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I've two GE 4510 6.4V 25W tractor bulbs with me. Unfortunately, the only power supply I've in my possession is capable of outputting only 12.02V. Can I connect the two lamps in series to the 12V supply? I'm slightly confused because most of the posts on internet that mention about bulbs in series connection have same or higher voltage than the power supply. Thanks everyone. Cheers!!

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    \$\begingroup\$ As long as your supply is capable of supplying over 50W, it should be fine. \$\endgroup\$ – Eugene Sh. May 10 '17 at 16:14
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    \$\begingroup\$ Thanks mate. The PSU is capable of 12V, 12Amps. Also I've a 12V 12Ah SLA which is also capable of giving 50W continiously for sometime I guess. But my main doubt was if its okay for the two bulbs to be connected to 12V. \$\endgroup\$ – The_Vintage_Collector May 10 '17 at 16:17
  • \$\begingroup\$ They won't "see" these 12V. If they are identical (or close), the voltage will divide equally. \$\endgroup\$ – Eugene Sh. May 10 '17 at 16:19
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Yes you can, as long as the power supply will handle the load. Anytime you have two identical lamps like this in series, the voltage will divide equally across each one.

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  • \$\begingroup\$ So, the 12V will get divided across the two bulbs. The current draw for each bulb is 4.1A. So, the total is 8.2A right? \$\endgroup\$ – The_Vintage_Collector May 10 '17 at 16:21
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    \$\begingroup\$ No. The current is the same. You might want to review the electric circuits basic theory. \$\endgroup\$ – Eugene Sh. May 10 '17 at 16:23
  • \$\begingroup\$ Oh okay. Got completely confused for a moment. \$\endgroup\$ – The_Vintage_Collector May 10 '17 at 16:27
  • \$\begingroup\$ Sorry for the noob question. I could have just checked it out with my multimeter. Unfortunately blew it up few days ago. \$\endgroup\$ – The_Vintage_Collector May 10 '17 at 16:28
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As Mike has said this will work.

However depending on what you plan to use these lights for be aware that failure of either bulb is likely to leave you with no light and quite possibly with two blown bulbs.

If a bulb fails open-circuit then both bulbs will be off until the failed bulb is replaced.

If a bulb fails with a brief short-circuit then the other bulb will see the full power supply voltage. This may well blow the good bulb as well.

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