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Old 09-23-2019, 08:46 AM   #1
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Merging solar controller output with stock rv converter output (splicing).. good idea?

Hi everyone.
Looking to add solar to my RV and I seem to remember seeing a youtube video where the person was splicing the output lines coming from the charge controller with the 12 volt output lines coming from the rv stock converter. That would allow for using the existing wiring and providing two sources of power for recharging the batteries, if needed.
I was looking at turning off the rv converter altogether (using the breaker) and letting the charge controller take care of the batteries (bulk/float), everything. I have enough battery storage. Then, if I'm running into two or more days of shade, then I would turn back on the breaker for the converter (shore power) and let it recharge the batteries for a bit. Thoughts?
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Old 09-23-2019, 09:11 AM   #2
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Usually that wiring is pretty small. Probably better to go straight to the batteries.

Also, no reason to turn converter off...
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Old 09-23-2019, 09:20 AM   #3
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Many of the battery charging devices used in RVs today control the charge by measuring the voltage of the battery(s). You can have two charging devices connected in parallel. If they are both producing the same charging voltage you will get approx twice the charging current. If however the two chargers produce different charging voltages you will get less than twice the charging current as the higher voltage charger will fool the lower voltage charger into thinking the battery is actually at a higher charge state than it is.

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Old 09-23-2019, 10:48 AM   #4
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Tying in into the existing 12v lines will work just fine. As said previous, no need to turn off the converter.

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Old 09-23-2019, 09:52 PM   #5
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Tying into the battery charge lines from the converter is the equivalent of hooking the wires from the solar panel directly to the battery with a little added wire resistance. There's nothing "wrong" with this but there could be some effects. A direct connection means that you are not using a solar controller between the panels and the battery. It follows from this that the output voltage from the panel will equal the battery voltage. A 12V panel produces its maximum output power when the output panel voltage is usually somewhere between 16 and 19 volts. It's the power that determines how quickly the panel can charge the battery.

Panel manufacturers have charts showing output current and power vs load for their panels. these charts always have a peak power point where the panel produces its rated output power, measured in watts. MPPT controllers are designed to adjust the current draw from the panel to whatever rate necessary to make the panel produce its maximum power. The newest controllers then feed this power to the battery at the voltage that maximizes the current flowing into the battery. It's the current that actually recharges the battery. Don't forget that as a battery charges, the voltage across the terminals rises. The newest MPPT controllers compensate for this while maintaining the three phase charging cycle.

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Old 09-24-2019, 06:46 AM   #6
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PMSHERMAN... if you read the 'title', I'm just asking if connecting the output of the solar charge controller and splicing it with the output line from the converter going to the battery is ok. So, yes, I do intend on having a charge controller between the solar panel and the rv stock converter. But thank you for the response though.
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Old 09-24-2019, 09:44 AM   #7
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You can connect your charge controller output to the converter lugs, in fact, if you have a PD converter there are two lugs for pos and two for neg so you can use the spare connection points.

HOWEVER, in many FR products, the converter first goes to the DC panel and then to the batteries through a disconnect switch. This means that if you turn off your batteries for storage, the solar system will not be able to keep you batteries charged during storage.

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