Calculation to determine what capacity generator is required

[Bryan Sawyer]

Add up the total max amperage draw and multiply by 110 (voltage) or is it 120? That will give you the number of Kw generator capacity required? How close to maximum capacity is sufficient? Do you need excess capacity to minimize the load on the generator?

Anybody having good luck with the super quiet water cooled generators like the Panda? My westerbeke is pretty dependable but it sure is noisy.

[Rick Beddoe]

I read a great article in PS (or was it CW) about DC generators a while back. Seems like a practical alternative to AC. They're smaller and quieter (and cheaper) than AC.

Wasn't it Thomas Edison who believed that AC was too dangerous?

[keffer]

I have the 4AGT. Very quiet, very compact; proven to be very reliable.

A few things to keep in mind:

The "auto-on" feature is unreliable. This feature automatically turns on the genset if battery voltage gets too low. I never use this feature anyway, as I don't like the idea of machinery going on and off unexpectedly.

It's a bulk charger. Don't expect to use it to equalize your batteries.

Because of its small size, there is not much of a margin for error in overcranking the engine and flooding the exhaust manifold. It's important to remember to close the seacock if the engine doesn't start right away in order to avoid flooding it.

Finally, because the Panda is so nicely packaged in its hard fiberglass shell, it's easy to treat it as a "black box," and perhaps not monitor it as carefully as a more exposed piece of machinery. You still need to check the oil, check belt tensions, check for leaks, etc. If you do, you'll be happy with its performance.

-tk

[Jeff C]

Yeah, Rick, Edison was adamant about DC because of safety. He even gave public demonstrations (with animals, if memory serves) to show how dangerous AC was. Problem was, the voltage drop over distance meant anyone who wanted electricity had to be situated within a thousand yards or so of a generating plant. His rival, Tesla, championed AC, and proved it could be sent endless miles. He finally won out, due to the greater practicality of AC for the kind of grid coverage we have today.

Those DC generators are inticing, esp. when you consider the efficiency of DC generation-to-DC batteries charging.

Sorry Bryan, that no one is addressing your question.

[Tim]

Add up the total max amperage draw and multiply by 110 (voltage) or is it 120? That will give you the number of Kw generator capacity required? How close to maximum capacity is sufficient? Do you need excess capacity to minimize the load on the generator?

Anybody having good luck with the super quiet water cooled generators like the Panda? My westerbeke is pretty dependable but it sure is noisy.

Bryan, I'll try to address your questions, though these are just what I would do and have done. They are not tech based answers.

First of all, I learned a long time ago to always have a 25% margin of performance over your highest anticipated need. 40% is better... This has worked in every endeavor from Electical to mechanical, to financial budgeting, etc.

Secondly, to calculate electrical consumption, I did a spreadsheet. As you mentioned, I determined the amperage draw per individual consumer, then multiplied the number of hours used by the amperage to determine Amp/hrs per day consumption. After the calculations were totaled, I added 25%.

Now, on several different levels, folks say to not discharge even a deep cycle battery below 50% So, after calculating total daily consumption, I decided I wanted to go for a week without charging. This worked out to 500 amp hrs/wk, so I needed a 1,000 amp hr battery bank.

My personal goal was to achieve total energy independance wrt electricity. So, after building my 1,000 amp hr battery bank. I calculated what I would need in terms of solar capacity to keep it charged.

A 125 watt Solar panel puts out about 8 nominal amps at full capacity. I've seen peaks of 12 and more, but the specs, if they are honest will tell you 7.5 - 10. So, I used 8. 8 amps X 2 panels = 16 amp hrs X 8 hrs = 256 amp hrs / day. Double my potential peak need.

I calculated that even though efficiency in Solar Panels drops quickly on cloudy days, because I would still likely be getting 20% charging efficiency even on cloudy days, it would take a month of cloudy days before I'd run out of battery. So, assuming that in that month, there would be at least a handful of sunny days, I would become potentially umbilical cord free.

Now, to take those calculations and turn them into running a generator, you will need to ask yourself, how many hrs per day are you willing to listen to the generator. Or if it's in a sound box and noise is not an issue, how many hrs per day are you willing to pour fuel through a generator?

As for the output calculations, if you have 120 v output, it will then be run through a charger which will need to charge at X amps to achieve your fully charge goal in Y hrs. I suspect your choice of charger will be more critical here than choice of generator, aside from the noise issue.

For, if your charger is only capable of 30 amps, it doesn't make much sense to get a 10kw genset. My 2kw Honda can keep up with my 20 amp charger.

Those are my thoughts and plans. Unfortunately the bottom dropped out of the job market before I could finish. I got it all done, except the solar panels and I'm now 8 yrs into a 5 yr plan to go away.

Good to see you made it out, Bryan. I remember when you were in Tx.