Electronics > Repair

DC power supply doesn't work with DC motor

(1/3) > >>

tjkolev:
Hello circuit wizards!

I have this 120VAC to 12VDC (rated at 5A) power supply that came with an Igloo cooler. I am also using it to power a (cheapo) 12VDC air pump (DC motor with impeller) to inflate/deflate our air mattresses.

The problem:  Switching on the air pump causes the motor to make ~ 1/4 turn, and then stops.

My workaround: I have added bullet type connectors on the air pump cable. I switch on the air pump. And then I keep connecting and disconnecting the bullet terminals on one of the wires progressively at a faster rate. The motor starts spinning faster, and after 5 - 6 of this it "catches on", I keep the terminals connected, and everything works like a charm. It feels like I am playing the role of a starter winding in an AC motor...

The need: If possible and practical, find some way so the above power supply and air pump work normally, without my workaround. I am thinking of adding something to the circuitry. Looks like the power supply isn't happy with inductive load.

What I've done:
* The air pump works normally when powered from my desktop power supply. Using 12 - 14V, it draws 3.1A.
* When I have it running off the Igloo power supply it draws 4.2A, and the motor spins faster. When the air pump can't start it draws 0.2A.
* The Igloo power supply shows 14V without load, and a nice, flat, unremarkable line on the oscilloscope.
* The air pump is glued/sealed. Through a grate I can see the two wires connected directly to the terminals on the back of the motor. There's no capacitor, or any anything else.

I am adding some photos. From what I can see, the three legged element with a heat sink on the low voltage side is a SBL2040 Schotkky diode. No clue how that works...

Cheers!
tjk :)

Xena E:
What voltage do you measure across the supply when the motor won't start?

It's starting current surge is probably putting the PSU into fold back limit.

inse:
You‘re going to need a bigger boat - err power supply

Ice-Tea:
Inrush causing foldback? Try a 5 \$\Omega\$ NTC...

CaptDon:
Those inflator motors draw a huge amount of current!! I measured one that runs on 4 D cells and was surprised at the current draw. The inrush at start could hit 10 amps. The motor is wound with heavy wire and the motor needs to spin up to a high RPM before the back EMF reduces the large current draw. No wonder they kill batteries so quickly. That motor has to spin like crazy to get any meaningful air flow from such a small impeller.

Navigation

[0] Message Index

[#] Next page