A question about relays

[default]

I was poking around in my truck the other day and had cause to open up
the starter relay. (not the solenoid, the relay that energizes the
solenoid)

I was amazed at the size of the contacts. They were under 1/8" in
diameter yet the relay is rated at 40 amps. The AC clutch relay-
ditto, tiny contacts. In the case of the clutch relay I know for a
fact the inductive kick must be >100 volts since it is shocking..

Now how can they do that, when I have lots of plug-in Potter Brumfield
12V relays with contacts easily 4 times the size and only rated at 10
amps. (240 volts AC or 28 VDC resistive)

(The actual problem with the truck was not the relay itself but the
intermittent neutral switch in the tranny.)

 

[Jim Thompson]

On Mon, 07 May 2018 05:38:49 -0400, default <default@defaulter.net>
wrote:

I was poking around in my truck the other day and had cause to open up
the starter relay. (not the solenoid, the relay that energizes the
solenoid)

I was amazed at the size of the contacts. They were under 1/8" in
diameter yet the relay is rated at 40 amps. The AC clutch relay-
ditto, tiny contacts. In the case of the clutch relay I know for a
fact the inductive kick must be >100 volts since it is shocking..

Now how can they do that, when I have lots of plug-in Potter Brumfield
12V relays with contacts easily 4 times the size and only rated at 10
amps. (240 volts AC or 28 VDC resistive)

(The actual problem with the truck was not the relay itself but the
intermittent neutral switch in the tranny.)

I know that queasy feeling. I just bought some 110VAC (coil and
contacts) relays. Contacts rated at 10A! Flying lead from contact to
spade connection looks like #20 :-(

...Jim Thompson
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is the secret of happiness." -James Barrie

 

[Ralph Mowery]

In article <ldc0fd5r7m3k5jrok0c3qceg90tkfbnr8e@4ax.com>, To-Email-Use-
The-Envelope-Icon@On-My-Web-Site.com says...

I know that queasy feeling. I just bought some 110VAC (coil and
contacts) relays. Contacts rated at 10A! Flying lead from contact to
spade connection looks like #20 :-(

The wires do look small. However they are short so the voltage drop
will not be very much. Wires in free air can carry a lot of current,but
if very long will have lots of voltage drop.

 

[Cursitor Doom]

On Mon, 07 May 2018 10:17:54 -0400, Ralph Mowery wrote:

In article <ldc0fd5r7m3k5jrok0c3qceg90tkfbnr8e@4ax.com>, To-Email-Use-
The-Envelope-Icon@On-My-Web-Site.com says...

I know that queasy feeling. I just bought some 110VAC (coil and
contacts) relays. Contacts rated at 10A! Flying lead from contact to
spade connection looks like #20 :-(



The wires do look small. However they are short so the voltage drop
will not be very much. Wires in free air can carry a lot of current,but
if very long will have lots of voltage drop.

But mainly it's the very, very short 'duty cycle' - a one-time 10s press
or so.




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[default]

On Mon, 7 May 2018 15:30:53 -0000 (UTC), Cursitor Doom
<curd@notformail.com> wrote:

On Mon, 07 May 2018 10:17:54 -0400, Ralph Mowery wrote:

In article <ldc0fd5r7m3k5jrok0c3qceg90tkfbnr8e@4ax.com>, To-Email-Use-
The-Envelope-Icon@On-My-Web-Site.com says...

I know that queasy feeling. I just bought some 110VAC (coil and
contacts) relays. Contacts rated at 10A! Flying lead from contact to
spade connection looks like #20 :-(



The wires do look small. However they are short so the voltage drop
will not be very much. Wires in free air can carry a lot of current,but
if very long will have lots of voltage drop.

But mainly it's the very, very short 'duty cycle' - a one-time 10s press
or so.

I don't ever remember seeing duty cycle as a spec on any relays.

Current and voltage for the contacts, nominal voltage for the coil and
must make must release voltages, and mechanical/environmental, number
of cycles, are all the specs you usually get.

 

[Phil Allison]

default wrote:

Cursitor Doom


But mainly it's the very, very short 'duty cycle' - a one-time 10s press
or so.

I don't ever remember seeing duty cycle as a spec on any relays.

** The total number of cycles and time spent in conduction are both low in this case. What you call it is not important.

Current and voltage for the contacts, nominal voltage for the coil and
must make must release voltages, and mechanical/environmental, number
of cycles, are all the specs you usually get.

** Relay contacts can pass more current than they can reliably switch - and even modest DC voltages are a big problem due to the likelihood of contacts arcing.


..... Phil

 

[default]

On Mon, 7 May 2018 18:35:53 -0700 (PDT), Phil Allison
<pallison49@gmail.com> wrote:

default wrote:

Cursitor Doom


But mainly it's the very, very short 'duty cycle' - a one-time 10s press
or so.

I don't ever remember seeing duty cycle as a spec on any relays.


** The total number of cycles and time spent in conduction are both low in this case. What you call it is not important.


Current and voltage for the contacts, nominal voltage for the coil and
must make must release voltages, and mechanical/environmental, number
of cycles, are all the specs you usually get.


** Relay contacts can pass more current than they can reliably switch - and even modest DC voltages are a big problem due to the likelihood of contacts arcing.

That's what gets me about these automotive types. The coil on
something like the AC clutch, and even the solenoid for the starter
motor, are relatively large inductors and those contacts seem mighty
small for the current and inductance.

Comparing that to the ratings on standard industrial switching types
versus size of the contacts I have to conclude that the auto types are
designed with cost as the predominant concern, or the industrial types
are very conservatively rated and could easily replace the auto type
and probably outlast them.

The auto parts store is charging me the same for the cheaply made
relay, as I can buy industrial control relays for.

Ebay, of course, has the auto relay much cheaper. Brand name
industrial relays are about the same on Ebay as I pay through a
distributor, unless they are used, or auctioned.

I'm wondering if it would be wiser to use an industrial relay in the
truck - I've had to replace the fuel pump and AC clutch relay in the
truck already.

 

>"** Relay contacts can pass more current than they can reliably switch - and even modest DC voltages are a big problem due to the likelihood of contacts arcing. "

Yes but they're still full of shit. They play the numbers. The A/C clutch relay obviously works for much longer, but that draws less current. In fact even the solenoid does not pull 40 amps. The starter itself maybe but that is switched by the solenoid.

If he has 1/8th" diameter contacts, well that's not so bad as long as they're nice and clean. I think it is bigger than # 12 wire. (on AWG) But those fingers that carry the electricity to the contacts... They are not very thick or wide. those little relays what size ya figure ? Maybe 0.02 thick and 0.25 wide ? I doubt it is the equivalent of 16 gauge. Maybe just barely, and # 16 will not carry 40 amps for long, I mean like a few seconds tops.

Sounds like they're using car stereo amp math for more than just car stereo amps.

 

[Tom Biasi]

On 5/7/2018 7:02 AM, Jim Thompson wrote:

On Mon, 07 May 2018 05:38:49 -0400, default <default@defaulter.net
wrote:

I was poking around in my truck the other day and had cause to open up
the starter relay. (not the solenoid, the relay that energizes the
solenoid)

I was amazed at the size of the contacts. They were under 1/8" in
diameter yet the relay is rated at 40 amps. The AC clutch relay-
ditto, tiny contacts. In the case of the clutch relay I know for a
fact the inductive kick must be >100 volts since it is shocking..

Now how can they do that, when I have lots of plug-in Potter Brumfield
12V relays with contacts easily 4 times the size and only rated at 10
amps. (240 volts AC or 28 VDC resistive)

(The actual problem with the truck was not the relay itself but the
intermittent neutral switch in the tranny.)

I know that queasy feeling. I just bought some 110VAC (coil and
contacts) relays. Contacts rated at 10A! Flying lead from contact to
spade connection looks like #20 :-(

...Jim Thompson

Auto manufactures want top reliability from their vendors but at a very
low cost. The engineers that design the relays play it very close and
play the odds.You probably would be surprised at what you would go
through if one of your relays failed in the field.

 

[whit3rd]

On Tuesday, May 8, 2018 at 7:38:14 AM UTC-7, default wrote:

... The coil on
something like the AC clutch, and even the solenoid for the starter
motor, are relatively large inductors and those contacts seem mighty
small for the current and inductance.

But small area means high contact pressure for a given solenoid-applied
force; unless you know WHY the old one failed, just get a replacement,
and you're good. Automotive goods are just as good (or bad) as industrial,
but for different service conditions. Shopping around won't substitute
for engineering.

 

[default]

On Tue, 8 May 2018 18:09:03 -0700 (PDT), whit3rd <whit3rd@gmail.com>
wrote:

On Tuesday, May 8, 2018 at 7:38:14 AM UTC-7, default wrote:

... The coil on
something like the AC clutch, and even the solenoid for the starter
motor, are relatively large inductors and those contacts seem mighty
small for the current and inductance.

But small area means high contact pressure for a given solenoid-applied
force; unless you know WHY the old one failed, just get a replacement,
and you're good. Automotive goods are just as good (or bad) as industrial,
but for different service conditions. Shopping around won't substitute
for engineering.

They fail because the contacts burn. Dressing the contacts with a
needle file will get it working for a time. When the fuel pump relay
goes out the vehicle won't start. That is annoying when your sitting
at a gas station 90 miles from home on a Sunday.

Philosophy won't substitute for engineering either

 

[Cursitor Doom]

On Mon, 07 May 2018 16:59:18 -0400, default wrote:

> I don't ever remember seeing duty cycle as a spec on any relays.

That's why I put it in inverted commas! The essence of it is, you will
have no trouble provided you energise your solenoid in well-spaced, short
bursts. Used that way it should last for years. If you hold it constantly
on, however, it'll burn out within 2-3 minutes.

Current and voltage for the contacts, nominal voltage for the coil and
must make must release voltages, and mechanical/environmental, number of
cycles, are all the specs you usually get.

Some people think they can save a small fortune by using auto solenoids
in place of the correct ones in applications like winches. They don't
realise it's the extended 'on' time capability that you're paying for.
Auto starter solenoids are NOT designed for what amounts to continual
duty and the manufacturers simply assume (not unreasonably) that you will
not use them for anything other than their stated purpose!



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[Cursitor Doom]

Starter motors are another example. When Robot Rumble (or whatever it was
called) first hit the screens over 20 years ago, some green-as-grass
wouldbe fighting robot builders tried to use scrap auto starter motors
for propulsion. Probably seems like a great idea for any keen novice to
get started with. Again, however, these are not designed for extended use
and quickly burned out. Think about it: they have none of the necessary
cooling in terms of air vents and fins that you find in true propulsion
motors. They had the torque all right; all the power, low-voltage/high
current, but.... no good for use outside of their intended purpose.



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[Ralph Mowery]

In article <pcveam$kn3$2@dont-email.me>, curd@notformail.com says...

Starter motors are another example. When Robot Rumble (or whatever it was
called) first hit the screens over 20 years ago, some green-as-grass
wouldbe fighting robot builders tried to use scrap auto starter motors
for propulsion. Probably seems like a great idea for any keen novice to
get started with. Again, however, these are not designed for extended use
and quickly burned out. Think about it: they have none of the necessary
cooling in terms of air vents and fins that you find in true propulsion
motors. They had the torque all right; all the power, low-voltage/high
current, but.... no good for use outside of their intended purpose.

Where I worked several motors of about 25 or 50 HP were burnt up when
they were put on inverters for speed control. Before that a magnetic
clutch was used.

I solved the problem for them. The motors were running very slow so
the fan on the motor shaft could not cool the motor. Extermal cool air
was blown across and into the motor and the motor lasted many years.

 

[Cursitor Doom]

On Wed, 09 May 2018 14:35:22 -0400, Ralph Mowery wrote:

I solved the problem for them. The motors were running very slow so
the fan on the motor shaft could not cool the motor. Extermal cool air
was blown across and into the motor and the motor lasted many years.

Yes, in so many areas, keeping things cool and longevity are heavily
correlated.





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[default]

On Wed, 9 May 2018 17:45:30 -0000 (UTC), Cursitor Doom
<curd@notformail.com> wrote:

On Mon, 07 May 2018 16:59:18 -0400, default wrote:

I don't ever remember seeing duty cycle as a spec on any relays.

That's why I put it in inverted commas! The essence of it is, you will
have no trouble provided you energise your solenoid in well-spaced, short
bursts. Used that way it should last for years. If you hold it constantly
on, however, it'll burn out within 2-3 minutes.

Current and voltage for the contacts, nominal voltage for the coil and
must make must release voltages, and mechanical/environmental, number of
cycles, are all the specs you usually get.

Some people think they can save a small fortune by using auto solenoids
in place of the correct ones in applications like winches. They don't
realise it's the extended 'on' time capability that you're paying for.
Auto starter solenoids are NOT designed for what amounts to continual
duty and the manufacturers simply assume (not unreasonably) that you will
not use them for anything other than their stated purpose!

Oh.. I only mention the solenoid because it is on the load side of
one of the ice-cube size small relays. I realize the actual starter
solenoid is a whole 'nother thing.

The tiny relays are rated for a 40 amp load and the contacts
eventually burn. They switch the starter solenoid, AC clutch, and
fuel pump. Strangely enough, the headlight and horn are wired direct
without relays.

 

[Cursitor Doom]

On Wed, 09 May 2018 19:31:26 -0400, default wrote:

Oh.. I only mention the solenoid because it is on the load side of one
of the ice-cube size small relays. I realize the actual starter
solenoid is a whole 'nother thing.

Oh, right. Sorry, I didn't read your original question correctly, then.
What they *may* have done is to silver pad the contact points. Silver has
a marginally lower electrical resistance than copper, but you would not
notice without specifically looking at the contact areas.

The tiny relays are rated for a 40 amp load and the contacts eventually
burn. They switch the starter solenoid, AC clutch, and fuel pump.
Strangely enough, the headlight and horn are wired direct without
relays.

Horn, no surprise. Doesn't use much current. Headlamps, yes, that is
'unusual' shall we say. I can't say I've ever come across that.





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>"Silver has a marginally lower electrical resistance than copper"

Something like 3.5 % only. While I was unable to get a specific figure on the electrical conductivity of silver oxide, it is said to be almost as conductive as silver, and is self limiting in thickness. Gold is not really a great conductor but it almost can't oxidise or anything, so if the coating is thin enough it works fine. Copper oxides and compounds are pretty much insulators so that, why there is plating. In my recent internet travels someone mentioned the palladium would work well. That may be but I don't know what it costs. Gold is not necessarily the most expensive substance on Earth.

 

[Jasen Betts]

On 2018-05-11, jurb6006@gmail.com <jurb6006@gmail.com> wrote:

"Silver has a marginally lower electrical resistance than copper"

Something like 3.5 % only. While I was unable to get a specific figure on the electrical conductivity of silver oxide, it is said to be almost as conductive as silver, and is self limiting in thickness. Gold is not really a great conductor but it almost can't oxidise or anything, so if the coating is thin enough it works fine. Copper oxides and compounds are pretty much insulators so that, why there is plating. In my recent internet travels someone mentioned the palladium would work well. That may be but I don't know what it costs. Gold is not necessarily the most expensive substance on Earth.

gold, palladiun, and platinum all cost about the same, currently gold
seems to be the most expensive of the three.

--
ŘŞ

 

[Phil Allison]

jurb...@gmail.com wrote:

"Silver has a marginally lower electrical resistance than copper"

Something like 3.5 % only. While I was unable to get a specific figure
on the electrical conductivity of silver oxide, it is said to be almost
as conductive as silver,

** The tarnish that forms on silver is "silver sulphide" - an insulator.

Being soft, it polishes or wears off fairly easily.


..... Phil