Best method for charging 48 volt battery bank with generator?

ELYNN4 · December 2014

Hello,

New to the forum and would be interested in what folks think - I am getting ready to build a new home off the grid. This is my chance to build a complete power system from the ground up, so all input is appreciated.

I will have a 48V 800 AHr battery bank. I will have a diesel powered gen set. Question is whether to charge the battery bank with a DC generator or AC?

I will be using Toyo heaters which are notoriously finicky when it comes to clean AC power. Many folks here in Alaska have a lot of trouble getting the Toyos to run while they are on the generator charging their battery bank. Many have had to wire in relays and run dedicated circuits to their Toyos so that they are turned off when the generator runs and the powered back up when they are on the clean inverter power.

My thought is that by charging the battery bank with A DC generator I can eliminate the power issues I've described above.

If I go with a DC generator is there a "stripped down" inverter system that you would recommend? Currently I am leaning toward the Radian system, but it has a charger that I wouldn't need.

Thoughts - thanks in advance

Cariboocoot · December 2014

Re: Best method for charging 48 volt battery bank with generator?

Welcome to the forum.

Your best bet is to use an AC generator because in fact all generators are AC. A DC generator is an AC one with its output rectified. Moreover a DC generator would need a charge controller on its output to regulate the battery charging, and that is not as easy as it sounds.

In fact an AC gen charging through an inverter-charger will give you the best performance. You should get a good generator of course. An inverter-generator will provide power as clean as any inverter, without the wide fluctuations in frequency and Voltage that fixed RPM generators experience.

The thing is your 800 Amp hour 48 Volt bank is going to need a lot of power to charge with; you're looking at 4kW+ just for charging. Honda makes some fairly large and excellent quality I-G's such as the EU7000is which is ~7kW.

ELYNN4 · December 2014

Re: Best method for charging 48 volt battery bank with generator?

Thanks Cariboucoot,

I've been looking at the Aurora and Polar DC generator systems which are 6 to 10 KW diesel units that burn less than a half gallon of fuel per hour. They have charge controllers and BMS that can handle most any battery type, even LiFePo4. These generators are rated for 20,000 hours, which I believe is more than I could get out of the Honda - of course they are more expensive.

Cariboocoot · December 2014

Re: Best method for charging 48 volt battery bank with generator?

ELYNN4 wrote: »

Thanks Cariboucoot,

I've been looking at the Aurora and Polar DC generator systems which are 6 to 10 KW diesel units that burn less than a half gallon of fuel per hour. They have charge controllers and BMS that can handle most any battery type, even LiFePo4. These generators are rated for 20,000 hours, which I believe is more than I could get out of the Honda - of course they are more expensive.

"More expensive" is probably an understatement.

Consider carefully how often and how much you would need to use the generator at your location before investing.

ELYNN4 · December 2014

Re: Best method for charging 48 volt battery bank with generator?

I will be living off the grid, so the generator will run daily through the winter. I estimate 600 hours per year minimum.

Cariboocoot · December 2014

Re: Best method for charging 48 volt battery bank with generator?

ELYNN4 wrote: »

I will be living off the grid, so the generator will run daily through the winter. I estimate 600 hours per year minimum.

If it means anything to you I've got over 6,000 hours on two different inexpensive Honda EU series generators with no issues at all. That would be like ten years use each by your plan.

In the system size you're looking at (48 Volt) you won't find many, if any, non-charger inverters.

Consider also the DC wire run from gen to batteries @ charging Voltage (around 60 peak, could be as low as 48 nominal or even lower) with full current (charging plus load demand). A 6kW gen at 48 VDC will be 125 Amps. The longer the wire run, the larger the wire will need to be above 2 AWG minimum. Of course if everything is housed in a 'power shed' this becomes much easier to deal with.

Les Nagy · December 2014

Re: Best method for charging 48 volt battery bank with generator?

If you have an inverter that will pass AC from te generator and also charge the batteries directly then get the Honda recommended. It will provide you with a total fall back system should you need to a complete shut down of the inverter for whatever reason.

If you don't have an inverter that will also charge the batteries (which is rare) and/or you want to buy a cheaper generator that has poor output quality then get an external battery charger to charge the batteries with the generator so that your inverter stays online and you keep the good AC quality. One good charger is this one:
http://www.atlantasolar.com/product_info.php/name/BCA1503-110-32%20Telcom%2032V%20AC%20Battery%20Charger/products_id/1972
I have not dealt with the reseller but have experience with the product.

BB. · December 2014

Re: Best method for charging 48 volt battery bank with generator?

With a quick look, I could not find the AC power requirements for those Toyo heaters...

If the do not like mechanically controlled generators--You might be able to get a second 48 volt inverter (hopefully not too large) and dedicated for the Toyo heating circuits (DC in, AC out, no transfer over to Generator AC). You can run that continuously (battery, battery+sun, battery+Genset)--A "Continuous Conversion" UPS -- Basically an AC inverter that always is on and converting from DC power -- Should give you very stable power with only a bit of extra losses when the genset is running (genst AC to DC back to AC).

A typical inverter-charger just runs the AC output from the genset--slightly varying voltage+frequency (depending on stability of the genset and how the power qualification limits are programmed on the inverter-charger).

-Bill

toothy · December 2014

Re: Best method for charging 48 volt battery bank with generator?

Hello fellow Alaskan

I have trouble with my smoke alarms going off when on generator, really annoying. They function properly for 6 or 8 months and then decide it's time to start driving the dogs nuts. I have a Toyo boiler and it seems fine but the stoves are different.

I wish I could come up with a way to leave the relatively clean inverter power on and separate the charge function as your trying to do.
I'm charging 1350 Ah of Rolls fla's with 2 Outback vfx3648's and a northern lights 10 Kw gen. I really need more charge capacity to effectively use the full gen output, I load it up with heaters and lights. Burned 54 gallons last year in the gen but we are a bit stingy with lights and stuff, standard house with wood boiler and masonry heater for heat. I'm also thinking of getting rid of my fla's and trying a new battery technology.

Watch the electrical consumption of gas cooking stoves they are pretty heavy loads when running the ovens.

You didn't say where you are building but I would say go big on solar panels and batteries, I wish I had more and would if I could find some more space. Seward has some lovely weather this time of year so I understand your dilemma. Use the extra solar for stored heat.

Wade

ELYNN4 · December 2014

Re: Best method for charging 48 volt battery bank with generator?

Thanks for the great input everyone. Sounds like the Honda generator is about half the cost of a diesel generator. It consumes maybe 30% more fuel and might last half as long as a diesel generator. You also give up the ability to scavenge waste heat from the cooling system, since it is air cooled. Scavenging waste heat from the exhaust could still be done.

Seems like it's another case of pay me now or pay me later, although I will need a good generator for construction and will want a backup generator.

I'll be building in Talkeetna, so appreciated Wade's observations from Seward.

Appreciated all the input!

toothy · December 2014

Re: Best method for charging 48 volt battery bank with generator?

Build your gen shed and some solar first before construction then you don't have to listen to the gen drone away ALL day. I built mine on 6x6 skids so it is moveable.

Wade

westbranch · December 2014

Re: Best method for charging 48 volt battery bank with generator?

Be sure to read the threads started by ChrisOlson on Generators , full of good info on how to chose one for your situation, also his comments on the Subaru/Robyn generators... small but seem bulletproof

hth

BB. · December 2014

Re: Best method for charging 48 volt battery bank with generator?

In addition to what Toothy said--Build separate generator (and possibly) solar shed(s) away from the immediate home structure.

Keep the major components that can catch fire (generator+fuel+fuel storage) away from the rest of the expensive components (batteries+solar panels+electronics). And keep both away from the home for safety.

-Bill

toothy · December 2014

Re: Best method for charging 48 volt battery bank with generator?

Well it looks like I've violated Bills rules from the above post.

I built an 8 X 12 shed with the gen on one end, inverter on the other and batteries on the long back wall across from the door with a 130 gallon aluminum truck saddle tank hanging on the outside of the gen end with the mounts from the original truck frame.

I worry more about the electronics causing a fire than the diesel gen, probably just what I grew up with.

My gen shed is 200 feet from the house and I have wished that the gen was closer to the house to use the waste heat. If you get a big enough battery bank so the gen only runs during the day I think it would be OK close to the house.

Up in Talkeetna you get a lot more sun than we do down here in the swamp. If your on a south slope with few trees you may be pleasantly surprised about your production. A guy from down here just built in Trapper creek and was running on gen and batteries with no panels and thought it was great. I told him to put up some panels, he was amazed at the reduced run times.

Wade

oil pan 4 · December 2014

Re: Best method for charging 48 volt battery bank with generator?

ELYNN4 wrote: »

I've been looking at the Aurora and Polar DC generator systems which are 6 to 10 KW diesel units that burn less than a half gallon of fuel per hour.

Wow that's horrible.
The 5.5kw Kubotas I worked on would burn between 0.25 and 0.33 gallons per hour running a 2kw load.

I say get a generator and get a battery charger BMS system to plug into it.
When you get the combined generator with BMS what are you going to do when one or the other takes a dump?
I have a feeling the all in one units for off grid power will be a lot like all in one welding/plasma cutting machines, very expensive and unreliable with very expensive if not impossible to get replacement parts.

For an engine something liquid cooled with a 4 pole generator so the engine only spins 1800 RPMs.
Liquid cooled so you can pump the hot coolant into your house for heat.
1800RPMs means it will be quiet and use less fuel than a 2 pole 3600 RPM fuel guzzling screamer.

mike95490 · December 2014

Re: Best method for charging 48 volt battery bank with generator?

If running diesel, be sure to have a plan for the cold starting (electric air heater for intake or glow plugs) and anti-gel fuel. And a way to keep the genset warm enough.

Best method for charging 48 volt battery bank with generator?

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