Overwhelmed by Battery Monitoring

[NotLost]

Hello everyone, I've found myself the owner of a Salem Cruise Lite with the exact Floorplan we wanted. After getting home, it turns out it has a 12v refrigerator, no propane. We camp without power much of the summer, this is going to be an issue.

To figure out how to overcome this, I think I'm going to need to start by finding out how much power the camper actually uses on 12v. Time for a battery monitor. And there are a ton of them!

I'm looking for recommendations on something simple, on the less expensive end that will just tell me enough information about how much I'm using so I can figure out charging/batteries from there. Bluetooth only would be nice, I don't really want to run wires and cut holes if I don't have to.

[BrandonSmith]

FWIW, my 12V pulls 1.5A constantly and 2.0A when compressor kicks on.

If you don't have a second battery, you will need one. Do the math for amp-hours and you'll find that a battery does not last very long. 10 hours @ 1.5 amps is 150 amp-hours needed to run the fridge alone, not including the times the compressor kicks on.

[tomkatb]

I own the old BM2 from Amazon. $40 5 minute installation.

It is a bluetooth voltmeter. It also records history and has alarms.

The information you said you wanted is a amp meter type. About $100 or more from Vitron.

However the information you need, not want, is on the charts listing amperage for devices and to learn how to minimize their use. The continuous monitoring is for folks that will be major users of power. Major systems. You are $10,000 away from that. Much to learn.

Typically you will use 50 amp per day for lights and stereo. Adding an electric refrigerator will add 50-150 amps per day depending on the weather.

My cpap uses about 40 amps per day.

If you use the refrigerator and the furnace be prepared to be awaken by the DW the first night at 3am with 100 available amps.

We have 430 amps of power. 200 available. Come hell or high water we can go a night without the generator. Two nights if we are careful. No electric fridge.

Today Costco is selling a set of lithium batteries for $1400. 180+ amps available.

[Theo]

My vote is for either of two Victron battery monitors:

• SmartShunt - a 500A "smart" shunt that has no display. The battery monitor info is sent via Bluetooth to your mobile device and the free Victron Connect app. These run ~ $130 USD.
• BMV-712 - a 500A "dumb" shunt with a "smart" display. The display also sends the battery monitor info via Bluetooth to your mobile device. These run ~ $206 USD.

I have a BMV-712, but I always check my battery data with the Victron mobile app. Were I to do it again, I'd go for the ($75 less expensive) SmartShunt.

Victron's products are durable, reliable and accurate. Their battery monitors offer a full range of parameters that one can adjust to dial-in their accuracy and to allow them to adapt to different battery chemistries. I have no experience with other premium manufacturers' products like the Bogart Engineering TriMetric.

My recommendation would be to forego the less expensive products as they may not give you all the features Victron offers. Since we do a lot of dry camping, the important data for me are: temperature-compensated state of charge, charging rate (in Ah), predicted amount of days/time before the battery hits the discharge floor (50% of LA battery capacity) and real-time Ah draw. Note that the last bit of data is important in inventorying the current draw of each 12V appliances/accessories.

HERE is a pretty good write-up for battery monitor introductory information.

HTH

[NotLost]

Thanks, I was initially looking at the smartshunt but the reviews weren't great. Mostly about the app itself. Which can be user/phone dependant.

Eventually I'll want more data, I'm trying to find out how much battery I'll need so I can balance capacity with solar, and if I go lithium. But I don't want to spend a ton now when a lithium setup might have the monitoring built in.

Basically I park my camper for weeks at a time at a family camp. Last year, LP refrigerator would be left on all week with 2 standard deep cycle batteries and ~100W solar, just cheap stuff. Run generator overnight Friday and Saturday, leave Sunday. Major power draw on this new camper will be keeping this new 12v refrigerator running.

At a minimum will be needing it to be able to cool down and run all day and recharge off generator at night. Measuring the actual usage will steer me to how much panel and battery I need.

[TitanMike]

Originally Posted by NotLost

Thanks, I was initially looking at the smartshunt but the reviews weren't great. Mostly about the app itself. Which can be user/phone dependant.

Eventually I'll want more data, I'm trying to find out how much battery I'll need so I can balance capacity with solar, and if I go lithium. But I don't want to spend a ton now when a lithium setup might have the monitoring built in.

Basically I park my camper for weeks at a time at a family camp. Last year, LP refrigerator would be left on all week with 2 standard deep cycle batteries and ~100W solar, just cheap stuff. Run generator overnight Friday and Saturday, leave Sunday. Major power draw on this new camper will be keeping this new 12v refrigerator running.

At a minimum will be needing it to be able to cool down and run all day and recharge off generator at night. Measuring the actual usage will steer me to how much panel and battery I need.

Based on what you said I'd recommend the BMV712 Victron monitor. It has a monitor "meter" that can be mounted on an interior panel so it isn't App dependent or it can just be placed in a zip-loc bag then put out of the way near the batteries. Then just use the app. The "meter" is the bluetooth device so it does have to be hooked up.

Advantage of the BMV-712 versus "Smart Shunt" model is it works without the app and also has a relay built in that can be programmed for any purpose you want based on battery state of charge, temperature, voltage, etc. I use the relay in mine to turn on or off the Converter when my Battleborn batteries reach a given state of charge I select. If you absolutely have to be warned when batteries are low, when inside or out of RV, this relay can be used to trigger a louder alarm. Just one example.

The biggest advantage to using the Victron versus some of the less expensive monitors is that it is more precise in measuring the state of charge than a meter that just measures "amps out/amps in". Using the Peukert factor, which you set for the type of battery chemistry you have, it takes into consideration the inherent inefficiencies of high current discharge, charging, and temperature to mention a few. For lead acid batteries this is critical if you really want to know the SOC and less so for Lithium.

The less expensive monitors are probably OK for those who only use their batteries during an overnight stop while traveling and spend the rest of their camping time hooked up in RV parks.

[DustyRoads]

I have the BMV-712 and love it. Keeps me posted on my phone via Bluetooth and display monitor I installed inside the trailer. I don't really look at the one inside the trailer. I like the app so much better.
I would highly recommend.

[Larry-NC]

Originally Posted by BrandonSmith

FWIW, my 12V pulls 1.5A constantly and 2.0A when compressor kicks on.

If you don't have a second battery, you will need one. Do the math for amp-hours and you'll find that a battery does not last very long. 10 hours @ 1.5 amps is 150 amp-hours needed to run the fridge alone, not including the times the compressor kicks on.

Brandon, your math is weak. 10 hours at 1.5 amps is 15 amp-hours, not 150.

And you also missed a step. It's called "duty cycle." Assume, for example, that at 70 degrees F, without opening the refrigerator very frequently, that the compressor and fan only run about 1/3 of the time.

So it would really only be 15 * 1/3 = 5 amp hours. That's 20 hours on a battery that has 100 usable amp-hours.

Maybe today, I'll play the role of arithmetic teacher and you can be the student.

[Adrian Gordon]

Originally Posted by Larry-NC

Brandon, your math is weak. 10 hours at 1.5 amps is 15 amp-hours, not 150.

And you also missed a step. It's called "duty cycle." Assume, for example, that at 70 degrees F, without opening the refrigerator very frequently, that the compressor and fan only run about 1/3 of the time.

So it would really only be 15 * 1/3 = 5 amp hours. That's 20 hours on a battery that has 100 usable amp-hours.

Maybe today, I'll play the role of arithmetic teacher and you can be the student.

I don't think the two of you together could add a column of two single digit numbers. :-)
You are correct that his math was wrong and that 10 hours at 1.5 amps is 15 amp hours. I will assume that you are also correct when you say the refridgerator only runs about 1/3 of the time and thus it uses only about 5 amp hours every 10 hours of clock time, or about 0.5 amp hours per hour of clock time. In that case, it's 200 hours on a battery that has 100 usable amp hours. I can't vouch for the accuracy of the input numbers, but I'm pretty sure on the math.

[Larry-NC]

Originally Posted by Adrian Gordon

I don't think the two of you together could add a column of two single digit numbers. :-)
You are correct that his math was wrong and that 10 hours at 1.5 amps is 15 amp hours. I will assume that you are also correct when you say the refridgerator only runs about 1/3 of the time and thus it uses only about 5 amp hours every 10 hours of clock time, or about 0.5 amp hours per hour of clock time. In that case, it's 200 hours on a battery that has 100 usable amp hours. I can't vouch for the accuracy of the input numbers, but I'm pretty sure on the math.

Thanks for catching that, Adrian. A little foggy today.

[ArkRVHog]

Originally Posted by Theo

My vote is for either of two Victron battery monitors:

• SmartShunt - a 500A "smart" shunt that has no display. The battery monitor info is sent via Bluetooth to your mobile device and the free Victron Connect app. These run ~ $130 USD.
• BMV-712 - a 500A "dumb" shunt with a "smart" display. The display also sends the battery monitor info via Bluetooth to your mobile device. These run ~ $206 USD.

I have a BMV-712, but I always check my battery data with the Victron mobile app. Were I to do it again, I'd go for the ($75 less expensive) SmartShunt.

Victron's products are durable, reliable and accurate. Their battery monitors offer a full range of parameters that one can adjust to dial-in their accuracy and to allow them to adapt to different battery chemistries. I have no experience with other premium manufacturers' products like the Bogart Engineering TriMetric.

My recommendation would be to forego the less expensive products as they may not give you all the features Victron offers. Since we do a lot of dry camping, the important data for me are: temperature-compensated state of charge, charging rate (in Ah), predicted amount of days/time before the battery hits the discharge floor (50% of LA battery capacity) and real-time Ah draw. Note that the last bit of data is important in inventorying the current draw of each 12V appliances/accessories.

HERE is a pretty good write-up for battery monitor introductory information.

HTH

X2 on the BMV-712...everything you will ever need and the bluetooth app is great even providing firmware upgrades as available.

[NotLost]

Thanks everyone, I moved those 2 to the top of my list.

[jwalt313]

I would just like to know when its time to charge my 2 6-volt batteries with my generator and also to know when they are fully charged so I can turn off the generator. If the BMV-712 is the best to use for that, I'll buy it but is there something else I should use instead?

[TitanMike]

Originally Posted by jwalt313

I would just like to know when its time to charge my 2 6-volt batteries with my generator and also to know when they are fully charged so I can turn off the generator. If the BMV-712 is the best to use for that, I'll buy it but is there something else I should use instead?

either of the victron units will be the most accurate especially with lead acid batteries. Also, I know the 712 will allow you to monitor the mid point voltage which will tell you if both the batteries in series are each fully charged and in good health. the shunt only model may too but I can only speak for the 712.

[mnoland30]

To get the last 10% charge on the batteries takes some time because the charge rate drops as the battery gets full. That is where solar power shines, because it charges all day. I think I'd want to have enough solar to run the fridge during the day, plus charge the batteries. I'd also want to have enough battery to run the fridge for a couple of days without running the generator. I'd tear out the fridge and put in a propane fridge before I'd spend $1400 for lithium batteries.

Back to math. If BrandonSmith is correct about his amp draw, and all the other assumptions are correct, then the daily draw just for the fridge is (16 hrs x 1.5 amps ) + (8 hrs x 2 amps) which comes out to 40 amp hours.

[regal81455]

Might look at the Powermon by Thornwave as well.

[Dodge Guy]

While you’re spending money, your going to need Solar. At least 400W.

[Tampa Dave]

Originally Posted by BrandonSmith

FWIW, my 12V pulls 1.5A constantly and 2.0A when compressor kicks on.

If you don't have a second battery, you will need one. Do the math for amp-hours and you'll find that a battery does not last very long. 10 hours @ 1.5 amps is 150 amp-hours needed to run the fridge alone, not including the times the compressor kicks on.

It is 15 amp hours not 150.

[sheading]

My dc fridge pulls 105 watts on defrost and 80 watts running. I always have 3 to 5 watt draw with everything off except the gas detector. I have 250 ah battery bank with 400 watts solar. Use Victron 100/30 charge controller and shunt. Works great.
Also added renogy 60 amp dc to dc charge controller. To supplement solar on a cloudy day. If you use a generator make sure your charging amps are sufficient to charge the battery in reasonable time.

[garywilson]

Looks like your generator is going to get a little extra run time.