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Tidbit of info that I picked up this morning in a conversation with IOTA Engineering about my AC-DC converter. There is a draw from the converter against the battery, even though there is no AC input. Small draw, less than .01 amp.
Enlighten us then. If close enough doesn't work for you.
To achieve reasonable accuracy for small loads (<10 A @ 12 Vdc), I’d recommend a DMM’s Ampere function. My Fluke DMM has 10A and 100 mA scales, and my everyday Lowe’s meter has a 10A scale.
A DC clamp meter may be a good choice as well, especially now that prices have dropped. Mine was ~$40, IIRC. The user just needs to remember to zero the DC Ammeter function per the user manual.
..... "So, how do you figure your power use? Think about what you have to use and add it all up. You can figure in watts, or in amphours. Watts is probably easier, but ultimately you will need to convert to amphours so I suggest you do your figuring in amps to start with. Look on the electric plate on the various devices and it will tell you what the device uses power-wise. Add them all up for the amount of time you run them. Don't count any 120-volt lights, because you will only use 12-volt lighting while boondocking. Remember, you can figure watts by knowing the voltage and the amperage that the device is rated at - both are on the electrical plate (and if you are lucky, the wattage is there) watts=volts x amps. Sometimes electric plates on devices list ratings as xxVA (e.g. 40 VA) - this is watts (VA means Volts x Amps; actually there is a little more involved with VA because it accounts for power factor, but we will ignore all that for this discussion).Here are the magic formulas that you learned in high school physics class and forgot after your test.
watts=amps x volts
volts=watts/amps
amps=watts/volts
And for some shortcuts: if you know the AC amps just multiply by ten. Four amps AC is 40 amps DC.
When you work with solar it is best to figure everything in DC voltage, because your battery bank is DC - that usually means converting all your AC measurements to DC. In electrical stuff, watts is the universal measure. If you have a watt rating on a 12-volt appliance, it can be directly added to the watt rating of a 120-volt appliance to get the total watts consumed. Amperage ratings have to be converted, based on the voltage. Sounds complicated, but some simple math will allow you to get the total DC amps consumed from your battery.
Here are some 12 volt examples: 2 - 20 watt lights for 4 hrs= 40 x 4 = 160 watts, refrigerator 2 watts for 24 hrs = 48 watts. Now you have to figure your 120-volt loads: hairdryer 1500 watts for 12 minutes = 300 watts. Microwave 1000 watts x 5 minutes = 83 watts. So all total we have (160+48+300+83) 591 watts in a 24 hour period. To convert to amps, divide by 12 or 120 - whichever voltage you are figuring for. We did not count TV, satellite receiver, etc. You need to add up everything. Why did we count the refrigerator in our example when it is running on propane? Because, even when on propane, the refrigerator uses 12-volt power for its control circuits.
With an estimation of the number of watts you use on a daily basis you can calculate how many panels you need to supply that, and estimate how long you will have to run your generator to fill the "gap", if generator use is part of your energy strategy. Don't forget to add in "phantom" loads. For most smaller RV's, these average around 2-3 amps DC (per hour). (Note: larger motorhomes and large 5ers can have a phantom load of 12-18 amps DC per hour, depending on the RV.) These are loads that occur when it seems everything is "off". They come from battery chargers, electronic boards in your propane appliances, propane and CO alarms, etc. You also need to factor in the inefficiencies of converting/using power. There is energy lost when inverting, and energy lost in wire runs. The rule of thumb is 30% lost when inverting, and 20% lost in direct 12-volt battery use. It generally will not be more than this - it may actually be less, depending on your system.
Don't get obsessed with figuring exactly what you need. Just get close and then usage will allow you to adjust. As a rule of thumb, the average RVer uses between 75 and 125 amphours of DC per "cycle" (partial day and overnight). Remember, when you are using power during the day (while charging) your instrumentation is not giving you a true count because power is being supplied while you are using it. The nice thing about a properly designed solar system is that you can easily expand it by adding panels (as long as you buy a large enough solar controller initially, and wire everything for future expansion). For an excellent discussion of sizing your system take a look at Mac McClellan's website Electrical System Sizing. Throughout the discussion here I'll continually "harp" on building for future expansion. It costs little additional when you design/build the initial system, and is lots of additional expense later if you do not do it."
I took a worst case approach on estimating my power usage. I took everything in the camper, except for the air conditioning and put the rated usage into a spreadsheet. Those items without a known rating I figured out manually using my clamp on DC ammeter. I came up with 143 amp hours per day. This was assuming a November-ish timeframe, which requires frequent use of the furnace. My maximum amperage draw at any one time was much higher at 344 amps, but that's kind of a silly total because there's no way I would turn EVERYTHING on at once. The tank heaters are the second highest amp draw, behind the coffee maker. Maybe I'm drinking too much coffee?
Most of my components for my solar upgrade have been delivered. There are a few key items like the solar panel mounting brackets and the lug crimper that aren't here yet. The batteries are still on the slow boat from China.
If I was putting in a bit more battery storage, pulling the on-board generator out would be a consideration. I'll have 1280 watts of solar, but only 640 of that is mounted on the roof. The remaining 640 will be deployed on the ground. I ran out of room on the roof.
I agree the AM Solar “cheat sheet” is a useful document, and I probably have it somewhere in my reference library.
My wife likes to tell me I’m the type of person who, when asked the time, tells you how to build a watch. A little about my background may be in order.
Before retiring in 2014, I was officially an application engineer and product manager in the solar industry for six+ years at Outback, Schneider (Xantrex), and Danfoss. I was a solar hobbyist and solar forum moderator for eight years before that. I wrote articles for Home Power and Solar Professional magazines as a paid author, and I conducted sales conferences, and product training- and application classes in the US, Canada, Denmark, the Dominican Republic, France, and Germany, mostly as an employee, but occasionally as a consultant. Some of those classes qualified the students for continuing NABCEP education credits, and they typically included a special emphasis on NEC Article 690, Solar Photovoltaic Systems. I also conducted field inspections.
A frequent theme in my classes and articles was system design- and performance optimization. One needs accurate measurements to achieve these goals. So, I’m skewed.
I also understand that design processes can be tailored to the project at hand. As I used to say to some of my colleagues while contracting for Boeing, “Don’t impose 777 design standards on a paper clip”.
Jim will you use 2 scc for the panels? 1 for the roof panels, 1 for the ground deployed panels.
Correct. Each string will use its own Victron 100/50. With two strings and two controllers I may play around with putting one string in series and the other in parallel to see what each charge controller does.
- Paper plates. No use wasting limited water on washing dishes.
- Extra water
- Wipes
- Extra clothes
- Box fans or similar will cut a couple of hours out per day of time necessary running the air conditioning
The key to the meter working is you pass the load-bearing circuit through the pickup choke/current transformer. That means you have to disconnect the circuit to pass a wire through it. Obviously, it is to be done when the power is off, as it is "hard wired".
There are versions of that meter that come with a split choke so you can install it without breaking a circuit open. See link below:
Yeah, the meters are cheap chinese imports - but they do actually work. I have had a Kill-A-Watt for years and, quite frankly, these cheap-o meters work a lot better for what I use them for.
If you want to monitor DC loads instead of AC (say, the supply to your inverter drawing power from house batteries) you can get DC versions of these as well:
The shunt in the higher amperage rated DC meters comes cut in places. Those cuts are from calibrating the shunts, the cuts aren't defects/damage. They take a strip of conductor and then make those cuts in it to fine tune the resistance to spec.
For what it is worth, those meters are cheap enough for a basic solar system you can use them to monitor a lot of different parameters:
- Solar production
- Charge going in to the house batteries
- Power consumed by everything
- Power drawn from house batteries
With 4 meters you can monitor all of the above. Granted, there is a lot of power monitoring that more complex solar installs can provide in and of themselves. However, the cheap-o meters make for an economical solution if you are going old-school solar with a more basic charge controller.
If you want to monitor DC loads instead of AC (say, the supply to your inverter drawing power from house batteries) you can get DC versions of these as well:
The shunt in the higher amperage rated DC meters comes cut in places. Those cuts are from calibrating the shunts, the cuts aren't defects/damage. They take a strip of conductor and then make those cuts in it to fine tune the resistance to spec.
For what it is worth, those meters are cheap enough for a basic solar system you can use them to monitor a lot of different parameters:
- Solar production
- Charge going in to the house batteries
- Power consumed by everything
- Power drawn from house batteries
With 4 meters you can monitor all of the above. Granted, there is a lot of power monitoring that more complex solar installs can provide in and of themselves. However, the cheap-o meters make for an economical solution if you are going old-school solar with a more basic charge controller.
The key to the meter working is you pass the load-bearing circuit through the pickup choke/current transformer. That means you have to disconnect the circuit to pass a wire through it. Obviously, it is to be done when the power is off, as it is "hard wired".
There are versions of that meter that come with a split choke so you can install it without breaking a circuit open. See link below:
Yeah, the meters are cheap chinese imports - but they do actually work. I have had a Kill-A-Watt for years and, quite frankly, these cheap-o meters work a lot better for what I use them for.
If you want to monitor DC loads instead of AC (say, the supply to your inverter drawing power from house batteries) you can get DC versions of these as well:
The shunt in the higher amperage rated DC meters comes cut in places. Those cuts are from calibrating the shunts, the cuts aren't defects/damage. They take a strip of conductor and then make those cuts in it to fine tune the resistance to spec.
For what it is worth, those meters are cheap enough for a basic solar system you can use them to monitor a lot of different parameters:
- Solar production
- Charge going in to the house batteries
- Power consumed by everything
- Power drawn from house batteries
With 4 meters you can monitor all of the above. Granted, there is a lot of power monitoring that more complex solar installs can provide in and of themselves. However, the cheap-o meters make for an economical solution if you are going old-school solar with a more basic charge controller.
Well, I tried it, I had to check with a few vendors to find the right wiring diagram, but it works nicely.
I currently have 4 Trojan 6v 305 batteries rated at 360 a/h for the 20 hr rate. I have a 3500 watt pure sine wave inverter. I can run several days, easily with the loads I have measured. I am looking to add a 300 watt suitcase type solar panel kit for now, and would like to put panels on the roof after I know for sure my "real world loads". I am going to upgrade to a mppt controller, as it looks like they are 10-15% more efficient and will work better with the future panels. Even if I don't fully replace the load for the day with this potential setup, I think I can run for a good while with the battery setup. I'm also going to run a heavy cable to the rear of the truck to charge the camper when towing.
Rezvani's Latest Post-Apocalytic Monster Is a Ford F-150 Raptor Underneath
Slideshow: Called the Fortress, the 850-horsepower pickup combines Raptor underpinnings with military-inspired features, survival equipment, and a starting price of $285,000.
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