Overwhelmed by Battery Monitoring

[sheading]

Solar setup

[DavidWJ]

Originally Posted by tomkatb

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.

Amps are an instantaneous value. Amp-Hours is a measure of capacity and Watts are a measure of power. To relate this to battery capacity, take Amps*Hours and check that against the batteries you have.


For a 3 Amp continuous draw, 3 Amps x 24 Hours = 72 Amp Hours are required from your battery. A 220 Amp-Hour battery will last about three days before becoming completely depleted. Now, a 12 V battery is effectively depleted at 6 V, so you only have 1/2 that time, or just about a day and a half.

[AlanMoor]

Your first paragraph is spot on, but your second paragraph is misleading. A 12V battery is at 100% around 12.6V, and is effectively dead at 10.5V. To avoid damaging the battery you want to avoid going below 50% of the batterie's capacity, which is around 12.06V.

I'm in the middle of building a 280AH LifePo4 battery pack, and will post my success/failure when I get it done. However, part of the build includes a USB interface with PC software AND Bluetooth ->Android/IOS interface which ultimately allows you to monitor and even graph your battery usage, and turn the battery on and off (charging or discharging). All for around $700 I think. It's not for the faint of heart though and you do have to have a few toys (like multimeter, power supply and a few tools) to do it. It's also a 2+ month process because you have to order the BMS and LifePo4 cells from China.

The reason I post this here is that I have a Victron 712 SmartShunt, but with the new battery I won't need it, so that effectively knocks $130 off the price of the battery system. It doesn't save me anything since I already have the SmartShunt though. The range on the SmartShunt for me is horrible, I have to be within 15' line of site, or 5' if I'm inside the trailer. Not everyone has had that experience, but I've heard it from a few. Also, with the SmartShunt you don't get the alarms you get if you buy the BMV-712 (I don't have any experience with the BMV-712 though).

Originally Posted by DavidWJ

Amps are an instantaneous value. Amp-Hours is a measure of capacity and Watts are a measure of power. To relate this to battery capacity, take Amps*Hours and check that against the batteries you have.


For a 3 Amp continuous draw, 3 Amps x 24 Hours = 72 Amp Hours are required from your battery. A 220 Amp-Hour battery will last about three days before becoming completely depleted. Now, a 12 V battery is effectively depleted at 6 V, so you only have 1/2 that time, or just about a day and a half.

[DuluthCamper]

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.

Last I checked, 10 hours at 1.5 amps is 15 amp-hours, not 150 amp-hours.

However, definitely stay with the concept of trying to use fewer amp-hours. A traditional flooded lead-acid battery should never be run down to have less than half its original amp-hours (e.g.: 100 amp-hour battery, run down to 50 amp-hours or fewer remaining). Doing so will reduce the total number of times that battery can be recharged, resulting in a ruined battery in a year or two, instead of getting four or six years of life out of it.

If feasible, only running a flooded lead-acid battery down to 80% before recharging will give you many years of use from it.

Or, moving to an Absorbent Glass Matt (AGM) battery, perhaps in Group 31 size, may be a good idea. They can be purchased with more amp-hours, if you're going longer periods between charges.

Gel and Lithium batteries are other options, and Lithium are nice for their lightweight characteristics (but you pay more for that lighter weight).

[Murph60]

Originally Posted by 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.

Just returned from my first trip with the A122S Aframe. Friday, Saturday and Sunday night. Ran heat all 3 nights as temps were in the 30s and low 40s. Ran fridge, lights, stove and stereo.

I have 2, 27 Group, 100 AH AGM deep cycles in parallel. Never ran the generator and my batteries were at 12.52 after resting 12 hours when we got home.

[Half Ton Heavy]

A fellow member here did testing on his 10cu ft 12 volt fridge using a bmv 712. He said it was eating 75 to 80 ah a day.
For that type of load, I would want 300ah of lithium and a charge source like 400+ watts solar, and / or dc to dc charger / generator.

[imjustdave]

Originally Posted by Murph60

Just returned from my first trip with the A122S Aframe. Friday, Saturday and Sunday night. Ran heat all 3 nights as temps were in the 30s and low 40s. Ran fridge, lights, stove and stereo.

I have 2, 27 Group, 100 AH AGM deep cycles in parallel. Never ran the generator and my batteries were at 12.52 after resting 12 hours when we got home.

Not to be rude but I suspect your info is flawed, here are my thoughts with some Q along the way.
How long was the drive home?
What was the voltage prior to hitching up?
I highly suspect your TV charged your batteries on the way home so your 12.52 is useless info OR your voltage has peaked back up but it literally has no amperage behind this value and simply turning on a small load will tank the voltage.

Define ran heat for 3 nights? how hot did you want it inside? furnace fans are anything but efficient, if it ran 25 - 50% of the time, no way you had 12.52 volts after 3 days. If you ran it once maybe twice to warm up the room while you got ready and dressed then maybe, your trailer is pretty small to be more efficient.

What type of fridge do you have LP or 12Volt. - I have read numerous threads with people getting 12v only fridges and batteries only lasting a portion of a day to 1. Obviously other loads and sizes of batteries plays a role. If LP fridge then those last multiple days no issues.
Also with it 30 to 40 outside your fridge is only really running long enough to offset the heat to chill your food.

Lights I suspect are LED so no real load and Radio 1 hr or 72 hrs.
Do you have any solar?
Do you have a LP detector that is hardwired in? If so this alone would have had a big enough draw that your batteries weren't 12.52 at the end of 3 nights camping.

[RedRoverComeOver]

Have a G16BH and took it out for the first time and didn't run out of juice during the 4 days. My fridge is DC and have it set to 4 to keep it at no more than 40° although the freezer is colder than I need. I have separate thermometers and basing it on them.

We dry camped and turned on the fridge maybe 3 hours before leaving and put in contents into the fridge before leaving...no freezer items. Only liquids in there were milk for my coffee and only opened for meal prep and some fruit snacks. And for coffee in the morning and night since I forgot my wine! It rained on/off all the time and only saw the sun on the day we left. Never saw batteries get to 100% and down to 38% the whole time.

Going out again this week and more rain in the forecast. Hope we don't fill up the gray water tank in under 24 hrs. like the last time. I'll do the dishes this time.

[Murph60]

Originally Posted by imjustdave

Not to be rude but I suspect your info is flawed, here are my thoughts with some Q along the way.
How long was the drive home?
What was the voltage prior to hitching up?
I highly suspect your TV charged your batteries on the way home so your 12.52 is useless info OR your voltage has peaked back up but it literally has no amperage behind this value and simply turning on a small load will tank the voltage.

Define ran heat for 3 nights? how hot did you want it inside? furnace fans are anything but efficient, if it ran 25 - 50% of the time, no way you had 12.52 volts after 3 days. If you ran it once maybe twice to warm up the room while you got ready and dressed then maybe, your trailer is pretty small to be more efficient.

What type of fridge do you have LP or 12Volt. - I have read numerous threads with people getting 12v only fridges and batteries only lasting a portion of a day to 1. Obviously other loads and sizes of batteries plays a role. If LP fridge then those last multiple days no issues.
Also with it 30 to 40 outside your fridge is only really running long enough to offset the heat to chill your food.

Lights I suspect are LED so no real load and Radio 1 hr or 72 hrs.
Do you have any solar?
Do you have a LP detector that is hardwired in? If so this alone would have had a big enough draw that your batteries weren't 12.52 at the end of 3 nights camping.

Going based on memory at this point, but measuring the battery at camp site, obviously not rested, measured 12.62 when we left. Got home and rested for 18 hours and it measured at 12.52. I was still well above the 50% rate of around 12.30. negative is disconnected now and ready for a charge before we leave for out next trip.

Ran heat for 3 nights. Where did I say I ran it all day? 10 PM to 6 AM at around 65 degrees or less as I don't remember the exact temp we had it at.

Fridge is 12v, 120 and LP. Ran it on 12v when trailering and LP at camp.

I have 2, 27 group, AGM 100 AH batteries

I know what I measured

[pgandw]

Originally Posted by Murph60

Going based on memory at this point, but measuring the battery at camp site, obviously not rested, measured 12.62 when we left. Got home and rested for 18 hours and it measured at 12.52. I was still well above the 50% rate of around 12.30. negative is disconnected now and ready for a charge before we leave for out next trip.

Ran heat for 3 nights. Where did I say I ran it all day? 10 PM to 6 AM at around 65 degrees or less as I don't remember the exact temp we had it at.

Fridge is 12v, 120 and LP. Ran it on 12v when trailering and LP at camp.

I have 2, 27 group, AGM 100 AH batteries

I know what I measured

Murph60

Concur with your readings. We did a dry camping trip at Twin Lakes, Colorado last summer. Day temps low 80s, night temps low 40s. Ran Fantastic Fan (on low) about 4 hrs in the afternoon, heat set at 58, turn up to 68 when DW gets up. Started at 12.6V, ended at 12.3V after 3 nights. About 0.1V (or 10%) per day on 2 GC-2 batteries (210AH).

Very little light and water pump use, stereo has power totally cut off (installed switch) when camping. Installed 2 manually switched 70ma 120mm computer case fans on fridge exhaust vent for consistent fridge cooling. These were on the entire time.

The heater and Fantastic Fan installed in the A-frames are reasonably miserly. I can easily make the 4 night dry camping goal without taking the batteries below 50%.

We tow with fridge on propane, so batteries get reasonable charge while towing (up to 10 amps).

Fred W
2019 Flagstaff T21TBHW A-frame with Costco/Interstate GC-2 batteries
2008 Hyundai Entourage minivan
camping Colorado and adjacent states one weekend at a time