diy solar

diy solar

What voltage and current to use selecting charge controller

coarsegoldkid

New Member
Joined
Nov 18, 2019
Messages
7
Will I enjoy your videos and now have your book as reference but all my questions are not answered.
Everyone bare with me please. It's likely very simple but I'm confused after looking at several vendors methodology in selecting a charge controller. Some vendors use a working voltage which must be a computed figure given the specs below. As an exercise I selected the specs on a Solar panel.

Rated Power: 340W
Open circuit voltage (VOC): 51.3 V
Max power voltage (VMP): 42.5 V
Short circuit current (ISC): 8.00 A
Max power current: 8.52 A
Maximum system voltage: 1500V UL and IEC
Power Tolerance: +5/-0 %
Fuse Rating: 15 A

Would I be correct in calling them 42.5v(max power voltage ) @ 8a(short circuit current) panels=340w in various configurations and use those figures in selecting a charge controller? But then there is that Power Tolerance of +5/-0% to contend with. What do I do with that? Power is watts. Which come to +/- 17watts. Plugging in those numbers would change the outcome. However, I've seen calculators that use the Max open circuit voltage to calculate total voltage.

What is the best method?
Some vendors apply a safety factor of 25%. And some a temperature coefficient? Not shown in specs.

thanks in advance
 
the best method is to use the given number and at the end keep a margin of 20%.
 
wow 51 volts from a 340 panel.

Not simply put: The charge controller (SCC) rules the roost simply.
- Panels set in Series increases voltage on the string.
- Panels set in Parallel increase the amperage delivered.
- Panel Strings "should" all go to a Combiner with each string going through a 15A breaker, then combined together for delivery to the SCC.
- Mounted Panels, Frames & Rails should be grounded @ the mounting location. (THIS is NOT the negative lead, it's the framework and metal)
- At the SCC side of the business, a Breaker capable of handling the "Combined Max Amperage" should preceed the SCC to protect it and the remain components.
- LIGHTNING Protection should be installed to protect gear at that point as well. it's fugly if you get hit !

Now SCC's and how to wire panels for them. They all give you two important numbers to meet & NOT exceed.
1) is the Max Voltage they can take from the solar panels at optimum delivery.
2) is the Max Amperage they can handle at optimal delivery.
Many SCC makers offer a software tool to work the numbers to maximize the configuration & setup of the panels. I use a Midnite Classic 200 (see links in signature) and Midnite offers a tool to work out the solar panel arrangement allowing you to play with different configurations. Classic Sizing Tool here to show you one such example. NB: Midnite is one of the very few that does HyperVOC which can be juggled with when over-panelling (do not do unless you REALLY know what your doing, lest the magic smoke appear in vast quatiities).
- Some SCC's (Like Midnite) allow you to "Daisy Chain" multiple SCC's together with inter-scc networking, so they work together and can be managed by one software, this also allows for staged increases in capacity as you expand later (if you have to).

NB, many of the Value Imports do not have such tools and terrible docs when it comes down to it. Midnite, Victron, Outback, Tristar and many others (1st & 2nd Tier products) are much better and generally have such software to figure things out.
** BEWARE: Not all SCC's support LFP or Lithium Ion directly so you need configurability & ability to program the SCC... This also applies to many inverters as well.

Hope that helps,
Steve
 
wow 51 volts from a 340 panel.

Not simply put: The charge controller (SCC) rules the roost simply.
- Panels set in Series increases voltage on the string.
- Panels set in Parallel increase the amperage delivered.
- Panel Strings "should" all go to a Combiner with each string going through a 15A breaker, then combined together for delivery to the SCC.
- Mounted Panels, Frames & Rails should be grounded @ the mounting location. (THIS is NOT the negative lead, it's the framework and metal)
- At the SCC side of the business, a Breaker capable of handling the "Combined Max Amperage" should preceed the SCC to protect it and the remain components.
- LIGHTNING Protection should be installed to protect gear at that point as well. it's fugly if you get hit !

Now SCC's and how to wire panels for them. They all give you two important numbers to meet & NOT exceed.
1) is the Max Voltage they can take from the solar panels at optimum delivery.
2) is the Max Amperage they can handle at optimal delivery.
Many SCC makers offer a software tool to work the numbers to maximize the configuration & setup of the panels. I use a Midnite Classic 200 (see links in signature) and Midnite offers a tool to work out the solar panel arrangement allowing you to play with different configurations. Classic Sizing Tool here to show you one such example. NB: Midnite is one of the very few that does HyperVOC which can be juggled with when over-panelling (do not do unless you REALLY know what your doing, lest the magic smoke appear in vast quatiities).
- Some SCC's (Like Midnite) allow you to "Daisy Chain" multiple SCC's together with inter-scc networking, so they work together and can be managed by one software, this also allows for staged increases in capacity as you expand later (if you have to).

NB, many of the Value Imports do not have such tools and terrible docs when it comes down to it. Midnite, Victron, Outback, Tristar and many others (1st & 2nd Tier products) are much better and generally have such software to figure things out.
** BEWARE: Not all SCC's support LFP or Lithium Ion directly so you need configurability & ability to program the SCC... This also applies to many inverters as well.

Hope that helps,
Steve
Those are 83 cell panels. I have some.
 
you always take the most conservative one.
here it is the max power.
then you substract or add the 20% as needed.
for example if the question is how many power can i use, you take the calculated one minus 20%
if the question is how much amps my cable should support, you take the calculated value +20%
 
Victron says VOC x 1.25 for calculating their controller sizes. Exceeding input current limit doesn't matter (they self-limit input current) but exceeding maximum input voltage kills their SCCs (well, more specifically, the voltage sensor inside the SCC), thus their conservatism in sizing their SCCs by voltage. Generally speaking, here in the shop we start by taking total panel wattage and dividing it by battery float voltage to establish ideal-condition charging amps; that gets us into the controller size range; then we factor in VOC of panels and sometimes need to size up, but rarely.

So, for your use example of one panel (and assuming a 12v nominal battery bank): 340/13.5=25.18A potentially being sent to your battery from the SCC under ideal conditions (top of a mountain on the equator at high noon on a clear day). Based on that single panel, I would recommend a 100/30 (100vDC input from PV, 30A charge capacity to battery) if you wanted to make absolutely certain that you captured every last mA of potential harvest from that panel... but I'd also mention that you'd likely never actually see that 25.18A because we're never in ideal conditions, and I'd mention that you could go with a 100/20 and sure, you'd occasionally clip an A or two but if you're budget-conscious and not overly power-hungry, the 100/20 would work for that one panel.

Now, if you had 2 panels wired in series, you'd have 102.6VOC and so you couldn't use a 100/anything because you'd be over the input voltage limit... so your next stop would be a 150/xx.

That's Victron, though... and as much as I love Victron, I kinda prefer MidNite Solar's Classic line because 1: I'm a sucker for the aesthetics, and 2: they have a cushion built in to their V input ratings that I really wish Victron had. This covers the times that the actual panel V goes over its VOC rating because of low temperatures, and man it's a nice feature... I forget what they call it, but it's super cool. Victron doesn't have that, thus their recommendation to take VOC and multiply by 1.25 safety margin... because if you're riding the edge of the V input limit on a Victron and you get a cold snap and go over it -even briefly- there's a good chance you've fried your controller :(
 
Back
Top