Author Topic: Disconnects and breakers for off grid  (Read 12569 times)

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Offline MountainDon

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Re: Disconnects and breakers for off grid
« Reply #25 on: October 26, 2007, 10:40:01 AM »
PK and Peter, can I ask what's your longest run of cable from source to point of use? And how many 12 V amps used?

Curious here, because I've gone back and forth between doing a major amount of 12 VDC or mostly (all?) AC through an inverter. When i run numbers and see voltage drops greater than 2% (in DC) I don't like it. Maybe I'm too particular.  :-/
Just because something has been done and has not failed, doesn’t mean it is good design.

Offline peter nap

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Re: Disconnects and breakers for off grid
« Reply #26 on: October 26, 2007, 11:11:31 AM »
2% is a pretty steep drop on your 12vdc system Don. Where are you measuring  that drop and what kind of load?
My runs are pretty short Don. I guess the longest one is 15'. They will be longer in the new place though.

I have 2/0 wire running to my main. From the main I run 10 ga to the sub panels and 16 ga directly to the  nearby outlets. The sub panels are just automotive fuse panels mounted in a disconnect case. This keeps the runs very short and easily configurable.

To be honest, I don't have any discernible drop on any of the legs. I also don't have more than 10 amps on any particular leg either.  I also have everything going through conduit so if I need a heavier wire, I can pull it by either using the old wire or using one of several strands of nylon line I pulled through with the wiring.


Offline MountainDon

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Re: Disconnects and breakers for off grid
« Reply #27 on: October 26, 2007, 11:54:10 AM »
Some of it's theory and some of it's practical from the RV.

3.8 amp RV furnace blower load with a run of 15 ft, 12 gauge wire measures out to a 1.96% [+-.05%] voltage drop, while my calculator comes out with a theoretical 1.83% drop. Pretty close.

So then to the cabin design: all theory at this time.
A theoretical 3 amp, 12 VDC load with a 25 ft 12 gauge run = 2.41% drop. 10 ga. comes out at 1.51%      That has made me wonder about the advisability of running 12 VDC. I've considered running 24 VDC but I don't really want to go there as some items are difficult or more expensive to get in 24 VDC. So I end up figuring that most everything thru a good inverter may be the best way. Most everything, as even then I'd wire in a couple of 12 VDC lights just in case the inverter crashes and burns someday. 120 VAC also has the advantage of making things easier to understand for my electrically challenged wife. [even tho' the 12 VDC would have plugs and recepacles of the 240 VAC as PK pointed out. It's the only safe way to mix systems.]
Just because something has been done and has not failed, doesn’t mean it is good design.

Offline peter nap

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Re: Disconnects and breakers for off grid
« Reply #28 on: October 26, 2007, 12:18:03 PM »
That's amazing Don. Your 3.8 amp load is 45.6 watts. That draw is the same as my vent fan on my composting septic system. Using 16 ga wire at 5 feet, I can't measure a system drop at all. There is one of course, but it won't show a measurable drop in the battery for hours. The battery bank has 10800 available watts at full charge.


Offline MountainDon

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Re: Disconnects and breakers for off grid
« Reply #29 on: October 26, 2007, 01:09:43 PM »
Analog or digital? I measure at the battery, or rather off a heavy copper distribution block very close to them. (inside the coach on the inside of the bulkhead) Digital meter hard wired in place.

 :-/  Here's what I saw. Meter reading 12.55 volts. turn on the furnace and the reading quickly scrolls down and settles at 12.30 with the fan running steadily. There's a momentary blip down when the igniter cuts in briefly, then the voltage returned to 12.30 with .01 skips down, then back up, every so often. Over a period of time the voltage drops in very small increments as the batteries discharge.

I am working off a battery set that's past their prime.  :-[ One 6 volt battery lost a cell a short time ago so I'm down to a bank of 4 batteries instead of six. [ 12 V series-parallel] 220 amp-hr theoretical new capacity per battery, so that's only 440 amp-hr max if new, and they're not. New ones planned for spring. I hate to buy new ones now when there's more than likely only a couple months of mountain access left this winter. Unless there's little snow like in '05-'06. I'm leaving the RV up there this winter and hauling the batteries out each visit starting in Nov some time.

If we do decide to buy a snowmobile (need a hot used deal, and those are hard to find in NM; snowmobiles themselves are relatively rare) I'll need a cargo sled to haul them back and forth.  :-/
« Last Edit: October 26, 2007, 01:17:39 PM by MountainDon »
Just because something has been done and has not failed, doesn’t mean it is good design.


Offline peter nap

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Re: Disconnects and breakers for off grid
« Reply #30 on: October 26, 2007, 01:47:31 PM »
That's the reason I'm determined to use only forklift batteries. While the Golf Cart batteries preform fine, their life is much shorter than the FLB's. Most of the data I read on the is that their life is 10 to 20 years. Well...I may or may not live another 10 years, but not 20 and it would be nice to not have to replace batteries again.

You know...that's disturbing to be able to say with a great deal of authority, that you won't outlive the new batteries....or the metal roof :(

Offline MountainDon

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Re: Disconnects and breakers for off grid
« Reply #31 on: October 26, 2007, 01:59:09 PM »
Quote
You know...that's disturbing to be able to say with a great deal of authority, that you won't outlive the new batteries....or the metal roof :(
Yep! We put a metal roof on the home last November. It replaced a 22 yr old asphalt shingle roof. It would have been nice to have had that metal on there originally to see how it fared over the years.

Re: the forklift battery. I read somewhere about someone in AZ who has, so far, got 25 years of use out of the one they purchased new.

My RV golf carts were installed in spring '03. That's 4+ years, 5 actual seasons, with some discharge abuse and those high summer temperatures. I feel lucky! It was only about $300 then.
« Last Edit: October 26, 2007, 02:03:14 PM by MountainDon »
Just because something has been done and has not failed, doesn’t mean it is good design.

Offline desdawg

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Re: Disconnects and breakers for off grid
« Reply #32 on: October 27, 2007, 04:13:25 AM »
The key to a long life is to start more projects. I will need to live to be 100 just to finish the one's I have going. If I start more, well, I am going to need an extension. And I have decided that I am not going to quit until they are done. A rocking chair is not my idea of a good time.
I have done so much with so little for so long that today I can do almost anything with absolutely nothing.

Offline glenn kangiser

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Re: Disconnects and breakers for off grid
« Reply #33 on: October 27, 2007, 06:08:34 AM »
Good plan, desdawg. :)
"Always work from the general to the specific." J. Raabe

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Offline Pa_Kettle

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Re: Disconnects and breakers for off grid
« Reply #34 on: October 27, 2007, 06:38:20 AM »
Quote
PK and Peter, can I ask what's your longest run of cable from source to point of use? And how many 12 V amps used?

Curious here, because I've gone back and forth between doing a major amount of 12 VDC or mostly (all?) AC through an inverter. When i run numbers and see voltage drops greater than 2% (in DC) I don't like it. Maybe I'm too particular.  :-/
I think my longest run will be about 25'.  Thats for a couple of 15W lights.   12 guage should be fine there.  I'll go 10 if it's not too much trouble.  These are lights for illumination when you enter the cabin, so they don't need to be super bright.  We will work out something else to read by if need be.

Most of my other runs should be under 15'.  A ceiling fan that pulls under 2A, more lights, the (maybe) DC fridge, etc.

One reason I'm going mostly DC is that we will not have inverter for a while and I still want some reasonable, permanent light and ventilation in the cabin, soon.

BTW- I picked up a Kill-A-Watt meter last weekend.  I highly recommend one.  I'd always just used my Fluke to measure current draw, but this thing calculates and displays power facter, Watts, VA and it keeps a running count of the KWH a device draws.  I'm running each appliance I plan to have through it for a week as a sanity check against calculated usage figures.

One interesting thing I immediately found was the small 800W microwave I bought, pulls 1520VA out of the socket and my 15W AC compact flourescents have a .6 power factor and pull closer to 25W.


PK

Offline glenn kangiser

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Re: Disconnects and breakers for off grid
« Reply #35 on: October 27, 2007, 06:45:00 AM »
Kill-a-watt meter is good.  I should play with mine more.

The microwave isn't so bad as it is only used for short periods, but I would check out the DC fridge because it is a heater device and will pull so much power over 24 hours you won't want to support it.  It pulls power every minute of the day and night.  Usually they can be used on propane - maybe 5 to 10 gallons a month.  We have one on propane.

"Always work from the general to the specific." J. Raabe

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Please put your area in your sig line so we can assist with location specific answers.

Offline peter nap

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Re: Disconnects and breakers for off grid
« Reply #36 on: October 27, 2007, 01:03:06 PM »
You can run your CFL's on pure DC. It takes 60VDC to start them though...then you drop back to 48. Some of these will buzz on modified sine AC. There is also some conversion loss with an inverter as well as an idle draw.

You get a whole new outlook on power usage when your off grid. ;)

Offline MountainDon

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Re: Disconnects and breakers for off grid
« Reply #37 on: October 27, 2007, 05:24:44 PM »
Interesting thing about the CFL's, Peter.  You can buy CFL that run directly off 12 VDC and 24 VDC. No need to mess with things. Pricey though compared to 120 VAC versions.

I have a Kill-A-Watt... it's a good study tool.

PK, you mentioned a DC fridge. What model/type are you thinking of? It seems Glenn interpreted that to be an RV fridge, normally propane or 120 VAC, but some have the option to run off 12 VDC. Bad idea for 12 VDC and bad idea for 120 VAC, unless the AC is coming from the power grid. There use a resistance heater.   The only 12 VDC fridges that make sense are the super insulated, high efficiency Danfoss compressor types.
« Last Edit: October 27, 2007, 05:25:33 PM by MountainDon »
Just because something has been done and has not failed, doesn’t mean it is good design.

Offline glenn kangiser

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Re: Disconnects and breakers for off grid
« Reply #38 on: October 27, 2007, 05:43:44 PM »
For someone who doesn't need a whole fridge, there is a pretty good solution -- 48 watts at 12 v.  A Coleman Stirling engine cooler.  Much different than the battery hogs.  Still a significant amount of power though.  Still only a  bit over  1 kwh per day if my round number math is correct.  Don? :-? :)


I don't know what the on time per hour is on this thing but power use may be much less if it cycles off and on.  If it doesn't cycle off and use less power then a good Energy Star fridge could be close to the same.

http://www.coleman.com/coleman/colemancom/detail.asp?product_id=5726-750&categoryid=8595

http://www.coleman.com/coleman/images/pdf/5726-750.pdf

"Always work from the general to the specific." J. Raabe

Glenn's Underground Cabin  http://countryplans.com/smf/index.php?topic=151.0

Please put your area in your sig line so we can assist with location specific answers.


Pa_Kettle

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Re: Disconnects and breakers for off grid
« Reply #39 on: October 29, 2007, 06:51:52 AM »
Quote
PK, you mentioned a DC fridge. What model/type are you thinking of? It seems Glenn interpreted that to be an RV fridge, normally propane or 120 VAC, but some have the option to run off 12 VDC. Bad idea for 12 VDC and bad idea for 120 VAC, unless the AC is coming from the power grid. There use a resistance heater.   The only 12 VDC fridges that make sense are the super insulated, high efficiency Danfoss compressor types.
I don't have a specific model in mind yet.  We won't need a fridge for at least a year since we only go up on weekends and our super-duper cooler keeps ice for days.  8-)

When I do pick one out, it will be as efficient a model as is resonable, but not an RV one or anything like that.

PK



 

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