Starting up a small Brushless air pump? - Page 1
Forum section: electronics / projects

author: makebit
author_rank: Unknown
timestamp: October 01, 2025, 08:14:31 pm
content: Hi,We are investigating use of the Bodenflo mini air pump.Part number is BD-02AB.Its Brushless.Catalog says it comes in "6v, 12v , 24v", but ours says "5V, 1A" on it.Ours won't start unless the PSU current limit is set to 4A.I thought brushless motors cleverly utilised the H bridge to really limit the startup current?(obviously not with ours).We are not even with the customer yet, and they are in an office where soldering is disallowed, andthey wont let us see the motor yet due to secrecy.Anyway, a 5V power supply limited to 1A wont start the motor, so we need the lowest possible current limit setting needed to assure starting the motor....what do you think this might be? I have to say it would amaze me if a 5V power supply with a current limit of 2A failed to start it?I mean the nominal is 1A at 5V for normal running current.Its a shame we cant measure the winding resistance. Presumably there are three windings.https://bodenpump.com/download/

author: Benta
author_rank: Super Contributor
timestamp: October 01, 2025, 08:25:43 pm
content: BLDC motors behave exactly like brushed ones.Meaning maximum current at locked rotor is limited only by winding resistance (and possible controller current limiting).Your 4 A experimental result does not seem unreasonable.But if the supplier won't give any more information, I'd look for a different business partner.

author: HumbleDeer
author_rank: Contributor
timestamp: October 01, 2025, 09:44:37 pm
content: You'll probably need something like a kick-starting. If you want an analog solution, something with an RC circuit, large reservoir and silicon switch might work? I agree that you'll want more info from the supplier though. If they don't wish to, that's a red flag to me.You kind of can measure the winding resistance if you're smart about it. Or if you're okay with opening the pump up to get to the star tap.

author: Benta
author_rank: Super Contributor
timestamp: October 01, 2025, 10:09:24 pm
content: The BLDCs I've run into are wired delta. No star tap there.

author: makebit
author_rank: Unknown
timestamp: October 01, 2025, 10:32:10 pm
content: Thanks, also, suppose we boost up from a 3.7V battery to 5V to feed this motor, and we turn the motor off (it has a disable/enable terminal for 0V/5V logic), then do you think it would draw much bias current? (ie draw much bias current while its disabled but still has the 5V at its terminals).Also, we would like to know how far above Vin (nominal) we can operate it?...its only going to be operated for say 5 minutes per day

author: Benta
author_rank: Super Contributor
timestamp: October 01, 2025, 10:34:25 pm
content: Again, this is a question for the pump supplier.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: October 03, 2025, 10:47:40 am
content: This all depends on the quality of the motor driver. Because commutation is electronic, and there is already a motor controller, it's easy to add things like a soft start, but if the controller does not support that, then just go buy a better one.And such a controller also works as a voltage regulator. The FET's combined with the motor windings effectively form a three phase buck converter, and you can even use a 24V power supply to run a 5V motor, provided you do not overload the motor too much. (You can for example run it at higher RPM, but with reduced torque, the motor power stays the same)

author: makebit
author_rank: Unknown
timestamp: October 03, 2025, 09:36:03 pm
content: Thanks, supposing you were going to use the pump to pump something up for 1 second every 10 seconds.....4 times in total.....Then would you restart the pump for each 1 second pumping session and get another high startup current episode for each of the 4 times.?Or would you start the pump up...get high starter current initially, and then just keep the pump chugging over for the 4 pumping episodes and so not keep getting a startup current spike?

author: Benta
author_rank: Super Contributor
timestamp: October 03, 2025, 10:09:24 pm
content: Do you mean using a bleeder valve or something like that?I'd certainly consider it, not because of the starting current, but more for less thermal and mechanical wear and stress and for better pressure regulation.A running pump will certainly draw more current when closing the valve, but much less than at startup.Also, it'll be running at stable speed and not have to build up pressure first.