Monitoring power usage

[mcguirev10]

Edit: I guess it would be more accurate to say "log" power usage rather than monitor...

Our trailer has a pretty basic little display that shows tank levels and current voltage, but I'm wondering if there's a go-to device that everyone uses to track consumption in a more detailed way?

I've been going through many of the threads here, and in one somebody posted a cool little chart of their power consumption over time. Looked like it might be some sort of smartphone app. It was late last night, I didn't save the link unfortunately. All I remember is that the product name started with a V (I know it's something popular, I've seen it mentioned before).

Is there a stand-alone monitoring device of some kind, or is this more of a feature associated with specific charge controllers? I'm a data kind of guy, the more the merrier.

[Byron Kinnaman]

Originally Posted by mcguirev10

Edit: I guess it would be more accurate to say "log" power usage rather than monitor...

Our trailer has a pretty basic little display that shows tank levels and current voltage, but I'm wondering if there's a go-to device that everyone uses to track consumption in a more detailed way?

I've been going through many of the threads here, and in one somebody posted a cool little chart of their power consumption over time. Looked like it might be some sort of smartphone app. It was late last night, I didn't save the link unfortunately. All I remember is that the product name started with a V (I know it's something popular, I've seen it mentioned before).

Is there a stand-alone monitoring device of some kind, or is this more of a feature associated with specific charge controllers? I'm a data kind of guy, the more the merrier.

I've been using my trailer for the past 15 years with the last 10 years over 100 nights per year. After a lot of usage I pretty well guess when things need attention. Examples: When the weather is cold enough that I use the furnace a bit in the morning and evening I need to recharge the battery about every 3r day and fill the propane tank about every two weeks. Since I never NEVER use the exchange propane If I fill it early not a problem. In the summer when the temps are warm and sun sets late I can go a month without charging the battery and don't have to worry about propane usage. This I've learned from experience.

[Lynn Eberhardt]

Usage Chart
I made a wattage use chart for all of our 12 volt devices.
With a Kill-A Watt meter between shore power and the trailer, I noted the watts used by the converter at idle - battery fully charged.
I then noted the watts used by each device - total minus idle.
Divide watts used by 10 to get a close enough idea of battery amps required for each device.
Keep track of how long you use each device and monitor your battery voltage to stay within safe limits.
It works for us.

[Jon Vermilye]

Originally Posted by mcguirev10

Edit: I guess it would be more accurate to say "log" power usage rather than monitor...

Our trailer has a pretty basic little display that shows tank levels and current voltage, but I'm wondering if there's a go-to device that everyone uses to track consumption in a more detailed way?

I've been going through many of the threads here, and in one somebody posted a cool little chart of their power consumption over time. Looked like it might be some sort of smartphone app. It was late last night, I didn't save the link unfortunately. All I remember is that the product name started with a V (I know it's something popular, I've seen it mentioned before).

Is there a stand-alone monitoring device of some kind, or is this more of a feature associated with specific charge controllers? I'm a data kind of guy, the more the merrier.

The device you are probably describing is the Victron 721. This is a battery monitor that uses a shunt in the negative battery lead that monitors current. The electronics keep track of the amount of current into & out of the battery & report it as amp hours. Properly set up, the monitor gives you a good record of usage. While the monitor can be used stand along, an app is available that allows using a cell phone to control settings & monitor remotely.

[Defenestrator]

The Victron BMV-712 lets you monitor current usage. To really get detailed usage-over-time you kind of have to go all-in on their gear, though. Something from their GX series (like the Color Control GX) in addition to the battery monitor to collect the data and send it to their cloud service. It works pretty well, but it's a big up-front cost.

[Raspy]

Originally Posted by Defenestrator

The Victron BMV-712 lets you monitor current usage. To really get detailed usage-over-time you kind of have to go all-in on their gear, though. Something from their GX series (like the Color Control GX) in addition to the battery monitor to collect the data and send it to their cloud service. It works pretty well, but it's a big up-front cost.

I don't see why any of that is necessary, other than just for fun or for a gadget enthusiast. It really only matters that you can run the things you want to run. If not, you know you need more panels, or more batteries, or better tracking, or to park in a more sunny spot, or find better weather, etc. Either way, you still have real time amps and battery voltage. It will soon become clear if your system keeps up, or not. Amps in, from the sun, is great. So much better than boondocking without hookups. Fun to look at. But battery volts tells a better story, as it varies throughout the day and night to reveal what is going on.

[CarlD]

I kind of have to go with Raspy on this one. In the scientific world one data point is not very revealing. Many, many data points is much better, for instance looking at trends. (i.e. Are coronavirus deaths increasing or decreasing). My big concern using battery voltage to measure SOC is you need to know what the battery is doing when you take readings, charging, discharging, resting, etc. Where as using a power monitoring device with % state of charge is independent of instantaneous battery usage. In my application, I usually just check my LFP battery in the morning and at night and don't worry about it unless it gets to around 30% in the morning.

[Defenestrator]

Originally Posted by Raspy

I don't see why any of that is necessary, other than just for fun or for a gadget enthusiast. It really only matters that you can run the things you want to run. If not, you know you need more panels, or more batteries, or better tracking, or to park in a more sunny spot, or find better weather, etc. Either way, you still have real time amps and battery voltage. It will soon become clear if your system keeps up, or not. Amps in, from the sun, is great. So much better than boondocking without hookups. Fun to look at. But battery volts tells a better story, as it varies throughout the day and night to reveal what is going on.

I find voltage to often be misleading, since it varies based on load as well as charge level. Surface charge can make it deceptive as well. Current draw over time can be useful in figuring out what's using how much power, though I did find that instantaneous current was usually good enough.

My main use case is probably pretty unusual. I want to be able to leave the dog in the travel trailer for an hour or two with the air conditioner on and be able to track temperature and charge state remotely to make sure he's ok.

[Raspy]

Battery monitors are great, but a simple voltage meter is all that is really needed. The volt meter can be as simple as a $5. item that plugs into a cigarette lighter socket, so they are excellent for getting started and protecting your batteries.

The variables in voltage readings can be perceived in two basic ways. First, it can simply be seen as a misleading variable. And it can be confusing. The second way is to see those variations as a detailed message. What is it telling you? Of course, voltage is a much simpler method of reading SOC than having a meter calculate it for you and present it any time you look, but is that a problem? I like gauges too, but I've used a simple volt meter much more than anything else for monitoring my batteries over the years. The volt meter is best suited for looking at trends, directions in charge levels, or rested State OF Charge, and worst at looking for small parasitic loads, or micro charging amps. And it cannot read anything other than real time values.

So, after the batteries are rested, like first thing in the morning, the voltage can be a good indicator of SOC and whether your solar is keeping up with use. You can decide that 12.2, for instance, is your lower limit and 50% of charge, so you know if you are OK or not, and how close you are to 50%. You can mentally factor in yesterday's use, the weather, special loads, or if you used the heater, and so on, to begin to develop a picture of what is happening and if your solar is sufficient. Develop a trend or general view.

Later in the morning, the voltage will go higher, and that increase alone tells you the solar is charging. In the afternoon, the voltage will get to 14.5, or not. If so, it pretty much means you are near full charged, especially if the charger program holds it there for absorption. If it stays in absorption until the sun weakens, and then declines, you know the batteries are within about 95% of full charge. It they settle to 13.2 while the sun is still bright, you have reached full charge and the batteries are in float. If you reach float, the solar has produced more than your usage. On days like that you might want to charge your bicycle. On cloudy days, not so much, or limit Microwave use.

If you see a lower voltage than you expect during the day, determine if something is running that causes a voltage drop. Disregard that lower voltage as an indicator of state of charge, it isn't. Abnormal voltage readings and the degree they are out of the normal range, help you see the size of the load, as well as finding parasitic loads you might otherwise disregard. My trailer has parasitic loads that I can never fully get rid of and seem larger than I would expect. It has a volt meter and shunt driven amp meter that reads at the electrical panel, instead of at the batteries. The volt meter, by itself, is a poor indictor of these small continuous loads. Where the meter picks up its readings is important. The solar controller voltage readout can be better than a meter in the electrical panel, because it is directly connected to the batteries with heavy gauge wire and not sharing the same wire as a load.

In extended cloudy weather, the voltage will probably be progressively lower each morning and you might want to reduce loads as needed to stop that trend.

These are some of the ways that voltage tells the story. While out camping, I guess we all have a sense of what the weather trends have been and how we've been using the batteries. We want confirmation that the solar is working, or that we are not hurting the batteries. I don't want to be constantly looking at the volt meter, but I do glance at it from time to time to see what's happening. It will also tell you if the shore power is still on, because the float voltage will remain near 13.2, night and day. If you unplug and re-connect, it will display your charger strategy by showing the various voltages as the batteries charges over time. If you switch to lithium batteries, it will help to confirm you programmed the charger, or the solar controller correctly, by watching the character of their outputs.

Going simply by computed data doesn't help you much more for determining if you can run some appliance for while. It might be a way to look forward and predict the result of a proposed load by crunching the numbers, but I don't want to do that. Or, it might read out collection history, or check the state of charge from your phone, but that is not important to me. However, getting a trailer interior temperature reading would be very nice to assure the dog was safe. I'd like that if we had to leave her unattended for a while.

Part of the appeal, or lack of appeal, comes from how much we want gadgets to read out exact values. But you still have to decide what to do with that information. The simple voltage reading won't give as much information, but it will give enough to tell very well what is going on, trends, power management, solar health, and battery SOC. It won't tell you if the batteries are getting sulfated. It encourages you to think about your system and understand what it's doing with a simple glance at the meter on your way by.

[Lockmasterjoe]

I hooked up to my 16’ Scamp to go from Florida to Minnesota and found I had no lights inside the trailer, lights worked on shore power but first night out at a Cracker Barrel we had no lights. Shouldn’t the batteries charge up while driving, where do even start troubleshooting?

[Raspy]

Not all vehicles charge through the seven pin and not all trailers are wired to take that power to the battery. You could start with a volt/ohm meter looking at the tow side of the seven pin, with the truck running, to see if it has power on the 12v terminal. Then go to the battery and test there. Search for a seven pin schematic to find the right pin.

[Defenestrator]

Even if the charging is working (you can tell by watching voltage at the batteries when the tow vehicle is running vs when it's not), it might not be enough current to overcome various loads. Especially if you're running the fridge on electric mode or something else power-hungry. At most it'll provide around 10A, but usually the voltage drop from the long thin wires drops that even further.

[Lynn Eberhardt]

Quick Check
Check voltage at the trailer battery - shore power unplugged, tow vehicle off.
Start car - Trailer battery voltage should go up to at least 13.5.
Voltage didn't go up? - Car to trailer wiring problem.
Voltage went up? - Good.
Start fridge on 12V.
Battery dropped to 12 volts or less? - Wiring not adequate to run fridge and charge battery. Common problem.

[CarlD]

Raspy, I agree you can realize the state of your battery using a voltmeter with an understanding of battery operating state. My overpriced Victron 700 ($145) makes SOC a no brainer. Between the Renogy Rover and the Victron, I have a complete picture of what is happening in my system. I know the current coming in, going to the battery and to the loads and the battery voltage plus the calculated parameters. There is no interpretation, just a simple reading and you can mentally keep track of trends. The most interesting thing about the Victron is that my wife knows how to use it and she is quite mechanically and electrically declined!

Our retirement philosophy is simple. Your heirs will inherit money and stuff when you are gone. You can only save or spend money, but you can do things with stuff, so they are going to inherit stuff!

That being said, I think the expenditure is a good value.

[redbarron55]

Here is the most important thing on state of charge, currently (pun intended)
Where are you going when the current debacle is over and it is safe to travel and will you keep your battery on some kind of battery maintainer til then?

[Raspy]

Carl,

I agree and I'm not saying people should avoid fine instruments. Not at all. Just that a lot more can be interpreted from simple stuff than what is evident at first glance. It takes some time to learn how to interpret voltage and it doesn't work for those that are not familiar with how it works, or just want to be told by the meter. I really like the Victron stuff and have installed a monitor, and charge controller on a set of Battle Born batteries in an Oliver. After that, my friend that owns that trailer was constantly looking at his phone with the bluetooth connection to the monitor and trying to decide if the readings made sense and why it was doing what it was doing. It was fun and we learned a lot.

At this point I've graduated from a simple volt meter, to a factory installed monitor that reads load and voltage, and an MT-50 solar monitor that reads voltage and solar amps. It's not all in one, but gets the job done.

[Jon Vermilye]

Originally Posted by Raspy

Carl,

I agree and I'm not saying people should avoid fine instruments. Not at all. Just that a lot more can be interpreted from simple stuff than what is evident at first glance. It takes some time to learn how to interpret voltage and it doesn't work for those that are not familiar with how it works, or just want to be told by the meter. I really like the Victron stuff and have installed a monitor, and charge controller on a set of Battle Born batteries in an Oliver. After that, my friend that owns that trailer was constantly looking at his phone with the bluetooth connection to the monitor and trying to decide if the readings made sense and why it was doing what it was doing. It was fun and we learned a lot.

At this point I've graduated from a simple volt meter, to a factory installed monitor that reads load and voltage, and an MT-50 solar monitor that reads voltage and solar amps. It's not all in one, but gets the job done.

A couple of places/situations where the Victron monitor proved mure useful than a volt meter - Discovering that the SAE connector on my portable panel was intermittent. Wiggling it didn't change the voltage since the two panels on the roof were also feeding the controller, but with the phone in hand 10' from the trailer I could watch the fluctuation of the current using my phone.

Another useful capability is to determine which lighting fixture draws more current. The capital's lights draw less than the overhead lights in my Escape. Not critical, but if you are trying to stretch your batteries, useful.

Under cloudy conditions, being able to see the charging rate (amps) is useful in deciding whether or not to use high wattage appliances.

If you don't dry camp, or if you do, but use very little electricity, a simple volt meter will do the trick, as long as you understand when it is indicating an accurate state of charge. If you are a heavy user of electricity, dry camp for long periods of time & want to determine that usage by the SOC of your batteries & the ability of your solar system to replace it, a battery monitor makes sense.

[CarlD]

JD

Currently we have been quarantined for almost 6 weeks, fortunately we have a lot of things to do around the place. I have cut down 2 70 foot spruce trees and a HUGE white ash killed by emerald ash borers. This morning I was in the back woods excavating a ditch to help dry out the area so I can put down some old, before Carl, concrete slabs to make a road so I can get my Lil Hauley into the woods so we can go CAMPING, HURRAY! My son thinks I might be a bit unstable but retired folks can get away with these kind of things.

Staying safe.

[Raspy]

Jon, Good points and I agree. it doesn't hurt, and is often fun or helpful to have more information. I really like your finding a bad connection by watching the instantaneous current. That could have gone unnoticed, or hard to find, with less monitoring.

[Raspy]

I am so ready to go somewhere without the worry about the current situation. My trailer is all ready to go with no more projects to do. There have been a lot of them, and they were interesting, but it's time to enjoy it and not just work on it!

After upgrading to an MPPT controller and installing a monitor, I went into the fresh water plumbing and spent a lot of time dialing that in for better freeze protection, less water waste, more cabinet space, and easier temperature regulation. Before that there was a long list of upgrades and adjustments that went on and on. One was figuring out how to align the wheels, at home with simple tools, on a tandem axle trailer with independent suspension. And the most practical way to balance them. Another was tracking down why the oven seemed to have so little power. And an early bearing inspection/re-pack proved to be a very good idea. The list goes on and on.

Now I want to go somewhere! But not while this virus mess is going on.