I have a 24 volt battery bank of 8 Fullriver AGS 6 v batteries and a Magnum MM250-30 D Inverter. I live in a small off-grid cabin. Generally all the power to run appliances comes from the battery's DC current changed to AC through inverter. Thus, keeping the battery charged is the only job of the solar array. Same goes for generator. I don't need a generator that can put out enough power to run all the appliances when the grid goes out. I am totally off grid. I only need a generator that can keep the batteries charged when the array isn't getting enough sun. All the generators I can find online seem directed toward users who will be using the generator in emergencies to run the whole house and I believe are more powerful and expensive than I need just to charge the battery bank. My current generator is a Kohler model 8 5RES 8.5 KW built in 2004. It predated the battery pack and solar array. I eould veey much appreciate hearing from any one who uses a generator to keep off grid battrry pack charged.
Advice on best generator for off grid battery charging:
- Thread starter Aoengus
- Start date
BentleyJ
Solar Wizard
Seems like the first item that needs to be identified is how many kW you actually need which is based on your usage plus how long it will take to recharge your batteries. Also do you need 240V or is 120V sufficient. A smaller generator (2 to 4 kW) will have to run longer and are generally 120V only but have a lower purchase cost and may be more economical to operate. However, the longer it has to run the more important a lower decibel rating becomes and the run hours add up faster so quality is important. Your choices range from very quiet fully enclosed Inverter generators, to open frame hybrid inverter generators to the lowest priced older style conventional generators. Its also worth noting that many of the 2 to 3 kW inverter generators are parallel capable meaning they can be connected together to double the output. Unfortunately most brands I'm aware of still do not produce 240V even when running in parallel they just double the amperage available at 120V.
MichaelK
Solar Wizard
Can you document the actual specs on your Fullriver batteries? I see that brand with 6V batteries ranging from 224Ah to 415Ah?
A general rule of thumb is you want to charge lead-acid batteries at 1/8th their capacity, and another rule is you don't want to run your generator at more than 50% load to keep the output stable enough for the inverter to accept. So, here's a formula you can use to predict generator size.
Plug in the actual Ah value of your battery once you determine it. I'll use the 224Ah model for the example
(224Ah/8) X 2 strings X 25Vcharging X 2times generator capacity = 2800W generator. I would get a 3-4kW generator. Like Bentley mentions, my inverter is designed to take 240VAC input.
A little more is usually better than a little less. Some inverters are quite fussy about receiving very clean power from the generator, so don't try to load it too high.
Remember to adjust your formula for the Ah capacity of your actual battery.
A general rule of thumb is you want to charge lead-acid batteries at 1/8th their capacity, and another rule is you don't want to run your generator at more than 50% load to keep the output stable enough for the inverter to accept. So, here's a formula you can use to predict generator size.
Plug in the actual Ah value of your battery once you determine it. I'll use the 224Ah model for the example
(224Ah/8) X 2 strings X 25Vcharging X 2times generator capacity = 2800W generator. I would get a 3-4kW generator. Like Bentley mentions, my inverter is designed to take 240VAC input.
A little more is usually better than a little less. Some inverters are quite fussy about receiving very clean power from the generator, so don't try to load it too high.
Remember to adjust your formula for the Ah capacity of your actual battery.
Steve_S
Offgrid Cabineer, N.E. Ontario, Canada
24V-LFP Offgrid Cabineer here.
Samlex EVO-4024 Inverter/Charger (capable of 100A charge max) takes Dual AC Input (Grid & Genset). I have no Grid (2 miles away).
This also provides "Pass-Through" power to the home during charging.
Charger Mode set to use 80A to charge my battery bank (1190AH) which I use during Winter on those "dark days" because I am quite North.
Charge from Genset Input is via the L5:30 (120V/30A) plug which goes to a Square-D 120V/40A Breaker then to the Inverter. @ 80A Charge it is pulling 120V/22-25A.
I use a Champion Inverter Generator (Canadian Version) but here is the US version. NB Starts everytime on 1st Pull and even in -35C/-31F temps.
With these settings the Gen does not run at "full tilt" and is at the edge of eco-mode but it steps up very nicely when needed (ie Well Pump kicks on) and steps down very nicely. Being PURE SINE that is what passes through, which is good for anything with a motor & fine electronics, the most obvious "noticeable" is the CLOCKS ! They do not speed up or slow down because the frequency is 60HZ and no deviations, regardless of load. It IS very clean power and at a very affordable price point as well.
$999.99 USD @ Tractor Supply USA (LINK)
I switched to this Genset from by big 9000W Construction genset (Another Champion Generator) because it was "overkill" and also NOT Pure Sine resulting in "dirty pass-through" as no Inverter will correct the incoming Sine Wave.
As I am LFP the info does not directly translate but IF I allow my bank to get down to where I need to use the Genny (it happens even with 7 days stored), I run the Generator for an 8 Hour cycle, that provides 4.5 days stored energy while also providing pass-through power.
NOTE: I have been using Champion Power Equipment for over 20 years and have not had any issues of significance at all. Some of it has had to survive "Extreme Hard Use" and everything still runs great. The GOTCHA ! Maintenance MUST be a Religion ! Change the oil when it must per specs & clean filter as well... and you will not have problems. I allow for "Natural Oil" during the 1st run break-in 3rd Oil Change goes to Pure Synthetic 0W50 and regular oil changes. Because I use Pure Synthetic Oil, I now do oil changes at 70 Hrs and it is still actually not bad. *Mobil -1 Pure Synthetic is very good oil BTW.
Hope it Helps, Good Luck.
Samlex EVO-4024 Inverter/Charger (capable of 100A charge max) takes Dual AC Input (Grid & Genset). I have no Grid (2 miles away).
This also provides "Pass-Through" power to the home during charging.
Charger Mode set to use 80A to charge my battery bank (1190AH) which I use during Winter on those "dark days" because I am quite North.
Charge from Genset Input is via the L5:30 (120V/30A) plug which goes to a Square-D 120V/40A Breaker then to the Inverter. @ 80A Charge it is pulling 120V/22-25A.
I use a Champion Inverter Generator (Canadian Version) but here is the US version. NB Starts everytime on 1st Pull and even in -35C/-31F temps.
With these settings the Gen does not run at "full tilt" and is at the edge of eco-mode but it steps up very nicely when needed (ie Well Pump kicks on) and steps down very nicely. Being PURE SINE that is what passes through, which is good for anything with a motor & fine electronics, the most obvious "noticeable" is the CLOCKS ! They do not speed up or slow down because the frequency is 60HZ and no deviations, regardless of load. It IS very clean power and at a very affordable price point as well.
$999.99 USD @ Tractor Supply USA (LINK)
I switched to this Genset from by big 9000W Construction genset (Another Champion Generator) because it was "overkill" and also NOT Pure Sine resulting in "dirty pass-through" as no Inverter will correct the incoming Sine Wave.
As I am LFP the info does not directly translate but IF I allow my bank to get down to where I need to use the Genny (it happens even with 7 days stored), I run the Generator for an 8 Hour cycle, that provides 4.5 days stored energy while also providing pass-through power.
NOTE: I have been using Champion Power Equipment for over 20 years and have not had any issues of significance at all. Some of it has had to survive "Extreme Hard Use" and everything still runs great. The GOTCHA ! Maintenance MUST be a Religion ! Change the oil when it must per specs & clean filter as well... and you will not have problems. I allow for "Natural Oil" during the 1st run break-in 3rd Oil Change goes to Pure Synthetic 0W50 and regular oil changes. Because I use Pure Synthetic Oil, I now do oil changes at 70 Hrs and it is still actually not bad. *Mobil -1 Pure Synthetic is very good oil BTW.
Hope it Helps, Good Luck.
Thanks to everyone for advice. I'll have to study it to make sense. Right now I have a 20 year old 7kW Kohler with an oil leak. I have an inverter that the power from the generator goes through to the battety bank so the term Inverter Generator is a mystety to me. Generac makes only one generator for use off grid ie only one is warranted. It is 15kW - way more than I need - and with installation would cost me about $8500. I do want a generator I can control with an AGS programed through the inverter.
12VoltInstalls
life passes by too quickly to not live in freedom
I’d be inclined to buy a HF Predator motor and a 24V alternator and fab up a DC generator to charge the batteries- no conversion losses
