A fellow Garage Vary fan! I like!
That's very kind of you to say, thank youA fellow Garage Vary fan! I like!
Relay current ratings aren't really to do with continues use capacity its more related to switching capacity. You shouldn't really see any temperature increase due to a larger current draw unless you are well outside of its rating. The bigger issue is that if for example you try and pull 100A at 12V through a 60A relay it may draw an arc internally across the contacts as there won't be enough air gap to instantly break the connection. This creates a huge amount of heat and will damage the contacts very quickly causing the relay to fail (either through the contacts melting or the plastic). This is one of the reasons the relays are often rated for much higher AC loads than DC as is AC is far easier to switch.
- How hot does the NA main relay get when used in my set up?
- How hot does the RX-7 relay get when used in my set up?
- Does moving the fuel pump to it's own relay lower the temperature of the main relay? If so why or why not?
This is incredibly helpful and so informative, thank you.Relay current ratings aren't really to do with continues use capacity its more related to switching capacity. You shouldn't really see any temperature increase due to a larger current draw unless you are well outside of its rating. The bigger issue is that if for example you try and pull 100A at 12V through a 60A relay it may draw an arc internally across the contacts as there won't be enough air gap to instantly break the connection. This creates a huge amount of heat and will damage the contacts very quickly causing the relay to fail (either through the contacts melting or the plastic). This is one of the reasons the relays are often rated for much higher AC loads than DC as is AC is far easier to switch.
Relays will get hot/warm in use but this is to do with the coil that holds the contacts open or closed. Moving the fuel pump to a separate relay is a good idea and I would always recommend this if you have seriously upgraded your fuel pump (very large or multiple in tank or external pump) as it means you can run larger feed wires but I doubt it will have much affect on the temperature of your main relay and with a walbro255 pump its probably not necessary.
Its also worth noting that fuel pumps are electric motors and motors are an inductive load meaning they normally draw a huge amount of current at the moment they are switched on and then drop down to there running levels. This is very aggressive on relay contacts over time so if you do switch the fuel pump to its own relay be sure to spec the relay correctly; some suppliers/manufacturers will list a different inductive load rating in the relay data sheet.
thanks,
Nix.
it depends on the relay and if you can find the part number for the main relay you may be able to find the full datasheet for it (not likely though) but I know that some I've seen relays have maximum coil temperatures of up to 70C (some industrial relays have operating temps of up to 90C) so I wouldn't worry to much. Relays are built to withstand some fairly serious temperatures; automotive relays are often built/specced to operate in engine bays with under bonnet temps of 50C+This is incredibly helpful and so informative, thank you.
Do you have any insight into what a normal temperature of the relay would be after a spirited drive. I'm getting a bit paranoid now that there is something else causing the relay to get hotter than it should be whilst driving. For what it's worth, my car still has the 60a main fuse in, am I right in thinking that if the car was pulling any higher current than 60a across the main relay, that the main fuse would blow? or is it not that straight forward?
Moving the fuel pump to it's own relay is a minimal job with minimal cost and sounds like it's worth doing anyway for safety but I appreciate that it might not be completely necessary then based on what you've said - at some point the car will be getting ITBs (or I might even go for a turbo again depending on how I'm feeling) so future proofing that too.
That's amazing thank you. I've got an infrared thermometer on the way so will have a play and see what temps are like.it depends on the relay and if you can find the part number for the main relay you may be able to find the full datasheet for it (not likely though) but I know that some I've seen relays have maximum coil temperatures of up to 70C (some industrial relays have operating temps of up to 90C) so I wouldn't worry to much. Relays are built to withstand some fairly serious temperatures; automotive relays are often built/specced to operate in engine bays with under bonnet temps of 50C+
Yes once the current through the main fuse surpasses its rating for a period of time it will blow; The main fuse is likely a slow-blow fuse so there will be a slight delay before it blows so that it doesn't blow every time there is momentary spike in current draw.
not particularly, if there is a short heat will always build up in the point of highest resistance which is normally the fuse. The same with high resistance, it will cause a voltage drop across the point of resistance, that voltage has to go somewhere so its converted to heat across the resistance. It shouldn't have any affect on anything else in the circuitThat's amazing thank you. I've got an infrared thermometer on the way so will have a play and see what temps are like.
Just one last question if you dont mind, is there anyway an issue post relay could have an adverse affect on the relay, say a short circuit or high resistance somewhere?
Perfect - my mind is at ease now, I'll stop obsessing over the weird suspected short I found on the switched live (white/red).not particularly, if there is a short heat will always build up in the point of highest resistance which is normally the fuse. The same with high resistance, it will cause a voltage drop across the point of resistance, that voltage has to go somewhere so its converted to heat across the resistance. It shouldn't have any affect on anything else in the circuit
I like your thinking, that would certainly surprise the MOT man next week!If it has a button to make fog it's a James Bond car.
so, it's an early car, has the wiper-rmotor pointing to the centre of the car that was dropped sometime mid 1990 iirc.
you've an aftermarket ecu, from the enginebay photo you're still running with the intake crossover pipe? not tempted to run the airfilter on the inlet side (either on the throttlebody or in the bumpers 'mouth')MS3 Mini ECU
Firstly, apologies for stealing your cars nick name!few questions...
so, it's an early car, has the wiper-rmotor pointing to the centre of the car that was dropped sometime mid 1990 iirc.
has it a single or twin hole slam-panel? (whats the numbers in the vin?)
you've an aftermarket ecu, from the enginebay photo you're still running with the intake crossover pipe? not tempted to run the airfilter on the inlet side (either on the throttlebody or in the bumpers 'mouth')
Rich.
I doubt we are the only people using thatapologies for stealing your cars nick name!
the stock cross over was just to get me home, initially the plan was always to go with ITBs but as you'll see on my thread I posted yesterday, I'm not happy with the way the car runs and really need help tuning and I want to get it right before I move on with changing any intake bits.
maybe better off withThe end goal was jenvey ITBs and possibly a light skim and big cams.
Thanks for all that info.I doubt we are the only people using that![]()
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from https://www.japan-partner.com/check-manufacture-year.html
made in 10/1990, year older than my silver heap but younger than my feb '90 white mess
^^guessing thats one of the last with that type of wipermotor? - little tip, if you need a replacement then it's the early type as the mounting baseplate & bulkhead holes differ (might be the same as a lefthand drive car though)