Proposed Solar Wireless Surveillance System

[RogerRetro]

OK, Sunking, I get it now...
Battery charge/discharge characteristics have not included these details in online discussions I had found on solar system design (until I got here!).
Thanks,
Roger

[Logan005]

Also do not count on the LVD in the SuperNight Dc to DC converter as it is as low as 10.5 volts. I would use a seperate LVD and set it no lower than 12volts

[Sunking]

In an Off-Grid system, everything revolves around the batteries and location. Get the batteries and location wrong, and everything else falls apart. Your application is rare with a consistent load around the clock which makes it very simple. Only thing you have to look out for due to your location being better than average, is making sure you provide the batteries with enough charge current. In your case more panel wattage than required to meet the load demands. You had to meet the batteries minimum demand rather than the load maximum demands. That is a good problem to have.

Take a look at the poor SOB's north of you like Portland Oregon and Gloomy Doomy Seattle with winter sun hours lower the 2 Sun Hours. The panel wattage has to be very high to where roughly Panel Wattage will be equal to daily Watt Hours. Example for 1 Kwh requires a 1000 watt panel which produces 80 amps of charge current at 12 volt battery. Well for 1 Kwh of daily power @ 12 volts is a 400 AH battery. Not only do FLA batteries have a minimum charge requirement of C/12, they also have a maximum current they can accept. For FLA batteries is roughly C/8 and on a 400 AH battery is 50 amps. Oops you get 80 amps at 1000 watts which is way too much. So WTF do you do?

You have two options. Make the battery larger, or use AGM. AGM can handle up to roughly C/4 charge current. However AGM batteries cost twice as much as FLA for a given size and last about half as long making them some 400% higher in cost over FLA. So from an economic POV you would use a larger FLA battery and up the size to 80 amps of charge current x 8 Hours = 640 AH rather than 400 AH you originally calculated to handle the higher wattage panels. So where you are at a 1Kwh/day system cost you roughly $2000. For the SOB's up north are looking at $3500. Want to use 400 AH AGM instead of 640 AH FLA the cost goes up to $4000, and you will be replacing AGM batteries ever 2 or 3 years instead of every 5 to 6 years if you used FLA.

[RogerRetro]

Logan005,
I don't understand... Would you please explain LVD (I'm assuming low voltage differential), with respect to supplying 5V to the load (from the controller's load output of 12V)? And how to implement a separate LVD?
Thanks,
Roger

[Sunking]

LVD = Low Voltage Disconnect.

LVD is a circuit to disconnect a load before it over discharges the battery.

[Logan005]

yes LVD Low voltage Disconnect. SuperNight converters will drain your bank down to as low as 10.5 volts, you do not want to go near that low as damage to battery's will occur. You should use an adjustable LVD and set it to 12 volts, this will greatly increase the life span of your cyclical battery. If you allow it to drop to 10.5, your battery will be useless in less than a year. if you allow it to go to 11.5 it might last 2 years. If you want the 5plus years don't let it drop below 12 volts and you will be on the right track. some say 11.5 to 11.9, but batteries are heavy and expensive. Better safe than sorry

[RogerRetro]

OK, I just got confused again... I thought that the controller, through it's connection to the load, managed the battery by controlling discharge rates through it's load output, as well as charge rates through it's battery connections. what am I missing? (boy, I feel dumb!)
Thanks,
Roger

[Logan005]

If you depend on the LVD built into your charge controller, you are taking a chance, they have been also known to allow as low as 10.5 volts and can be just as damaging. If your charge controller has an adjustable LVD, then set it and forget it. If it allows the battery to drain past 11volts, I would get separate LVD or a better charge controller with adjustable LVD. 40, 50 bucks now or new batteries every year or so.

[inetdog]

OK, I just got confused again... I thought that the controller, through it's connection to the load, managed the battery by controlling discharge rates through it's load output, as well as charge rates through it's battery connections. what am I missing? (boy, I feel dumb!)
Thanks,
Roger

OK, just the simple facts:
1. The Load output of most CCs is not intended for an inverter connection or even a large DC load. The inverter and large DC loads will connect (with their own fuses) directly to the battery terminals or bus bars.
2. The Load output of many CCs can be used for controlling night lighting and turning it off before the battery is totally flat (but still damaged cruelly) or operating a relay to open the higher current inverter and DC load circuit(s). For the latter use to make sense the trigger voltage of the Load output needs to be around 12V rather than 10.5V. Some CCs have an adjustable setting, others do not.
3. A threshold voltage of 10.5V is high enough to prevent or minimize reverse charging of the lowest capacity cell in a 12V battery (a truly catastrophic event) but not much more than that.

[RogerRetro]

OK, I don't intend using an inverter with this system. My idea was to use the "Load" output because of the small constant (4.5W) camera load. perhaps that was a bad idea. Yes? No? This Renogy Tracer 20A controller I have specifies the Discharging Limits Voltage as 10.8V. So now I understand that problem. I haven't seen any reference to separate low voltage disconnects in my past browsing... Can you point me towards some examples?
Thanks,
Roger

[Logan005]

There are many LVD's out there. My "Charge Ahead" by Battery mart was about $45. since this system will only run 4.5 watts it will work perfectly as is over rated rated for 15a but you may find something less duty for a better price. several Chinese company's make Din and rail mounts for much less..

[RogerRetro]

OK, I just didn't know what to look for... I'll shop around.
Thanks,
Roger

[RogerRetro]

A question about fuses and diodes... I asked a Renogy rep if fuses and diodes are necessary for this system using two of their 50W panels and 20A controller, and he claimed that neither is required. However... the Tracer manual indicates fuses for PV input and Battery output. I'd like to get a practical opinion on this.
Thanks,
Roger

[Mike90250]

a fuse between the batteries and controller is advised. Whatever the fuse size you chose, the wire used should exceed the amp capacity of the fuse (so the fuse blows, not the wire)

[RogerRetro]

OK, that's two votes for, and one against. majority wins.
I'll use fuses.
Thanks,
Roger