LED lights

[RMiller7]

New to me 8N, 1952 by serial number, 12V conversion. I installed some LED lights on the front. Connected fused hot wire to the terminal junction that was hot with key on to a switch and back out to lights. Grounds ran back to the dash structure. With engine off key on I tested lights and they worked. Started engine and they came on for a few seconds, started flickering and died. They are fried now and I'm not sure what happened. I used the same wiring and tested with an incandescent light and it works fine. Is there some kind of electrical noise in these older tractors that could have caused this? Voltmeter shows 12.5 at battery with engine off, 14.1 while running at 800RPM. I'm going to have the alternator tested to verify its good. Anyone else have this issue? Thanks.

 

[Hemmjo]

Are they 12v lights? Or are they made for 8n and really designed for
12v? Just asking.

 

[deanostoybox]

I am going to take a crack at this.

1) 'Voltmeter shows 12.5 at battery with engine off, 14.1 while running at 800RPM. I'm going to have the alternator tested to verify its good.' Seems good to me

2) 'Is there some kind of electrical noise in these older tractors...' Yes, enough to affect AM radio and cheap digital meters. Not enough to affect LED lighting in a typical installation.

With incandescent lighting it is usually recommended that the lights get their power from the unswitched terminal (constant hot, connected to battery all the time). The reasoning being that the lighting load may well exceed the capacity of the ignition switch. With LED lights maybe not as big of a deal.

When light power is taken from switched terminal (connects battery to coil primary when closed), what happens when ignition switch is turned off (from on) while points are closed? You get a spark. Maybe not at a sparkplug, but inside the ignition switch. Maybe the LED lights offer a lower impedance path than the spark between the switch contacts and absorb that high voltage spike which exceeds their maximum input voltage causing damage or degradation resulting in failure. Also the 'ground path' for the ignition secondary circuit passes from the engine block (plugs are grounded to the head) through whatever parts are between the block and ground terminal of battery cable, ground battery cable, battery, other battery cable to solenoid, wire from sol. to unswitched terminal, through ignition switch to switched terminal, wire to coil (+) terminal where the secondary winding in the coil's other end (from high voltage terminal) is terminated. So getting power from switched side of ignition results in an alternative path for the secondary circuit ground which may offer lower impedance than the long convoluted path which includes the battery voltage as a constant bias, thus overvolting the input to the LED lights. Just my hypothesis, it would take an oscilloscope to find out for sure.

 

[RMiller7]

Turns out it was just the lights. I had the alternator tested and it was good. I bought a set of cheapo LED lights and they are working fine. Didn't want to fry another expensive set if it was a issue in the tractor. Thanks for the help.

 

[Jim L WA]

(quoted from post at 04:21:28 12/19/23) Turns out it was just the lights. I had the alternator tested and it was good. I bought a set of cheapo LED lights and they are working fine. Didn't want to fry another expensive set if it was a issue in the tractor. Thanks for the help.

Nice to hear that the sights are working again. I would still move the power wire to the constant battery terminal like deanostoybox said.

 

[Dave G9N]

(quoted from post at 18:34:16 12/18/23) I am going to take a crack at this.

A) With incandescent lighting it is usually recommended that the lights get their power from the unswitched terminal (constant hot, connected to battery all the time). The reasoning being that the lighting load may well exceed the capacity of the ignition switch. With LED lights maybe not as big of a deal.

B) When light power is taken from switched terminal (connects battery to coil primary when closed), what happens when ignition switch is turned off (from on) while points are closed? You get a spark. Maybe not at a sparkplug, but inside the ignition switch.

) I think this is correct. This is why you have all the relays in a car. The switches for the starter, lights, wipers, fans and any other high current devices are wired to the relays, which are electrically operated switches that can carry high currents. The ignition switch can't handle that much current. The switches that you operate only provide a small current to the solenoids that operate the relays, which are the high current switches that power the lights etc. The current to operate the LED might not be much different from a relay, so it isn't as big of a deal unless you are looking at some really high output light bars. On the other hand, the 6V ignition in these tractors seems to need all the help it can get, so any added load on the switch might be bad. Better to separate them. If for no other reason, it is hard enough to track down the bad contact that is killing your spark when you only have a few of them.

B) You only get a small spark inside the ignition switch when you turn it off. The spark is caused by a back emf from shutting off power to the distributor. The hydraulic equivalent to back emf is water hammer. Turn off the tap too fast and the pipes bang. Small current small hammer. Adding lights to that circuit makes for a stronger spark. The back emf is rough on the switch, but probably not anything else.

There are two separate coils of wire in the ignition coil. The high voltage side is only connected to the spark plugs, and does not affect the switch.