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

[westend]

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.

[dddire]

Hey Tuna, ya, I was leaning that direction for sure.

Genny for now for coffee... but in time, upgrade to 2 6v, for 236amp hrs gross of battery and 200 watts solar. Are you saying with the two 6v's I would be better with 150w solar? Really appreciate the input.

[pianotuna]

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.

[dddire]

Length of stay on this trip is overnight, three nights, with aprox 6 hours drive time during the days. So I assume I'll arrive at the GC each night fully charged from the tow vehicle.

Due to size limits, I will only be able to upgrade battery bank to 2 GC2 but this likely won't happen till down the road, The Genny will come first as it will run the AC and Microwave and top up batteries. And other than a light inconvenience of running the genny more often for coffee in the morning, it will be the best option at first.

I'm learned enough about my use.. and my gp24 and hope of using the coffee making sans genny to know I'll just get up every morning and fire up the genny and not worry about it.

Over the next year or two, I will move to two gc2 6v and about 200 watts of solar. This will reduce the genny run times to only Microwave and AC use when needed.

As far as leaving the home appliances at home.... no way, I have a trailer because I want the convience of home, to be mobile and to see the world and build memories for the kids. I could go back to tenting... my my 45 year old bones are done with roughing it. 🙂

Any my wife just piped up and adv, she does not do instant coffee.

[Almot]

westend wrote:
Thinking further on the OP's situation, I would suggest that now is the perfect opportunity to increase the battery capacity...

This is the only thing - other than doing the audit - that they can do immediately, at relatively low cost, and that they can't go wrong with. Though, there are some variables there too. Another 24? Or a pair of GC? or 4 GC?

The audit should come first - and with it, the matter of coffee and daily genny time VS bank size VS the length of stay. Without the priorities set, it looks like another proverbial can of worms to me...

[westend]

I think at least the OP should get a small commendation for approaching his power situation by first doing the audit. How many threads have there been like, "I want all my stuff to work, what should I do"? Most of those posters are usually suggested to do the audit as a first step or queried about what they are operating.

Thinking further on the OP's situation, I would suggest that now is the perfect opportunity to increase the battery capacity. A single grp. 24 is just barely able to keep up with typical parasitic loads for a couple of days. I would suggest moving to a two battery system. With judicious use, that may be enough to remove the need for a generator every day and that, IMO, is worth well over the cost of upgrade.

[Almot]

Not clear, yes. Meaning - what stage are you on, or it's all just "thinking"? 🙂

Do the audit math anyway. Know thy daily draw. There is no recipe that works for everybody.

You can make it work with a genny 3 times a day, during meals and coffee.

Or you can re-think your meals and coffee arrangements, can be with or without use of MW and electric coffee maker, or with MW and stove-top coffee, and then increase the battery bank to 400-500 AH, no solar. The bank will last, say, 3-5 days with occasional genny runs or without, and then you will go home. People usually don't like to listen when they are being told that they can't take all their "shore" habits with them into the boons without inconveniencing themselves in some other way. Westend wrote about that 1000W coffee maker already, and I agree - powerful 120V devices make boondocking very energy-dependent. You either have to carry a lot of batteries, or cut your stay shorter, or run a genny longer.

Another solution is to increase the bank to 200-400 AH and install a solar. Smaller solar will let you stretch the bank for a few days without genny, and then you will go home. Bigger solar will let living off solar indefinitely or almost indefinitely.

Depends on what you want.

[westend]

Your Keurig will need 80 amps at 12 VDC according to your calculations. Since I believe your brew time to be minimized, I will use the time factor to be 10 mins. (maybe someone wants a second?). Theoretical amp hours used would be 13 AH at 12v but since Mr. Peukert is standing by with his constant in hand, that theoretical 13 AH will be more like 16. Also invited to the morning coffee table will be MS. Inverter Loss. She will account for another deviation of 6-10%. Thus, your morning coffee cabal will eliminate 17-18 AH, almost half of your usable amp hours from your Grp 24 battery.

I've read a few posts about the Keurig where owners could not operate them on a 1500 watt inverter. I think you would be better served by finding a different way to brew your morning Java.

[dddire]

Almot wrote:

dddire wrote:
...monning coffee and microwave use at meal times running on the genny

...and out of the hat comes the rabbit. You should've mentioned the planned generator use from the beginning.

dddire wrote:
So really with the Energy Audit, I want to figure out, morning coffee, lights, water running for clean up and washing. How many nights I could do this... (based on time used for each device of course)... if I would need to fire up the genny.. or would the tow vehicle be enough to top off the battery?

And of course, I'm a tech geek at heart and know that i'll be switching to a bigger battery and likely solar at some point.. so it's all good stuff to know. 🙂

LED TV draws very little, and so do other things that you mentioned (those that won't be run off the generator). You may or may not get get another battery, doesn't matter, since you plan on running a genny 2-3 times a day, just run it 10-15 minutes longer each time. For the same reason, I think you don't need a solar.

"Getting ready to a long trip next summer with a few nights boon docking and thinking generator, battery bank, inverters etc "

Sorry if I was not clear.....

[Almot]

dddire wrote:
...monning coffee and microwave use at meal times running on the genny

...and out of the hat comes the rabbit. You should've mentioned the planned generator use from the beginning.

dddire wrote:
So really with the Energy Audit, I want to figure out, morning coffee, lights, water running for clean up and washing. How many nights I could do this... (based on time used for each device of course)... if I would need to fire up the genny.. or would the tow vehicle be enough to top off the battery?

And of course, I'm a tech geek at heart and know that i'll be switching to a bigger battery and likely solar at some point.. so it's all good stuff to know. 🙂

LED TV draws very little, and so do other things that you mentioned (those that won't be run off the generator). Do you math now that have audit tools, to see what is "little" in you case, otherwise it's pointless to discuss. You may or may not get get another battery, doesn't matter much, since you plan on running a genny 2-3 times a day, just run it 10-15 minutes longer each time. For the same reason, I think you don't need a solar. You already have means to solve your problems now. Larger battery bank and/or solar would allow to solve it differently.

[dddire]

Hey Mex. I figured the Coffee maker draws about 1000 Watts.. so says the Killawatt... and about 8amps.

There will be three of us.. for morning coffees and it takes about 3 minutes brew time. If that will toast a battery then I have no issue firing up a genny... as there will be hell to pay if the Keuig is not operational.

Sure would be nice to not have to drag a 80lbs genny out of the truck if possible for about 10 minutes of run time.

So... what would one need to have for a battery bank for this? Again, the genny will be there regardless, so I know I won't be building a bank just for this.. but it puzzles me and I want to figure this out. 🙂

[MEXICOWANDERER]

Coffee. Electric coffeemaker. Not the least bit efficient. First of all, any inverter worth it's salt to deliver enough power is going to suck on that battery 'till it looks like a raisin. This is not a fine-grained critique - the coffeemaker is death to your small system.

Can you use maybe a Melitta for this chore? Boil water with dead dinosaurs, then pour the water through a filtered cone? Using a regular coffeemaker in your circumstance reminds me of a very stern master chief, lording over us and a couple of us scrubbing the barracks floor with tooth brushes.

[dddire]

Thanks for all the advice gang. The goal? Man, there are a few actually. For now, the goal is to figure out how long I "could" last on just my gp24 house "deep cycle/Marine" battery. I'm under the impression, it's 70 amp hour... so maybe 35 amp hour if at 50%

We've done three days, no furnace, fridge on gas/12v for control. All LED lighting and a 23" LED TV running off a small inverter into the cig adpt.

We plan on a two week trip next year and figure there will be three days of dry camping on either end for travel and staying at Camp Wallyworld. We'll have a genny for the trip.. so really, this is all moot but at the end of the day how long the house batt lasts will have a baring on how much time the genny needs to be running. Again, I'm sure that monning coffee and microwave use at meal times running on the genny will be more than enough for battery top up till we make it to the GC on day three or four.


I'm also trying to figure out, is it possible to make morning coffee off the inverter with out destroying the house battery? Then the house battery could top up on the drive for the day between Walmarts. So if there is no Microwave needed for breakfast.. and it's just the coffee maker.... will I want to fire up the genny?

I have a killawatt and was playing with it today. So far, what I've seen, running on shore power of course it that with everything on... and I mean, every light, the water pump running, the bathroom fan on, and microwave heating a cup of water, I'm drawing 16/17 amps AC. I"ve done the same, running the AC instead of the Microwave.. and the draw is about the same.

So really with the Energy Audit, I want to figure out, morning coffee, lights, water running for clean up and washing. How many nights I could do this... (based on time used for each device of course)... if I would need to fire up the genny.. or would the tow vehicle be enough to top off the battery?

And of course, I'm a tech geek at heart and know that i'll be switching to a bigger battery and likely solar at some point.. so it's all good stuff to know. 🙂

[MEXICOWANDERER]

It's hard! For instance because I am an oldfart I use my bedside lamp more than any other in the place. Chickens, sunset and all that crap. 26 watt CFL. Hooked to shore power with 1st tier CFE electrical power costing a chin whisker more than five US cents a kWh, a switch to a 3 watt LED lamp would save me a whopping ninety three cents US every two months. Yeah I used a kWh meter to prove how ridiculous an idea this was. But the folks love electrical water heaters in this area. Draw a line with a 70 degree incline. That is how kWh hour price increases react to kWh usages. One careless month can cost sixty dollars. Yeah smart, heat twelve gallons of water to do two gallons worth of dishes. Three gallons worth of shower. Now realizing THIS is an authentic "Energy Audit". So is dumping a gas refrigerator that sucks 12 gallons of gas a month, involves a THIRTY DOLLAR refill trip plus two sixty a gallon for gas, for an efficient 12 volt refrigerator powered by panels and batteries. Want to heat something? Burn it, don't try to electrocute it. Want to light up something? Use photons not BTU's. Want to stay warm in bed at night? Well, tell me, do they peas in the can in the cupboard need to stay warm as well? Get chilly on the way from the bed to the bathroom at night? Ok, does the dinette set and television set shiver as well?

It's warm down here. An inside AC freon refrigerator gets equally as warm. Warmer in fact, and warmer and warmer trying it's little heart out to do what it's paid to do. So it runs all the time, driving electrical costs way up making the kitchen and house hell on earth. Stupid? Oh hell yes. So a trip to the hardware store, sheets of plywood, cut 2X2's, some screened vents, enclosed the back of the refrigerator. Cut two vent holes through 8" of concrete. Mother nature and convection did the rest

Reduced electrical bill an average of 165 kWh every 2 months.

Reduced interior temps of reefer so much, I had to twist the dial down 7 to 4

The refrigerator motor wears out one third as fast.

Kitchen temperatures reduced an average of six degrees F.

THAT is an energy audit.

[mena661]

I agree with MEX, I did an energy audit before I got my battery bank and was WAY off in usage. In reality I used 3x less than I calculated. Even now with the "new" rig, I'm still nearly 50% under my original estimate.