Looking for a home UPS that is smart

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What is complicating my decision is whether today do i consider an inverter that can use solar in the future or not ?

If nothing interesting appears in this space for the next five years then maybe solar capability isn't necessary right now.

The choice is whether to gradually build a system you can add to over the years or just restart from scratch each time batteries or inverter dies.

You don't need a solar inverter, as long as your load is capable if being handled by your existing inverter, you can use your existing inverter and buy only a Solar charge controller.

In my case I had 2 x 800watt APC Ups powering two floors, they weren't enough for my current needs with a on board charger of 6amp, I could at max put 80ah batteries. I did think of buying a solar charge controller, so that I could connect even 200ah batteries but no matter what, I couldn't even run a non-inverter fridge or mixer grinder or any appliance that had a high Inrush current or power consumption greater then 800w, so that idea was shelved. So instead I got a 5000w solar inverter.

Also in my house no one was interested in spending on solar, there argument was when will they get the ROI. I said to them when will you get the ROI on their recently bought IphoneX or their 128gb Oneplus6, they had no answers. I won.

 

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Here in bangalore at best the battery dealers gives about 10% off a new battery in exchange of old battery. A battery like exide 200ah c10, the dry weight is 54kg dry,even if you subtract 7kg off it, thats like 4k to 4.5k per battery, but the battery dealer will only give you like 1.9k to 2k max, lead ingots on the other hand 10kg costs Rs 1500. So those scrap dealers would melt them into ingots and make more then 6k off a 200ah battery.

These guys are more generous. Only like for like though

I'm dealing with them and have to say i've been impressed with the service. Very helpful.

I have two choices

The Regalia 1550 at 90k.

The Zelio Wifi 1700 at 7.2k + 2 x exide C10 200AH for 42.2k or little over 50k

That exide C10's has no warranty whatsoever if not used with a solar panel. But the seller told me this wasn't a problem if they looked after refilling at a nominal charge per visit.

He seemed to agree with a lifetime expectancy of 8 - 10 years for those C10s and this is over the usual 5 -6 with the regular tubular C20's

I asked him how warranty replacements work for flooded batteries that fail in the warranty period. He told me unless the customer keeps a log to prove to the manufacturer that water filling was regular the company will reject the warranty. The user has to prove there was no negligence.

The part i find stunning with the regalia is it substitutes for a 2 battery system. Run times are pretty close even with C10's for higher loads.

the 900 is 2 x 80AH

1530 is like 2 x 120AH

1550 is like 2 x 200AH

its only when loads approach spec values that the flooded batteries get longer backup.

 

[NotMyRealName]

What is complicating my decision is whether today do i consider an inverter that can use solar in the future or not ?

If nothing interesting appears in this space for the next five years then maybe solar capability isn't necessary right now.

The choice is whether to gradually build a system you can add to over the years or just restart from scratch each time batteries or inverter dies.

About a solar inveter, i would agree with adder's advice.

About batteries, personally i think lead acid is a waste of money, there is no real savings, either short or long term. Lithium is too expensive now. So the best solution right now is to run solar directly and grid at night.

Also, the whole lead acid buyback thing is a huge scam technically, because the companies (and maybe the middlemen in the chain) get a lot of value from an old battery, while giving peanuts to the customer returning it.

 

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These guys are more generous. Only like for like though

I'm dealing with them and have to say i've been impressed with the service. Very helpful.

But the price they quote for the battery is high, The lowest I have seen online is 19.8k for that shipped from chennai to any where in the south. So the street price should be cheaper, take for example the 150ah exide solar c10 battery, the lowest quote I got was 15k.

That exide C10's has no warranty whatsoever if not used with a solar panel. But the seller told me this wasn't a problem if they looked after refilling at a nominal charge per visit.

He seemed to agree with a lifetime expectancy of 8 - 10 years for those C10s and this is over the usual 5 -6 with the regular tubular C20's

I asked him how warranty replacements work for flooded batteries that fail in the warranty period. He told me unless the customer keeps a log to prove to the manufacturer that water filling was regular the company will reject the warranty. The user has to prove there was no negligence.

Those dealers want like 200 bucks or something for putting distill water. I guess if one where to do it themself, keep the distill water bill receipts and then take a picture with a newspaper, of it being topped up.
Most dealer I spoke to are fine selling c10 batteries, as long as you solar panel installed during warranty claim, there shouldn't be a problem for solar criteria.

The part i find stunning with the regalia is it substitutes for a 2 battery system. Run times are pretty close even with C10's for higher loads.

the 900 is 2 x 80AH

1530 is like 2 x 120AH

1550 is like 2 x 200AH

its only when loads approach spec values that the flooded batteries get longer backup.

For the price of 1550, you could get 2x 200ah exide c10 batteries+ 3kw solar inverter minus the panels. So if your load is like 400watts you can run for 8 hrs with 80% dod or get 2.4kw for 1hr.

With regalia you can only discharge max of 900watt and you will theoretically get 2hr 42min at 900watt. Where as exide can give the same 900watt load for 4hr 2 min.

 

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About batteries, personally i think lead acid is a waste of money, there is no real savings, either short or long term. Lithium is too expensive now. So the best solution right now is to run solar directly and grid at night.

Also, the whole lead acid buyback thing is a huge scam technically, because the companies (and maybe the middlemen in the chain) get a lot of value from an old battery, while giving peanuts to the customer returning it.

The inverter that I bought can run without batteries, the fact that I need to spend 40k to 80k on 100ah and 200ah respectively, is the reason I have not yet bought the batteries. Also was still trying to find or get lower quotes for 4000cycle LFP packs, these will surely last full 10years or more. No luck in getting good prices.

Was also expecting a reputed solar panel brand who told me at the solarexpo back in december about their impending launch of lithium battery 2000 cycle life 12v 80ah equivalent for a retail price of anywhere between 18k to 25k+ GST. no launch so far.

So I may go for 4x 100ah and used the 40k saved(instead of 200ah) and could get some nice solar panels for that 40k. Which instantly starts saving money vs a battery.

May be 5 years later, LTO packs will be affordable.

 

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But the price they quote for the battery is high, The lowest I have seen online is 19.8k for that shipped from chennai to any where in the south. So the street price should be cheaper, take for example the 150ah exide solar c10 battery, the lowest quote I got was 15k.

Cheaper is always available but the question then is how fresh ? he assures me his batteries are no older than 3-4 months. This necessarily means asking price will be closer to list price. Clearly a case of getting what you pay for.

I'd ask for the serial#s to cross check with the manufacturer before buying as a general rule with any battery seller. Now how many sellers will be as transparent.

Then again people are happy to get something cheaper. Just accept that battery will be older and what you get isn't going to be rated capacity but less. How much less is tbd.

Those dealers want like 200 bucks or something for putting distill water. I guess if one where to do it themself, keep the distill water bill receipts and then take a picture with a newspaper, of it being topped up.
Most dealer I spoke to are fine selling c10 batteries, as long as you solar panel installed during warranty claim, there shouldn't be a problem for solar criteria.

This is the next bit. Water quality. If you have access to good quality water then you don't need the refill service. Was even considering getting a distiller so i could make it myself. 5ltr in 5h at the cost of 2.5units

How do you gauge how much water to put into the battery ? Do you just eyeball it and pour in.

If you keep a log in the way you described then i think the manufacturer will agree to the warranty.

For the price of 1550, you could get 2x 200ah exide c10 batteries+ 3kw solar inverter minus the panels. So if your load is like 400watts you can run for 8 hrs with 80% dod or get 2.4kw for 1hr.

With regalia you can only discharge max of 900watt and you will theoretically get 2hr 42min at 900watt. Where as exide can give the same 900watt load for 4hr 2 min.

The regalia will limit to 900W so the flinn can handle an unexpected surge and much higher load. I'm surprised there is a 3KVA model that works with just 24V. Cruze needs three batteries.

As for runtime, exide at 900W in a 24V system

900W is 37.5A draw. Which means 5.3h theoretical out of a flooded battery. At that high a draw the two C10's will be 80% so 4.2h. Taking into account the more efficient flinn inverter will decrease runtime by only 10% so ~3.8h till cutout. A whole hour+ longer.

I was just thinking there is no deduction here for 80% DOD as a C10 run flat like that will be 80% DOD when it cuts out anyway. The lithium will be entirely flat but the flooded battery isn't flat and the remainder can be withdrawn with a lower load but i'm leaving that out as it requires user intervention which i consider impractical over the long term. Good for an emergency though to have a little extra still left in the tank.

At 400W the regalia should manage 5.5h. The two C10's at 400W will have a runtime of 12h. No derating for C10 so take away 10% for inverter and the runtime will be 10.8h. Now the 80% DOD applies and the end result is 8h+ h

At a 2.4kW load, the two C10's will yield 2h. From the shakti table, 2h means 60% with the inverter efficency drops it to just over one hour.

Will have to study the flinn inverter. There are two things i need to know. Is there a way to run an ethernet cable to it which can be connected to a wifi router. Then it can be accessed over wifi from a laptop without needing a wired connection. Is that possible ?

And how long can the wire between inverter and battery be ? can use thicker gauge if needed. Is 2m cable too long or does it have to be shorter to reduce losses.

The flinn has two fans so it will be noisy. I wanted to stick it in the staircase room. Would need to make some vents in the wooden sheet that covers the space under the staircase for venting. Not sure how safe this will. Small enclosed area that collects hydrogen and only a small spark can set it off. So the batteries will have to be stored outside the room and here the longer cable comes in with the not so quiet flinn inside the room

In comparison the regalia just hooks up on the wall in living room and the household has more or less accepted it that way.

 

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Cheaper is always available but the question then is how fresh ? he assures me his batteries are no older than 3-4 months. This necessarily means asking price will be closer to list price. Clearly a case of getting what you pay for.

I'd ask for the serial#s to cross check with the manufacturer before buying as a general rule with any battery seller. Now how many sellers will be as transparent.

C10 batteries are rarely in ready stock with any dealer, one dealer who had it in stock back in December quoted a low price and the dates where within 2 months old, another dealer who doesn't normally deal with inverter batteries gave a even lower price then what ever is shown online, he has to order them from the distributor. So I am guessing it will be of newer stock.

This is the next bit. Water quality. If you have access to good quality water then you don't need the refill service. Was even considering getting a distiller so i could make it myself. 5ltr in 5h at the cost of 2.5units

How do you gauge how much water to put into the battery ? Do you just eyeball it and pour in.

If you keep a log in the way you described then i think the manufacturer will agree to the warranty.

This is how I was doing it for 9 years, I first visually determine which bottles have nil impurities in the shop,(when shell pumps used to sell them they where really good, they no longer sell it). I then use a TDS meter to determine the quality of water before pouring them into the battery. The distill water bottles that I get from a local HP petrol pump as some floating particles, which I filter it out. The TDS however is nearly zero.

I am already in the process of making my own distill water filter plant. Also experimented with rain water but never actually used it in battery.

The regalia will limit to 900W so the flinn can handle an unexpected surge and much higher load. I'm surprised there is a 3KVA model that works with just 24V. Cruze needs three batteries.

As for runtime, exide at 900W in a 24V system

900W is 37.5A draw. Which means 5.3h theoretical out of a flooded battery. At that high a draw the two C10's will be 80% so 4.2h. Taking into account the more efficient flinn inverter will decrease runtime by only 10% so ~3.8h till cutout. A whole hour+ longer.

I was just thinking there is no deduction here for 80% DOD as a C10 run flat like that will be 80% DOD when it cuts out anyway. The lithium will be entirely flat but the flooded battery isn't flat and the remainder can be withdrawn with a lower load but i'm leaving that out as it requires user intervention which i consider impractical over the long term. Good for an emergency though to have a little extra still left in the tank.

At 400W the regalia should manage 5.5h. The two C10's at 400W will have a runtime of 12h. No derating for C10 so take away 10% for inverter and the runtime will be 10.8h. Now the 80% DOD applies and the end result is 8h+ h

At a 2.4kW load, the two C10's will yield 2h. From the shakti table, 2h means 60% with the inverter efficency drops it to just over one hour.

Runtime chart from flin for gel/vrla/agm type c20 battery, PF 1 so va =watt.

Will have to study the flinn inverter. There are two things i need to know. Is there a way to run an ethernet cable to it which can be connected to a wifi router. Then it can be accessed over wifi from a laptop without needing a wired connection. Is that possible ?

And how long can the wire between inverter and battery be ? can use thicker gauge if needed. Is 2m cable too long or does it have to be shorter to reduce losses.

The flinn has two fans so it will be noisy. I wanted to stick it in the staircase room. Would need to make some vents in the wooden sheet that covers the space under the staircase for venting. Not sure how safe this will. Small enclosed area that collects hydrogen and only a small spark can set it off. So the batteries will have to be stored outside the room and here the longer cable comes in with the not so quiet flinn inside the room

In comparison the regalia just hooks up on the wall in living room and the household has more or less accepted it that way.

Some models can be monitored with a Ethernet via their proprietary adapter, some models like mine also has optional wifi and Cost 6k extra.
http://voltronicpower.com/en-US/Product/Detail/Wifi-Card and ethernet card http://voltronicpower.com/en-US/Product/Detail/SNMP-web-Card,-SNMP-Box

Some even use a long USB cable or Ethernet to RS232 adapter connected to a Ethernet wire. I will just use a atom based stick or a old laptop and use pc viewer from android.

Fan will get louder as the load increases, normally when running on AC it will be quiet. Many replace the fans with artic PC fans which are quieter.

I am also installing mine in a staircase room, so noise won't be an issue. I will be running a low powered 5 to 6 watt EC fan,( I am making a battery box since the nearly 58v dc is also lethal,) with a timer or a Hydrogen sensor. When solar is installed the fans will run only during solar charge period of roughly 9am to 5pm.

 

[NotMyRealName]

This is the next bit. Water quality. If you have access to good quality water then you don't need the refill service. Was even considering getting a distiller so i could make it myself. 5ltr in 5h at the cost of 2.5units

How do you gauge how much water to put into the battery ? Do you just eyeball it and pour in.

This is how I was doing it for 9 years, I first visually determine which bottles have nil impurities in the shop,(when shell pumps used to sell them they where really good, they no longer sell it). I then use a TDS meter to determine the quality of water before pouring them into the battery. The distill water bottles that I get from a local HP petrol pump as some floating particles, which I filter it out. The TDS however is nearly zero.

I am already in the process of making my own distill water filter plant. Also experimented with rain water but never actually used it in battery.

Rain water is theoretically the purest form of natural water, but in reality it collects some SPM and so can become ionised. Not a very good idea. But maybe even better than what comes below:

These days battery water is not distilled, but 'demineralised'. Read the label carefully. Which means they use RO to 'clean' it but there's always some amount of suspended shit left over in it. Not like proper distilled water. Over time this causes micro shorts in the battery and reduces life.

Filling should be done so the plates are completely covered. Manufacturers recommend filling till the water touches the bottom lip of the filling hole. Kinda like petrol in a motorcycle tank. The problem with too much water is that it will lower the specific gravity. So if you guys are investing so much time, effort and money into a top notch system, also get a hydrometer.

 

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Actually filling it right upto the hole in my case was a bad idea, when I first did that it in my Exide EL tubular battery(Not tall tubular) with micro porous vent cap, the acid water spilled over during the charge cycle.(my battery didn't come with floats). Was told by exide dealer to fill it just above the lead plates but this would cause me to frequently top it up, which PIA without float level indicators. After trail and error I fill it another .75 inch above what the dealer recommended height, again this is specific to my battery.

Yes I do have hydrometers, currently on my fourth one after previous one broke or materials inside disintegrated.

Yes distill water like the old days is not economically feasible. In one shop when I pointed out about the floating particles he said those are battery additives, I was like WTF. Those guys didn't even bother doing a basic suspended particle filtering, It looked a Snow globe. Never buy those 4 liter distill water blue, green opaque cans, one just cannot see the water inside.

Since I am not able to get consistent good distill water anymore, I am building RO based, deionizing plant. Currently my self built RO unit gives a reading of 2 to 3 TDS with input water TDS of 160 to 200. So with a deionizing filter I can get zero TDS.

 

[NotMyRealName]

Battery additives !

How about using a solar heater (non electric) to distill water? What is the cheapest method of distilling your own water?

 

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These days battery water is not distilled, but 'demineralised'. Read the label carefully. Which means they use RO to 'clean' it but there's always some amount of suspended shit left over in it. Not like proper distilled water. Over time this causes micro shorts in the battery and reduces life.

I've heard of people collecting water out of an AC and using that too.

Filling should be done so the plates are completely covered. Manufacturers recommend filling till the water touches the bottom lip of the filling hole. Kinda like petrol in a motorcycle tank. The problem with too much water is that it will lower the specific gravity. So if you guys are investing so much time, effort and money into a top notch system, also get a hydrometer.

Eyeball it in other words ?

The hydrometer in earlier discussions didn't matter too much i thought. yes, it can tell you SOC but that's about it. I picked this one up a while back

 

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Battery additives !

How about using a solar heater (non electric) to distill water? What is the cheapest method of distilling your own water?

Cheapest method depends on what one already has, most houses have RO unit, so adding a deionizing filter is the cheapest method to go.
Using a solar water heater can work but doing the pumbing to collect the water and to keep it clean is going to cumbersome. You will have to again filter the water for suspended particles, so why not just use the RO and deionizing filter.

I was using those Rs200 to 300 bucks hydrometers that explains why I am into using a fourth one, I guess you get what you pay for.

 

[NotMyRealName]

Eyeball it in other words ?

The hydrometer in earlier discussions didn't matter too much i thought. yes, it can tell you SOC but that's about it. I picked this one up a while back

Pretty much. No other way to realistically check level WHILE filling.

Specific gravity of the electrolyte is one of the most important things to maintain in a battery.

Cheapest method depends on what one already has, most houses have RO unit, so adding a deionizing filter is the cheapest method to go.
Using a solar water heater can work but doing the pumbing to collect the water and to keep it clean is going to cumbersome. You will have to again filter the water for suspended particles, so why not just use the RO and deionizing filter.

I was using those Rs200 to 300 bucks hydrometers that explains why I am into using a fourth one, I guess you get what you pay for.

Assume there's no existing RO system, and i was talking about real distillation, not deionising. Like boil, evap and condense. How can a person do that with adequate output quantity and reasonable cost.

 

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Assume there's no existing RO system, and i was talking about real distillation, not deionising. Like boil, evap and condense. How can a person do that with adequate output quantity and reasonable cost.

We have to boil water so you need to use electricity power or gas to do that. You can buy those distill water aparatus for like 1.5k or so. If you want to eliminate the cost of gas or electricity, you can use a mini or portable solar water heater, which is also used by solar water heater shops as a demo unit and then connect a ready made distill water apparatus or do one yourself by using copper tube and vessels. Again RO unit serves as dual purpose, consumes only 25watt max.
below is those mini solar heaters, not sure of the cost but have heard it costs like 3k to 5k or so.

 

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For the price of 1550, you could get 2x 200ah exide c10 batteries+ 3kw solar inverter minus the panels. So if your load is like 400watts you can run for 8 hrs with 80% dod or get 2.4kw for 1hr.

With regalia you can only discharge max of 900watt and you will theoretically get 2hr 42min at 900watt. Where as exide can give the same 900watt load for 4hr 2 min.

I'm trying to figure out which 3kW inverter you are recommending. Is it the 3kW variant of the one you have ? Amazon didn't list it on the link you posted earlier but here it is.

Because there are other 3kW inverters too.

Having the extra headroom to add more load is appealing. I realise now i can run the fridge, 0.5HP pump, CRT TV as well.

If its the fuzion then i notice in the specs it can handle up to 4kW of panels. The slim can only do 1.5kW. Fuzion has a MPPT the slim has a PWM. Any important differences between PWM & MPPT ?

It also has a battery equliazation feature, very important if you're using more than one battery.

What it does not have is net metering. For that you need the FlinInfini

Why didn't you consider an inverter with a grid feed in option ? you don't think you would generate enough for it to be worth it. Because here is another way to shorten the break even time

Yes Grid tie is cheaper but that is the only pro and rest are all cons.

As you said their will be no power to the house once the grid supply fails. Also being directly connected to the Grid voltage spikes can screw up the Grid tie inverter, higher failure rate vs off grid ones. The contract to supply power to utility is more then 20 years, also lots of red tape and bribes in getting Grid tie sanctioned. The bribes money can instead get you one or two batteries.

This is your reply i guess

The infini can run off batteries too, not limited to just sun. Actually there is no option to run the infini without batteries. That is a feature only with the fuzion you have. Hence hybrid.

 

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The difference between MPPT and PWM, is that former will deliver all available solar power generated from panel, where as the PWM is limited by battery voltage its like a buck circuit, where the solar voltage must be higher then the battery voltage. In Mppt on the other hand it can do all sorts of combination of volt x amps to get the desired maximum watt from the solar panel, it has a both boost and buck converter. There is more to it such as the ability to constantly adjust according to the sun light and it does a more efficient way of the DC to DC conversion to get the highest available output from solar panels.

The reason why I bought the fuzion version is that, it has a MPPT and secondly it accepts a solar voltage upto 500v, with mppt range of 120v to 450v. So it is easier to wire the panels just in series, you can get away by using just 4sq mm DC wire. Where as all the other models with MPPT charger accepts a solar voltage of 145v max with MPPT range 60 ~ 115 V, so you will have to wire panels in series and parallel. So now it requires some really thick DC solar cables which increases the cost of wiring, i.e from roof top to the location of the inverter.

But the main reason why I went with that is that, the solar voltage matches every other dedicated Grid-tie inverters both desi and rebadged ones which work in the range of 80 to 500v solar input, so later on if I wanted to add a Grid-tie inverter all I have to do is split the incoming solar wire two both the fuzion and the Grid tie inverter, using a parallel box.

Now the reason why I didn't go for the Infini model is that, (in addition to the previous posts about grid-tie.)
1 It costs 40k more for a 5kw unit.

2 It is not MNRE approved model, so you cannot use it to Export power to the grid anywhere in India. Only this smart infini series http://www.flinenergy.com/flininfini.html but not Flin branded one but rather from another Importer is MNRE approved(cannot recollect the rebadged name). But this below series rebadged offcourse is MNRE approved but costs twice as much as the Flin regular LiteInfini. The main OEM series that is MNRE approved http://voltronicpower.com/en-US/Product/Detail/InfiniSolar-2-10KW .

3 Putting all eggs in one basket is a bad idea. Having both functions grid tie and off grid more things to go wrong, especially when it's connected to Grid's horrible voltage. ( I had a lcd tv that wen't partially kaput thanks to bescom stupendous voltage range of 350v, despite have a APC smart ups and a V-guard stabilizer for the tv, heck the stabilizer manual says the stabilize will go kaput if the voltage crosses 320v, it is now protected with custom made Servo stabilizer, which I won't need If i had gone off the grid).

4 the Grid tie Liteinfini model cannot handle surge/inrush current from the load like the Off grid ones.

5 The price you pay for the Infini or any other make and model Hybrid ones which can export power/net metering and also self consume, will cost more then buying two separate inverters grid tie and off-grid. It's like those front load washer-dryer combo machine which sucks at drying vs a dedicated dryer.

 

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A really good accurate battery monitor with app costs $200+ https://www.amazon.com/Victron-BMV-702-Battery-Monitor/dp/B075RTSTKS?th=1
The above one will show the battery discharge in percentage and as well as Ah used.

Wanted to post this earlier, some other recommendations i read were..

Use a digital monitor, like the TriMetric (Bogart Engineering), IPNProRemote (Blue Sky Energy), or XBM battery monitor (Xantrex)

Unfortunately that homepower site seems to have gone offline, a month ago that article was accessible. Fortunately the time machine caught it. From Sept 2006. Better may have come out since.

So that is where the amp hour counter needs to go, in between inverter & battery

 

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So that is where the amp hour counter needs to go, in between inverter & battery

Yep, I have been saying that from the beginning .A dedicated battery monitor is however bi-directional, plus you can enter the battery details, so the battery monitor can show the remaining capacity or percentage more accurately.Even if you just attach a dc kw meter you will have to keep lot of logs, each time the power goes to deduce the ah capacity.Which is why no one really use them, instead they use a battery monitor.

 

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Victron also makes inverters. They cost twice as much as Flin and Victron has a good reputation in the market. The Multiplus looks interesting. Not too much representation in India but there are a few places in the country that show up as selling Victron gear.

How to get service in Bangalore ? Flin appears to be Bombay based. One of the comments on amazon stated he had to send the inverter to Flin from Calcutta and then wait for a month for it to get back. Is there any local service available ?[DOUBLEPOST=1549302796][/DOUBLEPOST]

Is this tried and tested behaviour?
Or a one - off case that the company is giving bogus answers so they don't have to repair.

I'm starting to think its standard behaviour especially with bigger size inverters. This no load disconnect is a way to keep the inverter draining the battery when there is no load ? So it enters sleep mode until load increases. Otherwise its own consumption can wear the battery down over time.

https://www.solar-facts.com/inverters/inverter-efficiency.php

 

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That's the thing, 90% of the time I don't consume more then 500w load (after making sure most of the electrical appliances are the highest efficiency devices at the time of purchase), yet I bought a 5000w inverter for that 10% of the time, so I am going for 150AH x 4 C10, so that's 720w continuous and the remaining 10% of the time I would probably consume like about 3500w when the water heater is switched On for a max of 1hr or microwave.

Let's talk about efficiency. Check out the article attached.

Every inverter has a point of maximum efficiency, a “sweet spot” where it is the most efficient at converting DC into AC. This peak efficiency point is usually between 20 and 30 percent of the inverter’s maximum rating. For example, an inverter with a 4,000-watt rating will be most efficient when operating between 800 and 1,200 watts.

Typical peak efficiencies vary from about 92 to 96 percent. The power versus efficiency curve shows that a given inverter will have a relatively low conversion efficiency at low power. Conversion efficiency increases as the inverter reaches its peak efficiency point. As power levels rise beyond the inverter’s point of peak efficiency, conversion efficiency will remain relatively linear, dropping only a few percent up to its rated power output.

If the sweetspot is 20-30% of the inverters rating then oversizing the inverter can have a bearing on run time.

If 90% of the time you are not beyond 500W then how long will the back up be ?

Whether it makes sense for me to go for a 3kW inverter when my avg will also be similar to yours. Sure, those 10% of time the extra power is welcome.