It's your Reinheitsgebot heritage!
;-)
--
"For a successful technology, reality must take precedence
over public relations, for nature cannot be fooled."
(Richard Feynman)
Most relays are not designed that way. The clapper hits up against a core and the magnetic circuit is then closed. The contact force is controlled by the spring constant of the contact leafs or something like that and the "overtravel"- it's independent of the coil current. The force to dislodge the clapper goes up dramatically when the relay closes. One can reduce the current when the relay has closed, but it reduces the required force to dislodge the clapper. There is an opposing force from a spring that is trying to open the relay, so a small shock could cause the contacts to open a bit and then close, or to open and stay open, depending on the nature of the shock, the relay design and current.
If you're designing using relays for wide temperature ranges, you also should be aware that they are actually current-operated devices that have a given resistance at a certain temperature. Since the coils are usually copper wire, they increase in resistance at about +0.4%/°C, which can be quite significant at high temperatures (the coils self-heat too, of course).
Generally, safer relays (better coil-to-contact breakdown and better open contact gap) are a bit less efficient, just the way the world works.
Yeah, I grew up in Westphalia where beer counts as "basic nutrition". I did violate the Reinheitsgebot a lot though. Not so much when making beer but for example by drinking Grolsch which had (has?) corn in it. When I asked the tour guide at that brewery whether they had any problems exporting to Germany because of that the guide (a retired brewmaster) said "Well, if they don't like it then they aren't going to get any!"
-- Regards, Joerg http://www.analogconsultants.com/
I know. T'is why I am getting some to test that. Also to exercise for endurance.
-- Regards, Joerg http://www.analogconsultants.com/
Yup, this is one of those proverbial "between a rock and a hard spot" situations.
-- Regards, Joerg http://www.analogconsultants.com/
If life is important you have to worry about the catch diode slowing the opening, which can result in less than the rated 50,000 or 100,000 operations at full load. Of course you can open that up electrically, but the driver starts to look a bit complicated.
Nah! Don't use a catch diode... protect differently and easily... but I don't "know anything about relays", so I guess I should just shut up :-) ...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
On injectors I usually let that fly up higher but not here. Essentially the relay remains engaged for hours on end. This is why I need to be mindful of the power consumption. What baffles me are the high frequencies in the typical "backoff type" solenoid driver. Their PWM runs above 100kHz. Ok, I can understand that they want to be above the audible range of humans and animal. But >100kHz sounds wasteful. Oh wait ... maybe the International Brotherhood of Bats fought that one through Congress :-)
-- Regards, Joerg http://www.analogconsultants.com/
yeh injectors are usually driven with a voltage clamped fet so it closes fast, that is fine for high impedance ~16 ohm automotive injectors
but it is a mess when you want to pwm low impedance ~1 ohm, then you want the slow decay from a diode or you will fry the fet, until you turn then off you want the fast decay from the higher voltage clamp.
what is needed is really a clamp diode you can "turn off"
-Lasse
-Lasse
He's talking about PWM'ing, which means you either compromise the relay life or you have to provide three output states, right?
Whether you PWM, or not, you still must provide some "catch" function, which will provide the "flywheel".
I don't understand the "compromise relay life"??
There _could_ be some issues with guaranteeing hold-in... maybe run
100% for pull-in, then drop back to PWM controlling at a specified current.I've done that linearly for old-fashioned fixed-inductive- energy-storage ignition systems... but linear dissipates power. ...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
The purpose of PWM'ing is to reduce the power consumed by the relay. If you dump that energy on each PWM off cycle into a high voltage dissipative catch device then you don't get as much saving. A diode (or active switch) that directs the current with little drop yields maximum energy savings.
If you just put a diode across the coil, then the relay opens more slowly so the relay life is reduced. The specs almost always assume that there is no catch diode.
I think for ICs you did this to save a pin for the catch diode to the relay supply (or maybe there's some reason to do with the process), but it also has other benefits (the downsides being a bit of dissipation in the catch element and perhaps a bit worse EMI).
Sure..
Nah, I PWM'd mine at tens of kHz, no problem.
Exactamente!
-- Regards, Joerg http://www.analogconsultants.com/
to
driver doesn't get hot when you dump all that energy in the clamping every cycle of the pwm?
I've looked at few ways of doing it but it required access to both ends of the injector or a floating gate drive
-Lasse
OK. Use my electronic "catch"... for PWM have it behave as a catch diode... upon "off command" have it go higher voltage... interesting problem... I already see how to do it on a chip :-)
For discrete applications, a wee-bit harder.
But Joerg indicated a "mostly-on" situation, so maybe just a catch diode will be OK... depends on whether the load can cause arcing.
Didn't want an external part... you know the drill ;-) And on-chip diodes produce undesirable substrate currents.
I don't know. My first application of the scheme was for Ethernet relays, and EMI was never complained of.
...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
So you can croak your driver ?:-) ...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
Can they legally sell it as "bier", or do they have to call it something else, like "auslandsbier"?
--
"For a successful technology, reality must take precedence
over public relations, for nature cannot be fooled."
(Richard Feynman)
I *love* pumpkin pie.Only trouble is, it goes through me like a 'possum up a drainpipe ;-)
--
"For a successful technology, reality must take precedence
over public relations, for nature cannot be fooled."
(Richard Feynman)
to
No, because during operation the current is being recycled. Only upon closure is it dissipated, and fast. I could have recycled that energy into the vehicle system as well but the client said it was unimportant because this energy spike was so miniscule.
Anyhow, nothing gets hot on there.
Mine doesn't need that :-)
But I can't post the schematic or I'll get shot.
-- Regards, Joerg http://www.analogconsultants.com/
to
Huh? Of course you don't let this get to lots of kilovolts. I cut under
100V but that sure made for a darn fast closure. Could have done 200V, 500V or whatever but with the piston I dealt with it made pretty much no difference once we were above a few tens of volts.-- Regards, Joerg http://www.analogconsultants.com/
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