Emergency Battery Backup - Utility Mode

I have a 3000 watt pure sign wave inverter that I hook directly to the Kona battery in the utility mode. I have a 100 amp dc circuit breaker in line with the negative side if the 12 volt cable leading from the battery to inverter to keep from overloading the DC to DC converter. I have used it during power outages to run my refrigerator, computer, TV and lights for several hours with no problem. I see no reason you could not run a battery charger off of it. On the other hand you could also just run direct off the utility mode. I know others beside my self have done this as well.

 

Here is an older thread with a lot more on the subject

https://insideevsforum.com/community/index.php?threads/kona-as-a-backup-battery-for-home-power-outage.7392/page-3#post-84058

 

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Actually in the utility mode the electricity comes from the large battery pack through the DC to DC converter and the small battery does not really come into play until you start to exceed the capacity of the DC to DC converter. This happens around 100 amps of draw.

The problem I see with using a 172 watt battery charger is that it is the length of time it would take to charge one of the batteries. Assuming you have two 100 amp hour batteries its going to take more 8 hours to recharge one of these batteries at 172 watts (12 volts * 14 amps). Your much better off connecting to the inverter to the 12 volt battery in the car.

The cigarette lighter is rated at 180 watts. That would be a pretty small inverter to be with in the range of the lighter. You would not be able to run much off of that.

If you truly want back up power you should be connecting to the battery directly as it can supply up to 1200 watts (12 volts * 100 amps ) You will want a 100 amp or smaller fuse to keep from blowing the cars fuses.

If you do use the the lighter I would use a fuse with your charger. Running the lighter at 180 watts for long periods of time probably would not be recommended. If you were to run it for long periods I would keep the wattage below 140 watts so as not to over heat the wire to the lighter.


Here are some pictures of my setup. The first show the battery connected with the inverter on the cart in the back ground. Second is a close up of the battery connection. Third is the inverter. Forth is my power monitor and the last is the 100 amp breaker on the inverter dc side.

inverter

 

Just noting the detail that there is a battery management sensor on the negative terminal of the aux battery. The inverter load should be on the 12V system side of the sensor rather than the battery negative terminal, which allows the sensor to provide valid data without having the LDC thinking the battery is drawing an extra 100 amps. The location for the inverter's negative connection is perfectly fine as shown in your photo but for others doing this, using the negative battery terminal literally would likely be problematic. The connection could also be made to the chassis of course.

 

As I always I appreciate your attention to detail and your expertise and input. Thanks

 

Hmmm, this makes me think that not only could a setup like this be used for emergency situations, but also more generally. i.e. supply some of the house's evening load electricity (when it's expensive), and replenish the main battery later when it's cheap. All it would take is an appropriately sized grid tie inverter.

The Kona has about 8 Telsa powerwalls worth of capacity in its main battery. Pulling 3 or 4 KW/hr's out of an evening is a drop in the bucket.

 

Outback makes a 12 volt 2800 watt grid tie hybrid inverter which would be perfect for that. I would probably add a 100 a hr battery to the mix so that there is a battery in the circuit when the Konas off on a drive.
Here's a link to the inverter
https://www.altestore.com/store/inverters/hybrid-inverters/outback-power-fxrvfxr-series-inverter-chargers-p40835/#OUTVFXR2812A

 

Hey Fastnf, in the old thread you linked I remember you were considering beastly split phase inverters to (selectively) power your entire panel. In the photos you shared it looks like you wound up with a vanilla 120V inverter. May I ask why you went with the latter, or perhaps your big bad 50+ pounder was simply off camera?

After the big US east coast storm knocked out my power for days this week, I'm feeling the need to get ahead of the next one.

 

The main reasons were code compliance, usage and cost. Originally I was looking at being able to run my well pump and and my heat pump which are my main 220 volt usage. In order to legally hook to my panel at my generator input I would need a UL listed 1741-sa inverter So I studied my usage to see what I needed for emergency back up. I used an emporia vue energy monitoring system and found that the pump only ran a couple of times a day to fill the water pressure tank. So I could just fire up my generator during the day for a few minuets to fill the water tank. For heat I decided that a small propane heater cover that need so I didn't need the 220 volts continuously. For lights, refrigerator, computer. internet, and TV I only need 120 volt and found I was using only about 500 watts. Which was great if I could run that in the evenings off of the Kona . The cost difference between a code compliant 240v inverter ($3000) and a mobile inexpensive 120 volt ($275) was significant. So in order to test the theory I went the least cost . Last December we had a snow storm that knocked out power for a week. I was able keep every thing 120 volt running with out having to listen to the generator drone on all day and night and suck my propane tank dry. Disadvantage to this set up is that I have individually plug things in to the inverter (with a power strip). Plus side I didn't spend a bunch of money to find out if it works. Eventually I want to install a whole house battery system and connect it to my solar array but for the time being this works great as a back up for the occasional power outage.

The other complication was that I couldn't find any code compliant 12 volt inverters. They were all 24, 48, or 400 (Tesla) volt inverters.

 

I lost power here in Connecticut for 4 days. My 1200 watt inverter powered my refrigerator, lights, fan, TV and cable/internet for that whole time. Averaged 2 miles/hour loss on the GOM.
Question is, how big an inverter will the Kona support? I've read here that 1200 watt is the max for an ongoing load. I've also read that people have used 1800,2000 or more. Is that drain sustainable for a day or more?

 

All I can contribute is that the LDC fuse is 150 amps and that's where all the power comes from at approx 14.5 V in utility mode. One approach is that at 80% of that fuse rating on a continuous basis is 1740 watts. Or, assuming Torque Pro data is accurate I've seen LDC current peaks up to around 60 amps but not any more. That would return 870 watts.
The data has also indicated to me that the LDC is actively current-limited, so you're not likely to hurt anything but will see a drop in voltage as you approach the current limit.

 

The DC to DC converter will put or around 1200 watts from Large battery. Usage above that will start to draw down the 12 volt battery. I have read that usage above 1500 watts will blow a fuse on the Kona. I have not tried it myself above 1200 watts. I have an 100 amp breaker going to my inverter which pops and can easily be reset if I exceed the 1200 watt limit.

I have been toying with putting a couple of 100 amp-hr battery in parallel with the Kona. This would lower the amperage draw from the Kona during any surges then when the surge passes the kona DC to DC converter would top off all three battery's. Thus allowing to run higher than 1200 watts with out popping the 100 breaker in line with the Kona battery. I will probably but breakers and instrumentation on each battery to monitor how it works. If and when I get around to it I will post my findings

 

What was the SOC drop during all of this then? About 50%?

Now you have me thinking that I ought to get such an inverter just to have it handy. We only lost power for 20 minutes - we contemplated sitting in the car to run the AC and listen to the radio. But the power came back on again before we got around to it.

 

To be honest It was over 6 months ago and I don't recall exact numbers. I know it wasn't enough for me to worry about. For reference I usually keep the car charged to 80 percent. It dropped but it wasn't enough for me to be concerned. I also have a 9KW generator so I could have charged the car if I needed to. I was keeping an eye on it at the time but was more interested in staying warm then documenting the data set. Next time the power goes out (as I am sure it will during fire season) I will document the details and post them.

 

I ran my refrigerator 24/7, lights 50%, fan 24/7, cable and TV and router 25% for three days. GOM started at 316. After three days it was around 240. Not accurate because I tried to run the a/c a couple of times too.

 

All of this has me thinking/wondering if there is a way to get juice from the solar panels on the roof during an outage. The way the system is designed is that if the grid is down, the system is off - mainly as a safety feature so that the system doesn't energize the grid when people are out there attempting to make repairs. But there is also this assumption that the grid can absorb as much power as the solar system can generate - if you were attempting to create some standalone "grid", this would not be the case, and the inverter simply isn't designed for such a circumstance.

People who have off-grid systems will have banks of batteries, and their systems are designed differently.

The specifics will depend on the type of system you have, of course. A micro-inverter system will be generating AC at each panel. Ours is not such a system - each panel has an "optimizer", the panels are strung together to generate high voltage DC (about 400V). The inverter on the side of the house is what converts that to AC. So both the solar system and the traction battery are roughly 400V DC. But there is no way to connect the two.

 

My system operates at 400DC volts off of the solar panels. The panels are connected in series and parallel. 2 sets of 10. I have been looking for a Hybrid inverter which would then allow a EV battery to be used for storage. I have found 2 so far Solar Edge and Generac make them there may be others. At this point I haven't found any information on Solar 400 volt charge controller. That's the missing piece. Though Midnite Solar makes a 400 volt dc input to 48 volt dc output charge controller that can used for battery back up but won't work for charging an EV. With that it could be connected to an EV battery. I am thinking of either from a wrecked EV or possibly from a conversion of one of my ICE cars. I was thinking of maybe a wrecked BMW i3 since there is a lot of information on it in Sandy Munro's tear down report that could be used to connect directly to the battery.

Ideally I would like a Vehicle to House inverter/ charger but it looks like we are still a few years away from that. May be I should just be patient. Nah I'd prefer to experiment.