Charge state disagreement between DC2DC and MPPT

[ConcordCarlos1]

House Battery Charge status/stage disagreement, so prepare your flamethrowers and red pen….

Issue : Displayed (via app) charging stage is different according to MPPT and DC to DC charger, regarding the house battery . Example , vehicle / camper sitting at work for 10 hours , MPPT showing “float” prior to vehicle start up and DC2DC powering on . DC2DC starts by showing bulk , 5-10 mins later into absorption and 40 mins latter float . Both Victron MPPT and DC2DC are set to the AGM preset .

System : 2021 Fourwheelcamper Hawk on a 2021 Tundra , stock 92ah AGM. Mostly 10g and smaller stock wiring . I think charging and battery runs are all 10g.

Removed stock ACR, Installed Victron 12/12/30 DC2DC in its place . Matched stock 10g wiring , ground to common / stock neg buss bar in same compartment. Can’t get a clear visual of exact layout , but I think one wire goes directly to the battery from
The stock fuse , one to the DC panel. My estimate is 12’ of stock 10g wire before it gets to the battery .

Solar : Did my own thing . Only stock components are the external plugs , roof / rear wall and 10g interior wiring . 210w panel on roof. Occasionally use a folding 100w plugged into the rear wall. From the stock wiring to 30amp breaker , then 10” of 8g to the Victron MPPT(100/30/12) , 10” of 8g to the battery from
MPPT. MPPT set to AGM preset charging profile, same as the DC2DC.

My guess is the 10g wire, and/or length is causing the dissimilar charge state reading.

Next year I plan on replacing the AGM with the 206ah SOK LifePo4, and moving the DC2DC into the battery compartment. This will reduce the length of wire from the DC2DC to the battery. In doing this the move , the power “out” from the onboard Iota DLS30IQ will also feed into the DC2DC. It doesn’t look like the Iota is LifePo4 compatible, so this should be a bonus. At the same time, I’ll replace the short run of 8g from the MPPT with 6g and the DC2DC will feed the battery with 6g.

 

[DiploStrat]

House Battery Charge status/stage disagreement, so prepare your flamethrowers and red pen….

Issue : Displayed (via app) charging stage is different according to MPPT and DC to DC charger, regarding the house battery . Example , vehicle / camper sitting at work for 10 hours , MPPT showing “float” prior to vehicle start up and DC2DC powering on . DC2DC starts by showing bulk , 5-10 mins later into absorption and 40 mins latter float . Both Victron MPPT and DC2DC are set to the AGM preset .
...

Actually sounds about right. Truck is sitting on solar charge, hits full charge, goes to float.

You start the engine and the B2B kicks in. It will automatically go to bulk, and then, as it reads the battery, cycle through absorb to float. Sounds like it is reading a rather full battery, and responding as designed. (N.B. The lithium fora are full of discussions about how to avoid chargers going to bulk every morning and attempting to over charge lithium batteries.)

FWIW - no two meters or chargers will ever agree.

Get yourself a decent wire/gauge/distance and replace that 10 AWG with something of proper size. (My only snark of the day.)

 

[Ozarker]

Having one small basket of oranges and a larger basket of apples, both floating in water, which weighs the most?


As @DiploStrat stated;
FWIW - no two meters or chargers will ever agree.

"Get yourself a decent wire/gauge/distance and replace that 10 AWG with something of proper size. (My only snark of the day."

 

[ConcordCarlos1]

I’m ok with wiring, but better at convincing myself there is a problem. 10-4 on the disagreement portion.

I would like to replace as much of the 10g as possible, but beyond what I can see with a hand held mirror and impossible flashlight angles, I can only take a guess at some of the 4WC wiring layout.

Is there harm in moving the DC2DC on the other side of my Non Lithium Iota shore charger ? That would capture power from the truck and Iota and give me access to the Victron‘s settings for use on both inputs.

 

[DiploStrat]

You lost me.

The Victron B2B should be grounded and the positive leads connected: Starter Battery>B2B>Camper Battery. It should have nothing to do with any shore charger. (Same deal with your solar charger, Panel(s)>Solar Charger/controller>Camper Battery.)

FWIW: A shore charger would be connected: 110v (in US)>Charger>Camper Battery.

Of course, you can use a common terminal or bus bar to connect all of these to the Camper Battery positive, the physical connection is whatever is easiest for you to install. But the logical connections are as above.

 

[ConcordCarlos1]

Currently, the feed from the Iota shore powered charger and truck>DC2DC>camper battery is carried on the same wire to the camper battery compartment . One of my thoughts was to use that wire on the input of the DC2DC, so it feeds from both, and would eliminate the issue of the Iota not having a Lifepo4 charge profile.

 

[ConcordCarlos1]

Solar and shore charger are currently wired exactly as you have stated.

 

[jonyjoe101]

All mppt controllers always read higher than the actual battery voltage. The mppt controller thinks the battery is fully charge and goes to float early. I encounter this with different controllers pwm or mppt. The battery terminals can be at 14 volts but the mppt is actually reading 14.4 volts,
Next time when the sun is overhead read the voltage at the battery terminals then bounce that with what the controller is reading. If the readings are different you might have to adjust the bulk voltage on the controller to compensate. If the controller isn't properly calibrated, using thicker gauge wire won't do much.

I have the makeskyblue 60a mppt controller and luckily that has voltage calibration but not many controller have that feature, thats why you might have to adjust the bulk voltage setting.
The dc to dc charger is probably much more accurate and is giving the batteries a better charge.

I discovered the voltage drop problems on the solar controllers when I switched to lifepo4 and my batteries weren't getting fully charged. Its when I realized I was undercharging my lead acids for years. At 14.4 volts the battery terminals werent even reaching 14 volts.

One sign of voltage drop is the batteries going to float too soon while on solar. Also charging at a very low amp rate is another sign. If the sun is overhead you should be getting at least 10 amps from your 200 watts of panels. If the controller thinks the battery is close to a full charge it drops the amps to 2 or 3 amps.

 

[ConcordCarlos1]

All mppt controllers always read higher than the actual battery voltage. The mppt controller thinks the battery is fully charge and goes to float early. I encounter this with different controllers pwm or mppt. The battery terminals can be at 14 volts but the mppt is actually reading 14.4 volts,
Next time when the sun is overhead read the voltage at the battery terminals then bounce that with what the controller is reading. If the readings are different you might have to adjust the bulk voltage on the controller to compensate. If the controller isn't properly calibrated, using thicker gauge wire won't do much.

I have the makeskyblue 60a mppt controller and luckily that has voltage calibration but not many controller have that feature, thats why you might have to adjust the bulk voltage setting.
The dc to dc charger is probably much more accurate and is giving the batteries a better charge.

I discovered the voltage drop problems on the solar controllers when I switched to lifepo4 and my batteries weren't getting fully charged. Its when I realized I was undercharging my lead acids for years. At 14.4 volts the battery terminals werent even reaching 14 volts.

One sign of voltage drop is the batteries going to float too soon while on solar. Also charging at a very low amp rate is another sign. If the sun is overhead you should be getting at least 10 amps from your 200 watts of panels. If the controller thinks the battery is close to a full charge it drops the amps to 2 or 3 amps.

Thank you for the leads . I’ll be doing some more testing . I’ll do a test set up with the DC2DC on the “other” side of the Iota . My goal is to convert power from the truck , and iota to what the soon to be installed SOK 206ah battery wants .

 

[ConcordCarlos1]

Update: I did the instal as intended, putting the DC to DC inline to convert the output of both the built in Iota and dc in from the truck to camper power. It didn’t work. I essentially cut the the battery off from the camper . Additionally , the voltage in from the Iota to the DC to DC kept dropping to 9v. I assume the Iota did not put out consistent voltage since it was no longer “sensing” a battery? I ended up moving the DC to DC back to where the VSR was , and it’s functional. I am no longer using the Iota to charge the SOK, as the solar is plenty to maintain the battery while the camper is not in use. @DiploStrat was right , but I learned some lessons via my mistakes.