Battery monitor is like a fuel gauge - get one

[Fair_Enough]

We hear the term usable rule of thumb or 50% discharge like its some kind of law of the land. 90% discharged still leaves you with about 11.5 vdc. But, doing this regularly will drastically shorten battery life span.

Who knows that a battery discharged to 50% has a resting voltage of about 12.0 (mol) and 12.65 (mol) is 100%? Who knows why you can't get a true indication of battery state of charge with a volt meter while being charged or being discharged? I digress.

This 50% schema is based on after the discharge, a full recharge is to ensue. This is typically not being done. The converters most of us have are not going to ever completely charge a battery, but will come close after several days on shore power. Even the better PD4655 converter doesn't enter the float stage for 34 hours. But that's better than never.

A bigger mystery to me is why so few of us DO NOT have a good state-of-charge monitor... not idiot lights... not a volt meter... a real monitor. It is like loading up the family for a trip in the car without a fuel gauge, but just hit the road with wing and prayer. Then getting on a forum and asking why they ran out of gas in the middle of nowhere! Or how many miles should it go??
These things called batteries are ballast, more of less, until power is lost.

Surely a Streamer that can pay $50K - $100K can afford another $200 - $400 to do it right. They spend thousands on glamping, decor and pink flamingos. Okay, so I just went from preaching to meddling.

But its not so much the cost as it is not having something spoil the fun!


Battery musings for the nerds out there (she would already know this)
Convert Reserve Capacity or RC to Ah...
140 * 60 - 8400 (converts minutes to seconds)
8400 * 25 - 210,000 (converts to coulombs)
210,000 / 3600 = 58.333 amp-hour

In this example I am using the advertised Reserve capacity rating of one SRM24 Interstate 12 volt battery, the kind that fits the older battery boxes. It is 58.33 amp-hour each; the pair is then 116.66 amp-hour.

Why do they only show RC rather than Ah? Marketing slight of hand.

Going the other way... taking a 230 Ah battery back to its RC value
230 * 3600 = 828,000
828,000 / 25 = 33,120
33,120 / 60 = 552

So, a 230 Ah pair of 6 volt battery (brand doesn't matter), has a reserve capacity of 552 minutes or 9.2 hours. That's nearly a 400% increase in capacity over the SRM24.

No, you cannot run your air conditioner on two of them... LOL

Think this is complicated, get into the LiFeP04 world and complexity just went up 10 fold.

[Zil]

Quicker and faster. Reserve Capacity divided by 2.4 equals rough estimate of Amp Hours (20 hour). Reserve capacity is used on non-deep cycle batteries and only comes close to reflecting any equivalence with a true deep cycle battery.

[Vantair]

Wolfwhistle,

150% agree with you on that human vs that battery logic.

Another missed area of battery sustenance is the value of “passive” savings.

By addressing constant demand items (fridge heater strip, minimal mood lighting, self contained Bluetooth speaker instead of 1-2 amp radio draw etc...) really adds up over a few days of boondock.

For example, adding a simple mini toggle switch to the fridge door heater strip “saves” the entire usable ah capacity of one fully charged/healthy Interstate SRM 24 12v battery over 4-5 days.

Emagine, zero weight add, no added batt storage, virtually no cost (@ hour of fun) accomplishes this. Combine this and other simple conversation tricks with the upgraded 6v ah capacity can 2X your boondock days. We figure can easily now go from a 4 to 8 days accordingly.

[Fair_Enough]

Originally Posted by Zil

Quicker and faster. Reserve Capacity divided by 2.4 equals rough estimate of Amp Hours (20 hour). Reserve capacity is used on non-deep cycle batteries and only comes close to reflecting any equivalence with a true deep cycle battery.

Thanks Zil. I might have made a good lawyer (now there is an oxymoron!). Why use 1 word, when 6 will do!

I like your factor (2.4) over the long-hand math. Thank you!

Standards are an interesting topic. But, interestingly "they" rate a battery designed for cranking using a small number... even a small engine will draw in the neighborhood of 100 amps while cranking... small gasoline fueled engine in warm conditions. Deep cycle discharge battery rating using that 20 hour standard seems more logical.
WW

[Fair_Enough]

Originally Posted by Vantair

Wolfwhistle,

150% agree with you on that human vs that battery logic.

Another missed area of battery sustenance is the value of “passive” savings.

By addressing constant demand items (fridge heater strip, minimal mood lighting, self contained Bluetooth speaker instead of 1-2 amp radio draw etc...) really adds up over a few days of boondock.

For example, adding a simple mini toggle switch to the fridge door heater strip “saves” the entire usable ah capacity of one fully charged/healthy Interstate SRM 24 12v battery over 4-5 days.

Emagine, zero weight add, no added batt storage, virtually no cost (@ hour of fun) accomplishes this. Combine this and other simple conversation tricks with the upgraded 6v ah capacity can 2X your boondock days. We figure can easily now go from a 4 to 8 days accordingly.

Exactly V... excellent points. I have measured the door element (J2 on the control board) and get 0.4 amps. This was on a model 2652... now I have a 2551. If it is on all the time, that adds up to around 10 Ah per day. Not sure if this 24x7 or if it cycles. I am also seeing similar draw from CO detector and believe it or not... a 24x7 subwoofer amp... an easy fix. More testing needed!

My contention in recommending a SOC monitor is that thinking you have a full battery, can be quite different than having a full battery.
WW

[Vantair]

Wolf,
Brand new DM2662RB replaced the original that leaked yellow space dust. (Later found out about the national recall).

This version heat strip alone draws .360a (8.64amps /day)

If there are 2 leads into the fridge light, the slightly larger one should be feeding the heater strip. at least in our case.

[marter]

Curious if anyone knows if a Dometic RM2451 has a heating strip? There is no light in the frig, and I'm not seeing anything on the manual or wiring diagram to indicate that there is, but if I have one I'd like to be able to switch it to avoid parasitic draw if possible.

Thanks,
Mike

[cazual6]

What monitor do you recommend?

[AlinCal]

https://www.victronenergy.com/batter.../bmv-712-smart

[gandttimes]

Originally Posted by cazual6

What monitor do you recommend?

Bogart Engineering TM 2030. I know you can't read it with your phone but I don't need to.

[TouringDan]

Originally Posted by Wolfwhistle

A bigger mystery to me is why so few of us DO NOT have a good state-of-charge monitor... not idiot lights... not a volt meter... a real monitor. It is like loading up the family for a trip in the car without a fuel gauge, but just hit the road with wing and prayer. Then getting on a forum and asking why they ran out of gas in the middle of nowhere! Or how many miles should it go??

Wolfwhistle

I completely agree with you. One reason may be that they never boondock, ie. they are always plugged in in some way or just lack of information, ie. they didn’t know they needed one. Thanks for this thread. This is what is needed to educate folks.

I will add here that before I got my state-of-charge monitor I used a simple voltmeter to determine my state of charge. It seemed to work quite well as I don’t seem to have any parasitic draws from my batteries. I would just read the battery voltage after it was resting for a while.

For example we camped in full shade for 7 days. The starting resting voltage was 12.70. After 7 days it was 12.32. So I figure we went from 100% SOC to 70% SOC. And 0.30x230 amp-hours/ 7 days equals 10 amp-hours per day. I would always measure the voltage just before going to bed and just after getting up and they would be the same. So I figure no parasitic loads. This seems to be possible with an older Airstream, but evidently not with a newer model.

Dan

[Fair_Enough]

Update: I finally checked and my Dometic fridge doesn't have a door heater. It also doesn't have an interior light. Kinda odd (read - cheap) that there is not interior light. Dometic made it but AS installed it. They go to the trouble of nicely, for the most part lighting things up. Nothing on J2 on the control board on this one. I am thinking its a RM2551??

[Fair_Enough]

Another update: And not talking Li... lead-acid... flooded, sealed, or AGM.
I did some testing with AS monitor panel as it relates to DC voltage. I know its just an idiot light, but its in an Airstream and I was thinking...
The tank levels seem to working, after all.

Here's the thing, when charging don't bother to look at it. As soon as voltage reaches 13.4, it shows full. However, you could be anywhere between 40% and 100%, although unlikely that your converter can truly ever attain 100%. Now when its in some state of discharge and has rested, it is still very optimistic. All you know, basically, is that there is a battery out there somewhere.

Having a battery monitor will accomplish a few things. First you will learn how to manage DC power. You will be able to know the health of your batteries and charging system. You will be prepared for that trip and batteries should no longer spoil the fun. With solar power you will get to see the percentage remaining go down as you use it and go back up when the sun shines... oh, you will learn a lot about solar too.
WW

[marter]

Originally Posted by Wolfwhistle

Update: I finally checked and my Dometic fridge doesn't have a door heater. It also doesn't have an interior light. Kinda odd (read - cheap) that there is not interior light. Dometic made it but AS installed it. They go to the trouble of nicely, for the most part lighting things up. Nothing on J2 on the control board on this one. I am thinking its a RM2551??

WW, thanks for the reply, and sorry for the hijack. I found the manual for the series (your RM2551 is the same series as my RM2451 but 5cf instead 4cf) and it describes the "Climate Control System" on other models but not ours. Guess I don't have to worry about parasitic draw.

Back to your point of the original thread, I just installed a BMV-712 yesterday and learning how to maximize the info from it. I love the real time amperage draw readout. In fact I found that the PO had not converted a couple lights to LEDs (in the overhead locker above the galley) and I hadn't noticed; turn on a couple LED puck lights and you see a 0.1ah increase, vs. the 2.5ah draw from three of the old puck light bulbs that weren't replaced.

Thanks again,
Mike

[68 Overlander]

Originally Posted by gandttimes

Bogart Engineering TM 2030. I know you can't read it with your phone but I don't need to.

It will soon have WIFI and the module will be backward compatible with all 2030 models. Advantage being only one software program to write and not limited to bluetooth range which I never quite understood anyway. The monitor is right there on the wall. Anyway, many like to check SOC from phone while the coach is in storage. I know not everybody has WIFI where they store but many do.

[rmkrum]

Please let us know when that module becomes available. Sounds interesting.

[farafield]

Ok guys, newbie silver sister here with a very basic knowledge of electricity and batteries. I do more boon docking than shore power camping. I have a solar panel on the roof. I have a battery. But there seems to be a lot more to this than I thought!

Y'all are way over my head. Where can I get enough knowledge to be able to make sense of this thread?

[gandttimes]

Originally Posted by farafield

Ok guys, newbie silver sister here with a very basic knowledge of electricity and batteries. I do more boon docking than shore power camping. I have a solar panel on the roof. I have a battery. But there seems to be a lot more to this than I thought!

Y'all are way over my head. Where can I get enough knowledge to be able to make sense of this thread?

Farafield this site should give you some good basic down to earth reading. https://handybobsolar.wordpress.com/


George

[Fair_Enough]

Originally Posted by farafield

Ok guys, newbie silver sister here with a very basic knowledge of electricity and batteries. I do more boon docking than shore power camping. I have a solar panel on the roof. I have a battery. But there seems to be a lot more to this than I thought!

Y'all are way over my head. Where can I get enough knowledge to be able to make sense of this thread?

Dear farafield,

It isn't as complicated as you think... well the science certainly is. But, do you have to be a metallurgist to drive a car? First look at this video.

https://www.youtube.com/watch?v=qxhuwqKW8Mk

How about that hair!

I assume you don't have the SC-2030 charge controller, so set up is easy peasy.

The TM-2030 comes with enough instructions / information to make you an expert and help me, if I have trouble. It could put you to sleep if you're not careful. You just have to read. There are things you have done in the past by reading instruction that have to be more complicated than this.

TM-2030 RV is the battery monitor, which will tell you how much battery you have left, the instant voltage and current readings. Current is either measured in amps or for power it is rated in watts. Different ways of saying the same thing, in effect. It shows you usage and state of charge rather than on inaccurate battery voltage only.

There are three main components. There several retailers of these, but I have used Alt E Store in the past and have had good experience from them.

Monitor
https://www.altestore.com/store/mete...onitor-p11263/

Shunt
https://www.altestore.com/store/mete...-meters-p4638/

Cable
https://www.altestore.com/store/mete...it-50ft-p2360/

Shop around you might find better prices.

You will need a battery cable (I call a strap) sold or made separately, 4- 8x3/4" philip head screws, tyraps or a whatever method to keep the monitor to shunt cable neat and secure.

A few hand tools. Philips screwdriver, small and medium straight drivers, a drill to make holes in the monitor mounting base and from point a to b in your trailer as needed and a crescent wrench. There might be other things needed depending on factors that I have no way to know at this point.

The very next thing is read the documentation that comes with the monitor and understand it. The key here is to realize you are only using it for monitor, makes programming and using is super easy. I can talk you through it if you want to give it a try.

The hardest part could be figuring where to mount the monitor. It is for me.. I like to make it convenient but don't like to make holes. I can show you where I came up with on my latest 23FB IS.

Before proceeding, disconnect all power from the trailer. Remove the negative battery cable at the battery, then the positive. Do not short out + and - at a battery. Then turn off shore power and / or disconnect the converter charger.

The battery negative cable runs from batteries to inside the coach and terminates with other negative (-) cables on a bus bar. After finding and isolating the cable that goes to the batteries, remove it from where its tied down and connect it to one of the large lugs on the shunt. At this point it doesn't matter which one.

A cable or strap of appropriate wire gauge and length (minimum 6 AWG) is then terminated on the other lug of the shunt and ran to where you just removed the battery negative cable from. You can make the strap or buy one ready made. The thing to remember here is nothing is connected to the negative battery cable directly. All negative current must travel thru the shunt.

Mount the monitor in a good place

Run the 4 conductor cable from the monitor to the shunt

Terminate the wires in the monitor (you will have to drill a hole in the base) and terminate the other end on the shunt, per detailed instruction you will have in your hand. You will also need to find a source of positive (+) 12 volts DC close to the shunt and run that to the red wire in that 4 conductor cable. The cable kit comes with the fuse as well.

After checking and rechecking and sure all connections are correct; power up the coach and reconnect the battery cables... first the positive then the negative last.

Go to the monitor and it should be working. Settings are by default at this point. You have to program your total amp-hours into the monitor and P1 value.

Here's quick video from Tito showing it working.

https://www.youtube.com/watch?v=9pk3ycLK7_c

So, keep the monitor in what they call L1 group of settings... at least at first. You will need to set P1 slightly lower the Absorb level your solar charger is set at... Mine is 14.4, so I left it 14.3 volts.

The other thing is to set P3 for the total amp-hours of your battery bank. I have two GC-2 6 volts that are rated at 230 amp-hour so that is what I set P3 at. You simple find out what the total amp-hours of your batteries are and set P3 for that value.

Here's a Justus showing you his set up.

https://www.youtube.com/watch?v=rKCB4oBqums

As you get familiar, go into L2 and have fun

Let me know if I can help further
Clint