DIY help for 18650 battery pack for video light (lower output to 12v)

bp_968

Newly Enlightened
Joined
Dec 29, 2005
Messages
48
Id like to build a battery pack for a 12v 50w video light using protected 18650 cells since they have gotten so cheap (3.50$ each on DX). I found a 4 cell pack (2S2P so I think its running 7.4v, 4800mAh with 2400mAh cells).



http://mike.baikov.ru/18650/



What I'm having trouble finding is something I can put between the pack and the light that will lower the voltage from 14.8 (over 16v when fully charged) to 12v for the light. The cells individual protection circuits should protect them from being over discharged by the light, and roughly 5Ah should work find for most video work I'll be doing.



Any suggestions?
 

bp_968

Newly Enlightened
Joined
Dec 29, 2005
Messages
48
Id like to build a battery pack for a 12v 50w video light using protected 18650 cells since they have gotten so cheap (3.50$ each on DX). I found a 4 cell pack (2S2P so I think its running 7.4v, 4800mAh with 2400mAh cells).



http://mike.baikov.ru/18650/



What I'm having trouble finding is something I can put between the pack and the light that will lower the voltage from 14.8 (over 16v when fully charged) to 12v for the light. The cells individual protection circuits should protect them from being over discharged by the light, and roughly 5Ah should work find for most video work I'll be doing.



Any suggestions?
 

videoman

Enlightened
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Jul 26, 2009
Messages
422
2S2P configuration ( 7.4 V)at 5A would equate 2.5 amps going through each cell hmm. That light would be very dim and orange in color at that voltage. That 12V 50W light I Imagine is a halogen type which really is a heating element that throws out a little light. How did you calculate the part where you say lower the voltage from 14.8 ? If you are planning to take apart the cells and series them for 14.8V then I can see that happening . Even if you have a voltage reducer from 14.8 to 12 volts, the amperage is 5A going through the batts. Ouch. I Have many times used a 12V 50 watt halogen running directly from my 14.4 volt Anton Bauer without any issues. If you really must use the 12V 50W bulb, I would check with the over limit voltage of that bulb . I agree that the cells fully charged would be over 16 V which may be too high, and even if you can make them work they will drain very quickly with horrendous color shift towards the yellow.
Have you considered LED's with that battery configuration ? as you would have the advantages of well over 5X run time over the bulbs with perhaps more light output to boost. Leds units with a driver usually have a wide input DC voltage range and can easily be dimmed. I was a videographer myself for 25 years. I made a custom led light that inputs 7.2 to 18 VDC, 1800 lumens (100w bulb equiv) draws less than 16 watts and with your battery set-up will last 3 hours without any color shift. Leds are really the way to go.
 

doctaq

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Feb 15, 2010
Messages
174
if you have room and money a switching regulator of some kind will get you the most cap out of your battery
 

Lynx_Arc

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Joined
Oct 1, 2004
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11,212
Location
Tulsa,OK
You could try sets in 3 series that would give you 12v or so when charged and a little less as you use it.
 
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