Stations are an example of this? Just LFP batteries with an inverter and other bells/whistles?

[persistent]

"1. I am imagining that an inverter rated for a 400 watt capacity can still run only 80 watts through it if that is all you are using, correct?"

Yes, I am running a 300 watt inverter through a cigarette lighter socket. My computer brick is 100 watts. The inverter only draws enough 12 volt power to run the brick.
300 / 12 = 25 amps
100 / 12 = 8.3 amps
The 12 volt TT circuit is fused for 15 amps. The fuse does not blow. It works fine.
15 X 12 = 180 watts (max the circuit can provide)
A 200 watt inverter would work just as well as a 300 watt, but cost less. A 150 watt would run my computer just as well.

2. You mention the 150 watt limitation due to camper wiring. That seems so low in contrast to the 400, 750, and 1000 watt inverters so many are buying. Hmmm... What would one do if they needed to run 350 watts of stuff inside their camper?

He cited 150 watts for use with a cigarette lighter socket with typical 12 volt lighting circuits. You would run heavier wire to connect larger inverters. You would add a larger fuse to protect the heavier wire.

3. So not owning a dedicated inverter yet, I was imagining connecting it directly to the battery (which I believe is an option). But it sounds like there is a way to connect the inverter inside the camper to the wiring??

Yes, small inverters can be connected to typical TT lighting circuits that usually run throughout the TT. To get more than 180 watts, you cannot use typical TT lighting circuits.

4. You mentioned "gas-less" generators. I presume the Goal Zero Power Stations are an example of this? Just LFP batteries with an inverter and other bells/whistles?

I am not familiar with that term. But the gas-less generator he was talking about seems to be a portable battery. In the case he referred to, it is a lithium battery that you would charge somewhere else and bring to the TT. The lithium battery is very light and easily carried.

[leisuresolar@gmail.com]

Persistent is correct, I wasn’t very clear on inverter power draw. Most inverters draw an amp or two even at idle. Then they need about 125% of however much power you draw from them (inefficient). Say you want to run your computer at 150W, then you will need to pull about 190W from your battery (190w/12.5V=15.2A) to power the inverter and your computer.

Most trailer wiring and fusing can handle this. But if you hook a 400W inverter to that wiring, I guarantee someone will plug something in that demands 400W (or more, HONEY, I plugged my blow dryer in here now it doesn’t work any more). I see it all the time. If you are lucky, the fuse will blow and no other harm done.

Inverters bigger than about 150-200W should be wired directly to the battery, with an in-line fuse or circuit breaker sized for the wiring. FUSES ARE SIZED TO PROTECT THE WIRING THEY ARE ATTACHED TO. You want the fuse to blow before the wires burn. Correct wire sizing is beyond the scope of this chat. Email me at leisuresolar@gmail.com if you want to discuss that.

The Yeti Goal Zero was way to expensive, so I built my own “gas-less” generator (see the attached picture). It uses a lithium battery (Battle Born) with a 1200W Inverter/Charger that I can charge up from solar, wall charger or car. We ran a pickup camper for five days, microwave, toaster, toaster oven, crock pot, lights, radio, everything except hot water heater and fridge (and no blow dryer, but it would do that on low), using two 100W portable panels (see picture). I actually built this 3 years ago, and have iterated the design 4 times, now it is nearly perfect. It works great and is VERY tough compared to the cheap Yeti design.

I’m a retired electrical engineer, and I just love this stuff! This forum is a ton of fun for me. I’m actually in Grand Junction, CO, so not so far from you. Come on down, we’ll find a way to get great solar on your camper.

[sundancer 87]

It has been stated a few times to wire an inverter directly to the battery bank, as close as possible and with size appropriate wire.


Totally correct except while trying to do this someone may want to place an inverter in the battery box. That covers the suggestions but is strongly discouraged.

[Hart_family]

Originally Posted by sundancer 87

It has been stated a few times to wire an inverter directly to the battery bank, as close as possible and with size appropriate wire.


Totally correct except while trying to do this someone may want to place an inverter in the battery box. That covers the suggestions but is strongly discouraged.

Why is that discouraged?

Not even sure how one would fit anything more inside the small battery boxes on a travel trailer. Unless you mean a larger battery compartment holding multiple batteries (bank like you said).

[sundancer 87]

Small OEM battery box or a larger one fitted for more batteries is all the same to an ignition source (inverter) and gasses contained in the battery box.

[Hart_family]

Ah yes. You would be correct.

Another wonderful benefit of lithium....not worrying about gases.

[franktafl]

Originally Posted by Hart_family

Ah yes. You would be correct.

Another wonderful benefit of lithium....not worrying about gases.

wouldn't heat be an issue?