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Using a generator to charge backup battery?

findlj

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May 12, 2022
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Hi, I'm new to the forum and am getting my 7.6kW solar array installed Monday. I have not bought a backup battery at this time but would like to do so and have the ability to recharge it via an Inverter/Generator. I intend to purchase a WEN GN875i 8750 Watt inverter/generator soon.
I'm finding it difficult to get information from my solar vendor on the logistics of attaching the battery they sell to a generator. While I like the company and the installation staff I've dealt with, they have not done this. They use the Enphase Encharge 10 primarily.

I'm looking for advice and recommendations on battery, transfer switch vs Interlock, installation issues, etc., especially from those who've already done this.

Thanks for the help in advance!

 
What are the circumstances where you think you would not have enough solar to charge the Encharge batteries? Is this a once a year scenerio or more often?
 
Hi, I'm new to the forum and am getting my 7.6kW solar array installed Monday. I have not bought a backup battery at this time but would like to do so and have the ability to recharge it via an Inverter/Generator. I intend to purchase a WEN GN875i 8750 Watt inverter/generator soon.
I'm finding it difficult to get information from my solar vendor on the logistics of attaching the battery they sell to a generator. While I like the company and the installation staff I've dealt with, they have not done this. They use the Enphase Encharge 10 primarily.

I'm looking for advice and recommendations on battery, transfer switch vs Interlock, installation issues, etc., especially from those who've already done this.

Thanks for the help in advance!

What type of solar install will you have? A backup to a grid tied system may have certain limitations. A battery backup to a micro inverter grid tied system will have different limitations. It depends on many factors.
 
What are the circumstances where you think you would not have enough solar to charge the Encharge batteries? Is this a once a year scenerio or more often?
I want to cover the case where the grid is down and there's very little sun for several days, as in winter for example. Also, the cost of the Enphase battery for 10kW is over $13K at this time. Not sure I want to put that much investment into a 10kW backup right now. I can buy a 8750 inverter/ generator for less than a grand and that would get me by in the emergency grid down scenario for most instances. After buying the generator, I want to use it to potentially charge the future battery.
 
What type of solar install will you have? A backup to a grid tied system may have certain limitations. A battery backup to a micro inverter grid tied system will have different limitations. It depends on many factors.
A 7.6kW grid tied system with Enphase iq8 micro inverters. I plan to purchase an Inverter/Generator at 8750W soon. Eventually a battery backup. See post to Ampster above.
 
What are the circumstances where you think you would not have enough solar to charge the Encharge batteries? Is this a once a year scenerio or more often?
Ampster, I'm very interested in the outback Hybrid battery system. Do you know, would that work with my Enphase IQ8 microinverters?
 
Ampster, I'm very interested in the outback Hybrid battery system. Do you know, would that work with my Enphase IQ8 microinverters?
If you are referring to the Outback Mohawk inverter and battery I am sure it can AC couple with IQ8 micros. Is that what you mean by, "work with"?
If you need a NEC 2020 compliant battery then the Mohawk inverter and Mohawk battery might be a good choice. If you are referring to an Outback Radian or Skybox hybrid, they both also do AC coupling so they would work with IQ8 micros. The question turns on cost and NEC 2020 compliance.

Technically I am not sure what a hybrid battery is? Inverters are described as "hybrid" because they interact with the grid like a GT inverter and operate like an Off Grid inverter when the grid is down. The battery is just a dumb storage device that is attached to the inverter.
The Tesla Powewall is actually an inverter and battery integrated in a package that is capable of AC coupling and is NEC 2020 compliant.
In this thread I talked about my experience with the Skybox:
Post in thread 'To Grid-Tie or Not' https://diysolarforum.com/threads/to-grid-tie-or-not.39917/post-505392
 
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Is this a split phase system? L1 L2 stuff?
My nightmare is the Neutral Ground connection.
I tried to run backup generator here in Florida (Ian), and it failed.

Make sure if split phase that the N/G connection will work with your Solar, and generator.

Support is hard to find, and that Value would be the reason I would buy a system. Lots of salesman out there, but not many techs.
This is a good site to get help.
 
Well, a generator puts out 120 and possibly 240v AC (probably both on an 8000w gen) and a battery is a DC device which is going to be at a much different voltage. How best to convert AC generator power to DC battery charging depends on what else is in the system. Lots of inverters can do it natively, but not all. I don't know much about grid-tied micro inverters but from what i do know they generally don't tie to a battery and don't have any kind of DC output, so no help there. You would need a standalone battery charger that takes 120 or 240v ac from the generator, and supplies the correct 'charge profile' of voltage and current (which changes throughout the charging process) to that battery.

I looked at that Enphase battery very briefly and it sure looks Apple/Tesla-ish in the sense of.. I doubt, given the appearance of the website/products and the descriptions therein, that their products are designed to play nicely with anything that doesn't say Enphase on it. They don't even show you any connections/ports in the pics on the listing. Comes across as they just want the product to look shiny and awesome for the know-nothing guy signing a big check to the installer. Hopefully i'm wrong.

This kind of ties into how 'ac coupled battery' is sort of a marketing term to begin with. Ugh. This is not my wheelhouse, should have stayed out of Enphase discussion. :censored:
 
You would need a standalone battery charger that takes 120 or 240v ac from the generator, and supplies the correct 'charge profile' of voltage and current (which changes throughout the charging process) to that battery.

It seems like you could use an MPPT charge controller, and feed it a full-wave rectified output from a generator... maybe some capacitive, inductive filtering. Sure, the charge controller has functionality you don't need... but it gives you a readily available back door into the battery.

I've got a Radian inverter, which is very capable. But, in generator mode, it rides the house load on the generator, so all the threadiness/fluctuations come through to house loads... not nearly as smooth as riding on the inverter. I'd rather charge directly, and let the battery take the swings.

Paul, Berkeley CA PSPS MODE (Public Safety Power Shutdown)
 
Thats a question i have not learned the answer to yet: how much ‘smoothing’ do you need to do to feed rectified ac to an mppt? I once tried feeding the rectifier output of a broken psu directly to mppt and it did work until i hit some component limits on the tiny psu..:ROFLMAO: But i dont want to do any more of it until i know what the potential longer term affect on the mppt might be.

I know a bunch of people dont care and think it’s a dumb idea but the mppt on my inverters has a huge advantage compared to the onboard chargers: it just ALWAYS takes what you put to it and uses it. It doesn’t matter what else is going on. It just works. A separate charger would too but an Mppt is essentially a very fancy dc-dc battery charger sitting around doing nothing whenever the sun is down anyway. Ive got 3..
 
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Do you want full auto or can you deal with a few switches?
Stone simple is an outboard charger ...https://www.altestore.com/store/charge-controllers/ac-battery-chargers-c473/
 
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My original grid tie PV system is Enphase iQ7's. I am using a Schneider XW-Pro for my hybrid battery inverter. When the grid is down, the system works great. The iQ7's are a little finicky while running off grid on the XW-Pro output, but some of it is the old firmware in my XW-Pro, I need to get it updated, but have to shut down my system to do it. As it is, 5 of my 16 iQ7's keep going off and back on, while the other 11 kept running without a problem. Enphase thinks it could just be a very slight different in the crystal frequency that is putting it closer to the edge of what a good grid is. It is all "in spec" and has gotten me through a few power failures now. Once the XW firmware is updated, I will try an off grid test and report how that goes. The "Problem" with the Schneider XW-Pro is when the grid is up and working fine, the charging goes stupid. It literally won't start a charge cycle with only AC coupled solar while on grid. We have had to use an external controller to send it commands to make it work for "Time of Use" daily energy shifting.

That WEN generator looks very good. Sure makes my 25+ year old Coleman look like the dinosaur that it is. The XW-Pro inverter has a second input, AC2, intended for a generator. During one of my longer power outages, of course it happened after I had used up most of the power in the batteries, I connected up my old generator to try and get some charge into the system. My generator is not an inverter type, the RPM of the rotor creates the AC wave. So the frequency varies directly with engine rpm. I got the governor dialed in fairly well on a new carburetor, so it was making 62 Hz with no load, and dropped to 60 Hz at about 700 watts. It is rated to output 5,000 watts with a 10 HP engine. When I connected the generator, the XW showed it was "Qualifying AC2". After about a minute, I heard the transfer relay kick in. The inverter stopped pulling battery current and the generator took on the loads. I heard the engine grunt a little as the revs dropped and caught. The loads only needed about 500 watts, so it was no problem, but then it tried to go into charge mode. I forgot what I had the charge rate set to, but it had to be over 1,500 watts. As the XW ramped up the charge current, the generator surged as the RPM dropped too low, causing the frequency to dip too low, so the X disconnected, taking the load off the generator, so the revs shot up. IT just could not hold steady enough, and kept surging and disconnecting, every time it tried to charge. That should not be a problem with the WEN inverter generator.

My "Fix" at the time was to just pug my refrigerator into the generator, and then I also plugged a 600 watt dumb charger into the generator and had that push some power into my battery bank. So the big 5,000 watt generator was only doing about 900 watts to keep my house alive. The new carb I installed on the generator has the wrong linkage to the governor. I hope to get it working a bit better for the next time I need it. I would hate to just scrap it for a new inverter generator. I have only needed it 3 times for maybe one day each, in 20 years. Hard to justify $900 on a new generator. I would rather put that into a few more solar panels.

Evidently, the Enphase system with iQ8's and an Encharge 10 does offer a generator input now. But yeah, the Enphase battery units are stupid expensive for the capacity and power capability. But what you are paying for is the development and integration. 400bird and I have had to do our own integration to make the XW-Pro inverter play nice with our existing grid tie PV solar.
 
Do you want full auto or can you deal with a few switches?
Stone simple is an outboard charger ...https://www.altestore.com/store/charge-controllers/ac-battery-chargers-c473/
I do not see an exact solution there… My generator is 240/120 and my battery is 65 V DC. That's a tall order for off-the-shelf battery chargers, but of course a standard configuration for an MPPT. The only rub is that even a half wave rectifier on center tapped 240 will generate 170 VDC, so we're looking at pricier 300 VDC input MPPT, though there are some oddball 250 volt units out there, etc.

I heard back from one manufacturer that they no longer support this application, though they once did. I'll follow up to see if they're willing to explain what the rub was!

Paul
 
Thats a question i have not learned the answer to yet: how much ‘smoothing’ do you need to do to feed rectified ac to an mppt? I once tried feeding the rectifier output of a broken psu directly to mppt and it did work until i hit some component limits on the tiny psu..:ROFLMAO: But i dont want to do any more of it until i know what the potential longer term affect on the mppt might be.

I know a bunch of people dont care and think it’s a dumb idea but the mppt on my inverters has a huge advantage compared to the onboard chargers: it just ALWAYS takes what you put to it and uses it. It doesn’t matter what else is going on. It just works. A separate charger would too but an Mppt is essentially a very fancy dc-dc battery charger sitting around doing nothing whenever the sun is down anyway. Ive got 3..
Would be nice if someone would make a generator injector to charge AC coupled batteries. So you could set the load on the generator. Would be easy for enphase to design.
 
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