Using a battery charger when RV has solar panel

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Intelliduner
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Using a battery charger when RV has solar panel

Post by Intelliduner » Mon Aug 03, 2009 4:49 pm

Gang,
I bought a new (to me) motorhome that has a pretty nice roof-mounted solar unit for charging the house battery. Is it safe to put a 110v battery charger on the house battery without first disconnecting the solar charger's wiring?

Reason I ask is that years ago I bought a tiny solar charger at Harbor Freight for use in some other vehicles. It plugs into the lighter/accessory port. The instructions that came with it said very clearly to *not* start the engine with it plugged in, so I'm assuming that the power coming from the alternator would fry the solar charger. I just don't know if the ones designed for RVs have protections built in to them--either internally or if perhaps they have another relay installed in the engine compartment to isolate them when the engine is running. If it's built-in, I'm probably ok in leaving the wires connected when I use my charger, but if it uses an external relay, then I probably should disconnect it first, as it wouldn't be in between the 110 charger's current and the solar stuff.

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Re: Using a battery charger when RV has solar panel

Post by ChuckZilla » Mon Aug 03, 2009 8:12 pm

It may be easy to disconnect the solar panel from the system, take a look.
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Re: Using a battery charger when RV has solar panel

Post by Doc » Mon Aug 03, 2009 8:30 pm

No problem in leaving the solar panel(s) connected.

The controller will manage the output from the panels and not let them overcharge the batteries.

I have my MH plugged in all the time and the controller just shuts off the panels when the batteries are fully charged. I have 300 watts of panels so the batteries are being kept at full charge all the time. My controller also charges the engine battery when the coach batteries are fully charged.

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Re: Using a battery charger when RV has solar panel

Post by Intelliduner » Mon Aug 03, 2009 10:20 pm

@ChuckZilla: there are 2 fuses in the info panel inside the RV. I pulled both of those but didn't want to risk anything so I pulled the wires from the battery too.

@Doc: I'm not worried about the solar panels overcharging my chassis battery. I'm worried that when I connect a 110v battery charger to the chassis battery the current will flow backward *into* the solar charger and cook something (either the control panel or the solar array itself). I'm not famililar with the circuitry of either and don't want to risk ruining an expensive piece of equipment.

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Re: Using a battery charger when RV has solar panel

Post by Doc » Tue Aug 04, 2009 7:17 am

You will not flow current back into the panels as there are diodes in there to keep that from happening. These diodes are there primarily to keep from draining the batteries at night when current could flow backward.

Also think for a second what happens when you drive your motor home. Every motor home I have seen will have some system of charging the MH batteries when you are driving. That is just like putting your charger on the coach batteries.

You don’t pull the fuses and disconnect the wires every time you start the MH do you?

Your MH alternator put’s out more current than your external battery charger or your internal MH converter/charger and it does not hurt the solar panels.

The system is designed to be able to handle multiple sources of current so don’t do any unnecessary work when it’s not needed.

The little plug in charger you had did not have a controller and probably did not have any diodes because diode’s do use some of the current and with such a small panel the current used by a diode would probably have used half of that small panels output. Those small panels are pretty much throw away units anyway so they have little or no internal protection.

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Re: Using a battery charger when RV has solar panel

Post by Intelliduner » Tue Dec 01, 2009 9:48 am

Doc wrote:Also think for a second what happens when you drive your motor home. Every motor home I have seen will have some system of charging the MH batteries when you are driving. That is just like putting your charger on the coach batteries.

You don’t pull the fuses and disconnect the wires every time you start the MH do you?
I just realized there was a reply to my thread...a few months later #-o

Re. the question above, yes, I know that the alternator charges the batteries without harming the solar charger, but I also know that there are solenoids that are triggered when the ignition is on and they prevent current from backtracking where it should not go (such as the inverter). I don't know how all of that stuff is wired or how it all works, but I do know that when I put a charger on my battery, those solenoids are not engaged and thus not protecting anything.

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Re: Using a battery charger when RV has solar panel

Post by Doc » Tue Dec 01, 2009 9:59 am

Intelliduner wrote:
Doc wrote:Also think for a second what happens when you drive your motor home. Every motor home I have seen will have some system of charging the MH batteries when you are driving. That is just like putting your charger on the coach batteries.

You don’t pull the fuses and disconnect the wires every time you start the MH do you?
I just realized there was a reply to my thread...a few months later #-o

Re. the question above, yes, I know that the alternator charges the batteries without harming the solar charger, but I also know that there are solenoids that are triggered when the ignition is on and they prevent current from backtracking where it should not go (such as the inverter). I don't know how all of that stuff is wired or how it all works, but I do know that when I put a charger on my battery, those solenoids are not engaged and thus not protecting anything.
These solenoids only keep the coach from draining the MH starting battery. When you are driving and the solenoid is picked up you are tieing all the sources of charging together. If you were to use the invereter while driving the alternator could be providing the amps for that.

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