Best Amazon Inverter

adam7118

Member
This is probably a loaded question, but Im in the market for a new Pure Sine Wave inverter. My budget is $300-500, around that area. I was running a MSW inverter previously and it could not keep up. The biggest draw by far is the water heater. I have 4 160 AH deep cycle batteries that are probably on their way out. I expect that 3000 watts is about right for what I need (completely guessing). 2000 watts seems too low, and I do not want to get one with wattage that is too high in fear that it would draw too much from the batteries. Im a little unsure of how the wattage works with these inverters though. I understand the sine waves but I don't understand the watts. Is 3000 Watts the outputs? If so what would be the input? Anyway, the reviews on these are all over the place. Here are the ones I found:

1. https://www.amazon.com/GoWISE-Power...690-f7e1-44eb-ad06-aebbef559a37&tag=cb-osp-20

2. https://www.amazon.com/Giandel-Inve...7e1-44eb-ad06-aebbef559a37&tag=cb-osp-20&th=1

3. https://www.amazon.com/WZRELB-RBP30...603371325&sprefix=pure+sine+w,aps,161&sr=8-11


Power sources:

1. Alternator/Isolater
2. 300 Watt Solar on roof.

Power Draws:

1. Bosch 2.5 Gallon Electric water heater (Huge draw)
2. Dometic 12v fridge
3. Chinese Diesel heater
4. plugs/outlets/the occasional TV
5. Sureflow water pump (small draw)
6. LED lights (Small draw)
 

sparkplug

Active member
There's a lot to unpick there...

The wattage of your inverter needs to be sufficient to cover the appliances that you connect directly to it (so your 12v fridge and anything that connects directly to the batteries on 12v is excluded)

Certain mains powered appliances, such as fridges, have a spike or surge of power they require on start up and your wattage needs to be high enough to cope with that. 2000w is actually quite a lot and will easily handle a domestic fridge or freezer.

My suggestion to you would be to make a proper list of all the appliances and their actual power demand and make your calculations from there.

I found these videos helpful to help plan mine, although I've opted for an exclusively 12v setup so don't have any need for an inverter. I keep thinking that I would like one, but I haven't yet figured out what for. I might end up with something like a Bluetti one day, who knows?


 

Kajtek1

2015 long/tall limo RV 2.1l
I bought 3000/6000W pure sine inverter on ebay for $98.
The only complain is that the cooling fan can get noisily.
For years I have been using modified sine inverters and they work with everything I have. Digital ovens, coffeemakers, TVs. No problem.
Other issue is checking static power draw.
Depends how you plan to use it, the efficiency can be more or less crucial.
For times when I turn inverter on only for few minutes of oven use- I don't care about efficiency much.
But on my Sprinter I use inverter for big refrigerator, who can run for hew hr on battery+ 100W solar. This is where efficiency is becoming crucial.
Bad news is that getting precise data on those units is very difficult.
Good luck searching, but frankly would I plan to spend $400 on inverter, I would go for reputable inverter/charger. Those usually are top end electronics and make whole wiring much simpler.
BTW the cheap inverter from ebay come with no remote switch, but I opened the housing and soldered parallel cable to its switch just fine.
 

elemental

Wherever you go, there you are.
This is probably a loaded question, but Im in the market for a new Pure Sine Wave inverter. My budget is $300-500, around that area. I was running a MSW inverter previously and it could not keep up. The biggest draw by far is the water heater. I have 4 160 AH deep cycle batteries that are probably on their way out. I expect that 3000 watts is about right for what I need (completely guessing). 2000 watts seems too low, and I do not want to get one with wattage that is too high in fear that it would draw too much from the batteries. Im a little unsure of how the wattage works with these inverters though. I understand the sine waves but I don't understand the watts. Is 3000 Watts the outputs? If so what would be the input? Anyway, the reviews on these are all over the place. Here are the ones I found:
[...]
Power sources:

1. Alternator/Isolater
2. 300 Watt Solar on roof.

Power Draws:

1. Bosch 2.5 Gallon Electric water heater (Huge draw)
2. Dometic 12v fridge
3. Chinese Diesel heater
4. plugs/outlets/the occasional TV
5. Sureflow water pump (small draw)
6. LED lights (Small draw)
The way you have specified your needs indicates you may not fully understand what the inverter is doing in your system.

Like sparkplug says, before you starting trying to specify the inverter capacity (in watts) you need to separate out the power draws that go through the inverter. Many of the things on your list (above) are probably or definitely 12 volt Direct Current (DC) loads:
  • Dometic 12v fridge (definitely)
  • Chinese diesel heater (definitely)
  • Sureflow water pump (? RV versions are 12 volts, but 120 volt AC units are available as well)
  • LED lights (probably 12 volt if they are RV models; could be 120 volt AC if they are household ones installed in RV)
Anything that runs off of 12 volts DC is not going through your inverter. The purpose of the inverter is to take a Direct Current (DC) power source and give it an Alternating Current (AC) waveform at certain voltage. Typical DC power sources are 12 volts or 24 volts, and in North America the expected AC voltage is usually 120 volts. Less expensive inverters don't achieve the actual waveform (a sine wave), but for some devices a "Modified Sine Wave" is good enough. (You don't have a microwave oven on your list; those are one of the devices that really wants to see a "Pure Sine Wave". No harm in going with a Pure Sine Wave inverter except the extra cost; benefit is making sure as many devices as possible are compatible.)

Your "plugs/outlets/the occasional TV" are domestic 120 volt AC loads. Some of these can be substantial draws (i.e., you plug in a 1,500 watt electric heater or an 1,800 watt four-slice toaster). You need to create your AC power budget based on what all of these are and how many you expect to run simultaneously in order to size your inverter. They should each have a data plate on them that specifies their power draw in either watts or amps (at 120 volts).

The Bosch 2.5 gallon electric water heater I found on-line was in the 3000 T series; these have a 1,440 watt power draw specification. I believe that a simple resistance heating element doesn't have a substantial variation in peak versus steady-state draw. If your Bosch 2.5 gallon electric heater is a 120 volt AC unit then you need to add its power needs to your AC power budget.

If your biggest load is the Bosch, and you don't plan to run the Bosch simultaneously with something like a four-slice toaster, then a 2,000 watt inverter might be the right size for you. Only you can know whether this is true, however, by creating your AC power budget based on your actual loads, the peak usages, and which might be run simultaneously.

Most of the inverter specifications that I have seen rate the inverter by the constant load they can handle in watts. A 2,000 watt inverter should be able to meet the steady state load of a 2,000 watt device or combination of devices; this is just under 17 amps at 120 volts AC. Depending upon the inverter, it may be able to handle higher temporary loads; if so these are usually specified as a "peak" or "maximum" load in watts, along with the length of time it can handle that peak load. The power (watts) drawn from the DC power source is greater than the power supplied (in watts) to the AC devices due to inefficiencies in the inversion and voltage conversion process. If the inverter is 90% efficient, then the power drawn from the DC source to supply 2,000 watts to the AC devices would be 2,000 watts/0.90 = 2,222 watts. If your battery system is at 12 volts (you didn't specify it) then the inverter would be drawing 2,222/12 = 185 amps to supply that 2,000 watt AC load.

That kind of amp draw is pretty sizable and it's possible that what wasn't "keeping up" was the DC power supply and not your inverter. You didn't specify whether the 160 amp-hour batteries were 6 volt or 12 volts; either is possible. If they are pairs of 6 volt batteries wired in series/parallel, then you have 320 amp-hours of 12 volt battery storage, and trying to suck 185 amps out of them would be a big hit. Before you buy a new inverter thinking it will solve all of your problems, calculating the actual draw you have through your inverter and what this inverter load draws from your batteries is in order. You might just be exceeding what your batteries can reasonably supply.

Different battery technologies have different rates at which power can be drawn from them. "Deep-cycle" battery capacity is typically specified at a 20-hour discharge rate; this means you only get the rated "amp-hour" of capacity if you discharge the batteries over 20 hours. If you only have 320 amp-hours (4 6-volt 160 amp-hour batteries) then the 20-hour discharge rate is 320/20 = 16 amps. Sucking 185 amps out of them is a 320/185 = 1.7 hour discharge rate. This substantially reduces the available energy because the amount of energy the batteries can supply is reduced when you discharge them more quickly (see https://en.wikipedia.org/wiki/Peukert's_law.) Even if your batteries are all 12-volt and you have 640 amp-hours of storage, a 185 amp draw is a 640/185 = 3.5 hour discharge rate, substantially higher than 20 hours. I would guess that you would have only about an hour of draw at this rate before your batteries would be down to 50% state of charge.
 

Kajtek1

2015 long/tall limo RV 2.1l
OH, 1 more observation - the wattage of inverter is 1 thing, when cooling it is another.
In the past, on my boat I was using 1200W inverter for powering 1500W oven.
Boat is always cooler than any RV, so usually it took 7 minutes before inverter would overheat and shut down.
2 minutes cool down and it was ready for another 7 minutes, what was good enough to warm up frozen finger food.
So don't go overboard with inverter size - work on proper cooling instead.
 

borabora

Active member
Elemental's post above gives you all the info you need.
The only minor point I can add is that for a water heater a pure sine wave output is not necessary. The heating element and thermostat are very likely to be fine with a modified sine wave inverter. The TV may need a PSW but if you ran it successfully before with a MSW inverter then it doesn't. No need to spend the extra money for a PSW unless you are certain that you need it or that it is likely that you will need it.
 
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adam7118

Member
Elemental,

Holy cow that was helpful. This basically tells me everything and furthers my suspicions that this may be a battery issue after all. Sparkplug and Elemental, you are right, I should have been more specific. There are two plugs that go to my inverter. One is for the hot water heater and the other is for the four outlets in the van. The plugs are used for a few different things, but it's usually just charging my phone or a rechargeable light. Borabora, I suspect you might be right about not needing a PSW, but the MSW inverter I have has been destroyed (another story) so I figured Id try and do it right this time.

The batteries are 6 volt run in parallel. Two 12 volt sources. I also believe they are getting old. It now sounds to me like the problem is batteries and not the inverter that worked perfectly fine before I screwed around with it.

Knowing that my domestic fridge and hot water heater are likely my biggest draws. Could you recommend a reasonable battery bank for this setup?

Sparkplug, do you have a shower? DO you have hot water? If so, how are you heating it?
 

glasseye

Well-known member
Your Dometic fridge: is it a compressor fridge? If it is, it's draw will be very low. 5A or less. If it's a "thermal" fridge, that's another story. It might draw as much as your water heater. If you're running out of power, I'd blame either or both of those two units.

I agree with elemental. Neither the heater nor the fridge (being resistive loads) require PSW. Your TV might. As will a microwave.

How old are the batteries?
 

sparkplug

Active member
Sparkplug, do you have a shower? DO you have hot water? If so, how are you heating it?
Not at the moment.

My hot water comes from boiling a kettle in the morning while I'm making coffee and then storing it in a catering pump action airpot. This keeps it hot all day and I dilute it with cold water in the sink to reach the desired temp.

I am considering installing a shower but if I do then it will be powered from my underslung propane tank with minimum electrical draw for the display and spark.

*edit* So, I suppose my hot water is being heated with propane as that's what my hob/grill/oven uses
 

elemental

Wherever you go, there you are.
The batteries are 6 volt run in parallel. Two 12 volt sources. I also believe they are getting old. It now sounds to me like the problem is batteries and not the inverter that worked perfectly fine before I screwed around with it.

Knowing that my domestic fridge and hot water heater are likely my biggest draws. Could you recommend a reasonable battery bank for this setup?
It sounds like your battery storage is a nominal 320 amp-hours at 12 volts (4 x 160 amp-hour 6 volt batteries), with a 300 watt solar recharge capability. Leaving the hot water heater out of the mix for a moment, that's a good-sized system for boondocking for many days with your other loads including the fridge. Your fridge might consume (very very rough estimate here) something like 40 amp-hours over 24 hours, but the 300 watts of solar probably recovers that plus your other incidental usage (LED lights, etc. except for the water heater) in half a day on a good solar day, and you have enough spare capacity to go as many as four days without even solar input (again, except for the water heater).

The electric water heater is the 800 pound gorilla load on the system. If it has the 1,440 watt heating element that the one I found on-line has (or something close to it), it is a real energy suck. Running it even just 30 minutes a day uses ( 1,440 watts / .9 eff. factor / 12 volts * 1/2 hour = 67 amp-hours) at a substantial discharge rate from your 320 amp-hour nominal capacity (320 amp-hours / 134 amps = 2 hour 24 minute discharge rate). Although that 67 amp-hours is only 21% of your battery storage, the fact that it gets sucked out 8 1/2 times faster than the 20-hour discharge rate on which the 320 amp-hours of storage is based means that it might take 40% off of the capacity in those 30 minutes of run time. Getting that 40% back using 300 watts of solar might take 6 1/2 hours on a good solar day.

If the batteries have been drawn down past 50% and not charged back up to 100% state of charge frequently, then their overall capacity is probably lower than the nominal 320 amp-hours, making the electric hot water heater's impact even greater.

Try disconnecting the hot water heater and see how well the battery storage works for you then. If you can find a way to carefully manage (i.e. limit the use of) the hot water system then your current set up should work. On the other hand, if easy access to hot water is important to your situation, then you need more battery storage, possibly a different battery technology, and more solar panels.

However, based on what you said about what you could afford to spend on a new inverter, I don't think battery storage system that's adequate for running the hot water heater freely is in the cards. A lithium battery technology (like LiFePO4) would give you a better ability to handle the discharge rate, and 300 amp-hours of LiFePO4 would give you as much as 300 * .8 = 240 amp-hours usable storage (at a great cost). If you use 60 amp-hours (fridge plus incidentals) plus 67 amp-hours (30 minutes of hot water heating) a day, that 240 amp-hours could last 240 amp-hours / 127 amp-hours/day = 1.8 days between re-charges. However, you would also might need to buy a new solar charge controller for the LiFePO4 batteries. In addition, the 300 watts of solar panel would probably not recover all of that energy usage on a daily basis except on a great solar day in the middle of the summer; upgrading to 600 watts solar in total wouldn't be out of line (very rough estimate). If you stick with lead-acid technology, you might need 600 amp-hours total storage to get 300 amp-hours usable storage that would last as long as the 300 amp-hours total (240 amp-hours usable) of LiFePO4 (due to the greater loss of capacity for lead-acid batteries from the high discharge rate needed for the hot water heater).

[Edit: These are SWAGs I put in at midnight... no warranty express or implied as to the correctness of my math]
 
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