Voltage at batteries (13.7) vs at Connext (12.x)

[ralphsmithiii]

I just installed two brand new AGM 31's replacing the factory start and house batteries. I also built a solar panel charging solution using a 100w panel and duo battery charge controller. With that, I'm setting 13.7 measured at the battery terminals with the boat off but still connected to the solar panel. However, I'm only seeing 12ish volts on the Connext screen when I turn the switches on. Unless I'm not using my multi-meter correctly, is this normal or is there something I should be looking for? I did see there was a Connext voltage fix that @Mainah came up with and @swatski has done but I believe thats to have accurate readings between the batteries versus what I feel like I'm experiencing.

The solar controller I'm using is showing slow flashing green lights which indicated per the instructions a fully charge battery (float @13.7v) but I'm not sure why I'm only seeing 12.x at the Connext. Prior to swapping the batteries, I had no issues seeing 14.0/14.1 with the motors on.

I also just double-checked the setup once again before posting this. Turning the house/start batteries on but NO motor, shows 12.9/13.0 on the Connext. As soon as I turn the blower on it drops to 12.4x. Turn the motors on (30 seconds give or take) it shows both batteries at 12.4/12.4.

 

[Mainah]

Everything is working as it should. The blowers being on causes significant voltage drop at the spu which is what sends the voltage reading to Connext. This is because the wires feeding the the spu are not very big and the SPU feeds the blowers. Once the engines are running they are feeding enough power to the batteries at a high enough voltage that the solar controller shuts off its output. On a side note it is important that the solar controller be desinged or configured for a cut off volatge that matches the spec for the agm batteries your are using.

I can have 13.0 volts in float mode and turning on my ballast pumps, blowers, high volume inflator, or inverter will cause connext to show 12.3 to 12.6 volts depending on the load. This is with two fully charged and healthly interstate group31 agms and the combine switch on. Even with the engines running 6k rpms I can see the voltage go up and down a bit second by second induced by heavy bass at high volumes from my heavily modified and customized stereo system drawing the voltage/current (power) to the amps which starves the SPU just a bit. All of this is normal.

Think about it like current being the volume of water coming out of your shower at home and voltage being the pressure. What happens when someone turns on the tub, outside spigot, flushes the toilet, or so forth? The volume and pressure coming from the source (street/well) has not changed; the load has. Same thing with the batteries. They are still outputting the same (well yes they lose some over the course of a day if not giving back to them but strictly speaking point in time) the load has changed and the spu is measuring the voltage (pressure) at just one of the load points (faucets).

Sorry for the three ways of explaining the same thing. Just hoping that one resonates better than the others as the principle of voltage drop has lots of applications.

 

[ralphsmithiii]

Awesome, thanks for the quick feedback @Mainah . After reading your explanation, I think the problem may be that I currently have the DVSR disconnected (was in the middle of doing the DVSR mod but ran out of time) so that may be why I never saw anything over 12.4 while running the boat for a few minutes on the lake the other day after seeing a full charge on the batteries and that's with the stereo turned 100% down but not off.

To clarify, I bought the solar charge controller you recommended here: Amazon.com : Temank Dual Battery Solar Charge Controller 20A 12V 24V Duo-Battery Solar Controller for RVs Caravans and Boats : Garden & Outdoor

I have two Group 31 AGMs from Sams: Duracell AGM Deep Cycle Marine and RV Battery - Group Size 31 - Sam's Club

The controller was set to charge: Sealed lead acid battery (default) and not gel or flooded battery
Charging priority is set to 50% / 50%.
Charging frequency is set to 25 Hz (default).

I suppose I need to finish the DVSR mod and see if that's why I'm not seeing over 12.4 at the Connext with nothing running other than the motors and factory accessories, if I understand you correctly =).

 

[Mainah]

Two ways to go about it and go figure I wrote a book. I had been doing good with much shorter and less frequent posts up until today.

One: leave the dvsr as it was (or complete the mod will not matter with this option), and keep the combine switch set to on all the time. This is creating one bank from two batteries. It helps with high loads but may slightly diminish the combined longevity of the batteries or just the opposite it may help of you have very high loads. This is what I am currently doing with the very high rms and peak loads. I am regularly drawing about 100 amps rms load during my average use. The batteries prefer 25 amps or less rms load each before the high load starts impacting their longevity so running the two as one bank is only 2x preferred vs 4x on one battery and the high load impact on longevity is more of a curve. The stators do also help offset the high draw some. This is something I became more aware of early this boating season after more audio upgrades. We do a lot of towing with the stereo cranked at a 1200 -1600 (country music is lower draw and beast mode/big air playlist is higher draw) watt rms load (3 amps, 2 polk mm subs, one pair jl m880 towers, and 8 polk mm650, all tuned with a DSP and oscilloscope to maximize and blend sound output). Point being not for everyone but if running very high power audio regularly then this may be for you. Note this first option is only for two of the same batteries put in new at the same time. It has been working well for me and I see less voltage drop when turning on 3 ballast pumps and the blowers. In very high ambient temps (100f +) and high water temps (92f +) at least one of my ballast pumps like to heat up and reach thermal overload protection when combined with the heat coming of recently running engine blocks in the same confined space so the blowers help All that plus the steeo playing at a low to mid level is quite a draw for 4-8 sustained minutes. Not to mention that batteries don’t like high heat (agms are better in temp extremes). Sorry trying to put things in perspective with that lengthy explanation.

Option Two: Finish the dvsr mod and run as two independent banks.

I do believe SLA setting on that controller is the one that most closely matches the cut on and off voltages of AGM but that deserves checking.

12.4 is a good low load resting AGM battery float voltage once charge/float voltage has dissipated.

 

[ralphsmithiii]

Two ways to go about it and go figure I wrote a book. I had been doing good with much shorter and less frequent posts up until today.

One: leave the dvsr as it was (or complete the mod will not matter with this option), and keep the combine switch set to on all the time. This is creating one bank from two batteries. It helps with high loads but may slightly diminish the combined longevity of the batteries or just the opposite it may help of you have very high loads. This is what I am currently doing with the very high rms and peak loads. I am regularly drawing about 100 amps rms load during my average use. The batteries prefer 25 amps or less rms load each before the high load starts impacting their longevity so running the two as one bank is only 2x preferred vs 4x on one battery and the high load impact on longevity is more of a curve. The stators do also help offset the high draw some. This is something I became more aware of early this boating season after more audio upgrades. We do a lot of towing with the stereo cranked at a 1200 -1600 (country music is lower draw and beast mode/big air playlist is higher draw) watt rms load (3 amps, 2 polk mm subs, one pair jl m880 towers, and 8 polk mm650, all tuned with a DSP and oscilloscope to maximize and blend sound output). Point being not for everyone but if running very high power audio regularly then this may be for you. Note this first option is only for two of the same batteries put in new at the same time. It has been working well for me and I see less voltage drop when turning on 3 ballast pumps and the blowers. In very high ambient temps (100f +) and high water temps (92f +) at least one of my ballast pumps like to heat up and reach thermal overload protection when combined with the heat coming of recently running engine blocks in the same confined space so the blowers help All that plus the steeo playing at a low to mid level is quite a draw for 4-8 sustained minutes. Not to mention that batteries don’t like high heat (agms are better in temp extremes). Sorry trying to put things in perspective with that lengthy explanation.

Option Two: Finish the dvsr mod and run as two independent banks.

I do believe SLA setting on that controller is the one that most closely matches the cut on and off voltages of AGM but that deserves checking.

12.4 is a good low load resting AGM battery float voltage once charge/float voltage has dissipated.

@Mainah I follow you so far and I appreciate the well written responses.

Let me ask you to make sure we're talking about the same thing.

If I have two fully charge batteries with the house and start turned on and I start the boat what I should see for voltage at the Connext?

 

[ralphsmithiii]

Hrm, after re-reading your comment here: "12.4 is a good low load resting AGM battery float voltage once charge/float voltage has dissipated", I'm wondering if thats what I'm seeing currently whereas before I'd see upwards of 13.9/14.0 with the engines running at rpm crusiing on the water. I was able to get into the diagnois screen (held CTRL I think for 3 seconds) and with the motors running even idle I was seeing 14.1/14.2v there. Does anyone know if that's what the stators are putting out or if that's the reading from the batteries themselves? If the latter is true, then I'm still not clear as to why the Connext is only showing 12.x with brand new matching AGM group 31 batteries while running (DVSR still not connected in this case but not sure that matters since we're talking full charge then maybe 1-2 minutes on the water with no real load on them).

 

[Mainah]

Hrm, after re-reading your comment here: "12.4 is a good low load resting AGM battery float voltage once charge/float voltage has dissipated", I'm wondering if thats what I'm seeing currently whereas before I'd see upwards of 13.9/14.0 with the engines running at rpm crusiing on the water. I was able to get into the diagnois screen (held CTRL I think for 3 seconds) and with the motors running even idle I was seeing 14.1/14.2v there. Does anyone know if that's what the stators are putting out or if that's the reading from the batteries themselves? If the latter is true, then I'm still not clear as to why the Connext is only showing 12.x with brand new matching AGM group 31 batteries while running (DVSR still not connected in this case but not sure that matters since we're talking full charge then maybe 1-2 minutes on the water with no real load on them).

Have you done the voltage reading fix? If not and dvsr not connected one battery is getting topped off by the stators and the other is not and that would explain 12.4 while engines running now vs 13.9-14.1 when the dvsr was connected. Connext is only reading the battery not getting a charge from the motors in this case. When motors are running the stators are outputting 13-14 volts to the battery connections and with no real load and that is what Connext is reading provided that battery is getting the power from the stators and Connext is reading that battery. One battery type/size to another and the health of the given battery will cause the running engine reading to vary as the absorption and dissipation rates will vary. Load will also impact this.

I would get that dvsr back connected asap especially if using solar as the shore charger option. Those stators will charge at a rate at least 10x of the solar depending on a few variables and help the battery not become overly discharged throughout the day.

 

[ralphsmithiii]

@Mainah That was it! I took the boat back out on the water today where I could work on it. Finished the DSVR mod and with the motors running I'm seeing what I see at the batteries, 13.7v+ and with it running for several minutes eventually back up to 14.0v without the stereo blasting.

For anyone else who may run into this (and your mileage may vary), IF you disconnect your DVSR 100%, you may experience what I did in that your Connext will show a lower voltage readout. Even though my batteries are showing 13.7v which is what my aftermarket solar controller is set to float charge to, I never saw anything north of 12.x even with the motors running. I reconnected (finished) the DVSR mod and wala, fixed.

I will do the Connext voltage fix as well but I ran out of time today. Thanks again for your help!