generator to top off a 24V 683 AH rolls off grid battery bank

[maple flats]

I have 4 Rolls Surrette 6V 683 AH (c20) batteries in series. I'm looking for a generator to charge them if I have an extended time with little or no sun. Prefer diesel genny if feasible. We have good voltage and reserve until we get 4 or 5 days with little or no sun, I want to be able to charge the bank at those times.
Please advise.

[stefan888]

Hello this is a quality product with auto adjustable battery voltage

-link deleted by moderator - There are many 60A solar charge controllers.

the unit will charge from solar you can connect up to 3600Wp from solar panels.

There is another low cost alternative where any ac generator can be connected to a combi inverter/charger . Average cost $500
( That's what the OP is asking for )

[Mike90250]

So, c10 would be 60A, which at 30V, is 1800watts, not counting any losses. C20, I'm guessing you want only 30A, or about 900W ?? That's a pretty light load for a diesel, most start about 5kw, and running a diesel that lightly loaded, can lead to cylinder glazing and "wet stacking". There are a boatload of diesel gensets out there. I can tell you my 3kw Subaru/Robin/Hatz has the cheapest alternator on it, and it can barely power my 1kw well pump because of lousy power factor.
You will need to account for the power factor of any charger you get, to select the proper size of alternator that will be able to drive it.

https://www.iotaengineering.com/ppapps_pfc.htm

Will you be using solar to complete the absorb cycle, or will you be running the genset to do both Bulk and Absorb ? That last 20% of charge in absorb, can take a couple hours at light load, and burn a lot of fuel. If you have to, I'd suggest an auto-throttle inverter generator.

here's some smallish ones, look to be well built, but anyone can make a spiffy web page

http://www.whisperpower.com/US/4/5/products/generators-sq-series-(low-rpm).html

[maple flats]

What I was thinking is that in decent sun, my 1710 watt array tops the charge off in about 3-4 hrs, and when the meter shows the array is inputting 1400-1500 watts. As such I likely want a 3 stage charger that at flood stage will input maybe 2000-2400 watts max, then the genny should be able to run 2-2.5 hrs to top off and get the bank to full, unless we are running lots of energy use at the same time. We can remove most things, except 2 sump pumps. I own a duplex and I have both sump pumps running off the bank. I don't recall the watts draw but when I had just 1 of the pumps running off the bank but nothing else, I did fine for a 6 day no sun time this spring and after the 6 days the bank was down to 24.6V when the pump was running. During that period the pump was cycling about every 30-45 seconds around the clock. Our home is at the bottom of a hill that rises 700' and is at a slope of about 10-12% average.

[maple flats]

I was thinking I wanted to get to but maybe not thru float, is it better to just get it thru bulk?

[Mike90250]

The economical way is to Bulk with generator, and then Absorb with solar Like I did This AM: (Red line is amps in/out of the inverter, Blue is Voltage)
I charged to the limit of the charger, knowing the sun was shortly due to come out, I used the sun to complete charging, not initiate it. (PV amps not shown)

Generator Bulk - PV Absorb.png