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diy solar

Small electronics project – Complete newbie

Tundrawalker

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Mar 31, 2021
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Greetings everyone,

I have finally dug into learning about solar to recharge a 12v lead acid battery to power a DSLR camera for remote long term construction time-lapse photography.

Here is what I have:

- Canon DSLR which uses up to a 8.4v 2.1a LiPo battery which can run on for up to 5 hours
- a USB 5v 2a/4a dummy battery. It requires 2a (10w) to function
- a 12v to 5v DC converter which outputs 5v/3a to dual USB female sockets to power the dummy battery and 1 additional USB powered low draw device
- a 40w solar cell with an 8.5a charge controller.
- a 12v 7ah lead acid battery

Hooking the DC converter directly to a 12v 7a battery works just fine. Now I want to recharge the 12v battery with solar so that I don’t have to check on it as often to replace with a freshly charged battery.

My issues stem from proper wire gauge. I believe the wire gauge I need is between 18 and 16 awg. I previously melted wires that I believe were 22awg connected from the battery to various electronics during tests while the battery was hooked up to the 40w solar cell.

Looking at why my 22awg wire melted seems to be that it can only handle 0.92a

The 40w solar cell is pushing I believe 2a of power to the battery. (40w/20v)

I believe I need to go with 18awg @ 2.3a or even 16awg @ 3.7a wire. This is my main concern/question.

If the electronics down the line only require 1ah of power do I need to somehow scale down the load from 2a to 1a so that nothing gets fired? The pushing vs drawing of power in this scenario is confusing which is why I expect the proper gauge of wire is so important.

So now the math...

A 12v 7Ah lead acid I believe should yield roughly between 84w to 95w (13.6w x 7a)

Will that mean only about 42w of effective power due to the 50% rule?

Does the same rule apply to the 8.4v 2.1a LiPo camera battery which mathematically yields 17.64w? Does that means it only provides about 8.5w (50%) of energy before it needs to recharge? If this is the case then my 12v battery has approx. 45w of potential power, will it have roughly 5x more energy than the internal battery?

The DC converter I believe, provides 15w of power (5v x 3a) therefore it needs at least a 12v 1.25a supply.

In terms of longevity the 8.4v 2.1a LiPo camera battery with 17.64w will run for about 45 minutes of constant use recording video. Shooting time-lapse stills at 12 pics/minute I can get 5hrs and 3500 pics. Looking at just the time-lapse scenario can I expect the lead acid to give me potentially 25 hrs of performance? (5hrs x 5)

Finally the solar recharging equation. It seems to me that the 40w solar cell will recharge the 12v 7a 96w battery in 2-3 hrs. But at 25 hrs of expected performance it will take a few days to use up a non constantly recharged battery at 12 hrs a day of actual use in my scenario. Therefore if the sun disappeared I figure I will get 2 days of use from the battery and when the sun reappears it will only require about 2 hours to recharge the battery. Does that make sense? Is it overkill? Should I drop to a 10w solar cell? If so then I assume it will require 8 hours to recharge the battery which should still be fine for my application. Would a 10w solar cell be only pushing 0.5a (10w/20v)? If that is the case then if I switched to the half size 12v 4.5a lead acid could I expect 54w/50%=27w of effective power? That would mean the 10w solar cell will recharge the battery in about 3hrs and I will get maybe about 8 hours of operation without constant recharging.

Thanks for every ones time. Dave
 
Charging at about 12volts, 40watts will be less than 4 amps. 18 gauge will work fine for 4 amps.
 
Thank you DThames. Do I have to worry about circuits down the line from the battery that only require 1amp as long as I using the right wire gauge?
 
Thank you DThames. Do I have to worry about circuits down the line from the battery that only require 1amp as long as I using the right wire gauge?
"...worry" could mean something other than what you are thinking or what I am thinking. Always worry enough to do a proper job.
I normally keep some silicone insulated 22 or 24 gauge for voltage sense type connections, where there is no power to speak of. Then I keep some 20 gauge for amps up to maybe 2 to 5, 18 gauge for amps up to about 7, etc. I avoid cheap automotive type wire that insulation is not great on. Wires should normally not be warm to the touch, but if you have good high temp insulation, warm is not a problem, just a sign you are losing some power in the wiring and maybe you should go to a larger wire gauge. You can find wire charts in the internet. I think I looked at 16ga is good for up to 10amps. Don't be afraid to use 20 gauge if the amps are only 2 or 3.
 
"...worry" could mean something other than what you are thinking or what I am thinking. Always worry enough to do a proper job.
I normally keep some silicone insulated 22 or 24 gauge for voltage sense type connections, where there is no power to speak of. Then I keep some 20 gauge for amps up to maybe 2 to 5, 18 gauge for amps up to about 7, etc. I avoid cheap automotive type wire that insulation is not great on. Wires should normally not be warm to the touch, but if you have good high temp insulation, warm is not a problem, just a sign you are losing some power in the wiring and maybe you should go to a larger wire gauge. You can find wire charts in the internet. I think I looked at 16ga is good for up to 10amps. Don't be afraid to use 20 gauge if the amps are only 2 or 3.
Interesting thoughts. Thank you. Silicone and high temp insulation makes sense. I looked at tons of wire charts already but none that i could find were geared towards smaller use applications like mine. Most were for higher volt/amp applications and distance. my applications are less than 6 feet and 2 to 4 amps at most. if I'm pumping 2-4 amps to my battery from the solar cell do you feel that electronics down the line from the battery that only require 1 or 2 amps will be fine as long as I am using proper awg high temp insulated wire to those components? I'm pretty sure those components are prewired with 18 guage wire.
 
Here is what I have:

- Canon DSLR which uses up to a 8.4v 2.1a LiPo battery which can run on for up to 5 hours
- a USB 5v 2a/4a dummy battery. It requires 2a (10w) to function
- a 12v to 5v DC converter which outputs 5v/3a to dual USB female sockets to power the dummy battery and 1 additional USB powered low draw device

I'm curious about what battery and electrical components you're using if you don't mind saying what they are.

Myself, I'm using a 50Wh V-mount battery to deliver power to the DC port of a Blackmagic Pocket 4K camera. However, lots of people use a Sony L-mount battery plus a dummy battery, with components from, for example, SmallRig.
 
I'm curious about what battery and electrical components you're using if you don't mind saying what they are.

Myself, I'm using a 50Wh V-mount battery to deliver power to the DC port of a Blackmagic Pocket 4K camera. However, lots of people use a Sony L-mount battery plus a dummy battery, with components from, for example, SmallRig.
 
The battery as mentioned above is a 12v 7ah lead acid. I created a page to easily share the images of my NEW setup. CLICK HERE At the bottom of the page is a recently completed job. Shot with inexpensive Canon point and shoots using CHDK, 2 x 4K Lorex Security Cameras, some iphones, and a Panasonic G7, I just put together 3x Canon T2i systems using the Pluto trigger to hopefully resolve some technical hurdles. Solar recharging is my next challenge to overcome. For the point and shoot cameras I was powering with 6v lead acids. Sometimes I'd get 5-7 days of energy from them but more than not the cameras would fail and I'd miss various setups. Not a big deal but I need to develop more dependable systems. The only thing I've used so far that has been dependable is the security cameras with on-line monitoring.
 
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