Small engines and LED bulbs

[dave110]

I learned something new the hard way the other day. I have a lawn tractor that is wired to have the headlights on all the time.. no switch. I went to the local alternator shop and bought a pair of 1156 LED direct replacements to put in figuring they would not get so hot and to help the charging system out. Put them in, started the tractor and nice bright lights. Took my tools to the bench and came back to darkness and the unmistakable stench of burnt electrics. Smoked the new LED's within a few seconds. I took them back and explained what happened to the old fellow there and he went on to explain that on a small engine charging system lights are run off the AC side and battery charging is DC. I was a little upset because he didn't tell me that when I bought them and I made it clear what I planned to use them for, and I was skeptical about the AC/DC explanation. I decided to check it out before going any further. I went home and started the tractor and put my meter on the light connector and sure enough it was 12.6 VAC. while on the battery VDC was present. I found a wire that was DC and hot with ignition on and used it to trigger a relay for the lights to run off the battery. LED's are in and happy now. So while LED's might say they are a direct replacement for a certain incadesent bulb you need to be sure of the application. FYI

[Mopar1973Man]

LEDs (Light Emitting Diodes)... Some diodes don't like AC power banging away on them. The reverse current creates a huge amount of heat. This is what burned it up. 

[dave110]

Yep, sure is.

[dave110]

For those who don't know I've discovered that LED are polarity specific where incadescent bulbs don't care which way the current flows through them.

[Dieselfuture]

Just found that out too, switched to leds in boat trailer and first I plugged it in and nothing, flipped the bulb around and got light.