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Subject: Re: Relay controlling electric doorstrike - kickback protection needed?
References: <3D9CD4D3.2A11DA3F@cox.net> <3DA0A0F7.firstname.lastname@example.org> <3DA0C4DC.A5F160C2@cox.net> <3DA19EE9.email@example.com>
Date: Tue, 08 Oct 2002 05:20:31 GMT
NNTP-Posting-Date: Tue, 08 Oct 2002 01:20:31 EDT
Organization: Cox Communications
Fred et al,
BTW, someone has suggested to me to also include a MOV from each side of
the incoming AC (i.e., the input to the XFRMR) to the 3rd prong GND.
This seems like a little overkill to me, but I'd be interested in
Fred Bloggs wrote:
> ohaya wrote:
> > Fred,
> > Thanks for the VERY detailed response and drawing! This is just what I
> > was looking for.
> > BTW, yes, I am going with the 16VAC Xfrmr (for the 'buzz').
> > Re. the capacitor across the Xfrmr secondary: What is it's purpose?
> This capacitor will shunt the high frequency noise components due to
> rapid turn-off around the transformer and prevent them from entering the
> power line.
> > Also, I'm assuming that since this is AC, I would use a ceramic .01uF?
> > What voltage rating would be safe?
> Some of the capacitors are quite strange about translating from DC to AC
> rating and vice versa. To be safe, use a capacitor with an explicit AC
> rating for "across the line" use. You can find these at Digi-Key also.
> > Fred Bloggs wrote:
> >>ohaya wrote:
> >>>I'm looking into control an electric doorstrike using a device made by a
> >>>company called B&B Electronics called the 232DRIO:
> >>> http://www.bb-elec.com/product.asp?sku=232DRIO&dept_id=83
> >>>According to the website (and the PDF manual there), this device has two
> >>>relay outputs, so I am thinking of using the relay to close the loop
> >>>between a 16VAC transformer and the doorstrike. Here's the page on the
> >>>doorstrike and transformer:
> >>> http://www.smarthome.com/5190.html
> >>>I spoke to (supposedly) and engineer at B&B today, and was asking if the
> >>>232DRIO is used with something like a doorstrike (i.e., an
> >>>electro-mechanical device), whether I needed to add anything to protect
> >>>the relay against kickback, or whether the 232DRIO has protection
> >>>already built in. She couldn't tell me, so I asked if she could tell me
> >>>specifically which relay(s) were used in the device so I could look up
> >>>the specs myself.
> >>>Unfortunately, I don't think the person I spoke to knew much, as she
> >>>kept telling me that there was no relay on the board, and that the relay
> >>>was "on the chip" (presumably the microcontroller) [Note that the
> >>>232DRIO is spec'ed to handle 120VAC].
> >>>I was wondering if anyone has had any experience with the 232DRIO? If
> >>>so, can you provide info about which relay is used?
> >>>If not, I was wondering, in general, if I should add any additional
> >>>circuitry between the relay and the doorstrike to protect the relay?
> >>>Thanks in advance!
> >>You are wise to consider protection for this application. I assume you
> >>are going with the 16VAC version of the door strike power supply. The
> >>nominal volt-ampere characteristics indicate a 64 ohm reactive load so
> >>this will be 170mH in series with about 7 ohms resistive. Because this
> >>application will see frequent activation, relay contact protection is a
> >>must. In this case, I suggest a series combination of low cost varistor
> >>and flameproof metal oxide resistor across the relay contacts, as well
> >>as a 0.01uF wired directly across the transformer secondary. In addition
> >>to protecting the contacts, there is always the typical wiring
> >>insulation rating of 150V to consider as well. If you go with the
> >>Panasonic D-series ZNR available from DIGI-Key, in particular the
> >>ERZV07D330, in series with a 2 Watt 100 ohm flameproof metal oxide
> >>resistor, you will limit the peak kickback voltage to just a little more
> >>than 100V in the absolute worst case extreme of 30% high line in
> >>coincidence with contact opening at exactly current peak. The resistor
> >>will ensure that turn off will be short and overdamped- less than 1msec-
> >>and this will place your operating point at well under the stress limits
> >>giving over 10^6 activations on the "Impulse Derating" chart of the ZNR.
> >>Connect the parts using gas tight uninsulated crimp connections to
> >>eyelet for the relay screw terminals- do not wrap the leads directly
> >>onto the terminals. The finished circuit will look like this and cost
> >>under a dollar.
> >> View in a fixed-width font such as Courier.
> >> ---------------------+---------+
> >> | | |
> >> | o COM |
> >> | / |
> >> | / ---
> >> | / /
> >> +-----+ o NO / ERZV07D330
> >> | | | ---
> >> ) | | |
> >> ) |0.01U | |
> >> XFMR ) --+-- | /
> >> SECNDRY ) ----- | 100
> >> 16VAC ) | | /
> >> ) | | \ 2W
> >> | | | |
> >> +-----+ +---------+
> >> | |
> >> | |
> >> | +-------------+
> >> | | DOOR STRIKE |
> >> | +-------------+
> >> | |
> >> | |
> >> +------------------------------+
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