12V fan amp draw

[dure16]

I just installed a 12V 4028 motor fan rated at 1.0 amps. My MMX BEC is set to 7.5V and is rated for 8 amps.

I was surprised to hear the fan slow down when I turn the tires. The big fan must be stressing the BEC. I’m also running a 30mm rocket fan. Stock servo.

The new fan should be pulling 1.6 amps at 7.5V, right? Any ideas why my 8amp BEC can’t handle those components?

 

[Diem Turner]

I just installed a 12V 4028 motor fan rated at 1.0 amps. My MMX BEC is set to 7.5V and is rated for 8 amps.

I was surprised to hear the fan slow down when I turn the tires. The big fan must be stressing the BEC. I’m also running a 30mm rocket fan. Stock servo.

The new fan should be pulling 1.6 amps at 7.5V, right? Any ideas why my 8amp BEC can’t handle those components?

It's not the fans. It's the servo. The servo is drawing enough amps to slow down the fans. Here's what I assume is happening. This is just speculative, but probably not far off. Say your servo draws 7A max. When your fan is running alone (let's use 1.5A) it runs just fine. When you stress the servo, you'd be drawing 8.5A which is causing your fan to lose a little power. This isn't meant to be any sort of exact description of anything, just a hypothetical that would explain what you're seeing. As for how much your fan is drawing, you could just hook up any old volt meter and take a reading.

 

[Hector_Fisher]

Electrical amp draw is all about what load you put on the specific component at any given voltage. If you put your finger on the center of the fan to slow it down, you'd increase the load on the fan and raise the amp draw.

High amp draws cause voltage dips. So when you're using a power hungry servo and pull high amps from the BEC, voltage will dip and slow down your max fan speed.

What servo?

 

[dure16]

What servo?

ADS-15. Stock 15kg infraction v2 servo.

 

[Engineer]

Is it happening when you are turning or at the end of the turn range? If at the end, are your endpoints adjusted correctly? A stall condition (reaching mechanical limits but trying to continue to turn) can cause the current draw to go way up.

 

[dure16]

Is it happening when you are turning or at the end of the turn range? If at the end, are your endpoints adjusted correctly? A stall condition (reaching mechanical limits but trying to continue to turn) can cause the current draw to go way up.

As soon as I start turning. Endpoints are set.

 

[Engineer]

As soon as I start turning. Endpoints are set.

If you lift the vehicle off the ground and steer, does it still happen? If not, then it's due to the friction of the tires and the ground causing increased current draw (which is much less when the vehicle is moving).

 

[dure16]

If you lift the vehicle off the ground and steer, does it still happen? If not, then it's due to the friction of the tires and the ground causing increased current draw (which is much less when the vehicle is moving).

I’m not sure - I’ll have to test it. Would you just drive it even with the voltage sag?

 

[Engineer]

I’m not sure - I’ll have to test it. Would you just drive it even with the voltage sag?

Good question - I'd probably replace the factory servo with a good servo first to see what the result is - but no reason why you couldn't put an ammeter in-line with each of the components to see what the current draw is and an extension cable can be modified to do so fairly quickly.