Question: What size Solar Controller for the Solar Panel?
- Thread starter matthewp
- Start date
G35Vortec454
Adventurer
The 140W panel is rated less than 8A max power current and less than 9A short circuit current, so a 10A controller is safe. Besides, most controllers have over-current protection.
matthewp
Combat Truck Monkey
After reading your post, I went back to the web page for the panel I'm planning to buy, it does specify 8A max output. Thanks for the info. Both you guys helped great showing me what I need to look for!
4x4junkie
Explorer
Exactly what I was going to say if you're looking at standard PWM type controllers.
It changes if you have a MPPT type controller however, in which case what 4RunAmok gave is correct (I would figure it as 140 (W) ÷ 13.2 (V), as that's a more typical voltage on a partially-drained battery during charging, this gives 10.6A into the battery under ideal conditions with a MPPT unit).
matthewp
Combat Truck Monkey
CRAP! Now you have me reading about MPPT vs. PWM controllers! I see the consensus on the internet is that MPPT controllers are better ("Bonjour!" and all that), but I'm not sure if the price difference is worth it!
dwh
Tail-End Charlie
Yes MPPT is better, but the general consensus among solar engineers is that MPPT is generally not worth the extra cost for a solar rig of less than 200w size.
(That is...REAL MPPT is not worth it. $30 dollar Chinese PWMs with an MPPT decal stuck on don't count.)
4x4junkie
Explorer
Well, it's roughly a 20-25% increase in power harvest with a MPPT unit vs a PWM... (or 10A going into your battery vs 8A in your case). A true MPPT controller will add about $100-150 I'm guessing to your system's grand total over using a good-quality PWM unit.
If you have limited space to mount panels (or you're trying to save weight, etc), the MPPT unit is likely worth having (as was the case for maximizing the output from a portable folding setup I have).
If you are hard-mounting the panels and have sufficient space available though, you should be able to get a similar amount of charging capacity using a 170 watt panel (or a pair of 85W ones) on a PWM unit for less total cost than a 140W panel on a MPPT unit.
G35Vortec454
Adventurer
That 20-25% mppt advantage is very difficult, if not impossible to realize, to translate in practical/actual terms because of the timing that the advantage is needed during the multi-stage spectrum of charging. That need presents itself during the bulk stage, which is the shortest charging stage in well-designed solar installations. That advantage can only be realized when peak production and peak battery charging demands are right on time. Otherwise the mppt will revert to pwm. For less than 500W, I would just get a good PWM controller and call it good.
4x4junkie
Explorer
I have measured a little over 12A of charging current on my setup (2×85W panels, each rated 4.87Imp & SunSaver MPPT-15 cont) using a Fluke multimeter. That is easily within the 20-25% advantage window I mentioned over having a PWM unit.
You are correct, the advantage is only realized during Bulk-stage charging, however that is the stage that returns the greatest amount of power into your battery. The quicker you can get your battery charged back up (and into Absorption mode), IMO the better it is for your whole system (especially if you happen to use up a lot of energy during the previous night).
I will say it again, a 170W panel w/PWM controller should work just as well as a 140W panel on a MPPT unit (and is cheaper). The OP's budget and/or space constraints are what will have to dictate which setup is best for his use.
Edit:
Perhaps it should be asked of the OP here before the thread strays too far off into this PWM vs MPPT thing...
What kind of loads are you planning to run with this solar setup? Fridge (size?)? LED lights? Computer? Car stereo most of the day? Other?
Maybe it might be worthwhile to tally up how many watt-hours or amp-hours you think you'll be using (if you haven't already), and figure out exactly how much solar it is you need.
A typical 40-50qt 12V fridge for example is likely to consume about 500-625 watt-hours on a warm day according to measurements I've taken on a couple units (kept out of direct sun). A 140W-capable solar setup should infact be enough for that however it might not leave much reserve for the running of other loads (playing the car stereo for example).
This is if you want to return a full charge to your battery the next day... If you don't plan on being parked for more than a couple days straight, then you can certainly get away with sizing your solar smaller.
You are correct, the advantage is only realized during Bulk-stage charging, however that is the stage that returns the greatest amount of power into your battery. The quicker you can get your battery charged back up (and into Absorption mode), IMO the better it is for your whole system (especially if you happen to use up a lot of energy during the previous night).
I will say it again, a 170W panel w/PWM controller should work just as well as a 140W panel on a MPPT unit (and is cheaper). The OP's budget and/or space constraints are what will have to dictate which setup is best for his use.
Edit:
Perhaps it should be asked of the OP here before the thread strays too far off into this PWM vs MPPT thing...
What kind of loads are you planning to run with this solar setup? Fridge (size?)? LED lights? Computer? Car stereo most of the day? Other?
Maybe it might be worthwhile to tally up how many watt-hours or amp-hours you think you'll be using (if you haven't already), and figure out exactly how much solar it is you need.
A typical 40-50qt 12V fridge for example is likely to consume about 500-625 watt-hours on a warm day according to measurements I've taken on a couple units (kept out of direct sun). A 140W-capable solar setup should infact be enough for that however it might not leave much reserve for the running of other loads (playing the car stereo for example).
This is if you want to return a full charge to your battery the next day... If you don't plan on being parked for more than a couple days straight, then you can certainly get away with sizing your solar smaller.
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G35Vortec454
Adventurer
Yes, that could easily be true. However, that 25% advantage is only realized during THAT short period of time, say one hour, out of the 6 hours of peak production. So maybe 25% divided by 6 = 4.17% advantage?
4x4junkie
Explorer
Certainly it depends on how much load is drawn from the battery during the night how long it'll remain in Bulk charge mode...
After a day & night of playing the car stereo (just the head unit, no sub or amp), running several LED lights for 5 hours, and my fridge, I was generating that 12A almost until 3:00 PM the next day before it finally entered into Absorb mode (this with repositioning the panels a few times during the day to follow the sun). So it'll all depend on how the system is used and it's capacity.
Also, see my edit above if you didn't yet. More info from the OP is best here.
After a day & night of playing the car stereo (just the head unit, no sub or amp), running several LED lights for 5 hours, and my fridge, I was generating that 12A almost until 3:00 PM the next day before it finally entered into Absorb mode (this with repositioning the panels a few times during the day to follow the sun). So it'll all depend on how the system is used and it's capacity.
Also, see my edit above if you didn't yet. More info from the OP is best here.
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