I am making a "lightbar" for my vehicle which consists of 7x 6" diameter spot lights linked together. The specs for each of the individual lights are below:
- LEDs: 14x 3w OSRAM
- Max Watts: 67w
- Input voltage: 9-32vdc
- Current Draw @ 13.8v: 5.6a
I have just finished wiring the lightbar, which I specced the wire thickness based on some previous bench testing of 2x lights connected to a 40a switching powersupply.
When I did this initial bench testing, 2 lights drew 6.5A @ 12v.
So, when I specced the wiring, I allowed for a total of 28a of peak load (6.5/2)x7 + bit for headroom.
I have just gone to test the whole array and my amp draw has increased considerably and I dont know what to do now, as I have some hard limitations which I need this lightbar to work to.
To bench test the power supply, I plugged in 1 light at a time, to check the amp draw. Instantly, just 1 light was drawing way more amps than my previous bench test!. The next odd thing that happened, was that at light 6, the volts dropped to 7.4 volts, but the amps stayed the same. The lights obviously dimmed as well. 30a was all I could push through the wiring and connectors as I didnt want to start a fire.
- 1 light: 4.8a @ 12v
- 2 lights: 8.4a @ 12v
- 3 lights: 13.8a @ 12v
- 4 lights: 17.9a @ 12v
- 5 lights: 17.9a @ 7.4v
- 6 lights: 22a @ 7.8v
- 7 lights: 30a @ 8.4v
So, the hard limits I need to work within are:
- I use a Switch Pros SP9100 to control lighting circuits, which has a max output of 35a. So ideally, I need the load to be below this. Obviously, I could run a 70a relay to switch more current, but its added complexity.
- I dont really want to have to rewire the lightbar, which is currently wired to handle 28a.
So, firstly, I would love help to understand the below questions.
- Why did my initial bench test show such a low draw compared to testing today?
- Based on the above load @ voltage results, whats the total estimated amp draw the lights would make if they were plugged into my vehicle, which can provide upto 14.6v when running.
for solutions, I have gotten to this point.
- Use a 12v-24v step up converter, which will from my understanding, half the amp draw? But, what I am confused about is; A) Does the converter still draw the full watts (7 x 67w = 469w / 12v = 40a)therefore my switch pros 35a output would still need to use a relay circuit?? B) Does the draw of the lights half @ 24v, so I would need a 20a step up like this https://www.ebay.com.au/itm/New-DC-12V-to-24V-20A-480W-Step-up-Boost-Converter-Power-Supply-Module-for-Car-/321846640256 ?
- Rip all of the wiring out, beef it up to handle 40a of current and then use a 70a relay, switched from my Switchpros?
Im sure this is all fundamental electrical stuff, but it really threw me how badly I got the draw estimates wrong.