relay minimum permissible load
relay minimum permissible load
(OP)
Hi Forum,
I was going to replace the push button switch in my input voltage divider by a bistable relay. Now I discovered that the relay has a minimum permissible load (10µA @ 10mVDC). Can I replace the switch by the relay and ignore the minimum load? Why doesn't the switch have such restraint?
Regards
I was going to replace the push button switch in my input voltage divider by a bistable relay. Now I discovered that the relay has a minimum permissible load (10µA @ 10mVDC). Can I replace the switch by the relay and ignore the minimum load? Why doesn't the switch have such restraint?
Regards





RE: relay minimum permissible load
If you don't already understand it, you will need to learn about Ohms Law, which will let you calculate the voltage, current, and resistance relationships. You will then need to evaluate your circuit, ie what is the supply voltage, what is the load resistance, etc, to calculate and make sure you are above the ratings of the relay.
RE: relay minimum permissible load
RE: relay minimum permissible load
I'm certainly aware of the relay specs but can anyone tell me the difference between a relay contact and a switch contact? That's the question that puzzles me.
RE: relay minimum permissible load
Switch contacts may be snap acting or operate at the speed that the button is pushed. Relay contacts are generally fast acting.
Better quality switches and relays will have a contact wiping action to clear any contact film.
A few generations ago, when solid state switching was being introduced to industrial automation, GE recommended about 100 volts to pierce contact film.
Your ratings sound like a solid state relay. Is it a solid state relay?
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: relay minimum permissible load
no, it's a usual TQ-relay by Panasonic (5V). When using solid state relays I suspect leakage currents and capacitances spoiling my signal. I'm just reading something about thermal emf of relay contacts, but shouldn't the same apply to switch contacts? There must be a significant difference.Don't all DMMs use switches to select the range?
RE: relay minimum permissible load
RE: relay minimum permissible load
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: relay minimum permissible load
that's a very valuable information. I've checked my TQ-Relay and it has Gold-clad silver contacts. Now it gets complicated, I fear.
RE: relay minimum permissible load
I've read somewhere that such contacts can be used for low level signals, provided that their not ever used for high current switching. Once they're used for high current switching, then the gold cladding may be arced away and then they become silver contacts good for only high current switching from then on.
Stand-by for others to confirm.
RE: relay minimum permissible load
A simple experiment might resolve this issue for you. Measure the contact resistance. Switch the relay once per second for 24 hours (86,000 cycles). With the contacts closed, measure the resistance and see if it has gone up.
RE: relay minimum permissible load
thank you for all your contributions. Probably I must face the truth that it is difficult to replace an ordinary push switch assembly like the ITT Cannon TJ type we've used so far. The problem is that hardly any distributor in Germany has such assemblies available. I was looking only for this reason for a substitute. Perhaps anyone can provide me with a link to a 'switchless' (professional) voltage divider with 2 ranges 1:1 and 10:1 with a voltage protection up to approx. 300Vac and an input resistance of 1 MOhm. Frequency is from dc to 10MHz.
Regards
RE: relay minimum permissible load
Let me also point out that the real key is the voltage. The voltage is what gets thru any contact resistance or oxides.
dau; If you're going to have more than a measly 10mV across this relay quit worrying about it and just use it.
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: relay minimum permissible load
Keep in mind that it does not take much magnetic field to close the circuit, so you have to keep them away from stray electromagnets and idiots with permanent magnets. (Mount in center of enclosure, and make the enclosure at least a few inches in size.)
Mercury-wetted relays can also be bought. They literally avoid the dry contact problem for small signals, yet the mercury surface is not damaged by high currents or reactive loads. (I bet the CE bureaucrats hate these.)
RE: relay minimum permissible load
RE: relay minimum permissible load
Reed relays are inappropriate, I think, because the device will be used in a power electronics environment. For Mercury-wetted relays I'll check the www, haven't heard of them before. But in one respect I agree with many of you: I'll buy such a gold-clad relay and simlply test it. The only difficulty probably is to convince my boss to give it a try.
RE: relay minimum permissible load
The gold plated silver contact relays that you are considering will probably out perform the push button you are replacing.
What are the specs of the switch?
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: relay minimum permissible load
I've tried to find a URL for our used switch but couldn't find one. I'm completely fed up with corporations that aren't able to find their own parts like Philips....and it seems also ITT Cannon. But perhaps they don't manufacture it anymore. I'll try to upload our old pdf. Our future strategy isn't decided yet so don't bother too much over this issue. But it's rather interesting to follow this conversation.
Regards