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I installed two 4" 18 watt LED light bars on my ATV. It is currently wired to the factory switch on the ATV handlebars and there is no relay being used. I have had to replace the right LED bar twice because it has died on me. Is this because I didn't use a relay? Will the relay help?

As a side note, the battery seems to be failing and not holding a charge well (old battery). When I start the ATV (can't use electric start, pull only), the lights will turn on but they will start to dim unless I rev the engine.

The ATV is a 1995 Polaris Magnum 425 4x4.

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4 Answers 4

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Change your battery first.

Unlike cars which use alternators, ATVs and motorcycles get power from very simple stator generators. How it works is that there's a permanent magnet on the flywheel which excites a stator coil, which is followed by a bridge rectifier. Unlike an alternator, regulation is done by measuring the output voltage and then shorting the stator coil to ground with SCRs.

How does the system convert rectified AC pulses to DC? It treats the battery as a capacitor. And unlike a car, the system is 1-phase, so the voltage does drop to 0 twice every revolution.

When the battery fails, the pulses and noise aren't filtered out, the regulation becomes poor, and you get overvoltages, killing the LEDs.

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  • \$\begingroup\$ I will replace the battery then. I used my ATV winch for my plow on the front and last winter I would have to rev the engine to get the winch to lift faster and not shut the lights off. \$\endgroup\$
    – Programmer
    Nov 8, 2018 at 13:47
  • \$\begingroup\$ This fixed the problem and everything works fine now. How can I prevent the LED's from dying in the future when the battery fails again? \$\endgroup\$
    – Programmer
    Nov 13, 2018 at 14:23
  • \$\begingroup\$ @Programmer Buy better LED lights. I suspect 99% of those things aren't designed for the rather impressive transient standards that cars have. Check out this page for some LED transient suppressor designs. \$\endgroup\$
    – user71659
    Nov 15, 2018 at 4:54
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No, a relay won't make a difference. You are either electrically or mechanically (maybe they are of a s**t construction?) overloading the LEDs. Do they just stop working, or they start to fade and go out one by one?

Change the battery; Depending on their chemistry they work for different periods of time, but eventually all of them die. Pay special attention to change it with one which is electrically compatible to the ATV.

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  • \$\begingroup\$ They will just stop working. It's always just the right one too. They are wired off of the same + wire \$\endgroup\$
    – Programmer
    Nov 7, 2018 at 21:58
  • \$\begingroup\$ Likely some mechanical issue, a connector gets wacky, a soldering breaks, smth like that. Have you tried to power it on after you took them down because they stopped working? Connect the power, then move them around, shake them etc. See if there is any life in them. If it does have contact problems it should flicker every now and then due to the physical vibration. The car might not be symmetrical, your usual rides might not be symmetrical (for example always bumping the right wheal into the edge of your driveway); the right might get more vibrations. Do the LEDs appear darker than new ones? \$\endgroup\$
    – Cerike
    Nov 7, 2018 at 22:16
  • \$\begingroup\$ The LED's are dead when I take them off and test them. I didn't notice if the LEDs were darker though. The lights don't flicker, they just are just dimmer until I rev the engine. \$\endgroup\$
    – Programmer
    Nov 8, 2018 at 13:51
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The alternator normally puts out a higher voltage (14.6 v or more) in order to push a charge into the battery. A good battery with good connections provides the load needed to stop runaway voltage from the alternator.
Your LED lights are probably getting too much voltage, therefore too much current. The right side LED may have a shorter wire or better connections, so it goes first.
Often, high current LEDs used for many hours can fade to half their original brightness. And of course excess current can pop the junction. If the ATV won't give you a satisfactory voltage you could add a wire-wound 1 ohm resistor into the circuit.

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have the aletenator tested, it may be faulty, test the battery too, when recharged it may still be good.

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  • \$\begingroup\$ There is no alternator on this ATV. \$\endgroup\$
    – Programmer
    Nov 8, 2018 at 13:48

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