Calculating how many smaller gauge wires are required to make up for a larger size gauge wire

How do I calculate how many parallel wires are needed to make up for a larger gauge wire in order to get them through an interface bulkhead motorsport connector?

I'm wiring a pair of Spal brushless fans which require 10 AWG power wire. They have to be connected directly to the battery, and my battery was relocated to the inside of the vehicle. I am planning to install an interface bulkhead connector and I am having a hard time finding a motorsport connector that will accommodate the larger size wire. Instead, I will be installing a parallel set of smaller gauge wires (16 awg or 20 awg) to make up for the 10 awg power wire.

Is there a formula to calculate this or guidelines?

Thanks,

I am currently wiring a car using the MS 3474 A 16-14P Connector which has six #12 (25A) pins, and eight #20 (7.5A) pins. You should try to measure your fans actual current, I've found the SPAL fans can have a huge inrush (75A), but drop significantly once started (< 20A).

That’s a lot of current. According to the fan spec sheet each fan draws between 23 and 27 amps.

Easiest thing would be to look at the current rating of that wire, the current/gauge ratings for the biggest pins compatable with the connector, and going from there.

Another option is to use a through-bulkhead battery post, which would allow you to use the biggest gauge wire you want, and also has the benefit of being available for other high-draw components.

Also, don't forget the ground/earth/return, as that has to match the current.

As David said, some electric motors have a very high initial/stall current and, further, some electric motors will draw more current when the voltage drops - fortunately those latter ones are (almost?) all AC motors.

Some PDMs can be configured to limit this 'inrush' current, and if you're usintg one it may be an option?

Depending on the wire and connection quality, voltage, and length, the amp capacity for reasonable temperature rise varies.

Depending on which reference you view, you'll also receive different info to base your decision on, so erring on the safe side is generally suggested since conditions won't always be ideal.

That said, 10 AWG will handle about 30 amps, 16 AWG about 7 amps in similar length, so 4 16 AWG wires per 1 10 AWG, but if the run is short enough 3 of them may be sufficient.

I would prefer to use an auto sport bulkhead connector rather than a battery post connector as I’m looking to connect the water pump controller through this connector as well.

So the fans will be pwm controlled via a TinyCWA controller which also has the soft start feature.

So is the amp rating based on the cross sectional area of the wire??

for example: a 10 awg wire is 5.27mm^2 which is capable of handling approximately 24 amps max per the table of HPA Wiring Fundamentals>EFI Wiring Design>Sizing The Wires. So in order to obtain the same amp rating using 20 awg (20 awg is 0.51mm^2 & 4 amp max/wire) in parallel I would have to use a minimum of (10) 20 awg wires to make up for (1) 10 awg wire??

5.27/0.51= 10.3

or

If one 20 awg wire is capable of 4 amp max current would it be:

10 awg about 24 amps max

24/4= 6 (20 awg wires)

#20 terminals (gold ones) are good for 7.5 Amps, so 4 terminals with 18 ga wire (which will fit) would work for you. Or the #12 terminals are good for 25 Amp each. See my connector suggestion above.

My charts show 10 awg is capable of 55 amps, probably depends on the type of insulation used.

Oh ok.

I’ll be using spec 55 wire.

Exactly WHICH SPAL fans are you planning to use? Depending on the model, there is a potential for continuous currents of well over 50A per fan, and some push 100A, under higher loads/duty cycles.

This is why I suggested using a 12V through-bulkhead fitting for the power side - not only does it make things much simpler, but it avoids tying up multiple pins in the connectors that can be used for other things as you'd just need the lighter control wires.

The other advantage is you can up-size the wire gauges to reduce voltage drops and so increase the efficiency of the fans for the same current(s), or have the same air-flow for less current.

[edit] Thank's Mike, I missed that.

He mentioned "According to the fan spec sheet each fan draws between 23 and 27 amps."

Sorry guys busy week at work.

So I'm running two 12" ABL320P brushless fans.

I attached some of specs I found for these fans.