Talk Morgan Forums Morgan Sports Cars Maintenance & Servicing Electric fan wiring -current limit

Hello all,

I need to go to an electric fan. I’m still running on my original Lucas C40 generator (original but fully rebuilt) so I’ll max out at around 22 Amps. I’ve already gone to all LED lamps, and that’s the only electric thing on my car, so my power consumption is otherwise very low. But I’m worried about inrush current on the fan. I’m looking at this Spal fan and max operating current will be about 9.6 A. I figure inrush at 3x that, clipping out my lights or something.

People talk of using an NTC thermistor to limit current. If I put an NTC thermistor (12A cont. rating, 0.7 ohms) in series with the fan input, would it do the trick? I would also put a time delay relay in parallel with the thermistor, shorting it out after 2 seconds to let it reset and keep it out of the loop during steady state fan operations.

Thoughts?

-Nelson

I know this post is not going to be what you are looking for as it is not a technically written response. For the last 12 years I have run the same fan on my 1964 4/4 using the original generator and wiring circuits, I simply inserted the correct rated fuse and wire rating into the fan wiring, also installed a fan override switch at the same time. No issues what so ever, sometimes I believe we over think issues and create our own problems.

Thanks Britmog. Don’t sell your reply short! KISS principle at play- certainly most reasonable to try it and see if it works just fine. Simple, cheaper, etc.

I suppose I will start exactly as you say. I’ll try the fan on the bench and see how much it pulls. Then in the car and see how it starts without and with lights on.

I just kept reading things that said “and use an inrush thermistor,” but the disconnect is there are almost no circuits shown for auto radiator fan use. And as most people are running alternators with their big amps output, unless you’re putting on a racing fan (or on a generator like me) it’s all moot. Most often I see circuits with thermistor limiters for power supplies.

Has anyone used a circuit like I describe? And fyi, am uninterested in going to the alternator side. I rebuilt that thing- is a job and a half if you’ve never done one- and I’m sticking to it!

I agree with Bruce's comments re the overthinking. The inrush current whilst motor gets up to speed will likely last barely a second and be taken from the battery, and remember that copes with hundreds of amps when you operate the starter. I doubt you will even see a blip on the lights especially as LED's work over a voltage range.

Hadn’t thought of the battery! It’s true. Probably a non issue entirely!

Thanks!

+1

Richard is correct, as a real life example I run a similar fan on the old F Super which has a very low charge rate and never had any issues, the control stat is a very basic bulb thermocouple
https://www.carbuilder.com/uk/adjustable-fan-controller-thermostat