# if i wish to power a 12V 50 watt LED...

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#1
if i wish to power a 12V 50 watt LED, the amp i need is 50watt/12v = 4.166A (assuming no resistance and power lost to resistance)

if i have a battery of 12V 7.2AH and i use this battery to power that LED , since the voltage rating is equivalent, no boost or buck converter is needed , and my battery will run out of power in less than 2 hours.

Is my calculation and assumption correct?

CoolCavy Please let me know if i post at wrong subforum...
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1 month ago
#2
So the battery capacity in terms of Energy would be amp-hours x voltage
12 x 7.2 = 86.4 Wh

And the light uses energy at an (assumed constant) rate of 50W.

so 86.4 / 50 = 1.7 hours

Of course batteries dont work like this at peak state of charge they discharge higher voltage, have a high drop off, then voltage steadily declines predictably before again rapidly dropping at low state of charge. And of course things like operating temperature (which changes in use) will impact performance directly.
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#3
(Original post by mnot)
So the battery capacity in terms of Energy would be amp-hours x voltage
12 x 7.2 = 86.4 Wh

And the light uses energy at an (assumed constant) rate of 50W.

so 86.4 / 50 = 1.7 hours

Of course batteries dont work like this at peak state of charge they discharge higher voltage, have a high drop off, then voltage steadily declines predictably before again rapidly dropping at low state of charge. And of course things like operating temperature (which changes in use) will impact performance directly.

If you dont mind

g[/s]~0UAAOSw765fs5k8]https://www.ebay.co.uk/itm/304018538543?hash=item46c8eac02f~0UAAOSw765fs5k8

i was checking out specs for solar lights, such as this

Specification:
Power:200W
Solar panel: polysilicon 6V 5W
Battery: lithium iron phosphate battery / 5000mah
LED: 129PCS
Lighting time:6-10H
Lighting range: 45-60 square
Lamp body size: 130*126*30mm
Solar panel size: 220*135*17mm
Extension cable: 5m/196.85"

i havent done the exact calculations but at the first glance, pretty sure no way in hell a 5 AH battery can support a 200W LED for 6-10 hours? What do you think?

I mean a 7AH battery can barely support a 50watt LED for 2 hours... let alone 200w for 6!
Last edited by HucktheForde; 1 month ago
0
1 month ago
#4
(Original post by HucktheForde)

If you dont mind

g[/s]~0UAAOSw765fs5k8]https://www.ebay.co.uk/itm/304018538543?hash=item46c8eac02f~0UAAOSw765fs5k8

i was checking out specs for solar lights, such as this

Specification:
Power:200W
Solar panel: polysilicon 6V 5W
Battery: lithium iron phosphate battery / 5000mah
LED: 129PCS
Lighting time:6-10H
Lighting range: 45-60 square
Lamp body size: 130*126*30mm
Solar panel size: 220*135*17mm
Extension cable: 5m/196.85"

i havent done the exact calculations but at the first glance, pretty sure no way in hell a 5 AH battery can support a 200W LED for 6-10 hours? What do you think?

I mean a 7AH battery can barely support a 50watt LED for 2 hours... let alone 200w for 6!
IDK but it looks like the light has a battery on board that you would assume they would size accordingly, and I assume the Solar panel sort of trickle charges it all day for use in the evening.

I would think they can guarantee a certain number of hours use depending on conditions
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