Adding a switch between panels and charge controller

[KirkB]

I'd like to add a switch to cut power from my panels to my controller. Couple of questions I couldn't find a good write up on:

1. For a 30amp system, will a 30a rather rocker switch work or should a battery cutoff switch be used.

2. Is it better to install the switch on the negative or positive line?

3. Does it matter if the switch is closer to the controller or panels?

4. Should the panels be fused (slightly off topic)?

Thanks.

[Naptown]

You should break both poles

Any switch you use needs to be rated for the DC volts and amps it is being used for.

[KirkB]

Can anyone recommend a good switch for my panel setup: peak voltage 42v, peak current 12a. Something that could handle a little more would be nice. I've scoured that amaz0n place and found nothing that seems to be rated high enough from a DC power perspective. I nice rocker switch (low profile) would be ideal for my setup.

[mapmaker]

1. For a 30amp system, will a 30a rather rocker switch work or should a battery cutoff switch be used.

Your best bet is to use a DC circuit breaker. Look at Midnite's selection.

2. Is it better to install the switch on the negative or positive line?

Positive

3. Does it matter if the switch is closer to the controller or panels?

It's more convenient next to the controller. When you connect your controller, turn on the breaker between the battery and the controller to power up the controller, then turn on the breaker from the PV array. If you do it in the wrong order your controller may not work.

4. Should the panels be fused (slightly off topic)?

Depends on how many you have and how they are configured. Need more details to answer this question.

--mapmaker

[Sunking]

If it were me, I would just install a SPST across the input wires which will short out the panels, thus turning them off and allows you to measure Isc.

[KirkB]

Depends on how many you have and how they are configured. Need more details to answer this question.

--mapmaker

2 x 100 watt panels in parallel wired in series to a 200 watt panel. The entire grid has a peak output of around 39v and 11a rounded up.

[KirkB]

If it were me, I would just install a SPST across the input wires which will short out the panels, thus turning them off and allows you to measure Isc.

Didn't realize you could do that without damage to the panels or the controller.

[mapmaker]

Didn't realize you could do that without damage to the panels or the controller.

But make sure you use a DC rated switch. I still think that a DC circuit breaker is your best option... they make excellent switches.

2 x 100 watt panels in parallel wired in series to a 200 watt panel. The entire grid has a peak output of around 39v and 11a rounded up.

Do you know the Vmp of your two panel types? If the 200 watt panel is a GT panel and the others are not, you have a mismatch which is hurting your efficiency.

--mapmaker

[KirkB]

But make sure you use a DC rated switch. I still think that a DC circuit breaker is your best option... they make excellent switches.



Do you know the Vmp of your two panel types? If the 200 watt panel is a GT panel and the others are not, you have a mismatch which is hurting your efficiency.

--mapmaker

Large panel:
VMP 18.2v
IMP 11.27a

Small panels x 2:
VMP 17.4v
IMP 5.75a

Two small panels in parallel should produce a max of 17.4v and 11.5a. Those are then wired in series to the large panel which should result in 35.6v (mis quoted above at 39v) and 11.27a. I'm definitely not getting that. At noon with the sun nicely above my panels (not perfectly aimed but close) and no shadows on the panels, I'm producing around 200 watts.

[Sunking]

Didn't realize you could do that without damage to the panels or the controller.

That is how you test a system to measure Isc.

[mapmaker]

Two small panels in parallel should produce a max of 17.4v and 11.5a. Those are then wired in series to the large panel which should result in 35.6v (mis quoted above at 39v) and 11.27a.

OK, that should work.

I'm definitely not getting that. At noon with the sun nicely above my panels (not perfectly aimed but close) and no shadows on the panels, I'm producing around 200 watts.

Well, that is a separate issue (from the switch question). First of all, that may not be a problem... what is your battery's SOC when you can only produce 200 watts? What is your battery voltage and capacity, and what charge controller are you using?

--mapmaker

[KirkB]

OK, that should work.



Well, that is a separate issue (from the switch question). First of all, that may not be a problem... what is your battery's SOC when you can only produce 200 watts? What is your battery voltage and capacity, and what charge controller are you using?

--mapmaker

The charge controller is a Tracer 30a MPPT. The remote panel is know to give weird SOC feedback. However, a battery meter was generally reporting around 80% charge while I was maxing out around 200w or so. I keep the trailer parked at a storage facility but will test each panel disconnected from the controller next time I get it back to my house. Gotta keep the HOA at bay ... Ugh.

Overall, the system is doing great for me. I'm just pretty confident I'm not maximizing my solar production. I'll report back once I get a chance to test the panels. May run down to the storage facility this weekend mid day to take some readings both disconnected and under load.