Pure Sine Wave Inverter using Two Lithium Ion Batteries

[Cody1944]

TL;DR Summary

Hello All, I am a licensed electrical contractor and have just now started to build portable ac power generators, would appreciate some opinions on this design.
My thoughts were to operate Batt 1 & Batt 2 Individually, to eliminate the need for a BMS.
However I am not certain this is the most desirable wiring method. I am curious if the Charger will work in this config.
Thank You
looking forward to a professional discussion.
Cody

 

[Baluncore]

Welcome to PF.
That looks like it might work.
What capacity batteries will you use?
What is the load on the sinewave inverter?

 

[Cody1944]

Hello Baluncore
I am using 23ah Lithium Ion Batteries, each has its own BMS built in.
The Inverter is a 600w, the intended load is end table lamps/standard refrigerator/cordless tool battery recharging/recharge electric bike batteries, small power tools/laptops/phones ...a stand alone unit for emergency power
My concern was is it possible electrons could flow into the fully charged battery and the inverter somehow while charging the depleted battery ? One thought is to build a bigger case and Just install two complete Individual systems.
here are some specs on the batteries,
Dakota Lithium 12v 23Ah Battery - Half the Weight & Twice the Power

 

[anorlunda]

I am using 23ah Lithium Ion Batteries, each has its own BMS built in.

If that's true, then the two BMS will control how much current is allowed into the batteries, not the inverter power supply. Therefore, the inverter doesn't matter.I'm assuming that BMS means Battery Management System.

 

[berkeman]

The Inverter is a 600w, the intended load is end table lamps/standard refrigerator/cordless tool battery recharging/recharge electric bike batteries, small power tools/laptops/phones ...a stand alone unit for emergency power

Have you considered the start-up current of your refrigerator? Are your other appliances okay with losing power for the second or two that the 600W inverter will struggle to put out 10A or so...?

https://findanyanswer.com/how-many-amps-does-a-refrigerator-draw-on-startup

 

[Cody1944]

If that's true, then the two BMS will control how much current is allowed into the batteries, not the inverter power supply. Therefore, the inverter doesn't matter.I'm assuming that BMS means Battery Management System.

I read that current flow in a battery is positive to negative, but electron flow is negative to positive, so will electrons flow from the negative on the charger, to the negative on both Batts, and then flow inside both Batts to the positive posts, causing some type of damage to the fully charged Battery.

So With independent BMS it should not cause any undesired conditions ?

 

[Cody1944]

Have you considered the start-up current of your refrigerator? Are your other appliances okay with losing power for the second or two that the 600W inverter will struggle to put out 10A or so...?

https://findanyanswer.com/how-many-amps-does-a-refrigerator-draw-on-startup

All of these devices will only be used one at a time
Its my first build so I built it primarily to recharge cordless tools, but realize it has more potential than that.

 

[berkeman]

I read that current flow in a battery is positive to negative, but electron flow is negative to positive, so will electrons flow from the negative on the charger, to the negative on both Batts, and then flow inside both Batts to the positive posts, causing some type of damage to the fully charged Battery.

So With independent BMS it should not cause any undesired conditions ?

Don't burden your thinking with electron flow. At your level of design, just thing in terms of positive current flow.

 

[Cody1944]

Welcome to PF.
That looks like it might work.
What capacity batteries will you use?
What is the load on the sinewave inverter?

I must be getting punchy in my older years, I just realized If I close both switches my batts are in parallel with each other.

 

[Cody1944]

Don't burden your thinking with electron flow. At your level of design, just thing in terms of positive current flow.

Ok Thank You

 

[Baluncore]

I just realized If I close both switches my batts are in parallel with each other.

If that was a problem you could use a 10 amp, two pole, two position switch, wired to cross over the batteries.

 

[sysprog]

Please do not for this use a design that is not UL approved.

 

[Baluncore]

Don't burden your thinking with electron flow.

Don't think negative. B+ve.

 

[maxwells_demon]

Summary:: Hello All, I am a licensed electrical contractor and have just now started to build portable ac power generators, would appreciate some opinions on this design.
My thoughts were to operate Batt 1 & Batt 2 Individually, to eliminate the need for a BMS.
However I am not certain this is the most desirable wiring method. I am curious if the Charger will work in this config.
Thank You
looking forward to a professional discussion.
Cody

View attachment 273935

basically, this would be what your circuit would look like if you integrated all those components into one portable unit:

assuming you all had the circuit protections and the approriate groundings in place, that switchboard is basically a black box at the moment, depending on what you want it to do (in your drawing, it's basically just two switches connected between battery and inverter).

basically it's at least a 5-port switchboard whose number of switches and wiring complexity is determined by what kind of switching you'd want to be able to do (you could always screw and then unscrew your charger if you want, but assuming you want to deploy your portable generator, and then charge it after as needed, without further modifications to the circuit, making your own little switchboard would be the way to go.).

so, time for some rules:
1) how do you want your batteries to charge? one at a time? or can your charger handle both at the same time? are both batteries load-carrying, or is one kept only for back-up?
2) do you want the option to operate the charger and inverter at the same time? like charging battery 1 while battery 2 supplies load? or do both of the batteries supply load together at one instance and get charged together afterwards, as needed?
3) anything else you might want the switchboard to be able to do?

cheers!

 

[Rive]

Regarding the usage of LiPo batteries: there is a reason why UPS setups still has Lead-Acid batteries, and that's the insane short term overcurrent capacity. If you plan to run any inductive load (like that refrigerator) through your setup then you would do better with simply buying an used UPS which has external battery connectors and is able to start up independently.

 

[Cody1944]

Please do not for this use a design that is not UL approved.

What are you talking about? All of my components are UL Listed.

 

[berkeman]

What are you talking about? All of my components are UL Listed.

Quiz Question -- what is the difference between a UL Listed component and a UL Approved device?

 

[sysprog]

Quiz Question -- what is the difference between a UL Listed component and a UL Approved device?

Thanks for beating me to that, @berkeman $-$ maybe the difference could mean not getting zapped $-$ a great guy that I knew who worked as an engineer for the City Water Department in Chicago had before then had a long career with UL $-$ according to him, some of the most excellently inventive assemblages were among those that didn't pass muster $\dots$

 

[berkeman]

Yeah, I've been involved in both kinds of certifications with UL.

I can definitely start a fire with UL certified components, but none of my UL certified devices has ever caught fire...

 

[Cody1944]

Thanks for beating me to that, @berkeman $-$ maybe the difference could mean not getting zapped $-$ a great guy that I knew who worked as an engineer for the City Water Department in Chicago had before then had a long career with UL $-$ according to him, some of the most excellently inventive assemblages were among those that didn't pass muster $\dots$

So everyone who buys an inverter and installs it into their truck needs to have that installation UL Approved I don't think so.

 

[berkeman]

So everyone who buys an inverter and installs it into their truck needs to have that installation UL Approved I don't think so.

Sure. Go to your local auto part store and check the labels. Duh.

 

[anorlunda]

I interviewed with UL as a college senior. I sometimes wonder if that choice would have been boring or fulfilling.

I also interviewed Wurlitzer Organ Company, and interviewed Disney for an "imagineer" position, and interviewed with Dr. Van de Graaff at his company High Voltage Engineering.

 

[sysprog]

That's super-cool @anorlunda $-$ my Grandfather (who was Major, Corps of Engineers, WWI, and Lt. Col., Chief, North African Sector, OSS, WWII), told me that he gave Van De Graff an early lesson in Physics $-$ VDG, who was about 5 years old at the time, was interested in rockets, and on seeing the exhaust from a passing automobile, asked Grandpa, who was then maybe 12 years old, how does the gas from that little pipe push that big car so fast, and Grandpa smiled and told VDG about internal combustion engines.

 

[sysprog]

So everyone who buys an inverter and installs it into their truck needs to have that installation UL Approved I don't think so.

Please, @Cody1944 , that's not what I was advocating $-$ I said

Please do not for this use a design that is not UL approved.

That's just a caution in reference to not using a design that is not UL approved $-$ it's not a caution as to exactly how you install things -- I'm confident that it's well and broadly understood that UL doesn't evaluate the safety and correctness of each specific instance of an inverter install $\dots$

 

[Cody1944]

I have worked in Industrial, Nuclear and Commercial Electrical Construction environments for 40 years, I was an Electrical Inspector for the Automatic Train Control System for the most complicated electric trains in the world for 10 years. UL is not the know all be all of Electrical Work.

 

[sysprog]

I have worked in Industrial, Nuclear and Commercial Electrical Construction environments for 40 years, I was an Electrical Inspector for the Automatic Train Control System for the most complicated electric trains in the world for 10 years. UL is not the know all be all of Electrical Work.

That's a very impressive work history, @Cody1944; however, I think that UL doesn't hold itself out to the public as "know all be all" $-$ wasn't it originally a service group for insurance underwriters $-$ isn't the main mission of UL to foster product safety?

 

[dlgoff]

... interviewed with Dr. Van de Graaff at his company High Voltage Engineering.

Wow. Having worked with my universities 4 Mev Van de Graaff generator(no longer there), I would have "given my right arm" for that opportunity.

 

[sysprog]

Wow. Having worked with my universities 4 Mev Van de Graaff generator(no longer there), I would have "given my right arm" for that opportunity.

When I was in HS Science Class someone grounded me out with an alligator clip wire the other end of which was connected to a water tap and I thought why are you grounding me out, and then someone else suddenly attached me to another alligator clip wire that was connected to the top of the running VDG generator and I got a brief jolt $-$ I laughed off the prank, but also said that attaching the wire from the VDG generator didn't continue the zap, as was apparently intended by at least one of the pranksters, because the globe was an accumulator that became depleted immediately on first contact $-$ the belt rubbing against the copper comb wasn't enough to deliver a steady charge.

 

[dlgoff]

the belt rubbing against the copper comb

Actually, there's no contact between the comb and belt.

"...the form of comb-shaped rows of sharp metal points, are positioned near the bottom of the lower roller ...

bold by me

 

[sysprog]

@dlgoff , I think that you're right about the Van De Graff generator design, but in order to avoid fussing about the exact belt-to-comb distance, in my school 'they' used 'slightly touching' instead of 'near' $-$ it was more wear on the belt, but I imagine that the teacher found it easier to explain it that way (avoided induction discussion).