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Post by ginjaturtles on Oct 28, 2016 10:02:37 GMT -8
Hello.
I have an existing system on my RV that I've been using for about a year. It has two 100 watt panels (wired parallel for a total of 16amps) going to a Renogy 20amp PWM dual output controller charging 2 battery packs. Due to weather and sun angle issues (they're mounted flat on the roof) I'm rarely making more than 10amps at a time unless it's a full sun day at the height of summer. This is not enough power to offset my usage, and even though i have quote a bit of storage i still find myself running my generator after a couple days of clouds.
My question is: Can i just add a 150w panel in parallel to my existing panels (total 350w/29a peak) and continue to use my 20a charge controller? I realize the peak amps is higher than the rated amps on the controller, but what does that mean? Will it blow fuses? Is there potentially a way i could wire in a switch or something that would automatically disengage one panel if the amps go over a certain level? From my experience so far i don't think the panels would exceed 20amps except on very rare occasions.
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Post by jsb2000 on Oct 28, 2016 14:37:13 GMT -8
My question is: Can i just add a 150w panel in parallel to my existing panels (total 350w/29a peak) and continue to use my 20a charge controller? I realize the peak amps is higher than the rated amps on the controller, but what does that mean? Will it blow fuses? Is there potentially a way i could wire in a switch or something that would automatically disengage one panel if the amps go over a certain level? From my experience so far i don't think the panels would exceed 20amps except on very rare occasions. Proper electrical safety procedures dictate that you NEVER exceed the maximum possible current ratings. Or, to put it plainly: If something CAN produce a certain amount of current, assume that it will, plus an additional safety margin amount. If you source 29 amps through a 20 amp controller, you will (at the very least) put additional stress on it. At worst, you could burn it out, heat the wiring up, cause a fire, and so on. My recommendation is to upgrade to a higher capacity controller (at least 30A, maybe even higher) if you plan to add that 150W panel. Play it safe! |
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Post by ginjaturtles on Oct 28, 2016 18:17:40 GMT -8
I had a feeling that was the case. That power has to go somewhere... Oh well.
Now to come up with a suitable replacement. I'm using the Renogy 20a pwm with dual battery outputs. One side goes to my main pack (2x 135ah flooded deep cycle) and the other charges my backup battery (85ah flooded deep cycle). I don't see that Renogy offers a similar model rated for 30a with dual outputs . Also, would i gain much from upgrading to MPPT here?
I'm also considering adding one or two more batteries. I have a nice space for them between the frame underneath.
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Post by jsb2000 on Oct 30, 2016 10:29:13 GMT -8
I had a feeling that was the case. That power has to go somewhere... Oh well. Now to come up with a suitable replacement. I'm using the Renogy 20a pwm with dual battery outputs. One side goes to my main pack (2x 135ah flooded deep cycle) and the other charges my backup battery (85ah flooded deep cycle). I don't see that Renogy offers a similar model rated for 30a with dual outputs . Also, would i gain much from upgrading to MPPT here? I'm also considering adding one or two more batteries. I have a nice space for them between the frame underneath. Based on my Google searches, it seems that controllers rated higher than 20 amps with dual battery output capability are few and far between. So, given that you are considering adding more batteries in the future, the solution seems obvious (at least to me): Just purchase an additional 30 amp controller and divide the system in two! As to MPPT, personally, I don't think the added efficiency merits the additional cost in smaller systems like yours and mine. |
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Post by vsheetz on Dec 20, 2016 16:30:39 GMT -8
With your panels mounted flat on the RV you will of course never experience full rated output. In my experience a 15-50% reduction from peak power occurs, depending on time of year and latitude. Using the PV Watts software you can also model this. So there is some headroom to oversubscribe a controller from this aspect. Additionally what does the controller do when it gets more than it can handle - some clip the power, some shut down to protect themselves, some are damaged. So the short answer is, it depends... In your case, I think a larger or two controller setup is best. YMMV.
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Post by Tuscany on Feb 25, 2017 19:41:06 GMT -8
How about doing just what you said in the first place: add the 150 watt panel and put a device to cut off the juice if it ever goes over w0 amps. That device is a 12 volt 20 amp circuit breaker. You think it may never reach 20 amps, but if it does then the breaker interrupts the circuit. When the breaker cools off it will reconnect and if the amps have reduced you are back in business making juice. You could even monitor it on a bright sunny day and see if it ever did cause an interruption.This plan allows you to add the 150 watts yet build it a safety net. I am not an expert in this field just suggesting a simple method to protect your controller. You could alternatively use a fuse so you could tell when/if it ever did exceed 20 amps. Best of luck.
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Post by ginjaturtles on Feb 28, 2017 8:44:38 GMT -8
Hi Tuscany. I think i'm going to do just that. I found a 12v 20a circuit breaker with automatic reset on Amazon for $10. If I install that on the line I believe I will will be able to add that third panel safely. I can use my Trimetric meter to monitor when the breaker engages. This will allow me to be sure it's working out to a net positive (it is possible that the time the circuit spends off will outweigh the benefit of a third panel). I'll post back here and let you know how it goes. If renogy ( Admin) is reading this, I am curious as to what their official position is on oversubscribing controllers. What does the controller do when it receives more amps than it is rated for. Also, what happens when the batteries are full and the sun is out? Does power get generated if there is nowhere for it to go? |
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