drop-off and cable length

[chasfromnorfolk]

I’m reluctant to post this in ‘Solar’ for fear of being jeered at. It’s just another boy’s toy of a system:

I have kept old batteries fully charged and ready for work at the Yurt for many years now, and have 5w and 10w panels.

My ride on mower battery is starting to get feeble and though replacement batteries aren’t all that expensive, I’d like to try solar trickle-charging on that too.

Trouble is the shed it’s stored in is 35/40m from the nearest sunlight.

I have spare 50m extension reel cables. If I put a 13a plug on the panel wires for the reel end and croc clips in place of the plug at the other end of the cable to attach to the batt, will it work? The wires fitted to the panels are generally such thin pathetic things I’m never sure if I need to match them or go for something beefier... something to do with resistance comes into play, I guess.

Cheers in advance for your kindness,

Chas

[nowty]

Not such a stupid question.

Assuming the 50m cable is 1.5mm cross sectional area, most extension leads are around this size. And assuming 5W of power at circa 13V charging voltage, then the current is about 0.3A.

Putting that through a DC volt drop calculator gives about a volt drop of about 0.5V.

So I guess it might work.

What output voltage is the solar panel ?, and do you know the cross sectional area of the extension lead, it might be embossed onto the cable itself.

And do you use a diode in the circuit for your other batteries you trickle charge ?, because the battery might back feed and discharge into the solar panel at night.

[rogeriko]

It will work fine because the solar panel will produce a higher voltage than the battery needs so it will cover the voltage loss.

[ecogeorge]

I have spare 50m extension reel cables.

 If you've got 50m extension leads why not get an electric mower ?      sorry ................................

[chasfromnorfolk]

What output voltage is the solar panel ?, and do you know the cross sectional area of the extension lead, it might be embossed onto the cable itself.

And do you use a diode in the circuit for your other batteries you trickle charge ?, because the battery might back feed and discharge into the solar panel at night.

Thanks All for taking an interest... output voltages seem to be around the 16/17 mark, and the panels do have blocking diodes (though thanks for reminding me it’s important when I buy the new one). The reel I’ll probably use is, on inspection, 45m not 50 - so I s’pose that’s good as it’s a bit shorter, but nothing as useful as 1.5 marked on it, this: ‘Kema-Keur 85 EN50525 HO5VV-F 361.25mm  MASTERPLUG’

It sounds from your responses it’s worth a punt, but for my education, why (economy? planned obsolescence?) do these
small panels get fitted with such vulnerable feeble connecting cables if they can squirt their load down something as reassuringly chunky as a cable reel?

Chas (would love an electric mower, but cordless. Are you listening, Tessla?)

[oliver90owner]

Chas (would love an electric mower, but cordless. Are you listening, Tessla?)

If you really want them to see it, you need to spell the name right.  They might check out alternative spellings, but better for a search engine if it is correct.

Personally, I would not buy an extension lead unless it had 2.5mm^2 conductors.  Nor would I entertain twin core ones! (seen that done on otherwise earthed appliances).

[Nickel2]

...'Chas (would love an electric mower, but cordless. Are you listening, Tessla?)'...

Like the Tesla, I'd like the mower to be voice-operated: "Mower: Cut and strim the front lawn first, then go round the side gate and do the back"

I use this calculator: https://photovoltaic-software.com/solar-tools/dc-ac-drop-voltage-calculator

It is one of many available.

[sam_cat]

...'Chas (would love an electric mower, but cordless. Are you listening, Tessla?)'...

https://www.husqvarna.com/uk/products/robotic-lawn-mowers/

[daveluck_uk]

...'Chas (would love an electric mower, but cordless. Are you listening, Tessla?)'...

https://www.husqvarna.com/uk/products/robotic-lawn-mowers/

I want one!!

[chasfromnorfolk]

Fear not, the cable reel is rated a full 3120w, three-core 13a, thermal cut-out jobby, as chunky as chunky can be. Can’t imagine a chunkier.

Sadly, as far as I can see, the electric mower has yet to be made that would cope a) with the a acreage concerned, b) a terrain shaped by rabbit scrapes and moles c) my relative impecuniosity.

As it is, I attack it with a thing slighly more powerful than my sainted father’s first car and astonishingly affordable. But the batteries are suspect. Or the charging. Either way they need help.

Chas

[chasfromnorfolk]

Well, just to update for anyone thinking of doing something similar, the little 5w panel arrived, and put out a surprising 20v in sunless cloudy weather.
Hooked temporarily to an unrolled 45m extension cable it put out... 20v.

Might be a goer then?

Chas

[Pat_]

Um. Was that with or without a load?

[chasfromnorfolk]

Well now Pat, that was without, and in view of the update I have to bring to you, that’s probably how it’ll stay:

I hooked it up to the twin of the intended mower - one kept in summer months in a paddock, ready for action without too much hopping on and off opening and closing gates - and all seemed well until today.

While wandering past on my way to footle with some bees, I noticed a strong smell of hot plastic. The tiny leads from the panel were hot - I guess because of the strain of pushing ‘trickery down 45m of cable to the battery. Today is the first sunny day since the weekend. I can only relate this to an experience with cheapo jump leads - it’s easy enough to get those hot.

Anyhow, I’ve removed the cable reel link, connected it back directly to the battery and all seems well at the moment.

Chas