Replies

1. 
   Guest_ | Sep 13, 1999 05:59pm | #1

   *
   Allthough this wire doesn't meet nec code, it is probably better. Some marine wire mfgrs. (Anchor?) make a wire that looks like romex but the wire colors are red and yellow instead of black and white. You could use it for your DC wiring to prevent mix up.

   The 240V 15A sockets are very good for DC, will fit duplex cover plates and will prevent the wrong voltage devices from being plugged in. DO NOT use cigar lighter plugs.

   Remember to use large enough wire to keep your full load voltage drop to under 5% and preferably under 3%. This will take larger wire at low voltage than at 120V for the same amps.

1. 
   Guest_ | Sep 14, 1999 05:13am | #2

   *"Remember to use large enough wire to keep your full load voltage drop to under 5% and preferably under 3%. This will take larger wire at low voltage than at 120V for the same amps."Really? Don't you mean for the same watts?

1. 
   Guest_ | Sep 14, 1999 07:29am | #3

   *Yeah, I agree with Andrew that you probably typo-ed the amps when you meant watts - the maximum ampacity of a wire remains pretty much the same for any voltage up to its maximum voltage. Thus for the 10 guage THHN, I think you would get a maximum allowable amp rating of 55 amps (open air) - thus at 10 volts you would get 550 watts while at 100 volts you would get 5,500 watts. The rating of other components is not necessarily the same for DC and AC, however. Some fuses are rated differently for AC and DC or not recommended for one or the other. The same may be true for switches, plugs, and some other components. In at least part, this appears to be because of the way AC and DC currents are rated in common usage. AC voltages are given as the RMS (root mean square) voltage in which the peak of the sine wave is actually 1.414 times the RMS value. (The RMS value is a type of averaging that is used so that you can readily figure power as RMS volts times amps without having to figure the peaks and valleys of sinusoidal current.) DC is most commonly a steady state voltage with only minor fluctuations. Of course, there is such a thing as pulsating DC which would seem to be a lot like AC and which can result from unfilted rectified power and.. (...and somehow I am lacking a punch line to end this thing gracefully...)

1. 
   Guest_ | Sep 14, 1999 09:30am | #4

   *AH, the life of the party. Hey, have another drink.

1. 
   Guest_ | Sep 14, 1999 10:25am | #5

   *My original post was on the other one, but this one has more traffic.Just curious. Why 120 vac at all?Side note::-) I always thought that when I have children, I am going to put a generator on an exercise bike, use it to charge a battery, then run an inverter for the TV ( or 12vdc TV) The more they want to watch, the more they improve physically. At least there would be a benifit from watching the tube. :-)ScottP.S. I mentioned the battery storage out of the cabin, not specifically outside. A battery left outside doesn't fair well in Sunny Florida either. We replace them constanty.

2. 
   Guest_ | Sep 14, 1999 12:15pm | #6

   *Dear Scott,Currently the 3 electrical devices used at the cabin are a Porter Cable 6" sawboss, an old Maytag ringer washing machine, and cordless drill battery chargers. That may not sound like much but, prewiring 115 VAC will be easier now than after insulation and paneling. Battery storage will have to be very well thought out; if I had those answers I wouldn't be picking your brains.As always thank you for your time and suggestions.Sincerely, Joe

3. 
   Guest_ | Sep 14, 1999 06:16pm | #7

   *Yes, I did mean amps. A 12V device will draw 1o times the amps at the same watts but many 12V devices will draw less watts than their 120VAC equivalents. DC moters in particular are more efficent than most AC moters. My DC circ. for the boiler draws less than 5 watts. The reason that I mentioned Amps was that is what the wire, fuses, breakers etc are rated at. At 120V, 5% is 6V but at 12V, 5% is only 6/10 of a volt. So at the same amperage the 12V wiring would have to be 10 times the cross sectional area. On my personal system the wire from the batteries to the inverter is 600MCM (about equal to 3 4/0 cables in parallel).Since inverters are getting better and DC appliances are hard to come by, It is a very good idea to pre wire for 120VAC. It helps with the bank too.

4. 
   Guest_ | Sep 14, 1999 08:16pm | #8

   *interesting

5. 
   Guest_ | Sep 15, 1999 04:53am | #9

   *Since I have done several of these a couple questions come to mind:Why 12VDC when you aren't using PV or wind generation?You don't say where this is, how often you are going to use it or in what seasons. All of these make a big difference on the blend of electricity sources.How do you plan to heat the cabin? Use a refrigerator?What I've found to be a good model to follow is to treat the cabin as a boat or an RV when thinking about how to address problems. Using marine or RV components, while not necessarily according to the code, does provide safe, efficient distribution. The codes really don't do a very good job of handling electrical distribution in what I presume to be a wilderness, or at least a country setting.I'm in and out of town but if I can answer any questions in the next few days I'll be happy to.Oh yes, batteries. A fully charged lead acid battery doesn't freeze until -70F or so. So putting them outside is just fine. Whether they are outside or inside is really a personal choice. I like mine outside and just use a couple more to make up for winter inefficiency. Other folks put them inside. Frankly, in about 20 years of this I've never seen a specific venting provision in a residential setting. Folks just leave them in an open area where the rising gases don't get trapped. Again though, why batteries unless you are using some type of PV or wind generation?Sounds like you are in SE Alaska. Where exactly?

6. 
   Guest_ | Sep 15, 1999 07:58am | #10

   *Reply to Fred B.,Fred, I'm going to handle your questions in order. I don't want to listen to a gasoline powered generator or go outside and fire it up just to turn on a light. Lights will be the primary function of the 12V DC circuits. Potentially we will occupy the cabin during any season. Wood is our heat source in potentially a well sealed and insulated `one room' 1-1/2 story cabin. The second half story is not a loft but, it is not sealed between floors. I anticipate installing a 24" propane range and a propane fridge. Ice and snow are available near sea level December thru mid June. They can be used in coolers when available. This cabin is on the Kenai Peninsula's Pacific Ocean coast in South Central Alaska over 30 miles from the nearest port. The unenclosed porch could have an enclosed but vented bench for battery housing if the additional enviromental safety warrants the extra work when `opening' or `closing' the cabin(IE moving the batteries in and out). We (my wife Mary and I) have the idea of a mini hydro plant for future battery charging. I believe if a sufficient amount of charging occurs combined with adequate storage, then we could run higher draw appliances through an inverter with the power distributed conveniently through the 115 VAC wiring. Thank you for taking your time to help me with these design issues Fred.Joe

7. 
   Guest_ | Sep 15, 1999 11:39am | #11

   *OK-Just happen to be around the computer twice in one day so can do a fast turn around.If you are on the Kenai wind is a viable alternative as is PV for battery charging. Or, you can just use the generator to charge a fairly large battery bank so you only have to run it once or twice a week. That is what I'll discuss here and now.Since cold weather starting isn't an issue in that relatively mild climate you can just enclose the generator with the batteries or in any other shed that is open to the earth at the bottom and insulated. Earth temp will warm it enough to start on all but themost rare occasions. Then you can open the shed to provide adequate cooling for the the generator.I recommend the "hockey puck" style halogen lights. Just cut the transformer off them and wire to your 12VDC system. They work great; put out a lot of light and consume little electricity. I don't care for flourecents due to their starting currrent and low light output. But that is a personal matter. Home Depot or Eagle both normally stock them.West Marine has some reasonable boat distribution panels that work fine. Just use large wire and the normal electrical practices.Back to batteries. You will probably find that 6V golf cart batteries wired in series will provide the best amps/dollar over time. Sams sells 220AH batteries for about 45-50 dollars each. They are practically indestructable. But, they have full charge at 12.7 Volts so some items, like cell phones, always report that the battery is low because they are expecting the 13.8V of an auto system. But everything I've ever tried works on this type system.None of this is particularly "code compliant". But it works and is safe and is relatively inexpensive. There are systems all over your country that use this type thing safely and efficiently year-in and year-out. Remember you are using components that have been time tested in golf carts and ships.I haven't found very many of the magazines useful for remote site design issues because they are more theological than practical. That is they approach the issue from some idea of conservation and minimalism rather than of necessity to have the creature comforts a person wants in a setting like yours.I assume you know how to size your battery system so haven't addressed that here.Best to you.

8. 
   Guest_ | Sep 16, 1999 08:36pm | #12

   *Don't know if you are still interested. But, it occurs to me that if all you want is lights you shouldn't dink around with batteries and wiring at all. Just use propane lights that are plumbed in with your range and refer. In fact, since you are in the Kenai I'm surprised you weren't encouraged to do that by some of the locals. I've used them in the Rockies and in the North and they are great, light and a little heat to take the chill off. Or, you could just use coleman lanterns. Either would be preferable to messing with 12V just for lights.

9. 
   Guest_ | Sep 16, 1999 09:02pm | #13

   *Just ran into your post on the shingles. So I gather you live in Oregon and will vacation in the Kenai. Reinforces my last post...don't mess with 12V, just use either propane or coleman lanterns(unleaded gas variety if you can find a quiet one).

10. 
    Guest_ | Sep 16, 1999 09:03pm | #14

    *Hello Fred,Yes I'm still interested and not quite ready to let go of this topic. Propane lights were considered but, in a small enclosed cabin like this we want to minimize interior air pollution. I thought I probably would install a couple of propane lights when I installed the fridg and range next spring.Thanks again Fred, were do you live, if I might enquire without giving offence?Joe

11. 
    Guest_ | Sep 16, 1999 09:06pm | #15

    *Hello Fred, I see we are working these keyboards at the same time. I have a Coleman lantern and I'm going to buy another in a couple of weeks.Joe

12. 
    Guest_ | Sep 16, 1999 09:28pm | #16

    *If the generator is watercooled you could put a radiator inside for extra heat. There are some nice 12V flourescent lamps made for RVs but I prefer in my house to run the 120V compact flourescents off of my inverter. I only have a few 12V lights left on my system.

13. 
    Guest_ | Sep 16, 1999 10:00pm | #17

    *Yep makes for a fast turnaround. Once one goes off the grid what counts is: "Does it work?" Lots of places use propane/coleman lanterns. As long as one is in the heating season any gases are sucked up the chimney. The rest of the time an open window does the job just fine.Did a job up in the Interior this summer. In that one the owner is using propane for cooking and refrigeration, Both PV 12V and Unleaded Coleman for lighting(it will be used at colder than the "freeze point" of propane), and wood for heat. The generator is used for heavier tools and to recharge batteries when needed. Heat is by wood.You might want to contact David Thomas. I notice he lives in the Kenai. Even if he might be strictly an urban type he might be able to turn you on to local suppliers.