1000 watt modified runs longer than 1500 pure sine

[TEDthebed]

Let's consider the "initial load, high current draw / low voltage shutting down" theory a sec. This is the same things as the "Can't start and run my AC on batts / inverter" dilemma.

The reason a household AC has a large starting or running capacitor in it, that capacitor store voltage for when the unit is shut off, and then the compressor cycles off.

To mitigate this in an RV people buy the AC quick start kits. Even people who have large well made inverters.

If this is the same principle and it's also the cause of this PSW inverter issues, a quick start kit might work.

Adding capacitors directly to the fridge compressor might work.



Let's go with that.

Thanks for the reply. I just checked out Quick/Easy Start kits on Amazon and they're all around $300, little more than I'd like to spend, but I might have to in order to accomplish my goal.

 

[MurphyGuy]

Thanks for the recommendations. I'll check out the inverters

Victron makes fine products, but there are other's as well. Along with Victron, there's Outback, Schneider, SMA, etc. The problem with these high quality inverters is that they are also expensive, and you're not likely to touch one of them for less than $1500 or so. You get what you pay for.

Inverters mostly come in three quality levels. 1) Non Chinese 2) Name Brand made in China 3) Generic branding made in China.

Nothing wrong with an inverter made in China by a non-Chinese company, but when you buy a Chinese brand (or no brand) inverter, then that's a problem.

For example, my main off-grid system uses SMA Sunny Islands, which have a normal price tag of just over $5500 each, and I have two of them. I also own an Outback Radian 8048 with a $4000 price tag. But beyond the split phase 240 stuff, I have a few 12 volt backup units as well, and for the small 12 volt stuff, I choose to stick with "GoPower!" brand. These are PSW inverters, made in China, but are not Chinese inverters. GoPower! brand has a reputation in the RV and boating industries and they are relatively cheap. GP inverters are not the only ones that are decent, there are others as well.. Lots of people go with AIMS, and while I'm not crazy about them myself, they seem to work well if you don't abuse them.

Even if your fridge works with a MSW inverter, the MSW inverter will most likely shorten the fridges life. They're not designed to operate on a modified sine wave.

 

[Boondock Saint]

Second that. However he could just branch off the supply leg for the fridge to the MSW and let the PSW handle everything else. Eventually the fridge will die and the problem will solve itself.

 

[Delmar]

Variable #1: when measuring draw is the defrost cycle which uses a heating element. My full-size Fridge nameplate is 11.6A however my kill-a-watt measures around one amp when running. I have yet to monitor power during the defrost cycle.

Variable #2: restarting the compressor. When the fridge shuts off there is considerable pressure in the line that makes starting even more difficult. The longer the fridge is off, the more the pressure bleeds down.

 

[TEDthebed]

One 100 watt 12 volt panel
Two 12 volt 100 AH Gel Batts
1500/3000 watt 12 volt to 120 volt pure sine Inverter
Or
1000/2000 watt modified sine inverter

Goal: power 11.2 amp 120 volt fridge

The 1000 watt modified sine will run the fridge for close to 8 hours, until the batteries are at minimums of 10-10.5 volts.

The 1500 pure sine shuts down after about 4 hours with the batteries around 12.5 volts.

The rub is that this is the second pure sine each from different companies exhibiting the same behavior.

What is happening here?

Batteries are connected to inverter by double 6 AWG wires (4 wires total) 18" long.

Batteries are parallel wired with 4 AWG wire (2 total wires) 18" long

Update: I've just been using the 1000/2000 watt Bestek MSW 12 volt inverter for a couple of years as backup during power outages which occur here once or twice a year. The Bestek MSW has been working fine, but the kitchen exhaust fan (which I don't use that much) sounded like it was running slower than normal and also sounded like the speed oscillated. That's why I decided to try and upgrade to a larger PSW inverter which did make the exhaust fan sound normal. Also, the MSW output voltage is 116 volts continuous which I know is within acceptable limits, but I don't think it's ideal for sensitive computer circuitry which maybe found in my fridge. Would changing the system from 12 volt to 24 volt help?

 

[TEDthebed]

Victron makes fine products, but there are other's as well. Along with Victron, there's Outback, Schneider, SMA, etc. The problem with these high quality inverters is that they are also expensive, and you're not likely to touch one of them for less than $1500 or so. You get what you pay for.

Inverters mostly come in three quality levels. 1) Non Chinese 2) Name Brand made in China 3) Generic branding made in China.

Nothing wrong with an inverter made in China by a non-Chinese company, but when you buy a Chinese brand (or no brand) inverter, then that's a problem.

For example, my main off-grid system uses SMA Sunny Islands, which have a normal price tag of just over $5500 each, and I have two of them. I also own an Outback Radian 8048 with a $4000 price tag. But beyond the split phase 240 stuff, I have a few 12 volt backup units as well, and for the small 12 volt stuff, I choose to stick with "GoPower!" brand. These are PSW inverters, made in China, but are not Chinese inverters. GoPower! brand has a reputation in the RV and boating industries and they are relatively cheap. GP inverters are not the only ones that are decent, there are others as well.. Lots of people go with AIMS, and while I'm not crazy about them myself, they seem to work well if you don't abuse them.

Even if your fridge works with a MSW inverter, the MSW inverter will most likely shorten the fridges life. They're not designed to operate on a modified sine wave.

Thanks, I'll check out the GP inverters and I agree that an MSW might shorten the life of my fridge.

 

[TEDthebed]

Second that. However he could just branch off the supply leg for the fridge to the MSW and let the PSW handle everything else. Eventually the fridge will die and the problem will solve itself.

Yeah, the fridge probably would die prematurely running on the MSW

 

[Delmar]

Would changing the system from 12 volt to 24 volt help?

I have a Reliable WZRELB 2500W/5000W that is 48V connected to my golf cart FLA. Has no problem starting my fridge but will brown-out the house starting my 1/2HP garbage disposal. Fridge running draws around 2.5A @ 50V = 125W. When the fridge was disconnected the no-load amps was 0.4A = 20W. Additional information.

If you are going to buy a new inverter might as well go 24V for future expansion.

 

[TEDthebed]

Variable #1: when measuring draw is the defrost cycle which uses a heating element. My full-size Fridge nameplate is 11.6A however my kill-a-watt measures around one amp when running. I have yet to monitor power during the defrost cycle.

Variable #2: restarting the compressor. When the fridge shuts off there is considerable pressure in the line that makes starting even more difficult. The longer the fridge is off, the more the pressure bleeds down.

I will check again, but as I remember, continuous run on my 11.2 amp GE fridge was 740 watts according to kill-a-watt. So, the defrost heater (which I believe draw normally around 500 watts) is probably pushing the draw to 1300 watts and that's were the 11.2 amps comes from. So when the defrost turns on at around 4 hours the PSW's shutdown. So, why doesn't the smaller capacity MSW shutdown as well??? There's a discussion thread I've been told about MSW's and PSW's which I am going to read ASAP. Thanks

 

[TEDthebed]

I have a Reliable WZRELB 2500W/5000W that is 48V connected to my golf cart FLA. Has no problem starting my fridge but will brown-out the house starting my 1/2HP garbage disposal. Fridge running draws around 2.5A @ 50V = 125W. When the fridge was disconnected the no-load amps was 0.4A = 20W. Additional information.

If you are going to buy a new inverter might as well go 24V for future expansion.

Thanks, I agree on going to 24 volt for future expansion. Interesting about the 1/2 hp disposal taxing your inverter that much.

 

[Supervstech]

Possibly.
The issue then would be the need for large battery cables.
2000W is going to be in the neighborhood of 200 amps on startup... and surge can hit 400...
make sure you have #2copper or larger to handle the surge without voltage drop.

 

[TEDthebed]

Good point, thanks. 2 AWG it will be

 

[TEDthebed]

Good point, thanks. 2 AWG it will be

Aims has an inverter with what they call "soft start technology". Anyone know anything about it?

 

[Supervstech]

Aims has an inverter with what they call "soft start technology". Anyone know anything about it?

I found this in the manual...

 

[Boondock Saint]

Thanks for the reply. I just checked out Quick/Easy Start kits on Amazon and they're all around $300, little more than I'd like to spend, but I might have to in order to accomplish my goal.

If the AIMS soft start actually works for your scenario and doesn't buckle then you spent the $300 as part of a single unit plus the cable upgrade cost. Sounds like a lot less hassles to me. Unless of course it still doesn't work. You have replacement insurance on your RV and belongings? :D

 

[TEDthebed]

I found this in the manual...

Thanks, but I'm not sure that soft start tech would help, but it might. However, my more important concern is that it's an MSW not PSW.

 

[MorganCarey]

You seem to have a potential solution mapped out by some pretty knowledgeable folks here.

What about this though? I know car audio enthusiasts use large capacitors wired in before their amps to help with stressing the alternator of the car (headlight dimming with every beat). Could something similar be done here?

Wire a large capacitor between the battery and inverter?

 

[Boondock Saint]

Wire a large capacitor between the battery and inverter?

NO.