Need help to give advice to complete single line diagram with AGM storage battery

[David Christian]

I am a graduate engineer. I really need your help to give me advice to complete single line diagram with AGM storage battery.



The picture above is my single line diagram. I keep reading the battery design guide, but I lack of working experience for it.

The scope is as follows:
This is a house, the electric system is 200A, 120/240V single phase, three wire.
The client wants to use 6V AGM storage battery as a backup power to feed existing 100A sub-panel.

I just make a summary about what I learn:

1. Select inverter

a. Determine the total wattage required
I get puzzled by how to determine the total wattage. I need to ask the client which load he wants to feed.

b. Determine the inverter size. Total VA=Total wattage/Efficiency, Efficiency=0.7~0.9?

2. Select battery size

a. Determine DC Amperage: Total wattage/12VDC?
b. Determind active runtime
c. Estimated battery amp-hour required
Estimated battery amp-hour= DC Amperage X active runtime x 1.2

 

[mgookin]

Can't read your drawing but comments are below in red.

I am a graduate engineer. I really need your help to give me advice to complete single line diagram with AGM storage battery.

View attachment 16261

The picture above is my single line diagram. I keep reading the battery design guide, but I lack of working experience for it.

The scope is as follows:
This is a house, the electric system is 200A, 120/240V single phase, three wire.
The client wants to use 6V AGM storage battery as a backup power to feed existing 100A sub-panel.

I just make a summary about what I learn:

1. Select inverter

a. Determine the total wattage required
I get puzzled by how to determine the total wattage. I need to ask the client which load he wants to feed.

b. Determine the inverter size. Total VA=Total wattage * Efficiency, Efficiency=0.7~0.9?

2. Select battery size

a. Determine DC Amperage: Total wattage/6VDC? * efficiency of the inverter.
b. Determind active runtime
c. Estimated battery amp-hour required
Estimated battery amp-hour= DC Amperage X active runtime

In school you're allowed to assume as long as you note it. Find some inverter spec sheets and see what efficiency they have, then write a note "efficiency assumed nn% based on spec sheets from 3 manufacturers..." and cite the sources.

You need a transfer switch.

 

[GoldDigger]

If the load is much above 600W you really do not want to design around a 12V DC battery bank, much less 6V!
You can find 2400W 12V inverters advertised, but trying to handle 200A DC is going to be scary and you will also end up putting too many batteries in parallel. (Some will tell you that even two in parallel is too many.)
The available DC short circuit current, particularly from a low internal resistance AGM will be very high, and the voltage drop in the wiring under normal load will be high.
The absolute voltage drop will be the same as for higher voltage AC, but the % drop out of 12V will be 20 times what it is for the same current at 240V AC.

Eight 6V batteries in series to make 48V is a much better design.

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[pv_n00b]

How are you switching the source to the 100A sub-panel? I can't read your single line but it looks like you are just feeding the sub-panel from two sources.

 

[David Christian]

Single line diagram

Single line diagram

Could you check my single line diagram? I am not sure it is correct.

The first question is that how to charge the battery. In my single line diagram, I have no idea how to feed battery first.

The second question is that how to select inverter, if the client wants to use battery as backup power to feed 100 Amps sub-panel. The calculated current for this panel is about 80 Amps. 120 volt x 80 Amps=9600 Watt.

The total wattage is so high. 9600W/0.9(Efficiency)=10.7kW. I need to select the inverter based on this calculation?

The third question is that I am not sure whether the transfer switch is correct.

Thanks for all your advice. I really need example single line diagram, so that I can learn how to design. I really appreciate all your times and patience!

 

[GoldDigger]

The diagram looks OK., but the inverter is way too small. And it will not be possible to use a 22V battery bank!
The charging circuit will be separate, taking AC from a breaker off the main and feeding DC directly to the battery bank.
You can also specify a combination inverter and charger, which will generally include its own transfer switch.
The double throw switch should be either a manual transfer switch or a mechanically interlocked pair of breakers.
You really need to find out what the load will be on the E panel.
And with the inverter you specify there cannot be any 240V loads or multiwire branch circuits in that panel.

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[David Christian]

Revised single line diagram with 6V AGM Battery

Revised single line diagram with 6V AGM Battery

Could you help me to see whether my revised single line diagram is correct?

Thank you so much.

 

[David Christian]

Here is the inverter cut-sheet the client wants to use:

Range of product	XW
Device short name	XW6048-230-50
Product or component type	Hybrid inverter / charger
Network number of phases	Single phase
Type of signal	True sine wave
Continuous power	6000 W - 230 V AC (tolerance: +/- 3 %)

Complementary
Output current	26.1 A
Feature available	53 A, duration : 15 s
Network frequency	50 Hz +/- 0.1 Hz (output)
Cos phi	0.98
Harmonic distortion	< 5 %
Input voltage	230 V AC50.4 V DC
Input voltage limits	156...280 V AC - bypass/charge mode44...64 V DC
Input current	131 A DC at rated power
Input frequency	44...70 Hz - bypass/charge mode (allowable)55...65 Hz - bypass/charge mode (default)59.4...60.4 Hz +/- 0.05 Hz - sell mode
Charging current	100 A
Efficiency	95.4 % peak
Power consumption in W	< 7 W - search mode
Communication network type	Xanbus
Device mounting	Wall mounted
Provided equipment	Battery temperature sensor included for temperature compensation
Height	580 mm
Width	410 mm
Depth	230 mm
Product weight	55.2 kg

Environment
IP degree of protection	IP20
Ambient air temperature for operation	-25...70 C
Electromagnetic compatibility	Limitation of voltage changes, voltage fluctuations and flicker in low-voltage conforming to EN 61000-3-3Limits for harmonic current emissions conforming to EN 61000-3-2Emission standard for residential, commercial and light-industrial environments conforming to EN 61000-6-3Immunity for residential, commercial and light-industrial environments conforming to EN 61000-6-1
Standards	EN 50178
Product certifications	CE

 

[GoldDigger]

That inverter is a very respected product and should be able to meet your customer's needs.
Note that it takes a 48V battery bank.
It also, as I predicted, includes it's own transfer switch. The grid AC goes to the AC1 input of the inverter/charger. The AC output goes to the E panel.
If your customer still wants to go with AGM type batteries (which are more expensive and shorter lived than Flooded Lead Acid (FLA), you will need to size that battery bank based on the longest outage that it must ride through and also how much DC current it must deliver to the inverter continuously.
For rated power the battery must deliver 130A.
For AGM that should have a 130AH rating. For FLA it should be at least 500AH.
Which is feasible depends on the time duration needed.
For four hours at maximum power you will need at least 500AH regardless of what type you choose.

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[gadfly56]

I am a graduate engineer. I really need your help to give me advice to complete single line diagram with AGM storage battery.

View attachment 16261

The picture above is my single line diagram. I keep reading the battery design guide, but I lack of working experience for it.

The scope is as follows:
This is a house, the electric system is 200A, 120/240V single phase, three wire.
The client wants to use 6V AGM storage battery as a backup power to feed existing 100A sub-panel.

I just make a summary about what I learn:

1. Select inverter

a. Determine the total wattage required
I get puzzled by how to determine the total wattage. I need to ask the client which load he wants to feed.

b. Determine the inverter size. Total VA=Total wattage/Efficiency, Efficiency=0.7~0.9?

2. Select battery size

a. Determine DC Amperage: Total wattage/12VDC?
b. Determind active runtime
c. Estimated battery amp-hour required
Estimated battery amp-hour= DC Amperage X active runtime x 1.2

Assuming any reasonable loads off the 100 amp panel a ground up design of this sort would be a non-ideal choice. It would be better to get a line interactive or double-conversion UPS with bypass and feed the 100 amp sub panel from that. Something like this would be a place to start. The setup I linked to is about $6,500 or so and will do a full load (12,000 VA) for 7 minutes. Optional battery packs are available to extend the run time.

And as others have pointed out, 6 volt batteries are not where you want to be either. The key to being a really successful engineer is not to design the best wheel, it's to use someone else's wheel to get your job done.

 

[pv_n00b]

I hate to say it but it looks like you are in over your head on this project. You really should come clean with your client and connect them with someone who can design a system that will work for them. There are plenty of PV installers that can do this type of design easily. Multi-mode PV system design is not normally something taught in college engineering classes so it's understandable that you don't have the background. I would recommend starting with Photovoltaic Systems by Dunlop and work your way up from there.

 

[pv_n00b]

The key to being a really successful engineer is not to design the best wheel, it's to use someone else's wheel to get your job done.

I would say that's more the key to being a successful trades person.

An engineer would take the concept of a wheel and make a working example out of available materials and construction techniques.

 

[GoldDigger]

Although the thread is in the PV section there is nothing in the OP to indicate that there is a renewable energy component in the system.
The particular inverter mentioned is suitable for both grid tied (net metered) and stand alone backup use. And it price is correspondingly high.
It is possible that the customer does not want just a UPS.

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[mgookin]

I thought this was a class assigned project with the 6V as a given to the question.
Color me wrong.

 

[gadfly56]

I would say that's more the key to being a successful trades person.

An engineer would take the concept of a wheel and make a working example out of available materials and construction techniques.

I respectfully disagree. You describe a tinkerer, not an engineer. The vast majority of engineers are employed in positions where they are expected to solve a problem. Today. Right now! Make it HAPPEN!!!! You don't have the luxury of playing McGyver. The customer, whether internal or external either wants to start making money or stop losing it. The solution has to be effective and robust. Do I sit in front of my AutoCAD workstation and design something to hold a cart-load of 6V batteries which might take 6 weeks by the time I specify every component, put it on the drawing with enough information to allow construction, write the specification for said components, and oh yeah, push it all through the engineering QA/QC process (let's not even think about NRTL approval) OR do I find a battery module on the 'Net with the voltage and capacity I need? Very few engineers are in a position to work on ground-up projects. NASA is one of the few exceptions that comes to mind.

 

[PWDickerson]

The revised single line diagram indicates that you will be installing 32 batteries in 4 parallel strings of 8 batteries each in series. Most experts agree that you should not exceed 2 strings if you can help it, and keeping it to 1 string would be ideal. This is easy to achieve with industrial AGM batteries made by Outback Power (EnerSys), Absolyte GP, Deka, and others. 4 parallel strings is a mistake.

I noticed that you attached the wrong spec sheet. You need to specify a 120/240V, 60Hz inverter instead of 230V, 50Hz. unit if you are installing in California. Also, the Context XW is discontinued. The current generation is the Context XW+, which comes in 6.8kW and 5.5 kW sizes. This inverter/charger has two AC inputs (grid and generator), and one AC output. You will want to run a circuit from the main electrical panel to the grid input of the inverter. This is how the batteries are charged. You will want to connect a generator as well so you can charge the batteries when the grid is down. The output goes to the 100 amp backup loads panel as shown on the single line.

Outback Power, Magnum Energy, and Midnite Solar have lots of great wiring diagrams on their websites. You can learn a ton by looking them over.

I agree with others that you are in over your head on this project. I would highly recommend working with an experienced battery-based system designer on the project. You will be so glad you did. Design mistakes on this kind of project can be very expensive! Good luck.

 

[GoldDigger]

The worst potential problems with the design are those that may not show up until the first power outage or until the batteries have been destroyed in a few months instead of a few years.

 

[pv_n00b]

I respectfully disagree. You describe a tinkerer, not an engineer. The vast majority of engineers are employed in positions where they are expected to solve a problem. Today. Right now! Make it HAPPEN!!!! You don't have the luxury of playing McGyver. The customer, whether internal or external either wants to start making money or stop losing it. The solution has to be effective and robust. Do I sit in front of my AutoCAD workstation and design something to hold a cart-load of 6V batteries which might take 6 weeks by the time I specify every component, put it on the drawing with enough information to allow construction, write the specification for said components, and oh yeah, push it all through the engineering QA/QC process (let's not even think about NRTL approval) OR do I find a battery module on the 'Net with the voltage and capacity I need? Very few engineers are in a position to work on ground-up projects. NASA is one of the few exceptions that comes to mind.

I don't agree Gadfly. Someone who just integrates parts from a catalog is a designer at best. Not that a lot of engineers have not just become designers. My first job out of college at an MEP firm had me working for a PE that had vendors to all his engineering design for him. About the only thing he did was lay it all out for the drafters and stamp the final designs.

An engineer takes ideas and concepts and makes them real. I'm sorry if that is not the job of many engineers but IMO it's what defines engineers.