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120V AC inverter with 40V battery

Diyfan

Jul 27, 2023
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Hi diyers,
I have 2 x 1000Wh lion batteries I would love to put to work during electricity outages. My ultimate goal would be to hook them on an inverter with a capacity of between 500 to 1000W.

My batteries are 40V.

What would be your recommendation:
1- hook a dc to dc converter, from 40v to 12v and buy a commercial 12V inverter
2- Buy a more expensive inverter, 48V, and hope it would work Ok with 40V battery
3- Diy an inverter from scratch, with a nominal input voltage of 40V

Any wisdom to share?
Many thanks
 

kellys_eye

Jun 25, 2010
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Where did you get a 40V battery? That's definitely 'non-standard'. How is it made up? Individual lower voltage cells? If so then rewiring the cells to a lower, more practical voltage, would be the way to go.
 

Diyfan

Jul 27, 2023
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Thanks for your reply kellys_eye.
The cells are enclosed into a housing. The battery is in fact a commercial battery used to power an outboard boat motor. Brand is ePropulsion, model Spirit 1.0.
It is the first version based of off 40V system. The newer motors are now 48V...
 

kellys_eye

Jun 25, 2010
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Every additional stage of conversion you might add only decreases the efficiency of the overall system. Not to mention the additional cost.

I doubt a system intended for a 48V input will work with only 40V (it will report a 'low input' error).

Of course, putting another converter in (to take the 40V up - i.e. boost converter to 48V or down i.e. buck converter to 24V or whatever) is perfectly feasible - the efficiency of such devices can be as good as 85-90% assuming you use a quality device.

If you can get the schematic for a 48V input inverter you might be able to hack the low volts detector circuitry to ignore the lower input alarm level.
 

bidrohini

Feb 1, 2023
165
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Feb 1, 2023
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Hi diyers,
I have 2 x 1000Wh lion batteries I would love to put to work during electricity outages. My ultimate goal would be to hook them on an inverter with a capacity of between 500 to 1000W.

My batteries are 40V.

What would be your recommendation:
1- hook a dc to dc converter, from 40v to 12v and buy a commercial 12V inverter
2- Buy a more expensive inverter, 48V, and hope it would work Ok with 40V battery
3- Diy an inverter from scratch, with a nominal input voltage of 40V

Any wisdom to share?
Many thanks
I think using a DC-DC converter will be easy.
 

Delta Prime

Jul 29, 2020
1,979
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Any wisdom to share?
ePropulsion, model Spirit 1.0.
40volt battery
There are no industries standards for advertisement when it comes to lithium ion battery packs. That 40 volt battery pack is advertised using the high side when lithium ion battery packs are fully charged
One lithium ion cell, nominal voltage is 3.7v.
One lithium ion cell fully charged voltage is 4.2v.
36v÷3.7V=9.73(rounded up)
Meaning it takes 10 lithium ion cells connected in series to reach
a nominal 37 volts, they just used 36Volts for advertisement
Therefore 10 lithium ion cells fully charged equals 42 volts they just use 40 volt for advertisement. So you may see it advertised as 40 volt system or battery pack but that is same as same 36 volt system or battery pack.
Now they flip it around when it comes to 48 volts they're using the nominal low side battery pack voltage of 48volts.
48V÷3.7V=12.973(rounded up).
Meaning it takes 13 lithium ion battery cells connected in series to reach 48 volts( nominal voltage)
Therefore 13 lithium ion battery cells connected in Series fully charged equals 54.6V they just use 54 volts for advertisement. you'll see advertisements for 48 volts battery pack or system and that is the same as 54volt battery pack or system. So this is what you need. Now the below photo if you notice on the upper right hand corner it says 50 Hz at 225VAC.
You could easily find them with an output of 60 Hertz at 110 or 120 VAC.
This is only an example I didn't find the exact inverter for you but you'll find them easilyScreenshot_20230729_001020.jpg

Diy an inverter from scratch, with a nominal input voltage of 40V
Incorrect statement nominal voltage as stated above would be 36 volts.
Now tou have to worry about is your load on the inverter how many watts or in this case the Watt hours. In short what are you going to power a washing machine or a coffee maker or both you got to add them up on the inverter output & must fit your batteries capability input to the inverter. Sorry about that last statement it came out all convoluted I got to get some sleep good night.
 

Delta Prime

Jul 29, 2020
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Forgive me if you've already seen the manufacturer's website but they will tell you how to connect them in parallel charging and discharging since you have two it would maximize your power curve if you connect them in parallel to your inverter.
Although the link says Plus I believe that's your 48 volt version just browse the website and you'll find your particular battery good luck to you
 
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