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jbbcd

Can I split my solar panels wiring to 2 charge controllers to house and rv batteries?

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Hi & Thanks for any input,

A bit new here for solar. I don't have all my specs yet , just bought a used RV set up with solar. I have not seen any fuses or breakers on this set up yet. yikes!

1) The hardware:

a) 2 (two) solar panels on roof (higher voltage, I see read outs up to 27 volts & higher) I'm not familiar with these panels yet

b) 1 (one) PWM Duo battery solar charge controller 

c) 1 (one) MT-1 dual meter

d)1 (one) Victron MPPT 30amp smart charge controller. (this currently is NOT installed)

e) 2 (two) 12 volt deep cycle house batteries

f) 1 (one) vehicle 12 volt starter battery

I purchased the RV with a dual charge controller (PWM Duo battery solar controller ) charging both the house & RV batteries

I would like to add the Victron  MPPT charge controller to this system.

My question is: Could I splice the leads from the solar panels to go to both charge controllers? one set of leads to the PWM charge controller charging the RV battery & one set of leads to the MPPT charge controller for the house batteries?

If so, as I'm adding a 2nd charge controller I would like to add the proper fuses at the correct locations.

pic.thumb.jpg.20f3b207a7a02ddecbfc4ab266d8f6c2.jpg

 

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jb, I don't have any specs or data to back it up BUT I DON'T LIKE THE IDEA OF WIRING YOUR SOLAR PANELS TO TWO DIFFERENT CHARGE CONTROLLERS. The MPPT is more efficient and the PWM (if like ones I owned) sort of switch the charging amps into the battery on and off so at times more power might go to one controller and at other times the other. In addition, charge controllers can have more fixed voltages, like 12 or 24 etc Ive seen in PWM, while an MPPT can accept a wider range. I doubt the resistance of the two controllers is the same, meaning they wouldn't draw equally from the panels and likewise not charge the two batteries the same... I like to use all the available solar power to charge ONLY my house battery bank.  

Again no specs no data nor info to base it on but I just don't like it. Another thing I don't like for EITHER charging or load sharing is using two batteries together that may be different chemistry or size or even age. I prefer identical matched batteries when using more then one together. 

FWIW I have used my engines alternator to charge BOTH my starter and house batteries via a selector/emergency switch but its more for short term emergency type charging NOT day to day use in which my Converter/Charger or my solar panels charge the house batteries and the alternator the starting battery. The better way is to use a DC to DC Converter Charger to let the alternator charge the house batteries   

They make solid state dual battery charging and isolation systems to charge multiple batteries yet not allow one to discharge the other  

The Vmp of a panel is NOT the same as its given voltage rating. My so called 24 Volt panels have a Vmp of like 36 or so. The charge controller takes that raw energy at X volts and supplies the correct amount of charging volts to match the battery. 

I bet the other fine sparkies and gents on here have a better more scientific answer, all I'm saying is I don't like what you proposed lol If you just have to use solar to charge two different types of batteries, Id use one panel and PWM controller for the engine battery and the other panel and MPPT controller for the house batteries......... How about a battery maintainer trickle charger for the engine battery ?? Why does it need auxiliary charging ???

John T

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No. Use a smaller panel to keep the starting battery topped up. The only loads on it are likely the chassis radio memory, and the ECM for the engine/chassis. Minor loads only require a small panel.

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You can use two charge controllers in a system, but each controller has to be fed from separate solar panels.  You should not do it the way you are proposing.

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Thanks everyone for your input!

Looks like Tom_M nailed it! 

I will definitely consult back to this post when I start the project of adding items & fuses. 

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jb, is there a reason why you need to be charging the engine battery ??? Is it running down quickly ??? Does temporarily unhooking prevent the discharge ???  Is unhooking an easy viable option for you ???

  If its one, absolutely necessary and two, you choose for whatever reason to do it using solar as you posted instead of a battery trickle charger, in that case I (as discussed above) wouldn't get rid of the PWM charge controller but instead use it (with a small separate solar panel) for the less critical engine battery charging and use the more expensive more efficient MPPT charge controller for your house battery bank.   Hey there's no  necessarily right or wrong answer here, it strictly a matter of YOUR choice.

Good luck jb, take care now

John T

Edited by oldjohnt

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On 7/16/2020 at 3:05 PM, oldjohnt said:

jb, is there a reason why you need to be charging the engine battery ??? Is it running down quickly ??? Does temporarily unhooking prevent the discharge ???  Is unhooking an easy viable option for you ???

  If its one, absolutely necessary and two, you choose for whatever reason to do it using solar as you posted instead of a battery trickle charger, in that case I (as discussed above) wouldn't get rid of the PWM charge controller but instead use it (with a small separate solar panel) for the less critical engine battery charging and use the more expensive more efficient MPPT charge controller for your house battery bank.   Hey there's no  necessarily right or wrong answer here, it strictly a matter of YOUR choice.

Good luck jb, take care now

John T

oldjohnnt: Its just that we boondock for weeks at a time, during these times we do plug into chassis battery for small fans cell phone chargers etc....mostly for my wife. I know better...lol. just trying to prevent the day were ready to roll & the chassis battery is dead cause the wife drained it with out me knowing..... etc etc

Thanks again every one :) 

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On 8/1/2020 at 4:49 PM, jbbcd said:

oldjohnnt: Its just that we boondock for weeks at a time, during these times we do plug into chassis battery for small fans cell phone chargers etc....mostly for my wife. I know better...lol. just trying to prevent the day were ready to roll & the chassis battery is dead cause the wife drained it with out me knowing..... etc etc

Thanks for the feedback, hey I hear your concern. One cheap n easy (even if NOT ideal engineering method) method is to have a switchable and overcurrent protected jumper circuit (motorhomes can have an emergency jumper switch/solenoid) that connects the house battery to the engine battery whereby if any solar charging is active (or the Converter/Charger is operating via a genset) on the RV it could also supply some degree of charging to the engine battery (caution but similar drain it if not managed). An inline diode could prevent reverse discharge, but there's a 0.6 voltage drop across it. Of course, starting the engine now and then as/if needed should allow the alternator to top off the engine battery.  Then there are trickle charger/maintainers or again small separate solar panels as discussed above. 

 Your concern is sure legitimate and I know people have been stranded and/or looking for jumper cables when the engine battery is dead grrrrrrrrrrrrrrrrr My preferred method is to ONLY use house batteries if dry camped instead of the engine to avoid any such problems..........

John T

Edited by oldjohnt

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