Solar Upgrade Part 3: a 12 volt audit

When one gets a new gizmo, there is a strong tendency to gravitate towards using it all the time...it's only natural. I would have to say that the Trimetric has had a bit of this effect on me...I just have to press that little button to open up the new world of information it has to offer. This is not a bad thing mind you, I have a much better understanding of what is going on with the state of our solar/battery setup than I ever did before.

Once I got past the fascination with the raw data, it was time to put it to use to figure out exactly what each 12 volt device in the Alto costs, in terms of impact to the battery. Energy conservation while off grid is a bit of a pursuit of ours, so knowing what the real loads are will be great. So I began an energy audit, and along the way, learned a little bit more about how some devices actually work.

First I put together a list of the devices that run on 12 volts, or have a 12 volt component in their operation, such as the 2-way fridge. It may be propane and electric, but the overall operation is controlled by a 12 volt circuit board. Same goes for the water heater. There are a surprising number on board, 19 unique devices in our Alto, not double counting any of the similar light fixtures.  Once I had the list, I then set about to determine the amp hour draw of each one.  This involved turning devices on one at a time, and recording the draw as measured by the Trimetric.

With the display off, the draw of the Trimetric is .01 amp/hr. This came right from the spec sheet, as with no display, how would you get this info? With the display on, the draw is .03 amp/hr. This became the phantom draw to be removed from each reading taken. Next up were the detectors, of which our Alto has the two separate units, LP & CO. As they are both on the same circuit, it was easy to find the combined draw. I might add that all this detective work was done well after darkness had fallen. I wanted to completely eliminate any residual power generation from the solar panels.  The amp/hr calculations done by the Trimetric are based on what is going in & out of the battery. If there is a bit of solar amps going in, then the reading of a device’s draw will be skewed by this positive value. This also fluctuates, as the Trimetric is sensitive enough to pick up the solar output changes caused by even a tiny little cloud.  After dark, I know the readings are truly for the device draw, with no other influences.

From there, it was just a matter of putting the various devices into use one at a time, and watching the Trimetric calculate the negative impact on the battery. Pretty straight forward stuff, or so I thought. I had assumed that once the detectors were on, that was the draw. Not so. While I was finding the draw for one of the LED lights, I saw the amp display move from a stable value, and jump up a fair bit.  There was nothing else on, other than the detectors, so it was a tad puzzling. A bit later, the draw dropped back down to what it was when the light went on.  I turned the light on and off, and monitored the draw further...sure enough, up it jumped again. I timed the on/off cycles. It was soon clear that one of the detectors was "sniffing" the air on a regular 1 minute on, 1 minute off cycle. Based on this, the phantom draw of the detectors was certainly more than I first recorded, and you would be surprised how this changes the calculations over a 24 hour period. The fridge has a cycle as well. There is the control board, and then when the fridge is called upon to cool, there is a little solenoid that opens to allow the propane to flow for the cycle. Holding that solenoid opens makes up the bulk of the draw, and needs to be factored into the amp/hr cost.

Once everything was mapped, I created a little spreadsheet (of course) that would calculate the draw of each device, over different periods of time. Anything with a phantom draw as well as a functioning draw is calculated over a 24  hour period, and this required some adjustments to blend the amp/hr rate. Yes...this is all very geeky.

The chart is pretty interesting, especially when you start to play with the amount of time that a device is running in a day. Take the water pump, a huge amp hog, but then look at how long it actually runs in a day. Even including the possibility of a Dale outdoor shower, would that pump run 10 minutes, 15 perhaps, in a day. This works out to about 1 amp/hr a day. Now look at those little detectors, no motor in them, yet over the 24 hours they are on, they eat over 3 amp/hrs! Now who is the power hog??? But that's not to say those are not worthwhile amps, and certainly not going to try to save any there.

When trying to figure out just how many amps were being used in a day, I think there are a couple of groups, what I call the driveway and camping core draws. These are consumptions that are just simply going to be there, regardless. The driveway consists of the Trimetric and the detectors, and over a 24 hour period, adds up to over 3 amp/hrs. I've heard some people pull the fuse on their detectors at times, but I'm just not comfortable with that, even if it is just simply sitting there, waiting for the next adventure.  The core camping draw are the same devices, but adds in the fridge and water pump. If you are out, you are pretty much using these, and they are pulling amps out of the battery. I'm sure you could find some savings if you are able to adjust the temp of the fridge, or even turn it off, but for the sake of not getting too crazy with the calculations, I'm assuming a relatively normal manner of operations.

From there, I used this core group and came up with a couple of scenarios, to try and estimate just how much we may be using. These definitely lean towards conservative consumption. You can see how it could be very easy to use up all your available amp hours, as devices go on, it add up quickly. If you are out for a while off grid, you also have to keep in mind that you need to replace the amps you take out, and this requires good solar conditions...which means lots of sunlight. As well, from what I have read, the amp hours come out of a battery a lot easier than they get replaced, which is probably the main reason I upgraded the solar controller, to make sure this process was as effective as it could be.

So after a few outings with the new solar components, am I satisfied it has been a good investment? Most definitely! Not only do I know exactly what is coming and going from the battery, I know that the battery is being charged as effectively as possible. Can I quantify this. I think so. The battery recovers its charge a little faster, from the parameters programmed in it is certainly fully charged, and when I initiate an equalization phase, I know I am prolonging the overall battery life as per Trojan specs. Sounds pretty good to me.

I would certainly recommend the additional of a Trimetric monitor for those planning on a lot of off grid camping. It really helps you know exactly what the battery state of charge is.

Have a look over the chart, and although some of the equipment in the Alto has changed over the years, it will give you a high level picture of how amp hour usage can accumulate over the course of a day, and how your own camping style will impact this.  The raw numbers are there to help you calculate your own scenarios. Pretty interesting stuff.

Item	Device	Phantom Draw	Amp Draw	Approx Mins Day	Approx Hrs Day	Daily A/hrs	Notes
1	Trimetric (display off)	0.010	0.010	1440	24.00	0.240
2	Trimetric (display on)		0.030	30	0.50	0.015
3	LP/CO detectors (individual units, same circuit)	0.09 (0.18 sniffing)	0.135	1440	24.00	3.240	- one detector sniffs for 1 minute, then phantom for 1 minute - amps prorated over 24 hrs
4	Fridge (Dometic 2-way propane)	0.07 (0.32 cooling)	0.284	1440	24.00	6.816	- estimates fridge cools approx. 40 min/hr  -amps prorated over 24hrs
5	Fridge Vent Fan (single 50CFM fan)		0.170	300	5.00	0.850	- only used during hot weather
6	Water Heater (Suburban propane)		0.750	30	0.50	0.375	- morning/evening cycles
7	Furnace (Propex propane)		2.170	180	3.00	6.510	- morning/evening occasional cycles
8	Water Pump		5.630	10	0.17	0.938
9	Roof fan (setting 1)		0.960	180	3.00	2.880
10	Roof fan (setting 2)		1.490	120	2.00	2.980
11	Roof fan (setting 3)		2.240	0	0	0	- rarely used
12	Roof lifts		6.030	1	0.02	0.101
13	Bench lift		1.160	1	0.02	0.019
14	Light fixture (single LED tube retrofit)		0.420	60	1.00	0.420	- Luci lights factor into all lighting estimations
15	Light fixture (double LED tube retrofit)		0.910				- rarely used
16	LED strip (front cabinet, dimmer low)		0.030	60	1.00	0.030
17	LED strip (front cabinet, dimmer high)		0.270
18	LED strip (sink)		0.150	30	0.50	0.075
19	LED strip (ceiling ambient)		0.220	60	1.00	0.220
20	Exterior light (incandescent)		0.930				- rarely used
21	TV (tv mode)	0.050
22	TV (dvd mode)	0.050	1.750	120	2.00	3.50
23	Tank monitor		0.130	2	0.03	0.004
24	Fantastic fan (portable, setting 1)		1.330	180	3.00	3.990
25	Fantastic fan (portable, setting 2)		1.980
26	Fantastic fan (portable, setting 3)		2.760
27	Tivoli (radio charging)
28	Core draw (driveway)		0.145	1440	24.00	3.480	- items: 1, 3 - amps prorated over 24hrs
29	Core draw (camping)		0.429	1440	24.00	11.234	- items: 1, 3, 4, 8 - amps prorated over 24hrs
30	Cool day scenario					18.644	- items: 6, 7, 14, 16, 18, 29
31	Hot day scenario					22.834	- items: 5, 6, 9, 10, 14, 16, 18, 24, 25, 29
32	Conserving day scenario					14.114	- items: 9, 29