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default
Guest

Mon May 07, 2018 10:45 am   



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
Guest

Mon May 07, 2018 12:45 pm   



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

Quote:
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 Sad

...Jim Thompson
--
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| Analog Innovations | et |
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is the secret of happiness." -James Barrie

Ralph Mowery
Guest

Mon May 07, 2018 3:45 pm   



In article <ldc0fd5r7m3k5jrok0c3qceg90tkfbnr8e_at_4ax.com>, To-Email-Use-
The-Envelope-Icon_at_On-My-Web-Site.com says...
Quote:

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
Guest

Mon May 07, 2018 4:45 pm   



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

Quote:
In article <ldc0fd5r7m3k5jrok0c3qceg90tkfbnr8e_at_4ax.com>, To-Email-Use-
The-Envelope-Icon_at_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
Guest

Mon May 07, 2018 10:45 pm   



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

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

In article <ldc0fd5r7m3k5jrok0c3qceg90tkfbnr8e_at_4ax.com>, To-Email-Use-
The-Envelope-Icon_at_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
Guest

Tue May 08, 2018 2:45 am   



default wrote:

Quote:
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.


Quote:
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
Guest

Tue May 08, 2018 3:45 pm   



On Mon, 7 May 2018 18:35:53 -0700 (PDT), Phil Allison
<pallison49_at_gmail.com> wrote:

Quote:
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.


Guest

Tue May 08, 2018 11:45 pm   



>"** 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
Guest

Wed May 09, 2018 1:45 am   



On 5/7/2018 7:02 AM, Jim Thompson wrote:
Quote:
On Mon, 07 May 2018 05:38:49 -0400, default <default_at_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 Sad

...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
Guest

Wed May 09, 2018 2:45 am   



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

Quote:
... 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
Guest

Wed May 09, 2018 11:45 am   



On Tue, 8 May 2018 18:09:03 -0700 (PDT), whit3rd <whit3rd_at_gmail.com>
wrote:

Quote:
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 Sad

Ralph Mowery
Guest

Wed May 09, 2018 7:45 pm   



In article <pcveam$kn3$2_at_dont-email.me>, curd_at_notformail.com says...
Quote:

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
Guest

Wed May 09, 2018 7:45 pm   



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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This message may be freely reproduced without limit or charge only via
the Usenet protocol. Reproduction in whole or part through other
protocols, whether for profit or not, is conditional upon a charge of
GBP10.00 per reproduction. Publication in this manner via non-Usenet
protocols constitutes acceptance of this condition.

Cursitor Doom
Guest

Wed May 09, 2018 7:45 pm   



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.

Quote:
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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This message may be freely reproduced without limit or charge only via
the Usenet protocol. Reproduction in whole or part through other
protocols, whether for profit or not, is conditional upon a charge of
GBP10.00 per reproduction. Publication in this manner via non-Usenet
protocols constitutes acceptance of this condition.

Cursitor Doom
Guest

Thu May 10, 2018 12:45 am   



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

Quote:
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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This message may be freely reproduced without limit or charge only via
the Usenet protocol. Reproduction in whole or part through other
protocols, whether for profit or not, is conditional upon a charge of
GBP10.00 per reproduction. Publication in this manner via non-Usenet
protocols constitutes acceptance of this condition.

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