CountryPlans Forum

I'm putting my new Charge controller in this week and re doing the breakers and disconnects as well.

Since we're getting a lot of off grid interest now, I thought I'd throw in a few tips.

You can buy very expensive 12 volt equipment. It isn't necessary though.

There is NO difference between DC amperage and AC, There is a twist I'll get to in a minute.

For 12 volt systems, use standard Breaker panels. My new one is a 220 volt 60 amp breaker, That allows me to hook both the wind and the solar in the same box and still not exceed the rated amperage of the charge controller.
For the panel and battery disconnects, I just use unfused heat pump disconnects. About 8.00.

Here's the twist. While the current is the same on AC and DC.....Dc has a longer arc. At 12 volts, this isn't a problem however at 24 volts and above, it slows the breaker speed considerably. Either reduce the amperage of the breaker by 10% or better yet, use fuses. The fus bus's are hard to find sometimes but give a cleaner break than breakers.

The Square D brand, series QO breakers are UL approved for up to 24 VDC, breakers available up to 60 amp maximum, and available at Home Depot.

You can use one 60 amp as the main and back feed it into other breakers for individual circuits.

Not suitable for inverter feeds as the amps are usually way too low.

I believe the big difference in breaking an AC circuit compared to DC is that because AC alternates 60 times per second that makes it much easier to break the circuit.

Fuses are also rate AC or DC.  DC-rated fuses include Class T, Class R and Class ANN. Dc rating is probably most important when using them for high current applications such as between the batteries and the inverter. Class T are usually code approved.

Additional note: Simple on-off switches that are designed for AC loads will burn out quickly if used for DC power circuits. It's because of that arc. DC rated switches are not easy to find if one is looking for a switch to fit in a standard house electrical box. Cooper makes one or two, but they are hard to find.

High current DC rated breakers suitable for protecting an inverter can be found at golf cart suppliers. Kind of pricey, but cheaper than some solar specialists. You may have a time finding a box for them.

I've bought a couple from solarseller.com   He has lots of sometimes harder to find stuff. The ones I bought a while back were on a sale, part of a special purchase, not his regular stock. $65 for a 250 amp 125 VDC rated breaker.
http://solarseller.com/dc_circuit_breakers__dc_circuit_breaker_ul_listed_to_125_volts_dc.htm

As usual Don, you've done your homework and yes, Square D is what I use. The Square D main will work to 48 volts but in order to get a quick break, you do need to reduce the amperage breaker.

It will NOT pass code at 48 volts, just as as you stated.

The disconnects I use are the pull type. I've never had a problem with them burning.

For fusesm I use marine fuses and fuse bus. I haven't looked at the ones on the solar page but the marine units are tough and inexpensive. They are made for DC and work very well.

The code issue comes in though. I doubt they will pass code. That's not something I worry about but for those getting inspections, you need to pay attention to it's certification.

Needing to meet code casts a different light on component choices.

Personally I believe the only time you may have a problem arise with the AC pullouts on DC is if you pulled it under a condition of heavy load. Probably would spark, but it's not every day you pull them. Absolutely no problem with them just sitting there. If there's a code guy lurking they wouldn't fly. They sure beat the prices on DC rated disconnect switches.   :)

QuoteDC rated switches are not easy to find if one is looking for a switch to fit in a standard house electrical box. Cooper makes one or two, but they are hard to find.

FYI, Cooper Wiring Devices, item# 711 is a double switch AC/DC rated (a duplex receptacle cover trims it)

I thought about this post last night and think it needs a little more detail. It was intended to show people new to off grid, that less expensive methods and equipment can be used on yjeir systems.

Don in his normal, detailed way, showed the possible errors and I agree with him. A little explanation on DC vs AC breakers. Even though there is no difference in the current, AC chops it into 60 pieces per second thus shortening the arc. DC will in essence, try to weld a breaker closed. This is the reason I prefer fuses for high amperage protection....actually, I prefer them for all applications. Circuit breakers aren't better, just more convenient....anyway

A DC fuse is designed to soften as it reaches it's blow rating. When the current eceeds that rating, a large chunk of fusible metal drops out rather than just a spot. This eliminates the welding effect.

Even marine fuses in the 400+ amp rating are expensive, just not as much as the special T fuses for solar. There really isn't any difference. They all come out of the same box, it's just that specialty equipment is always higher.

In an industrial setting, fuses are often paralleled to increase the current carrying rating. There are some what/ifs associated with doing this including the ambient temperature of each fuse.

As a practical matter though, two 10 amp fuses will carry 20 amps. Even if one blows before the rest, it increases the current on the others and they fall like domino's

I'm going to put together a high amperage block today just to do it and will post it later. I want to stress though, that it will not pass code!

For non code systems these automotive disconnects are rated at 500 to 1000 amps at 12,24, 36v

http://www.jcwhitney.com/autoparts/Product/Pr-p_Product.CATENTRY_ID:2006124/c-10101/Nty-1/p-2006124/Ntx-mode+matchallpartial/N-10101/tf-Browse/currentRecordCount-5/s-10101/Ntk-AllTextSearchGroup?Ntt=battery+disconnect

Why not use regular auto fuses that you can get at any auto parts store?

Kevin

I am but you can't get large enough fuses for the inverter. I have a 5K inverter and that worked out to a little over 400 amps. The largest I could find this morning were 175 amps. I'll make a block to parallel  them for 350 amps.

QuoteWhy not use regular auto fuses that you can get at any auto parts store?

As Peter stated you can, with an IF...

The big IF is IF there are no inspections necessary. And IF you select your components with care. There are auxiliary fuse blocks available in some auto stores I wouldn't use in an auto. Some of it's cheaply made crap. At least in my experience.

IF there are inspectors your work and components must meet the NEC (National Electrical Code) in most locations. Meeting code, using UL approved equipment, could also be a factor if you ever have a fire and the insurance adjusters look real careful. That's not to say you can't do safe work with components that are not code approved.

I'm not endorsing the use of non approved materials or methods and I don't think Peter is either. But in a situation where you don't have to strictly meet code.... well you decide. Some alternate choices to wire, cable, fuses, breakers, may be perfectly safe... the suppliers have just spent the money to run them through the tests. Just because you have an alternative power source (non grid) does not exempt one from the NEC rules and regs. A lot of the rules make a lot of sense, some may not on the surface, and some... well... :-/  ya gotta wonder about.

Those disconnect switches Glenn mentioned seem to work very well. They are simple and reliable in operation. They are available from many sources. I use a few in my RV power system. One nice thing about the ones with the red handle is that the red handle is removable in the OFF, or disconnected position to reduce danger of an accidental turning ON.

One example of a common "mistake" that may or may not get by your inspector is found in alternative power system battery banks; the battery cables and their connectors. Common automobile battery cable does not carry the UL label. The NEC does not allow non UL listed cables and wires. Some inspectors won't give them a second glance and will pass the system that uses automotive cables. Other anal retentive do-everything-by-the=book inspectors look for things like that so they can use their red tags. Once again what to do depends on your local situation. Ditto all the above on the connectors. Some carry UL approval, but only if crimped in the approved manner. Naturally all these approvals add to the cost of each component. Oh, some solar equipment vendors sell non UL approved cables. They are probably excellent cables, but un-approved. Pardon me for belaboring that point. But if you go ahead and do it your own way, just remember that you're on your own.

I'll close these current thoughts with my personal belief that being neat and tidy, running cables neatly in straight lines with nice turns rather than criss-crossing willy-nilly here and there may sometimes make it easier for some inspectors to gloss over some of the little things.

A final note: New Mexico State University has a website where a host of articles on the NEC and how it specifically interacts with low voltage power systems. The articles go back years and make interesting reading when you note how some things have over time. The articles have appeared in Homepower Magazine.

http://www.nmsu.edu/~tdi/Photovoltaics/Codes-Stds/codecorner.html

What Don Said.

I didn't have a lot of extra time today but I did get the block finished. It still needs the cover which I'll use Kydex and heat form it to give an inch airspace between it and the fuses.

The base is Corian, 1/8" copper and stainless bolts.

It will handle 350 amps and total cost is under 13.00.

I'm not sure where I'm going to put it yet because I already have a fuse at the inverter. Maybe as a doomsday fuse at the battery box.

(https://i198.photobucket.com/albums/aa57/peternap/fus.jpg)

Looks good Peter. I'm curious;  ::) how are the bolt heads protected behind? I've made similar devices, bus connectors and have recessed the heads and then placed another layer of insulating material behind. But some of those were mounted on metal, like an auto firewall, fender, etc.

Kydex is a nice plastic. Tough, abrasion resistant.
I used to use some of it for some playground equipment.
Have lots of scraps around still, handy for all kinds of things.

Ah, a subject I've just been researching!  (In addition to insulation, plumbing and AC wiring...)

I've attached a rough diagram of what I plan to install.  I plan to use the Midnight Solar Mini-DC panel for the charge controller/PV/Inverter breakers/connections and the Square-D QO612L100S panel for the DC distribution panel.  Lowes has the DC panel for like $30.  I may use another Square D panel of the same kind for the AC panel.

http://www.midnitesolar.com/MidNite%20Mini-DC.html

One thing I'd like to setup is a low voltage disconnect for the DC load panel.  I'd like to have it as automated as possible.  Basically it should cut power to the DC panel when the batteries drop to, say 11.7 volts and reconnect power when the batteries reach 12.6V for example.

The charge controller will probably have the ability to control a relay at the right voltages, but I cannot find a relay that can handle 60+ amps DC, be actuated with 12v-200ma and not be a major kludge.

Any ideas on a low voltage disconnect?  I saw one (for ambulances) that was self contained and rated for 100+ A, but I can't find a supplier for it yet.
http://www.ecnmag.com/Low-Voltage-Disconnect-Switch.aspx?menuid=304

PK

Erm... I have the inverter labeled 2500 KW in my diagram... I meant 2500 W...

Lets see 2500 KW.. I'd need a 250,000A breaker from the batteries to the inverter... How big would the handle be on a breaker that size...

PK

I'd check with someplace that repairs winches. A lot of the heavy 36 volt models use 3-12 volt relays connected to the voltage doubler caps. They should be heavy enough.

[highlight][highlight]I'm curious;  Roll Eyes how are the bolt heads protected behind? I've made similar devices, bus connectors and have recessed the heads and then placed another layer of insulating material behind. But some of those were mounted on metal, like an auto firewall, fender, etc.
[/highlight][/highlight]

Sorry Don....I missed that part of your post.
That's exactly how I did it. The bolt heads are recessed in and I have a second piece of Corian behind.

Re: the Cole Hersee LVD. All I found were about a dozen different new product announcements in various magazines. There are 4 models, 1 up to 200 amps.

I also found another company reference with a similar product.

     Intra Technologies recently introduced a solid-state low-voltage disconnect (LVD) designed for aftermarket or OEM factory installation.
     The LVD is an automatic switch that allows truck drivers to enjoy appliances and comfort items during key-off periods -- while preserving battery power needed to start the engine. Using patented technology, the Intra LVD monitors battery levels, automatically disconnecting non-critical power loads when battery voltage reaches critical levels. The unit can be easily installed in any truck by a qualified technician in less than an hour.
     Benefits include savings for jump starts and extended battery life.
     [highlight]Aftermarket Intra LVD's are currently available at Kenworth, Peterbilt and Volvo dealers.[/highlight] According to Intra officials, the products will soon be available at most truck dealers for all makes.

Maybe try one of those truck dealers?

QuoteI plan to use the Midnight Solar Mini-DC panel for the charge controller/PV/Inverter breakers/connections

Hey PK, are you in a code observant situation?

I ask because if you are not you can save a bundle on that Midnite item by buying one of the breakers from solarsell.com. Thing is you have to come up with a way to mount it safely.

Just thought I'd mention it.

QuoteI meant 2500 W......  Lets see 2500 KW.. I'd need a 250,000A breaker from the batteries to the inverter... How big would the handle be on a breaker that size...

I wouldn't want to be anywhere near that when it blew.  :o  

QuoteAny ideas on a low voltage disconnect?

PK, do any of the things on these links look like they'd help?

http://www.pplmotorhomes.com/parts/rv-converters/battery-brain-monitor.htm

http://www.pplmotorhomes.com/parts/rv-converters/002733.htm

http://www.pplmotorhomes.com/parts/rv-converters/battery-relay.htm

QuoteThat's exactly how I did it. The bolt heads are recessed in and I have a second piece of Corian behind.

:) Just wondered if you'd hit upon some other method. Guess that cat's gonna be skinned the one way and that's that.  :-/

Quote

QuoteI plan to use the Midnight Solar Mini-DC panel for the charge controller/PV/Inverter breakers/connections

Hey PK, are you in a code observant situation?

I ask because if you are not you can save a bundle on that Midnite item by buying one of the breakers from solarsell.com. Thing is you have to come up with a way to mount it safely.

Just thought I'd mention it.

I checked that site out.  Good stuff. I quickly realized it's the same site I bought a tiny charge controller from a while back.  I remember the quick delivery.

I'm not in a code area, but I'm buidling as close as reasonable to code.  The nice thing about the Mini-DC is it has a spot for a shunt and extra bus bars on top of having an area for the incoming PV breaker and the charge controller breaker.    I would most likely end up with multiple boxes without it and I'm tight on space.

QuoteMaybe try one of those truck dealers?

Good call! Thanks!  I'll look around.

QuoteI'd check with someplace that repairs winches. A lot of the heavy 36 volt models use 3-12 volt relays connected to the voltage doubler caps. They should be heavy enough.

Thanks for the lead.  I'll see what I can find.

One thing I've had trouble finding is specific/detailed info on small mostly DC installations.  Most solar places assume you'll run everything off the inverter, but we are going to have all the lights, ceiling fan, many plugs and probably the fridge on DC.  I think I've got it handled now, but I've had to pull info from 100 different places.

Thanks again,
PK

I'm running 80% off of DC. That's the biggest reason I've stayed at 12 volts. What kind of information are you looking for?

Here's a pretty good post on 12V.
http://www.fieldlines.com/story/2007/10/25/174452/34

QuoteI'm running 80% off of DC. That's the biggest reason I've stayed at 12 volts. What kind of information are you looking for?

Well, I think I have it mostly together now.  I was trying to find out what breakers, junctions boxes, wiring gauges, switches and plugs to use. :)

For the most part I think I can get away with 12 gauge wire and 20A high quality AC switches.  For the DC plugs, I plan to use 240V sockets like these:
http://www.backwoodssolar.com/catalog/electrical.htm

I would be much obliged if you would post some details about your DC setup, or point me to a thread about it if you already have one.


Thanks,
PK

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.  :-/

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.

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.]

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.

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.  :-/

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 :(

QuoteYou 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.

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.

Good plan, desdawg. :)

QuotePK 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

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.

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. ;)

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.

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

QuotePK, 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