Constant Duty Relay .... NOT

[Slug]

After frying the second constant duty relay in 6 months in my patrol I am looking for something a litle more "Constant"...

It's wired to switch the power to the fridge in the back and the max it ever switches is a bloody Waeco fridge on and off. Left the fridge on overnight and came back to a hot fridge and a relay that clicks but wont pass voltage at all
Anyone know of a better solution than the Ingrams style, steel cased things?

Something electronic perhaps....


Cheers
Dan

[mickyd555]

whats the current rating on the fridge?

can you use a 70 A narva relay,

like this http://www.narva.com.au/Switches_Relays_1.html


has wide pins on it for the line and load though, so you need the big lugs for them. 68012 is the part no.

[Slug]

I likely used the wrong terminology in saying "Relay"
What I use is a 100amp constant duty solenoid to switch power via a 6 B&S cable to the back of my patrol (It runs a 50lt Waeco which pulls perhaps 10-12 amps at full load at a guess)

Just got me beat why these solenoids seem to fry inside a few months with relatively light useage.

[chimpboy]

It sounds like it would be the coil frying, not the contacts for the heavy power.

I would be more inclined to use a relay if you are only ever going to be putting 10-12A on it. Even a 30A horn relay should be fine; I use these for headlights all the time and they have never failed me.

But anyway a 70A hella or narva relay as suggested by mickyd would easily do it, just make sure you get a good quality one.

[Lately I have been opening up relays I buy (when I need them to be reliable) and checking their operation. Many of them have the contacts a little bit out of alignment so instead of a nice flat contact point they are only in contact on the edge, and this leads to scorching etc. It's shitty that you have to do it but it's worth it. Another issue I have seen is that the contact arm sits too far from the electromagnet, so the magnet is much less effective than it should be, meaning the spring has to be weaker than it should be. A little bit of bending and adjusting the contact arm, and shortening the spring, and a fairly pissweak relay becomes really snappy. I had to do this to fix a relay that was staying on due to a weak spring.]

Jason

[murcod]

What about simply using a heavy duty switch? You'd have less drain on your battery then too as there isn't a relay/ solenoid coil constantly energised (relays usually draw at least 0.3A; solenoids most likely even more?)

Something like this : http://www.jaycar.com.au/productView.as ... BCATID=264

If the link doesn't work go to www.jaycar.com.au and search for SK0955 - 12VDC 30 Amp switch.

Some others worth a look are : ST0574 , ST0579

[-Scott-]

Even a 30A horn relay should be fine; I use these for headlights all the time and they have never failed me.

What sort of horn relay? I tried to use one for a spotlight once, and it lasted only a few hours before the coil fried. I figured it was because horn relays would only be intended for (very) intermittent operation.

Scott

[chimpboy]

What about simply using a heavy duty switch? You'd have less drain on your battery then too as there isn't a relay/ solenoid coil constantly energised (relays usually draw at least 0.3A; solenoids most likely even more?)

Something like this : http://www.jaycar.com.au/productView.as ... BCATID=264

If the link doesn't work go to www.jaycar.com.au and search for SK0955 - 12VDC 30 Amp switch.

Some others worth a look are : ST0574 , ST0579

That's a really good idea and I am embarrassed I didn't think of it as well.

[chimpboy]

Even a 30A horn relay should be fine; I use these for headlights all the time and they have never failed me.

What sort of horn relay? I tried to use one for a spotlight once, and it lasted only a few hours before the coil fried. I figured it was because horn relays would only be intended for (very) intermittent operation.

Scott

Just the standard 30A ones from jaycar... they call them horn relays but they are just ordinary relays. I've never ahd any problems with them, is that the type you tried?

Jason

[murcod]

If you shop around at auto places you can sometimes find decent brand relays eg. Bosch, for around $6. I bought some a while back and they appear a lot better quality than generic "horn" relays.

[mickyd555]

i would actual;ly prefer to use something solid state, but im sure its still too expensive at this stage.

anyone have any ideas on using an SCR or similar??

[-Scott-]

Just the standard 30A ones from jaycar... they call them horn relays but they are just ordinary relays. I've never ahd any problems with them, is that the type you tried?

Jason

No, the one I tried was in a metal can, with screw terminals. Haven't seen any like it for years, they all seem to be the Hella style cube. I guess I'm just a little edgy about using anything designated "horn" relay.

anyone have any ideas on using an SCR or similar??

A simple bipolar transistor should suffice, if you get it to saturate. But you'll need a base resistor and a flywheel diode too, and then you have to assemble and mount it all somehow.

And solid state relays can fail short circuit, so you may not notice it hasn't switched off until your battery is flat.

Hella style relays are so easy.

Scott

[murcod]

You can buy solid state relays. I'm fairly sure Jaycar had them advertised as while back?

[Slug]

You can buy solid state relays. I'm fairly sure Jaycar had them advertised as while back?

You are right ...
http://www.jaycar.com.au
CAT. NO. SY4086

Not sure if they are rated for constant duty or not but may be worth an ask?
Beats me why these howling great metal canned things keep nuking themselves

[murcod]

Google to the rescue- all the spec from the manufacturer.

http://www.hongfa.com/product/pdf/HFS33 ... d2a7f17a04

BTW the Jaycar one appears to be the D400D version (RHS column in specs sheet.) Some of the specs are a bit of a worry eg. max voltage drop of 2.4V!?

[Slug]

2.4v is a bit too much drop to be useful.... I would use a standard 30A spotlight type relay however, getting crimp style terminals for those small relays to suit a howling great 6B&S cable might prove difficult.

I tested the solenoid tonight with my lamp... no voltage on the "output" side, smacked it with the handle of a screwdriver and the bastard worked. Powered up after the above percussive maintenance she was shagged again

[-Scott-]

These SSRs use a FET as the switching device, which have a "residual" resistance when they're turned on. You're looking at the 400V version, with a 0.24 ohm resistance and 10A rating - that's where the 2.4V comes from.

Look at the 30V version. There's a 100A rating with 3.5 milliohm resistance. You'll drop less than 35mV for every 100W of load. This is a much nicer proposition, but I still prefer the good old simple mechanical relay.

Slug, your solenoids have shitty contacts - throw them away. Buy one of the common Hella/Narva relays with a 30A rating and see how that goes.

Cheers,

Scott

[jacrabbits]

Dan id say your biggest problem may be your ability with wiring.

[Slug]

Nice one Cutty

Bastard

[mgundle]

we use at work coal hearse continous duty relays they are super super heavy duty bout 100amps continous with 200 burst very very good and never fail
bit $$ but well worth it
personally i would stay away with electronics too easy for complications keep it simple thats the go
my two cents any way

[Slug]

Any idea what breed mgundle ?
Cheers
Dan

[mgundle]

just a heavy duty 12v coal hearse is the go Slug

[festy]

Oatley Electronics sell a dual battery kit for $19 that makes a very good low voltage cut out for a fridge. It's based around an 80amp latching relay (no burnt coils), the kit would probably be worth buying just for the relay alone.

[Slug]

just a heavy duty 12v coal hearse is the go Slug

Nice one bloke
Once I figured the correct spelling I found the buggers via google, found the distributor in the NT and managed to snavvel one reasonably cheaply. Apparently oil filled so they dont arc and burn

Thanks again
Dan