Generator questions

Rance

I'm helping a friend add generator backup to his off grid system.   His inverter is Midnite solar, not sure of the exact model but its 48VDC.  The AC input is 120V only.   Nearly all generators these days are 240V.   Any problem just pulling power for battery charging from just one leg of the generator's 240V output?   The technical solution would be to add a 240V>120V stepdown transformer, but those are pretty pricey.

Second question:  Generac says they sell only one generator for off grid installations-a 15KW, (about $5K) they don't warrant any of their others for off grid use.  We'd like to use their 7.5KW (About $2K) but they say it should only used for grid tie systems.   I don't get it.  Is there a difference between generators for grid tie vs off grid use?

Last question, for my own system: Anyone know of a decent 48VDC generator (head only)? I have a 600 RPM Lister diesel that'd be perfect for dumping about a KWh or so directly into the batteries (with diversion control of course).

Thanks!

706jim

Wow, 600 rpm Lister! Haven't seen one since I was a kid 60 years ago. I recall it exuded oil at every pore while running and was painted green. Otherwise I'm of no help to you.

Rance

That's about right.   It was made in 1939 and its green.   Pretty tight oil-wise though.   For those mystified by this,  its a single cylinder, 3HP cold start diesel, weighs in at well over 600 lbs.  Burns just about any type of oil and designed to pretty much run forever.  

BB.

Do you have more information about the generator (technically, is this an alternator?). Outside of the USA, many alternators are 230 VAC @ 50 Hz and they are simply L1/L2 output, no "center tap" Neutral connection for 120 VAC... For the USA, the alternator can be 120 VAC @ 60 Hz, or 120/240 VAC @ 60 Hz with L1/L2/Neutral outputs. It depends on how the alternator is wound internally, and sometimes how they are wired (120 VAC windings in parallel or two 120 VAC windings in series for 120/240 VAC).

And there are older systems that are actually 120 VDC (not AC) generators. Back in the day, 110-120 VDC ran lights, brushed (universal motors) just fine...

Regarding Generac, I am not sure what happened there... Did they want to avoid off grid installations that ran 24 hours per day and 365 days a year--And avoid breakdowns that required immediate repairs (and possible court actions for systems that "failed earlier than the customer expected"... Or simply that they did not want to expose their produce running 1,000 of hours per year--And they just are not designed for near continuous operation. That no off grid warranty limitation has been around for many years now.

It would seem that modern off grid systems that use solar for most of the year and genset just for bad weather in the winter would not be a bad application for a well designed genset.

One (minor) issue... For Generac (and many others?) gensets with electric start, they keep the starting battery charged from the 120/240 VAC--And you would need an alternate charging source (such as a smaller solar panel+solar charger) to keep the battery charged for off grid use...

From what I have seen posted here, a "cheap/average quality" inexpensive genset would have a "good life" at 600 to 1,000 Hours before something broke. And a "good quality" portable/residential genset (such as the Honda gensets) can get 2,000 to 6,000 hours with good maintenance/regular oil changes... For a "real" off grid genset--You are probably looking for >30,000 hour life between overhauls (pure guess).

While a step down 240 VAC to 120 VAC transformer can work--As you have seen they are not cheap, you have extra losses because of the transformer, you need a large enough "genset" that can power up the transformer (a large transformer and smaller genset may not be cable to power up such a transformer).

I personally (if you have a 240 VAC only genset), would suggest looking out for a 240 VAC battery charger (there are also some 120/240 VAC input chargers too)...

Depending on the size of charger you choose (say more than ~500 Watts or so--Guessing), many of the larger battery chargers are 240 VAC input units... And there are more modern smaller chargers that are 120/240 VAC input (usually the more expensive brands/models).

I do not know much about the "generator/alternator" head market... You might have to do a lot of searches/talking to vendors to find a head that is in the lower power range (a "3 hp" genset would technically drive a ~2,000-2,500 Watt head). Many of the heads out there seem to be close to the 10 kWatt or larger range and are usually 3 phase output...

Here is one site (I know nothing about the site--Just a quick web search) that has some information (including a way to wire a 3 phase alternator for 1 phase 120/240 VAC output (zig-zag connection)--An interesting option (don't know anything about how well it works):

https://www.auroragenerators.com/alternators

I don't know much about Lister installations--But have read about some folks that say they can see the lights brighten/dim with every power stroke from a 600 RPM diesel driving a 1,800/3,600 RPM alternator head...

If you are looking for a 48 VDC alternator, you can sometimes find some interesting units by searching for Marine Alternators... Balmar used to be a good brand (I think they have been sold to a new owner--Don't know anything about their present quality):

https://balmar.net/96-series-48v-alternators/

The "marine" units are nice because the controllers are usually designed for properly charging battery banks (vs just holding 48 VDC to operate loads)....

-Bill

m151

Some generators will have a switch to combine both legs (Honda EU7000). Will your system have auto start? Then you will need propane or diesel or a fuel injected gas model.