Charge with generator when lacking solar.

medic149

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I have a small 12 volt setup to just run a small refrigerator and it has been working very well so far. I currently use the generator to charge the 12 volt 200 amp hour battery once every 3 or 4 days. I am using an inverter going from the 12 volt battery to the 120 side to the cabin. I also have a 12-volt charger that I run off of my generator to charge the battery when I need to.

I now have a 100 watt solar panel system that I want to use to charge the battery. However I still want to be able to charge the battery with the generator during times when there's not a lot of sun. I am trying to figure out how to isolate between the solar power coming in to the batteries and the generator to charge the battery.

Any thoughts? A switch to isolate the solar side while the generator is plugged in?

Thanks
Andy
 

Wellbuilt

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Nope just fire it up and charge , they can both be charging at the same time .
I would run the generator in the morning at sun up then the solar can take over
You should charge with the genarator every other day don’t run the battery down so much .
 

medic149

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Nope just fire it up and charge , they can both be charging at the same time .
I would run the generator in the morning at sun up then the solar can take over
You should charge with the genarator every other day don’t run the battery down so much .
Thanks. And no worries about back feeding 12v charging to the solar charge controller?
 

Short_Shot

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Thanks. And no worries about back feeding 12v charging to the solar charge controller?
That's not any different from and electrical standpoint as when the scc is just hooked up to the batteries in the first place tbh.

The only change when charging is the battery side voltage increases slightly.

Hook it up and life will be good without intervention, and come see us when you get hooked on solar and want more.

Depending on your power draw from the fridge you may find that adding another 100-200w of solar will mean you rarely ever need the generator.


And if you have a lead acid battery, you should try to fully charge it every day. It'll last a lot longer. However with a generator this adds up in maintenance costs so solar looks even better.
 

medic149

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Than
That's not any different from and electrical standpoint as when the scc is just hooked up to the batteries in the first place tbh.

The only change when charging is the battery side voltage increases slightly.

Hook it up and life will be good without intervention, and come see us when you get hooked on solar and want more.

Depending on your power draw from the fridge you may find that adding another 100-200w of solar will mean you rarely ever need the generator.


And if you have a lead acid battery, you should try to fully charge it every day. It'll last a lot longer. However with a generator this adds up in maintenance costs so solar looks even better.t

That's not any different from and electrical standpoint as when the scc is just hooked up to the batteries in the first place tbh.

The only change when charging is the battery side voltage increases slightly.

Hook it up and life will be good without intervention, and come see us when you get hooked on solar and want more.

Depending on your power draw from the fridge you may find that adding another 100-200w of solar will mean you rarely ever need the generator.


And if you have a lead acid battery, you should try to fully charge it every day. It'll last a lot longer. However with a generator this adds up in maintenance costs so solar looks even better.
Thank you very much!
 

MichaelK

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For a 200Ah battery, I'd think you could get far better charging with more solar. Assuming a lead-acid battery wants to be charged at 1/8th of C, the math works out to be.... 200Ah X 1/8C X 13V charging = 325W. Assuming you only get 85% output that works out to be 325W/85% =381W. I'd charge with four panels, not one.
 

medic149

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For a 200Ah battery, I'd think you could get far better charging with more solar. Assuming a lead-acid battery wants to be charged at 1/8th of C, the math works out to be.... 200Ah X 1/8C X 13V charging = 325W. Assuming you only get 85% output that works out to be 325W/85% =381W. I'd charge with four panels, not one.

I totally agree. This is just a temporary setup. I am in waiting hell for my LiFePO4 batteries that have been on order since February.
 

medic149

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Thanks! I actually have the system set up and has been working great! I go 3-4 days on the battery before need to run the generator for a few hours to charge it up. I just installed the single solar panel, which should charge it up for when I'm back at the cabin in a week or two. Been running the small fridge, two lamps with 9 watt LED bulbs, and computer. No issues at all!
 

Wellbuilt

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You really can’t leave your battery depleted for days it will start to sulfate and the capacity will get walked down slowly
over a few days ,weeks .
One panel can help but it’s better to get to 90%charged every day . And full charge every third day
 

jbatx

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Great thread. I am considering how to use my 9kw gas generator as a back up. My array is 5kw with 440ah at 48v in LiFePO4 batteries. I think the ideal solution would be to sense when the system is near a low voltage cut off situation using an esp32 based device and then have the device start the generator.
 

crossy

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Great thread. I am considering how to use my 9k gas generator as a back up. My array is 5kw with 440ah at 48v in LiFePO4 batteries. I think the ideal solution would be to sense when the system is near a low voltage cut off situation using an esp32 based device and then have the device start the generator.

Great minds are thinking alike here :)

The ESP is a super little device for all sorts of little jobs.
 

Wellbuilt

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Great thread. I am considering how to use my 9kw gas generator as a back up. My array is 5kw with 440ah at 48v in LiFePO4 batteries. I think the ideal solution would be to sense when the system is near a low voltage cut off situation using an esp32 based device and then have the device start the generator.
A 9000kw generator would use a lot of fuel
I’m using a 2800 watt Honda unit and can charge at 1900watts run the house and well pump .
My 3600 watt inverters max charging is 1900 watts .
I just have to charge For 30 mins befor I turn the well pump on .
 

jbatx

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A 9000kw generator would use a lot of fuel
I’m using a 2800 watt Honda unit and can charge at 1900watts run the house and well pump .
My 3600 watt inverters max charging is 1900 watts .
I just have to charge For 30 mins befor I turn the well pump on .
It would, yes. 13hrs on 5gal. I have it for remote job sites that have no power at all and while it's not being used for that I'm going to use it for backup. If I were buying one just for backup, I'd get a smaller one.

This particular generator is a HF predator 9000 (7200w runtime). It has a 12v dc socket that I want to connect into the pv input. I'd switch off the pv input, switch on the generator input, start the generator. The scc is a renogy 100amp rover. I think that'll work. It won't provide a lot of power to system, but its the only available dc source without buying another part.

Also, I could use an AC output on the generator and a transfer switch to supply power to the loads while the DC output charges the batteries...

...Or get an AC to DC transformer and connect AC output to the transformer and the transformer DC output to the pv input on the scc. That'd deliver a lot more charging current than the 12v from the generator.

what would you all do and am I missing something that might cause some damage?

.
 

time2roll

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Great thread. I am considering how to use my 9kw gas generator as a back up. My array is 5kw with 440ah at 48v in LiFePO4 batteries. I think the ideal solution would be to sense when the system is near a low voltage cut off situation using an esp32 based device and then have the device start the generator.
Set the generator auto start higher than the low voltage cut off and you will have power as long as you have food for the beast.
 

tigerwillow1

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This particular generator is a HF predator 9000 (7200w runtime). It has a 12v dc socket that I want to connect into the pv input. I'd switch off the pv input, switch on the generator input, start the generator. The scc is a renogy 100amp rover. I think that'll work. It won't provide a lot of power to system, but its the only available dc source without buying another part..
Not a good plan. HF doesn't include a wiring diagram in their manuals but from their description there's no reason to think the DC output is any different than Honda's, which is a dedicated AC winding simply passed through a full wave rectifier to the DC output. It is unfiltered and unregulated, and I doubt a SCC would like any part of it. With their large inverter generators the manual says it's suitable only for charging lead acid batteries, has an 8 amp maximum output, and the Economy switch must be off when using it. In other words, there's a high likelihood the SCC would not play well with the DC output, but if it did, you'd get a maximum 96 watt output while running the engine at an elevated RPM. The manuals for the non-inverter models don't say much at all about the DC output. The better plan is to plug in a good battery charger or power converter into an AC outlet, using that to power the SCC.
 

Wellbuilt

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Hmmm the 12v charging on the generators
Usually doesn’t put out much charging at all Really the best way to charge in bad weather is with a inverter / charger .
My charger puts out 1900watts at 62 volts temp compensated .
The12v charger on your generator is small at best and unregulated .
It would need automatic choke to self start . The AC in put to dc out put thingamabob seams like you are reinventing the wheel
And charging go’s to the battery’s not thru a charge controller just saying ?
Look up iota 48volt battery charger charger I think they can charge LiFeP battery’s
I think they put out 13 or 15 amps at 48 volts .
You could use 3 of them for 45amps
At least you could use the large generator efficiently .
If you are in a sunny area you could probably get away with out back up power
Your battery’s could take fill power for charging .
 

Short_Shot

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Third on not using the 12v output.

It will be extremely limited at best. Likely not more than a couple hundred watts max.

Huge waste of generator potential.
 

offgriddave

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The 12v on your generator is probably something like 40-80w only.

I bought one of these bench power supplies for experiments, and now use it to charge my 48v batteries because of storms:

Riden RD6018 DC Power Supply Variable Adjustable Lab Bench Power Supply Buck Converter Step Down Switching Regulated 4-Digital LCD Display 60V 12-18A 800W​


Looks like it will do 18A * 12v, which is only 216watt so this might not be a good solution for you. But for me it works (48v * 18a = +800w

Anyone have a better solution?
 

DJSmiley

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Get a old powersupply from a router or so. Lot of them can be adjusted (48V adjust to 52V or so)

They also do have a remote on/off switch. If you install a decent shunt you can interface with an ESP or Arduino and eg autostart when SOC <20%, stop charging when SOC >40%.

Charging with high amps is no issue for LFP, and it limits the runtime of the generator (Which usually make a shitload of noise). By not charging to 100% you always leave room for any available sun. In the end, its useless to spend $$ on fuel and noise, while the sun might do the same job for free.

Good options are eg Meanwell chargers (new), but cheaper DIY options include Eltek Flatpacks or old APC rectifiers like https://www.ebay.com/itm/392753355836
(I have three of these - they are massive beasts - Charges at 50 amps and voltage can be adjusted)
Installed in the chassis (3 pieces) they provide 50V / 150A and require 3-phase powerfeed.. They used to power our Foundry MG8 routers in the past. Those went to a scrapyard but I took the PSU to my place..)


For cheap 12V charging look eg at HP 1200W powersupplies. Those can be modified to output >12V (approx 14.2V would be ideal for LFP) and provide 100A current for cheap.
 
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