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Old 04-02-2021, 09:44 PM   #1
Mini-Skoolie
 
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Is it worth it to have multiple inverters?

To preface this: I'm planning on an all-electric setup, no propane stoves or inverter generators. I also plan on having a workshop area at the back with welders, induction forge, power saws etc.
So as for my power needs: the induction forge can pull up to 12kW, and will only be used for a few minutes at a time. The range can pull 3kW and might be on for an hour or so if I'm simmering something. My computer pulls less than a kilowatt but, depending on the day, may be running for multiple hours straight, and the fridge will run much of the time.
Does it make sense to have three inverters to handle these different load levels? Or should I have a single inverter that's capable of up to 12 kW and run everything off of that? Various inverters promise "low idle draw" but I have no idea what the draw is if they're not idle, but running at a fraction of capacity.
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Old 04-02-2021, 10:23 PM   #2
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Quote:
Originally Posted by skykooler View Post
To preface this: I'm planning on an all-electric setup, no propane stoves or inverter generators. I also plan on having a workshop area at the back with welders, induction forge, power saws etc.
So as for my power needs: the induction forge can pull up to 12kW, and will only be used for a few minutes at a time. The range can pull 3kW and might be on for an hour or so if I'm simmering something. My computer pulls less than a kilowatt but, depending on the day, may be running for multiple hours straight, and the fridge will run much of the time.
Does it make sense to have three inverters to handle these different load levels? Or should I have a single inverter that's capable of up to 12 kW and run everything off of that? Various inverters promise "low idle draw" but I have no idea what the draw is if they're not idle, but running at a fraction of capacity.
Okay. Wow! Ummmm. Cool? Help us out here and give us some more info.

So, you say no "Inverter Generator". Are you going to have a regular generator? If so, how many watts?

If you're not using a generator, how many batteries, voltage, ah, connecting (parallel or series) are you planning and where will you put all the batteries and solar panels (not sure even a 40' bus roof will have enough room)

Even at a few minutes at a time, at 12kw, you'll need a huge bank to draw upon even for a few minutes at a time. How much total time per day?

Seems if you have all three "systems" pulling from the same bank, one inverter would be fine, as long as the inverter and bank was designed to run all systems at the same time, even for "a few minutes".

Seems to me though, You would want to separate your "house" system from your "workshop" systems. So, two inverters with separate banks supporting each. That way, if for some reason your workshop system has an issue, you still have house function.

Per the workshop system, I think the question is the physical size, cost, wiring etc. to run 18kw ((12kw + 3kw) * 1.20) at the same time. It might be easier, lower cost to isolate the 12kw and 3kw from each other.

There's one person I know of that has worked with big electrical situations like this. Depending on your answers, he might be worth talking to.

Interesting project.
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Old 04-02-2021, 10:33 PM   #3
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It sounds like your planning to be using a lot of power, perhaps beyond what a reasonably sized battery bank could offer. An invertor is unnecessary if you're tapping straight into a generator or shore power as it's already AC.

That induction forge is likely only going to able to run with a very large generator, perhaps of at least 16 kw to handle the load spike. How many phases does it require, I don't believe most invertors can generate more than one phase.

Before considering how many invertors you will need, I recommend considering your overall power needs for living and determining how large your battery bank will need to be to last between recharging. You may find the battery bank you require is impractical for space or cost reasons, forcing you to reevaluate your choices.
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Old 04-02-2021, 10:37 PM   #4
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Figure out how many kw genset you would need to do the work you require and size everything off of that. And add in a % for cloudy days
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Old 04-02-2021, 10:52 PM   #5
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My bus came with 2, 16kW, generators installed on it. It was built that way for the original owner who did something at trade shows. You're going to need something about that size to do what you want to do. The only other way would be a solar array the you take down to move and a trailer to carry the panels and massive battery bank you'll need
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Old 04-02-2021, 10:59 PM   #6
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Quote:
Originally Posted by skykooler View Post
To preface this: I'm planning on an all-electric setup, no propane stoves or inverter generators. I also plan on having a workshop area at the back with welders, induction forge, power saws etc.
So as for my power needs: the induction forge can pull up to 12kW, and will only be used for a few minutes at a time. The range can pull 3kW and might be on for an hour or so if I'm simmering something. My computer pulls less than a kilowatt but, depending on the day, may be running for multiple hours straight, and the fridge will run much of the time.
Does it make sense to have three inverters to handle these different load levels? Or should I have a single inverter that's capable of up to 12 kW and run everything off of that? Various inverters promise "low idle draw" but I have no idea what the draw is if they're not idle, but running at a fraction of capacity.
What's your budget? Too many degrees of freedom in the calculations without that.
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Old 04-02-2021, 11:01 PM   #7
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Yes where are all these kW coming from?

Multiple inverters are definitely a good way to go for efficiency

but usually the biggest wasteful one is 2-3kW, the smaller efficient ones a couple/few hundred watts.

Have you priced good quality inverters that put out the specific type of AC power your biggest consumers require?

Why would you want to run non-inverter type gensets?

Inverters are only needed if your source is batteries, but you'd need a semi-trailer to carry that much storage around, and the bank would cost more than the rig!
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Old 04-03-2021, 09:07 AM   #8
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In terms of power, my plan is 6kW of solar panels - 3kW flat on the roof, and another 3kW that hangs on the sides and can be propped out like awnings.I'm also looking at adding a 2kW wind turbine to supplement the solar in the winter and at night.


The plan for batteries is a 80kWh battery pack salvaged from a crashed Tesla. By my calculation that gives me between three days to a week of buffer for bad weather depending on my usage.


The induction forge is single-phase, 240V; I don't have any 3-phase tools as I haven't had 3-phase power available in the past.



My budget for inverters is about $6k.
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Old 04-03-2021, 11:09 AM   #9
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What is your plan for dealing with the 400 VDC from the salvaged Tesla battery?
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Old 04-03-2021, 11:14 AM   #10
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The battery consists of nominally 22V modules wired in series. My plan is to rewire it to run them in parallel instead (which should also make it easier to find a compatible BMS) and use that to run 24v appliances, inverters, etc.
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Old 04-03-2021, 02:39 PM   #11
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A couple of recommendations:

Look into will prowse and the Tesla battery.

My recollection is that itís not really all that great for what youíre doing because the voltages donít line up well with conventional equipment and I think he ended up with something like 50% of nominal capacity in order to prevent low and high voltage shut offs with the bms and what he was running and it ended up not being quite ideal.

For the loads you are running you are almost definitely going to want to run 48v, the wire sizes at 12kw is going to be enormous, exceeding 4/0 I think; and 48v will half that and allow relatively conventional welding cable, like a single 4/0 depending on distance, and may make inverters cheaper too perhaps.
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Old 04-03-2021, 03:28 PM   #12
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My recollection is that it’s not really all that great for what you’re doing because the voltages don’t line up well with conventional equipment and I think he ended up with something like 50% of nominal capacity in order to prevent low and high voltage shut offs with the bms and what he was running and it ended up not being quite ideal.
This. OP, I run Tesla packs currently, and I hope to save you some headache. These were at one point a great option for high capacity/low cost in solar. Today they are "meh" at best. A few thoughts:
  • You WILL need a special inverter to support the voltage range of Tesla packs. They are 6S LiCoO2- 7S would be "normal" 24V for this chemistry. A standard 24V inverter will only have access to around 30% of your battery capacity, and since you should only charge these to around 80%, the unusable energy figure is actually even higher.

    I charge to 4.0V/cell, no more, and I recommend anyone with these do the same.
  • If you plan on paralleling a ton of packs, it is not advised. Internally each pack is wired in series 6S and parallelizing those groups of series packs is not recommended anywhere. Energy can move uncontrollably between packs this way, reducing cycle life and opening up for some nasty failure scenarios.
  • You WILL need a 6S BMS _for every pack_. And think beyond balancing- how are those going to communicate to your inverter/solar charge controller(s) for LVP/HVP?
  • Its likely cheaper LFP options exist than the 80kWh battery bank you're looking at out of pocket, not to mention that LiCoO2 has 1/4 of the number of usable cycle life.
  • LiCoO2 is a chemistry that does not allow for abuse. Have you seen videos of 18650 cells getting punctured or overcharged?
Three or even two years ago, I would have been for it. Today... not so much. I say look hard at the EVE 280Ah LiFePO4 cells before pulling the trigger on a Tesla setup, which is what I'm upgrading to (43kWh).

Btw, I'm one of the only other nuts on this forum trying for 6000W of solar, I'm not doing hinges, but rather a slide out system (starting that upgrade from 3000W tomorrow)! Definitely post pics of how you do this.

Going back to your use cases, Genetry Solar is currently prototyping a true, 12kW inverter. Check them out:
https://forums.genetrysolar.com/topi...2kw-prototype/

You can currently daisy chain their 6kW inverters to get 12kW. I have one of the 6kW preorder units, which just shipped, so availability is currently limited.


Best of luck!
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Old 04-03-2021, 04:26 PM   #13
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Thanks, I may look at other alternatives then. My main thought with the Tesla modules was that they would have been cheaper per kWh but considering the reduction in capacity they're probably not worth the effort. I had been planning on paralleling the modules on a cell level so as to use a single BMS, but that's a lot of surgery for not a lot of gain.


I've been working with EVs for a while but am somewhat new to solar. What are LVP and HVP in this context? Low/high voltage power?


I was thinking 24V because there are more accessories that run off of that - for example, I'm looking at a 12/24V freezer and I know there are certainly more options for 24v lights. If I go with a 48V system, does it make more sense to power that sort of stuff through an inverter or a DC/DC converter?


The Genetry inverters look like an excellent option; I'm a bit disappointed they never showed up in my search results.
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Old 04-03-2021, 04:42 PM   #14
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Quote:
Originally Posted by skykooler View Post
Thanks, I may look at other alternatives then. My main thought with the Tesla modules was that they would have been cheaper per kWh but considering the reduction in capacity they're probably not worth the effort. I had been planning on paralleling the modules on a cell level so as to use a single BMS, but that's a lot of surgery for not a lot of gain.
Yeah, I considered getting a few more packs since I was already invested, doing this as a workaround. It just wasn't worth it- cost per watt the EVE cells were like half the price.


Quote:
Originally Posted by skykooler View Post
I've been working with EVs for a while but am somewhat new to solar. What are LVP and HVP in this context? Low/high voltage power?
Low Voltage Protection / High Voltage Protection- the ability of the BMS to tell the MPPT/Inverter to stop charging/discharging.


Understandable that Tesla looks attractive if you've been working with EV stuff.



Quote:
Originally Posted by skykooler View Post
I was thinking 24V because there are more accessories that run off of that - for example, I'm looking at a 12/24V freezer and I know there are certainly more options for 24v lights. If I go with a 48V system, does it make more sense to power that sort of stuff through an inverter or a DC/DC converter?
I upgraded from 24V (3 Tesla packs in parallel) to 48V (2 Tesla packs in series) a while back. This allowed me to use a single Victron 250V/100A MPPT for up to 4800W of solar (the same controller previously topped out at 2400W with a 24V battery bank). Now that I'm upgrading to 6000W, I'll eventually need to get another MPPT for the second string.



I use a 48V->24V stepdown for 24V appliances and 48V->12V stepdown for 12V appliances. This also was advantageous for my water pump- rather than run 12V to my pump and suffer severe voltage drop when it kicks on, I ran 48V to the pump and put the pump on its own 12V step down- MUCH better performance there (and even more performance changing to a square-D pressure switch).



There's really no advantage to 24V for your use case. You even considering 12kW draws, 48V is a requirement IMO. I sized my system for 5000W continuous (residential electric dryer), NONE of my cabling heats up. The maximum draw I'll ever see is 6000W (125A) and most of the time I'm well under 1000W (21A).


Quote:
Originally Posted by skykooler View Post
The Genetry inverters look like an excellent option; I'm a bit disappointed they never showed up in my search results.
They are brand new to market- I preordered in October and mine shipped two days ago. I was in the first batch, I imagine they'll be stocking up after all of the preorders are fulfilled. Daisy chaining might support your use case well, as you can run 0/1/2(/3+?) inverters as needed.


I found Genetry through Sean's YouTube channel- he services PowerJack inverters. Manufacturered by PowerJack, Genetry inverters are "true to rating"- meaning they will do 6000W continuous, 24/7/365 at their rated ambient temperature- whereas PJ inverters are rated to about 250% continuous, although they'll do higher surges. The GS inverter will be my upgrade from a PJ 8000W, which can currently do around 2500W continuous.
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Old 04-07-2021, 10:16 PM   #15
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Quote:
Originally Posted by skykooler View Post
To preface this: I'm planning on an all-electric setup, no propane stoves or inverter generators. I also plan on having a workshop area at the back with welders, induction forge, power saws etc.
So as for my power needs: the induction forge can pull up to 12kW, and will only be used for a few minutes at a time. The range can pull 3kW and might be on for an hour or so if I'm simmering something. My computer pulls less than a kilowatt but, depending on the day, may be running for multiple hours straight, and the fridge will run much of the time.
Does it make sense to have three inverters to handle these different load levels? Or should I have a single inverter that's capable of up to 12 kW and run everything off of that? Various inverters promise "low idle draw" but I have no idea what the draw is if they're not idle, but running at a fraction of capacity.

maybe you should consider a diesel powered welder/generator or contractor style welder/generator/air compressor for the shop. More compact, simpler, less complicated, and you can do what you want as long as you want (as long as you have fuel) Save the solar for your everyday use.
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Old 04-08-2021, 07:40 AM   #16
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High end duel conversion ups systems use no transformers but high voltage batteries.
They are used cheap.. since the batteries voltage makes them undesirable for most applications. Mostly sold for scrap value for the lead acid batteries.


Good luck,
Johan
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