DC generators

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timmartin
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(32 cells paired together, 1 string = 51.2V 800Ah)

DC generators

Post by timmartin » Thu Oct 04, 2018 6:25 pm

Even before switching to lithium I become very curious about DC generators. Although having a bypass switch and a full power AC generator that can power the house is very useful, the fact is that I have a backup portable that can do just that. So in an effort to boost efficiency, reliability, and reduce problems such as buzzing lights and flickers, I am thinking about changing my main generator (for when its rainy and gray) to a DC genset.

Anyone have any experience with this? Any gotchas or issues I should be aware of?

I do know that finding a suitable DC generator is surprisingly hard. But there are some places selling the Kohler 6VSG. I had an AC 8.5 kW Kohlers before and was happy. Although itÔÇÖs air-cooled itÔÇÖs much less expensive than custom built LP DC gens. ItÔÇÖs also half the power but since it doesnÔÇÖt need to power the house AND charge at the same time, itÔÇÖs not a big deal. Anything over 5kW would be fine.

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Kurt Lundquist
Alpha Energy Engineering
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My RE system: VFX3524, Mate3, 200Ah 24V AGM Battery Bank
Location: Arlington, WA

Re: DC generators

Post by Kurt Lundquist » Fri Oct 05, 2018 7:33 am

I have some experience with 48V DC generators. All of them are more expensive than a comparable AC generator. The Kohler units that I know of are not prime rated. I think the lifespan is ~1000 hours based on the claim of 10 years at 100hrs/yr. As for the prime rated DC gens I have found the service/support to be lacking (I'm putting it mildly). Most of the 48V gens are designed for the Telco world which means -48Vdc (positive ground) instead of the typical +48Vdc that is used in residential DC power systems.

DC gens have the ability to adjust rpm based on the output load (charging) needs so they can be more efficient. Inverter-based AC generators can do the same. You can buy two of the 7.0kW Honda EU Inverter gens for the price of a well built 6.0kW DC generator. If this were my system I would put the money on an AC inverter generator. Purchase from a local reputable dealer and you should have quick and easy access to parts and advice when a problem happens.

I know of some people that have paired a 3.0kW Inverter Gen with a single VFX3648 to create an alternate battery charger circuit. If you are off-grid having the extra inverter around is nice when something happens to one or both of your main inverters.

Let us know what you decide to do.

Thanks,

-Kurt
Kurt Lundquist
Renewable Energy Project Engineer
http://alphaenergy.us/

sodamo
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Re: DC generators

Post by sodamo » Fri Oct 05, 2018 8:08 pm

Kurt Lundquist wrote:
I know of some people that have paired a 3.0kW Inverter Gen with a single VFX3648 to create an alternate battery charger circuit. If you are off-grid having the extra inverter around is nice when something happens to one or both of your main inverters.

-Kurt
I like the idea of a DC charger as well, or since not having good luck researching that option, I am more enthused about being able to charge my battery bank without also powering the house. As my current inverters are are FX3048 and no longer replaceable i figure i will replace them all in next year or so and set the FXÔÇÖs as a direct battery charging setup with no AC out. What would be idea would if battery charging only was an option with our Outback inverter/chargers. I just dont understand why they have to charge and send AC from generator to house load at same time. To my thinking the choice ought to be ByPass (all current to house load) or Charge (all current to charger). I can only recall one time since installing system to go on By Pass mode.
David
Please visit http://vacation.ninolehawaii.com

timmartin
Forum Guru
Posts: 278
Joined: Thu Dec 02, 2010 8:31 am
My RE system: ...
Sharp 120W Panels (12)
SunPerfect 230W Panels (9)
Whisper 100 Wind Turbine
Outback FM60 charge controller
Outback FM80 charge controller
Outback VFX3648 inverter/chargers (2)
Outback FlexNet DC
CALB CA400 LiFePO4 3.2V batteries
(32 cells paired together, 1 string = 51.2V 800Ah)

Re: DC generators

Post by timmartin » Fri Oct 05, 2018 8:22 pm

You canÔÇÖt understand why people would want to continue powering their house while charging? You think a lot of people would prefer to shut down the house in order to charge the batteries? That would seem unlikely to me. Even if the circuitry was physically possible to act as a charger and inverter at the same time it be rather inefficient to generate AC, convert to DC, then convert some of it back to AC.

However, it certainly is true that the inverted DC is way higher quality and consistent than the generators output. For my generator at least.

sodamo
Forum Czar
Posts: 768
Joined: Mon Apr 03, 2006 1:55 am
My RE system: Totally off grid - Hamakua side, Big Island, Hi

36 Trina 280 & 16 Phono 250 in 48 volt array (fixed) 14080w
Radians GG8048/GS4048 w GSLCs
4 FM 80 charge controllers
Hub 10.3
FNDC w/3 shunts
Mate 3s
OpticsRE - MMKL - Ninole Hi
12 SimpliPhi 3.8
14Kw Kohler 14RESA Propane

Charging Only
2FX3048T
Hub
FNDC. - shared shunt feeds from Radian FNDC
Mate 3s
10Kw MEP 803a Military gen

Honda EU7000i

Davis VantagePro2 Wx Station
On line at: https://www.wunderground.com/dashboard/pws/KHININOL2
Location: Ninole, Hi

Re: DC generators

Post by sodamo » Fri Oct 05, 2018 9:53 pm

Ok Tim, ya got me on that one. Kinda forgot it was just a single transformer doing double duty. :grin:
David
Please visit http://vacation.ninolehawaii.com

JRHill
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Re: DC generators

Post by JRHill » Sat Oct 06, 2018 10:24 am

I gave up on the DC generator for the reasons Kurt mentioned and haven't looked back. We're already a unique, special purpose group when it comes to integrating generators with solar and going in the direction of DC takes special purpose to new thresholds.

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