Switch controller leads between batteries?

[Primal1]

I have a wanderer cc and 200w of panels, my batteries are all different sizes. I charge them all individually. I've been switching the leads when each one hits float. The manual says I should hook up the cc to the battery before connecting to the panels. Do I need to disconnect the panels each time before switching to the different battery? Am I endangering myself or the gear by moving the leads while the panels are connected?

 

[highdesertranger]

"Do I need to disconnect the panels each time before switching to the different battery?"

short answer, yes. you are running the risk of burning out your controller. in fact I am surprised you haven't already.

highdesertranger

 

[jonyjoe303]

As long as the voltage of the batteries is the same 12 volts, why don't you just connect another battery at the same time? Thats what I do. With lead acid its no big deal just plug it in. Which ever battery needs more amps, gets more amps. It would be almost the same as when your charging  your start battery from an alternator and then the isolator connects your house battery. Both batteries will charge at the same time.

Right now my house battery is 220ah lifepo4, but I also have a 28ah agm lead acid that I will connect into the system from time to time to top it off. I never leave 2 batteries connected unless they are charging otherwise one will drain into the other.

But doing your way you need to always disconnect the panel before changing the battery. The controller requires battery power to power its computer, if only panel is connected with no battery the controller will start cycling back and forth.  

Another secret I found out is you can charge another 12 volt lead acid battery from the aux out. My controller doesnt show that it can do it, but when I connect another battery there I can get up to 12 amps of charge current (depending on panel). So you can charge 2 batteries at the same time, one from the batt out, and the other from aux out.

I use xt60 connectors, so for me its as simple as plugging in the extra battery into the system.

 

[Weight]

My much researched opinion. You will not burn out the controller. You will get small sparks. If you have a very high voltage system, such as a s&b roof top panels, you could get shocked.

 

[Trebor English]

MPPT controllers turn off an inductor and let the inductor take current through a diode as part of the process of stepping down the voltage and stepping up the current.  Some designs are prone to self destruction if the current is shut off (by disconnecting the battery) with no place for the induced current to go.  There is a voltage surge.  The exact timing of the disconnection will affect the amount of the surge.  

All of the controllers that I have known about that did self destruct were MPPT and not cheap.  It almost seems like the higher the price the more likely the failure.

My cheap PWM controller contains no inductors.  It is very unlikely to die as a result of a disconnection.  Light loads connected to the load output may not be tolerant of the no battery 20 volt panel open circuit voltage.  Heavier loads will pull down the panel voltage.

 

[Primal1]

Thank you. The batteries are all vastly different, 18, 65, & 105AH so charging them all at once is a no go. I will try to only use the 105 and make sure I disconnect the panels if I need to charge one of the others.

Is covering the panels sufficient or do they need to be physically disconnected?

 

[Weight]

I would be interested in direct evidence of a solar controller self destructing when a battery is disconnected. If there is a short and a fuse or breaker opens, are the controllers designed to fail and need replacement?

 

[highdesertranger]

from what I know is most controllers state in the instruction sheet to disconnect the panels first and reconnect them last. now if y'all know more then the people who design/build the controllers and put that in the instruction sheet, well what can I say. knowingly disregarding the instruction is fine if you are footing the bill, but to give that advice to some one else who has already stated that his instruction sheet said don't do it, is plain bad advice. highdesertranger

 

[tx2sturgis]

Also, most MPPT controllers do a 'set-up' based upon when you first connect them to a battery. The controller determines what voltage the battery bank is, ie, 12v or 24v.

I dont know what they default to, but connecting panels FIRST and then the battery SECOND could lead to a controller that is trying to charge 12v batteries at 24v, or 24v batteries at 12v, or possibly, other negative results.

Best Practice dictates hooking up the batteries first, THEN the panels. 

None of my controllers have 'fried' doing it the wrong way accidently, but I never do it that way on purpose.

 

[Primal1]

My controller is a PWM and I've switched it about 3 times a day for the last week. It just continues to flash the float lights while disconnected.

 

[Seminole Wind]

covering them or turning them upside down should be sufficient.

while i have not fried a controller by connecting/disconnection contrary to the instructions. i have had controllers fault andneed to be reset and hooked up in the right order to get them to work.

connecting and especially disconnecting anything especially dc circuits is just bad practice.

 

[B and C]

The best way would be to put a switch on one of the cables from the panels near the controller or pull the fuse in the panel circuit (you do have one don't you?). You don't have to cover/turn over the panels this way. Only takes a few minutes to install the switch to save a lot of aggravation from messing with the panels each time.

My controller manual specifically states to connect the battery to it before the panels are connected and to disconnect the panels before disconnecting the battery. They don't state this to be just making stuff up. YMMV

 

[Weight]

Yes that is in all the instruction pamphlets. A cover-your-azz clause. Who has talked to engineers at the manufacture and were told disconnecting the battery will fry the controller? Who has direct experience frying a controller? Why do all the controllers have a fuse on the battery side? Fuses and breakers do fail, then you must buy a new controller? I am talking about our typical low voltage, low amperes systems as found to fit on a RV.

 

[B and C]

And these are the typical low voltage, low amp system these controllers are designed for. It is not good to give advice that goes contrary to what is in every manual. The fuses are to keep from burning down your house. If you lose a controller too, that is part of the cost of a shoddy install IMO.

 

[Trebor English]

Yes that is in all the instruction pamphlets. A cover-your-azz clause.  Who has talked to engineers at the manufacture and were told disconnecting the battery will fry the controller? Who has direct experience frying a controller? Why do all the controllers have a fuse on the battery side? Fuses and breakers do fail, then you must buy a new controller? I am talking about our typical low voltage, low amperes systems as found to fit on a RV.

Yes, the fuse blows and you need a new solar charge controller.  Most people put in a cable  capable of carrying more current than the panel can generate in order to have a cable big enough to have a low voltage drop.  With the fat cable you need a fuse at the battery that can deliver 1000 amps and roast the wire but at the solar charge controller the source is limited and cannot produce a current sufficient to overheat the fat wire.  Also, you don't want a sunny day to routinely blow a fuse so you use a wire big enough so the controller cannot overload the wire.

Spring of 2017 reddit user named "crap_allnamesaretaken" had a controller die.  


This was in England where there is very little experience with solar electric systems.  The 2 x 150 watt panels connected to a 30 amp MPPT controller produced more than ever since the system was installed the prior December.  There was a 7.5 amp fuse connecting the controller to the battery.  That was wrong as a 300 watt system should normally be able to produce more than 7.5 amps.  The system was doomed from the start.  

The MPPT controller was doing the buck converter thing pulsing of the inductors at 7.5 amps when the fuse opened.  The inductive kick that happened blew the controller.  Yes, it can happen.  

Similarly, do not disconnect the battery from a running engine.  That can cause the alternator windings to do the same inductive kick thing.  You may do it with no problem but it can go bad.  High voltage pulses in DC systems can destroy charge controllers, alternators, and loads like lights and engine control computers.  Just because bad things can happen doesn't guarantee that bad things will happen every time.

A 1957 Chevy ignition dystem uses the inductive kick.  The points turn on 12 volts to the ignition coil.  Due to the inductance the current slowly increases over time.  Energy gets stored in the magnetic field created by the coil primary winding.  At just the right time the points open, the current flow stops, the magnetic field collapses, the energy stored there creates a high voltage that rises until the spark plug arcs.  That arcing allows current to flow and the stored energy is dissipated as heat in the arc.  

Do not pull a plug wire off a spark plug of a running engine with electronic ignition.  The lack of the spark plug arc allows the voltage to go too high destroying the electronics or the coil with internal insulation damage.  Also follow the recommended spark plug change interval recommendation.  As the spark plugs wear the gap increases and the peak voltage increases destroying the electronics or the coil.  

The common appearance of the same warning in the literature for many products is not due to lawyers or bean counters.  It is a physics thing.  Circuitry could be added to any system to make it more resistant to damage.  That's where the bean counters come in.  It is circuitry that is normally not being used and adds to product cost.

 

[Spaceman Spiff]

Yes that is in all the instruction pamphlets. A cover-your-azz clause.  Who has talked to engineers at the manufacture and were told disconnecting the battery will fry the controller?  . . . Why do all the controllers have a fuse on the battery side? Fuses and breakers do fail, then you must buy a new controller? I am talking about our typical low voltage, low amperes systems as found to fit on a RV.

Have you "talked to engineers at the manufacture" so you can claim with confidence its a "cover-your-azz clause" or are you just making an uninformed guess?

A fuse on the battery side is for the positive battery cable (and should be as close to the battery as possible).  A 12V automotive battery can create an arc in excess of 5000ºK, hot enough to weld steel.  And yes if that happens your controller or any other electrical device in the short circuit will be trashed.

Have you ever known a fuse to fail in the unprotect (failure to open) state?

 

[wayne49]

What happens if the fuse/breaker between the controller and the battery bank blows/trips?
The solar circuit is still connected.
They don't sell protective equipment that opens the solar side when the battery bank is disconnected.
They tell you to fuse/break the two sides independently without regard for the resulting situation.

There's a "disconnect" there.

I haven't lost a controller due to the solar side blowing out. At the same time I don't disconnect the battery bank as SOP. But it happens.

I lost one PWM by failing to find the tiny print towards the back of the manual in a table of numbers that stated the max input was 236 watts.
Something that should be out front like "20AMP". Not very consumer friendly.

 

[B and C]

So what I am getting out of this is you are advising new solar operators to disregard the manual no matter what it says. Just because it hasn't happened to you it won't happen to them. I hope the new people take all this bad advice and look at where it comes from, untrained individuals on the internet. Fuses are there to protect against burning your house down. If the solar controller goes because a fuse blew at least your house didn't catch on fire. If a fuse blows, something was installed or sized incorrectly to begin with. Reader beware.

 

[wayne49]

If there is a situation when I would have to disconnect the bank post haste, I will do it. Just as a fuse would. Not SOP.
Not Standard Operating Procedure. Stuff Happens at times.

The bigger issue is will the OP be able to charge the separate batteries fully each time?

 

[wayne49]

Note: I installed a DC circuit breaker on the solar cabling on the board with the controller. I use that to disconnect the solar when doing work on the battery bank, controller, or panels.
Push the button. Do whatever is necessary. Rearm the breaker.
Easier than carrying a blanket up a ladder to throw over the array. Or working at night.