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  1. #1
    Long Hauler bertschb's Avatar
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    Checking battery voltage using Level-Up control panel plus Victron BMV-712 questions

    I've been monitoring my battery voltage while my RV is in storage and I'm confused about the state of charge and need some help from the electrical gurus here. First some background - my RV came with two 12v batteries. The battery cut off switch in the pass through is off and I have a Battery Tender 15w solar panel plugged into the factory solar port. Yes, I know many folks here recommend just disconnecting the negative cable on the battery while in storage but I choose to use the solar charger.

    My confusion stems from the results I get by looking at the voltage on the Level Up control panel. It's an easy way to check battery voltage but I'm wondering if it's not accurate because of the readings I get.

    Here are some battery voltage readings I've captured since we put the RV in storage last month-
    4/3/19 - 12.6v After driving home for 10 hours with fridge running on the inverter and parking RV in storage lot
    4/4/19 - 12.5v No charging
    4/5/19 - 12.5v No charging
    4/6/19 - 12.4v No charging
    4/6/19 - Plugged RV into 30 amp A/C shore power
    4/17/19 - 12.9v Plugged into shore power for 11 days
    4/18/19 - Unplugged A/C power and plugged in solar panel
    4/21/19 - 13.2v Solar charger plugged in (measured in the afternoon)
    4/26/19 - 12.9v Solar charger plugged in (measured in the afternoon)
    5/2/19 - 12.4v Solar charger plugged in (measured in the morning)

    It's been sunny every day for the past couple of weeks and things looked good until I measured the voltage this morning at 12.4v. I assumed that the batteries were fully charged a couple weeks ago (12.9v) and the solar charger would easily maintain them so why did the voltage drop to 12.4? I would expect voltage to be slightly lower in the morning and higher late in the afternoon after a full day of charging but 12.4v is about 75% charged. That seems way low.

    I'm tempted to get the Victron BMV-712 battery monitor to get more accurate information but I've looked at the Victron install video, the manual and a bunch of YouTube videos and I'm still puzzled as to how exactly to install it. I understand the basic idea but I want to make sure I do it right and I've yet to find anybody that just has two 12v batteries and documents what they did to install it. I think I'd need to get a short battery cable to put the shunt inline between the battery and the grounding screw. I looked at the batteries in my RV and the negative battery cable is attached to the side wall in the front compartment with three other wires attached to that one screw. Seems like a hokey install. I expected to see a ground block.

    So I guess my questions are-
    1- Is the voltage readout from the Level Up control panel an accurate way to measure battery voltage?
    2- Is it normal for two 12v batteries to drop from 12.9v (100% charged) to 12.4v (75% charged) over night while the RV is in storage?
    3- I've looked at battery charge charts that show 12.7v is 100% charged. If so, why did I get readings of 12.9v and 13.2v?
    4- Do I need to buy a short battery cable in order to install the Victron battery monitor with my two 12v batteries?

    Sorry for all the rookie questions. I just want to keep my batteries topped off while in storage and being the gadget geek that I am, I'd like to get the Victron monitor just because it's cool. And Howard @howson - your post this morning showing your Victron battery monitor app is going to cost me another 200 bucks!
    Brian & Kellie
    2020 Solitude 310GK-R, FBP, 1,460w solar, 540ah BBGC3, MORryde IS w/disc brakes
    2020 F-350 Platinum SRW Powerstroke Tremor, 60g TF fuel tank, Hensley BD3-F air bag hitch

    Previous setups:
    2019 Solitude 373FB-R, 2019 F-350 Platinum DRW Powerstroke, Hensley BD5 air bag hitch
    2016 Reflection 318RST, 2016 GMC 3500 Denali SRW Duramax, Hensley BD3 air bag hitch

  2. #2
    Seasoned Camper Clanker24's Avatar
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    I checked my battery with a meter before I put it in the trailer and it read 12.6 v. After I put it in I turned on the level up controller and it said 12.2 v.
    John & Joanne
    2018 Solitude 374TH
    2018 GMC 3500HD Duramax CC DRW
    2001 Harley Ultra Classic

  3. #3
    Rolling Along JColeman's Avatar
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    I can't believe that the Level Up controller is an accurate voltage meter. Depending on where it was mounted or how much cable they put on it the readings will be different. The only way to be sure is to measure voltage from a shunt or at the terminals. The Victron uses a shunt and will be much more accurate.
    Jeff and Jen
    2016 F250 CC Lariat 4x4 6.7L, Firestone Airbags, Pullrite Superglide
    2017 Solitude 310GK, a little solar, a little lithium, disc brakes and a few suspension mods

    Those who would give up essential Liberty, to purchase a little temporary Safety, deserve neither Liberty nor Safety. - Ben Franklin

  4. #4
    King Pin
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    Hi Brian.

    First of all, lets address the drop from 12.9V to 12.4V with the solar charger installed. Since it's only 15 watts, that means that 15W/12.4V = 1.2A of charging current. That really is just a trickle, and may not be enough to keep up with the parasitic voltage draws that may be on your unit. Items like stereo memory and gas detectors have some current draw all the time. And then if you accidentally left something turned on, it's an even bigger draw. Even just leaving the antenna booster on will cause more current flow. And remember, that current flow will happen all night long while the sun is down. So it makes sense that you'd have less voltage on the battery bank in the morning than you would in the afternoon.

    I'm running three 12V batteries in parallel on my TT. I did just what you said and installed a short wire between the negative cable of the battery and the shunt. You can see it here in this picture.



    And I also was frustrated with how the grounds were hooked up on my travel trailer. So I installed a ground bus bar to clean things up. Here is a before pic:



    And here is the after pic (before I ran the ground wire from the shunt to it)



    Jim

  5. #5
    Long Hauler howson's Avatar
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    Quote Originally Posted by bertschb View Post
    And Howard @howson - your post this morning showing your Victron battery monitor app is going to cost me another 200 bucks!
    I had to take an extensive test showing I was capable of inducing RV-envy before I was inducted into the lofty realm reserved for moderators. Spending other people's money was job requirement #1 , if I remember correctly. (Of course I'm kidding.)

    Seriously, the BMV-712 is worth every penny. I set mine up almost exactly like Jim did. If you look at the summary document near the end of my electrical thread I have part numbers listed for the project box, lug connectors, and the tools to make the battery cables. More $!
    2017 Ford F-350 DRW 6.7L Platinum
    2019 315RLTS (purchased 16 Jul 18 from Campers Inn RV in Byron, GA)

  6. #6
    Site Sponsor Cate&Rob's Avatar
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    Hi Brian,

    I concur with the advice so far. The main thing that I would add is that if you are upgrading your wiring, install a 1/2/both/off four way battery switch. These are common marine switches. This allows you to use one battery or the other or both. More importantly, this allows you to compare the charge and discharge rates of each battery.

    When batteries are hard-wired into a bank, there is no easy way to know when one battery is failing but the other is fine. In your case, you might have one cell in one battery which is failing and dragging down the other battery voltage as well.

    Upgrading cable size and using proper crimped terminals when you are doing this, is also good advice.

    Rob
    Cate & Rob
    2015 Reflection 303RLS

  7. #7
    Long Hauler bertschb's Avatar
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    I really appreciate the feedback guys! I went back to the RV this evening and voltage had gone up from 12.4 this morning to 12.7. I have no idea if either of those numbers are accurate but it made me feel better - temporarily.

    Jim- Thanks for the pics with notations. Very helpful!

    I'm going to order the Victron BMV-712, a battery switch, bus bar and some cables/connectors/cable tools.

    Rob - Does this battery switch look OK?
    https://www.amazon.com/gp/product/B0...KIKX0DER&psc=1

    Howard - You mentioned links for the lug connectors and tools for making cables but I couldn't find them. Could you share them again? Also, what kind of wire/cabling do I need?

    Can anybody recommend a bus bar for grounding?

    I need to look inside the front compartment again at the wiring before I order stuff just to make sure I understand what I'm doing. Do you guys recommend replacing all the positive and negative battery cables that came with the RV?

    Thanks again for your help!
    Brian & Kellie
    2020 Solitude 310GK-R, FBP, 1,460w solar, 540ah BBGC3, MORryde IS w/disc brakes
    2020 F-350 Platinum SRW Powerstroke Tremor, 60g TF fuel tank, Hensley BD3-F air bag hitch

    Previous setups:
    2019 Solitude 373FB-R, 2019 F-350 Platinum DRW Powerstroke, Hensley BD5 air bag hitch
    2016 Reflection 318RST, 2016 GMC 3500 Denali SRW Duramax, Hensley BD3 air bag hitch

  8. #8
    Long Hauler howson's Avatar
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    Quote Originally Posted by bertschb View Post

    Howard - You mentioned links for the lug connectors and tools for making cables but I couldn't find them. Could you share them again? Also, what kind of wire/cabling do I need?
    https://www.mygrandrv.com/fo...l=1#post231623
    2017 Ford F-350 DRW 6.7L Platinum
    2019 315RLTS (purchased 16 Jul 18 from Campers Inn RV in Byron, GA)

  9. #9
    Long Hauler bertschb's Avatar
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    Thanks again Howard. Not sure how I missed your excellent write-up! Wow! Well done!
    Brian & Kellie
    2020 Solitude 310GK-R, FBP, 1,460w solar, 540ah BBGC3, MORryde IS w/disc brakes
    2020 F-350 Platinum SRW Powerstroke Tremor, 60g TF fuel tank, Hensley BD3-F air bag hitch

    Previous setups:
    2019 Solitude 373FB-R, 2019 F-350 Platinum DRW Powerstroke, Hensley BD5 air bag hitch
    2016 Reflection 318RST, 2016 GMC 3500 Denali SRW Duramax, Hensley BD3 air bag hitch

  10. #10
    Long Hauler howson's Avatar
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    Quote Originally Posted by bertschb View Post
    Thanks again Howard. Not sure how I missed your excellent write-up! Wow! Well done!
    No problem. Note the system diagram has the wire size documented, but (of course) you'll need to verify the wire you use is appropriate for your installation. The references on the last page should help with that task.
    2017 Ford F-350 DRW 6.7L Platinum
    2019 315RLTS (purchased 16 Jul 18 from Campers Inn RV in Byron, GA)

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