Sizing Inverter to battery

[WNCGUY]

I have on backorder a single SOK 206ah 12.8-volt battery and will be buying an inverter to run with it. This SOK battery has a maximum continuous discharge current of 100A. If my math is right the max inverter size for this battery is 1200 watts, 1200/12 = 100 amp?

When I look at these smaller inverters 1000-1200 watts, I find many only have lead posts that are hand tightened, seems like a very bad idea.

Would there be any pros/cons of going with a 1500-watt inverter, I think max current draw is 125 amps and simply not run a continuous current that exceeded 100 amp?

 

[wmgeorge]

I have on backorder a single SOK 206ah 12.8-volt battery and will be buying an inverter to run with it. This SOK battery has a maximum continuous discharge current of 100A. If my math is right the max inverter size for this battery is 1200 watts, 1200/12 = 100 amp?

When I look at these smaller inverters 1000-1200 watts, I find many only have lead posts that are hand tightened, seems like a very bad idea.

Would there be any pros/cons of going with a 1500-watt inverter, I think max current draw is 125 amps and simply not run a continuous current that exceeded 100 amp?

My 1000 watt Renogy I just received and will go in my camper, Pure Sine Wave has terminals that are bolted connectors for your battery connections. I can not give you expert advice but I would go up to a 2000 watt in case you decide to expand your system in the future. I am very impressed with Renogy so far but there prices for the exact same thing vary depending on where you shop. Ebay right now seems to have their best prices.

 

[John Frum]

I have on backorder a single SOK 206ah 12.8-volt battery and will be buying an inverter to run with it. This SOK battery has a maximum continuous discharge current of 100A. If my math is right the max inverter size for this battery is 1200 watts, 1200/12 = 100 amp?

When I look at these smaller inverters 1000-1200 watts, I find many only have lead posts that are hand tightened, seems like a very bad idea.

Would there be any pros/cons of going with a 1500-watt inverter, I think max current draw is 125 amps and simply not run a continuous current that exceeded 100 amp?

100 continuous dc amps * 10 volts low cutoff * .85 inverter efficiency factor = 850 ac watts.

 

[chrisski]

Post Deleted. Already covered.

 

[WNCGUY]

100 continuous dc amps * 10 volts low cutoff * .85 inverter efficiency factor = 850 ac watts.

For my clarification, you are suggesting no more than an 850-watt inverter?

 

[time2roll]

Keep the horse in front of the cart....

Size the inverter based on the load. Size the battery based on the inverter. May need 2 or 3 of those batteries.

Unless it is something specific I would get about 400w for small stuff and if going bigger jump right to 2000.

 

[Roswell Bob]

Larger inverters tend to be more efficient, but not always the case. Larger transistors and more heatsink reduces losses. And yes, larger inverters will have better connections. I can't think of any issues with sizing inverter on the larger side. Inverters in this range tend to be good bargains. I have a couple of Meanwell inverters which are higher quality. The come from the other China.

 

[John Frum]

For my clarification, you are suggesting no more than an 850-watt inverter?

That is what the math says for 10 volts low cutoff.

Alternatively you could use an inverter that disconnects at 12 volts.
100 dc amps * 12 volts low cutoff * .85 conversion factor = 1020 watts.

 

[Zil]

wmgeorge makes sense.

I have a 2000W psw inverter from Samlex. Best in the price point.

 

[WNCGUY]

My 1000 watt Renogy I just received and will go in my camper, Pure Sine Wave has terminals that are bolted connectors for your battery connections. I can not give you expert advice but I would go up to a 2000 watt in case you decide to expand your system in the future. I am very impressed with Renogy so far but there prices for the exact same thing vary depending on where you shop. Ebay right now seems to have their best prices

I am just learning but my understanding is that my SOK 206ah 12.8-volt battery with a maximum continuous discharge current of 100A will not supply the current requirements 1000 - 2000 watt inverter.

 

[John Frum]

I am just learning but my understanding is that my SOK 206ah 12.8-volt battery with a maximum continuous discharge current of 100A will not supply the current requirements 1000 - 2000 watt inverter.

As I've said it can handle the full amp draw of a 1000 watt inverter down to 12 volts.

 

[WNCGUY]

Keep the horse in front of the cart....

Size the inverter based on the load. Size the battery based on the inverter. May need 2 or 3 of those batteries.

Unless it is something specific I would get about 400w for small stuff and if going bigger jump right to 2000.

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 total load is about 1100 watts but everything would not be used at the same time.

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.

 

[WNCGUY]

Larger inverters tend to be more efficient, but not always the case. Larger transistors and more heatsink reduces losses. And yes, larger inverters will have better connections. I can't think of any issues with sizing inverter on the larger side. Inverters in this range tend to be good bargains. I have a couple of Meanwell inverters which are higher quality. The come from the other China.

That is what the math says for 10 volts low cutoff.

Alternatively you could use an inverter that disconnects at 12 volts.
100 dc amps * 12 volts low cutoff * .85 conversion factor = 1020 watts.

I randomly checked specifications for a AIMS, Giandel and GOWISE inverter, all have battery low voltage shutdown/under voltage protection of 10 volt +/-. Not sure there is anything in the price range of the above brands with 12 volt protection?

 

[John Frum]

I randomly checked specifications for a AIMS, Giandel and GOWISE inverter, all have battery low voltage shutdown/under voltage protection of 10 volt +/-. Not sure there is anything in the price range of the above brands with 12 volt protection?

The only discrete inverter that has programmable low voltage disconnect is this one

Inverter VE.Direct - Victron Energy

Inverters allow you to power domestic equipment - requiring 230V/120V AC - using 'leisure' or 'automotive' batteries rated at 12V, 24V or 48V DC.

www.victronenergy.com

It will cost significantly more that the brands you listed.

 

[WNCGUY]

As I've said it can handle the full amp draw of a 1000 watt inverter down to 12 volts.

As I've said it can handle the full amp draw of a 1000 watt inverter down to 12 volts.

Please be patient with me as I learn about all of this....
Am I correct to understand that using a larger inverter, example 1500 watt is permissible as long as I monitor battery voltage and assure voltage doesn't drop below 12 volts?

If this is correct I may just go with the 1500 watt inverter.

 

[John Frum]

I can't think of any issues with sizing inverter on the larger side.

The problem with a 2000-3000 watt inverter in this usage model is...
Having the bms try to open the discharge fets at 200+ amps is liable to weld those fets closed.
Thus rendering have have the bms protections inoperable and not evidently so.

 

[John Frum]

Please be patient with me as I learn about all of this....
Am I correct to understand that using a larger inverter, example 1500 watt is permissible as long as I monitor battery voltage and assure voltage doesn't drop below 12 volts?

If this is correct I may just go with the 1500 watt inverter.

If you can do this without fail then my objections are addressed.
In this case you are the battery management system.
I prefer to 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.

 

[Zil]

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.

 

[John Frum]

Here is the math for a 1500 watt inverter.
1500 ac watts / .85 conversion factor / 13.8 volts = 127.877237852

That means even if the battery is absolutely full the bms will still be running out of spec high.
13.8 volts is absolutely full.

 

[time2roll]

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.