Some solar panel charger questions

[WagoneerSX4]

I've been reading up on them for a few days now since I'm thinking about investing in a 40watt panel to charge my car battery on camping trips. Basically I just want to be able to run my aux lights at night with the engine off and not have to worry about not being to start the car whenever we start off in the morning (of course if there's enough usable light in the morning while we're having breakfast/packing up the campsite). I realize it won't fully charge in this time period, but I'm not planning on completely depleting the battery at night. Though I would like to be able to run my 12v cooler constantly day and night.

So my first question, can you hook up a panel to charge your battery while there's load on the battery? During the day, it will just be my cooler, that's it. I'm going to assume that any load on the battery will probably be more than what the panel can produce so overcharging will never occur? The panel would charge at 3.3amps, in clear sunlight (40w panel). Is a solar charger regulator absolutely needed or is that just basically for keeping battery topped off for long periods of time?

Speaking of overcharging, these new panels run at 42-44V so that they can work in low-light conditions, so in a normal day of full sunlight, can they overcharge a battery to the point of damaging it or will that take days and days of trickle charging? My math says no, but I'm still curious. Do I need a 40w panel for my needs, or will a much more compact 18w panel be enough?

And lastly, are they worth it to lug around every camping trip and do they work well enough? Space is always an issue with my rig, so if it's not actually worth bringing along, I'm not going to bring it. Is bringing along an emergency booster pack just a more fail-safe alternative to a solar panel charger?

I'm sure I know the answers to these questions already, I'm just getting confused by trying to weed out all the bad info floating around out there about solar panels.

 

[WagoneerSX4]

Out of all the searching on this site I missed the sticky thread...

Nevermind guys, I think I found my answers.

 

[JIMBO]

:sombrero: Yeah, there's a lotta info out there-

I've used my 60w panel for over 5 years and it's been/w coolers/ vehicle/ batteries/lights/ on 24/7, I use a 7amp controller that was supplied /w the panel and -

With any panel, the only time you will get fuul output, is between 10am and 2 afternoon and the pane has to be full exposured-

Mine puts out 23vdc during those hours and about 14v at the charging end--because of line ineffeciency--close to 3 amps

Early morning--nope, late afternoon-nope any shadows nope-

They're great, but require some position maintenance-

Good luck

:costumed-smiley-007:wings: JIMBO

 

[chris snell]

I. Basically I just want to be able to run my aux lights at night with the engine off and not have to worry about not being to start the car whenever we start off in the morning (of course if there's enough usable light in the morning while we're having breakfast/packing up the campsite).

I think that you're misunderstanding the function of the solar panel. It's not going to help your situation. Since you're running your lights at night, you need a solution that will leave you with enough battery to start your vehicle the next day. That's a function of battery capacity, not battery charging. What you need is a big deep-cycle battery or potentially two batteries. I'm not a fan of dual batteries because the management systems add another potential point of failure, but if you're going to to really run the battery down, a dual-battery setup may be the ticket.

Once you vehicle starts during the day, the alternator will charge your batteries back up.

 

[Arclight]

I have one of these:

http://www.prioritystart.com/12vpromax.php

It's a low voltage disconnect. It will at least keep your starting battery from running down all the way. Remember, it shortens your battery's life every time you cycle it below 50% or so. The real answer as Chris stated is to either get more capacity or reduce your loads. Have you looked at switching out some stuff for LEDs?


John

I think that you're misunderstanding the function of the solar panel. It's not going to help your situation. Since you're running your lights at night, you need a solution that will leave you with enough battery to start your vehicle the next day. That's a function of battery capacity, not battery charging. What you need is a big deep-cycle battery or potentially two batteries. I'm not a fan of dual batteries because the management systems add another potential point of failure, but if you're going to to really run the battery down, a dual-battery setup may be the ticket.

Once you vehicle starts during the day, the alternator will charge your batteries back up.

 

[WagoneerSX4]

Thanks guys, I've been researching this for a few weeks and I think my only option is basically a dual battery system (http://www.expeditionportal.com/for...ke-a-cheap-isolated-dual-battery-setup-for-50) and said solar panel to keep the 2nd battery charged up during the day. That will at least completely isolate my main battery so I don't have to worry.

My next question, is it safe to put the 2nd battery in my spare tire well in the trunk? My full-size spare will be outside the car so that's empty except for my sub and I'm thinking of taking out my sub enclosure for the 2nd battery. Do I need a sealed battery container to do that? I keep my dogs in the car at night (always with the windows cracked) while we're up in the tent on the roof which is why I'm concerned. That and obviously while we're in the car driving. Can I just use my amplifier wiring that's already run back there? It's 8 gauge, which seems to be the bare minimum, and grounded straight to the body.

I have one of these:

http://www.prioritystart.com/12vpromax.php

It's a low voltage disconnect. It will at least keep your starting battery from running down all the way. Remember, it shortens your battery's life every time you cycle it below 50% or so. The real answer as Chris stated is to either get more capacity or reduce your loads. Have you looked at switching out some stuff for LEDs?

All my lights are LED's. Both my aux campsite lights and aux campsite lights on the car are LED's. But I also plan to run a little 12v tent fan at night on the really humid nights. That and the cooler running 24/7 is probably going to draw quite a bit every night.

 

[chris snell]

Given what you're running, I really dont think you need dual batteries. You should be fine with one good battery. By good, I don't mean Optima. More like Odyssey Batteries PC2150 aka Sears DieHard Platinum Marine PM-1. Those are legit batteries than are more than strong enough to run accessories like fridges with the truck turned off. Much less complexity, too.

 

[WagoneerSX4]

Well I'm also hoping to be able to run my brother's sleep apnea machine when he comes along so we don't have to lug around his own separate 12v battery. Not to mention an air compressor for both the car's tires and bikes.

Think I could get away with a single deep cycle?

 

[chris snell]

Definitely.

 

[WagoneerSX4]

Hmm, as much encouragement as that gives me, I don't think I want to risk it. I guess I could do a trial run in my driveway one night and see how long the battery lasts with everything running. I could also just buy an automatic battery shut-off to make sure the main battery doesn't get down below 50% charge. But that would be about the same money as a dual battery setup as I already have a spare deep cycle battery.

Are there any downsides to a dual battery setup other than the weight (no difference with me as I'm removing my sub for the 2nd battery)? Are they prone to failure? It seems like if you buy quality parts to build it, it would be a "set it and forget it" sort of scenario would it not? Sorry for bringing up a slogan from that horrible commercial...

 

[dwh]

So my first question, can you hook up a panel to charge your battery while there's load on the battery? During the day, it will just be my cooler, that's it. I'm going to assume that any load on the battery will probably be more than what the panel can produce so overcharging will never occur? The panel would charge at 3.3amps, in clear sunlight (40w panel). Is a solar charger regulator absolutely needed or is that just basically for keeping battery topped off for long periods of time?

Most lead-acid batteries are considered fully charged at 14.4v. In order to overcome the battery's internal resistance and be able to "push" current though the battery to charge it, most "12v nominal" solar panels actually put out anywhere from 16v-21v. Since that could potentially push the battery up to too high a voltage, the solar charge controller (a.k.a. regulator) is used to cut off the power from the solar panel and make sure that the battery is not overcharged.

That is the primary purpose of a solar charge controller - to prevent overcharging. But, if you are gonna do that anyway, you might as well add some features to the charge controller in order to get the best charge into the battery in the least time.

A plain ol' solar regulator just connects the solar to the battery when the battery voltage drops to a certain point (generally 11.5v) and disconnects the solar when the battery reaches a certain point (generally 14.4v).

A PWM controller does it by connecting/disconnecting very fast (hundreds of times per second) and can hold the battery voltage in a tighter range, rather than allowing it to rise and fall as much as a regulator does.

An MPPT charge controller is basically a PWM charger, but it uses a voltage converter (sort or the DC equivalent of a transformer) to reduce the voltage from the solar, which has the effect of also increasing the amperage. Sort of like down-shifting to get more torque.


And yes - you CAN supply power to the battery at the same time you draw power from the battery. Of course, if the load is more than the supply, the battery will drain, just not as fast as it would without the charger helping out.

Speaking of overcharging, these new panels run at 42-44V so that they can work in low-light conditions, so in a normal day of full sunlight, can they overcharge a battery to the point of damaging it or will that take days and days of trickle charging? My math says no, but I'm still curious. Do I need a 40w panel for my needs, or will a much more compact 18w panel be enough?

You are laboring under a mis-conception.

All glass solar cells put out around .5 (1/2) volt. They are rigged in series in the solar panel (PV module) in what are called "series strings". The manufacturer sets up their strings to get whatever voltage they want the panel to put out. For instance, for a "12v" panel, they'll commonly rig a string of 36 .5v cells in series to get 18v output, which is just about right for charging a "12v" battery.

72 .5v cells in series will get a 36v output, which is good for charging "24v" systems.

Higher voltage PV modules are generally intended for use with buildings and large "whole house" inverters, and/or grid-tied inverters.

But the cell strings rigged for whatever voltage has absolutely nothing to do with the light gathering ability. Higher voltage panels do not work better in low light conditions just because they are at a higher voltage. Working better in low light conditions depends on how the cells were made - mono-crystalline, poly-crystalline or thin-film.

Using a 40v PV module to charge a 12v battery is horribly inefficient, due to the extreme voltage differential. However, that differential can be exploited, by using an MPPT type solar charge controller, which will "down-convert" the incoming voltage to something more appropriate for charging a 12v battery. This has the secondary effect of increasing the amperage available to "push" through the battery.

watts = volts x amps

If you lower the volts, you increase the amps - but the watts doesn't change.

For example a 30w PV that puts out 30v will be making 1a of current. If you drop the voltage to 15v, then you now have 2a of current from the same 30w PV.