sldl
New Member
Posts: 4 
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Post by sldl on Jan 31, 2017 13:33:51 GMT
I have 2 175Watt panels @ 24V each. they are actually making 42v ea. In my mind, which they tell me is twisted beyond repair, 175W divided by 24v= 7.3A x 2 panels = 14.6A.
If I want to charge two 12V batteries in paralell that would make 2 x 14.6 = 28.6A into the batteries. What sized controller do I need? 20A or 40A. I am thinking 30 A is too little fudge factor.
If I want to change the batteries to series 24V does that cut the controller amperage required in half?
Do I need to do the math at 42V instead of 24v. That would require a much bigger controller and prompt me to use only one panel as it would become cost prohibitive.
I have been working with 45 watts so 175 watts would be more than sufficient. I only bought two because they were 50.00 each and only 2 years old. Some rich guy was upgrading. The rich have their uses.
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usernameinvalid
New Member
Even if you're on the right track if you stand still you'll get run over.
Posts: 16
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Post by usernameinvalid on Jan 31, 2017 16:50:10 GMT
I'm still learning this myself so If I'm wrong someone set me straight.
Your panels will only produce 175w @ 42v for a very short period of time at ideal conditions with the sun at the perfect angle.
Most of the time on a clear sunny day they will be at 80% or less. So roughly 140w @ 33.6v. around 4.2 amps each.
There should be a sticker on the back of the panels that has the max watts, volts and amps.
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usernameinvalid
New Member
Even if you're on the right track if you stand still you'll get run over.
Posts: 16
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Post by usernameinvalid on Jan 31, 2017 17:02:05 GMT
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sldl
New Member
Posts: 4
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Post by sldl on Jan 31, 2017 22:08:18 GMT
That makes sense but I am still trying to figure out what size controller I need. In your example, 4.2 being pretty close to my panels at 4.83 Pmax, 140 watts x 2 panels = 280 watts but when that is converted to 12v (280w/12v = 23.3A. Mine actually comes out to 29.2 Amps. So do I need a 10 amp, 20 amp or 30 Amp controller? that is what I am trying to figure out. Is the controller sized by the input from the panels or the input to the batteries.
In my case, by the label, Pmax is 175w, Volts Vmp = 35.5, Imp = 4.95, Open Circuit voltage is 44.2 so 175/35.5=4.93. When converted to 12V will this triple 35.5/12= 2.95 x 4.93 = 8.875A x 2 panels = 17.75 total max amps. So if that is valid I need either 2 10A controllers or 1 20 A controller.
I don't mind over kill but i would rather buy 2 small controllers and run 2 banks of batteries than 1 large controller and still have only 2 batteries and swap them periodically if the controllers could be had for less than a 30 or 40 amp costs. MPPT controllers are expensive.
By the same idea, if I set up the batteries in series for 24V system can I use a pwm controller with a dc-dc (24-12) inverter without losing much over the MPPT 12v system without the inverter. In that case what size inverter do I need.
It gets even more confusing. The controller will not charge at 12v. It will charge at around 13.7 (guess). so that 17.75 really will be 12/13.7 x 17.75 = 15.5 for both or 7.75 each.
Does my math make sense?
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Post by dennis461 on Feb 1, 2017 1:08:56 GMT
Since you asked, yes your math is wrong.
"...by the label, Pmax is 175w, Volts Vmp = 35.5, Imp = 4.95,....."
No need for math, one panel will put put around 5 amps, two panels connected in parallel will put out around 10 amps.
Get a single 10 amp controller unless you plan to expand later.
Are you going to go with 12 volt system or 24 volt DC?
Your panels are more suited to 24VDC IMHO.
There are some controllers which are dual voltage and 20 amp rated.
Dual voltage means you connect the 12V or 24V battery up first.
The controller then decides how much voltage to supply during charging.
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sldl
New Member
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Post by sldl on Feb 1, 2017 2:51:35 GMT
Wow. Two nasty responses in 1 night. You must be exhausted. Sure can tell you're from NJ. I have been part of this group since 2009 on and off from when Renewable Ray ran it as the HF site. Never once had an response like yours. Let alone 2. I thought I was glad to have found this one with some of the old people. Don't respond I won't be coming back to check it if that's how this site is going to be now. Too bad. people got a lot of good info and some of us had some good laughs.
Really too bad.
As for my other question, that was just that, a separate question from this one which is why I posted it in a different thread.
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Post by dennis461 on Feb 1, 2017 3:07:00 GMT
Did not intend to be nasty, sorry you took it that way.
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Post by tytower on Feb 2, 2017 8:56:30 GMT
Wow. Two nasty responses in 1 night. You must be exhausted. Sure can tell you're from NJ. I have been part of this group since 2009 on and off from when Renewable Ray ran it as the HF site. Never once had an response like yours. Let alone 2. I thought I was glad to have found this one with some of the old people. Don't respond I won't be coming back to check it if that's how this site is going to be now. Too bad. people got a lot of good info and some of us had some good laughs. Really too bad. As for my other question, that was just that, a separate question from this one which is why I posted it in a different thread. Gee ,bit touchy. I can't see what the fuss is about . Don't Go ,I cant see anything nasty . Criticism is healthy and I for one relish it because if the criticiser is right I have learnt and if he is wrong I have reinforced my correct view |
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Dave Simmo
Junior Member
Recovering from Surgery. Shoulders had to be rebuilt. End Stage joint damage
Posts: 76
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Post by Dave Simmo on Feb 2, 2017 14:05:43 GMT
Hi
I hope everyone has a great day.
Go for a 30 amp controller they are on Amazon for the same price as a 10 amp CC. You will expand.
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Post by Admin on Feb 2, 2017 14:45:39 GMT
@ SLDL ....I have re read numerous times. I don't see anything nasty...accept your comment about what state someone is from. Please enlighten us, please.
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Post by Admin on Feb 2, 2017 14:46:48 GMT
Did not intend to be nasty, sorry you took it that way. I didn't see it either Dennis...Thanks for your response! |
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Johann
Junior Member
Posts: 56
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Post by Johann on Feb 4, 2017 4:23:52 GMT
Wow. Two nasty responses in 1 night. You must be exhausted. Sure can tell you're from NJ. I have been part of this group since 2009 on and off from when Renewable Ray ran it as the HF site. Never once had an response like yours. Let alone 2. I thought I was glad to have found this one with some of the old people. Don't respond I won't be coming back to check it if that's how this site is going to be now. Too bad. people got a lot of good info and some of us had some good laughs. Really too bad. As for my other question, that was just that, a separate question from this one which is why I posted it in a different thread. That is exactly why I deleted all my comments and pictures etc etc. I do not come here to have a rat race and I do not need one. I offered my knowledge, but apparently some do not appreciate nor want real true and save knowledge and the same ones are misguiding others just to make them look good. I am like you, this forum is not like the old one. Don't expect me to give any more input. Johann....... |
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Post by tytower on Apr 16, 2017 22:33:22 GMT
That is exactly why I deleted all my comments and pictures etc etc. I do not come here to have a rat race and I do not need one. I offered my knowledge, but apparently some do not appreciate nor want real true and save knowledge and the same ones are misguiding others just to make them look good. I am like you, this forum is not like the old one. Don't expect me to give any more input. Johann....... Hmm What this guy did was go to another forum and then start rubbishing me ? So I think he needs some adjustment to his attitude anyway. I'm taking my bat and ball and going home approach. |
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