[pvusers] Mounting PVs on camper & RFI problems

["Robert Warren" <robertwarren@mail.com>]

Bill,
 Your RFI problems are not from your PV array: they produce good clean DC power. The Powerstar inverter is your problem--it is a fairly cheap device. I used to sell them years ago, and stopped selling them because we had such a high failure rate with them. So, next time it fails, invest in an Exeltech sine wave inverter, it is one of the best inverters on the market. I have no financial interest to promote here, these are simply good and reliable inverters.
 But in order to cut out the inverter RFI and EMI (in fact, it is the electromagnetic interference which is the real problem) , what you need to do is to build a Faraday cage around the inverter. To do this, make a box out of a metal screening material. The best material to use would be expanded metal, such as is used for stair steps on metal buildings, but this stuff is expensive. The metal cage should be grounded, so it you ground the box to the frame of your truck, then when you park it overnight, you should have a small grounding rod you can drive in temporarily. But knocking out the EMI isn't done just by earthing the frame of the inverter; it is already outside the inverter. The metal cage can be just 2 inches larger than the inverter or even 6 inches larger, but it must entirely enclose the inverter. You should make it with a little door so you can get to the inverter inside. But the box is best if it is not a solid box. You could make it out of a wire fencing material, but chicken wire it probably too thin. Window screens might work OK, though. If you are using fencing material, criss-cross it to make a better metal grid, and earth the wires. 
 Also, you will need to pass your AC inverter output through a ferrite core, as well. Ever notice the little block on modem plugs? That is a ferrite core. The wire leads make only one loop through the core, but that knocks out RFI.   
 There is no connection between the frame of the PV and the negative inside the PV junction box. You don't need diodes because your controller takes care of switching off the PV at night so your batteries don't drain. As for what you are seeing as peak charging current, that is the best you can do with flat panels. Also, if the batteries are partially full, then they don't accept a full charge. It sounds like you are using 6 x 6 volt golf cart batteries at 12 VDC, so you probably have around 660 A/hrs storage. The C-10 rate is 60 amps, but a C-20 rate is only 30 amps and this will give you a better life on your batteries. The problem is, you may not fully charge your batteries when they get too low and you have cloudy weather. Also, you ought to have an amp hour meter such as the E-meter so you know how much you take out and how much you put back in. You should try to never go below 50% of their capacity, and even better, to keep them most of the time above 80 % of full battery capacity. This may mean reducing your load, like turning off the refrigerator for a few hours at night.   The best thing is to also have a small generator and battery charger as a backup. Then you can keep the batteries happy and have a lot more enjoyment out of your PV system.
--Robert Warren


----- Original Message -----
From: Bill Neill <solarbill2002@yahoo.com>
Date: Sat, 9 Nov 2002 14:32:45 -0800 (PST)
To: Joel Davidson <joeldavidson@earthlink.net>, Ron Byrd <byrdelc@directcon.net>
Subject: [pvusers] Mounting PVs on camper 


> I have written to this list about RFI issues. Here is some more info.
> 
> All five pvs are mounted in aluminum welded frames that are bolted to
> the aluminum metal fabric of the camper. The layout is 2 pvs front, 1
> pv sideways, and 2 pvs rear. All mountings are flat except the 1 which
> is at 20 degrees up, South facing. Here is the layout on the camper
> roof:
> -   -
>   |    ->South
> -   -
> I have no way of tracking the sun and would ask if you all have a feel
> for just how much of an advantage I am missing during October 15 to
> April 15th (during winter months) without tracking.
> 
> Notice that all five pvs are electrically grounded to the aluminum
> fabric of the camper. That is the frame of the pv is aluminum, but the
> electrical box and connections to the pv are in the upper center of the
> back of the pv. I suspect the negative side is in-fact in common with
> the frame of the truck, because the control panel has a charge circuit
> for the truck battery that I do have connected and so ground is
> provided through the truck negative side.
> 
> Is it true that no electrical connection exists between the frame of
> the pv and the pv negative connection on the back?
> 
> I called the factory and they told me not to use the diode in series
> with each pv as it is not required - so I am not using these diodes. Is
> this good or bad?
> 
> My max charge current is 22 Amps (tip top of the bell charge curve)
> lasting only about 30 minutes, then starting down.
> 
> I have some experience with golf cart batteries and know that the 36
> volt or 48 volt units all have 25 Amp range meters on the chargers. It
> is typical for current to be at about 20 Amps for the first hour or so
> and then reducing and finally staying around 10 Amps for several hours
> and finally kicking off at 3 to 5 Amps as a fully charged battery pack.
> 
> Thus my observation is that I have 3 series strings of 2 6 volt
> batteries making a 12 volt system at 3 times the current. Thus,
> applying the knowledge about golf cart charging, 60 Amps is needed for
> about 1 hour or so and dwindling down from there to 5 or so. Clearly I
> never make enough charge to get this battery pack fully charged in a
> day sun cycle in the summer and not even close in the overcast winter.
> 
> Is this close to what you all have experienced and thus the need for a
> gas generator or line power is required in the winter months.
> 
> Bill



What will we do if there is another fuel shortage? 
Did you know that there is a pollution free, completely renewable fuel which you can use right now in your own car? 
Don't replace the engine, replace the fuel. Check out my website on making your own fuel: 
http://running_on_alcohol.tripod.com 
robertwarren@mail.com

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