Relays making Mulgo Exbox hot

[Kayak1]

Well it's been a bit warm here in VIC for the last fortnight. My Mulgo exbox has always got warm, but the last few weeks it's got hot. I've been thinking the heat has been coming from the transfer case, but no.
Yesterday I was drive home 35* A/C going all the way home and the exbox got very hot so opened it up to take a look. Well the main relay, A/C and cooling fan relays were so hot I was only able to touch them for a second with my asbestos fingers !
The relays have been heating up the box not the transfer cases as the floor of the exbox was relatively cool.
Question.
So how hot should those relays get ??? Is this normal ? How do others keeep their exbox cool ?

Thanks Steve

[martnH]

Hi relays will get hot and it has resistence
May be around 150 ohm so it will naturally create some heat. also here is no air flow in the ebox so that doesn't help

How hot is too hot? I don't know but the heat will reach a equilibrium and temperate will not rise anymore.

[martnH]

I would say as long as the wires are not melt, you should be good. But its land rover so maybe we need to baby the defender. .....
put a fan in if you want....just remember the insulation that some would suggest, works both ways and it will retain the heat created by the relay inside then box, maybe not what you want

Cheers

[DeanoH]

Several potential issues here.

Are the relays getting hot because of heat from the relay coils or because of high resistance of the contacts or inadequate ventilation ?

Your relays should be warm not hot especially not too hot to touch. Relays can degrade with 'shorted turns' in its coil, the effect of this is that the relay will still operate but will draw more current and get hotter creating more shorted turns and more heat eventually failing but with the potential of catching fire, burning out wiring/switching components or if lucky just blowing a fuse.

My initial response would be a visit to my local auto elec with a view to getting better quality relays, ie higher resistance windings for less heat dissipation and correctly/over rated contacts.

Oils aint oils. There's definitely 3 different 'levels' of auto relays, cheap Chinese junk, consumer, and quality. You're only after 2 so financially not a big deal to get the quality ones.

I had an issue several years ago with my ARB twin motor compressor which is a well engineered and built machine but was let down with the cheap Chinese relays fitted. They rattled themselves to pieces on the 'Highway' between Taralinga Well and Emu. I replaced them with quality, at the time $20, relays and haven't had a failure since (4 years).

A trick if the issue is that the relay is running at or close to maximum current is to replace it with a 'driving light' type relay which has two sets of contacts (one for each light) and common these to halve the current through each contact.

Electronic 'relays' are readily available with very small operate current and low heat dissipation but must be correctly installed on a 'heat sink' surface. Not suitable in some applications but very good in an on/off application.

Deano :)

[martnH]

Hi the OP was refering the the land rover factory relays...that are relocated into the ebox

Most likely British rubbish relays nevertheless....so good idea to replace them. Just how easy to source a replacement?


Also I believe locally you can't buy relays not made in China. NARVA relays or hella relays are made in China....you can only choose between cheap Chinese relay or expensive Chinese relays....where did you source yours?

Cheers

Several potential issues here.

Are the relays getting hot because of heat from the relay coils or because of high resistance of the contacts or inadequate ventilation ?

Your relays should be warm not hot especially not too hot to touch. Relays can degrade with 'shorted turns' in its coil, the effect of this is that the relay will still operate but will draw more current and get hotter creating more shorted turns and more heat eventually failing but with the potential of catching fire, burning out wiring/switching components or if lucky just blowing a fuse.

My initial response would be a visit to my local auto elec with a view to getting better quality relays, ie higher resistance windings for less heat dissipation and correctly/over rated contacts.

Oils aint oils. There's definitely 3 different 'levels' of auto relays, cheap Chinese junk, consumer, and quality. You're only after 2 so financially not a big deal to get the quality ones.

I had an issue several years ago with my ARB twin motor compressor which is a well engineered and built machine but was let down with the cheap Chinese relays fitted. They rattled themselves to pieces on the 'Highway' between Taralinga Well and Emu. I replaced them with quality, at the time $20, relays and haven't had a failure since (4 years).

A trick if the issue is that the relay is running at or close to maximum current is to replace it with a 'driving light' type relay which has two sets of contacts (one for each light) and common these to halve the current through each contact.

Deano :)

[DeanoH]

Hi martnH,

The Bosch relays I favour are made in Germany as are the solid state relays I use. If Bosch or Hella have moved their relay manufacturing to China I would expect them to be built/quality controlled to German standards as opposed to a 'local product' possibly made to less exacting standards.

Relays age like every thing else and deteriorate internally typically with shorted turns, burnt/pitted and thus high resistance contacts. Both of these conditions will cause excessive heat which can cascade to eventual failure. Mechanical failure of the contact mechanism can also happen, it has moving parts after all, but is less common than electrical failure in good relays. The original Defender relays can be what, 30 years old ? Perhaps they just need replacing due to normal wear and tear.

Another source of abnormal heat can be high resistance contacts on the switched contact connectors in the relay base. These plug into a spade connector in the relay socket which can lose tension creating a high resistance connection which can generate enough heat to melt the usually plastic base.

A good auto electrician will have a range of relays suited to various purposes.

Solid state relays have been available for many years and are a good option in some applications, they're relatively expensive compared to conventional relays and if installed properly and not abused seldom fail. A good option here if just on/off type switching of +ve. Very little heat dissipation and no moving parts.

As a (retired) technician I source my relays from various places but typically my local auto elec for 'day to day' stuff. He has a good range of relays as his work is varied. I don't know where your'e located so can't direct you to somewhere local.

Deano :)

[filcar]

....I believe locally you can't buy relays not made in China. NARVA relays or hella relays are made in China....

Interesting, I have a Hella relay sitting here in front of me marked as made in New Zealand.

[DeanoH]

A good source of relays is abandoned/wrecked cars but you need to be able to recognise the electrical differences between them. Most auto relays have the same 'form factor' ie. they're about an inch cube and plug into a standardised 4/5 pin base. Whilst they all look the same there are many variations electrically. The operating voltage/current capacity should be clearly marked and the standardised pin out on the base and will typically have a number stamped at each contact to assist in identifying its purpose. Some relays actually have the relay circuit diagram stamped on the side. It's a good idea to keep one of these handy as the pin out is standardised and common for all relays of this type.

What the relay won't have shown is the operating coil resistance as this is generally not an issue but if heat generation is an issue the higher the resistance (for the correct voltage) the better. Some relays have an internal diode fitted across the coil which affects its operation/release characteristics and will usually be shown on the attached circuit diagram but not an issue in general purpose applications. Some have an electronic timer.

It is not uncommon for 'non relay' items to be built into the standard relay package and my Tdi Defender had several of these so you need to be aware of the 'odd bods' which look like a relay but aren't really. It is very easy to mix up relays when removing several at a time as they all look the same at first glance.

Deano :)

[Kayak1]

Thanks for the replays. I'll be off to the local auto electrician today.
I will report back after our next hot day.