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DIY or Buy? Charging from generator on dark days or grid down. (48v system)

schmism said:
Another option is to DIY mod some server power supplies (see link in sig) and either direct charge or run to the PV input and have them pretend to be solar. This option allows you to 1) not have to worry about frequency stablity for the AIO's to "lock on" to. 2) charge at low wattage rates which some AIO dont like if you go AC route.

So you could use a inverter style 1500w generator instead of having to run a 5-8kw one on the AC side.
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I have thought about modding/using PC supplies. I have a small stack of them. This is a 48V system however so I'd need like 3-4 identical PSUs (I don't trust track spacing to push them beyond double, plus if you go too much above 12V you're replacing caps etc. I've also though about using DC-DC boost but then you've got chained efficiency etc.

I'm going to read though the link in your sig and see what new info I learn :)


Edit: The other thing that comes up as an idea is rectified AC into MPPT input. My understanding is that is a Bad Idea(tm).
 
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AFAIK, all hybrid inverters (meaning grid-tie or off-grid capable) can run in a "grid support" mode, which will let you program in a max grid/generator input amperage. If you have one of these, then you're done. Set this as appropriate for your generator.

As @sunshine_eggo notes, it still can't charge and invert at the same time, but it will seamlessly switch from inverting to charging whenever loads are below what you permit it to draw from the generator.
 
The title doesn't say that this system has an AIO but there are a lot of posts trying to make such a system work.

A normal system would not have those issues. In a component-based system all you need to do is wire the generator go-signal through the courtesy output on the charge controller and drive a 48v charger directly into the battery bus.
 
Similar concern for my system, especially since the power outages we have been having lately are all poor sun days. Signature Solar now has an adjustable 48V/100A charger at $400 that looks really compelling to me.
 
Mithril said:
... a small 2kw gen or so running a ~$100 AC-DC supply seems far more reasonable as a supplement to solar for "grid-down" (storm, drunk driver hits a pole, etc)
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A couple of weeks back I lost utility power for a day and a 1/2 at my place following a Winter storm. I use my Honda 2800w inverter generator (cost me ~$1000) for about 6 hours to carry house loads (selected by me to run) and also charge the batteries through my AIO at a rate of 5a, 10a, finally 15a for the last hour since my other load needs were less. This required me to alter the max charge rate setting from Utility on the AIO. Teh genrator was turned off for the night and my batteries carried me til morning when the sun came out and charging happened.

One does not need to be elaborate with how they accomplish tasks or spend a fortune on overly complex auto response systems. The power goes out and you walk outdoors to the generator pull the cord until it starts. Hookup the plug to the manual transfer switch. Throw the switch and off you go. Watch loading to not exceed the supply. All this done with this marvelous device called your mind.
 
I have a 120V 3500W inverter generator. If I was relying on my solar and batteries due to a bad grid down situation (bad ice storm or w/e, don't think I'd be able to survive an apocalypse lol) and say it is winter with bad weather, I currently have to switch my most critical loads over to generator only. This is ok, but I would like to be able to just charge the batteries with the generator at times too (get through the night without it running, for example) and that way I could also not have to switch loads around. I've considered a simple 48V LFP charger. Not sure what the sweet spot for my generator's output is. It is capable of 3500W/4250W peak but I suspect ideal is lower than full bore.

Can't run the generator into my inverter's "GEN" input due to only being a 120V and the inverter requires 240V.
 
SparkyJJO said:
I have a 120V 3500W inverter generator. If I was relying on my solar and batteries due to a bad grid down situation (bad ice storm or w/e, don't think I'd be able to survive an apocalypse lol) and say it is winter with bad weather, I currently have to switch my most critical loads over to generator only. This is ok, but I would like to be able to just charge the batteries with the generator at times too (get through the night without it running, for example) and that way I could also not have to switch loads around. I've considered a simple 48V LFP charger. Not sure what the sweet spot for my generator's output is. It is capable of 3500W/4250W peak but I suspect ideal is lower than full bore.

Can't run the generator into my inverter's "GEN" input due to only being a 120V and the inverter requires 240V.
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For most generators, max efficiency is at max power. Sweet spot for economy and durability is 70-80% rated. For efficiency, this may not hold true for inverter generators as they tend to be more efficient over over a wider range of partial power, but it should hold true for max durability.
 
Leeds said:
Seems like all you need is a simple 1:2 transformer
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I have one but it is only 1500VA so that would leave over half my gen capacity behind. Maybe a bigger one would be cheaper than a dedicated 120V input LFP charger though.
 
So to comment on the OP's overall scheme.. I'm doing it?!

I have experimented a bunch with cheap meanwell knockoff PSUs hooked directly to batteries and i currently have a pile of cheap PSUs mounted to a wall in my inverter closet which can do 55amps @ 48v, and i power these from a 3500w generator. I actually have a little more than that, but that's what's hooked to the generator.

With that setup, im able to run my electric clothes drier, which is 4500w, from a generator that could not run it, using my inverters/batteries to bridge the gap and i can do this on a cloudy 'no-solar' day because even though ~2600w of PSU is not 4500w of drier, i always have enough battery to get to the point that the drier hits temp and starts 'cycling' its heating element, at which point yes 2600w is more than enough on average.

So i fully agree with the intent of this thread and while my setup is ugly and probably inefficient it is totally possible to do it.

Rectified 60Hz AC into an MPPT is anything from "unlikely to work" to "will damage/destroy something" (not many people seem willing to try, understandably!)
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Oh, and im getting REAL close to trying it on the kW scale. I'm getting a little more comfortable that it's not a suicide mission. I WILL do it.
 
Vigo said:
So to comment on the OP's overall scheme.. I'm doing it?!

I have experimented a bunch with cheap meanwell knockoff PSUs hooked directly to batteries and i currently have a pile of cheap PSUs mounted to a wall in my inverter closet which can do 55amps @ 48v, and i power these from a 3500w generator. I actually have a little more than that, but that's what's hooked to the generator.

With that setup, im able to run my electric clothes drier, which is 4500w, from a generator that could not run it, using my inverters/batteries to bridge the gap and i can do this on a cloudy 'no-solar' day because even though ~2600w of PSU is not 4500w of drier, i always have enough battery to get to the point that the drier hits temp and starts 'cycling' its heating element, at which point yes 2600w is more than enough on average.

So i fully agree with the intent of this thread and while my setup is ugly and probably inefficient it is totally possible to do it.


Oh, and im getting REAL close to trying it on the kW scale. I'm getting a little more comfortable that it's not a suicide mission. I WILL do it.
Click to expand...

Are those power supplies putting out 48V and just supplementing, basically, or are they putting out enough voltage to actually charge the LFP bank?
 
Shimmy said:
Similar concern for my system, especially since the power outages we have been having lately are all poor sun days. Signature Solar now has an adjustable 48V/100A charger at $400 that looks really compelling to me.
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This is the charger: https://signaturesolar.com/eg4-chargeverter-battery-charger-48v-100a-5120w-output-240/120v-input

I prefer this approach over a more manual process as it simplifies (more idiot-proof) everything and allows for a single-cord connection to the portable generator.
 
Shimmy said:
This is the charger: https://signaturesolar.com/eg4-chargeverter-battery-charger-48v-100a-5120w-output-240/120v-input

I prefer this approach over a more manual process as it simplifies (more idiot-proof) everything and allows for a single-cord connection to the portable generator.
Click to expand...
That looks perfect. I have an inverter generator so clean power isn't an issue but I have not found a good 120V inpit LFP charger with any sort of decent output power for a decent price yet.
 
Are those power supplies putting out 48V and just supplementing, basically, or are they putting out enough voltage to actually charge the LFP bank?
Click to expand...
So with these cheap power supplies their actual max voltage they can be adjusted to varies, but in my case i can only do the full ~55A into something around ~48.5v or lower. It's actually an FLA pack in my case so ~48v correlates with the generic 'stay above 50% SOC for best cycle life' thing on FLA. I generally don't run the generator unless my FLA would be going below 48v for a longish period and i don't expect the generator to 'recharge' the FLA per se, just allow me to consume more or less normally on a poor solar day without dropping the pack to very low voltage. Because it's not 'charging' per se that means the generator fuel consumption also tapers off 'automatically' if the system voltage rises much above 49v. I've tested that these little power supplies only use 2-6w 'idle consumption' or around there. If i had an inverter generator powering them (i do have one, but it's a ~1700w) the generator would 'idle' when the power supplies 'idle', but as is if the system goes above 49v for a long enough time and i notice the generator is running at no load i just go shut it off.

Because of where i live i don't really go long periods between 'fully charging' the pack off solar, so i don't really need my generator setup to do that. If i needed to (i've done it once, probably took $15-20 in gas) i would have to route the generator through the AC input of my Growatts and let them charge while in AC bypass. But my hatred for that approach is why i started doing this 'double conversion' generator power thing in the first place!

This is the charger: https://signaturesolar.com/eg4-chargeverter-battery-charger-48v-100a-5120w-output-240/120v-input
Click to expand...
That is nice!! There wasn't anything like that that i found at a reasonable price point when i started testing this concept with cheap power supplies. Even their smaller 18a model I would have ended up with 3 of them and that starts to get both expensive and inelegant. Preferably I would have done as Timselectric has and just bought a full 3rd (in my case) Growatt AIO and simply use it as a charger in this scenario, but my PSU collection is way under that price point and does work. I will do that eventually, but my PSU collection has yet to give me enough of a headache to spring for the extra ~$800 Growatt. That $400 charger does look like a really good option for a lot of people, especially because it's a name you could potentially get some service/support/warranty coverage from. If one didn't care about that there are some 48v AIOs you can get at barely over $500 and just use them as a charger if one wanted to.
 
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Yup I seen that they were coming soon.
I can't believe it took this long for someone to think of it. And it is very affordable.
Weird naming, but I kinda get why it was chosen.
Of course you need to connect it to 240v to get the full output. But still a good price for a 120v 40a charger. (80% continuous draw from a 120v/20a circuit)
I'll probably add one to my list.
 
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