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

My current key question really boils down to this:

Given a CV power supply where the maximum AMPs is less then 0.5C of any single lifepo4 battery and the ability to set the voltage to tenths of a volt; can you safely charge to around 80-90% SOC?

Based on what I have read this should be "yes" assuming you A) Select the correct voltage (insert yet another "fun" debate on correct charging voltage, that I will short circuit (pun intended) by not remotely attempting to reach 100% SOC or top balance AT ALL when charging this way) B) make sure the charger doesn't stay on longer than needed C) make sure the charger doesn't self immolate by going over it's actual ability due to LifePo4's low resistance.
 
The short answer to your question is "Yes."

Longer answer, that's basically all your SCC is anyway, as far as your batteries are concerned: a power supply regulated to the maximum safe charging voltage, and current limited to a safe charge current, which you just did by selecting a power supply that can't supply more current than the battery can safely take.
 
My current key question really boils down to this:

Given a CV power supply where the maximum AMPs is less then 0.5C of any single lifepo4 battery and the ability to set the voltage to tenths of a volt; can you safely charge to around 80-90% SOC?

Based on what I have read this should be "yes" assuming you A) Select the correct voltage (insert yet another "fun" debate on correct charging voltage, that I will short circuit (pun intended) by not remotely attempting to reach 100% SOC or top balance AT ALL when charging this way) B) make sure the charger doesn't stay on longer than needed C) make sure the charger doesn't self immolate by going over it's actual ability due to LifePo4's low resistance.
Yes, it will be selectable, within its nominal range.
Same as any other SCC.
 
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
That's a lot of good info there. I think my concern trying to replicate is that LifePo4 has such low resistance that without CC many power supplies will go over their rated Amps (or shutdown). One of the "hacks" I saw suggested is to add resistance (say a 0.05 Ohm power resistor) tuned to regulate the input power.

I'm also very much in the tinkering stages of things, which is why buying a whole other generator, or another AIO, etc just doesn't make sense *for me*. If I had a larger system, and/or was fully off grid that would change things IMHO.
 
The short answer to your question is "Yes."

Longer answer, that's basically all your SCC is anyway, as far as your batteries are concerned: a power supply regulated to the maximum safe charging voltage, and current limited to a safe charge current, which you just did by selecting a power supply that can't supply more current than the battery can safely take.
Ok, so now onto a perhaps spicier part... For a 16s LifePo4 if I am shopping for a AC-DC supply to be used as discussed, what should I look for as a voltage? Basically "I should have a Maximum at least X volts or it will never charge" and "it should have a minumum of no more then Y volts or you risk damage" (I know it feels a bit backwards to say it that way...)

Another way to put it, lets say you have an adjustable power supply what range MUST it include to be used for this, noting that I don't need or care about hitting 100% SOC, in the range of 80-90% would be fine. Obviously the ideal supply would have an adjustment range of something like 48-60V, but what is sort of the "minimum feature set" range wise?
 
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From what i have recently learned, it seems like if you actually want to be safe ‘ignoring’ an input to lifepo4 ‘indefinitely’ it must be below 3.37v/cell. That is a crappy voltage for charging because it will charge slowly unless the lifepo4 is at very low SoC and will take an eternity to “fully” charge, BUT you can supposedly ignore it an forget about it.

But that’s fine! Because i’m not trying to ‘charge’ with my system, im trying to ‘avoid discharging beyond a certain point’. I have described my contraption as more of a ‘voltage backstop’ than a charger. When i leave the 100w supplies on overnight it does do some superficial charging according to my voltage, but im dubious of it being ‘real’ in terms of kwh because it’s technically like .01C on my 3000lb of used FLA and ive heard that below a certain minimum c rate its not doing what you think it is.

So yes i think it is possible to have some psus running long periods or 24/7 that is far enough below your fully charged voltage that they wont cook lifepo4 and other than ‘idle consumption’ can be ignored. Only caveat is your system has to actually drop to that voltage before they do anything. But yeah im doing that and i like it and in my mind it works.
 
About what Vigo said. If you want to slow charge, it should be 3.37-3.40V/cell=53.92-54.4V. This should also get somewhere approaching a full charge about as the current starts to really trail off. Above that to about 3.5V/cell=56V will maintain current, and thus draw on a generator probably all the way up to the knee, which is pretty close to max possible charge.
 
Yeah, if the people who wrote the manual can't tell up from down I can only imagine how much they butcher the written word!
I’m not too happy with their tech support so far. I think they must’ve hired a lot of new people. They don’t seem to have thorough knowledge. I’m not sure I can trust the answers they give me.
 
Read the subject of this thread.
What does that have to do with the price of tea in China? From the very first post and I quote: ”Many (most?) AIO can't charge and invert at the same time.”

Your response was all of them can’t.
 
What does that have to do with the price of tea in China? From the very first post and I quote: ”Many (most?) AIO can't charge and invert at the same time.”

Your response was all of them can’t.

You don't get to ignore the context of the information.

Charging from generator​


Please show me an AiO that can both charge from generator and invert.
 
substitute above lined out text with below:

"ALL AiO and ALL inverter/chargers..."
I have no horse in this race and I'm not here to start an argument or debate, but this just isn't true.

Victron Multiplus and Quattro units can absolutely charge and invert at the same time. This is a standard feature and they're absolutely "inverter/chargers".
 
Victron Multiplus and Quattro units can absolutely charge and invert at the same time. This is a standard feature and they're absolutely "inverter/chargers".

How? Where would the energy come from? If it's charging the battery, that means there is more AC power entering the system than is being consumed by loads, and therefore it can't invert from battery without letting out magic smoke. If there's less AC power entering the system than loads are consuming, then it will invert from battery — but there's no power available to charge the battery.

Since thinking in numbers can help, try these:

Generator supplies 2kW, loads consume 1kW: Inverter/charger operates in charge mode, sending the remaining 1kW to batteries. Not inverting
Generator supplies 2kW, loads consume 2kW: Inverter/charger passes 2kW through to loads, sits quiescent otherwise. Not inverting.
Generator supplies 2kW, loads consume 3kW: Inverter/charger passes 2kW to loads, inverts 1kW from battery to not overload generator. This is the only inverting state, and it's not charging.

A simple matter of power flows. It can only do one at a time, because to do both at once would be nonsensical at best, and magic smoke-emitting at worst.

This applies to *all* inverter/chargers and all inverter/charger segments of AIOs. AFAIK, all grid-tie capable inverter/chargers can operate in all three modes. Most (many?) off-grid only inverter/chargers can only operate in the first two.
 
How? Where would the energy come from? If it's charging the battery, that means there is more AC power entering the system than is being consumed by loads, and therefore it can't invert from battery without letting out magic smoke. If there's less AC power entering the system than loads are consuming, then it will invert from battery — but there's no power available to charge the battery.

A simple matter of power flows.
Correct. The OP wants to use a generator to charge the batteries and also use the batteries to invert to AC.

It is nonsensical as any excess power from the generator could just have gone directly to AC and not through (or to) the batteries to be inverted.
 
I have no horse in this race and I'm not here to start an argument or debate, but this just isn't true.

Victron Multiplus and Quattro units can absolutely charge and invert at the same time. This is a standard feature and they're absolutely "inverter/chargers".

I own two Quattros and can tell you this is is completely false.

They can both invert and charge... just not at the same time.
 
I cannot think of a time that a unit would be trying to do both at the same time. Either you're pulling from the batteries (inverting) or you're charging the batteries (charging).

If you're using batteries to supplement a load that the AC passthrough cannot support, you're clearly not charging them from the AC. And if you're running on solar, AFAIK in most cases the MPPT is vharging the batteries while the inverter is running the loads.
 
I cannot think of a time that a unit would be trying to do both at the same time. Either you're pulling from the batteries (inverting) or you're charging the batteries (charging).

If you're using batteries to supplement a load that the AC passthrough cannot support, you're clearly not charging them from the AC. And if you're running on solar, AFAIK in most cases the MPPT is vharging the batteries while the inverter is running the loads.
I suppose I’m saying the same thing.

The victron units are absolutely capable of accepting a generator input and, “intelligently routing that power as needed in real time”. If there is no major AC demand, they’re charging, as AC demand ramps up they divert charging power to meet the load, if load exceeds generator input they will pull from batteries and assist.

All of which is programmable. That said, I guess what I’m saying is they do what needs to be done, far smarter than picking one or the other.
 
It is nonsensical as any excess power from the generator could just have gone directly to AC and not through (or to) the batteries to be inverted.
It is not nonsensical because it divorces the power limit of your load side from the power limit of your generator, and protects all your loads from any hiccups in the AC created by your generator. For this convenience, you 'pay' in extra conversion losses.

Expensive high-stakes UPS's do double conversion by default. Automatic transfer switches often have timers and other conditions before transitioning your loads back to 'grid' because of the large possibility that that AC source is worse than the other one you have. This whole concept is pretty standard and well-established in industry. It is preferable for me to let my 10kw of inverters make up to 10kw of relatively clean AC at a moment's notice, than for me to run 10kw or 20-friggin-thousand-watts of generator ('conventional wisdom' 2x gen sizing) when i can't or don't want to charge my battery bank at 10-20kw to begin with, and if i put a 10kw or 20kw load on it too fast it will stall anyway because it has to mechanically build up to its max power over a MUCH longer time frame than an inverter going from 10w to 10,000w faster than you can snap your fingers. Pure sine inverters are better at making AC than generators are (otherwise they wouldn't put inverters on generators) so.. let them!

My generator feed only has to average more than i consume, to charge the system. It only has to offset my total draw, if that's all im trying to do. But i don't want it directly powering all my AC loads because even in the best case it is irksome. I'd rather pay the extra conversion losses and only worry about what happens on average, over time.
 
My thoughts are that if paired correctly. A generator and charger can be set up for very good fuel efficiency. Even with the double conversion losses.
 
@Vigo Sure, you can configure for that usecase, but AFAIK, all such double conversion UPSs use *two* separate stages. First a charger stage that produces DC, and second an inverter stage to produce AC. Each one can still only do one job at a time. To my knowledge, there is nothing sold as a whole house/RV/etc. inverter that does that. A hybrid inverter is already designed to synchronize and invert to the grid/gen input line, so they can just do that.

If there were an inverter sold that did double conversion, I'm sure it would be a major bullet point on the sales sheet, probably talking about how it could make use of very AC dirty power and still produce a clean, accurate 60Hz output.

That said, in a major stationary system, you can easily set up your own double-conversion just by installing a separate charger, which has been discussed in this thread, and which has merit in various usecases.
 
About what Vigo said. If you want to slow charge, it should be 3.37-3.40V/cell=53.92-54.4V. This should also get somewhere approaching a full charge about as the current starts to really trail off. Above that to about 3.5V/cell=56V will maintain current, and thus draw on a generator probably all the way up to the knee, which is pretty close to max possible charge.

Considering I've got control over when the generator runs (and that it wouldn't be all that hard to do a microcontroller as well) I think that's what I would aim for. It looks like that beefy 100A chargeverter targets ~57V. But my needs are not "get to 100% SOC", hitting 80-90% would be fine
 

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