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

[Mattb4]

... 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)

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.

 

[sunshine_eggo]

What? All AIO inverters (like Sol-Ark) can’t invert and charge at same time?

Yep. Neither can my Victrons.

 

[SparkyJJO]

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.

 

[sunshine_eggo]

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.

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]

Can't run the generator into my inverter's "GEN" input due to only being a 120V and the inverter requires 240V.

Seems like all you need is a simple 1:2 transformer

 

[SparkyJJO]

Seems like all you need is a simple 1:2 transformer

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.

 

[Danke]

Yep. Neither can my Victrons.

You may want to contact the engineers at Sol-Ark and let them know that.

 

[sunshine_eggo]

You may want to contact the engineers at Sol-Ark and let them know that.

View attachment 134788

The inverter isn't charging the battery. The MPPT is.

 

[Leeds]

You may want to contact the engineers at Sol-Ark and let them know that.

I fixed that drawing for you (attached below).

Why it showed lightbulbs generating energy is beyond me!

 

[Vigo]

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!)

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.

 

[SparkyJJO]

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.

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]

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.

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.

 

[SparkyJJO]

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.

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.

 

[Vigo]

Are those power supplies putting out 48V and just supplementing, basically, or are they putting out enough voltage to actually charge the LFP bank?

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

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.

 

[timselectric]

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.

 

[TorC]

@timselectric Looks like max output 3050W at 120VAC in. Given efficiency, I'd guess that's the 120VAC, 28A input mentioned. Would be nice if it had a <20A input limit available, as 120V, 30A circuits are rare.

ETA: Ah, nice. Manual says it does have an output current selection, likely by 1A increments or better, though I don't see a specification.

 

[Vigo]

It does, sort of.

100A max charging current for quick charging rates - adjustable from 0A-100A.

You'd have to do a single instance of Watt's Law to get in the ballpark and then experiment from there.

 

[timselectric]

@timselectric Looks like max output 3050W at 120VAC in. Given efficiency, I'd guess that's the 120VAC, 28A input mentioned. Would be nice if it had a <20A input limit available, as 120V, 30A circuits are rare.

ETA: Ah, nice. Manual says it does have an output current selection, likely by 1A increments or better, though I don't see a specification.

Yes it is adjustable. It's a Voltronics inverter/charger board. With display in a new case.

 

[Mithril]

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.

My AIO can't do that, and from what I've read it's not as common as one would think/hope.

There's also the issue that many generators don't have the cleanest power, even inverter ones.

 

[Mithril]

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.

Appreciate the far more on topic reply!

Questions for you, what specific voltage are you running? 48V exactly? Are you charging the batteries while doing this? Have you had issues with the DC supplies supplying more amps than they can handle steady state (or are your supplies also CC so they self regulate)
Still reading through the flood of replies so sorry if I'm asking twice

And yeah, my two big things are doing this with as much of what I have already *if* possible (I feel like the people jumping to "just buy all this stuff, don't even bother" might be on the wrong subforum if not the wrong site I say this is good sport, please do not flame :D ), and what the actual requirements are. If all of us could afford whole house setups with mult-day battery capacity and whole house generators I'm sure most of us would :D Some day "buy another AIO as a spare and use it as your charger too" might make sense, but not today. Even the new EG4 dedicated charger is a bit overkill for me *right now*. Plus no reviews and the manual is (as typical for Eg4) light on details such as exact charging rates (not just min-max)

 

[TorC]

Is your AIO capable of selling power to the grid as well as running as an off-grid? If not, then most or all such do not have grid-support option, which means a generator must supply the entire load plus any charge power. Grid support is predicated on the inverter being able to synchronize power output with the incoming power while inverting. This is needed for grid tie; for an off-grid only inverter it's added complexity usually sidestepped by a transfer relay.

BTW, "grid support" specifically may be a proprietary marketing name, so devices without that name may still have the relevant setting.

Any voltage regulated power supply will act as a CC/CV within its parameters. That means, voltage (hopefully) as specified on the nameplate, and amperage limited to nominal output. If you don't need full speed charge to max power, or can watch for hitting peak voltage, as long as the voltage is regulated to a safe level for your batteries it'll work. Once the batteries approach as full as the power supply can get them the current will drop off.

Whether the power supply will be happy running flat out for an extended time during bulk charge is another question. Devices sold as chargers should have thermal management to handle this. Same for anything sold as a general power supply. A "power supply for X device" however, has a somewhat higher chance of relying on average draw being low enough to get away with less thermal dissipation.

 

[Mithril]

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.

This is sort of what I'm looking to do, just not at $400. Also, at a $400 pricepoint for just a charger I would also expect good efficiency, good adjustability (resolution of Amps) and ability to adjust "supply side" (set it by watts in). When I looked earlier no one had yet done a youtube/website review.

 

[Mithril]

Yes it is adjustable. It's a Voltronics inverter/charger board. With display in a new case.

Oh nice that someone knows the internals! :D Any idea as to just how adjustable it is? Basically, does it have 1A step in the lower ranges?

 

[Vigo]

So I have 4x “48v 10a” power supplies, ostensibly 500w each. 3 of them are ‘fixed’ 48v with just a trim pot and wont go past 49.x volts, one is a 0-48 model which will go almost to 53v. Also have a 60v 7ish amp i run off my 12v system into the 48v sometimes, and 4x 100w 54.6v little charge cords. All this feeds into the same set of bus bars which is hooked to my 48v system.

The reason for the mix of voltages etc is because if you use a voltage you actually expect your pack to reach there is considerable variability of how much power is consumed and delivered between each side of things. The little 100w 54v units will never bring my system to 54 volts, so they stay ~100w for as long as they’re on. I usually use those to feed from the ~5kwh lifepo4 120v system in my Rv into my 48 house pack overnight to ‘shift cycles’ from the fla to the lifepo4, and i bought 4x 100w instead of a 400w because it let me experiment in 100w increments. Ive seen those as low as $8/ea on amazon. The 60v ~7a (~$30) is likewise ‘always’ 400w and runs off a 12v inverter hooked to my silly 12v bus of cars and tractors parked outside my house. ? Im essentially using voltages as a cheap hack for not buying things with adjustable current limiting.

The 49v psu’s (30-something $) may actually push the system to 49 and when hooked to my generator that’s ideal because i dont actually want my generator use to get ‘even more ridiculously inefficient’ by trying to actually charge my large FLA pack at FLA charging efficiencies, off gasoline. My thinking is that if you are using the power as you make it, you are not subjecting that power to an extra conversion/efficiency loss by actually trying to put it in your battery before you use it. It is just going on the 48v bus and ‘offsetting’ battery consumption by however much it can supply, and if the load drops off to the point that the system raises to ~49 the psu’s ‘idle’ at a few watts each and my generator essentially ‘idles’ as well, although this is a cheap non-inverter gen so its still out there churning 3600rpm at no load, sadly.

If i turn them all on at once (3 switches) it’s ~3kw into my 48v system and doesnt require me to do anything on the 48v side, change any settings flip any disconnects etc. Ac bypass irritates me on my Growatts so im avoiding it with this setup. I used to use a 5kw gas generator into growatts and it was too loud, too thirsty, and required me to spend too much time thinking about what i was doing on the loads side and wouldn’t actually charge batteries anyway unless i didnt plan to do a single thing that would push the 5k gen past its comfort zone. It was something that required me to be aware of it basically the whole time it was happening. On the other hand, between a 3500w generator running at less than max making considerably less noise and never ever overloading, 5kwh in my rv and untold kwh in the >12+ vehicles hooked up outside which would also mostly charge that system at 600-700w each if i wanted a car engine running, I just dont realy have to think about those systems when they’re on. The 12v ‘feeds’ operate at basically fixed rates that i can ballpark kwh with a couple seconds of mental math and then ignore for that many hours. The generator feed basically only comes up if i want to run the clothes drier with no sun, in which case i turn it off when im done and am fairly convinced i havent used much more gas than i really had to because if it went above 49v it just ‘idled’.

Its just one big science experiment done incrementaly with the cheapest stuff i could get my hands on as ‘proof of concept’ of my crazy thoughts, and now that it’s proven it may get ‘upgraded’ with better components if it ever breaks. But, my experience so far is that if a fan doesnt fail (which they do, cheap stuff) and the units are oriented and spaced for airflow they do seem to be able to run at max output for long periods. The outputs are hooked to the 48v system 24/7 so no damage from ‘pre-charge’ issues and i suspect that softens the inrush on the AC side as well. The ones that are hooked to gen are plugged in before its ever running and i suspect the 0-3600rpm runup softens the inrush there as well. So i think they are being treated better than some of the early 12v 30a models which i did kill parts on but mostly seemed to come down to ‘connections etiquette’ of how they were hooked or unhooked from power.

So there’s an essay.. lol

 

[timselectric]

Oh nice that someone knows the internals! :D Any idea as to just how adjustable it is? Basically, does it have 1A step in the lower ranges?

It will have the same adjustability as a Voltronics AIO's SCC. I can't check mine at the moment.