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diy solar

Generator to auto charge batteries when batteries reach set level

guybarth

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Jul 3, 2022
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Hello,

We are currently building two houses (one to rent out) in Guatemala. Our electricity will be completely off grid. Our system planned is 70KW of solar and 35kw of battery back-up (usage during non solar hours). I would like to also have a gas generator that the control unit (I don't know if that is the inverter or charge controller) automatically turns on the generator when the batteries reach a set level. I'm thinking a 3-4kw inverter generator is about right (72-96kw per day) to charge the batteries during times of low solar available. I can find plenty of 3-4kw inverter generators, but I'm having a hard time finding one with auto start (I think I understand this to be a 2-wire capability?). I also intend on having the electrician install a switch that allows me to bypass the solar/battery system and have the generator go right to the electrical panel (in the case of solar/battery component failure). I realize that 3-4kw will be well short of the demand needed for 2 houses when going directly to the panel, but in this rare scenario we would be planning on just powering the essentials (fridges, internet, some lights, and hot water).

Can you please recommend a 3-4kw inverter generator that has auto start and would be a good choice for my objectives? Next, do you agree with my 3-4kw inverter generator selection? Does the generator need to charge at 240, is 120 okay?

Thank you!
 
Small generators are usually lacking auto start features. You have to spend up for larger units for autostart.
There is a DIY alternative though. First you need a generator that actually does have a true push-button electric start. Many generators have an electric starter, but they still require you to manually operate the choke. Check out the Westinghouse generators. The iGen4500df is a small, quiet inverter generator that has both electic start and electric choke. A true 1 button push-start. 120V output
The WGen7500df is a larger, open frame, standard generator. Loud and noisy, but it puts out 240V split phase if you need that. It also is a true push button start.
I have and use both of these units at my off grid house and recommend them. They are also dual fuel. I run them on propane only, hooked up to my big 1000gal tank, so no worries about refilling tanks with gas.
They supposedly also support remote start, but there is almost no information on how to actually accomplish it.
Instead, I did a brute force DIY option with a remote control push button. Check out switch-bot. With the switch, you can turn on the generator from anywhere in the world.
120 or 240V. Which you need depends on your inverter and setup. If you do need 240V, you will have a hard time finding an inverter generator that puts out 240V split phase.
 
Any standard rotating generator puts out a natural sine wave. Although this can be affected by the reactance of the load and the frequency may vary a bit as the regulator adjusts to sudden load changes. This will not affect a battery charger or most anything else for that matter.

Most autostart generators will be triggered by low battery voltage. 120v or 240v just needs to match with the charging system.
 
+1 for propane. No fuel storage time limits versus petrol or diesel storage which need additives / rotating your fuel and don't have to drain the carb like with a petrol one after use. You can get propane adapter kits for some brands/models but better to get one ready to take propane.
 
Hi, here in the UK off grid reliable bullet proof auto start generator is a Lister.
DC voltage down AC wiring to light switch turn on the switch starts generator.
Single cylinder Lister with additional piggy backed generator including additional cooling system running house and workshop during the day and charging the solar battery bank.
Still working well for over 30 years.
 
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