RV alternator and controller charging bank simultaneously ok ?

[Teocalli]

Wondering if there are any concerns when driving and the alternator is cranking out amps to the bank, is it an issue if the MPPT controller is still doing it's thing ?
The Blue Sky 3024 controller changes from float 0.3 to 7 when driving. I imagine the dual sources are competing with each other but there shouldn't be any harm in that correct ?
Or should I shut off the controller when driving ?

cheers,

Dave

[SunEagle]

Most RV's have a way of isolating the power coming from the alternator or another source like generator or solar charge controller.

If you have two devices tied directly to the battery and each can provide a way to charge the battery at the same time you may end up with an overcharged battery or backfeeding one charging system with the other.

[Teocalli]

The isolation solenoid is there but it's designed to keep the engine battery and the coach batteries isolated except when the engine is running, then the charge is delivered to the coach batteries. Short of powering off the controller when driving there must be an automatic way for the controller to detect the primary charge and go into a standby mode perhaps ?

[Teocalli]

I found this article which is useful - http://roadslesstraveled.us/charging...r-shore-power/

[SunEagle]

The isolation solenoid is there but it's designed to keep the engine battery and the coach batteries isolated except when the engine is running, then the charge is delivered to the coach batteries. Short of powering off the controller when driving there must be an automatic way for the controller to detect the primary charge and go into a standby mode perhaps ?

Maybe a quality charge controller would work that way but most cheaper controllers wouldn't have a clue and only measure battery voltage. For that matter those CC may cycle on and off depending what voltage the alternator was providing.

[ewarnerusa]

I regularly read RV forums and the consensus there is that multiple charging sources play together just fine. It is true that they may trick and confuse each other, but no harm is done to the batteries if each charging source is controlled by tapering amps in order to not exceed maximum voltage setpoints. That means if the charging sources have different setpoints, say one is 14.4V and another is 14.8V, they both contribute their full capacity until the batteries reach 14.4V. Once that happens, the 14.4V source will simply stop providing amps because the 14.8V charging source will continue to contribute and raise the voltage.

Doesn't a solar charge controller prevent backfeeding by design? Otherwise they would allow batteries to discharge in to the panels every night after the sun goes down.

[jflorey2]

I regularly read RV forums and the consensus there is that multiple charging sources play together just fine. It is true that they may trick and confuse each other, but no harm is done to the batteries if each charging source is controlled by tapering amps in order to not exceed maximum voltage setpoints. That means if the charging sources have different setpoints, say one is 14.4V and another is 14.8V, they both contribute their full capacity until the batteries reach 14.4V. Once that happens, the 14.4V source will simply stop providing amps because the 14.8V charging source will continue to contribute and raise the voltage.

That is true; in terms of voltage they play well together. However, together, the two may exceed the maximum safe charge rate of the battery. Heed the manufacturer's recommendations and make sure that the maximum current that both of the sources can deliver together does not exceed the maximum charge rate of the battery.

[Teocalli]

I have noticed when driving the controller runs anywhere between 10-25 amps always in bulk charge mode because it sees less than 14.4v apparently all the time. I have no idea what the 2006 Sprinter alternator is delivering to the bank simultaneously but it's a safe bet that together they exceed the C20 rate of the two 6v T-105's right ?

I would have thought once the engine delivers enough charge it would allow the controller to function normally ?

Wondering if I am damaging the batteries ?

[Sunking]

I have noticed when driving the controller runs anywhere between 10-25 amps always in bulk charge mode because it sees less than 14.4v apparently all the time. I have no idea what the 2006 Sprinter alternator is delivering to the bank simultaneously but it's a safe bet that together they exceed the C20 rate of the two 6v T-105's right ?

I would have thought once the engine delivers enough charge it would allow the controller to function normally ?

Wondering if I am damaging the batteries ?

No not at all. A battery self regulates itself up to a point

Bet the first mistake is you are using a mechanical or Diode type battery isolator. That is the wrong hardware. You want an Electronic Battery Isolator that takes the alternator Voltage Regulator out of the Alternator, and puts it in the Electronic Battery Isolator. Very few do that. You have to buy one like a Sure Power Isolator. That is why there are so many models as they are made for specific vehicle manufactures and amperage. Run the right Isolator, and whenever the engine is running, your solar system will deliver no power because it is no longer the higher order power source which is what you want.

Most Isolators use a Diode. Your vehicle Alternator Voltage Regulator in modern vehicles is set to 14.2 volts which is the proper voltage for a lead Calcium SLI battery. A FLA Deep Cycle Battery is lead antimony and requires 14.4 volts. That diode drops the regulator voltage from 14.2 to 13.5 volts which is OK for a float voltage and will work if time is of no concern.

Use the Sure Power Isolator, and it controls the voltage of the vehicle alternator giving both your SLI cranking battery and your Depp Cycle House battery their proper voltages. 14.2 to the SLI battery, and 14.4 to the House Battery. Your vehicle alternator can generate more power in an hour than your panels can generate in a week.

So if the engine is running using the correct Isolator, the solar system will deliver no to little power. The higher energy source always dominates.

[Sunking]

A battery self regulates its charge current via the Internal Resistance of the battery.

Example if you have a 30 amp charge controller, the battery resting open circuit voltage is 12.6 volts and a 100 AH battery is going to have an Ri of roughly .020 Ohms. If you had the controller voltae set to 14.4 volts and assuming full noon sun capable of producing 30 amps is only going to raise the voltage of the battery from 12.6 volts to 12.6 volts + [30 amps x .020 Ohms] = 13.2 volts despite the voltage set at 14.4 volts.

The danger point of any lead acid battery is reaching the Gassing Voltage where corrosion gassing takes place, and that depends on temperature. But for a 12 volt battery is 14.6 volts when very cold, and dropping to 14 volts when very hot. To take that same battery from 12.6 volts to to say 14.4 volts would take [14.4 - 12.6] / .02 Ohms = 90 amps which is still not a big problem other than excessive gassing and minor corrosion. However the current would taper off very fast to zero amps within a 10 to 15 minute period as the battery charges faster.

Point of the exercise above is I could have a 1000 amp battery charger on a 100 AH battery, and the battery would self limit the charge as it could only take 90 amps.

Having said all that as a general rule of thumb for FLA batteries you want to limit the maximum charrge rate to about C/8. Keep in mind batteries are not created equal. Some can take much higher rates. But at C/8 any can handle that.