Power Consumption


I have posted in the past about our power consumption on the boat, but I thought I would do a quick new post based on our latest data. Back in Grenada in the summer of 2016 we installed a Victron BMV700 battery monitor. This device uses a current shunt and some fancy programing to keep an accurate count of all the energy we generate and consume. Frankly, installing that device is one of the best things we have ever done. It has really enabled us to not only be better educated about our usage, but to manage our batteries better. A device like this is a must for any cruising boat. Last summer while back in Canada we purchased the optional Bluetooth dongle to allow us to see the history data.


So lets start with a screenshot of that history data the device has captured in the last 22 months since the install. We can then analyze and discuss that data.



First lets start with the top right panel called “Discharge”



This panel contains some really interesting information. However the number I’m most interested in is the “Average Discharge” value. This number is the average of all the power we have used during nights on our boat (when the solar panels are not producing anything). 3 years ago when we started cruising I would have given “lefty” to know this actual number, since it would have been very useful in deciding how big of a battery bank we built. The goal is to build a bank that will allow 2 days of cloud and rain before you need to run a generator to recharge the bank (at least for us).  My initial guess at this number wasn’t too far off at 130ah.  If you factor in our wind generator averaging about 25Ah over the night then the real number is about 120Ah.  So for new cruisers (or potential cruisers) playing along at home. It takes about 120ah/night to run the following items:

1. LED anchor light

2. Marine refrigerator (4.6 cubic feet).

3. Freezer (4.4 cubic feet).

4. 4 X Caframo fans on low.

5. VHF radio

6. 2 X CO detectors

7. 2 X WIFI routers (one regular WIFI device and one MIFI device)

8. Victron MPPT controllers with custom gauges.

9. Water and sump pumps for nightly showers




NOW THIS PANEL… Although this panel only has 2 numbers, it contains the most mind blowing information. The “Charged Energy” number is all the energy we have consumed over the last 18 months. Yes, 18 months, since we need to remove 4 months that we were not on the boat consuming or “charging” during last hurricane season.  So that means we have consumed 962.3kWh over 18 months, or 53.46KwH/month. Why is that mind blowing? It mind blowing because the average North American household consumes 897 kWh/month. Yup, we use about %6 of the power an average North American household consumes in a month. I’m actually stunned by that number. I knew we were using way less power than our previous “landlubber” life, but I didn’t think it was that much smaller. Seriously, %6 and that includes the days where we have too much power and heat water for a nice warm water shower using our solar array.


The other take away on this panel is the difference between the 2 numbers. The “Discharged energy” number is the total amount of energy we have discharged from our battery bank in the last 18 months. As I said above “Charged energy” is the total amount of energy we have used in those same 18 months. The difference between the two numbers is the extra power the solar panels are able to generate during the day that the batteries can’t absorb (because they are full). It’s the power we use to power our laptops, run fans, charge tablets and heat water (when we are really flush). It shows that we are using our solar array pretty efficiently.




The final panel I was interested in is the battery voltage panel. It shows the highest and lower voltage our batteries have ever been. Many people are going to look at this and immediately point out that 11.28V is not good. I would agree, however, that low voltage is not from a deep discharge, but from a heavy load and voltage sag. When we heat water with our 220V inverter it lays the boots to the batteries and draws about 130A from the bank. However those draws are for a very short duration (about 12 min) and once we turn the water heater off, the batteries immediately rebound in voltage.


The thing I’m more concerned about is the Max battery Voltage. According to some battery manufacturers, 15V is too low for a lead acid battery equalization. Some manufacturers recommend as high as 16.2V, but I feel that is too high. After looking at these numbers I will be upping my equalization voltage to about 15.5V.


What I’m really excited about is to see how these numbers change once we install our new LiFePo4 battery bank. Of particular interest will be the difference between the “Discharged energy” and “Charged energy” numbers. Since LiFePo4 batteries are almost %100 efficient and our current lead acid bank is only about %85 we should see those numbers get further apart. However only time will tell.

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