RV panel disconnect?

[calstar]

Two 100watt 12v panels, will this standard auto battery disconnect safely work as a disconnect between the panels and the charger?
I need to install in the negative line, right?
thanks, Brian

[Mike90250]

Conventionally, I would install it in the + line, leaving the - line connected to ground.

are panels wired in series or parallel ?

what model is your charge controller -PWM or MPPT ?

[calstar]

Conventionally, I would install it in the + line, leaving the - line connected to ground.
are panels wired in series or parallel ?
what model is your charge controller -PWM or MPPT ?


Panels are wired parallel, Blue Sky SB3000i mppt charger. This is installed on a truck camper. For some reason I thought the -line was used with a disconnect, why is positive conventionally used? Also is this disconnect adequate for the system(it will be installed inside the camper between the panels and the cc)?

thanks, Brian

[Mike90250]

In a vehicle, the chassis frame is nearly always negative or "Return". Look at your battery and fuse box, all the fuses are on the + cables.


Your bigger problem is that a MPPT charger works by down-converting a high voltage to the battery voltage. 12V panels are only about 20v which does not leave enough overhead for the MPPT circuit to work very well. Read your documentation and make sure your gear is matched and going to work together.

[calstar]

Your bigger problem is that a MPPT charger works by down-converting a high voltage to the battery voltage. 12V panels are only about 20v which does not leave enough overhead for the MPPT circuit to work very well.

This is the system I just purchased(after discussions with the well regarded vendor)so its what I have to work with. Does this mean the MPPT will not work as well as a PWM in this instance, or that the MPPT is not functioning at its full potential?

thanks for the input,

Brian

[calstar]

Just got off the phone with the vendor(altE), they said wire panels in series to double the voltage going to the 3000i.
Thoughts?

thanks, Brian

[Mike90250]

Yes, if you wire the panels in series, then the MPPT will work fine. Any tiny bit of shade on either panel, will likely shut down all charging. Gotta park in full sun

[zamboni]

Mike, I'm a little surprised by your last comment. I have intentionally shaded one panel in a 2s string and it did not shut down "all charging". Yes, all charging from the shaded panel, definitely -- but the unshaded panel was still outputting fine (minus a small drop in voltage which i presume was the bias of the shaded panel's diodes). Is there more to the story that i'm overlooking? My panels are 24V whereas calstar is talking about series-stacking 12V panels...is that the difference?

I'm not saying this to be a jerk; it's just that i see so many people spun around by the series/parallel shading issue, and have watched people turn away from an otherwise really good MPPT configuration because they were freaking out about the risk of getting a possible shadow a few times a year. The benefits of MPPT in low light, overcast, and limited space on an RV roof seem to far outweigh the lower shaded performance that comes from putting panels in series.

- Jerud
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1220W array / 1000Ah LFP house bank
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www.livesmallridefree.com

[Mike90250]

Mike, I'm a little surprised by your last comment. I have intentionally shaded one panel in a 2s string and it did not shut down "all charging". Yes, all charging from the shaded panel, definitely -- but the unshaded panel was still outputting fine (minus a small drop in voltage which i presume was the bias of the shaded panel's diodes). Is there more to the story that i'm overlooking? My panels are 24V whereas calstar is talking about series-stacking 12V panels...is that the difference? .......

Generally, if you have the reserve voltage to keep the MPPT functioning, you can keep charging. With only 2 series panels, unless they are higher voltage (36V) it's quite possible to lower the voltage to where the MPPT stops (if a user had 2, 100w panels in series) Loose one, and you are in the 19-26V panel range. Will the MPPT work in that range, gotta read the manual.

What are your panels specs for the 2S you used for the test ?

[zamboni]

Okay, i take your point about string voltage dropping too low. My panels are "24V" and my CC wants "at least 130% of high battery voltage" on a 12V system, so that's why I saw no issue. With ~18V max 12V panels I see what you're saying about not meeting the minimum input to the MPPT.

- Jerud