another led question

varmint · Oct 12, 2015

Paystar, something is amiss with you amperage... if you are running 14.2 volts, then 4.86A equals 69 watts... just the way the laws of physics compute.

Paystar · Oct 12, 2015

varmint said:
Paystar, something is amiss with you amperage... if you are running 14.2 volts, then 4.86A equals 69 watts... just the way the laws of physics compute.

No idea? That's what the manufacturer said? All I know is they are super bright and I am running three of them with the 20A fuse.

Here's what my dealer sent me:

the beauty about these lights being high quality they take no power compared to not so good lights of the same power. The 70w will run 3.42A each light and the 80w will run 4.86A each light. For your alternator it will be fine as long as the battery is good and the system is not overloaded. I have up to 300w light bars on Polaris and Honda side by sides plus they run a winch light bar and other stuff with no problem. The bigger 300w light bars run at 9A-10.5A so they can be used all the way down to solar power applications only requiring 9V-30VDC to opporate.

k0ua · Oct 12, 2015

It is rather obvious that apparently some of these wattage claims of these LED lamps are being overinflated. In DC circuits. Watts= volts X amps. Period, end of story. Example, 14 volts at 10 amps is 140 watts input to a device. Doesn't matter if the device is a heater coil a solenoid or a LED lamp or an incandescent lamp. Output watts is very hard to measure because we may not know the efficiency of the device. But input power measured in watts is very easy to measure. I think some of the distributors have taken a bit of "license" with their measurement's.

Threepoint · Oct 12, 2015

CCWKen said:
Fuses protect the wiring. It's not advisable to just put in a larger fuse for the circuit. [snip]

True, very unwise to over-fuse a circuit rated for a specific amperage. Hopefully nobody here is doing that. :shocked:

woodlandfarms · Oct 12, 2015

So I am not expert on this, and my background is classic cars and big stereos, but I was always told never to exceed the amperage of Alternator. Yes, a battery can provide "missing amps" but the strain on the alternator (heat) can be really great and tends to make them fail quickly. Also, when you go to idle your alternator is no longer producing anywhere near enough amps so your lights may dim and you will put a strain on your electrical system.

I was told headroom is important. give yourself a minimum of a 10 amps of headroom when putting in high amperage devices.

k0ua · Oct 12, 2015

woodlandfarms said:
So I am not expert on this, and my background is classic cars and big stereos, but I was always told never to exceed the amperage of Alternator. Yes, a battery can provide "missing amps" but the strain on the alternator (heat) can be really great and tends to make them fail quickly. Also, when you go to idle your alternator is no longer producing anywhere near enough amps so your lights may dim and you will put a strain on your electrical system.

I was told headroom is important. give yourself a minimum of a 10 amps of headroom when putting in high amperage devices.

I would tend to agree with this advice. Just look at the output curve on an alternator showing rpm vs current and then how heat affects the output will give you an education. When we say a tractor has a 50 amp alternator, we mean at full rpm an while it is still cool. Yes you can Rob the battery for a short period but for how long?. It still has to be made up by the alternator.

ishiboo · Oct 12, 2015

Quick lesson on LEDs which will answer some of these wattage questions.

You can drive a LED off any voltage with a simple resistor. It will be on 100% of the time, and produce more heat.

But the most efficient way to do so is to pulse the LED, so it is only on part of the time - but still peaks at the same brightness. Above a certain hz this cannot be seen by the human eye. This allows the LED to make less heat, since it's only "on" part of the time. So, LEDs used in most applications (especially light bars/offroad lights/etc) use a LED driver to do this. They regulate to a specific "signal" (PWM) to the LED at a specific voltage themselves, so the input voltage may vary, but the output to the diodes will always be a constant voltage and current.

This is why there is a wider range of input voltages, why the output power/lumens/brightness stays the same no matter the input voltage, and the high-pitched "humming" you hear from some.

Take a 180W light. It's typically rated because it has 180 1W diodes, or 60 3W diodes, or whatever. You then have to consider the efficiency of the LED driver, which will means watts in != watts out. Then, also consider that the output could even be exactly 180W *peak*, but if it's only "on" 75% of the time, that's effectively 135W of constant current drawn.

Think about AC in your house - we call it 120v at the outlet, but it really goes between 0V and 170V! It averages out (RMS) to 120v.

Paystar · Oct 12, 2015

Thanks ishiboo, my LED guy tried explaining all that to me, but I didn't understand, LOL.

I do remember him saying that watts divided by volts equals amps isn't always cut and dry.

k0ua · Oct 13, 2015

ishiboo said:
Quick lesson on LEDs which will answer some of these wattage questions.

You can drive a LED off any voltage with a simple resistor. It will be on 100% of the time, and produce more heat.

But the most efficient way to do so is to pulse the LED, so it is only on part of the time - but still peaks at the same brightness. Above a certain hz this cannot be seen by the human eye. This allows the LED to make less heat, since it's only "on" part of the time. So, LEDs used in most applications (especially light bars/offroad lights/etc) use a LED driver to do this. They regulate to a specific "signal" (PWM) to the LED at a specific voltage themselves, so the input voltage may vary, but the output to the diodes will always be a constant voltage and current.

This is why there is a wider range of input voltages, why the output power/lumens/brightness stays the same no matter the input voltage, and the high-pitched "humming" you hear from some.

Take a 180W light. It's typically rated because it has 180 1W diodes, or 60 3W diodes, or whatever. You then have to consider the efficiency of the LED driver, which will means watts in != watts out. Then, also consider that the output could even be exactly 180W *peak*, but if it's only "on" 75% of the time, that's effectively 135W of constant current drawn.

Think about AC in your house - we call it 120v at the outlet, but it really goes between 0V and 170V! It averages out (RMS) to 120v.

Aha, the old Pulse Width Modulation... I should have thought of that,. I just considered a simple linear power supply. I never considered they were pulsed. Thanks for the explanation.:thumbsup: