Why not stack for variable loads to start?

[Stewfish]

I have a 10k btu frigidaire 450 watt high seer low start capacitor window AC that easily runs off my 2000watt generator.

If you have a 4kw inverter running off of a battery to run a 500 watt AC all night long it seems like the inverter would be overpowered and draw unneeded power all night from your battery just to run 500w. Is this correct? If not how much power would be drained off my batteries? 500w x 10 hrs = 5kwh or is it closer to 4000w x 10hrs? If it is 500watt x 10nhrs then the price is not much more from a 2kw to 4kw inverter, so then why do people not always buy the 4kw inverters?

My thought is to make a variable output system and get a couple automatic stackable 2000w inverters then if you run the AC all night but you need to use the microwave or coffee maker in the morning then a second inverter would turn on. We are super tired of turning things on and off for our 3500watt 2500 continuous generator Thus you would only be using half the power all night. Is my logic correct? I wonder if a 800w and one or two of the 2.4kw MPP can all stack together and only run the extra 2.4kw inverters for microwave, washer, coffee pot etc all at once type of scenario.

My energy needs are about 5,000 to 6000 KW for 3 hours when I get home. I may get a third to kick on if my wife wants to run her insta pot or microwave without turning off the RV roof AC or the 120v LG washer/dryer combo. Then when we go to bed we only use about 500w for window AC in our room. We would need about a dozen battle born batteries for two days of power.

Can the MPP PIP do this with the parralell modules but then also have auto generator start if the batteries go too low bc of a cloudy day or something?

I'm also thinking 48v is the way to go. I read the Tesla batteries put out 60v so 48 nominal and when they get cheaper as people upgrade their batteries I'd like to keep adding more old tesla car batteries. Is this logic correct - It's from Handeeman Youtube channel. I seem to now see 24v modules all over ebay so maybe the clear plastic model S is 24v modules not an older 48v style. 48v kicks me up into the 4k inverters though arg so if I can get old tesla 24v modules then 24v seems the way to go.

I think it's smarter to have a variable output system like I'm thinking to save battery power and if the price difference is only $699 more for another inverter vs more 1000s for more batteries to power the 4kw. I can always add more batteries as they get cheaper and stack 3 inverters later to get 6kw if my wife wants it.

Summary ?s
1.) So can multiple MPPs charge a single battery bank when stacked and slaved?

2.) Is there auto Genny battery charge? Or I have to turn on the Genny? Update: yes the LV2424 has Genny start.

3.) Are Tesla batteries 24v now?

4.) Can an 800w MPP run my night AC and be stacked with a 2.4kw MPP. Then I have an even lower consumption but high available when I need it.

 

[RCinFLA]

Many inverters have staged drivers to conserve idle power. Much of the idle power is to drive the capacitance of the switching MOSFETs.

They back down the number of parallel MOSFETs that are active when load is light.

Issue is handling sudden surge currents as it takes some time to bring extra drive online. High frequency inverters, ones that have a DC to DC converter to provide about 200vdc to run sinewave PWM output stage have multiple high frequency transformers staged in parallel as load requires. They are also the most vunerable to damage from surge loads.

 

[Stewfish]

Issue is handling sudden surge currents as it takes some time to bring extra drive online. High frequency inverters, ones that have a DC to DC converter to provide about 200vdc to run sinewave PWM output stage have multiple high frequency transformers staged in parallel as load requires. They are also the most vunerable to damage from surge loads.

Ok...

Way above my head. How much do they back it down with a lite load? 50% of nominal voltage or down to the voltage being used?

Brands and models and their ability to vary their loads would be more applicable. I can calculate my usage, PV input/number of solar panels, install them. Brands don't mention if they are DC to DC or not.

More relatable to the average Joe would be:
So how much load is 500w window AC pulling out of your batteries through a 4kw MPP vs a Outback 4kw inverter?

Are you trying to say the MPP brand doesn't have enough capacitors for the surges to turn on the slaved/stacked inverter? I don't know what brands are dc to dc brand is vs non dc to dc.

Are you trying to say a surge load of a microwave is too fast for a stacked MPP system? How would a stacked system work then? There has to be a surge at some point to turn on the slaved inverter and thus capacitors fill that gap of quick power needed

Idle power is not 500w continuously be used

 

[schmism]

Its almost like we had a debate about how much a 30a RV hookup might actually use in daily practice. With my side arguing that short term high watt loads are a very real thing even in a RV/Tiny home and that would significantly impact the sizeing of the required inverter/system. (friendly jab @Craig )

as to OP question
1) I have 2 3kw growatt inverters that are (intended to be) paralleled. While they are not load shareing at the moment, they are both charging the same battery pack off their own PV array. Infact the instructions specifically say they MUST share the same battery pack.

3) seems there are several Tesla module configurations however most are in the 25v max range.

4) AFAIK the growatt/MPP units have to be identical to parallel

 

[MichaelK]

Way above my head. I can calculate my usage, PV input/number of solar panels, install them, but capacitance, amount of mofsets etc I don't have time for and I dont think 90% of people would.

The primary reason for you not to do this. If you can't comprehend how to do this, then you really shouldn't be attempting it. I have a 7Kw inverter, and leave it on all night to power the 200W the fridge is using. I don't even concern myself with it.

One important thing to consider is the the on/off cycling of a lot of electronics is a little harder on them then staying either continuously on or continuously off. That means, take two inverters of the same make an model, and leave one on continuously, and repeatedly turn the second on and off all day long. The one repeatedly turned on and off will have a shorter lifespan then the continuous unit.

A far simpler solution is just to add additional solar panels to deal with the extra idle consumption of a larger inverter.

 

[schmism]

as a side note, there are many that would no recommend Tesla modules for beginners due to the risk associated with them which are gennerally considered higher than that of LFP batts.

 

[schmism]

A far simpler solution is just to add additional solar panels to deal with the extra idle consumption of a larger inverter.

While I dont dissagree and often times offer the same advise, in this case the OP indicates he is in an RV and therefor likely has space limitations.

 

[Stewfish]

While I dont dissagree and often times offer the same advise, in this case the OP indicates he is in an RV and therefor likely has space limitations.

The panels will be ground mounted on our property and a utility shed.

Another question can a 2.4kw be stacked with a 3kw or do they have to be the same model?

 

[Stewfish]

The primary reason for you not to do this. If you can't comprehend how to do this, then you really shouldn't be attempting it. I have a 7Kw inverter, and leave it on all night to power the 200W the fridge is using. I don't even concern myself with it.

One important thing to consider is the the on/off cycling of a lot of electronics is a little harder on them then staying either continuously on or continuously off. That means, take two inverters of the same make an model, and leave one on continuously, and repeatedly turn the second on and off all day long. The one repeatedly turned on and off will have a shorter lifespan then the continuous unit.

A far simpler solution is just to add additional solar panels to deal with the extra idle consumption of a larger inverter.

Lots off cycling is not a continuous 500 watts all night, nor is it any situation I described above when I arrive home. A well pump would be your example or a fridge compressor, again not how an RV works.

An RV fridge works off propane or a heating element.

The microwave insta pot is not like a fridge compressor or well pump.

A 500 watt high seer AC that has hard start capacitors, set to high all night where it is not cycling on and off is not like a fridge or well pump.

 

[Stewfish]

The primary reason for you not to do this. If you can't comprehend how to do this, then you really shouldn't be attempting it. I have a 7Kw inverter, and leave it on all night to power the 200W the fridge is using. I don't even concern myself with it.

One important thing to consider is the the on/off cycling of a lot of electronics is a little harder on them then staying either continuously on or continuously off. That means, take two inverters of the same make an model, and leave one on continuously, and repeatedly turn the second on and off all day long. The one repeatedly turned on and off will have a shorter lifespan then the continuous unit.

A far simpler solution is just to add additional solar panels to deal with the extra idle consumption of a larger inverter.

How big is your battery bank?

 

[Stewfish]

as a side note, there are many that would no recommend Tesla modules for beginners due to the risk associated with them which are gennerally considered higher than that of LFP batts.

Why? Doesn't have a BMS built in? Is it bc of fire/explosion risk? I plan to put it in a shed on our property - probably a 20 ft shipping container.

 

[schmism]

Why? Doesn't have a BMS built in? Is it bc of fire/explosion risk? I plan to put it in a shed on our property - probably a 20 ft shipping container.

I dont have a lot (read none) experience with them. Its my understanding that the included BMS is propritary and can not be used (which is to say, some people have hacked their way into them however that is far from a DIY process) so typically they have to have an external BMS added that is programmable for the cells they have. And yes, many feel they are at a higher risk of fire as one of the cons for that battery chemistry is they can have a thermal runaway issue that (i thought) LFP cells did not have. (granted each cell is fused however that doesnt prevent the viral videos of yet another Tesla battery pack in thermal runaway)

 

[Stewfish]

I dont have a lot (read none) experience with them. Its my understanding that the included BMS is propritary and can not be used (which is to say, some people have hacked their way into them however that is far from a DIY process) so typically they have to have an external BMS added that is programmable for the cells they have. And yes, many feel they are at a higher risk of fire as one of the cons for that battery chemistry is they can have a thermal runaway issue that (i thought) LFP cells did not have. (granted each cell is fused however that doesnt prevent the viral videos of yet another Tesla battery pack in thermal runaway)

The bigbattery.com lithium iron phos 5 kwh is $1699 and is 300 to 600 to more than an ebay tesla battery. That doesn't seem bad to have a BMS, anderson connector, and case.

Or $949 for their tesla battery box which is cheaper than an ebay battery

 

[schmism]

The bigbattery.com pack for 1699 is 300 to 600 to more than an ebay tesla battery. That doesn't seem bad to have a BMS, anderson connector, and case.

If your considering a $1600 battery then I would seriously consider 280ah cells in the group buy section. $1600 will get you 16 cells for a 48v pack or 560ah of 24v. Granted you still have to round up a BMS and enclosure but In terms of dollars for performance it cant be beat.

 

[Stewfish]

Its almost like we had a debate about how much a 30a RV hookup might actually use in daily practice. With my side arguing that short term high watt loads are a very real thing even in a RV/Tiny home and that would significantly impact the sizeing of the required inverter/system. (friendly jab @Craig )

as to OP question
1) I have 2 3kw growatt inverters that are (intended to be) paralleled. While they are not load shareing at the moment, they are both charging the same battery pack off their own PV array. Infact the instructions specifically say they MUST share the same battery pack.

3) seems there are several Tesla module configurations however most are in the 25v max range.

4) AFAIK the growatt/MPP units have to be identical to parallel

Is there anything you regret about your system or do you love it?

The 3k MPP looks like it can have 4000w PV input vs 3k Growatt is only 2000w. I guess 4k watts in with the two stacked is plenty.

I saw growatt has a generator part in the listing but does it start your generator if the batteries go low or just has AC input? Update: it will auto start your generator.

For $80 why is it better than MPP?

Thanks for the help, just shopping and getting ready for my buy

Update: I see it comes parallel ready vs MPP is $70 for the kit. So I guess they are the same price.

 

[Stewfish]

Update:

Growatt details = Tesla batteries not recommended, as they are actually 20V batteries sold as 24V.


So that's why Handee man did a 48v system and he mentioned 60 volt battery 20v x 3, and his controller takes like 40 to 64 volts.

 

[schmism]

Is there anything you regret about your system or do you love it?

The 3k MPP looks like it can have 4000w PV input vs 3k Growatt is only 2000w.

I saw growatt has a generator part in the listing but does it start your generator if the batteries go low or just has AC input?

For $80 why is it better than MPP?

Thanks for the help, just shopping and getting ready for my buy

Update: I see it comes parallel ready vs MPP is $70 for the kit. Still all I can find is generator charging info and voltage levels not if it starts your generator for you.

I am having difficulties getting my 2 3k 48v units to talk to each other. I think it has to do with an issue on the second unit itself and nothing in my hookup/settings. The other unit is working great. As intended. the 48v version supports up to 4500w of solar. You can over panel them some as my 2760w of panels ( per unit) I've only seen put out about 2100w (its only been online for the past month)

Growatt was thought to have better support, less chinese knockoff copies and better instructions.

I do not have mine hooked up to start a generator. I am on grid and take advantage of grid pass through for overloads and low battery conditions.

Nothing I regret. The wifi dongle that is supposed to upload data to the cloud I cant get workign because china instructions. The local pc-usb software mostly sucks for data logging. Am I upset with that, not really. There are going to be some trade offs for the $750 price tag.

Would I do it again? The trouble I have had getting them to parallel is unclear. I cant find many posts across the web of people who have ACTUALLY done this. The few that I find say they hooked it up and turned it on and it worked. <shurg>
At the time the 6kw low frequency version that watts247 currently offers was not listed. For what I'm doing I would have likely bought the 1 unit for roughly the same price.

The plan was to have both 3k units and be able to fall back to a single unit if the SHTF and a unit went down, I could still manage my loads closer and move to the single unit. I like that idea better than a single 6kw unit however the implimentation of said idea has been more frustrating than I anticipated.

 

[Stewfish]

I am having difficulties getting my 2 3k 48v units to talk to each other. I think it has to do with an issue on the second unit itself and nothing in my hookup/settings. The other unit is working great. As intended. the 48v version supports up to 4500w of solar. You can over panel them some as my 2760w of panels ( per unit) I've only seen put out about 2100w (its only been online for the past month)

Growatt was thought to have better support, less chinese knockoff copies and better instructions.

I do not have mine hooked up to start a generator. I am on grid and take advantage of grid pass through for overloads and low battery conditions.

Nothing I regret. The wifi dongle that is supposed to upload data to the cloud I cant get workign because china instructions. The local pc-usb software mostly sucks for data logging. Am I upset with that, not really. There are going to be some trade offs for the $750 price tag.

Would I do it again? The trouble I have had getting them to parallel is unclear. I cant find many posts across the web of people who have ACTUALLY done this. The few that I find say they hooked it up and turned it on and it worked. <shurg>
At the time the 6kw low frequency version that watts247 currently offers was not listed. For what I'm doing I would have likely bought the 1 unit for roughly the same price.

The plan was to have both 3k units and be able to fall back to a single unit if the SHTF and a unit went down, I could still manage my loads closer and move to the single unit. I like that idea better than a single 6kw unit however the implimentation of said idea has been more frustrating than I anticipated.

I called the website earlier and they said that MPP is easier software, but the wifi dongle is great for Growatt. He said growatt has less issues overall. Now you have me worried bc I really want to stack them for many reasons. This guy slaved the MPP fast. Maybe call up watts247. Let me know how it goes.