Use of a PMW to lower voltage from panel to controler

Shadowcatcher · January 2012

Just a thought, there are some high voltage flexible panels available very cheaply on Ebay. For some one equipping a tear drop trailer these would be ideal (conform to the shape). But having to shell out for a MPPT controller off sets the savings. I use a PMW speed controller to control the speed on a 12V bilge blower. Would it be possible to lower the voltage from a panel to the point that you could feed a PMW controller?

Cariboocoot · January 2012

Re: Use of a PMW to lower voltage from panel to controler

PWM controllers don't actually lower Voltage. They switch the connection between panel and battery on/off when battery Voltage reaches the appropriate set point. This switching can occur very slowly or very rapidly and is not necessary 50/50 on off.

Panels are current sources, not Voltage sources. When connected to a load their Voltage drops and their current rises. Depending on what the load is they will reach a Vmp * Imp point which hopefully matches the "ideal" as specified by the manufacturer.

Some DC motors can run directly from panels, their speed varying with the panels' output. If you know the specifications for the motor you can get an idea of how much panel would be needed to run it.

Generally, though, this is why you run devices from batteries and use the panel & controller to recharge same.

BB. · January 2012

Re: Use of a PMW to lower voltage from panel to controler

Just remember that most flexible panels are amorphous type... Meaning that they are about 1/2 as efficient at capturing the sun and turning it into electricity. So, for such a trailer, you would need to cover about 2x the surface area of the roof to capture an equal amount of power.

May not be the best choice.

-Bill

Shadowcatcher · January 2012

Re: Use of a PMW to lower voltage from panel to controler

This is a Unisolar PVL 144 which I found for $67 and my intent is to use it as a supplement to the 185 W monochrystalline solar panel already attached. It is a tear drop trailer with a 6X10 roof and the 185 takes up half of that. A number of places we camp are shaded and to be able to unroll this and stake it out in the sun on an extension cord

Cariboocoot · January 2012

Re: Use of a PMW to lower voltage from panel to controler

Those have unusual specs: Vmp 33, Imp 4.36, Voc 46.2, Isc 5.3
Not very compatible with a 12 Volt system or fan. Roughly speaking you'd get somewhere between 30% and 40% of the rated power.
For battery charging it could be used with the Morningstar MPPT 15 Amp controller.

Shadowcatcher · January 2012

Re: Use of a PMW to lower voltage from panel to controler

I picked up a Steca PRS 3030 for $41 on Ebay which is good up to 47V so for about $145 I have an additional capacity, it will be interesting to see what I can get out of it.

waynefromnscanada · January 2012

Re: Use of a PMW to lower voltage from panel to controler

You'll be pushing that controller right to it's max (voltage wise), and if you live in an area of cold winter temperatures, don't be one bit surprised to see substantially higher OC voltage.
Cariboocoot is right, you'll be far, far ahead with a Morningstar MPPT controller for battery charging. It not only can handle the job, but take all that excess voltage and efficiently and reliably turn it into extra charging amps. He's NOT pulling your leg. Nor am I! We've tried to help and you can learn from our experience, but the final decision, right or wrong, is yours.

Shadowcatcher · January 2012

Re: Use of a PMW to lower voltage from panel to controler

One of my criteria with the teardrop trailer is modularity. Things like the AC unit or Dish network satellite antenna, Espar heater... can be left home if they will not be needed as we have limited space. There is now a 185W solar panel attached to the roof (most of the time) that is because it is a grid tie type panel currently putting out 47 volts and sitting on top of our garage feeding a grid tie inverter (might as well get something out of it off season). Come spring time it will again be attached to the roof of the trailer and will feed a Morningstar MPPT controller.
The idea behind having the Unisolar flexible is that it can be brought along and when we are camping in shaded camp sites (much of the time) it can be staked out in the sun and the battery topped off.
Wayne one of our favorite camp grounds is Agawa Bay, Lake Superior Provincial Park.
The Unisolar panel will be on a 10ga extension cord 10' to 30' long and I am anticipating a voltage drop. I have made up adapters using Anderson Power Pole's that will plug into the extension cords that we normally carry and into the back of the trailer. I used Power Pole's through out the trailer for 12V applications and this includes the solar connections so that if I need to components can be connected in a different configuration i.e. the Unisolar panel could be connected to the MPPT controller.
To give you an idea of what the trailer looks like I am attaching a couple of pictures, pre panel install. With most of the living going on outside the trailer we don't cold camp, though I am working on ideas to add sides to the rear tarp 6' wide at the trailer opening out to 14' at its widest and 14' long.

Attachment not found.

Attachment not found.

Windsun · January 2012

Re: Use of a PMW to lower voltage from panel to controler

Shadowcatcher wrote: »

I picked up a Steca PRS 3030 for $41 on Ebay which is good up to 47V so for about $145 I have an additional capacity, it will be interesting to see what I can get out of it.

The most you will get out of that panel is around 4.4 amps, and the voltage may be too high for the controller. Essentially for a 12 volt system you have about a 50 watt panel.

Use of a PMW to lower voltage from panel to controler

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