Battery backup system without solar

[welnat]

All,

Any input would be great, this is what I'm planning on building.

24 volt 5.3kWh emergency battery backup
Battery - Used Model S
Inverter - MPP Solar inverter/charger - PIP-LV2424MSD 2400W -14kW 24V 120VAC Charge 80A MPPT Solar, 60A Utility
Solar - none at this time
Generator - Honda 2000 (already own)

Just to clarify - you are then going to run extension cords to power your loads?

Can the used model s battery factory balance system be used or do you have to buy and and BMS?

 

[Donald Siegel]

Right, but when do you know about a grid shut down? Sure, PG&E might send you a notification, but what if it was sudden? Storm, wildfire, etc. Wouldn't having your battery pack charged up just-in-case be the way to go in that situation? That would mean charging your pack every day with the generator, just-in-case. Or at least making sure it was charged up and ready.

For example, our power went out this morning for about 4 minutes. If we had a battery pack charged up and ready to go, with an automatic transfer switch, then we wouldn't have even noticed. IT guys like me call that "uninterruptible power supply". Our datacenters have both a generator and a battery bank, with the battery bank charging off the grid when all things are OK. The generator is only used if the outage goes longer than the battery bank can support. Then the generator does both...it charges the battery bank as well as running necessary systems.

I'm picturing a battery bank that is charged off the grid at grid costs, with the ability to charge off the generator should it be needed. Depending on how you size your battery bank, you might go an entire outage in your area without ever needing to fire up the generator at all.

I am sure he would maintain the battery for an emergency with grid power but use the generator only when there is power outage to charge it up. A family member uses a CPAP and is just south of the Kincaid fire zone, and in the likely power outage zone. A good battery inverter combination is all that's needed to keep his 60 watt CPAP going for many nights.

 

[madsci1016]

Just found the forum because I'm weighing options on adding solar to the battery backup system I already have that might suit you well. I tried DIY at first and then returned/sold it all off because it drove me nuts. Then I just bought a 2KW AIMs inverter/charger with 30A automatic transfer switch. IT charges at 30A too. Basically all in one solution for whole house battery backup.

Paid $770 for inverter/charger on Amazon and just added batteries. Also sub-ed some of my house circuits out to a standalone 30A sub panel, so all the devices I want to run through blackout were moved to that sub panel. It keeps the batteries charged and transfers to inverter in 10ms during power outage. Battery chemistry selection switch and a switch where you can prioritize battery over grid power and convert it into a solar inverter just that, where it will transfer load back to the grid automatically when your batteries get low.

 

[svetz]

How do you like the Aims and how long have you been using it? They seem like a good company, but I hear a lot of bad things about off-name brands that have inverters that look identical.

 

[madsci1016]

How do you like the Aims and how long have you been using it? They seem like a good company, but I hear a lot of bad things about off-name brands that have inverters that look identical.

I'm an Electrical Engineer btw, with experience in power systems and electronics design. But don't have much practical experience with installing solar. FYI for the following opinions.

I had this low frequency one for about a week and I'm mostly impressed. It's overload ratting is nuts. I pushed this 2KW one to just under 3KW and it didn't bat an eye. It's got a little red overload LED on it that comes on around 2200W and the manual says it should be able to handle that for 10 to 15 minutes before cutting you off. With some beeping during the last minute to warn you. It claims it will do 300% load (6KW!) for 10 seconds. There's a guy online that put 8kW on their 6KW just fine. It's feature list is nearly perfect for wiring into your home like this as a backup solution, with just a little dip switch flip to change it's behavior to be an off grid (grid interactive? still lost on the terminology) inverter.

I did only measure 18A charge current, I'm going to call their support line about that because on paper it should be 30A. Though I wonder if they can sense battery impedance and decided to not try and put more than 18A in my 180AH bank to be safe and not cook the batteries. 0.1C is a good safe charge current and their sales flier talks up wonder about how they claim to take the best care of your batteries.

I had a AIMs 1500W high frequency one originally for this project because it was cheaper. No charger or transfer switch, I used a Duracell charger and built my own transfer switch. I had the most trouble with that charger... But as far as the inverter it would go into overload at about 1200 watts and shut off. I realized with some measurements that the 1500W sticker rating for the high frequency models is really for input power, as when you discount efficiency loss and power factor of load, you get about 1200W out for 1500W in. Or at least thats what i measured. To be fair to it, it did mange to start and run my 1200W,12,000 BTU portable AC if it was the only load. But it got hot doing so.

I did a bunch of research online and AIMs seemed to be a well liked brand. Some of the tear down videos of these low frequency models were nice, I saw some good design practices inside.

 

[svetz]

Thanks for that review! I suspect the the look-alikes are cheapo-clones just because Aims is so good they want to copy it; but appreciate the confirmation.

 

[PSPS]

Just to clarify - you are then going to run extension cords to power your loads?

Can the used model s battery factory balance system be used or do you have to buy and and BMS?

My original plan was to use extension cords, now looking at this manual transfer switch.

There is an online shop selling the battery with a pre-installed BMS

 

[krby]

I'm building a portable one of these. I've been asking questions over in the planning/sizing sub-forum:

Advice for non-solar power box / electric generator

UPDATE: I'm posting updated parts and diagrams in the thread as I go, leaving the existing drawings in place so the thread makes sense. In another thread, someone suggested I could post here for advice. I'm building a portable electric generator similar to Goal Zero or Kodiak but without the...

www.diysolarforum.com

Sizing it for ~4kW and 2000W of power. Given what I want to power during a blackouts, that should give me 2-3days.

 

[PSPS]

I'm an Electrical Engineer btw, with experience in power systems and electronics design. But don't have much practical experience with installing solar. FYI for the following opinions.

I had this low frequency one for about a week and I'm mostly impressed. It's overload ratting is nuts. I pushed this 2KW one to just under 3KW and it didn't bat an eye. It's got a little red overload LED on it that comes on around 2200W and the manual says it should be able to handle that for 10 to 15 minutes before cutting you off. With some beeping during the last minute to warn you. It claims it will do 300% load (6KW!) for 10 seconds. There's a guy online that put 8kW on their 6KW just fine. It's feature list is nearly perfect for wiring into your home like this as a backup solution, with just a little dip switch flip to change it's behavior to be an off grid (grid interactive? still lost on the terminology) inverter.

I did only measure 18A charge current, I'm going to call their support line about that because on paper it should be 30A. Though I wonder if they can sense battery impedance and decided to not try and put more than 18A in my 180AH bank to be safe and not cook the batteries. 0.1C is a good safe charge current and their sales flier talks up wonder about how they claim to take the best care of your batteries.

I had a AIMs 1500W high frequency one originally for this project because it was cheaper. No charger or transfer switch, I used a Duracell charger and built my own transfer switch. I had the most trouble with that charger... But as far as the inverter it would go into overload at about 1200 watts and shut off. I realized with some measurements that the 1500W sticker rating for the high frequency models is really for input power, as when you discount efficiency loss and power factor of load, you get about 1200W out for 1500W in. Or at least thats what i measured. To be fair to it, it did mange to start and run my 1200W,12,000 BTU portable AC if it was the only load. But it got hot doing so.

I did a bunch of research online and AIMs seemed to be a well liked brand. Some of the tear down videos of these low frequency models were nice, I saw some good design practices inside.

Can you let us know what you are using for batteries? Do you know how long they will last and at what rate of power consumption?

thanks

 

[madsci1016]

Can you let us know what you are using for batteries? Do you know how long they will last and at what rate of power consumption?

thanks

Right now I have 4x 90AH Flooded Lead Acid (from here as this was the cheapest $ per KWH I could find) plus 2x 90AH SLA I got for free-ish all tied together as a 24V system. I get about 4-5 hours of run time as my usual draw of all my lights/fans/security camera system plus TV is about 1kw. I just ordered 30KWhrs of LifePO4 from here to make this a off grid solar system.

 

[Slymp]

I am in the process of building a home backup battery bank myself (as a total rookie). Just curious, why would you charge your battery pack with a generator? AFAIK that's the most expensive and least efficient way to do it. Why not just charge from the grid? That's the same thing a Tesla Powerwall does and even at CA PG&E rates, the cost of the grid power should be much cheaper than the cost of gasoline for the same power. Then you wouldn't have worries about noise, exhaust, heat, etc.

Will has a Youtube video on comparing the Goal Zero and Inergy with lithium, lead-acid and others which might be helpful with respect to cost comparisons.

Either way, as a newbie I think how your bank is charged comes down to the inverter/charger and sizing it correctly with the right inputs and outputs. I'm sure one of the experts here in the forum could provide pointers to recommended components.

On second thought, I guess having the ability to charge three ways (solar, grid, generator) would be pretty handy. Maybe some sort of automatic transfer switch? Will has a video about that, too:

Hi,
I'm a newbie too (engineer, but not electrical). Just my first thoughts and plans.
My plan is a battery, around 6kwh (used lifepo4), to charge at night (5p per kwh here in UK), to use during the day with ~5kw inverter. Save a few £, and save the grid from dirty peak-hour generation.
Do you know of any schematics for that? I'm thinking of the BMS and how that should be connected. Well, that's my first unknown! I have a 4 hour cheap rate window, so I suppose I need a 1.5kw charger. (I see there are combined charger-inverters)
Cheers
Steve