Sizing Inverter to battery

rmaddy

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I do understand that the system should be designed to load requirements. Space restrictions limit the design to one battery, this system will be in a Toyota Sienna minivan
Instead of 1 SOK 12V 206Ah battery you can get 2 SOK 12V 100Ah. Put them in parallel. Now you have a max continuous discharge current of 200A instead of 100A. Now the batteries will support up to a 2000W inverter. The 2 100Ah batteries are only a little larger than 1 206Ah battery.

The largest current is a 900 watt coffee maker which would only run for about 15 minutes, second largest is a refrigerator that is yet to be purchased but since they cycle on/off it appears they only draw about 60 watts per day.
It's important to understand power usage. You need to work out how many watt hours per day you need.

A 900W coffee maker that is used 1/4 hour per day uses a total of 900W x 0.25h/day = 225Wh/day.
A fridge might run at a 20% duty cycle meaning it's on 20% of the time and off 80%. Let's say the fridge you get uses 60W when running. This means in a day it uses 60W x 24h/day x 20% = 288Wh/day. Put in real numbers when you know them.

Do this for all of your items and add up the total watt hours per day and you will know how much you use.

If you go with 2 12.8V 100Ah batteries then you have 2 x 12.8V x 100Ah = 2560Wh of battery capacity. But really 90% of that since you won't use 100% of the battery each day.
 

WNCGUY

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Have you checked the 12 V DC compressor fridges? No inverter needed.
With the limited battery, you should use the smallest inverter you can. Do Not Trust Manual Operation.
I incorrectly included the fridge in my AC loads, since it operates on AC/DC it will run on DC.
 
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WNCGUY

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If you can do this without fail then my objections are addressed.
In this case you are the battery management system.
I prefer t o engineer people out of the loop as they are notoriously un-reliable.

UPDATE: you could do a 1000 watt inverter but not a 1500 watt inverter.
For the 1500 watt inverter you need to manage the load and the voltage.
It sounds like selecting a 1000 Watt inverter eliminates all concerns and I will not have to manage voltage drop or anything else for that matter, just to be sure, your concern in post #11 is no longer an issue?

I am looking at two 1000 watt inverters.
GOWISE 1000 watt, it has robust lead connectors, tightened with a wrench, the same as seen on most 1200 watt and up inverters.
AIMS 1000 watt, lead connectors appear to be hand tightened with plastic knobs?

Any thoughts or suggestions?
 
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It sounds like selecting a 1000 Watt inverter eliminates all concerns and I will not have to manage voltage drop or anything else for that matter, just to be sure, your concern in post #11 is no longer an issue?
You still need to ensure you don't discharge lower than 12 volts.
 

WNCGUY

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Go with 1000 max and get a lower wattage coffee maker. Should find something closer to 600 watts.
If there will be propane I recommend using it for coffee.
Possibly assemble a compact battery from cells with a 200 amp BMS.
A quick review of coffee makers at the store the other day I did not find anything around 600 watts, will need to look further. I do plan to have propane but prefer not to use it inside and we are not always in a location where it would be practical to set up outside.

At this time not interested in assembling my own battery.
 

WNCGUY

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Instead of 1 SOK 12V 206Ah battery you can get 2 SOK 12V 100Ah. Put them in parallel. Now you have a max continuous discharge current of 200A instead of 100A. Now the batteries will support up to a 2000W inverter. The 2 100Ah batteries are only a little larger than 1 206Ah battery.


It's important to understand power usage. You need to work out how many watt hours per day you need.

A 900W coffee maker that is used 1/4 hour per day uses a total of 900W x 0.25h/day = 225Wh/day.
A fridge might run at a 20% duty cycle meaning it's on 20% of the time and off 80%. Let's say the fridge you get uses 60W when running. This means in a day it uses 60W x 24h/day x 20% = 288Wh/day. Put in real numbers when you know them.

Do this for all of your items and add up the total watt hours per day and you will know how much you use.

If you go with 2 12.8V 100Ah batteries then you have 2 x 12.8V x 100Ah = 2560Wh of battery capacity. But really 90% of that since you won't use 100% of the battery each day.
Good idea and I have thought of going with two 100ah batteries, I would have to see if SOK would let me make the change since I already prepaid for a backordered 206ah battery.
Reviewing the specks, it appears the 100ah battery is 10.6 x 7.9 x 9.1 and the 206ah battery is 12.9 x 7.9 x 12.3, using the 100ah battery will take up quite a bit more space considering this will be placed in a minivan where space is already limited and every since matters.

My only other known loads.
AC loads.
Coffee maker 900 watts, 20 minutes a day.
Rice cooker 350 watts 30 minutes a day.

DC loads
Lighting 15 watts, 120 minutes a day.
2 usb Fans 6 watts each for about 500 minutes a day (use while sleeping).
Two Phone charging?

The goal is to be in the van as little as possible, sleep, breakfast, brief rests during the day, and evening rest. The rest of the time we plan to be outside.
 

WNCGUY

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You still need to ensure you don't discharge lower than 12 volts.
Do not discharge battery below 12.0 volts, thank you for the clarification.

I have to ask, what are the ramifications of discharging below 12.0 volts, battery damage?
 
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Do not discharge battery below 12.0 volts, thank you for the clarification.

I have to ask, what are the ramifications of discharging below 12.0 volts, battery damage?
The current shoots up as the voltage drops off a cliff.
The bms may disconnect on over-current or under voltage at significant amperage.
Either of these scenarios may result in the bms discharge fets getting welded closed.
That would mean your bms could no longer protect your battery from over-current or under-voltage.
You would not know there was a problem until your battery was destroyed.
I said this quite a few times in this thread alone.
I hope it is clear this time.
 

wmgeorge

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Wondering why when the 206 Ah is backordered you don't go with 2 100 Ah as suggested above? I have been ordering Renogy 12.8 volt LiFePO4 100 Ah for $469 plus tax for me off eBay. I will have three total and then going with the Renogy 2000 watt Inverter / charger which is around $600. Only issue I have with it thanks to the built in BMS you can not put them in Series .
 
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WNCGUY

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Wondering why when the 206 Ah is backordered you don't go with 2 100 Ah as suggested above? I have been ordering Renogy 12.8 volt LiFePO4 100 Ah for $469 plus tax for me off eBay. I will have three total and then going with the Renogy 2000 watt Inverter / charger which is around $600. Only issue I have with it thanks to the built in BMS you can not put them in Series .
I am evaluating the 2, 100ah wired in parallel suggestion to determine if space is available. In such a small vehicle, space is a premium, everything is a trade off, I just need to take some measurements and decide if I want to give up storage space.

The battery or batteries along with other electrical components will be housed in the area that normally is used to store the fold down third row seats, seats will be removed from vehicle leaving an oven void in rear van floor for the electrical system and storage.

@smoothJoey and others.
What are your thoughts on the 2 100ah battery suggestion?

I think regardless inverter size, number of batteries, and 100 or 200 amp discharge current, I must always mind the battery monitor gauge to assure the battery doesn't drop belove 12 volts.

Edit
So it seems my options are.
1) 206ah battery with 1000 watt inverter and watch to make sure battery voltage doesn't drop below 12 volts.
2) Change to 2 100ah batteries and get a 1500 or 2000 watt inverter.
 
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@smoothJoey and others.
What are your thoughts on the 2 100ah battery suggestion?
2 of those batteries can supply ~200 amps continuous.
Suggest you go with a 1500 watt inverter.
1500 ac watts / .85 conversion factor / 10 volts = 176.470588235 service amps.
Its still going to be rough on the BMS to open at ~175 amps.
So try to avoid drawing the battery dead empty at significant load.
 

chrisski

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A quick review of coffee makers at the store the other day I did not find anything around 600 watts, will need to look further. I do plan to have propane but prefer not to use it inside and we are not always in a location where it would be practical to set up outside.
I could not find wattage on most applances anymore. Used to be you found it somewhere on the box, but no more. Usually in an amazon review I can find someone has used a kilawatt meter to measure the wattage. I was going to link my k-cup, but Here is a thread;

 

WNCGUY

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I could not find wattage on most applances anymore. Used to be you found it somewhere on the box, but no more. Usually in an amazon review I can find someone has used a kilawatt meter to measure the wattage. I was going to link my k-cup, but Here is a thread;

It looks like the 900 watt, 12 cup Mr. Coffee (That I currently have) mentioned in post 14 of your attachment is the winner.
I found a DC coffee maker but the ones I found were only about 5 cups, we need at a minimum 8 cups.
 

WNCGUY

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2 of those batteries can supply ~200 amps continuous.
Suggest you go with a 1500 watt inverter.
1500 ac watts / .85 conversion factor / 10 volts = 176.470588235 service amps.
Its still going to be rough on the BMS to open at ~175 amps.
So try to avoid drawing the battery dead empty at significant load.
Now for another stupid question. Regardless of the system built, wouldn't I always have to monitor to assure my battery never drops to below 12 volts?

I am tempted to see if I can do without an inverter, buy a 12 volt coffee maker and rice cooker and call it good.
 
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Now for another stupid question. Regardless of the system built, wouldn't I always have to monitor to assure my battery never drops to below 12 volts?

I am tempted to see if I can do without an inverter, buy a 12 volt coffee maker and rice cooker and call it good.
inverter/chargers have a configurable low voltage disconnect.
For pure dc loads I use a...
Some of the better discrete inverters have a remote switching feature that allows them to be controlled by the battery protect which is in turn controlled by the bms.
Here is an example...
Warning: you can't put a battery protect in the current path of an inverter and the in-rush current will melt the battery protect.
Another Warning: battery protects are uni-directional so you can put them in front of a charge source.
 

chrisski

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I am tempted to see if I can do without an inverter, buy a 12 volt coffee maker and rice cooker and call it good
After about a year I realized the reason 12 volt DC high wattage items are not available is they're too dangerous. a 900 watt coffee maker or rice cooker would need around 80 amps DC to make a cup. The inverter works because AC does not have the arcing and the wires can be quite a bit smaller. Without going into a lot of detail, that's the short answer.

I know there's some 12 Volt DC coffee maers and slow cookers out there, but I doubt it will make that much.

You will not regret gettign an inverter, because it opens up so much more and makes finding appliances easier.
 

12VoltInstalls

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largest current is a 900 watt coffee maker which would only run for about 15 minutes,
Should find something closer to 600 watts
I have 3 different auto drip coffeemakers - a 16oz single serving unit 780W, a 5-cup walmartha special 660W, and my old favorite coffeemaker, Hamilton Beach 5-cup 580W.
second largest is a refrigerator that is yet to be purchased but since they cycle on/off it appears they only draw about 60 watts per day.
Many small refrigerators run at about 60W. If it ran one hour out of 24hrs it would use 60Wh per day. But it will likely run at the very least 20% or more of the day; 25% is what mine does currently (guessing) at 60W so 360Wh - 360 watt hours.
 

RVLiFe

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I wouldn’t buy a 1000w inverter. Instead I’d get a minimum 1500W or even a 2000W one. Just put a 100A breaker on it if your concerned with going over 100A with one SOK battery. If you ever decide to get a second battery(which you very well might) you will be glad that you don’t have to pay twice for another inverter.
I ran a larger inverter then what I needed for quite some time before buying a second battery. Glad I went bigger in the first place. Never blew the breaker or put the battery in any over current state. Just know your limitations and you will be fine. I also went with higher gauge wire right off the bat as well so there was no need to redo anything.
 

WNCGUY

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I sent an email to SOK this morning asking to change my order from 1, 206ah battery to 2, 100ah batteries. Received a reply back 3 minutes later and after paying the cost difference received notice they would ship today.

Edit.
It is going to be a couple of months before I have the van ready for battery installation, I did order a Victron IP22 30-amp charger will need to build some cables. I believe the batteries need balanced and charged before use, where would be the best place to learn about this and overall safety when installing and working around the electrical system?
 
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