RV System Advice Needed

Glenne

I am planning on installing a solar system in my RV. I have one Kyocera KC 85 watt panel and 2 Siemens M 75 48 watt panels. I am going to use a MPPT 250 controller by BZ. My question, what is the best way to wire the panels? Do I wire the 2 48 watt panels in series, then parallel them with the 85 watt panel or wire all 3 parallel? Any advice will be appreciated.

Thanks,

Glenn

BB.

Re: RV System Advice Needed

The first question is the BZ products controller... If you have not purchased one--or have the ability to return it--you may want to.

BZ Controller discussion



Regarding your solar panels:

KC85T (PDF):

Vmpp=17.4 vdc
Impp=5.04 amps

Siemens M 75 48 (I think this is it):

Vmpp=15.9v
Impp=3.02 amps

You really don't have a great choice here... You should not put the Kyocera and the Siemens panels in series with each other (Vmpp=~48 vdc) because their current is too different.

You could put all three in parallel, but the 15.9 VDC of the Siemens is a bit low for charging your batteries (equalization would require ~15.5v for the battery + 2 volts for controller drop = ~17.5 volts).

The three panels will work OK in parallel, but if you choose an MPPT type controller--the voltage difference between the Kyocera and Siemens may cost you a dozen watts or so (vs "matched" panels).

In the end, assuming you have the solar panels (the Siemens are upwards 10 years old?) and they all work fine (no cracks. wiring/wiring box is clean, good voltage and current when tested in full sun with a DVM and load), and if this is enough wattage for you--I would get standard PCM type charge controller.

An MPPT type controller will not buy you much with these panels and at this low of system power. And, you may be better off just dumping the BZ controller and getting a good Morning Star or similar charge controller.

My 2 cents. If there is something different in your requirements, let us know.

-Bill

SolarJohn

Re: RV System Advice Needed

Glenn,

If you decide to follow Bill's advice and go for matched panels, I would be interested in the Kyocera 85-watt panel you already have. I have 5 of them on my roof, and I add a panel whenever my budget allows me to. Let me know.

John

Solar Guppy

Re: RV System Advice Needed

Don't buy a BZ, they don't work properly.

Concider either a BlueSky or the New MorningStar Mppt units for this power range

Glenne

Re: RV System Advice Needed

Thanks to all for the reply. I guess I am pretty much SOL on this. I wish I had known about this forum before I bought all of this stuff. I though I was getting a good deal. John, I guess I better keep the Kyocera 85-watt panel as it apparently the best part of this system. Anyone want a good deal on a BZ controller?

Thanks again for the info,

Glenn

Glenne

Re: RV System Advice Needed

Hello again,

Ok, I am going to install the panels with the BZ controller. I know now that I probably should not have bought the BZ, but I did and cannot return it. So I guess I am stuck with it. I am going to go ahead and install the panels that I have in parallel, since that is apparently the only option I have with what I have. Does it matter which order I have them? Should the 2 Siemens panels be first and then the Kyocera? Or does it matter?

Thanks again,

Glenn

BB.

Re: RV System Advice Needed

Assuming that you are running a 12 volt battery system, wire all three panels in parallel... Does not matter "which is first"...

And watch the BZ controller--as long as it gives you reasonable charging current and the battery voltage is OK--just use it.

If it fails, then you will have to look through all of this again anyway...

-Bill

niel

Re: RV System Advice Needed

consider getting another controller anyway to outright replace the bz (replacement recommended). you could hang onto that bz as a backup, but you probably couldn't give one of them away here let alone get $ for it. sorry for your loss, but you are welcome to try to get rid of it here if you can.

Glenne

Re: RV System Advice Needed

Once again thank you for the information. I still wish I had found the forum before buying all the stuff. I guess that you have me convinced to go ahead and get another controller. What about the Morningstar brand? I have seen them mentioned here a few times and they seem to get a good review. Does anyone have a good deal one?

Thanks again,

Glenn

niel

Re: RV System Advice Needed

they are fine to use and there are also others available that would suit. our host sells many, but personnally i don't like the shunt style that stecca has.
http://store.solar-electric.com/chco.html

Solar Guppy

Re: RV System Advice Needed

For your three panels I would suggest you get the MorningStar Sunsaver Mppt

Wire the two 48watt panels in parrallel and then put that in series with the 85watt kyocera.

This will really helps as in a RV the panels get extermly hot being flush mounted to a metal roof. Heat decreases the voltage out of the panels ( to the point you can't even get a charge voltage to perform Bulk mode charging.

With the Series configuration the Mppt unit will down-convert the voltage into current and will allow a much better harvest and charging of the batterys

Now some might point out that the two 48 watt panels current is a bit more than the single 85 watt panel, the reality is the vmp point is pretty wide and the 48 watt panels will just operate at a slightly higher Voltage to match the lower current of the 85 watt panel, actual losses as compare to perfect panel matching is very minor.