Is this a good charge controller????

[Harry-O]

What I was trying to say, we are trying to protect the system from over heating through breakers and fuses. If the wires like 8 gauge is 30 amps, use 30 amp breaker to protect the wire in turn protecting the panels, controllers, inverter-converter and batteries. Whatever is inline with the breakers and fuses is protected from overheating.

 

[Harry-O]

I wasn’t making a statement but more like asking if I have it right.

 

[wildbill]

that's a great question.....does somebody have a chart that shows: amps = wire size = fuse/breaker ????????????

 

[B and C]

Here is the one at Blue Seas: https://www.bluesea.com/support/art...oosing_the_Correct_Wire_Size_for_a_DC_Circuit

 

[Awjuhl]

I have this controller it works great and the are complete programmable.
So compatible with any batterys.
I'm running it with 600 watts of solar. Just be mindful it caps out at 40amps. Recomend getting the usb to rs485 cable so you can change settings and such.

Sent from my SM-G965U1 using Tapatalk

 

[wildbill]

I was going with the 50 amp controller

 

[Elbear1]

20 amp Renogy Rover MPPT specs say 236 watt solar input maximum.
This limit is not listed in the specifications on line, it is found in the manual that comes with the unit.

I just want to clear this up. I was sure back when this is posted this was being interpreted wrong. I was right, the wattage max they quote is an assumption of panel voltage to equal amp capacity of controller. Mine says 260w MAX. I just got another 160w panel to bring my system to 390w. My 20A tracer still handles them right up to 20A.

Generally with generator bulk charging im just under 19A. With periodic clouds the system gets very near exactly 20A. So I feel confident a 20A controller is an appropriate size for up to 400w with FLA. Very few times it may loose an amp or 2 if youre not bulk charging or running AGM or lithium that will accept higher charge current.

 

[regis101]

How did you come to the conclusion? Additionally, in the AC electrical world, the 80% system capacity is a thing. My pea brain adheres to that in the DC world as well. I believe an MPPT can act as a buck xfmr at times which is why I'd limit to the 80% thing.
I'm using a Renogy 20a and it has the same specs as you show.

* I just want to clear this up. I was sure back when this is posted this was being interpreted wrong. I was right, the wattage max they quote is an assumption of panel voltage to equal amp capacity of controller. *

 

[Giuseppe Hardblast]

Most charge controllers recommend 10-25% more than the rated input. Definitely epever.

 

[regis101]

Well now my noodles is baking. I found this on the Renogy site. Never thought much about boost current
copy/paste.

*Firstly we can see, as we did before, that his controller can handle 12V or 24V battery banks.

Second, we will be looking at the Rov-40, which is rated for 40 amps of current.

Thirdly we can look at the Max Solar Input Voltage, in this case 100 Volts. This particular MPPT Controller can accept 100 Volts input. It will then take this (up to) 100 Volts and step it down to your 12V or 24V battery.

Let’s take an example of a 400W system in series. You have 4 x 100 Watt panels, each with an open-circuit voltage of 22.5V. Those 4 in series will be 4 x 22.5 V = 90 Volts, which the controller can accept. Now if we ignored boost current, we would see that string only has 5.29 amps, so then if the controller is 40 amps, couldn’t we have (40/5.29 = 7.5) 7 strings, bringing us 2800 Watts? Why does the spec sheet say 520 W maximum? To answer this, we need the boost current.

Boost current can be calculated by taking the system array wattage divided by the battery bank voltage. In the case of 2800 Watts we have 2800 Watts / 12 V = 233 Amps, which would destroy the controller. Realistically we find that 520 Watts / 12V = 43 Amps. We can ignore this result as 12V is a voltage you will probably never see. More accurately you would divide by boost voltage which is more common (you will learn about this in next section), so 520 Watts/14.4V = 36 Amps. We can now see why the boost current is an important part of sizing the controller. *

Here's the link. * https://www.renogy.com/learn-charge-controller-types/ *

 

[Giuseppe Hardblast]

Yea. The boost makes sense. That's probably where the 10-25% comes from.

There probably an easier way to do this

14.4-12= 2.4

I messed up I have to do the math again lol. It made sense before but I

 

[Gypsy Freedom]

Well now my noodles is baking.  I found this on the Renogy site.  Never thought much about boost current
copy/paste.

*Firstly we can see, as we did before, that his controller can handle 12V or 24V battery banks.

Second, we will be looking at the Rov-40, which is rated for 40 amps of current.

Thirdly we can look at the Max Solar Input Voltage, in this case 100 Volts. This particular MPPT Controller can accept 100 Volts input. It will then take this (up to) 100 Volts and step it down to your 12V or 24V battery.

Let’s take an example of a 400W system in series. You have 4 x 100 Watt panels, each with an open-circuit voltage of 22.5V. Those 4 in series will be 4 x 22.5 V = 90 Volts, which the controller can accept. Now if we ignored boost current, we would see that string only has 5.29 amps, so then if the controller is 40 amps, couldn’t we have (40/5.29 = 7.5) 7 strings, bringing us 2800 Watts? Why does the spec sheet say 520 W maximum? To answer this, we need the boost current.

Boost current can be calculated by taking the system array wattage divided by the battery bank voltage. In the case of 2800 Watts we have 2800 Watts / 12 V = 233 Amps, which would destroy the controller. Realistically we find that 520 Watts / 12V = 43 Amps. We can ignore this result as 12V is a voltage you will probably never see. More accurately you would divide by boost voltage which is more common (you will learn about this in next section), so 520 Watts/14.4V = 36 Amps. We can now see why the boost current is an important part of sizing the controller.  *

Here's the link.  * https://www.renogy.com/learn-charge-controller-types/ *

 considering that as a rough number 12 volts on a 12v battery is about 50% charge. seeing 12v can be very common. there are also a lot of people out there that knowingly or unknowingly discharge their batteries much further each night. many inverters wont shut down or warn you till you hit 11.5/11/or even 10.5 volts.

some charge controllers do bad things if you go over the rated current output. yes, as you explained. the current ratting has nothing to do with panel current. it is only concerned with the current output from the controller to the battery(ies). my old BlueSky 2430 did not get damaged if it went over current but it would fault and shut down if it went over current briefly. they it would stay shut down till you reset it. to reset it you had to disconnect solar input and battery and let it sit. sometimes for a day or 2. that sucked, but at least it didnt break. i had this happen running 405 watts of solar panels.

some controllers out there will fry/melt down/let the magic smoke out if you over current them. check your manual.

the controllers i use now for my self and installations i do are the victron mppt controllers and they can handle some over current without shutting down or getting hurt. when the current reaches the ratting the controller just adjusts for a lower power point and just keeps right on trucking. during the winter in the PNW i will double up on panels sometimes and run 2x the rating. but with the low sun and clouds it never gets much over the rating since the panels are not putting out full capacity. i contacted victron and asked how much i could over current the controller with out damage and they really couldnt give me a number. or didnt want to. they said i should not do too much...

but as an example, dont try this at home. i had a customer where we installed 520 watts of panels on a victron 20amp mppt last fall in the PNW with the plan to either add more controller in the spring as the sun got higher and the clouds went away or to disconnect half the panels. well he called me a few weeks ago and wanted to upgrade and add more panels so we talked about what he wanted and what he could aford and we got some panels coming. fast forward a couple weeks and i stop by to check on the delivery and go over the upgrade with him. as i am refreshing my self with his system. i notice he still has all 520watts hooked to the one little 20 amp controller. i logged on to the controller with my bluetooth and saw at 10 am it was maxed out at 20 amps. oops...

just for giggles i switched out my 50 amp victron into his system and by noon we were pulling right around 42 amps and just barely 12 volts. he has 6 golf cart batteries and had recently added a freezer to his set up and was drawing the batteries down well under 12 volts each night. so the big battery bank took a long time charging to get even above 12v.

but that victron 20 handle double over for the whole summer without faltering. i cant guaranty you'd get the same results, but i was impressed.

there is "what you can get away with" and what are good practices.

most of the time getting 80% of the rated output

 

[Gypsy Freedom]

there is "what you can get away with" and then their are "good practices"

most of the time you are lucky to get around 80% of the rated watts out of your panels. but good practice is to use 115% of the rated output when doing the math. just today, sept 16, far from the peak of the solar year. on the coast of southern oregon rained off and on and then cleared up midday to good sun. with flat mounted 435 watt panels i saw a peak watt output of 440 watts. that is just over 100% rated and that is 3 months after the sun was highest in the sky. it doesnt happen every day, but it happens quite abit. one of the thigs that allowed this to happen to day is the rain in the morning did not let the solar start charging slowly as the sun moved up in the sky. useually by the time the sun is nice and high and able to make max power, these batteries are already in absorb so the panel output is reduced anyways. but today no charging happened till the clouds cleared midday and bam, full power available and lower batteries ready to accept it. so that 115% of rated power output for specking a system is pretty realisting on the solar panel output side.

then it is good practice to set your fuses and wire sizes based on rated load X125% as a safety cushion.

can you get away with less, sure. most of the time. when you are doing your own installation, only you can decide if the risk/benefit is worth it. if you are doing or making recommendations to someone else that does not know. to not follow good practices and properly speck out a system leaves you open to lost friendships or financial loss if a problem comes up

 

[Elbear1]

Fantastic convo. But the point is these chinese controllers max wattage input is just a generic estimate based on current limit of unit. If anyone can actually get 20A out of 260w consistently you got some magic panels.

 

[regis101]

I am of the opinion that its not safe practice to exceed the manufacturers recommendations.

It's not the magic from the panels that come into play. It's the magic of the MPPT that is the factor.

It's all good. I'm all good.

 

[Elbear1]

Again its a generic estimate of how many panel watts equal the maximum amperage. Not any kind of technical limit nor anywhere near reality unlike voltage and current maximums.

Over and over and over ad naseum do people post actual real results in various areas and this community ignores it and promulgates reckoning.

 

[Gypsy Freedom]

Fantastic convo. But the point is these chinese controllers max wattage input is just a generic estimate based on current limit of unit. If anyone can actually get 20A out of 260w consistently you got some magic panels.

during the summer with the sun high and clear skies, it is common to see 20 amps out of a 260 watt panel. not continuous for the whole day but it does happen often. especially if the batteries are low, or you are drawing lots of power during the day.

no controller can get more out of a panel than it is capable of producing, Chinese, American or European... a HIGH QUALITY mppt is more likely to wring out more of the available power than so cheap imports, but it is the cheap import controllers that are more likely to fail if you put too many watts of panels on them.

it is not some generic estimate. it is hard n fast specs. you take the rated watts of the panels and divide by the lowest battery volts you may have and that will give you your peak potential amps of current. then to truly protect your system, give that a 115% buffer and design your system for that. if you dont, you are liable to get bit in the butt. it is just like choosing wire size, you dont pick the smallest wire to handle the normal or usual current. NO you size it to be safe when the MAX current is flowing.

there are 2 easy ways to protect the system, spec your controller to handle the max amps you systeam CAN produce. or make sure to buy a controller that will clip any excess input and not be damaged if exposed to too many watts of panels

a third more difficult approach would be to set up a diversion load on the panels BEFORE the controller that would use up extra power before it got to the controller. it is complicated and if you have to ask how to do it, you're not ready.

 

[Gypsy Freedom]

if we go back to the OP's question. is it a good controller and is it good for the panel in question.

in general, that controller and others in the model line have a decent reputation for reliability and performance. it has the availability of a computer connection for monitoring and programing, or a cell phone connection. i am not familiar with the capabilities of that software, but just being available is a benifit. something to check into if you are interested

as for this or other application

first off more info is needed that it is a 300 watt panel. it is not safe to assume that it is a "24v panel" or that "most panels that size will be around 36 volts and most controllers can handle 45 volts" or any other guesstimate.

we need to know the full specs of the panel. speciffically the max open circuit voltage at standard test conditions (STC). max VOC as it is often labeled. when it is cold out and the skies are clear you can easily exceed the max VOC and it is generally recommended to give yourself a buffer.

then you need to compare that max VOC to the max volt ratting of the controller. the one in question is rated 92v at 25c. 25c is close to standard test conditions so i would use that number. there are some sun power brand panels and maybe others in the 300 watt range that will put out over 80v on a regular basis. i dont know if i would feel comfortable with a 92 volt rated controller

the max volts is definitely a spec you dont want to fudge or push. most controllers will be damaged if that is exceeded. once you confirm the volt specs are good. then you can get into figuring the right current rating

the 40 amp version for a 300 watt panel is a little over kill with no real room for expanding. with a 300 watt panel in good sun and batteries down to 11 volts you are looking at around 27 amps. that even gives you a little buffer with a 30 amp version

since you dont want to mix and match different size or ratings of panels on the same controller. there is not enough left over in the amp rating to add a second panel. so buying the 40 on speculation you might expand is not a good investment IMHO

so basically the suggested controller should be a good fit all be it a bit over kill for a 300 watt panel assuming the max voltage spec of the panel is also compatible