120V AC Air Pump connect to 240V, is that a bad idea? - Page 1
Forum section: electronics / beginners

author: amergen
author_rank: Newbie
timestamp: May 29, 2023, 05:25:30 am
content: Hi Guys,I recently purchased Scalpfun S9 Laser engraver with Air Assist. The problem is the air pump, it says on it 120V 60Hz which we all know is for the US market and not Australia. So for the last 2 weeks, I've been in communication with the supplier, informing him that he send me the wrong voltage air pump, explaining in detail about Australian 240V requirements. However, he kept insisting that it will work on 240V as well! He sent me US to AU plug converter, and said to use that to connect to AU socket!This has been going on for 2 weeks, so I finally said, if I plug the unit into 240V will you take responsibility? And of course, he said yes, so I did yesterday (with a fire extinguisher ready) and to my surprise, it worked! The pump model is Scalpfun AP30A, see pictures. I believe it's a piston pump driven by an electric motor.So my question here is (Q) What is going on here, will this pump/motor be damaged in the short/long term?Much appreciated for your help, Regards Gordon.

author: Simon
author_rank: Unknown
timestamp: May 29, 2023, 09:41:42 am
content: Of course it will work, but for how long, 50/60Hz is a problem in itself as at a lower frequency the same coil will have less impedance and let more current flow. Then you also double the voltage. Now it could be one of those situations where given the small power level although in absolute terms it's much more heat it may handle it in relative terms to the electromagnet. It's like the old phone chargers that had a center tapped transformer with just two rectifier diodes therefore wasting half the power availability. But on such a small transformer it would probably have been the same expense to make a non center tapped transformer but 2 more diodes were required. It could be a similar logic here. However the manufacturer has marked it for one voltage and frequency.As for the seller being liable, well try suing them when your house burns down, you will get no justice over a foreign entity. I would be very careful. This is why it is more ideal to import stuff so that you have a local importer to point your local authorities to. But often they do not care either. Here in the UK trading standards have been whittled down to something that joe public can no longer talk to so it's hard to report issues and so the few people left can get on with the now reduced work load.

author: wraper
author_rank: Unknown
timestamp: May 29, 2023, 09:50:54 am
content: Is it actually connected to 240V directly?

author: amergen
author_rank: Newbie
timestamp: May 29, 2023, 12:15:48 pm
content: Yes, it does.I also have a variable transformer (variac) that can go from 100V to 250V and tested at both 120 & 240, at 120V it sounded OK, however, it was noticeable at 240V it was making a crackling, humming noise, but it was pumping air, but I switch it off fearing any damage.Regards,Gordon

author: tunk
author_rank: Super Contributor
timestamp: May 29, 2023, 12:25:38 pm
content: How much power does it draw at 120V and 230V?If it's significantly higher at 230V then it may be a problem.Would it be possible to use a resistor in series to drop 110V?

author: wasedadoc
author_rank: Super Contributor
timestamp: May 29, 2023, 12:28:06 pm
content: Are you talking to the manufacturer -https://sculpfun.com/pages/contact-us- or a seller?

author: amergen
author_rank: Newbie
timestamp: May 30, 2023, 08:39:28 pm
content: Yes of course, if you look at my initial post, it has been a painful two weeks of gross "misunderstandings"until now no resolution, however, Aliexpress is now "stepping in", I don't know what that means, is that to help the supplier or me?

author: amergen
author_rank: Newbie
timestamp: May 30, 2023, 08:47:02 pm
content: Good suggestion, I will measure power consumption at 120V and 240V, however using a resister to reduce the voltage from 240 to 120 is a huge waste of power, better to use a step-down transformer, but that is an additional $$ and it's not a good long term solution.

author: floobydust
author_rank: Super Contributor
timestamp: May 30, 2023, 09:16:34 pm
content: Are the two coils wired in parallel or series?

author: inse
author_rank: Super Contributor
timestamp: May 31, 2023, 04:39:31 am
content: Judging by photo #1, I would say in series.You can add a capacitor in the 4uF range as dropper in series with the pump. You might need some experimenting to determine the best value as the pump is not a resistive load and we don’t know it’s inductance.But maybe it’s not that critical…Above that you don’t need to worry about burning down your house as there is obviously a thermal fuse at the winding.Let it run and check the winding temperature - above 100C things get critical

author: floobydust
author_rank: Super Contributor
timestamp: May 31, 2023, 04:43:02 am
content: But photo #1 I think is from a marketing ad, I thought maybe a 240VAC version with coils in series.

author: amergen
author_rank: Newbie
timestamp: May 31, 2023, 09:46:22 pm
content: Hi, thanks for all your feedback & comments.Yesterday I had the opportunity to open the pump up, and I've included some pictures.It seems the 2 coils are connected in series, also the motor is speed controlled by a TRIAC BT136, this triac is rated 600V @ 4A, maybe by using this we can reduce the voltage to a safe level, but also try not to overhead the triac and waste energy. I will need to do more experimenting this weekend.In the meantime NO feedback from the supplier or Aliexpress for a replacement or partial refund.Regards,Gordon

author: Simon
author_rank: Unknown
timestamp: June 01, 2023, 04:27:43 pm
content: is the speed variable?

author: amergen
author_rank: Newbie
timestamp: June 05, 2023, 06:40:38 am
content: Hi All, quick updates.1. Aliexpress has finally stepped in and decided that the supplier was in the wrong and has already refunded me the full amount for the air pump including delivery!2. I have tested the air pump with 120V & 240V AC (using a variac & watt meter), here are the results:o. @120V min speed 109mA & max speed 162mAo. @240V min speed 342mA & max speed 432mA, the air pressure was noticeably much greator.3. I let the pump run for 10 minutes @240V min speed, and the temperature reached 40 degrees Celsius, did the same at 120V it was cooler at 27 degrees.In summary, I'll use the current pump at 240V low speed until it craps out, in the meantime I will order a new one, hopefully, this time it will be a 240V version.I was glad aliexpress resolved this pointless debate between me and the supplier, I am not sure if it is because of English or the supplier playing dumb.Anyway, thanks for your help and comments.

author: barshatriplee
author_rank: Regular Contributor
timestamp: June 05, 2023, 07:07:06 am
content: You need a step-down transformer like this:https://www.amazon.com/Watt-Step-Down-Converter-International/dp/B086H3DXF1/ref=sr_1_1?keywords=240v+to+120v+converter&qid=1685948539&sr=8-1

author: Simon
author_rank: Unknown
timestamp: June 09, 2023, 07:19:06 pm
content: Quote from: amergen on June 05, 2023, 06:40:38 amThe supplier is chinese, playing dumb and wanting to rip you off are both a factor.I suspect hat the pump will always run with the frequency, it is coils right? it will oscillate the diaphragm pump at the frequency supplied. but at 240V you see you get more current, so more deflaction so greater volume with each cycle. But (342/109)^2 = 9.84 times the heat.

author: amyk
author_rank: Super Contributor
timestamp: June 09, 2023, 07:45:29 pm
content: That sounds like an electromagnet-driven reciprocating pump with a phase angle control. As others have mentioned, the winding temperature is the most important thing to monitor. If you have a logging temperature sensor it would be useful to see if the temperature gets to dangerous levels or just rises more quickly and stabilises at a higher but still safe (which can still be too hot to touch) temperature.

author: Seekonk
author_rank: Super Contributor
timestamp: June 09, 2023, 08:27:16 pm
content: I actually use that trick, but for a different purpose. I put a capacitor in series with 240V muffin fans so I can use them on 120V AC. Choosing the right capacitor will develop about 180V on the motor. I don't like loud fans and that voltage slows them down enough.Remember what happens to voltage when a capacitor and inductor are near resonance. A capacitor in series can easily burn out a motor.

author: james_s
author_rank: Super Contributor
timestamp: June 09, 2023, 10:50:23 pm
content: I think I would just pick up a cheap transformer based travel converter and toss that in there, shouldn't cost more than about 20 bucks for one that is good enough quality to at least not catch on fire. The pump only draws about 20 watts so one of the common 50W buck transformers meant for shavers and such ought to work fine. The pump may in fact tolerate being overdriven and run like that for years without failing, but why chance it?

author: amergen
author_rank: Newbie
timestamp: June 10, 2023, 08:56:02 am
content: Hi Guys,Thanks for your feedback, I've finally decided to purchase a small low-cost 150W stepdown transformer (this onehttps://tinyurl.com/mr3haat9) instead of buying another air pump, with a total savings of just under a hundred dollars, thanks to my "play dumb" supplier.I think running it at 120V will definitely increase its lifespan. Overall I am happy with the outcome, now I can finally focus on what I really bought this laser engraver for, and that is engraving! Cheers!

author: james_s
author_rank: Super Contributor
timestamp: June 12, 2023, 09:04:58 pm
content: I seriously doubt that transformer is capable of anywhere near 150 watts, but for your needs it will probably be work perfectly.

author: Simon
author_rank: Unknown
timestamp: June 13, 2023, 06:53:18 am
content: 150W PMPO ?

author: EPAIII
author_rank: Super Contributor
timestamp: June 13, 2023, 08:58:25 am
content: A series resistor may waste power, but not as much as running it directly on 220V.220V direct connection:Rp = effective resistance of pumpPower used = 220^2 / Rp = 48400 / Rp220V connection with resistor:Rp = effective resistance of pumpRs = series resistance = RpPower used = 220^2 / (Rp + Rs) = 48400 / 2Rp = 24200 / RpThe series resistor cuts the total power IN HALF. The direct connection to 220 V is clearly the biggest power waster.Of course, a transformer will cut the wasted power even more. But transformers cost a LOT more than resistors. That extra cost also represents a waste of power and/or resources. Care to do a "break even" calculation?And if it goes up in smoke then there is the replacement cost for the overall device. And possibly for whatever else catches fire.I would NOT run it directly on 220 Volts. Either of the options is clearly a better one than that.BTW, just why is a step down transformer such a bad long term solution? Other than cost, of course.Quote from: amergen on May 30, 2023, 08:47:02 pm

author: inse
author_rank: Super Contributor
timestamp: June 17, 2023, 06:17:18 am
content: CAPACITIVE DROPPER is the way to go