Is 27.0 volts too high for 24 volt headlights?

belfert · August 24, 2011, 04:06:03 PM

I ran new 8 AWG wires from my chassis batteries back by the engine up to the front of the bus. I am upgrading to 24 volt ECE headlights. I choose 24 volt because the size of the wire for 12 volt to avoid voltage drop would have been too large and expensive. I am carrying spare bulbs in case one blows.

Anyhow, will 27.0 volts be too high for 24 volt bulbs? I know the European design spec for bulbs is 13.2 volts at 12 volts, so I am assuming they are speced at 26.4 or so for 24 volt bulbs. I suppose the voltage my drop a bit once there is a load on the circuit.

Ralph7 · August 24, 2011, 05:05:35 PM

Both my Mc-7&8 the voltage regulators had 27.8 V. for max charge rate.

belfert · August 24, 2011, 08:09:46 PM

Anyone else? I would think it will be all right, but I wonder if my bulb life could be reduced?

My original 12 volt setup was running a bit low on the voltage side and now my 24 volt setup seems like it could have too much voltage.

Busted Knuckle · August 24, 2011, 08:15:30 PM

I personally don't think it'll be an issue.

Most systems run around 27-28 volts and many of the things on our buses say 24-28 volts right on them.

The only way to be sure is to contact the manufacture and ask.

Or you could put a voltage regulator inline on them.

BK

Lin · August 24, 2011, 10:41:11 PM

I don't think it is an issue. When buying 24v lights from Napa, you sometimes have to ask to 28v or they won't find them.

RoyJ · August 24, 2011, 11:37:17 PM

The voltage itself is not a problem at all. 27V is like 13.5V on a 12V system, which is perfectly normal, almost on the low side. A 12V battery would take DAYS to charge at 13.5V. Newer GM cars with calcium chemistry batteries are measuring 14.7 from the factory, or 29.4V on a 24V system!

Bulbs can usually be overdriven (the term we use in flashlight hobbies) quite a bit. The exact amount depends on initial bulb life rating. In my custom light, I drive a 6V 5000hr bulb at (gasp!) 12V. The bulb is very bright, and white (high filament temp) at double its rated voltage, and still have about 100 hr life according to some big formula.

Automotive bulbs are in the 300hr - 1000hr range, so you definitely won't want overdrive them by 100%. But 13.2V to 13.5V is all but unoticeable for most bulbs.

gus · August 26, 2011, 12:59:46 PM

It is no problem. Some small aircraft use a 24v battery but the electrical system is called 28v and radios and etc are rated at 28v.