Learning and rethinking my cabin power system

Posted by Jerry Wenzel on August 06, 2008, 11:45:34 AM

Learning and rethinking my cabin power system
I’ve been learning a lot on the forums.  I’ve been asking questions regarding a cabin with a 2000W inverter system and the maximum current I can pull from a set of golf cart batteries. (See Lead Acid Max Discharge thread) I wanted to be able to run a couple of small kitchen appliances, along with CFL lighting.  At this point the appliances were a 1000W microwave and 800W toaster. 

I bought a remanufactured Xantrex Prosine 2000W Inverter/Charger.  I liked it because it has a built in charger, pure sine output, and a sophisticated remote display with a lot of monitoring functions and settings.  However, I underestimated the cost, wiring size and battery bank to provide this inverter with 200 to 400 AMPS of 12VDC.  1500+ Watt loads would be short term, but still the system needs to be sized to handle what the inverter can pull.

When looking at my other AC loads, they are 165W of CFL (Assuming all the lights are on) and maybe a small TV or a Fan.  I’m now rethinking my approach and considering a smaller inverter with the bigger loads run by the generator if needed.  The generator would also charge the batteries whenever it’s running.

With taking the big loads out of the equation, I now estimate 450 watt hours per day.  At 20% DOD, my battery capacity should be 222 A/H which can be met by a set of 6 Volt GC2(T-105) in series.

I’m looking for feedback on this new design and suggestions for the equipment. (My initial selections are in parens)

Inverter, pure sine.  (300W MorningStar SureSine)

Battery Monitor (MorningStar Remote Meter connected to Inverter)

Charger, Could I use a solar charge controller and feed it with a DC power supply or unregulated battery charger run by the generator?  When I add PV panels I could use a relay or diodes to allow either the generator DC power or PV panels to feed the controller? (Xantrex C35)

If I use a pair of T-105 225Ah Batteries in series, is 30A bulk charging current to much?

I know I need to fully charge the batteries on a regular basis, but do deep cycle batteries mind getting intermittent bulk charging as the generator is started and stopped for other uses? 

Thank you,

Jerry
 

Posted by Ken Hall on August 06, 2008, 04:30:17 PM

Re: Learning and rethinking my cabin power system (Reply #1)
Jerry:
I am glad you took the warnings about battery sizing to heart. But I think you misunderstood the message.  There is nothing wrong with using the large inverter. You just have to be careful not to put too much load on it.

You can install the Prosine off of a breaker in your main electrical panel, using a 15-20 amp breaker. You tell the Prosine what size that breaker is.  You run the inverter output to another distribution panel, usually next to the existing main panel. You then transfer your lights and a couple of outlets to this panel.  This will involve some rewiring. How much, I can’t tell you.  In some cases it is easier to run a new system (wiring, lights, and outlets) off of the new panel, rather than to try to unscramble and reconnect “parts” of the old system.  It might look funny having 2 ceiling lights in the same room, but that would also give you generator driven lights, should the inverter/battery system fail for some reason.
I like to use different color outlets or label them, so that everyone has a visual reminder of which outlets are the inverter outlets.

By limiting the outlets (and lights) that are connected to this inverter distribution panel, you are limiting the load that you are placing on the inverter/batteries.  All other electric, remains in the main panel.  Your generator is connected to feed the main panel.

When you fire the generator to support the larger loads, the Prosine will limit the current that it draws for charging, so that it will not trip the breaker.  Because you tell it what size battery you have, it will limit the charging current to the battery to a safe level.

I would still give some thought to increasing the battery size. 4 T105’s would give you 2 days storage at 20% DOD.  Nice to have on that overcast weekend when the generator fails.  Also gives you better discharge/charge rates.  But whether the benefits of the larger battery, will offset the cost increase, is ultimately your decision to make.

Ken
 

Posted by Jerry Wenzel on August 06, 2008, 05:50:20 PM

Re: Learning and rethinking my cabin power system (Reply #2)
Ken,

Initially I wanted the convenience of the family being able to have lighting and use of small appliances "at their finger tips"  IE They need to conserve but power is there when they need it.  The 2 appliances I thought we would make intermittent use of were a microwave and toaster.  To run one of those at a time and have extra for lighting, I got the 2kw inverter.

After doing more homework, I began to realize the challenges and expenses of feeding a 2kw inverter with adequate DC power.

In looking at my loads, I had the 1000+ watts to run a appliance and 165 watts of lighting load.

It got me to thinking whether I could simplify and reduce costs on my system by giving up the ability to use 2 appliances or putting them on the generator.  I'm also thinking a 300W inverter is going to be more efficient at providing 100 watts of lighting load than a 2000W inverter.  I have questionable solar exposure and think I have a better chance of future PV panels keeping up with replacing lighting power than what the 2000W inverter will consume.  I also plan on eventually upgrading to a remote start genset so using kitchen appliances would be able to be used with the flick of a generator start switch.  A kitchen on a genset also allows the use of long running heating appliances like griddles, quesadilla makers, blow dryers etc.

I rushed into getting the 2000W inverter. But I have learned in the past weeks that off grid power systems require some thought to serve a family’s needs and still be cost effective. I want to step back and take a realistic look at what best fits my needs and budget.  The cabin is new, no wiring yet and the walls are wide open. 

My question at this point is do I spend the extra $500+ on upsized batteries & DC cabling/breakers or do I sell the Prosine and put in a system that can provide power for CFL lighting and other small loads.  I’m not in a rush to make that decision and I want to take the time to get the system right for our needs. 

This forum has been great for learning and I welcome more feedback.
« Last Edit: August 06, 2008, 09:32:45 PM by Jerry Wenzel »
 

Posted by Ken Hall on August 07, 2008, 07:23:43 PM

Re: Learning and rethinking my cabin power system (Reply #3)
Jerry:
What do you mean with “questionable solar exposure” ?? This is the first mention of that.
Also, what is the meaning of “future PV panels” ?  Is it just a general reference that the entire system is in the future, or are you thinking that the PV might be installed later than the batteries ??
Also, what size generator are you thinking about ?

Meanwhile, you can toss the idea of feeding a solar charger with a generator based dc source.

Ken
 

Posted by Jerry Wenzel on August 09, 2008, 01:22:52 AM

Re: Learning and rethinking my cabin power system (Reply #4)
With my solar exposure, there are 2 trees south of the cabin that may block sun in the non-summer months.  I could cut them down if needed.

The reason I said future PV panels is because I was planning on not installing them until late fall or spring.  We are busy finishing the cabin and using a 3500W genset to run tools and it could charge the batteries at the same time.  However, if I want to leave the batteries at the cabin this winter, I think I should have the PVs up to keep a float charge on the batteries and prevent them from freezing.

I have a 3500 watt Kohler genset with manual start.  I also have access to a 1000 watt "cheapo" generator.  At this point I'm trying to decide if I should size my batteries and inverter to handle a 1000W kitchen appliance load and a 200W lighting/small TV/fan load or nix the ability to run kitchen appliances off the inverter and put in a 300W inverter.

If I do just the lights, I will likely put in a remote start genset for other high power, low use kitchen loads.  If I do that, I could possibly depend on the genset for most of my battery charging and use a PV to do the finish charging.

In regards to using a charge controller (cc) for charging from a genset powered DC supply.  It looks like some ccs can take DC from a variety of sources.  The Xantrex C series appeared to be able to do this.  I have a 24VDC 25A power supply I was thinking of putting between a genset and a cc. 

Could you let me know what problems you see with that approach?  I know its more pieces.

Also, do you know of AC multi-stage battery chargers that allow you to limit the max charge current so as to not exceed 10% of the ah rating of the batteries?

Thank you for you patience.
 
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