Lighting relays 6V

[arcturus]

Hi, i have noticed that the relays are getting quite hot on use. Is this normal? Also,can't quite make out fuse rating on schematic. Is it 5Amp or 8Amp?
Just remembered, I'm running 60/55 H4 lamps instead of the normal 45/40.

[Derek UK]

Volvo didn't fit any relays so I guess these were added by you? Good earths where needed are always worth checking. Small fuses will be 8amp. Big dumpy ones are 25amp. 4 x 8amp and 2 x 25amp I think on your fuse box.

[arcturus]

Still having problems with hot relays. Confirm that this is the correct connecting please. Haven't got earth and switch reversed? Power terminal from battery gets very hot. Will revert to non relay until I get to the bottom of this.

[Derek UK]

That looks OK.
http://floraoflangkawi.org/relay-wir...diagram-4-pin/

[Ron Kwas]

Guys;

In general, heat is produced as a result of current through a less than adequate contact, or conductor cross section, or connection etc. for the magnetude of current passing...it is governed by the Ohms Law derived formula of P=I(squared) x R. [Note the R factor!]

Specifically, if a relay is getting hot, try to determine exactly where the heat is being generated...if it is the coil which is generating the heat (maybe its not intended to be under power continuously [see: https://www.sw-em.com/Ignition_Slave...us_duty_relays ], or maybe it is being subjected to more voltage than intended [unlikely in this case], rating on the case will refer to nominal voltage intended to be applied to coil) OR it is the working contact (carbonized, so low cross-sectional area for the amount of current flowing, or more current flowing than it is rated for) OR maybe a riveted interconnection of external contact to internal parts, OR even high resistance at the connecting crimp(s) themselves is loose or corroded...yes there can be a lot of heat sources...and don't forget, heat can be and typically is also conducted away from the actual source, down metal paths, so where you feel it might not be the (hotter!) source...any one of these phenomenon (or even combinations) can be what Arcturus is experiencing at the term 30.

Locating source of heat: Direct - feel around (Carefully!) for the hottest point...if connections look OK by inspection, measure or calculate or estimate current (too much?)...Indirect - probe around with Voltmeter...remember, voltage drop is supposed to occur only across Load!!...a VD anywhere else in the current path means Load is not getting full(maximum) voltage, but more importantly in this case, that VD is being turned into heat, which can eventually do damage...note also that unintentional VDs seldom get less with time...their causes (corrosion, terminal looseness, contact inadequacy, etc) typically don't get better with time...they get worse...

I really dislike the "Black Box" drawings for relays, showing only terminal numbers...because half the important info is still not shown...I want to see ALL the internal happenings!...this gives me an immediate overview and helps with visualizing the various current paths for troubleshooting. I prefer drawings such as this:


"Haven't got earth and switch reversed? " ...this does not matter from the point of current direction in the circuit, magnetism being generated within the relay, or heat generation in the current path...the only time polarity maters is when the is a snubber diode internal (or external!) to the relay (see pic!) then polarity must be observed such that the diode (intended to quench the high voltage and resulting plasma at the switch-contact) occurring when shutting OFF the coil current path, would otherwise represent a short circuit.

Hope this explanation helps...Good Hunting!

[arcturus]

Can you recommend a continuous use 6V relay? The ones I'm using more likely are for intermittent use

[Derek UK]

The make/break ones here might be OK, the basic one is 20amp. The fused one is only a little more expensive and that is rated at 30amps.
https://www.autoelectricsupplies.co.uk/product_list/161
The company has a lot of useful items.

[Ron Kwas]

...a good find by Derek!