formulas for energy audit?

[dddire]

Getting ready to a long trip next summer with a few nights boon docking and thinking generator, battery bank, inverters etc and know I need to do an energy audit for my trailer. Trying to put together a spread sheet and realize I'm just far enough out of high school to find this a challenge.

What formulas do I use to find my 120 V, x wattage consumption, to 12dc amp hours needed in my battery bank?

https://docs.google.com/spreadsheet/ccc?key=0AnPcD7QoHLy2dDVuN0xhXzZPVFp2QkpwMEktMk9YX3c&usp=sharing

[dddire]

pianotuna wrote:
Hi,

And what was the specific gravity of this fully charged battery? Or resting voltage? (i.e. sitting for 24 hours with no charging and no loads?)

dddire wrote:

pianotuna wrote:
Hi,

Unless you have beefed up the charging path, very little will be sent to the "house" battery bank from the alternator. Think BIG fat wire (#4?).

With a small battery bank it is better to do closer to 150 watts of panels for each 100 amp-hours of storage. With that small a bank, Keurig is going to be a gen set run.

We have run the gp24 down to about half a couple times, then by the time we've got home, it's full. When the brake control/7 pin was put in, I mentioned I wanted the ability to makre sure it charged the house battery and the tech response was "nothing to worry about"... and I guess I never really thought about it after that. lol

hahahah.. .what you mean the little 4 dummy lights on the TT control panel are not accurate Tuna?

No idea good Sir. I'll take a volt reading before I slam the battery this week with the coffee maker and get back to you with before and after readings. I'll pick up a hydrometer as well. 😉

[pianotuna]

Hi,

And what was the specific gravity of this fully charged battery? Or resting voltage? (i.e. sitting for 24 hours with no charging and no loads?)

dddire wrote:

pianotuna wrote:
Hi,

Unless you have beefed up the charging path, very little will be sent to the "house" battery bank from the alternator. Think BIG fat wire (#4?).

With a small battery bank it is better to do closer to 150 watts of panels for each 100 amp-hours of storage. With that small a bank, Keurig is going to be a gen set run.

We have run the gp24 down to about half a couple times, then by the time we've got home, it's full. When the brake control/7 pin was put in, I mentioned I wanted the ability to makre sure it charged the house battery and the tech response was "nothing to worry about"... and I guess I never really thought about it after that. lol

[dddire]

vermilye wrote:
For what it is worth, here is my experience. I have an Escape 17B, a small fiberglass "egg" with a pair of 232 amp/hr 6V batteries, a GoPower 95 watt solar panel & controller, and a 1000 watt inverter. All LED lighting, a furnace that only draws 1.8 amps, and a bunch of electronic junk, including a laptop that draws 8 amps @ 12V, various camera & cell phone chargers, and a combined cell phone amp & router that draws 2 amps. No TV - I prefer to read.

During a 2 week stay in Leadville, CO (at 10,000' so the mornings required about 45 minutes of furnace running even in August), I made a pot of coffee using a 600 watt drip coffee maker every day. The coffee maker uses about 10 amp/hrs, and my overall usage averaged 25 amp/hrs per day. Because i was dry camping for 2 weeks, I only ran the cell phone amp & router as needed, and was careful with electrical usage.


Sometimes I think this world gets smaller and smaller every day. lol
While the cool weather & high altitude probably helped with the solar panel efficiency, I was able to restore the used amp/hrs each day, often by mid day, and always be evening. I don't carry a generator.

You know, the more I looked at your pick of the Toyota and your Escape, I kept thinking, you know, I seen the EXACT same set up .. some where on the road this summer. Then see in your blog, you did a trip around the Maritimes. I could swear we passed each other on the road. And at the time, I even mentioned to the wife.. "that's a nice set up"

[dddire]

pianotuna wrote:
Hi,

Unless you have beefed up the charging path, very little will be sent to the "house" battery bank from the alternator. Think BIG fat wire (#4?).

With a small battery bank it is better to do closer to 150 watts of panels for each 100 amp-hours of storage. With that small a bank, Keurig is going to be a gen set run.

We have run the gp24 down to about half a couple times, then by the time we've got home, it's full. When the brake control/7 pin was put in, I mentioned I wanted the ability to makre sure it charged the house battery and the tech response was "nothing to worry about"... and I guess I never really thought about it after that. lol

[dddire]

vermilye's set up and use pretty much is identical to mine.. or at least to what I want to set up.

That 1000w drip coffee, I wonder how that compares to the Keurig... one cup at a time as far as how many amp hours it's consuming. Time will tell as you all must know by know, I'm gonna try a cup on battery and figure out amp hour consumption. It's just in my nature.

As far as the "safe" state of charge and how far we can draw them down. I look at batteries as I would gas for the tow vehicle. If you wanna play, you gotta pay. So if I can abuse them for a 2 or 3 seasons, then have to replace them.. I'm cool with that. And remember, our camping season up here is pretty short and most of the time, we're in a CG... so dry camping will never really be more then about 10 days a year I'm guessing. In short, I don't like to throw money away.. but the battery must work for me, I don't work for the battery.

I already have a 3000 Watt inverter and a 400 W and 100W that we use for various things.. so we'll give the 3K a shot of coffee here as a test run and just see how much damage I do to that gp 24. Then I can play stupid to DW and say we need to get new batteries. 😮

[mena661]

dddire wrote:
I note on the Trojan site, they indicate the T105's are safe for 80% discharge. How does everyone feel about this? I'm thinking 50% obviously is safer.. but maybe the odd 80% in there?

I would keep 70% and above. That would still get you 500 cycles and there is a member here who routinely does that to his T105's and has had them last 7 or 8 years so far.

pianotuna wrote:
Hi,

80% sounds like salesman speak to me.

It's not salesman speak but you'll drop a ton of cycle life. Keep it 70% and higher. These aren't marine hybrid batteries guys. These are top notch deep cycles. That said, unless you're WELL versed in battery maintenance, keep the discharges above 50% or you'll kill your batteries in short order. I'll agree with the others and say keep the coffee maker on the generator with just two 6V's.

[Almot]

pianotuna wrote:
With that small a bank, Keurig is going to be a gen set run.

Why do I always have to agree with Maestro 🙂 ...

Yes. Between 1000W Keurig and 1500W "real rating" of MW, 225 AH bank of 2*T105 will only last 15-20 minutes before the charge drops to 50%. They don't "have" to have a 110A coffee and 130A meals, but if they choose to, they will have to run a genny every time.

[Almot]

Safe 80% discharge is a BS for sure. Otherwise, get a pair of those GC and a 3-day trip with a generator is not really that "long".

Yes, people are running gennies in a Walmart lot while running the sat receiver and AC - if this is what you want. I think you don't even need an RV if those big plans "to see the world" mean seeing it through the TV screen 🙂

When you do start long trips, you will find that AC is needed less than you think. Summer in Canada is one thing, and snowbirding in the South is another. 12V fans like Fan-Tastic will do most of the time. Long trips further South than the US would require a bit more than adding a fan though. You may read blogs on Mexico and S.A. Essentially, those rigs are self-contained in the way unknown to people who travel a day or two in Canada or US. Solar, small compressor fridge that needs no propane, and other things.

vermilye wrote:
I don't carry a generator.

Another proof to what I've found long time ago - people carry generators because they want to. The only device that is necessary AND can't be powered off the batteries and/or solar is AC, and only when it's really hot. Everything else can be modified to work off 12V.

[pianotuna]

Hi,

80% sounds like salesman speak to me.

dddire wrote:
I note on the Trojan site, they indicate the T105's are safe for 80% discharge. How does everyone feel about this? I'm thinking 50% obviously is safer.. but maybe the odd 80% in there?

[vermilye]

For what it is worth, here is my experience. I have an Escape 17B, a small fiberglass "egg" with a pair of 232 amp/hr 6V batteries, a GoPower 95 watt solar panel & controller, and a 1000 watt inverter. All LED lighting, a furnace that only draws 1.8 amps, and a bunch of electronic junk, including a laptop that draws 8 amps @ 12V, various camera & cell phone chargers, and a combined cell phone amp & router that draws 2 amps. No TV - I prefer to read.

During a 2 week stay in Leadville, CO (at 10,000' so the mornings required about 45 minutes of furnace running even in August), I made a pot of coffee using a 600 watt drip coffee maker every day. The coffee maker uses about 10 amp/hrs, and my overall usage averaged 25 amp/hrs per day. Because i was dry camping for 2 weeks, I only ran the cell phone amp & router as needed, and was careful with electrical usage.

While the cool weather & high altitude probably helped with the solar panel efficiency, I was able to restore the used amp/hrs each day, often by mid day, and always be evening. I don't carry a generator.

[dddire]

I note on the Trojan site, they indicate the T105's are safe for 80% discharge. How does everyone feel about this? I'm thinking 50% obviously is safer.. but maybe the odd 80% in there?

[dddire]

pianotuna wrote:
Hi dddire,

No, I'm saying you would be better off with ~350 watts of solar.

On a sunny day you might get one coffee maker run without the genny. But you need a way to rapidly replace the energy so used.

Ahhh.. ok, I appreciate that train of thought. Our trailer is 17ft.. so I'm thinking I might not get more than about two panels up there. But I love the idea of making the whole roof, one giant panel. Now the wife might not like that. lol

[dddire]

westend wrote:
There are more ways to make coffee than using a Keurig or choosing instant coffee. I reread through some of the posts here and it brought up a question: How are you going to fire up a generator in a Walmart parking lot. I guess this assumes you drink your coffee right after you get up in the morning and not later at another location.

ya, we're Keurig snobs for sure. Love the variety etc.
You are correct, morning coffee is fine for us. Maybe a starbucks/Tim's on the road at some point. Or just lunch in the trailer at a rest stop.. and a coffee (on genny) to go. 😉

I don't see any issues with a Genny at Camp Wallyworld. Seems everyone else is running them. Including every coach we see. I assume they're keeping the AC and big screen/sat tv working.

[pianotuna]

Hi dddire,

No, I'm saying you would be better off with ~350 watts of solar.

On a sunny day you might get one coffee maker run without the genny. But you need a way to rapidly replace the energy so used.