Next help with a backup trickle charge

davecla
davecla Registered Users Posts: 8 ✭
in Solar Beginners Corner #1
Last year I built a new chook house about 50m from my house.

I wanted to experiment using solar power, so I added a couple of LED lights (one inside and one out) and a 12v linear actuator to drive the chicken "pop" door up and down. This is powered off a 10W panel, regulator and an old car battery.

In the summer, this all works well, but over winter the sun skirts around a bit lower and the panel doest get enough sun to keep the battery topped off. Every 3-4 weeks, I need to give the battery a boost on a mains charger. There is no option to move the panel to a position with better sun without a long run of cable and dropping a bunch of trees.

I've been thinking about running a bit of data cable down to the house, mostly so I could operate the pop door remotely - to open and close on rainy days so save walking over.

What I was wondering was is it possible to trickle a charge voltage back over this cable to help out over winter? The cable I was going to use is CAT5 data cable (as i have a box lying around). Small conductors, but I thinking with just a small trickle current it might be ok?

Thoughts?

thanks in advance,

dave
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #2
    Re: Next help with a backup trickle charge

    Any wire (properly fused) can carry power. You should enter the wire data and length into the Voltage Drop caculator, and see what can safely be delivered. I think CAT5 cable is about 24ga solid wire, and won't take much flex at all.
    You should be able to put 50-100ma through it, and add a little charge to the battery 24/7
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

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  • BB.
    BB. Super Moderators, Administrators Posts: 33,622 admin
    #3
    Re: Next help with a backup trickle charge

    Call it 24 awg for a maximum of 0.4 to 1.0 amps per wire maximum.

    Using a genetic voltage drop calculator for 165 foot one way run gives for 0.5 amp about a 5.1 volt drop. 1.0 amp would give around 10.2 volt drop.

    You have 3 pairs of wires, so you can parallel more wires for more current/less drop.

    Put 25vdc on house end and a battery charger/regulator next to battery.

    POE (power over internet) uses 48 volts on cat 5 cable.

    Check my math, did this post on my phone.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • davecla
    davecla Registered Users Posts: 8 ✭
    #4
    Re: Next help with a backup trickle charge

    So using 100mA as a starting figure..

    I'm guessing I'd need to add a resister in line to stop too much current flowing. R = 12 / 0.1 so 120 ohms?

    I'd add this power in feed into the same connectors as a solar panel on the charging regulator?

    Would 100mA 24/7 make a difference? My basic math show's the 10W panel (best case) is giving (W = V x I) about 833mA.

    What happens when the battery is full - what does the regulator do, do it simply turn off the input, or shunt the load?

    thanks again,
    dave
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #5
    Re: Next help with a backup trickle charge

    What is your power source going to be ? 14V battery charger ? 5W PV panel ? 18V computer power brick ?
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

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  • davecla
    davecla Registered Users Posts: 8 ✭
    #6
    Re: Next help with a backup trickle charge

    i don't have anything specific in mind, I have a box full of old power bricks, was probably going to use of of those.
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #7
    Re: Next help with a backup trickle charge

    If you feed the input of the charge controller, you will have to be careful not to dump power into the connected PV panel.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

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  • davecla
    davecla Registered Users Posts: 8 ✭
    #8
    Re: Next help with a backup trickle charge

    I hadn't thought that would be a problem, wouldn't that happen if there where two more more panels in parallel anyway (and one was shaded)?

    I could add a diode on the charger leg, but then that adds a small unwanted voltage drop.

    Any other suggestions?
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  • vcallaway
    vcallaway Solar Expert Posts: 157 ✭✭✭✭✭
    #9
    Re: Next help with a backup trickle charge

    Cat5 carries power in small quantities.

    There are network devices designed to power from the line, POE. Typically 48v with a max of 13 watts. At least that is what my hub is rated at. Power is transmitted over one pair of wires. You could in theory carry 4 times that using all 4 pair. Never tried it.

    I ran into a similar issue. I have a xantrex C10 controller hooked up to some cheapie harbor freight panels. Does not keep up in the winter. I wound up disconnecting them in the winter and connecting a wall work transformer to the xantrex. It is 18v dc @ 5A. Allows the xantrex to control the charging. Probably going to leave that setup and dump the panels on craigslist.
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  • davecla
    davecla Registered Users Posts: 8 ✭
    #10
    Re: Need help with a backup trickle charge

    Seems like a pity to dump the panel, but perhaps running a trickle from a wall wart with no panel is the easiest approach.

    I've found a reasonably new power pack from a Dell laptop that gives 19.5v DC @ 3.3 amps, so I might give this a shot.

    I'll run a couple of runs of Cat5 in the trench, so I can double up on the conductors if needed.

    I'm guessing I should add a resister in the circuit to reduce the current to something more suitable for Cat5? The PoE spec looks like is good for at least 350mA on one pair, and that should be plenty for me.
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  • techntrek
    techntrek Solar Expert Posts: 1,372 ✭✭✭
    #11
    Re: Need help with a backup trickle charge

    Are you running the cable inside a conduit? Cat 5 isn't rated for direct burial so it won't last long if you lay it in a trench.
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is
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  • davecla
    davecla Registered Users Posts: 8 ✭
    #12
    Re: Next help with a backup trickle charge

    yep, either in conduit or some tubing.
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