I finished up most of my solar install today and I noticed an issue when hooking up the solar controller to the batteries. I'm using an A/B Both switch to control what bank or banks I want to run.Prior to the solar controller I had only two things tied to the output of the battery switch, my inverter and the connection to the converter in the distribution panel. Which worked fine.When I went to connect the output or battery connection of the solar controller to the A/B switches output terminal, out of habit I just lightly touched the wire to the terminal and noticed a spark nothing big but as spark none the less. At the time I was running on the generator so I'm assuming the voltage was from the converters output. Sure enough when I measured the voltage it was 14.7 volts DC which is the output voltage of the converter/charger. I'm guessing I shouldn't have made the connection with the converter being powered up.So as a sanity check before I make the connection permanent I want to make sure I'm not doing something wrong. I'm assuming that the solar controller is made to accept the converters output when running shore power. And the small spark was just normal :-) Ron W.

If your controller is like mine, it gets its power from the battery bank. Just connecting it could cause a small spark.

I haven't got to do any installing yet but I think there is some DIODES involved to keep certain things out of the solar picture... Sounds like theleg beween the solar controller and the on-board converter might be a good spot for a DIODE...Ro Ken

Double check, then triple check the polarity and make the battery connection.Check the instructions but I believe you should connect the battery side first then connect the panels to the controller. Controller may have issues if you disconnect the battery before you disconnect the panels. May need to be careful of using the switch OFF position but again check the instructions.

Hi,The output of the solar controller should be in the 13.2 to 13.8 volt range. However if it is a PWM controller, it might be as high as 21 volts when not connected to the battery.Once you connect the solar controller to the output of the battery, then the controller output will be slightly higher than the battery voltage before making the connection, or if over 13.8 volts (or the shut off voltage for your controller) it might not read any different than the battery voltage. As for the spark, if the polarity was wrong, you probably tripped a fuse, or everything is OK if the polarity is right. A tiny spark is acceptable. Good luck!Fred.

the controller will "IGNORE" ? the converter voltage applied at the output side from the batteriesit will NOT accept it on the Input sidethe correct procedure for hook up1. batteries only, no converter no generator no shore2. connect controller to the batteries first, controller needs to sense battery system voltage before panels are connected3. connect solar panels to batteriesDO not get these steps backwards..some controllers will be damaged if connected to solar panels and there are no batteries to accept power output4. you can now use any additional charging you want..shore, generator, driving, external battery charger

Question on solar controller hook up? | Good Sam Community

30 Replies

rjsurfer
Explorer
Dec 14, 2014
Op back, rechecked everything and re-connected all the wires and everything is good. I was just a worried about that little spark when hooking up the solar controller battery terminals. In retrospect I should have flipped the breaker off for the converter before connecting the solar controller.

One last issue concerns my new 2000 watt Samlex inverter, when running at half to three quarters power (1000-1200 watts) my battery levels quickly drop to 11.70 to 11.60 volts then stabilize. If I shut things down the levels pop to 12.5 + volts.

I'm running 4 Trojan T-105's which should enough for that load?

Could inadequate battery cables be the cause? I'm using 4 gauge for all the power hookups.

Thanks for all the help...its a comfort to know I can bounce these stupid questions out there and get decent responses.

Ron W
time2roll
Nomad
Dec 14, 2014
Johnny G1 wrote:
Why do people keep insisting that there should be a fuse between controller and battery???? Mine has had no problem in 12 yrs with a C40 controller and the only fuse is between panels and controller.
All wires connected to the battery need to be fused within 18" on the positive terminal.
Although if the wire is short, clearly visible, larger gauge and away from hazards I would probably skip it too.
Fuse or breaker can provide a convenient shut-off for service.
CA_Traveler
Explorer III
Dec 14, 2014
Johnny G1 wrote:
Why do people keep insisting that there should be a fuse between controller and battery???? Mine has had no problem in 12 yrs with a C40 controller and the only fuse is between panels and controller.
The MS MPPT 60 manual says you "must" for one reason.

For maintenance I have a switchable CB on the + battery cable and a 2 pole disconnect for the high voltage panels. This was also a consideration for covered storage to eliminate all controller draws.
CA_Traveler
Explorer III
Dec 14, 2014
Anyone know for sure about connecting/disconnecting the MS MPPT 60? The manual isn't clear on this subject. It does say under the Power On section to connect the battery first, but this appears to be related to correct wiring and the very first power on. In another section it suggests a dual breaker for both the battery and solar.

I want to know because my battery disconnect switch is not close to the controller and I have a battery and solar panel disconnect switches near the controller.
jrnymn7
Explorer
Dec 14, 2014
My understanding is the fuse is to protect the controller from a shorted battery, not the other way round. Am I mistaken?

If correct, that fuse being open would create the same situation as hooking up the panel first, like traveler said, no? So you would end up with a bad battery and controller.

So what is the issue with connecting the panel first? Is there a sudden inrush of power?

And what would be an effective safe gaurd to dummy proof a wrong connection order?
CA_Traveler
Explorer III
Dec 14, 2014
A more general question to the blown fuse sequence is that the connection to the battery becomes open due to bad battery, loose connection or disconnect switch. I'm not surprised that it's controller dependent.
BFL13
Explorer II
Dec 14, 2014
Johnny G1 wrote:
Why do people keep insisting that there should be a fuse between controller and battery???? Mine has had no problem in 12 yrs with a C40 controller and the only fuse is between panels and controller.

Because the usual solar controller user's manual says to have a fuse between controller and battery on the positive wire close to the battery.

The usual fusing instructions say you don't need a fuse between panel and controller except in unusual circumstances.

http://www1.cooperbussmann.com/pdf/9df1f7ec-8c62-4210-8cf8-9504927394f0.pdf
Johnny_G1
Explorer
Dec 14, 2014
Why do people keep insisting that there should be a fuse between controller and battery???? Mine has had no problem in 12 yrs with a C40 controller and the only fuse is between panels and controller.
time2roll
Nomad
Dec 14, 2014
CA Traveler wrote:
OK, If the controller doesn't like a panel only connection what happens if the fuse to the battery blows?
What do the instructions say?
Maybe a non issue. What controller?
MrWizard
Moderator
Dec 14, 2014
Even if the battery shorted internally
The controller would not allow more than the set amount of amps into the battery
If the fuse in between blows, then the controller has exceeded it's rated output

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Question on solar controller hook up?

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