Antistatic mat - Page 1
Forum section: electronics / beginners

author: tony3d
author_rank: Frequent Contributor
timestamp: November 15, 2013, 06:27:03 pm
content: Hi All, I just bought an antistatic mat which has a banana plug for earth ground. Is it safe to plug this into my Korad's green ground on my power supply? There would be no chance of hurting the power supply from a large static shock correct? My new solder station does not have a banana plug like my old one did. I checked with my multimeter, and the Korad does have continuity between the plug, and the ground lug on the power cord. Thanks.

author: ejeffrey
author_rank: Super Contributor
timestamp: November 15, 2013, 06:33:34 pm
content: This is fine. The ground strap has a high resistance anyway, so there will be no large current flows. The idea is to slowly bleed away charge and avoid a sudden discharge. The only potential problem is that you might unplug the power supply and forget that your mat is no longer grounded. For that reason it would be preferable (but not necessary) to have a dedicated ground connection. This should only be a problem if you physically unplug the supply. The main power switch should not disconnect the ground pin.

author: wraper
author_rank: Unknown
timestamp: November 15, 2013, 09:06:15 pm
content: Connect mat through 1M resistor to the mains earth.

author: wraper
author_rank: Unknown
timestamp: November 15, 2013, 09:09:42 pm
content: or maybe it already have that resistor.

author: rolycat
author_rank: Super Contributor
timestamp: November 15, 2013, 10:22:57 pm
content: For optimum safety, don't use any old 1M resistor - not all of them are rated for mains voltages.Our very own free_electron recommends three 470K resistors - 1/2 Watt or better. Solder in series, cover in heat-shrink tubing and wire into a mains plug between the earth pin and a firmly attached banana jack. Remove the supply pins or insulate them with hot snot glue.Or if you have the money, you could always just buy an earth bonding plug.

author: gotvolts
author_rank: Contributor
timestamp: November 15, 2013, 10:55:52 pm
content: Do not plug your anti-static mat into your power supply.Why? Because your power supply may become unplugged and at that point you will lose your ground connection without even knowing it. Just run a wire from your antistatic mat to a hard ground connection at the outlet or nearby.Also, do not use anti-static mats when running voltages over 30V, and ESPECIALLY do not use wrist straps for any energized voltage period over 30V as well, especially if there is line voltage present. Major safety hazard.

author: rolycat
author_rank: Super Contributor
timestamp: November 16, 2013, 12:02:25 am
content: Quote from: gotvolts on November 15, 2013, 10:55:52 pmejeffrey made this point earlier. A power supply earth terminal is better than nothing if the OP doesn't (yet) have a safe earth bonding point. However, running a wire directly to any hard ground is potentially dangerous, and the connection should have a suitable resistance in series.QuoteDave recently did a teardown of a 250V power supply. The PCBs were sitting on his anti-static mat while he probed voltages in excess of 500V. Are you saying he doesn't know what he's doing?

author: tony3d
author_rank: Frequent Contributor
timestamp: November 17, 2013, 03:36:47 am
content: Quote from: wraper on November 15, 2013, 09:06:15 pmThe mat does have a 1 mega ohm resister in line.

author: G7PSK
author_rank: Super Contributor
timestamp: November 17, 2013, 11:36:59 am
content: Either get an antistatic plug or a bench connector like one of these. They are cheap enough not to have to bother with compromises.http://www.ebay.co.uk/itm/Antistatic-ESD-Earth-Bonding-Plug-UK-1M-OHM-Multi-Listing-/321092991965?pt=LH_DefaultDomain_3&var=&hash=item4ac2a23bddhttp://www.ebay.co.uk/itm/ESD-Ground-Block-Under-Bench-Common-Point-for-Anti-Static-Armband-Wrist-Strap-/281157859534?pt=UK_Computing_Other_Computing_Networking&hash=item41765078ce

author: rolycat
author_rank: Super Contributor
timestamp: November 17, 2013, 12:15:31 pm
content: Quote from: G7PSK on November 17, 2013, 11:36:59 amI think I'd rather trust a competently home-made earth bonding plug than that Chinese POS, and you're still going to need a grounding point to connect it to.From the description:"Wrist strap group withou resistor"Sounds like it doesn't have a high value resistor, and even if it does would you trust it?Also, UK earth bonding plugs like the one linked to aren't going to be much use to the OP, who is in the States. I couldn't find a US plug for a reasonable price; maybe that's why free_electron suggests making your own?

author: SLJ
author_rank: Frequent Contributor
timestamp: November 17, 2013, 01:10:28 pm
content: AS I said somewhere else, just make your own.

author: Nerull
author_rank: Frequent Contributor
timestamp: November 17, 2013, 02:39:35 pm
content: Quote from: rolycat on November 17, 2013, 12:15:31 pmMost straps put the resistor in the cord not the bonding point. A resistor in the bonding point will not protect you against something plugged into the second grounding point from touching something grounded directly.

author: rolycat
author_rank: Super Contributor
timestamp: November 17, 2013, 03:18:13 pm
content: Quote from: Nerull on November 17, 2013, 02:39:35 pmMy bonding point was bought from a company specializing in ESD products and contains three 1M resistors; one for each connection:I believe Dave has a similar item mounted under his bench.The cord for the wrist strap also has a 1M resistor.

author: SLJ
author_rank: Frequent Contributor
timestamp: November 17, 2013, 03:38:25 pm
content: Grounding points don't need resistors. As was said above wrist straps have a 1M resistor already and mats are about a zillion ohms anyway.If you have a wrist strap without a resistor that goes straight to ground throw it away as it's dangerous as f*#!.

author: G7PSK
author_rank: Super Contributor
timestamp: November 17, 2013, 04:33:04 pm
content: All grounding points seem to have built in resistors as do the wrist strap and mat leads so you end up with 2 meg of resistance, dose not appear to make any difference to static bleed off though.

author: rolycat
author_rank: Super Contributor
timestamp: November 17, 2013, 04:40:47 pm
content: Quote from: G7PSK on November 17, 2013, 04:33:04 pmI'm beginning to suspect that - as usual - US practice differs from the rest of the world on this issue.

author: zapta
author_rank: Super Contributor
timestamp: November 26, 2013, 04:49:25 am
content: Quote from: G7PSK on November 17, 2013, 04:33:04 pmThe one I got did not have resistor on the long wire, just on the one that connects to the wrist.

author: Avotronics
author_rank: Regular Contributor
timestamp: November 26, 2013, 08:14:49 pm
content: Mine has 1M resistor in wrist strap, none n the long wire, then another 1M in the plug. UK

author: Fsck
author_rank: Super Contributor
timestamp: November 26, 2013, 08:37:52 pm
content: my system has a 0.2ohm grounding point to which I connect the mat or the 1M wrist strap.so, only one 1M resistor between me and earth.

author: nanofrog
author_rank: Super Contributor
timestamp: November 26, 2013, 10:32:08 pm
content: No resistor in thegrounding blockI have at all.So only the 1M in the wrist strap in my case.

author: Avotronics
author_rank: Regular Contributor
timestamp: November 26, 2013, 10:53:00 pm
content: 1M is fine.

author: wilheldp
author_rank: Regular Contributor
timestamp: November 26, 2013, 11:29:49 pm
content: How important is it that you wear the wrist strap when working on the mat? Will the mat just dissipate the static if you touch it periodically, or do you need to be in constant contact with either the mat or strap?

author: lewis
author_rank: Frequent Contributor
timestamp: November 26, 2013, 11:42:30 pm
content: Quote from: nanofrog on November 26, 2013, 10:32:08 pmCrimp terminal

author: rolycat
author_rank: Super Contributor
timestamp: November 27, 2013, 01:23:29 am
content: Quote from: wilheldp on November 26, 2013, 11:29:49 pmAny static-safe workstation in industry has a minimum requirement that a table mat and a wrist strap are both used and both grounded through a safety resistor.You can build up a static charge in seconds just by wearing polyester clothing, so if you happen to touch a sensitive component after building up such a charge you could damage it.Also, bear in mind that the surface of an ESD mat will typically have a resistance to ground in the hundreds of megohms, so discharge will be much slower than through a wrist strap.You can work out how long it will take using the equations for capacitor discharge, since the human body has a capacitance of around 10 to 200 pF, depending on environmental conditions. For example, a static charge of 3 kV will take around a third of a second to discharge to below a volt, assuming a body capacitance of 200 pF and a mat with a 200 megohm resistance to ground.

author: nanofrog
author_rank: Super Contributor
timestamp: November 27, 2013, 04:57:04 am
content: Quote from: Avotronics on November 26, 2013, 10:53:00 pmJust putting it out there for comparison's sake between US & UK grounding products/practices.Quote from: lewis on November 26, 2013, 11:42:30 pmYeah, the one in the pic is really pathetic.

author: GoatZero
author_rank: Regular Contributor
timestamp: November 27, 2013, 07:29:42 am
content: does anyone here know of a way to test is the mat is doing its work?, i have my grounding point and mat conected to mains earth however sometimes i unplugit by mistake, and i dont even notice, how can i test the "antistatic" in the mat?

author: nanofrog
author_rank: Super Contributor
timestamp: November 27, 2013, 07:45:49 am
content: Quote from: GoatZero on November 27, 2013, 07:29:42 amESD Workstation Monitor (example)

author: GoatZero
author_rank: Regular Contributor
timestamp: November 27, 2013, 08:45:08 am
content: Quote from: nanofrog on November 27, 2013, 07:45:49 amIs there a way to test the mat without having to pay 160 USD? a DIY monitor maybe?

author: rolycat
author_rank: Super Contributor
timestamp: November 27, 2013, 10:26:59 am
content: Quote from: GoatZero on November 27, 2013, 08:45:08 amA multimeter would work fine. The resistance between one of the snaps on the mat and ground should be just a few megohms. If you wanted a dedicated visual tester, a simple LED circuit with a high impedance input should do the job.

author: G7PSK
author_rank: Super Contributor
timestamp: November 27, 2013, 03:54:55 pm
content: The grounding plug that I have has a 1 meg. resistor for each of the 3 attainment points, so you get 1 meg between terminal and earth pin and 2 meg between two terminals. That makes it 4 meg ohms between my wrist strap an the ESD mat.

author: nanofrog
author_rank: Super Contributor
timestamp: November 27, 2013, 07:13:48 pm
content: Quote from: GoatZero on November 27, 2013, 08:45:08 amSure. Check eBay if you're after a ready-made product (used or Chinese clone), or even look for circuit designs online & build one yourself (impedance monitor that indicates high, low, pass; add an audible signal if you want if it's not within pass range <750k - 10M is what they're commonly designed for Pass range IIRC>).Quote from: rolycat on November 27, 2013, 10:26:59 amIf GoatZero was to do so each time before starting work on the bench, absolutely.But the way I read that post (forgetfulness of what's plugged into a mains socket or not), it seemed a continuous monitor would help with this issue better than a spot check method/device (still has limits, such as needing a working battery). One with an audible alert would be better than just an LED indicator IMHO, as the sound is a "hey, you unplugged the ground" reminder.

author: zapta
author_rank: Super Contributor
timestamp: November 27, 2013, 09:15:54 pm
content: Is it important to actually connect to ground or is it sufficient to have the mat, strap, solder iron, etc at the same potential?

author: JohnnyGringo
author_rank: Regular Contributor
timestamp: November 27, 2013, 09:42:23 pm
content: Quote from: zapta on November 27, 2013, 09:15:54 pmAnd you, hence the wrist strap.

author: rolycat
author_rank: Super Contributor
timestamp: November 27, 2013, 10:01:39 pm
content: Quote from: zapta on November 27, 2013, 09:15:54 pmWithout such a connection the whole system could reach a high potential with respect to ground. That's fine until you introduce anything thatisgrounded, like a scope probe, or a USB cable. It's really not a good idea.

author: Dave Turner
author_rank: Frequent Contributor
timestamp: November 27, 2013, 10:02:25 pm
content: I plug my Grounding plug into the same distribution strip that all my equipment plugs into. The plug has an inbuilt 1Mohm between the earth pin and the external clip. The cord that connects this clip to the splitter clip on my ESD mat also includes a 1Mohm resistor. Between the splitter clip and the wrist-strap there is a 2Mohm resistance.I bought my ESD mat fromwww.PCValet.co.uk1200 x 500 x 2mm for approx £50. Solder resistant etc. just as Dave advises, except I prefer the grey rather than the blue.

author: Kjelt
author_rank: Super Contributor
timestamp: November 27, 2013, 10:19:26 pm
content: So what to do if your entire workbench is behind an isolation transformer?The only thing I could think of is still to make sure that the new virtual ground point is high impedance coupled to the real ground, thus to have two high voltage 1/2W resistors of 560k to earth ground.It would still be safe since through 1,2M no lethal current can flow and it remains ESD safe.

author: KJDS
author_rank: Super Contributor
timestamp: November 28, 2013, 09:14:05 am
content: The resistance of an antistatic mat is non-linear with voltage. Think of it as islands of conductors in a sea of insulator. Once the voltage applied is enough to break down the gaps between the conductors it becomes a good conductor to dissipate static. A charge decay meter is the most accurate way of determining its effectiveness.http://www.idbsystems.co.uk/ESW/Files/ID-489_New_Data_Sheet.pdf

author: Avotronics
author_rank: Regular Contributor
timestamp: November 28, 2013, 09:36:21 pm
content: Quote from: Dave Turner on November 27, 2013, 10:02:25 pmDitto. I got mine there, they aren't bad quality. 2M total resistance also.

author: zapta
author_rank: Super Contributor
timestamp: November 29, 2013, 12:13:58 am
content: Desco has a ground only plug with banana socket. There are similar products for other socket types.http://desco.descoindustries.com/DescoCatalog/GroundingHardware/BananaPlugAdaptors/09838/#.UpfbAmRDuPA