Best Relay

[audiomick]

I think so, and am assuming so until I learn something that contradicts that.

As far as I understand it, inductive and capacitive loads are more to do with A.C. circuits than D.C. .

We have inrush current to an extent on the motorcycle: conventional light bulbs, starter solenoid, the starter motor.

However, the inrush current on the relatively small light globes on a motorcycle is not such an issue, I think.

As far as the starter solenoid goes, there is enough discussion about that elsewhere in the forum (Startus Interruptus etc.), and the starter motor itself gets its power more or less direct from the battery, so that is not an issue regarding the relays.

The ECU probably has a certain amount of inrush current, but I can't imagine it is large enough to be relevant. The steady state of the electronics should resemble a resistive load, as far as I know.

 

It occurs to me to mention why I am spending so much effort on this when there are known relay types that are adequate for the job. The answer to that is, I want to understand why they are sufficient, and which of the myriad of specifications are actually directly relevant to the application on a motorcycle. It is not really neccessary to know all that, but I am curious.

[audiomick]

15 hours ago, docc said:

 these relay contact ratings:

Carry = Continuous = Resistive = Resistance Load ?

Hold the presses. I think that is turned around. It should be "resistive load" and "resistance".

Resistance is how much a component resists the flow of current through itself. As noted earlier, work done (power in Watt) is the product of Volts and resistance. Resistance seems generally to be quoted in the spec. sheets for the switching coil, and therefore isn't related to the current capacity on the load side of the relay.

Resistive load is the load that is induced by a resistance. As far as I understand it, this is related to what is called "carry" and / or "continous" load in as much as it specifies what sort of load is being continously carried.

[audiomick]

more thoughts, which may or may not be useful.

 

The relevance of the "maximum temp." specs have been floating around in my head all day.

This confims what I already knew, i.e. that the resistance of a metallic conducter increases with increasing temperature:

https://www.toppr.com/ask/question/why-does-resistance-of-a-metallic-conductor-increase-with-increase-in-temperature/

The relevant temperature seems to me to be the temperature of the coil. Given that the coil presents a resistance to the volts applied to it, it is going to get warm when it is activated. A resistor (in this case the coil) always gets warm when current passes through it.

Something that is warm or hot is at a higher energy level than something that is cold, so the heat in the relay from the coil will be trying to get to the cooler air around the relay. Energy always travels from the higher state to the lower state.

Therefore the ambient temperature is relevant to the operation of the coil.

We already had made the point that the coil needs more volts to activate the relay when it gets warmer. If we take it as given that the available electrical potential (volts) is a constant, then the various formulae show that the coil is going to exert a weaker pull when it gets warmer.

Power = volts x current

https://en.wikipedia.org/wiki/Electric_power

Volt is constant, so power is reduced when current is reduced

Current = volts divided by resistance

https://en.wikipedia.org/wiki/Ohm's_law

so the higher the resistance, the lower the current.

i.e. the warmer the coil gets, the less "pull" it can generate to acivate the relay.

Secondary to that, the load contact, i.e. the contact that the relay is making, is also a resistance. Contacts always are. If the relay is switching close to or over its rated current, this contact is also going to be getting warm, and that heat is most likely adding to the heat in the coil because they are all in a tiny little box together.

When the coil gets too warm, and "weak" as a result, it seems to me to be likely that the contact that the relay is making is likely to start jittering, or even open slightly and stay that way. This would lead to arcing, as has been referred to earlier, with the result that the load contact would either weld closed or erode away into uselessness. At this point, the relay has failed.

 

Having said all that, I seriously doubt that the ambient temperature around the relays in a V11 would even get close to the numbers I have been seeing in spec. sheets (typically 85°C and 125°C). I have an idea how I might be able to check on that, but I'll get back to that sometime when I have had a chance to try it out.

 

Anyway, I tend towards the following conclusion: We have discussed the lower permissable switching current at higher temperature ( e.g. 20 A. @ 85°C when the nominal switching current is 35 A.). Obviously the highest possible switching current is desirable, but I don't think that the maximum temperature is likely to be reached in our application. Therefore, I don't think we need to get leery about those "maximum temp." specs. .

 

If anyone can see a fault in the logic, please say so.

[audiomick]

a P.S. to the last post:

16 hours ago, audiomick said:

When the coil gets too warm, and "weak" as a result, it seems to me to be likely that the contact that the relay is making is likely to start jittering, or even open slightly and stay that way....

... I seriously doubt that the ambient temperature around the relays in a V11 would even get close to the numbers I have been seeing in spec. sheets (typically 85°C and 125°C). ...

... I don't think that the maximum temperature is likely to be reached in our application. Therefore, I don't think we need to get leery about those "maximum temp." specs. .

I spoke to my electronic technician colleague again today. He confirmed those assumptions, and went on to say that for our application, pretty much only the stated switching current is directly relevant.

[docc]

How shall we apply this knowledge to this particular datasheet for the Picker Components relay? . . .

CONTACT RATING:

     1C |  30A @ 14VDC, resistive

          |   25A @ 14VDC, resistive

CONTACT DATA:

     Maximum Continuous Current  |  35A *

https://pickercomponents.com/pdf/Relays/PC782.pdf

[* Probably the Form 1A SPST specification.]

 

[audiomick]

I find it interesting that they quote "Maximum Switching Power 350 W" (power rather than current). Given that, they are a little inconsistent (I think) by not quoting a voltage for the maximum continuous current. Note that there are voltages given in the contact ratings. I consider it impossible that the maximum current could be the same at any voltage, but I might be wrong.

That they specify maximum switching power allows the assumption that a voltage other than 12V could be switched by the relay.

Further up I linked to this:

https://en.wikipedia.org/wiki/Electric_power

where we can see that p = VI, i.e. power is the product of Volts x current.

We are talking about motorcycles with a nominal (there's that word again...) voltage in the wiring system of 12 V. That means that, according to the specification of 350W switching power, the relay can safely switch 29,17 A. at the nominal 12 V.

As we all know, in a healthy electrical system on a motorcycle the voltage is more like 12.8 V or so, so the real world current that can be safely switched is slightly lower. That this figure is lower than the the continuous carrying current should be no surprise, as we had already established further up that it is generally the case that the "carry" current is higher than the "switching" current.

If we consider other voltages and the specification of maximum switching power, then the relay can safely switch anything between 350 A @ 1V to 1A @ 350V. Theoretically, at least.

Some more maths:

Take the spec 1C : NO 30A@ 14V DC.

30x14= 420 Watt.

go back to the nominal 12V in the electrical system:

420 / 12 = 35

which is the stated continous current. Once again, I think they are a bit inconsistent in those specs, i.e. jumping around with the voltages they are assuming,  but I'm guessing.

 

Anyway, on the basis of those specs I would assume a safe switching current on a motorcycle of around 30 A., and a safe continuous (carrying) current of 35 A as stated on the spec sheet.

If the relay gets really hot, those figures will both be lower, but I as already mentioned, I don't think the relays are likely to get that hot on a V11.

 

[docc]

I'll have to read that last post more thoroughly, but let's accept that "nominal" "operating" voltage of a DC vehicle is not "12V." It really is more like the stated 14V, running while charging.  For our V11: 13.8 - 14.2 VDC.

Most valid mathematical calculations are probably best derived from 14VDC.

Regarding hot relays? That may be the most reliable indicator of relay "quality" for a particular application.  A particular V11 really gets "hot?"  Time to replace it or install a higher rated relay in that position.

 

[docc]

Thanks to @MartyNZ for also taking these temperature readings:

 

[audiomick]

10 hours ago, docc said:

.. let's accept that "nominal" "operating" voltage of a DC vehicle is not "12V."

No. It's nit-picking, but it's also only about the definition of "nominal". In the accepted jargon, bikes and cars (nearly always) have a "12V electrical system".

Look here:

https://www.collinsdictionary.com/dictionary/english/nominal

one talks about a "12V system" even though everyone knows the real voltage is not 12V. Therefore, per Definition, 12V is the nominal voltage.

Nevertheless

Quote

 It really is more like the stated 14V, running while charging.  For our V11: 13.8 - 14.2 VDC.

Most valid mathematical calculations are probably best derived from 14VDC.

Yes. According to my limited knowledge of electrics, absolutely correct.

and...

Quote

Regarding hot relays? That may be the most reliable indicator of relay "quality" for a particular application.  A particular V11 really gets "hot?"  Time to replace it or install a higher rated relay in that position.

Yes. An electrical part getting hotter than normal is an almost certain sign that a resistance is increasing or increased. By that I don't mean the component "resistor", but rather the resistance, for instance, across the contacts.

i.e. if the relay starts getting hotter than it normally should be, it is a fair assumption that the contacts might be going bad = replace it.

Edit: I suppose a bad contact in or to the socket could also make the relay heat up. That would be worth a look at before spending money on a new relay.

another Edit: if a particular relay is always running a bit warmer than the others, then of course one could consider a higher rated relay in that position. One with a higher rating would most likely run cooler.

The question is, is the relay in question running too hot? The temperatures you reported in that linked post, docc, don't look "too hot" to me. Highest reported temp. 147° F = just short of 64°C. That is still 20°C below the "max. temp." specs of typically 85°C that appear on various spec. sheets. So probably ok.

[docc]

The fact that micro relays have been reported to fail in Position #5, and that the operating temperature can be significantly lowered with a better quality/higher rated relay motivated many of us to install those relays, at least in the most demanding position on the V11 (Fuel/Ignition, #5).

The idea that any old relay is "good enough" has seen many a V11 suffer electrical, starting, and running issues.

Along with marginal ("good enough") battery condition and a collection of equally marginal connections, the issues can be rather maddening.

[p6x]

1 hour ago, docc said:

The fact that micro relays have been reported to fail in Position #5, and that the operating temperature can be significantly lowered with a better quality/higher rated relay motivated many of us to install those relays, at least in the most demanding position on the V11 (Fuel/Ignition, #5).

The idea that any old relay is "good enough" has seen many a V11 suffer electrical, starting, and running issues.

Along with marginal ("good enough") battery condition and a collection of equally marginal connections, the issues can be rather maddening.

@docc I am still running the stock relays in mine, even if I carry spare ones.

But I am seriously thinking to replace all these bullet connections with something more reliable. So far, the battery has not let me down, but I change them every three years.

The strenuous Texas sun is taking its toll on everything exposed to UVs. Including the wire's isolation which becomes brittle with time. And my V11 is garaged at all times, unless I am riding it.

[al_roethlisberger]

20 minutes ago, docc said:

The fact that micro relays have been reported to fail in Position #5, and that the operating temperature can be significantly lowered with a better quality/higher rated relay motivated many of us to install those relays, at least in the most demanding position on the V11 (Fuel/Ignition, #5).

The idea that any old relay is "good enough" has seen many a V11 suffer electrical, starting, and running issues.

Along with marginal ("good enough") battery condition and a collection of equally marginal connections, the issues can be rather maddening.

 

And therein probably lay some of the variables between bikes... the accumulation of issues that make the whole thing stop, like teeeen-iny bits of friction accumulating in a clock mechanism bringing it to a halt

 

With these bikes all at or near 20 years old, maintenance of electrical connections and contacts should be done to keep them clean and with good continuity.

[audiomick]

9 hours ago, docc said:

Along with marginal ("good enough") battery condition and a collection of equally marginal connections, the issues can be rather maddening.

That is probably the pertinent point. A "middle class" relay may well be "good enough" when the rest of the circuit is well maintained.

When everything else is marginal, the problem is going to show up some where.

[docc]

The matter of failure due to "stacked tolerances?" Quite valid, in this case, I would venture.

Again, my only failed relays came from a combination of a dodgy regulator with stator (alternator) failure.  Would lesser relays have failed sooner or more dramatically? Perhaps. 

Can we conclude, based on most recent investigation and input, that both of these relay data sheets support their claimed ratings for our purposes?

https://pickercomponents.com/pdf/Relays/PC782.pdf   (Picker Components 30A/25A)

https://www.onlinecomponents.com/en/datasheet/a11csq12vdc15r-51176058/   (CIT Relay 30A/20A)

 

[audiomick]

On 4/4/2023 at 1:50 AM, docc said:

Can we conclude...that both of these relay data sheets support their claimed ratings for our purposes?

Splitting hairs: the manufacturer would most likely say that the spec. sheets support the claimed rating. We can only trust the spec. sheets, or not.

Nevertheless, they both seem to be at the top of the range that I have seen for "high current" relays. "Bigger" ones, i.e. 40 A. or more, seem to jump to a 9.3 mm blade on the load connections (30 and 87/ 87a), so they wouldn't fit in the sockets.

I like the Picker a little better, because the NC contact claims a higher rating (25A. vs 20A, both @ 14V). The "vibration resistance" spec has a higher number next to it (2.7mm double amplitude), but I don't know if that is relevant to our application.