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48V Charger Alongside Inverter?

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smdl

New Member
Joined
Jan 8, 2022
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34
Hi, folks.

I'm in the process of building my first system, and while I have done a lot of reading on the subject, I am still working through a few remaining questions. Apologies if my lack of knowledge shows.

A few details:
  • My use case is basically a big UPS for my home as I have sump pumps that I want to make sure keep running (and it would be nice to have other comforts, too). No solar initially -- just a way to store grid power.
  • The all-in-one unit is a Growatt SPF 6000T
  • The battery is a 48V 16S EVE LF280K in a Seplos Mason DIY kit with Seplos BMS. I'll likely add a second one in parallel sometime soon.
  • I have an 8000/10000 generator to provide auxiliary charging during extended outages
My question relates to how best to bring the generator into the mix, when needed. If I connect it to the grid input (as the Growatt manual shows), the inverter will go into bypass, and the generator will be attempting to support both the charging load, and any other loads that might be present at the time. Some of those loads will be significant, including two separate sump pumps, a well pump, and whatever else might be running on the sub-panel at that time. So, as an alternative, I thought it might make sense to add a separate 48V charger in parallel to the Growatt unit, and connect the generator output to that. This would mean that, during extended outages, I could simply start (or auto-start) the generator, and it would feed the standalone charger to recharge the batteries (or at least extend the run time). This would avoid any issues of potentially overloading the generator, and it would also seem to be a much more efficient use of the generator with a consistent charge load vs. all the ups and downs associated with all of the other loads.

Before I do this, though, I just want to make sure that I won't be causing myself any issues. Any thoughts on the subject would be very much appreciated!

If it does make sense to do this, I'd welcome any recommendations on 48V chargers. I am aware of the AIMS unit, but have heard a number of concerns expressed (especially about noise). I've seen a few recommendations of the Dakota Lithium unit, and a number of good reviews of the Mean Well units like this:


Are the any other chargers that I should be considering?

Thanks in advance for any insight!

Cheers,
Shaun
 
I highly doubt the numbers make practical sense And the concept itself doesn’t make a lot of sense to me. You WANT the generator to directly support the loads as that is the most direct and efficient way to run them if you have that source available. Even if you went through a separate charger the generator is still indirectly going to support the loads first before the batteries get charged. Just because you go a roundabout way doesn’t magically create power.

The generator is 8-10kw and the inverter is 6kw so if you overload the generator you would have also overload the inverter if it was powering the same loads?

I don’t know anything about growatt but Victron inverters have AC input current limit settings and power assist which allows you to take full advantage of the genset output but also not overload it. It helps with the peaks and valleys and startup loads etc. If your inverter offers these features that’s what you wanna do.

That charger you linked is 18a so at 48v nominal which is 864 watts. If this is all that you connected to your generator you would be wasting about 90% of genset potential output, Your loads are likely greater than 864w so your battery would not charge And in fact would keep discharging until BMS shut down.

If you were gonna do this we need a charger that’s at least same Kva as the inverter but if loads are pushing toward the capacity of the inverter you really need a charger larger than that as the charger would have to support the 6KW loads going through the inverter AND have enough access to actually charge the battery. If it exists this would be a very expensive charger.

I did not consider PV contribution in the above.
 
That's why you need to match the charger to the generator sweet spot.
But if the generator can cover the loads and charge the batteries, that would be more efficient. Avoiding the efficiency losses from the double conversion.
But the fluctuating loads make it hard to get the settings right.
I'm still in favor of the stand alone charger.
The best option would be a 48v DC generator.
 
Many cheap HF AIO inverters do not support load shaving. This means you manually have to manage AC loads and battery charging to avoid overloading generator.

An inverter with load shaving can limit AC input maximum current demand, supplementing AC output with inverter battery power and automatically backing down charging consumption when higher priority AC output load demand happens, to keep AC input current below maximum set by user.

Load shaving requires a near instant ability for inverter to switch power flow direction. This is hard for a high frequency inverter to do. SolArk and Deye HF inverters have a large bank of high voltage DC capacitors to provide the power while the inverter switches flow direction.

A low frequency inverter is inherently bi-directional, so you are more likely to find load shaving capability on LF inverters.
 
Last edited:
HI, folks.

Thanks for all the great feedback. I realize that there are multiple ways to look at this, which is why I wanted to get some insight from those with more experience. Here are a few additional thoughts:

  • As Tim mentions, the concern I have with using the generator to support the inverter and loads directly is that the load is highly variable due to the three pumps (2 x 1/3 HP sump, 1 x 1 HP well pump) in service. The generator is 8K with 10K surge capacity, while the inverter is 6K with 18K surge capacity.
  • I agree that the charger won't use much of the generator capacity, which is inefficient. However, as a further level of redundancy, I am planning to use a manual transfer switch to be able to cut the sub-panel over to the generator directly in the event of an inverter failure. So, the extra capacity of the generator would be helpful, at that point, to allow the critical loads to keep running while also charging the batteries. Under these circumstances, I would naturally need to turn off some of the breakers to avoid overloading the generator with the surge load. For example, I would probably shut off the well pump, as the cushion tank provides enough water pressure to last for hours (if used sparingly). Every once in a while, I could cycle the sump pumps off, and well pump on, to refill the tank.
  • Thanks for the info on load shaving, as I can see that this could avoid the generator overload issue when the inverter is supporting the loads and recharging the batteries at 60A. If the Growatt unit supports this, I wouldn't need a separate charger at all. I'll take a look at this more closely to figure out if this is supported.
  • I agree that a DC generator would be nice, but I just bought the one I have (short notice when my Generac system failed during a cold snap and power outage!) and really want to avoid having to buy another one. Most of the outages in our area are fairly brief, so I think that the inverter will likely meet almost all of our needs, with the generator only being used for another level of backup. Also, using an AC generator allows me the option to support the critical AC loads directly in the event of an inverter failure (as described above). Trying to keep my options as flexible as possible.
  • I suppose that if it does make sense to use a separate charger, I could look at something with more capacity than the one I listed originally. This would use a bit more of the generator capacity. Maybe something like this:

From the feedback so far, it doesn't seem like there is anything harmful about running a separate charger from the generator -- it's just that this might not be the most efficient thing to do. Am I understanding this correctly?

Again, I really appreciate the info so far. It's really helpful to have experienced opinions when I'm still learning.

Cheers,
Shaun
 
Last edited:
smdl said:
HI, folks.

Thanks for all the great feedback. I realize that there are multiple ways to look at this, which is why I wanted to get some insight from those with more experience. Here are a few additional thoughts:

  • As Tim mentions, the concern I have with using the generator to support the inverter and loads directly is that the load is highly variable due to the three pumps (2 x 1/3 HP sump, 1 x 1 HP well pump) in service. The generator is 8K with 10K surge capacity, while the inverter is 6K with 18K surge capacity.
  • I agree that the charger won't use much of the generator capacity, which is inefficient. However, as a further level of redundancy, I am planning to use a manual transfer switch to be able to cut the sub-panel over to the generator directly in the event of an inverter failure. So, the extra capacity of the generator would be helpful, at that point, to allow the critical loads to keep running while also charging the batteries. Under these circumstances, I would naturally need to turn off some of the breakers to avoid overloading the generator with the surge load. For example, I would probably shut off the well pump, as the cushion tank provides enough water pressure to last for hours (if used sparingly). Every once in a while, I could cycle the sump pumps off, and well pump on, to refill the tank.
  • Thanks for the info on load shaving, as I can see that this could avoid the generator overload issue when the inverter is supporting the loads and recharging the batteries at 60A. If the Growatt unit supports this, I wouldn't need a separate charger at all. I'll take a look at this more closely to figure out if this is supported.
  • I agree that a DC generator would be nice, but I just bought the one I have (short notice when my Generac system failed during a cold snap and power outage!) and really want to avoid having to buy another one. Most of the outages in our area are fairly brief, so I think that the inverter will likely meet almost all of our needs, with the generator only being used for another level of backup. Also, using an AC generator allows me the option to support the critical AC loads directly in the event of an inverter failure (as described above). Trying to keep my options as flexible as possible.
  • I suppose that if it does make sense to use a separate charger, I could look at something with more capacity than the one I listed originally. This would use a bit more of the generator capacity. Maybe something like this:

From the feedback so far, it doesn't seem like there is anything harmful about running a separate generator -- it's just that this might not be the most efficient thing to do. Am I understanding this correctly?

Again, I really appreciate the info so far. It's really helpful to have experienced opinions when I'm still learning.

Cheers,
Shaun
Click to expand...
Yup, you seem to have a good handle on what you need. But it is always good to bounce ideas off of each other, to get different perspectives.
 
smdl said:
Hi, folks.

I'm in the process of building my first system, and while I have done a lot of reading on the subject, I am still working through a few remaining questions. Apologies if my lack of knowledge shows.

A few details:
  • My use case is basically a big UPS for my home as I have sump pumps that I want to make sure keep running (and it would be nice to have other comforts, too). No solar initially -- just a way to store grid power.
  • The all-in-one unit is a Growatt SPF 6000T
  • The battery is a 48V 16S EVE LF280K in a Seplos Mason DIY kit with Seplos BMS. I'll likely add a second one in parallel sometime soon.
  • I have an 8000/10000 generator to provide auxiliary charging during extended outages
My question relates to how best to bring the generator into the mix, when needed. If I connect it to the grid input (as the Growatt manual shows), the inverter will go into bypass, and the generator will be attempting to support both the charging load, and any other loads that might be present at the time. Some of those loads will be significant, including two separate sump pumps, a well pump, and whatever else might be running on the sub-panel at that time. So, as an alternative, I thought it might make sense to add a separate 48V charger in parallel to the Growatt unit, and connect the generator output to that. This would mean that, during extended outages, I could simply start (or auto-start) the generator, and it would feed the standalone charger to recharge the batteries (or at least extend the run time). This would avoid any issues of potentially overloading the generator, and it would also seem to be a much more efficient use of the generator with a consistent charge load vs. all the ups and downs associated with all of the other loads.

Before I do this, though, I just want to make sure that I won't be causing myself any issues. Any thoughts on the subject would be very much appreciated!

If it does make sense to do this, I'd welcome any recommendations on 48V chargers. I am aware of the AIMS unit, but have heard a number of concerns expressed (especially about noise). I've seen a few recommendations of the Dakota Lithium unit, and a number of good reviews of the Mean Well units like this:


Are the any other chargers that I should be considering?

Thanks in advance for any insight!

Cheers,
Shaun
Click to expand...
 
I use one of their 18 amp chargers with a 1650w generator since they no longer offer the 25amp. Not idea but gets me though the cloudy days.
 
When buying a significant charge current capable charger to be fed from a generator look for a charger with power factor correction.

Most chargers just use simple rectifier-filter capacitor to convert AC input to DC for charging. These have a short duty cycle peak current pulse near peak of input AC sinewave voltage yielding a power factor between 0.60 and 0.65.

That means a 1500-watt output charger needs a generator capable of 3000 VA when charger 80% conversion efficiency and 0.6 power factor is factored in.

A similar charging output, power factor corrected charger needs a generator capable of 2000 VA with charger 80% efficiency and 0.9 power factor.

If a charger does not specify its AC input power factor, then you can assume it is not power factor corrected. Power factor corrected chargers do cost a bit more.

Most inverter-chargers provide power factor corrected charging from AC input. You can often find an inverter-charger with a similar charging current capability for about the same price as a power factor corrected charger only, so it may be a viable option to just buy an inverter-charger to use only as an AC input charger.
 
Last edited:
That's exactly what I am doing. Because I couldn't find a more cost effective option.
 
Jack Rabbit Off Grid said:
I use one of their 18 amp chargers with a 1650w generator since they no longer offer the 25amp. Not idea but gets me though the cloudy days.
Click to expand...
Thanks -- this is exactly what I was concerned about, and why I was considering a separate charger.
 
RCinFLA said:
When buying a significant charge current capable charger to be fed from a generator look for a charger with power factor correction.

Most chargers just use simple rectifier-filter capacitor to convert AC input to DC for charging. These have a short duty cycle peak current pulse near peak of input AC sinewave voltage yielding a power factor between 0.60 and 0.65.

That means a 1500-watt output charger needs a generator capable of 3000 VA when charger 80% conversion efficiency and 0.6 power factor is factored in.

A similar charging output, power factor corrected charger needs a generator capable of 2000 VA with charger 80% efficiency and 0.9 power factor.

If a charger does not specify its AC input power factor, then you can assume it is not power factor corrected. Power factor corrected chargers do cost a bit more.

Most inverter-chargers provide power factor corrected charging from AC input. You can often find an inverter-charger with a similar charging current capability for about the same price as a power factor corrected charger only, so it may be a viable option to just buy an inverter-charger to use only as an AC input charger.
Click to expand...

Very well put, thanks. Lots of good information in your post.

I hadn't thought about using another inverter-charger for connecting to the generator, but I think it really makes a lot of sense to consider. After all, not only would this provide sufficient (and clean) power for charging the batteries from the generator, in the event of a primary inverter failure, I suppose that I could also employ a transfer switch to use this secondary inverter to power the sub panel?

I'll need to think that through. ?

Is there a particular inverter-charger that you might recommend for something like this?

Thanks,
Shaun
 
RCinFLA said:
When buying a significant charge current capable charger to be fed from a generator look for a charger with power factor correction.

Most chargers just use simple rectifier-filter capacitor to convert AC input to DC for charging. These have a short duty cycle peak current pulse near peak of input AC sinewave voltage yielding a power factor between 0.60 and 0.65.

That means a 1500-watt output charger needs a generator capable of 3000 VA when charger 80% conversion efficiency and 0.6 power factor is factored in.

A similar charging output, power factor corrected charger needs a generator capable of 2000 VA with charger 80% efficiency and 0.9 power factor.

If a charger does not specify its AC input power factor, then you can assume it is not power factor corrected. Power factor corrected chargers do cost a bit more.

Most inverter-chargers provide power factor corrected charging from AC input. You can often find an inverter-charger with a similar charging current capability for about the same price as a power factor corrected charger only, so it may be a viable option to just buy an inverter-charger to use only as an AC input charger.
Click to expand...
I plan on in the future using my spare inverter as my sole charger as you have explained. But right now it’s being used as my primary inverter since my primary needs repaired. The charge boards bad.
 
Have not used my Meanwell much as it is mostly for difficult solar conditions. Works as designed as best I can tell during a few tests.
 
I’m off grid. My primary inverter is an MPP5048 running 120/240 split phase output. For split phase out, the MPP requires split phase input for a generator. This means a big, loud, open frame 7000W or larger generator. I wanted something much smaller and quieter for battery charging. I also use Chevy volt batteries with a non-standard 40-49v operating range. “Normal” 48v chargers aren’t suitable with any decent amount of current.
I ended up using a growatt 3000. It has all the programmable charging parameters needed and will charge at 40A. This pairs nicely with a 3000W inverter generator that is quiet and connects to my propane infrastructure. I’m a fan of the Westinghouse igen4500df. Gas+propane and true push-button electric start which works well with an automated button pusher for remote start.
When I went to expand my solar array, this also gave me a handy solar charger which also supports my Chevy batts.
The growatt also gives me a backup (single phase only of course) inverter in case the MPP fails
 
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