Heater fan has  inrush current  at start-up? - Page 1
Forum section: electronics / beginners

author: ocset
author_rank: Super Contributor
timestamp: December 22, 2017, 09:31:46 am
content: Hello,Is there inrush current, up above the normal operating current peak, when these type of fans start?...They are heater fans..https://uk.rs-online.com/web/p/space-heaters-radiators/0488201/?origin=PSF_438309|althttp://www.thesafetysupplycompany.co.uk/p/8738241/status-portable-dual-position-fan-heater-2000w---af-180321.html?gclid=EAIaIQobChMI0qj6yKWd2AIV7ZPtCh1YvASAEAQYAiABEgJoEfD_BwEI assume that when it starts, its at first stationary, so there will be no back EMF.....so i assume there is high inrush current at switch-ON.?Is the inrush current at switch-ON reducable by starting at mains zero crossing?

author: capt bullshot
author_rank: Super Contributor
timestamp: December 22, 2017, 10:37:20 am
content: I assume they use some kind of shaded pole motor, then there's no significant inrush current to expect.

author: dmills
author_rank: Super Contributor
timestamp: December 22, 2017, 01:21:29 pm
content: If you set them to fan only mode, they do however produce one hell of a kick on contact opening, been there, done that, when using them as dummy loads for testing power products.Regards, Dan.

author: SeanB
author_rank: Super Contributor
timestamp: December 22, 2017, 02:02:01 pm
content: There is an inrush current, not because of the motor, which will only add an extra 100VA of inrush to the load, but because the main heating elements will be cold, and have a quite low initial resistance. Expect a current of around 1.5 times the rated for a half second or so, as the coils heat up to warm, which will drop to normal over the half second.

author: ocset
author_rank: Super Contributor
timestamp: December 22, 2017, 02:41:58 pm
content: QuoteThanks, that “kick” (ie high amplitude voltage spike) must have been from the breaking of the inductive current flow in the motor coils.Since the inductive current being broken is at the motor side of the contactor, the “kick” (ie spike in voltage), must have been at the motor side of the contactor?.....as such, this ‘kick’ would not have been ‘visible’ to other equipment fed from the same mains phase?Do you believe that this ‘kick’ or voltage spike actually damages the motor at all?....leading to shorter lifetime?Would it be better if when turned off, the turn-OFF happened at the mains zero crossing, then there would be less of a “kick”?

author: Zero999
author_rank: Super Contributor
timestamp: December 22, 2017, 03:15:30 pm
content: Quote from: treez on December 22, 2017, 02:41:58 pmThere is no high voltage spike when the motor is turned on. That only happens when the motor is turned off. In the case of an AC motor, the spike will occur if it's turned off, close to be point when the AC voltage crosses zero, because that's when the current will be at the highest point, assuming it's lightly loaded and appears inductive.In this case, there's a resistor with a much lower value, in parallel with the motor, which will act as a snubber and absorb any high voltage spike.As mentioned above, the inrush current, due to the motor starting will be tiny, because the current taken by motor is very small, compared to the heating element. I don't even think the heating element will give that greater inrush current, because it will run at a fairly low temperature, compared with a radiant heater. The only way to be sure is to measure it.

author: ocset
author_rank: Super Contributor
timestamp: December 22, 2017, 05:19:27 pm
content: QuoteThanks, i assumed the motor of the fan is always fully loaded (not light loaded)? , when the fan is on, because its rotating at its fixed speed in air. That surely is max load?....if it isnt max load, then the question would be, what is max load?

author: edpalmer42
author_rank: Super Contributor
timestamp: December 22, 2017, 06:54:10 pm
content: Quote from: SeanB on December 22, 2017, 02:02:01 pmI think that would depend of the type of element.Something like an electric stove element - no.Quartz element - basically a light bulb so maybe.ceramic heater - basically a PTC (Positive Temperature Coefficient) resistor - don't knowHere in North America, the maximum you can pull out of a typical circuit is ~1800 watts and you many heaters are rated for 1500W so you won't see much in the way of surge currents or you'll blow the breaker.Ed

author: Zero999
author_rank: Super Contributor
timestamp: December 22, 2017, 07:15:34 pm
content: Quote from: treez on December 22, 2017, 05:19:27 pmI was wrong about the fully loaded statement. All AC motors are inductive, even at full load. Some more than others. It turns out a fan would be quite inductive:I looked at the data sheet for a fan, so see what the power factor is:Power at 50Hz: 45WCurrent at 50Hz: 310mAApparent power: 230×0.31 = 71.3VAPower factor = 45/71.3 = 0.63http://docs-europe.electrocomponents.com/webdocs/121e/0900766b8121e610.pdf

author: SeanB
author_rank: Super Contributor
timestamp: December 22, 2017, 08:27:50 pm
content: Quote from: edpalmer42 on December 22, 2017, 06:54:10 pmElectric stove element internally will be a dull red heat when in use, so quite a big change in resistance cold to hot, that the outside is not glowing is not relevant to the inner in the insulating magnesia powder fill.Quartz element a really big change, seeing as it goes from cold to bright cherry, giving off a fair amount of visible light.Ceramic non PTC heater is more or less just resistive and only a slight tempco, but still there in spades.PTC heater whacking great big current till it gets near the transition temperature, then the resistance varies wildly till losses are balanced by dissipation, which is why you get the cheap glue guns with a PTC that are operable from 90VAC to 260VAC with absolutely no changes, they just run a tiny bit hotter at 250VAC, and tend to fail eventually by blowing the PTC element to powder.

author: Seekonk
author_rank: Super Contributor
timestamp: December 22, 2017, 09:13:03 pm
content: Coiled heating elements that I have seen in applications like clothes dryers are not made og anything much better than cheap steel, definitely not nichrome. there would be a resistance change. Every heating element I've seen, water heater, portable filled oil heater, etc has a far higher resistance and lower wattage than the nameplate specifies.

author: drussell
author_rank: Super Contributor
timestamp: December 22, 2017, 09:55:34 pm
content: Quote from: Seekonk on December 22, 2017, 09:13:03 pmInteresting... I have generally found that most heating elements of various types and styles have drawn remarkably close to their nameplate ratings when they up to operating temperature running on their rated voltage.

author: dmills
author_rank: Super Contributor
timestamp: December 22, 2017, 11:29:17 pm
content: That inductive kick (Which is only really noticeable when in Fan only mode (Hence no big shunt resistor) was found to arc the relay contacts in a power control product I was testing and managed to crash the control processor (It probably kept the contact open verification from working hence putting the system into fail safe).Hey, I did not design the piece of crap system.Those things by the way, even on full heat will cycle the heater, so you cannot really just use them as a dummy load in the 100% sense, but they are a cheap way to dump a couple of kW semi continuously.Regards, Dan.

author: edpalmer42
author_rank: Super Contributor
timestamp: December 22, 2017, 11:41:56 pm
content: Quote from: SeanB on December 22, 2017, 08:27:50 pmI just tested an ancient hot ribbon style heater (~1100W) and a new PTC ceramic heater (~1500W). Neither had a visible startup surge when measured with a Kill-a-watt. The ratings on the PTC heater are interesting. It's actually 1500W @ 25C and 1650W @ 0C.I also have a few stove elements that I use for test loads. Their ratings & measurements are:240V, 1325W (therefore, 43R5 hot), measured 43R0 (cold)" , " 44R7 " (two allegedly identical elements)240V, 2350W (therefore, 24R5 hot), measured 24R0 (cold)The cold measurements were made with a 4-wire milliohmmeter with a 0R1 resolution and 0R0 reading when the leads are shorted.IOW, no surges in these items. Do you have any test data to share?Ed

author: SeanB
author_rank: Super Contributor
timestamp: December 23, 2017, 08:58:49 am
content: No elements easily to hand, but took a Bosch glue gun as test animal. cold resitance 1.47k, and started at 375W when plugged in, then started running down rapidly as it heated up. Gun is rated 2120-240VAC 50-500W, quite a wide swing in power for the PTC element heater in there.

author: Zero999
author_rank: Super Contributor
timestamp: December 23, 2017, 12:52:30 pm
content: Quote from: dmills on December 22, 2017, 11:29:17 pmI didn't consider the fan only mode. I wonder if a small incandescent lamp (15W to 60W) in parallel would fix that issue?

author: dmills
author_rank: Super Contributor
timestamp: December 23, 2017, 04:55:12 pm
content: Oh I was trying to break the control equipment! That is the first step to improving it....I do not doubt that an incandescent load would be well behaved, but that is not the point, the gear should work with **ANY** load within ratings!Regards, Dan.

author: edpalmer42
author_rank: Super Contributor
timestamp: December 23, 2017, 05:41:32 pm
content: Quote from: SeanB on December 23, 2017, 08:58:49 amThe only Bosch glue gun I can find with ratings like that is the GKP 200 CE, but I can't find any mention that it includes a PTC heater. I did see a couple of references that it containstwoheaters. I also see that your 1.47K resistance ( = 32W @ 220V) is close to the wattage (30W) used to keep the unit hot as listed in the manual.The PKP18E glue gun (200W) is widely stated as including a PTC heater.Is yours one of these?Ed