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Bought this on Amazon as a dryer 240V SPD. I was trying to find out if this device is an outright scam. I found a similar post on here from several years ago but that did not answer my question. Apparently this device was originally sold as a "power recovery device," but it appears they rebranded them as dryer surge protectors. Decided to open up the one I bought to see if it even had MOVs inside.

All I found is this giant capacitor.

  • Is this literally a capacitor with a switch that turns on a light?
  • Would this capacitor provide any surge protection in either direction?
  • Might it prevent the dryer from creating a surge?

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enter image description here My best attempt at a schematic. Wire colors are correctly represented, blue is "white" and marked as such. Terminals are as marked on the receptacle.

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    \$\begingroup\$ This is an a usual question from someone tat bought into a questionable technology. Usually the buyer words a post asking us to confirmation that he was right in making the purchase. I commend you in asking, essentially, if you bought into a scam. \$\endgroup\$ Jan 25 at 16:10
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    \$\begingroup\$ @GTElectronics I was desperate to find a surge protector for my new dryer since they all have computers inside now. There seems to be much debate about whether 240V SPDs are needed for new appliances so I thought adding one can't hurt. Hopefully I can prevent others from making the same mistake. \$\endgroup\$
    – Jason P
    Jan 25 at 16:28
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    \$\begingroup\$ The label: "suitable for wet locations." I think not. \$\endgroup\$ Jan 25 at 19:56
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    \$\begingroup\$ The electroncis in the dryer should already be very well "surge" protected as the control board has to operate inside a box with a large motor, several solenoids, as well as moisture & heat & humidity... anything you put externally to that is likely to have almost no benefit, it's like erecting a wooden fence outside a castle wall to protect the houses inside. \$\endgroup\$
    – John U
    Jan 26 at 14:56
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    \$\begingroup\$ The lamp wired across the capacitor provides a discharge path. Nonetheless, treat the cap with caution. \$\endgroup\$ Jan 27 at 6:15

3 Answers 3

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All I find is this giant capacitor. Is this literally a capacitor with a switch that turns on a light? Would this capacitor provide any surge protection in either direction? Wondering if it might prevent the dryer from creating a surge?

This device is NOT a surge protector. While it may have been advertised as such on Amazon (there is not really any control about what vendors say there, so you're on your own) it's clearly labelled as a "Power Factor Correction" device.

Whether this does anything useful depends on your situation. Generally dryers are not really a problem with power factor as the majority of the load is purely resistive with the only inductive load being the small motor that drives the barrel.

Generally homeowners don't care much about PF anyway because in most places the power company doesn't bill residential customers for having bad PF.

So the bottom line is that this device will have little to no effect on "surges" and its impact on your PF is likely insignificant or irrelevant.

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    \$\begingroup\$ Thanks so much! I had a suspicion, reading about how this device was originally marketed as an "energy harvester" being basically a scam. As a ME I can drill the rivets out and crack open the case but that's about it :) \$\endgroup\$
    – Jason P
    Jan 25 at 16:21
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    \$\begingroup\$ Well now that you've got a nice grounded case and a pair of somewhat expensive NEMA 14-30 receptacles, you could toss the capacitor and wire in a surge protection module. \$\endgroup\$
    – vir
    Jan 25 at 17:32
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    \$\begingroup\$ Fully agree with your assessment. Just a little note about dryers: Some (All?) modern dryers use heat exchangers. Those are mostly electric pumps as loads. But those Machines must already have PFC aniway, so no need for an external PFC-Device. Also, an external PFC only helps if it's tuned to the use case. So anything you can buy of the shelf is probably a scam. \$\endgroup\$
    – kruemi
    Jan 26 at 6:20
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    \$\begingroup\$ Related question on Skeptics: Does the "Spike Buster" reduce electricity consumption? \$\endgroup\$ Jan 27 at 8:07
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    \$\begingroup\$ @ratchetfreak: If during each half-cycle at 60Hz a device draws 1.0 joule of energy and then returns 0.75, I think old-style meters would bill that as a 30W load. Are you saying newer meters would bill that as a 120W load, or a 210W load, or something else? \$\endgroup\$
    – supercat
    Jan 27 at 21:28
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A pretty thorough debunking of these ‘power saving’ devices can be found here: http://www.nlcpr.com/Deceptions1.php

Besides this, the box appears to be shoddily made and has no safety approvals. You should unplug it at once, it’s a hazard.

Like many scams, these boxes are based on a small kernel of truth. And that kernel is, applying a capacitor across the line compensates for inductive load influence on power factor. Properly sized (and connected, more below), a capacitor will reduce the dryer’s apparent power, which has a reactive component (the motor’s inductance).

Some background here: https://electricalacademia.com/basic-electrical/power-factor-correction/

So technically it could do something kind of useful, at least when the dryer is running and if its capacitor were connected correctly. Note the weasel-words ‘technically’ and ‘kind of’ and of course, 'if'. We’ll dig into this a bit.

It doesn’t do much of anything to protect against surges however, and being a capacitor, it’s vulnerable to them.

Why bother with a capacitor across the line at all? Non-ideal power factor adds additional load to the utility which must up-provision its infrastructure to handle apparent power, even though the reactive part of apparent power it delivers does no actual work at the consumer side. Utilities will charge large customers for this extra kVA capacity, often as a surcharge for less-than-ideal power factor.

So this power-factor correction technique, capacitors across the line, is used at big plants with lots of large motors. Unlike this dumb box, the plant’s capacitance is adjusted to achieve the best possible PF depending on the load at the time. Capacitors are switched in and out as needed to match the capacitor ‘lead’ with inductor ‘lag’ and thus cancel out the reactive power component seen by the utility.

More about that here: https://www.eaton.com/ecm/groups/public/@pub/@electrical/documents/content/sa02607001e.pdf

For home users, as it stands presently, this simple kind of power factor correction makes no economic sense. The reason is, home utility metering only measures real power regardless of power factor. You don’t get charged for less-than unity power factor like those big plants do.

Because home utility meter only tallies real, not reactive power, you will not save on your electric bill with this device.*

(*This could change down the line, as newer ‘smart’ meters can measure power factor. More here: How do residential analog and smart meters measure power?)

So, yeah, a scam.

That said, correcting power factor in the household is not nothing. There are regulatory initiatives to improve the power factor of appliances and electronics, as a means to make more efficient use of infrastructure.

IT gear is especially of concern these days, so you see power factor correction (PFC) being designed into power supplies above a certain wattage. Another major, emergent power factor pain point would be EV chargers, given their high power and long connection times, so these too benefit from PFC.

But your dryer? Not enough to bother. It’s kind of a small motor anyway (1/2 HP / 375W or so, compared to 5kW for the heating element.)

But the closer you look, the more dodgy this thing gets. The box wires the cap between L1 to L2 (black and red wires.) Dryers sold in 120V countries use a 'split-phase' arrangement, where the 120V motor is wired L1 or L2 to Neutral (white wire), while the heating element is wired between L1 and L2.

(Why? Gas and electric dryers sold in North America generally use the same 120V motor, saving cost and allowing them to be converted in the field. Gas dryers use a 120V plug, electric uses split-phase 240V.)

So the cap is not even connected correctly for a 120V dryer motor: any reactive cancelling it's doing is making its way all the way back to the opposite phase, to the utility pole, then back to neutral.

And even worse, as @Peter Green points out, having this capacitor across the line all the time, even when the dryer isn’t running, actually uses apparent power, working directly against the goal of optimizing household PF. Instead, it should be placed on the motor itself, sized appropriately to give the correct phase shift, and only switched in when the motor is on.

(Ed note: the box has a switch for the cap. You would need to remember to flip it on whenever you start the dryer, then flip it off again when the dryer stops. Not very practical.)

Finally, I see no UL approval on this thing. If it catches fire, and your insurance finds out about it they could use it as a basis to deny your claim.

Like I said, I’d disconnect it at once, and return it to Amazon if you can.

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  • \$\begingroup\$ A "electrical power saving product" is advertised today on a Microsoft Bing News ad. \$\endgroup\$
    – Audioguru
    Jan 25 at 17:52
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    \$\begingroup\$ The other issue I see is that the dryers motor spends more time not running than running. So unless there is a system to disconnect the capacitor when the dryer it not in use I'm doubtful if there is any benefit at all. \$\endgroup\$ Jan 25 at 17:59
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    \$\begingroup\$ Yes, having this gizmo across the line all the time is actually a net loser, PFC wise. So it’s worse than nothing. \$\endgroup\$ Jan 25 at 18:03
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    \$\begingroup\$ @Audioguru the fact that you see an ad on M$ Bing News doesn't make it any more reliable than something you find one the end of a sub-redit. M$ doesn't check the accuracy of claims made in the ads they serve. \$\endgroup\$
    – brhans
    Jan 25 at 20:08
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    \$\begingroup\$ I vaguely recall a lot of washing machine motors have these correctors in-line, located near the motor itself. For a washing machine it makes sense during centrifuge, for a dryer it does not. \$\endgroup\$
    – Mast
    Jan 27 at 12:49
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It's for mains power factor correction, which is what the capacitor is doing across the supply. The box is labelled as such.

Correcting power factor is not a scam but a single box that can correct it for all loads is.

In correcting the power factor, it is attempting to get as much as possible of the power drawn from the supply (apparent power) to be delivered to the load (real power). The power factor is the ratio of the two: ap/rp.

Mains-powered equipment is required to have a power factor of specified value, close to 1, to gain and meet approval standards. The required standards vary by country and region worldwide but the rule's goal is the same.

The amount of power factor correction required by a particular AC load depends on the characteristics of that load circuit. So a single box can't do it for any AC mains load - it depends on the load. Your one may be designed for a particular equipment but it's not marked as such.

Power factor correction is very well documented on the internet. You can read about it here.

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    \$\begingroup\$ But a power factor correction on a resistive load (dryer) will not save too much. It would only be for the low power motor, not the heating elements. And over correcting can cause it's own problems. It is not a one-size-fits-all device, right? \$\endgroup\$ Jan 25 at 16:13
  • \$\begingroup\$ @GTElectronics, correct - I was filling out my answer and managed to miss that out the first time, fixed now. Hasn't satisfied the nameless downvoter, though. \$\endgroup\$
    – TonyM
    Jan 25 at 16:18
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    \$\begingroup\$ @GTElectronics By "too much" you mean "anything at all". :) A resistive load is what we want - power factor correction is used to deal with inductive loads (i.e. motors) and make them appear resistive to the grid. \$\endgroup\$
    – Graham
    Jan 26 at 0:49
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    \$\begingroup\$ @GTElectronics yes, AND anything for the motor should only be connected to the line when the motor is powered, not 24/7. \$\endgroup\$ Jan 27 at 4:11
  • \$\begingroup\$ Re "have a power factor of specified value": Doesn't it depend on the power level? Why would a 2 W device need one? \$\endgroup\$ Jan 27 at 13:58

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