I am planning to use two coil latching relays - Panasonic *TX2-L2-12V* -
in a control circuit. I have discovered a rare condition in which both set and reset coils couls be energised. Would this damage the relay and, if not, how would it operate? IO presume that it depends on which coil is energised first __________________________________________ David C Brown 43 Bings Road Whaley Bridge High Peak Phone: 01663 733236 Derbyshire eMail: [hidden email] SK23 7ND web: www.bings-knowle.co.uk/dcb <http://www.jb.man.ac.uk/~dcb> *Sent from my etch-a-sketch* -- http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist |
David C Brown wrote:
> I am planning to use two coil latching relays - Panasonic *TX2-L2-12V* - > in a control circuit. I have discovered a rare condition in which both set > and reset coils couls be energised. > > Would this damage the relay ... Probably not. > ... and, if not, how would it operate? I'd presume that it depends on which > coil is energised first Actually, just like any electronic S-R latch, it's more likely that it depends on which coil is energized *last*. -- Dave Tweed -- http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist |
The datasheet gives very little information on how this relay actually
works, but I think there is a permanent magnet in there that holds the contacts in the latched position. I think we have three magnetic fields: the permanent magnet, the latch coil, and the unlatch coil. When neither coil is energized, the permanent magnet is strong enough to hold the contacts in the latch state, but not strong enough to pull the contacts from the unlatched state to the latched state. When the latch coil is energized, its magnetic field is added to the permanent magnet field creating a field that is strong enough to overcome the relay hysteresis and pull the contacts to the latched position. When the latch coil current is removed, the permanent magnet holds the contacts in the latched position. When the unlatch coil is energized, it generates a magnetic field that opposes that of the permanent magnet. The total field is no longer strong enough to hold the contacts in the latched position, and the contacts move to the unlatched position. When the unlatch coil current is removed, the permanent magnet field is the only field present, but it is not strong enough to pull the contacts to the latched position. There are several possibilities for when both coils are energized. In general, I think the contacts will stay in the position of the first coil to be energized while both are energized, but then move to the position indicated by the last to be energized. For example: 1. Latch coil energized - move to latched positon. 2. Unlatch coil energized - Total magnetic field now just the permanent magnet (latch and unlatch fields cancel), so we stay in the current latched position. 3. Latch coil de-energized - Now the unlatch coil cancels the permanent magnet field, so the contacts move to the unlatched position. Latching relays are interesting! Many years ago I needed to convert momentary contact closures to ground to a set of latched contacts. I did this by putting two resistors in series with the relay coil, one on each side. So the circuit was +12V to resistor to coil to resistor to ground. To latch the relay, the resistor to ground was shorted by grounding that side of the relay coil. This increased the coil current above the pull-in current so the relay pulled in. When the momentary closure was removed, the relay coil current was above the hold current, so the relay stayed latched. To unlatch the relay, the side of the coil with the resistor to plus supply was grounded. This removed the relay current, so the relay released. When the short to ground was removed, relay current returned, but it was not enough to pull in the relay, so it stayed released. Finally, on powering both coils, the only issue I can think of is that if this is done for a long period of time, the dissipation in the coils will be higher than normal. This would result in higher coil temperature, higher coil resistance, and change in relay characteristics. As I recall, the datasheet has information on temperature characteristics. Harold > David C Brown wrote: >> I am planning to use two coil latching relays - Panasonic *TX2-L2-12V* - >> in a control circuit. I have discovered a rare condition in which both >> set >> and reset coils couls be energised. >> >> Would this damage the relay ... > > Probably not. > >> ... and, if not, how would it operate? I'd presume that it depends on >> which >> coil is energised first > > Actually, just like any electronic S-R latch, it's more likely that it > depends > on which coil is energized *last*. > > -- Dave Tweed > -- > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > -- FCC Rules Updated Daily at http://www.hallikainen.com Not sent from an iPhone. -- http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist |
It is possible that there would be contact damage due to low pressure.
When a normal relay is "off" the spring holds the NC contacts closed with a certain amount of force. When "on", the coil holds the armature, and there is usually some spring action in the armature, actually reducing the contact force. Without seeing the mechanicals, my best guess would be that the armature would be weakly touching one side or the other. At high currents this could cause heating of the contacts, or if you get it just perfectly wrong it could arc. Just my supposition, not saying this will happen. On Sat, Jun 27, 2020 at 11:06 AM Harold Hallikainen < [hidden email]> wrote: > The datasheet gives very little information on how this relay actually > works, but I think there is a permanent magnet in there that holds the > contacts in the latched position. > > I think we have three magnetic fields: the permanent magnet, the latch > coil, and the unlatch coil. When neither coil is energized, the permanent > magnet is strong enough to hold the contacts in the latch state, but not > strong enough to pull the contacts from the unlatched state to the latched > state. When the latch coil is energized, its magnetic field is added to > the permanent magnet field creating a field that is strong enough to > overcome the relay hysteresis and pull the contacts to the latched > position. When the latch coil current is removed, the permanent magnet > holds the contacts in the latched position. > > When the unlatch coil is energized, it generates a magnetic field that > opposes that of the permanent magnet. The total field is no longer strong > enough to hold the contacts in the latched position, and the contacts move > to the unlatched position. When the unlatch coil current is removed, the > permanent magnet field is the only field present, but it is not strong > enough to pull the contacts to the latched position. > > There are several possibilities for when both coils are energized. In > general, I think the contacts will stay in the position of the first coil > to be energized while both are energized, but then move to the position > indicated by the last to be energized. For example: > > 1. Latch coil energized - move to latched positon. > > 2. Unlatch coil energized - Total magnetic field now just the permanent > magnet (latch and unlatch fields cancel), so we stay in the current > latched position. > > 3. Latch coil de-energized - Now the unlatch coil cancels the permanent > magnet field, so the contacts move to the unlatched position. > > Latching relays are interesting! Many years ago I needed to convert > momentary contact closures to ground to a set of latched contacts. I did > this by putting two resistors in series with the relay coil, one on each > side. So the circuit was +12V to resistor to coil to resistor to ground. > > To latch the relay, the resistor to ground was shorted by grounding that > side of the relay coil. This increased the coil current above the pull-in > current so the relay pulled in. When the momentary closure was removed, > the relay coil current was above the hold current, so the relay stayed > latched. > > To unlatch the relay, the side of the coil with the resistor to plus > supply was grounded. This removed the relay current, so the relay > released. When the short to ground was removed, relay current returned, > but it was not enough to pull in the relay, so it stayed released. > > Finally, on powering both coils, the only issue I can think of is that if > this is done for a long period of time, the dissipation in the coils will > be higher than normal. This would result in higher coil temperature, > higher coil resistance, and change in relay characteristics. As I recall, > the datasheet has information on temperature characteristics. > > Harold > > > > > David C Brown wrote: > >> I am planning to use two coil latching relays - Panasonic *TX2-L2-12V* - > >> in a control circuit. I have discovered a rare condition in which both > >> set > >> and reset coils couls be energised. > >> > >> Would this damage the relay ... > > > > Probably not. > > > >> ... and, if not, how would it operate? I'd presume that it depends on > >> which > >> coil is energised first > > > > Actually, just like any electronic S-R latch, it's more likely that it > > depends > > on which coil is energized *last*. > > > > -- Dave Tweed > > -- > > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > > View/change your membership options at > > http://mailman.mit.edu/mailman/listinfo/piclist > > > > > -- > FCC Rules Updated Daily at http://www.hallikainen.com > Not sent from an iPhone. > -- > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist |
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