Size of my backup generator

blindcowboy · May 2016

First off I am new here and new to solar so I could be missing something.

I have a 48v 370ah battery bank. I'm looking at the Honda EU3000 as a backup to charge my system when needed. If I'm charging at 20% and if I did my math right then I should need approximately 1800 watts to charge which this should be able to provide. Please correct me if I am wrong? Thanks in advance.

vtmaps · May 2016

Welcome to the forum,

I am not sure exactly what you mean by "charging at 20%". In these calculations I assume you want to be able to push 74 amps (20% of 370) into the battery at a charging voltage of 59 volts.

74 amps X 59 volts = 4366 watts. Assuming your charger is 90% efficient, you would be drawing 4851 watts. Way too much for a honda eu3000. What are you using for a charger? If it is not power factor corrected, it will require a generator of more than 4851 watt capacity.

From the ah size of your battery bank, I guess that you have a string of eight L-16 batteries. You should be able to charge them just fine with the eu3000.... you don't need a 20% charge rate to charge them.

--vtMaps

blindcowboy · May 2016

first thanks for the welcome and the answer.

I made a typo that should have been 10%. I would like to blame it on insomnia but I'm used to insomnia by now so it was just a typo.

oil pan 4 · May 2016

What charger were you going to get or do you have?

Get what you think you need. Then go one size bigger. Just because it generator is rated for say 3kw does not mean it can run 3kw continuously. They are usually rated to run half load and designed to run at around 2/3 load continuously.

blindcowboy · May 2016

Midnite Classic 200 Charge Controller.

BB. · May 2016

The Midnite is a "solar" charge controller--You have to feed it DC voltage (around Vbatt+10-20 volts) to a maximum of 150 VDC or so...

Generally, you would buy a standard AC to DC Battery charger... You can start with this (perhaps with the IQ4 option if you will be using grid power sometimes for charging):

http://www.solar-electric.com/batteries-meters-accessories/bach2/bach1.html

-Bill

blindcowboy · May 2016

I won't be using grid power to charge. It was going to cost me $15,000 to get the grid to come to me so I decided that even though it would cost just as much in the short run to get a system to do all I wanted I would be happier off the grid in the long run.

The learning curve is steep and I'm falling off of it occasionally as you saw with the charger vs charge controller mishap. I have a Magnum 4400w 48v parallel inverter with charger included.

blindcowboy · May 2016

It doesn't help that I bought most of the system a year ago but due to medical issues I'm just now getting to put it together. I seemed to have forgotten much of what I learned while I wasn't using it.

oil pan 4 · May 2016

So if you have the magnum 4400w charger you likely want up to a 6 or 7 kw generator.

My 7kw really could only handle 5kw continuously.

mike95490 · May 2016

Another voice saying beware of generator ratings. My antique generator (6hp, 3,000W) can push an honest 3Kw all day long. My new Robin/Subaru/Hatz 3Kw can run my 1Kw pump or charge batteries, or open the garage door. It's power factor is so poor/intolerant that it cannot put 3Kw into a load, unless it's my inverter (PF .9) charging batteries,

oil pan 4 · May 2016

The old generator is likely over rated.

Even with a seemingly high power factor single phase system, say 0.80 it will actually need 30% more torque to hold the load with out dropping off.

This is one of the reasons I am building a DC generator. I can build a high power battery charger cheaper than what a big battery charger costs and it will be more efficient than a single phase generator powering a battery charger, since the power will be created by a 3 phase alternator, at the required voltage and sent straight to the battery.

I do not recommend using the engine driven alternator DC battery charger as a power source to run the inverter and charge batteries, I believe they should only be used for charging batteries.

blindcowboy · May 2016

Thanks for the advice everyone. I was hoping to go ahead and move to a generator I could set up for auto start but anything that has the quality I want that is the size mentioned is out of my budget so I'll stick with my pull start generator for now.

oil pan 4 · May 2016

auto start for low charge has been pretty difficult to attain with out one of the $4,000+ turn key units.

animatt · May 2016

Depends on loads but I think the honda EU 3000 is not a bad choice. Although I like to go small on generator. Usually better for fuel economy.
I have the same inverter you have although smaller battery bank and have a cheap champion generator(around 3500w) it also has 240 output which makes it somewhat flexible. For the cost I am happy with it .

I also have a large construction grade generator that I have used on occasion when I needed to have something welded. But usually just exercise it every 60 days for about 10 minutes. It is a screamer. And burns thru fuel fast. But always good to have a backup and other options .

blindcowboy · May 2016

I should add this is for a cabin we are using on weekends right now so it's not full time. Second I should add that I'm blind so anything I can automate instead of having someone read me information helps. My wife doesn't mind reading to me but I'm the technical mind of the 2 of us.

blindcowboy · May 2016

Also the nice thing about my inverter it automatically diverts charge to use for power when necessary and I need something to run when I use the water heater. I currently have a 1500 watt water heater. The previous owner of this place left a propane water heater in the shed but I haven't had a chance to install it.

blindcowboy · May 2016

animatt said:

Depends on loads but I think the honda EU 3000 is not a bad choice. Although I like to go small on generator. Usually better for fuel economy.
I have the same inverter you have although smaller battery bank and have a cheap champion generator(around 3500w) it also has 240 output which makes it somewhat flexible. For the cost I am happy with it .

I also have a large construction grade generator that I have used on occasion when I needed to have something welded. But usually just exercise it every 60 days for about 10 minutes. It is a screamer. And burns thru fuel fast. But always good to have a backup and other options .

I'm guessing that's the champion 46565 just from looking at champion models?

animatt · May 2016

My champion us a manual start . Something lIke the 46596 but with a small switch that allows generator to output 240v power or 120v power. I did not see the toggle switch in the provided photos.
I would imagine but not sure that there are 2 coils in the generator and the toggle switch either runs coils in parellel or series.

that machine you linked to looks to be a step up. I believe it said somewherr it is a 3000w continous run generator. Still under $500 . Seems to have good reviews.

Mangas · May 2016

Cummins Onan are now building smaller gas, propane, or diesel fueled gensets.

I have a larger one. Well engineered and a quality unit.

Size of my backup generator

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