# Current limiting voltage regulator to power 12VDC fans

I'm building a ventilation system that will blow air into the back of our parked SUV. Creating a plastic fan enclosure and installing the fans is no problem, but the electronics... well, that's a different story.

I have a 12VDC PowerStation PSX2 car jump starter for powering three or four Kingwin CF-08LB 12VDC case fans wired in parallel.

Online reading leads me to believe that I need to wire some sort of current limiting voltage regulator between the power supply and the fans, and it looks like I can easily buy that kind of module. Unfortunately, I can't figure out exactly what I need - I don't understand the terminology used to describe the components I've found online and virtually all the posts here that deal with the topic use terminology that I don't understand.

I've got no problem putting an on/off switch and voltage regulator in an enclosure and doing the necessary soldering, but I sure could use some help selecting whatever voltage regulator I might need.

The PowerStation jump starter specs:

Volts: 12
Peak Amps: 1000
Cranking Amps: 400
Charger Rating: 650mA
Polarity Reversal Protection: LED Warning
Battery Type: 18 Ah


The KingWin fan specs:

Rated Voltage: 12 VDC
Operational Voltage: 10.8 – 13.3 V
Wattage: 0.96 W


As I understand it, each fan will draw about 0.08 amps, so wiring three fans in parallel will draw about 0.24 amps. If the jump starter's 18 Ah Battery Type means the battery has an 18 amp hour rating, it could theoretically power the three fans for 72 hours.

I'd really appreciate it if someone could suggest a brand and model number for whatever component(s) I might need to wire between the on/off switch and the fans, and also confirm that my understanding of the power usage is correct and I'll have no trouble using the jump starter to power the three or four fans for as long as five or six hours.

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So you want to power some 12V fans from a 12V power source? If yes then you don't need current limiting. –  Cornelius Jun 7 at 16:23
Well, you don't NEED any kind of component between the jump starter and the fans, the fans are rated for the same voltage and will happily run from the output of the jump starter. You will want to consider a fuse of some sort in case of a short downstream so that you don't create a safety hazard, but you don't really need a voltage regulator. –  John D Jun 7 at 16:25
THANKS!!! I've got the three fans hooked up and running, using a cigarette lighter plug that has an integral fuse. When I first turned the fans on, the jump starter's voltage indicator read 12.8 volts. After an hour of operation, it looks like the needle hasn't moved a bit, so it appears I'll be able to run the fans for a long time without coming close to draining the battery. –  user44204 Jun 8 at 13:54

Those are 12V fans, so you can power them using just the 12V from the PowerStation. No extra components needed. No need for a voltage regulator.

A voltage regulator will lower the voltage, what you don't need. It does this by converting the extra voltage into heat, what you don't want.

You only need to add components if you want to run the fans at a lower speed. E.g. to lower power consumption.

$$\dfrac{18Ah}{0.08A} = 75\;hours$$

However the current the fans will use also depends on the voltage provided. So they will use more when the battery is full, and less when it is "empty" (11V).

Just be sure to not let them run for that long. As the manual states:

Check the battery voltage regularly when using the 12V outlet. Do not allow the battery voltage to drop below 11V before recharging or damage to the battery can occur.

The PSX2 will NOT automatically turn off power to the DC outlet. Continuing to use 12V DC appliances after the battery has been depleted can permanently damage the unit.

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You can just wire the fans through a switch to the jump starter, and they will run until the battery is exhausted. They just draw as much current as they need so long as you match the voltage. Use a cig lighter plug with integral fuse and add a series switch.

Observe polarity on the fans or you'll most likely kill them instantly.

Note that if you deep-discharge the battery, you'll probably kill it fairly quickly, so you might want to price replacement SLA batteries. IME, even from discount sources, they're not much cheaper than the entire jump starter.

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