Generator distance from

the house. What is maximum? Seems like this would be easy to find, but it is not. I though someone wi;d have it top of mind...or pretty close.

4000 watts. Will be used to charge batteries, but as doing that will also power things.

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That's because there is not just one answer

Fixing my bogus formula. I was going to work in terms of power loss, not voltage loss and, well, got half and half. Sorry. I also address a comment about power factor.
The magic formula (that I have told Brad all too many times is E=I*R. The complicated part is what does that mean?

I am assuming you are talking 120V from the generator. if that is the case, the maximum current (I) is 4000/120 or 33.3 amps. You need to know that for two reasons:

  1. The minimum wire size you can use.
  2. To calculate the voltage drop.

If you grab a wire guage table, (this will do if you don't have your favorite you will see that you need at least 10 gauge wire for this much current. That number comes assuming you have wire with insulation capable of handling a 75C temperature. If not, you should go to a heavier wire, namely 8 gauge.

The voltage drop is the next piece to calculate. Here you can be pretty subjective. Are you happy with a 10% voltage drop? 5%? A typical standard is actually 2%? You get to pick.

Armed with the wire size you picked and the voltage drop you can tolerate, you are ready for the forumla I presented. It will be more convenient in the form R=E/I. E will be the voltage drop you are willing to accept and I is 33.3.

If you picked 5% drop, you are talking 6 volts. That gives you a value of .18 ohms. that means you need to keep the wire resistance below that value. 10 gauge wire has a resistance of 3.277 mili-ohms per meter. Dividing .18 by .003277 you get 54 meters. As that is the total wire length, the actual distance is half of that or about 27 meters. Larger wire will, of course, allow you to increase that distance.

That's the legitimate arithmetic. You now need to consider how much power you really will be running to the load, how much voltage drop you are willing to tolerate and allow for the Nicaraguan fudge factor.

These calculations assume RMS (root mean squared) current for a load with a power factor of 1. That is, the equivalent current in a DC circuit which is the normal way to do these calculations. If you have a load (such as a motor) that is inductive, for example, then the picture changes. For power factors less than 1, the apparent power (voltage times current, measured in volt-amperes) will need to be greater in order to deliver the specified number of watts to the load.

I^2*R is specific to DC for wire loss

Since this AC it has more to do with "power factor" .

Avoiding the math, here is a table that breaks out by wire gauge vs power factor.

Typical would be your instantaneous draw (or supply that your generator can give) plus a few percent.

So if we are talking coffee pot, Fridge, Toaster and TV then you are around 4800VA power factor selecting the wire for worst case (all on at the same time) .

Watch your neutral grounding is your lengths increase ..


Table sums it all up

without the math. Might be useful to others who are not related to Tesla. As a not, the ditance calculation (in the next to last paragraph of the answer) seems to be at odds with other references, or maybe I did not get something. In that I read the distance of the cable to be 1.65 meters, but that, of course, is way too short. At any rate the table does it for you nicely. Cuts off at 10 gauge, but if you use 8 gauge, you can extrapolate.

I Experimented

quite a bit at my place in Mexico (beach). trying to eliminate the noise from our generator. I found out a couple of things.

You can mute the noise considerably with distance and a structure but not eliminate it. 100 ft and a 3-sided structure with a roof helps a lot wile still maintaining the necessary ventilation. I needed a structure to slow down potential thieves anyway. Generators in rural Mexico were prime theft targets.

I always planned to experiment with some open faced fiberglass insulation in the wall that faced our house but never got around to it.

Use the biggest wire you can conveniently get your hands on. I would hit the power people up for a length of the wire they use for house drops (I believe Phil said this was #6). I was already offered wire at my farm if I needed it, unsolicited. If you are charging batteries you want every possible volt you can get. Use No-Ox where you make the connections.

Generator speed makes a big difference in the noise level. Quality diesel generators usually run at 1800 rpm. Very large diesel generators run as low as 900. Most gas generators run at 3600. Better quality ones have better mufflers. Not only does your generator consume less fuel at the lower RPM but it will last a lot longer. You can expect 10K hours from a stationary diesel generator if it is well taken care of (oil changed regularly, not overloaded). My Northern Lights 7.5KW weighs about 900 lbs, not impossible to steal but would required some planning.

There is a lot of quality diesel power plants available on the surplus market at very good prices. Buy what you need as you will be paying for those cylinders to fill and empty even if the generator is not loaded. Diesels run best at a steady speed at their rated load. You don't want to overload your plant but you don't want to baby it either.

Actually now that I re-read...

What is your voltage that you want to transport from the generator??

If it is AC - 120V this is quite easy..

If it is 12V at high current it is impractical to transport more than lets say 10-15A more than 20' ..

If your end goal is a 12V charge delivered to your batteries you may have to transport 120V @ 30ish A from the generator to a couple of 120V large battery chargers (e.g 100A plus) at the battery location itself..

Right On!

There are commercial transformers available to boost your voltage if you have to run a really long distance from the generator. But, with 220V (two hot legs and a neutral) you would be able to go 200 feet with the #6 at 50 amps without significant loss.

DC of course won't go through a transformer. The aux DC from most generators is designed to charge the generator battery, will not really make a dent in your battery charging requirements.

Convert your AC to DC for battery charging right at the battery location. There are also 220V battery chargers available, widely available from marine sources.

The best chargers will be 3 stage, with thermocouple feedback to avoid overheating the battery bank. They will maximize the charge into your batteries while at the same time protecting them from overcharge.

Would also work @ 220V ...

To feed a typical household panel rather than a cludge of a 110 wire in to the pannel (e.g. only one rail of the breaker box...)

DC can go through a transformer... Once...

My Dad's ol Lyster 4 cyl diesel could keep the 2 Cleaver-brooks Volcano 1,000,000 BTU boilers and associated circulation pumps going on those cold January storms when the power went out.. But I am not sure which was louder .. The gale force winds over the greenhouse or the generator exhaust at 50 yards away :-)

Watch the battery ESR vs your charger... IIRC from my days as Minkota trolling motor repair twenty (mumble) yrs ago... Deep cycles like both slow charge and slow draw while car batteries can charge and discharge quite freely.. Has something to do with the size of the lead oxide flakes on the plates IIRC..