Solar Charging Question.
Submitted: Wednesday, Feb 09, 2005 at 16:47
ThreadID:
20281
Views:
3163
Replies:
11
FollowUps:
50
This Thread has been Archived
Member - Jeff M (WA)
Ok, there's been a quite a bit of discussion about batteries, charging and solar latley but I've had an idea and want to know if it's worth bothering with.
SO TO ALL BATTERY EXPERTS:
BACKGROUND
My Auxillary battery (which runs all accessories, internal lights, cooler etc) is an 85amp//hr Wet Cell. It obviously doesn't get a full charge of the vehicle's alternator but get's pretty close.
About once a month or before a trip I give it a good charge with an 8amp 240v charger which seems to bring it voltage up nicley for about a week, then it drops again obviously struggling with the alternators charge.
QUESTION
If I were to permantally install a solar panel on the roof connected via a solar 3 stage regulator, what would be the minimum size panel I would need to fully charge the battery. I'm not interested in trying to charge the battery only via sola, I'm not interested in trying to stop the battery going flat under load.
All I want is the solar to be able to finish the job the alternator has started but can't complete fully. That is give the battery the extra 5% or 10% charge it's not getting from the alternator.
And no I can't afford an 80w pannel.
I was thinking of a 6w or 10w style panel, would it have the guts to charge it?
The car is currently parked outside even at
home so it would get plenty of sunlight.
Reply By: drivesafe - Wednesday, Feb 09, 2005 at 19:01
Wednesday, Feb 09, 2005 at 19:01
Jeff M, if you specifically want to use a solar panel, for what ever reason, a 5 watt panel would be able to charge your battery but the time it would take depends on a number of things. The size of the battery, it’s condition, state of charge when you connect the panel up and so on.
Those little 100ma trickle panels can maintain most batteries so a 5 watt panel, which is about 250 to 300ma max would give you some benefit.
Also, you would not need to put a regulator on such a small output panel, the voltage difference between the battery and the maximum output current of the panel means that the battery would rarely get much over 14 volts, if at all.
Cheers
AnswerID:
97518
Follow Up By: Member - Jeff M (WA) - Wednesday, Feb 09, 2005 at 19:12
Wednesday, Feb 09, 2005 at 19:12
Drivesafe thankyou, however I did provide these details in the origional post. Here they are in point form:
Battery: 85amp/h Wet Cell Deep Cycle
State of Charge: would be probally about 90% (charged from vehicle)
Time to Charge: 1 day or 5-7 hours Sun light.
FollowupID:
356085
Follow Up By: Member - Jeff M (WA) - Wednesday, Feb 09, 2005 at 19:21
Wednesday, Feb 09, 2005 at 19:21
Well at this point it is being driven every day but only for about 15-20 minutes. The deep cycle however is operating off a smart relay so does not take any load when the vehicle is started. All it is operating normally is the interior lights and the car stereo. All the other accessories are normally switched off around town.
FollowupID:
356089
Reply By: drivesafe - Wednesday, Feb 09, 2005 at 20:23
Wednesday, Feb 09, 2005 at 20:23
Hi again Jeff M, the 5 watt panel would probably do the job, taking into account that the battery will probably be near full charge by the time you get back from each of your trips, depending on how long you drive on the return trip.
Because there is such a short time between your long trips, you would probably get a greater benefit from a 10 watt panel because it can obviously put that little more into the battery in the short time available.
Again, I don’t think you would need to fit a regulator for the same reasons I posted earlier. It would still pay you to keep an eye on the battery’s voltage for the first few weeks to make sure the voltage does not rise to high. Again, the voltage difference between the battery and the solar panels output is pretty
well going to guaranty that the output current of the panel is still not going to be able to raise the battery’s voltage to a damaging level.
The 10 watt panel is going to be a bit expensive for what you are using it for but on the other hand, the panel is going to be able to supply top up power for this battery and probably you next 5 or 6 batteries so over all it’s not that expensive.
Cheers and hope this is of some help.
And if anybody has any legitimate cirisisim please jump in.
We can all learn more then.
AnswerID:
97532
Follow Up By: drivesafe - Wednesday, Feb 09, 2005 at 21:04
Wednesday, Feb 09, 2005 at 21:04
I’m surprised, dave actually had some helpful info.
I forgot to mention, with caravans, boats and the likes, fitted with a solar panels usually have to fit a switch to isolate the solar panel while the motor is running.
A cheap, quick and simple way to avoid the switch and automate isolating the solar panel is to fit a small SPDT relay that is powered by the ignition circuit of your vehicle.
Because of the small amount of current it will be handling, you don’t need an automotive type relay, just a small relay from Dick Smiths or Jaycar and should only cost a couple of dollars.
Cheers.
FollowupID:
356105
Reply By: drivesafe - Wednesday, Feb 09, 2005 at 22:30
Wednesday, Feb 09, 2005 at 22:30
Jeff M, one suggestion, why not get a 4 or 5 watt panel and see if it works. If it does great you have saved some money but if you find that it is not enough to achieve what you want just add a second panel.
Doing it this way, if you do have to add another panel, it will cost a little more than just buying a 10 watt panel in the first place but I personally think you will be OK with a 4 or 5 watt panel BUT this is my opinion not a scientific fact so don’t scream at me if it doesn’t work.
Cheers and I AM sure the smaller panel will do the job.
Oh by the way, the reason for isolating the solar panel is to avoid having the panel damaged by voltage spikes. It is not all that common to happen but for the few dollars to guaranty it won’t, I’ll leave it up to you. Also some of the panels are supplied with literature that gives you more of an idea as to how and why to connect the panels up to a powered source.
Thanks Jimbo and yes I was just ignoring him and don’t get yourself kicked off because of the moron. Cheers.
AnswerID:
97572
Reply By: drivesafe - Thursday, Feb 10, 2005 at 14:04
Thursday, Feb 10, 2005 at 14:04
Hi Jeff M, here is a question regarding your original post. Irrespective of what size solar panel you get, as you say, you drive for about 15 to 20 minutes avery day. If this the solar panel manages to charge the second battery up over 14 to 14.2 volts then when your isolator cuts in wouldn’t any additional voltage simply be transferred to the main battery because of battery equalisation. The instant the alternator sensed the higher voltage, it would just back off until the voltage came back down to the required operating level.
This is just a theoretical suggestion and if it is correct then there could be two possible out comes as well.
One, any beneficial boosting of the second battery would be lost when the two batteries equalised.
Two, the flip side is that even if the solar panel was big enough to push up the second battery’s voltage, every time the vehicle was driven, the batteries would equalise and in doing so keep the second battery’s voltage in check and this would mean there is no need for a regulator no matter how big the solar panel is.
One more thing, at the end of each mowing season, I connect my mower battery up to a 100ma solar panel and this has made sure that at the beginning of the next season, after 4 to 7 months of not being used, I have a fully charged battery. I’ve done this for the past 5 years and still have the same battery. Your situation is only slightly different in that you are going to be charging a bigger battery in a much shorter time, but I can’t see why it won’t work without fitting a reg.
Just some thoughts, cheers
AnswerID:
97643
Follow Up By: Member - Jeff M (WA) - Thursday, Feb 10, 2005 at 14:34
Thursday, Feb 10, 2005 at 14:34
drivesafe, that and extremly valid point! Hmmm, the
redarc voltage sensing relay would probally have solved that, then the deep cycle would not cut in unless it needed somthing from the alternator. I might still try it as the starter is a 17 plate jobby and doesn't seem to take too long to "recover" from the start, I spose it'll make sure the both batteries are topped up. Might need the bigger pannel. I had a look around I can get those good "blue" coloured 10 year warrant 12w pannels for about $140 locally. Might go that way...
FollowupID:
356218
Follow Up By: drivesafe - Thursday, Feb 10, 2005 at 14:38
Thursday, Feb 10, 2005 at 14:38
Jeff M, Keep us all informed, be interesting to see how you go and what the results are.
Cheers
FollowupID:
356219
Follow Up By: Member - Jeff M (WA) - Thursday, Feb 10, 2005 at 14:49
Thursday, Feb 10, 2005 at 14:49
No worries, you know me, I'll go to the "nth" degree with my experiments! LOL My missus just shakes her head when I'm continually out the garage with my stopwatch and thermotres, pressure guages, volt metres, etc etc.
Oh well, you gotta have somthing to keep your mind occupied!
FollowupID:
356220